The MK8 drive gear arrived today. It appears to be well made and has small sharp teeth to grip the filament. Not much else to say about it, except that I think the purchase was a wise decision.
A new descriptive front view is now provided to show all changes, including the heatsink.
Please note that the core now extends above the 1/8 X 2 X 2 wind tunnel, and the core is now much closer to the drive gear and idler. This will slightly increase the amount of friction in the drive system, but I am hoping it will make it easier to load the filament. Additionally, the visible portion of the core will be threaded to allow attachment to a compressed air line for jamb removal, as discussed in previous posts.
I think you might want to consider a more conventional approach using PEEK/PTFE materials.
The reason for that is the high thermal conductivity of the brass and aluminum.
The current design has a short brass/aluminum rod that will need to be in the vicinity of 200 degrees Celsius on one end and under 100 degrees Celsius on the other.
It takes considerable power to drive that large of a temperature differential over that short a distance given that much area of brass/aluminum.
Perhaps you are correct and you probably are correct, but I am at a point where I like the design and the concept, so I at least have to try it out. One thing to keep in mind, is the fact that it is an evolving design and the design is still subject to change. For instance, I have been thinking about raising the heatsink off of the resistance wire bobbin, reducing the cross sectional diameter of the core in that area, and placing a thermal barrier there, such as PEEK.
I highly doubt that I am finished with the design.
As I am sitting here pondering my selection, it has dawned on me that another variable must be considered, especially when going after speed. Besides the limitation or ability of the X axis to reliably push the Y axis around, the speed at which the filament can be processed by the hot end also comes into play. Luckyily I purchased enough raw materials to experiment with making several hot ends, but I would imagine there is a maximum speed at which the plastic can be reliably extruded, regardless of the extruder motor speed or torque.
While doing some research this afternoon, I came across this web page, which directly relates to the conclusion I made above:
After putting some thought into my extruder, I have come to the conclusion that I will be making a major change to the current design, which will be as follows:
Pertaining to the heatsink, the cooling fins will still have the same outter diameter, whereas the the main body diameter will be reduced in size. Additionally, the heatsink will also be raised above the resistance wire bobbin and a thermal barrier will be placed in between the heatsink and bobbin. At this point, I am unwilling to change the cross sectional diameter of the core, but that may change in the event of a thermal meltdown
I will post a new front view, when the drawing has been changed.
Okay, I have an idea for a slightly different extruder.
While studying heat transfer, thermal conductivity, and heatsink design, I came across an image, which made the old bell ring.
By the end of the day, I will post a new design, which will have less components, be less costly, and the height of the extruder will be drastically cut. Additionally, it should be much easier to make.
The heatsink shown is just a rough draft, but it is 2" Wide X 2" Deep X 1" High.
As I see it, unless I am missing something, the main job of the heatsink is to support the hot end, with the added task of disapating enough heat so that the thermal resistant mounting spacers don't melt or carry too much heat to the motor mount bar.
In order to provide a better overall understanding of the new extruder design shown in Post #249, I am now providing a partial descriptive side view. Some of the parts have been ommitted in this drawing, but by reviewing the drawing of Post #249 and reading previous discussion, the design of the extruder should become apparent.
I believe we are now very close to the final design. In this post, I am including both a front view and a partial side view. Out of all the drawings, these two are my favorite design so far.
In these drawings, I have mainly altered the design of the heatsink and added a set screw for holding the hot end. Instead of being a pin type heatsink, it is now a fin type. In my opinion, it is a pretty decent extruder design, but I believe it may take some experimentation to find the proper heatsink setup. The hot end set screw is a new concept for me that I thought of this morning. Instead of hassling around with unthreading the core, for whatever reason necessary, such as changing a nozzle, I am thinking that loosening a set screw will be much easier. The main drawback of this scheme, is that the core will not be in complete direct contact with the heatsink, which I may regret, but I will make it as tight as possible, without being a press fit. At this point, it is my intention to make hot end assemblies that are comprised of the nozzle, the heat sink bobbin, and the core, all pressed together. To change a nozzle size or remove a jamb, I simply want to remove all hot end electrical connections and loosen a set screw. And of course the core will have a set screw flat.
Additionally and although not shown, it may become necessary to add a PEEK tube to the top of the core, just in case it is too hot for the filament to enter at that point. If added, the PEEK tube would be secured to the core with the aid of another set screw.
I would thermally insulate the nozzle from the heat sink. The way it is now the heat sink will be near nozzle temperature and just be wasting the heat applied to the nozzle.
I would thermally insulate the nozzle from the heat sink. The way it is now the heat sink will be near nozzle temperature and just be wasting the heat applied to the nozzle.
I realize the heatsink will be near nozzle temperature and that it will be wasting energy, however one of my main goals is the rigidity of the nozzle. I have read about cores coming loose from plastic due to excessive heat and I certainly don't want that. Considering my ignorance of 3D printers, my biggest fear is not being able to cool down the hot end if necessary.
I suppose I am trying to take the easy way out and just say "oh well". However I want you to know that I agree 100%. The simple fact that it wastes energy, makes it a poor design. With that in mind, I will attempt to replace the aluminum heatsink with an inexpensive, sturdy material that has low thermal conductivity and a material that can also be easily drilled and threaded.
If I can find such a material, besides plastic, not only would it be more energy efficient, but it would also reduce the height of the extruder, because the spacers would no longer be necessary.
I suppose I am trying to take the easy way out and just say "oh well". However I want you to know that I agree 100%. The simple fact that it wastes energy, makes it a poor design. With that in mind, I will attempt to replace the aluminum heatsink with an inexpensive, sturdy material that has low thermal conductivity and a material that can also be easily drilled and threaded.
If I can find such a material, besides plastic, not only would it be more energy efficient, but it would also reduce the height of the extruder, because the spacers would no longer be necessary.
I understand, sometime it pays to be pragmatic and get a version built to try things out.
I'm interested in this because I have a zenbot 3D router that I may modify to do 3D printing.
Oak has a lower thermal conductivity rating than Teflon.
So a piece of Oak with two brass inserts. One insert could be used for the hot end set screw and the other could have the ID drilled out to accept the core.
Having experienced an issue with an extruder where the distance between the drive-gear/hobbed-bolt and the top of the hot-end was more than just a few millimeters, I would recommend, a tube or guide that keeps the filament straight between those two points. The filament would buckle during slightly-faster extrusion attempts.
On my PrintrBot Jr's original hot-end, I had to add a guide (built on the 3d printer) that kept the filament straight between those points. And, on the newly designed direct-drive extruder (see below) that I now use reduced that spacing and works quite well. This pic shows the extruder upside-down, but should show the tight spacing between the gears and the entry to the hot-end...
I sincerely appreciate the advice, however I am fully aware of how space in between guides can cause trouble. With one of my previous machines, a wire bending CNC, this was the cause of many headaches, until I remedied the problem. Please refer to Post #240, although I did not point out that specific issue, it was definitely in my mind.
Pertaining to the drawing that you cited, one of the main reasons that I rendered the core so short, with a large gap in between the drive gear and the core, is because heat may transfer up the tube and melt the plastic as it enters the core. If this does not become an issue, I will simply lengthen the core to bring it closer to the drive gear. On the other hand, if it does become an issue, the core will need an extension, using some type of material with low thermal conductivity, such as PEEK, as mentioned at the bottom of Post #253.
However, I am glad that you pointed it out, because I failed to do so. The space between guides should be limited to a very short distance, especially when pushing wire or filament with a drive gear or drive roller. MY DISCLAIMER
Going a step further in relation to Post #258, here is another document that has specific information pertaining to the thermal conductivity of both hardwoods and softwoods (http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_04.pdf), but more paticularly Table 4-7 of that document. Basically most species of wood have low thermal conductivity, however due to incomplete and unavailable information, it is currently unknown at what temperature specific species will ignite when subjected to a heat source as compared to an open flame source.
It is my opinion, through the study of available online docuents, that although PEEK and PTFE have been successfully used in creating many highly functional extruders, there also have been many failures along the way. Meanwhile also taking into the consideration the high cost of these materials, and although it may sound a little absurd, wood just may be a viable alternative for certain extruder parts, but most particularly parts that are intended to provide thermal isolation.
In my extruder design, there are two potential parts that require thermal isolation, with one being where the hot end mounts to the extruder and the other being any extension tube or guide being used by the core. Although not finalized, I do plan to test and attempt a replacement of the aluminum heatsink shown in Post #253, with a species of wood, and if necessary, a guide or an extension tube may also be made of wood. The replacement of the aluminum heatsink with wood is a direct attempt to conserve energy, while maintaining the structural integrity of the extruder and keeping the cost down. Considering the availabilty of White Oak in my region, I will use this species of wood for my testing. If the wood becomes slightly charred during testing, this alternative will immediately be discarded. Additionally, if wood is utilized as an isolation material, I would also imagine that other fail safes need to be provided in order to ensure proper and safe use of the extruder.
Okay maybe I will need a smoke detector
EDIT: On second thought, I never really liked working with Oak, so I think I may change the test species to Maple.
With a wooden thermal isolater in mind, I went back to the drawing board and seriously revised several parts of the design. Besides incorporating the wooden isolator, my key objectives were to:
Reduce height
Reduce weight
Reduce cost
Key changes include:
Replaced the aluminum heatsink with a thermal isolator (wood)
The size of the tension screw, spring, and knob have all been reduced in size
Tension screw, spring, and knob, now pivot towards the rear
Tension screw, spring, and knob are now retained by the motor mount bar, instead of the mounting bar and filament guide
The height of the mounting bar and filament guide has been reduced
The idler and tension lever has been highly revised to accommodate the other changes and to open to a ninety degree angle
With this new design, complexity and cost should be greatly reduced, as well as the height, width, and weight. The extruder now measures 3-7/64" in height, as compared to 5-7/16" back in Post 232.
In this post, I am providing a preliminary front view, without all the item descriptions, but by reviewing the documentation and other drawings, you should be able to visualize the extruder.
This design will be my first prototype, just to see if the wooden thermal isolators will work without smoking or charring.
Okay so I did a little experimenting this morning.....
After coming to the conclusion that a plastic ashtray might make a nice thermal isolator for a hot end, I decided to take a Mapp gas torch to a 4" diamenter ashtray I had sitting around. I heated up the ashtray until the plastic just started to bubble and then I shut down the torch. Methodically working my way from the furthest point to where the heat was applied, I tested various points for temperature, using my thumb and index finger. All testing was completed within approximately 10 seconds of shutting down the torch. To simplify the description of the test results, I will simply provide a picture of the ashtray and general temperature.
With as much heat as I applied, if this ashtray had been made of aluminum, the slightly warm areas would have been too hot to touch. Additionally, within approximately 35 seconds of shutting down the torch, I tested the temperature at the location where the flame was applied, and it was hot, but not too hot that I could not hold onto it.
In my opinion, ashtray plastic should make a nice thermal isolator for replacing the heatsink, and thus conserve energy. I will be making my thermal isolator from the bottom of the following ashtray, because it is much larger, or maybe not, I will take a second look at the smaller ashtray to see if I can make it out of that one. If that does not work, here is the other one.
EDIT: This still does not account for an isolater at the top of the core, if one is required.
EDIT: Additionally, this should shrink the extruder height by approximately another 1/8".
EDIT: In molded form, the ashtray plastic seems pretty sturdy, but I won't really know until I chop one up.
Well the smaller ashtray provided enough material, so I chopped it up. This material is 1/8" thick, and it is pretty stout for plastic. I have seen these types of ashtrays break, so I know it will break if to much pressure is applied. Anyhow the cost of the ashtray is about $2, so for $2, I have my thermal isolator, and these ashtrays are available in a variety of colors, to suit your decor.
I still like the idea of being able to remove the hot end with a set screw, but I still have not figured out how to incorporate that with the new material.
Just figured it out...... Instead of a set screw, there will be two small screws coming down from the top of and through the thermal isolator and into the top of the resistance wire bobbin.
I just hope that I do not need an isolator on the top of the core.
EDIT: After pondering things for I while, I now wonder or should I say worry that this material might flex a little, when feeding the filament, especially considering the torque of the stepper motor. Either way, I will have to test it and see what happens. Additionally, I may be changing my mind about the two screws holding the hot end.
For those folks that have been following along, here is a couple more drawings.
These drawings incorporate the new thermal isolator. The side view is descriptive, but the front view is not. For more information pertaining to the front view, please refer to earlier drawings and discussion. When convenient, I will provide a new front view with part descriptions.
In the side view, you will notice that I have now included the extruder mounting holes, as well as a representation of X-axis and carriage. In numerous previous discussions, I believe I incorrectly stated that the extruder would be attached to the Y-axis, but I was wrong.
Anyhow, the side view has been altered a little to accommodate the new thermal isolator, and the Mounting Bar And Filament Guide has been lengthed, to accommodate mounting and to provide provisions for fan mounting. Please note that the filament guide of the Mounting Bar And Filament Guide has been altered to include champhers at the top and bottom to prevent scraping of the filament. The new drawing also shows a fan. The top front face of the fan will be flush or close to flush with the Mounting Bar And Filament Guide. The bottom front face of the fan will be flush or close to flush with the new thermal isolator.
I still have not determined just exactly how I am going to secure the core, nor have I determined how I am going to secure the fan. However, I do know that I want the fan to be hinged, so that it may pivot upward and out of the way, when loading the filament.
EDIT: There is one more item worth mentioning. In the previous post, I expressed concern about the the thermal isolator flexing during filament feeds. In addition to the fan providing cooling needs, when secured to the thermal isolator, the fan will act as a brace to keep the thermal isolator from flexing.
The extruder design is almost complete and I am including another side view to show recent changes.
In reference to the drawing below, you will notice that I have added two pieces of angle to the front of the fan. The top piece of angle will provide a means for attaching the fan to the extruder with a hinge. The hinge will allow the fan to be rotated upwards, which will allow ready access to the drive gear, the filament, and the core for easy filament loading. The bottom piece of angle is simply a support for the thermal isolator to prevent it from flexing downward when extruding filament, however it does not compensate for upward flexing do to filament withdraw, which is common practice. Any upward flexing that may be encountered will be compensated by software. Since the bottom of the fan is not held in place by screws, it is my intention to prevent fan movement by making a very slight press fit against the thermal isolator. In other words, since the thermal isolator is capable of slight flexing, I will use this to my advantage by creating tension between the thermal isolator and thermal isolator support, and the thermal isolator will act as a compression spring against the the thermal isolator support.
If necessary, I will add a spacer in between the X-Axis Carriage and the Mounting Bar And Filament Guide to prevent accidental collision with the unseen Y-Axis above, although at this point, I do not believe this will be necessary.
Although not compensated for in this drawing, I do want the fan to be held in place by gravity when rotated upwards. In order to do this, it will be necessary to slightly extend the length of the Thermal Isolator and the Mounting Bar And Filament Guide, to prevent interference with the filament. Additionally, although not shown in this drawing, a set screw will be utilized to prevent over-rotation of the fan and to keep the lengthening of the Thermal Isolator and the Mounting Bar And Filament Guide to a minimum.
I finally made a decision concerning the mounting of the hot end... And so I present yet another side view.
First and foremost, I want the hot end to be rigid, but I also want to be able to easily remove it. After long consideration, I finally came to the conclusion, that the entire hot end will be one assembly, which includes the Core, the Resistance Wire Bobbin, the Nozzle, and the Thermistor. Since I will be making my own hot ends, this should not be a problem for me, however others will not be able to purchase this assembly. So if you like the drawings so far, but don't like the idea of making your own hot ends, then you may have to change to a thicker thermal isolator, in order to accommodate for a set screw to hold purchased core and hot ends. However, if you make this extruder, you should have no problem making these assemblies.
Anyhow, as mentioned, and as shown in the view below, the hot end will be an entire assembly which will be secured to the Thermal Isolator with the aid of two Hot End Mounting Screws. These screws will be readily accessible from the two Screwdriver Access Holes in the Mounting Bar And Filament Guide, however the front Hot End Mounting Screw will not be accessible when the Fan is rotated upward to a full open position. To accommodate the screws, it was necessary to enlarge the diameter of the upper portion of the Resistance Wire Bobbin.
Additionally, although not shown in this drawing, a set screw will be utilized to prevent over-rotation of the fan and to keep the lengthening of the Thermal Isolator and the Mounting Bar And Filament Guide to a minimum.
In reference to my comment above, since the Fan Hinge will be secured with button head cap screws and since the heads of these screws would be approximately equal to the installed height of the set screw, the set screw idea has been abandoned.
If necessary, I will add a spacer in between the X-Axis Carriage and the Mounting Bar And Filament Guide to prevent accidental collision with the unseen Y-Axis above, although at this point, I do not believe this will be necessary.
And in reference to this comment, it was necessary to add the spacer to avoid collision with the Y-Axis, however, this would only be true, if the Y-Axis was moved, while the fan was rotated to the upward position, which I probably won't do.
Although not compensated for in this drawing, I do want the fan to be held in place by gravity when rotated upwards. In order to do this, it will be necessary to slightly extend the length of the Thermal Isolator and the Mounting Bar And Filament Guide, to prevent interference with the filament.
And in reference to this comment, when the Fan is rotated upward, there is clearance for the filament, when the Fan is perpendicular to the Mounting Bar And Filament Guide, and when it goes past, it will most likely touch the filament, but I don't see this as a problem, so the length of the Mounting Bar And Filament Guide has remained unaltered.
So without further delay, here is the new side view, showing all significant changes.
EDIT: The spacer shown in the descriptive side view does not have adequate thickness to clear the Y-Axis.
EDIT: In order to promote a better understanding of the extruder, a combined front and side view has been added to this post. In this combined view, all descriptions have been removed, the Fan is rotated to an upright position in the side view, the Idler And Tension Lever is rotated to an open postion in the front view, and several parts have been removed from both views.
Comments
Duh... Now I get it. That's pretty creative thinking.
Bruce,
I think you might want to consider a more conventional approach using PEEK/PTFE materials.
The reason for that is the high thermal conductivity of the brass and aluminum.
The current design has a short brass/aluminum rod that will need to be in the vicinity of 200 degrees Celsius on one end and under 100 degrees Celsius on the other.
It takes considerable power to drive that large of a temperature differential over that short a distance given that much area of brass/aluminum.
Chris Wardell
Perhaps you are correct and you probably are correct, but I am at a point where I like the design and the concept, so I at least have to try it out. One thing to keep in mind, is the fact that it is an evolving design and the design is still subject to change. For instance, I have been thinking about raising the heatsink off of the resistance wire bobbin, reducing the cross sectional diameter of the core in that area, and placing a thermal barrier there, such as PEEK.
I highly doubt that I am finished with the design.
- Pertaining to the heatsink, the cooling fins will still have the same outter diameter, whereas the the main body diameter will be reduced in size. Additionally, the heatsink will also be raised above the resistance wire bobbin and a thermal barrier will be placed in between the heatsink and bobbin. At this point, I am unwilling to change the cross sectional diameter of the core, but that may change in the event of a thermal meltdown
I will post a new front view, when the drawing has been changed.Happy Mothers Day to everyone!!!
While studying heat transfer, thermal conductivity, and heatsink design, I came across an image, which made the old bell ring.
By the end of the day, I will post a new design, which will have less components, be less costly, and the height of the extruder will be drastically cut. Additionally, it should be much easier to make.
I will be starting on the new design NOW. Time me
This design should be:
- Easier to make.
- Less costly.
- Less components.
- Less weight.
- Less height.
I believe this design will work very efficiently. The overall height is in the ballpark of 3-1/2".The main disadvantage is that I lost my circuit board mounting area.
The heatsink shown is just a rough draft, but it is 2" Wide X 2" Deep X 1" High.
As I see it, unless I am missing something, the main job of the heatsink is to support the hot end, with the added task of disapating enough heat so that the thermal resistant mounting spacers don't melt or carry too much heat to the motor mount bar.
I think so.
In these drawings, I have mainly altered the design of the heatsink and added a set screw for holding the hot end. Instead of being a pin type heatsink, it is now a fin type. In my opinion, it is a pretty decent extruder design, but I believe it may take some experimentation to find the proper heatsink setup. The hot end set screw is a new concept for me that I thought of this morning. Instead of hassling around with unthreading the core, for whatever reason necessary, such as changing a nozzle, I am thinking that loosening a set screw will be much easier. The main drawback of this scheme, is that the core will not be in complete direct contact with the heatsink, which I may regret, but I will make it as tight as possible, without being a press fit. At this point, it is my intention to make hot end assemblies that are comprised of the nozzle, the heat sink bobbin, and the core, all pressed together. To change a nozzle size or remove a jamb, I simply want to remove all hot end electrical connections and loosen a set screw. And of course the core will have a set screw flat.
Additionally and although not shown, it may become necessary to add a PEEK tube to the top of the core, just in case it is too hot for the filament to enter at that point. If added, the PEEK tube would be secured to the core with the aid of another set screw.
I would thermally insulate the nozzle from the heat sink. The way it is now the heat sink will be near nozzle temperature and just be wasting the heat applied to the nozzle.
C.W.
I realize the heatsink will be near nozzle temperature and that it will be wasting energy, however one of my main goals is the rigidity of the nozzle. I have read about cores coming loose from plastic due to excessive heat and I certainly don't want that. Considering my ignorance of 3D printers, my biggest fear is not being able to cool down the hot end if necessary.
I suppose I am trying to take the easy way out and just say "oh well". However I want you to know that I agree 100%. The simple fact that it wastes energy, makes it a poor design. With that in mind, I will attempt to replace the aluminum heatsink with an inexpensive, sturdy material that has low thermal conductivity and a material that can also be easily drilled and threaded.
If I can find such a material, besides plastic, not only would it be more energy efficient, but it would also reduce the height of the extruder, because the spacers would no longer be necessary.
I understand, sometime it pays to be pragmatic and get a version built to try things out.
I'm interested in this because I have a zenbot 3D router that I may modify to do 3D printing.
C.W.
Oak has a lower thermal conductivity rating than Teflon.
So a piece of Oak with two brass inserts. One insert could be used for the hot end set screw and the other could have the ID drilled out to accept the core.
However one must be concerned about it bursting into flames
So testing needs to be performed
Having experienced an issue with an extruder where the distance between the drive-gear/hobbed-bolt and the top of the hot-end was more than just a few millimeters, I would recommend, a tube or guide that keeps the filament straight between those two points. The filament would buckle during slightly-faster extrusion attempts.
On my PrintrBot Jr's original hot-end, I had to add a guide (built on the 3d printer) that kept the filament straight between those points. And, on the newly designed direct-drive extruder (see below) that I now use reduced that spacing and works quite well. This pic shows the extruder upside-down, but should show the tight spacing between the gears and the entry to the hot-end...
dgately
I sincerely appreciate the advice, however I am fully aware of how space in between guides can cause trouble. With one of my previous machines, a wire bending CNC, this was the cause of many headaches, until I remedied the problem. Please refer to Post #240, although I did not point out that specific issue, it was definitely in my mind.
Pertaining to the drawing that you cited, one of the main reasons that I rendered the core so short, with a large gap in between the drive gear and the core, is because heat may transfer up the tube and melt the plastic as it enters the core. If this does not become an issue, I will simply lengthen the core to bring it closer to the drive gear. On the other hand, if it does become an issue, the core will need an extension, using some type of material with low thermal conductivity, such as PEEK, as mentioned at the bottom of Post #253.
However, I am glad that you pointed it out, because I failed to do so. The space between guides should be limited to a very short distance, especially when pushing wire or filament with a drive gear or drive roller. MY DISCLAIMER
Going a step further in relation to Post #258, here is another document that has specific information pertaining to the thermal conductivity of both hardwoods and softwoods (http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_04.pdf), but more paticularly Table 4-7 of that document. Basically most species of wood have low thermal conductivity, however due to incomplete and unavailable information, it is currently unknown at what temperature specific species will ignite when subjected to a heat source as compared to an open flame source.
It is my opinion, through the study of available online docuents, that although PEEK and PTFE have been successfully used in creating many highly functional extruders, there also have been many failures along the way. Meanwhile also taking into the consideration the high cost of these materials, and although it may sound a little absurd, wood just may be a viable alternative for certain extruder parts, but most particularly parts that are intended to provide thermal isolation.
In my extruder design, there are two potential parts that require thermal isolation, with one being where the hot end mounts to the extruder and the other being any extension tube or guide being used by the core. Although not finalized, I do plan to test and attempt a replacement of the aluminum heatsink shown in Post #253, with a species of wood, and if necessary, a guide or an extension tube may also be made of wood. The replacement of the aluminum heatsink with wood is a direct attempt to conserve energy, while maintaining the structural integrity of the extruder and keeping the cost down. Considering the availabilty of White Oak in my region, I will use this species of wood for my testing. If the wood becomes slightly charred during testing, this alternative will immediately be discarded. Additionally, if wood is utilized as an isolation material, I would also imagine that other fail safes need to be provided in order to ensure proper and safe use of the extruder.
Okay maybe I will need a smoke detector
EDIT: On second thought, I never really liked working with Oak, so I think I may change the test species to Maple.
- Reduce height
- Reduce weight
- Reduce cost
Key changes include:- Replaced the aluminum heatsink with a thermal isolator (wood)
- The size of the tension screw, spring, and knob have all been reduced in size
- Tension screw, spring, and knob, now pivot towards the rear
- Tension screw, spring, and knob are now retained by the motor mount bar, instead of the mounting bar and filament guide
- The height of the mounting bar and filament guide has been reduced
- The idler and tension lever has been highly revised to accommodate the other changes and to open to a ninety degree angle
With this new design, complexity and cost should be greatly reduced, as well as the height, width, and weight. The extruder now measures 3-7/64" in height, as compared to 5-7/16" back in Post 232.In this post, I am providing a preliminary front view, without all the item descriptions, but by reviewing the documentation and other drawings, you should be able to visualize the extruder.
This design will be my first prototype, just to see if the wooden thermal isolators will work without smoking or charring.
http://www.fpl.fs.fed.us/documnts/fplmisc/rpt1464.pdf
C.W.
Interesting document....
It certainly sounds bad for Maple
After coming to the conclusion that a plastic ashtray might make a nice thermal isolator for a hot end, I decided to take a Mapp gas torch to a 4" diamenter ashtray I had sitting around. I heated up the ashtray until the plastic just started to bubble and then I shut down the torch. Methodically working my way from the furthest point to where the heat was applied, I tested various points for temperature, using my thumb and index finger. All testing was completed within approximately 10 seconds of shutting down the torch. To simplify the description of the test results, I will simply provide a picture of the ashtray and general temperature.
With as much heat as I applied, if this ashtray had been made of aluminum, the slightly warm areas would have been too hot to touch. Additionally, within approximately 35 seconds of shutting down the torch, I tested the temperature at the location where the flame was applied, and it was hot, but not too hot that I could not hold onto it.
In my opinion, ashtray plastic should make a nice thermal isolator for replacing the heatsink, and thus conserve energy. I will be making my thermal isolator from the bottom of the following ashtray, because it is much larger, or maybe not, I will take a second look at the smaller ashtray to see if I can make it out of that one. If that does not work, here is the other one.
EDIT: This still does not account for an isolater at the top of the core, if one is required.
EDIT: Additionally, this should shrink the extruder height by approximately another 1/8".
EDIT: In molded form, the ashtray plastic seems pretty sturdy, but I won't really know until I chop one up.
I still like the idea of being able to remove the hot end with a set screw, but I still have not figured out how to incorporate that with the new material.
Just figured it out...... Instead of a set screw, there will be two small screws coming down from the top of and through the thermal isolator and into the top of the resistance wire bobbin.
I just hope that I do not need an isolator on the top of the core.
EDIT: After pondering things for I while, I now wonder or should I say worry that this material might flex a little, when feeding the filament, especially considering the torque of the stepper motor. Either way, I will have to test it and see what happens. Additionally, I may be changing my mind about the two screws holding the hot end.
These drawings incorporate the new thermal isolator. The side view is descriptive, but the front view is not. For more information pertaining to the front view, please refer to earlier drawings and discussion. When convenient, I will provide a new front view with part descriptions.
In the side view, you will notice that I have now included the extruder mounting holes, as well as a representation of X-axis and carriage. In numerous previous discussions, I believe I incorrectly stated that the extruder would be attached to the Y-axis, but I was wrong.
Anyhow, the side view has been altered a little to accommodate the new thermal isolator, and the Mounting Bar And Filament Guide has been lengthed, to accommodate mounting and to provide provisions for fan mounting. Please note that the filament guide of the Mounting Bar And Filament Guide has been altered to include champhers at the top and bottom to prevent scraping of the filament. The new drawing also shows a fan. The top front face of the fan will be flush or close to flush with the Mounting Bar And Filament Guide. The bottom front face of the fan will be flush or close to flush with the new thermal isolator.
I still have not determined just exactly how I am going to secure the core, nor have I determined how I am going to secure the fan. However, I do know that I want the fan to be hinged, so that it may pivot upward and out of the way, when loading the filament.
EDIT: There is one more item worth mentioning. In the previous post, I expressed concern about the the thermal isolator flexing during filament feeds. In addition to the fan providing cooling needs, when secured to the thermal isolator, the fan will act as a brace to keep the thermal isolator from flexing.
In reference to the drawing below, you will notice that I have added two pieces of angle to the front of the fan. The top piece of angle will provide a means for attaching the fan to the extruder with a hinge. The hinge will allow the fan to be rotated upwards, which will allow ready access to the drive gear, the filament, and the core for easy filament loading. The bottom piece of angle is simply a support for the thermal isolator to prevent it from flexing downward when extruding filament, however it does not compensate for upward flexing do to filament withdraw, which is common practice. Any upward flexing that may be encountered will be compensated by software. Since the bottom of the fan is not held in place by screws, it is my intention to prevent fan movement by making a very slight press fit against the thermal isolator. In other words, since the thermal isolator is capable of slight flexing, I will use this to my advantage by creating tension between the thermal isolator and thermal isolator support, and the thermal isolator will act as a compression spring against the the thermal isolator support.
If necessary, I will add a spacer in between the X-Axis Carriage and the Mounting Bar And Filament Guide to prevent accidental collision with the unseen Y-Axis above, although at this point, I do not believe this will be necessary.
Although not compensated for in this drawing, I do want the fan to be held in place by gravity when rotated upwards. In order to do this, it will be necessary to slightly extend the length of the Thermal Isolator and the Mounting Bar And Filament Guide, to prevent interference with the filament. Additionally, although not shown in this drawing, a set screw will be utilized to prevent over-rotation of the fan and to keep the lengthening of the Thermal Isolator and the Mounting Bar And Filament Guide to a minimum.
First and foremost, I want the hot end to be rigid, but I also want to be able to easily remove it. After long consideration, I finally came to the conclusion, that the entire hot end will be one assembly, which includes the Core, the Resistance Wire Bobbin, the Nozzle, and the Thermistor. Since I will be making my own hot ends, this should not be a problem for me, however others will not be able to purchase this assembly. So if you like the drawings so far, but don't like the idea of making your own hot ends, then you may have to change to a thicker thermal isolator, in order to accommodate for a set screw to hold purchased core and hot ends. However, if you make this extruder, you should have no problem making these assemblies.
Anyhow, as mentioned, and as shown in the view below, the hot end will be an entire assembly which will be secured to the Thermal Isolator with the aid of two Hot End Mounting Screws. These screws will be readily accessible from the two Screwdriver Access Holes in the Mounting Bar And Filament Guide, however the front Hot End Mounting Screw will not be accessible when the Fan is rotated upward to a full open position. To accommodate the screws, it was necessary to enlarge the diameter of the upper portion of the Resistance Wire Bobbin.
So without further delay, here is the new side view, showing all significant changes.
EDIT: The spacer shown in the descriptive side view does not have adequate thickness to clear the Y-Axis.
EDIT: In order to promote a better understanding of the extruder, a combined front and side view has been added to this post. In this combined view, all descriptions have been removed, the Fan is rotated to an upright position in the side view, the Idler And Tension Lever is rotated to an open postion in the front view, and several parts have been removed from both views.
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Have you tried this out yet?
No, I have not built it yet, but that is the design for me. Lately I have been working on this thread, in an attempt to design a controller for the printer. This thread has come a long way also. Take a peek, http://forums.parallax.com/showthread.php/155404-Input-Needed-Combining-Propeller-Proto-Board-Prop-DIP-40-and-ADC-for-3D-Printer/page5