How To Make Shaft Couplings, Lead Screws, And Pillow Blocks - Backyard Style
Hello Everyone
EDIT: The title has been altered to accurately reflect the entire content of the thread
Let me begin this article by simply stating that this article is not intended for those people that have access to a lathe, mill, and other expensive machine shop equipment. However it is intended for those on a limited budget and for those with limited access to machine shop equipment.
Without expensive equipment, making accurate couplings can be very difficult to say the least. To sum it up, deep bores are difficult to drill straight. To get primed for this article, you should first read http://forums.parallax.com/showthread.php?139882-Drilling-Very-Accurate-Holes-In-Metal, because many of the same tools will be used.
In case you are wondering, I am currently taking a break from making several shaft couplings, so I thought I would share what I have learned over the past several years about making accurate shaft couplings in the backyard style. So why make your own? Because they are expensive! Take for instance this 0.25"/0.25" aluminum coupling: http://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=52209&GroupID=196. For an XYZ machine, that is $75 just in couplings. Additionally, if you decide to make your own couplings, you don't want to just bore holes in a round piece of metal, because you want the couplings to be balanced to preserve any bearings within the drive train.
From this point on, I will assume that you have read the article that is linked above.
In addition to the tools mentioned in that article, you will also need approximately 6 inches of 3/4" keystock and one of these carbide tool bits: http://www.fastenal.com/web/products/detail.ex?sku=0303666. The keystock and bit must be combined to form a complete turning tool. At one end of the keystock, in the top-left corner, drill and tap a 10-32 hole, then measure back 1", and drill and tap another 10-32 hole on the righthand side of the keystock. Using (2) 10-32 screws, firmly secure the "AR-4 C5 Brazed Carbide Tool Bit" to the keystock with the point facing upward. So what is the purpose? We are going to use the drill press as a mini lathe.
Unless you have several stages that utilize the same motor and shafting, each application will be different, but the basic procedure will always be the same. For the purpose of this article, I will describe the fabrication of a 5.0MM/0.25IN coupling, which can be used to couple a NEMA 17 stepper motor with 1/4 inch shafting. When making couplings, I generally use aluminum stock, because it is much easier to work with, as compared to steel. If you decide to make couplings out of steel, you can always buy a low grade steel bolt and cut your blanks from the bolt, instead of buying a full length rod. I do this quite often, especially if I only need a small piece of round steel rod. Whatever material you decide to use, cut your blanks 1/16 of inch oversize in length, and always start this project with a diameter of 1/16-1/8"" larger than the final desired diameter. Clamp a blank in the milling vise and use a rotary file to true the ends. Using a printer, print out a template for the rod end which indicates the center point. Using the wiggler, center the drill press spindle over the blank center. First make a dimple and then drill a 5.0MM whole completely through the blank. After marking out the 1/4" drill bit to the proper depth, drill the blank to the proper depth with the 1/4" drill. Reorientate the blank so that the hole is parallel to the milling vise table. Center the wiggler to the hole. Move to the appropriate location for one of the setscrews, dimple, drill, and tap a hole. Insert a flated shaft into the hole and secure with a setscrew, and then chuck this assembly into the drill press. Now secure the combination keystock/bit assembly into the milling vise. Turn on the drill press and slowly move the cutting bit into the bottom edge of the rotating blank. When it just barely touches, slowly move the spindle down and up to remove excess metal. Several passes must be made to remove this excess metal. Repeat this process until the blank has be trued around the entire circumference, but do not turn it to the final diameter just yet. It will be very obvious when the blank has been trued. When removing metal from the blank, do it a little at a time, otherwise you will destroy your carbide bit. While the drill is still rotating, use a file or some emery cloth to remove any sharp burrs. Turn off the drill press to remove the blank and shaft. Coat the additional set screw locations with paint, remove the shaft, and mark additional setscrew locations. Now remove the setscrew and install a small piece of threaded rod in it's place. Place the blank in the milling vise and also install an appropriately sized drill bit into the chuck of the drill press. Rotate the blank until the threaded rod is parallel with the drill bit. Remove the drill bit and chuck up the wiggler. With the drill running, center the wiggler with the hole going through the center of the blank (X axis). Now move the milling vise so that the wiggler is over the next setscrew location. Remove wiggler, dimple, drill, and tap. Repeat this procedure until all setscrew holes have been drilled and tapped. Reinstall the flatted shaft and rechuck it into the drill press and turn it to remove all excess metal, until the final diameter is achieved. Polish and remove burrs with emery cloth. Remove blank and shaft from the drill press chuck. Remove the shaft from the blank. Chuck the blank, making sure that setscrew holes do not align with the chuck jaws, start the drillpress, and bring the blank end down on top of the carbide bit to true the end, and then polish the end with emery cloth. Repeat this procedure for the other end.
And there you have it. The backyard coupling.
Time for me to get back to my own couplings.
Bruce
EDIT: The title has been altered to accurately reflect the entire content of the thread
Let me begin this article by simply stating that this article is not intended for those people that have access to a lathe, mill, and other expensive machine shop equipment. However it is intended for those on a limited budget and for those with limited access to machine shop equipment.
Without expensive equipment, making accurate couplings can be very difficult to say the least. To sum it up, deep bores are difficult to drill straight. To get primed for this article, you should first read http://forums.parallax.com/showthread.php?139882-Drilling-Very-Accurate-Holes-In-Metal, because many of the same tools will be used.
In case you are wondering, I am currently taking a break from making several shaft couplings, so I thought I would share what I have learned over the past several years about making accurate shaft couplings in the backyard style. So why make your own? Because they are expensive! Take for instance this 0.25"/0.25" aluminum coupling: http://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=52209&GroupID=196. For an XYZ machine, that is $75 just in couplings. Additionally, if you decide to make your own couplings, you don't want to just bore holes in a round piece of metal, because you want the couplings to be balanced to preserve any bearings within the drive train.
From this point on, I will assume that you have read the article that is linked above.
In addition to the tools mentioned in that article, you will also need approximately 6 inches of 3/4" keystock and one of these carbide tool bits: http://www.fastenal.com/web/products/detail.ex?sku=0303666. The keystock and bit must be combined to form a complete turning tool. At one end of the keystock, in the top-left corner, drill and tap a 10-32 hole, then measure back 1", and drill and tap another 10-32 hole on the righthand side of the keystock. Using (2) 10-32 screws, firmly secure the "AR-4 C5 Brazed Carbide Tool Bit" to the keystock with the point facing upward. So what is the purpose? We are going to use the drill press as a mini lathe.
Unless you have several stages that utilize the same motor and shafting, each application will be different, but the basic procedure will always be the same. For the purpose of this article, I will describe the fabrication of a 5.0MM/0.25IN coupling, which can be used to couple a NEMA 17 stepper motor with 1/4 inch shafting. When making couplings, I generally use aluminum stock, because it is much easier to work with, as compared to steel. If you decide to make couplings out of steel, you can always buy a low grade steel bolt and cut your blanks from the bolt, instead of buying a full length rod. I do this quite often, especially if I only need a small piece of round steel rod. Whatever material you decide to use, cut your blanks 1/16 of inch oversize in length, and always start this project with a diameter of 1/16-1/8"" larger than the final desired diameter. Clamp a blank in the milling vise and use a rotary file to true the ends. Using a printer, print out a template for the rod end which indicates the center point. Using the wiggler, center the drill press spindle over the blank center. First make a dimple and then drill a 5.0MM whole completely through the blank. After marking out the 1/4" drill bit to the proper depth, drill the blank to the proper depth with the 1/4" drill. Reorientate the blank so that the hole is parallel to the milling vise table. Center the wiggler to the hole. Move to the appropriate location for one of the setscrews, dimple, drill, and tap a hole. Insert a flated shaft into the hole and secure with a setscrew, and then chuck this assembly into the drill press. Now secure the combination keystock/bit assembly into the milling vise. Turn on the drill press and slowly move the cutting bit into the bottom edge of the rotating blank. When it just barely touches, slowly move the spindle down and up to remove excess metal. Several passes must be made to remove this excess metal. Repeat this process until the blank has be trued around the entire circumference, but do not turn it to the final diameter just yet. It will be very obvious when the blank has been trued. When removing metal from the blank, do it a little at a time, otherwise you will destroy your carbide bit. While the drill is still rotating, use a file or some emery cloth to remove any sharp burrs. Turn off the drill press to remove the blank and shaft. Coat the additional set screw locations with paint, remove the shaft, and mark additional setscrew locations. Now remove the setscrew and install a small piece of threaded rod in it's place. Place the blank in the milling vise and also install an appropriately sized drill bit into the chuck of the drill press. Rotate the blank until the threaded rod is parallel with the drill bit. Remove the drill bit and chuck up the wiggler. With the drill running, center the wiggler with the hole going through the center of the blank (X axis). Now move the milling vise so that the wiggler is over the next setscrew location. Remove wiggler, dimple, drill, and tap. Repeat this procedure until all setscrew holes have been drilled and tapped. Reinstall the flatted shaft and rechuck it into the drill press and turn it to remove all excess metal, until the final diameter is achieved. Polish and remove burrs with emery cloth. Remove blank and shaft from the drill press chuck. Remove the shaft from the blank. Chuck the blank, making sure that setscrew holes do not align with the chuck jaws, start the drillpress, and bring the blank end down on top of the carbide bit to true the end, and then polish the end with emery cloth. Repeat this procedure for the other end.
And there you have it. The backyard coupling.
Time for me to get back to my own couplings.
Bruce
Comments
As mentioned in the previous article, making accurate couplings can be very difficult. In addition to boring deep holes, shaft to shaft alignment is very difficult, yet it is critical. Upon trial assembly of the machine that I am building, I became discontent with the shaft to shaft alignment of the couplings that I made, so I decided to make a new batch of couplings. While it is possible to make nice couplings with the previous method, it is still difficult. In an effort to simplify the process and create couplings with good shaft to shaft alignment, I decided to create my own custom drill bits for making couplings. As Phil mentioned in the other thread, drill bits have a tendancy to walk, which drives the drill bit at an angle. When boring deep holes, such as with couplings, this angle can become quite severe from one end of the coupling to the other. This is not a major problem if you are coupling two shafts of the same size, but when you are coupling two different size shafts, the second bore may not align with the first bore. The trick to overcoming this problem is to bore both sizes in one operation, with the shortest drill bit possible. So without further delay, I present you with a plan to custom make your own coupling boring drill bits and couplings.
Let's start with the specifics:
- 5/8" Dia X 1-1/4" 6061 Aluminum Rod blanks
- 1/2" finished diameter X 1-1/32 finished length
- (4) 8-32 cup point set screws, spaced 1/8 and 11/32 from each end
As with the previous example, are current couplings will adapt 5MM (NEMA 17) to 1/4" shafting. Actually, since it might help someone further down the line, I will be a little more specific this time. My couplings are intended to adapt 1/4" threaded rod (instead of 1/4" shafting) to NEMA 17 motors. Your average 1/4" threaded rod, available at most hardware stores, has a diameter of somewhere around 0.237 - 0.238". To accurately adapt the threaded rod to the NEMA 17 motor, we need to start with a drill bit of this diameter, which happens to be a Letter "B" drill bit size. Additionally, the drill bit should be as short as possible, to help ensure a straight bore. For easy accessability, I chose to use this bit: http://www.fastenal.com/web/products/detail.ex?sku=0356258, however, this bit has a split point tip, which makes it slightly more difficult to modify.There are several ways I could to describe the modification procedure, but I suppose the easiest for me would be to describe what I used and what I did. Your materials and tools available may be slightly different, but don't be afraid to experiment. To begin with, I set the drill press on the lowest speed, and mounted a fine grit 6" Dia. X 5/8" Thick grinding wheel. I then trued the grinding wheel with tuckpointed diamond blade used for removing mortar, which was securely fastened to the milling vise and mentioned in this thread: http://forums.parallax.com/showthread.php?139882-Drilling-Very-Accurate-Holes-In-Metal. After truing the grinding wheel, I placed the Letter "B" drill bit in a spare chuck, which was mounted to a broken spindle with the bearing still attached. I then clamped the bearing in the milling vise, with the Letter "B" drill bit being parallel to the drill press spindle and edge of the grinding wheel. The height of the milling vise was then adjusted so that 33/64" of drill bit would be ground when touching the grinding stone. As you have probably already guessed, I started the drill press and moved the milling vise so that the drill bit came into contact with the grinding wheel. As it was grinding, I slowly rotated the bit in the spare chuck, and kept moving the vise forward and grinding until the diameter of the bit was 5MM.
The result of this effort was a double size drill bit that made two bores in perfect alignment
It is noteworthy to mention that this method probably won't work for steel couplings, because such grinding removes a significant part of the drill bit fluting.
Bruce
As I have learned many times in my life, what appears to be a perfect coupling, may in fact be quite imperfect, and such is my current situation, with couplings created with a ground drill bit. So needless to say, I am back to making couplings and striving for perfection.
After some in depth study and consideration of my not so perfect shaft to shaft alignment, I have come to the conclusion that my drill bit(s) were improperly ground down to size. If the drill bit is not properly ground true to the two size sizes (meaning parallel), it will either throw your cutting tip out of alignment or one of your shafts will run at an angle. If the cutting tip is out of alignment, then the bit will making a slightly larger hole, resulting in a sloppy fit, and if the shaft runs at an angle, it will either cause binding or runout. I attribute my current problems to poor rigging, inadequate setup, and lack of patience. To actually create the "perfect" homemade coupling, I first need to create the "perfect" custom drill bit, and to create the "perfect" custom drill bit, I first need to build a high quality jig and take the time to properly align it with the drill press and grinding wheel.
In addition to my other spare chuck, I also have a spare cordless screw gun torque adjuster and chuck. The bottom side of the torque adjuster has a round opening, for which I have made a round adapter with a couple of threaded holes for fastening the torque adjuster and chuck assembly to the adapter. Additionally, the adapter has a hole in the center for mounting it to a piece of 1/2" X 2" X 2" aluminum bar stock. With this setup, I should be able to perfectly angle the jig within the milling vise to match the front of the drill press spindle, and it should be nice and solid, with not possible way for movement. Once the front has been perfectly aligned, I will then move it along to one side of the spindle, and ensure that is in perfect alignment as well.
After the new grinding jig has been made, I will then attempt grinding a new bit very, very slowly.
If you will be attempting such a procedure, just remember to obtain extra drill bits.
Wish Me Luck
Bruce
As it turns out, to my surprise and dismay, the spindle on the cordless chuck assembly did not align very well with the chuck. Perhaps there could have been some debris deep within the chuck, but I cleaned it the best I could to no avil of solving the problem. Additionally, being a keyless threaded chuck, there was quite a bit of slop that allowed side to side movement. After messing around with this chuck for a while, I decided to go back to the initial chuck. I could go into all the drama and problems that I had to deal with, but instead, I will simply tell you what I did to obtain a nice drill bit grinding jig. First I removed the bearing from the broken spindle and measured the bearing journal. I then bored a slightly undersize hole into a square chunk of some 1" thick Ultra High Molecular Weight Polyethylene (UHMWPE) and pressed the spindle into this bore. With the chuck attached and a little torque (wrist action), the chuck spins quite nicely and true. After truing the jig to the drill press within the milling vise, I have started grinding another bit, and I must say that this bit is starting to look pretty darn nice and true. There is no doubt in my mind that this bit will produce the best couplers I have ever made, however I could be WRONG
I will keep you posted.
Bruce
EDIT: As a side note, the chuck that I am using for this jig accepts 1/2" bits, so with this jig, I should be able to make aluminum shaft to shaft coupling adapters being 1/2" or smaller.
After grinding the drill bit, I gave it a quick polish with some fine emery cloth. I then gave the bit a close inspection, and that baby looked sweet. The two sides of the tip appeared to be equal, as well as the amount of cut into each flute. Without any delay, I then chucked the bit into the drill press, just to see if the bit ran true. I must say that it appeared to run as true as a brand new drill bit. Needless to say that I was quite impressed my modified bit, so I decided to make a test hole with the 5MM ground end. During the drilling process, the bit performed very nicely, cutting very effeciently through the aluminum. After drilling a hole in a scrap piece of aluminum, I then grabbed a NEMA 17 motor with a 5MM shaft, and fitted the scrap to the motor shaft. It was a very tight fit with literally no slop. I had to push it onto the shaft with minimal hand pressure, and I could only remove it by rotating the motor shaft knob and by pulling outward on the scrap.
From all appearences and indications, it looks as though I now have a "perfect" bit for making my new couplings.
It may be worth mentioning that even though the 5MM ground end drilled very nicely, my past experience in this experimentation has shown me that the drilling becomes much more difficult when the second size has been reached, and it requires more patience, with plenty of oil. However I am sure this problem can be overcome, by creating a bevel in the grinding stone, which in turn would create a less severe chamfer from one size to the next.
Bruce
At this point, the couplings have been bored and trimmed to near final length. I must say that the new drill bit far exceeded my expectations. In regards to my last post...
When it got to the point of boring the second size, the drill bit went right through it without any problems this time. However I did stop the drilling process several times to remove chip build up from the bit.
Of course it is all still conjecture at this point, but it appears that these couplings will turn out just fine. I believe I finally found the key to making great couplings. Later tonight I will drill and tap the four set screws for each coupling, and I will additionally turn the couplings to the final diameter.
I normally don't admit faults and mistakes too much, but just to give you an idea how difficult it can be to make good couplings without the proper equipment, this is my fourth batch of couplings for the current machine that I am working on. The previous three batches all looked professionally made or store bought, but for the alignment that I wanted, well it just wasn't good enough.
Hopefully this batch will be right on the money.
Bruce
I have not updated this thread for a few days, because I have come to the realization that my lead screws are a huge contributing factor to my misalignment. I have never tried building a machine this accurate before, and I am learning the hard way that accuracy has a price. I am certain that my new couplers are now well within tolerances now, but now I will have to custom make my lead screws, both the threading and the journals. The are a couple problems associated with using threaded rod that is available at any hardware store, which are:
- The major diameter of the thread is very highly inconsistent. When inserting these threads directly into a coupling, these thread diameter deviations can cause the screw to go askew. Just a couple thousandths, will cause some pretty severe runout
- Additionally, once again concerning the major diameter, since it fluctuates, it is very difficult to get a nice fit with the coupler. If the thread diameter is several thousandths less than the bore diameter of the coupling, this will also cause some runout, although not as severe as the lead screw going askew.
For the reasons stated above, I will now custom make my own lead screws with journals on both ends, one journal for the coupling and the other for the bearing. Additionally, even though I now believe that the couplings are now very accurate, I will probably make a new set of couplings to match the new lead screws, especially since I will be using a journal on the coupling end. For the lead screw project, I will be using 1/4" drill rod, since this can be a natural journal for the coupling, as well as providing a base diater for the 1/4-20 threads.Please be patient and I will eventually let you know how it all works out.
Bruce
EDIT: Just realized that I cannot use the 1/4" for a journal due to design, assembly, and disassembly purposes. I will have to grind it down to a smaller diameter.
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It all sounds easy until you apply it.
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This is why I'm a Mopar fan.
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Engeering at it's finest
Solutions can be easy once you have identified the problems and put some thought into resolving them. Here at Bruce Central (A.K.A. Novel Solutions), we don't let the problems get in our way, we solve them
If you visit my website, http://www.novelsolutionsonline.com/, you will see my company motto, which is:
Backyard Engineering at it's finest.
Read the next post for the proposed solution to my lead screw problem.
Bruce
Concerning Post #7 and custom made lead screws, I have change my mind on my plan of attack. Instead of creating the lead screws from scratch, I have decided to return to the threaded rod. As previously mentioned, premanufactured threaded rod has a deviating major diameter along it's length, so finding the exact average center and turning the threaded rod to be true with this center could be very difficult for the homebrew lead screw. To resolve this problem, I will be using a similar technique that I used for modifying the previously mentioned drill bits. My goal will be to find the exact average center of the largest available major diameter on the threaded rod. To fully understand what I am about to say, you should probably read the proceeding information concerning the modification of drill bits.
To obtain my 1/4-20 lead screws, I will be creating a jig that utilizes a chunk of aluminum angle that will be parallel to the drill press spindle. This jig will be mounted to the milling vise that is mounted to my drill press, which will allow me to slowly move the jig toward the drill press spindle and attached grinding wheel. The proposed threaded rod will be forced into the corner of the aluminum angle and held in place by several rotating rollers, which will give me access to the average center of the largest available major diameter on the threaded rod. As the threaded rod is moved into the grinding wheel, the rotating rollers will allow the threaded rod to be rotated and ground true to the average center. Once the threaded rod has been ground true to a predetermined diameter, I can either use that surface as a journal for the coupler and/or bearing, or I can press a journal onto the threaded rod and grind it true in a similar fashion.
Bruce
I have changed my mind on the rollers for creating the lead screw grinding jig. I will use numerous and staggered 45 degree beveled UHMWPE clamps instead, to hold the lead screw in place. This should greatly simplify the making of the jig and these plastic clamps should provide adequate clamping force, but still allow the screw to rotate for full grinding. I have attached a pic below for those that can understand it.
Bruce
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Your thinking like an Electrician and not a Machinist on this lead screw project.
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Set-Focus
LOL You got a laugh out of me
Walt, even if the 1/4-20 rods don't work well for me, I still want to be able to fabricate my own couplings and grind my own lead screw ends. I sincerely believe that a lathe in combination with the custom ground drill bits is the way to go for the couplings. As for the lead screws, I think this experimentation may pay off for me in the long run. If I rely on off the shelf lead screws, then I will be designing my machines around such screws, and I don't like that concept. Even if I end up using ACME threads in the long run, I still want to either turn or grind my on journals.
As it stands, I have had to design my own screw and nuts for the last several years for several machines, but I never took the time to try and achieve a nice method. I realize some people may be laughing at me, but then my machines would not exist if I listened to everyones advice and let a little laughter scare me. And by no means am I afraid to experiment a little. Take for example the wire cutter on my wire bending CNC. It took a lot of experimentation to make one that reliably cuts 0.031" music wire. The cutter that is on there now is a third generation cutter with a screw driven guilotine, all custom made, screw, nut, slide, and blades. To create a machine that will reliably feed 0.031" wire through a 0.032" and reliably cut it 25,000 times a day takes a little experimentation.
Bruce
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Glad you liked the joke.
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When I was a kid.I took the cam out of a 5HP B&S engine, Welded the lobe's up, And re-ground them by hand to add longer valve timing."I hot-rodded the lobe profile".
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I won the first race I used this motor in, But I was disqualified later for having a cam way out of spec."Cheating"
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Doing things in an un-Orthodox way does work with some experimentation.
I really liked that story, except for the part of being disqualified. If you were only a kid, they should have given you a bonus prize for being ingenuitive.
"Adapt and overcome."
Bruce
-Phil
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My chest was burnt-up from the little blue light while I was figuring out how to weld with no shirt on.(It was hot out)
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You live and learn.
Source: Merriam-Webster New Words And Slang
http://www3.merriam-webster.com/opendictionary/newword_display_recent.php?id=9896
Bruce
chude (noun) : an androgynous person
adultescence (noun) : a period of apparent adolescent habits or behavior continued into adulthood
frequest (noun) : a request to be added to someone's list of friends on a social networking Web site
athleadership (noun) : leadership skills derived from participation in athletics
It really deserves better company than that.
-Phil
Possibly, but I disagree with the second definition:
"Not stabilized" implies that stability is still possible; "unstable" is the proper term only when that possibility is doubtful. I'll go with the first definition.
-Phil
EDIT: CORRECT:)
Last night I finished making the lead screw/shaft grinding jig that I talked about building and I must say that it turned out much nicer than I anticipated. Fabricating the beveled UHMWPE clamping blocks were a little more difficult than intended, because of their small size. Like I said, the jig is pretty nice, but it will only clamp short sections of rod with diameters in the 0.220 - 0.250" range. One of these days, I might expand upon this grinding jig idea and make it more adaptable to several diameters and lengths. Anyhow, it is all finished now, and I can once again proceed with working on my machine.
Since clamping the threaded rod directly to the coupling provides inconsistent runout (hence the reason for the grinding jig), I have altered my drive train stategy, with the intention of grinding off the threads on the end that is inserted into the coupling. In order to accommodate easy disassembly of the linear actuators, one end of the lead screws must be of a smaller diameter than the threads used for the lead nuts on the carriage. Basically, I want to be able to remove the lead screws, by loosening two set screws on the motor couplings, and unscrewing the lead screws from the carriage assemblies, in order to avoid removal of the pilow block bearing assemblies, which would then require drive train realignment.
Removing the threads of standard 1/4" threaded rod, results in a diameter of nearly 11/64", so the adapter couplings will be drilled 5MM on one end to adapt a snug fit to the NEMA 17 motors and 11/64" on the other end to adapt a snug fit to the custom ground lead screws. To make these couplings, I will have to grind another drill bit, but this time I will grinding a 5MM bit down to 11/64". Here is a link to the drill bits that I will be grinding: http://www.fastenal.com/web/products/detail.ex?sku=3298719
Since I have gone this far in describing my plans to you, I might as well disclose the rest to you in order to provide a complete solution. Considering that I was in a rush, I constructed and shaped the pillow block bearing assemblies from 1/2" extruded aluminum. When I have more time, I will create a sand cast mold to make the pillow blocks more rapidly through a sand casting process. Anyhow, the pillow blocks were drilled and reamed to a diameter of 0373" and 1/2" long X 3/8" O.D. X 5/16" sleeve bearings were installed with a pilot. The actual bearing part number is 6391K153 and can be ordered from McMaster-Carr at this link: http://www.mcmaster.com/#catalog/118/1129/=ibv6oz. To find out more about installing sleeve bearings, you should refer to this thread: http://forums.parallax.com/showthread.php?136980-Proper-insertion-of-sintered-bronze-bearings. To accommodate the 5/16" I.D. sleeve bearings, the lead screws all require a 5/16" bearing journal. The journals on my previous lead screws were created in the following fashion. Drill an 11/64" hole in the center of a 3/8" diameter by 1/2" long rod, and grind the receiving end of the lead screw down to a diameter of approximately 0.174", tap the created sleeve onto the screw, and grind the permanently installed sleeve (journal) down to a diameter of 0.310".
Anyhow, this is the latest update with just a little more information.
Bruce
It took a while to find the motivation, but early this morning, I decided to try and salvage my existing threaded rod with a "regrind". I started out by dressing the grinding wheel and aligning the jig with the drill press spindle. After loading a screw into the jig and grinding on it for a while, I removed the screw to measure the grind from top to bottom. It is worthy to mention that the grind was very nice and looked professionally ground, however there was a deviation of 0.004" from the top of the grind to the bottom which is unacceptable.
After dressing the grinding wheel and while aligning the jig, I discovered that the table was a slight bit out of alignment, so I readjusted the table without giving the grinding wheel a second thought. I now believe the 0.004" deviation is a direct result of dressing the grinding wheel on a different vertical plane from the final aligned position of the jig. As previously mentioned in this thread, I have been using a diamond embedded tuckpointers wheel to true the grinding wheel, but this method is about to change because of the 0.004" deviation. Without any doubt, to help ensure an accurate grind of the lead screws, I want the grinding wheel face to be parallel to the vertical aligned position of the grinding jig. In an effort to resolve this problem, I will be modifying a "AR-4 C5 Brazed Carbide Tool Bit" by boring two holes in it, and after drilling and tapping two holes in the grinding jig, I will be mounting the modified Carbide bit to the top of the grinding jig. I am hoping that this new attachment will dress up the grinding wheels to be in perfect alignment with the jig. If all goes well, I believe I will have the perfect jig for grinding small shafts and lead screws. It will be an especially nice addition if it works, because I will be able to dress the grinding wheel while a grinding operation is in progress.
I will keep you posted.
Bruce
When you build something new and unique, of course there has to be a little experimentation to learn how to use it properly, and such is the case with my new grinding jig. After fiddling around with the grinding wheel and keeping it dressed all the time, I came to the conclusion that it was a real pain and it just was not providing accurate enough results to make me happy, so I decided to try something new. Last night, I briefly tried a 1/2" rotary file instead of the grinding wheel, but the 0.004" discrepancy remained, and in addition to that discrepancy, it left swirl marks on the journal. In disgust, I abandoned the task and washed windows instead
RESULTS: Within a 1/2" span, there is less than a 0.00025" difference in the diameter, which should equate to less than a 0.0025" runout from center at a 10" span, but more particularly, in my case, 7.125" (lead screw length) X 0.00025" (runout per inch from center) = less than 0.00178125" runout for my lead screws ( EDIT: Theoretically speaking). I believe that should be good enough, considering the sleeve bearings on my pillow blocks have 0.002" clearance.
It is now time to remake all my lead screws and couplings, and hopefully I will be able to maintain the >0.00025" (runout per inch from center) tolerance.
Bruce
Well it took a while, but I finally got around to machining another lead screw end, and this end, turned out just as nice as the first. So the rotary file and my new jig are a match made in heaven. The previous drawing of the jig does not include it's evolution to it's current state, but it gives you the basic idea. However for more clarity, I will provide a better description. For centering the threaded rod, I used a piece of angle aluminum, and the threaded rod is held in the corner of the angle with six pieces of UHMWPE which are beveled at a 45 degree angle and held in place by 4-40 screws. This setup is bolted to a 1 X 1 X 3-5/8 piece of bar aluminum with (2) 10-32 screws. Within this bar, I cut a 45 degree 1/2" slot so that I could add a handwheel and locknut to the threaded rod for easier rotation during the macining process. Located below this machined slot, I drilled and tapped (2) 4-40 holes and attached a small chunk of 1/2 X 1/2 aluminum angle, for the threaded rod to rest upon. The handwheel was constructed from a small chunk of 1/4 X 1-1/4 aluminum bar stock and turned down to a diameter of 1-3/16, with a hole drilled in the center and tapped with 1/4-20 threads.
To use the jig, you simply mount the 1 X 1 bar stock in the milling vise and align the drill press spindle to the jig. Once the alignment has been performed, the UHMWPE clamps are removed, the handwheel and locknut are threaded onto the intended workpiece, and the workpiece is then placed within the jig and adjusted so that the workpiece sits upon the rest and the handwheel and locknut are within the machined slot. The UHMWPE clamps are then put back and screwed into their intended positions. With the workpiece firmly held in place by the UHMWPE clamps, the last clamp, the one being closest to the handwheel, is adjusted so that it extends a couples thousands of an inch below the main part of the jig, which gives the handwheel a nice slippery surface to glide upon. The handwheel is then threaded up to this last clamp, and the locknut secures it's position. The drill press table and rotary file are then adjusted to obtain the proper depth of machining. Keep in mind that the clamps do not need to be real tight which would make it difficult to turn the workpiece and wear the aluminum angle much quicker. To begin the machining process, start the drill press and move the workpiece into the rotary file while turning the workpiece and advancing the milling vise. Do a little at a time and you will get very nice results.
Being basically lazy, I have decided to adapt a small motor to the handwheel to eliminate the need for 100% involvement with the work being performed. By adapting a motor to the jig, I will only need to advance the milling vise a couple times until I get the proper diameter.
Bruce
My guess at possible causes would be:
I have decided to change my strategy just a little bit.
Over the last several days I have been taking it kind of easy while I experiment with the new jig and deciding my best course of action to move forward with making my own lead screws and couplings. After serious deliberation, I decided to accept my loss, make a fresh start, and completely abandon all previous attempts and parts. Since I want to remove as little material as possible, this morning I carefully removed the threads from some threaded rod, which resulted in a diameter of 0.1775", and I will make this measurement the basis of my new design. However, considering that this diameter may fluctuate, I figure I can be reasonably safe, if I grind both ends of each lead screw to a diameter of 0.1740". However, please keep in mind that a 0.3100" O.D. journal will be pressed onto one of these ends. I will be drilling these journals with a #17 drill bit for a 0.1730" I.D, which should result in a nice press fit. Additionally, when making my new couplings, I will be modifying a 5MM machine screw drill bit this time, instead of a Letter B drill bit. The 5MM bit will be altered to snuggly adapt the other end of the lead screw with the remaining 0.1740" diameter. To help facilitate the fabrication of these new parts, I recently purchased a new rotary file (Carbide Burr (SB-5D) Cylindrical End Cut - Double Cut - 1/4 x 1/2 x 1 x 2 3/4) from ebay and I am awaiting it's arrival. Additionally, I went shopping this morning and picked up the following items:
- (2) 1/4-20 X 36" threaded rods
- #17 drill bit
- 11/64 drill bit (just in case)
- #432 Dremel 120 grit sanding bands (just in case)
- #408 Dremel 60 grit sanding bands (just in case)
- 3/4" dia. X 3/4" grinding point (just in case)
As you can see, I purchased several "just in case" parts and accessories. I believe I have it down to a science now, but you never know how something will turn out when you are not using industrialized equipment, such as lathes, mills, etc... And finally, the 5MM drill bits are going to require a special order, so I will order several of them, "just in case". When using NEMA 17 motors, 5MM is the common shaft size, so the extra 5MM bits will eventually be used on various projects.Wish me luck
Bruce
At this point in time, I still have not succeeded. I am having a very difficult time of measuring the lead screws while it is still in the jig, and in my haste, I have destroyed several screws. I either have to acquire more patience or build a different jig.
EDIT: Since making this post, instead of using a dial caliper, I have decided to start using an outside micrometer for taking my measurements, which should make the process a whole lot less tedious. Additionally, I have decided to put on my patience hat and drudge my way through it, without making a new jig or adding a motor at this time. In reality, it probably won't take too long, but I have always been an impatient man.
I will eventually supply pictures of the end result.
I am finally getting it dialed in. Ever since I quit using a grinding wheel and began using the new carbide burr (rotary file), I've been having problems with the press fit (tap on) of the sleeve (journal) to the lead screw. After abandoning the dial calipers in exchange for an outside micrometer to obtain more accurate measurements, I measured the #17 drill end diameter, and it measured 0.172". So with this measurement in hand and using an outside micrometer, I shot for a new measurement of 0.173" diameter for the journal end of the lead screw. After machining the journal end with the carbide burr, I attempted to tap on a sleeve, and it went right place, resulting in a nice and solid fit. This is now my new procedure as compared to what was previously stated:
I believe my difficulties were due to a combination of problems:
- The #17 drill bit was 0.001" smaller than I thought
- The carbide burr leaves very small swirls (barely noticable) and I believe the dial caliper was measuring the minor diameter of the swirl, which probably meant that the major diameter had an extra 0.001 - 0.002". EDIT: The swirls actually account for 0.002" of the diameter.
So I figure there was probably somewhere in the ballpark of 0.003" of interference between the shaft and the sleeve, which was way too much and explains the damage that occurred to several of the proceeding screws.As previously mentioned within the thread, the sleeves (journals) have a starting diameter of 0.375" and will be machined down to a diameter of 0.310" to true them up with the lead screw. I am currently in the process of truing one of the journals using the my new jig, and I must say that during the machining process, the carbide burr grabs at the journal much more than lead screws, so hold on tight. Additionally, machining the journals with the carbide burr will also leave small swirls, so I will machine them down to approximately 0.312", and then I will polish them down to 0.310" with emery cloth to remove the swirls and add a nice surface finish. EDIT: I decided to stop machining the journal at a diameter of 0.313", and polish them down to a diameter of 0.311" which should give me less clearance at the bearing. I am hoping that 0.001" will be enough clearance for any flaws, if not, then I will have to polish it a little more and get it down to the previously stated diameter of 0.310".
In summary, it is beginning to look promising once again.
Bruce
EDIT: I also thought it was worth noting that I do not intend to polish the end of the lead screw that will be inserted into the motor coupling. I do believe that the lead screw will be much more accurate without polishing this end, so the swirls will just have to remain, and I will just have to chalk this up as a flaw of homemade lead screws. However, nobody will ever be able to see the swirls, because they will be inside the coupling.