Cutters

Newzed

Does anyone have a good source for high-speed steel or carbide cutters smaller than .032 diameter?

Thanks

Sid

Ken Gracey

Sid,

J&L Industrial has ball and square mini end mills down to 0.01" diameter on page 338L of their current catalog. These end mills are solid carbide and require some·perfect feed rates for the·material·selected and·the right RPM. A bad choice of one of these three factors will send one·shooting sideways from the mill.

I used a square end mill·(0.025" diameter) yesterday to engrave Parallax EFX on the front of these ABS glass skull·bases for·trade show props. The front·square measurements are 1" x 2.75" so you can envision the engraving dimensions. It's a lot more fun to use 3/32" ball end mills and get·some big fat letters, but that would have created blob letters. These·bases·have·five holes for LEDs which are controlled by a Prop-1 to create a lighting effect in the glass skull. The bottom cutout holds the Prop-1·and the power supply comes out the back.·Most of this was milled with 3/8" square end mills.

If you think this is·strange, you should see the Linda Blair head the EFX crew wants to buy on eBay. Thankfully, that auction has closed and it is no longer available. Hopefully one of my EFXers didn't·win the auction (they'd probably like to·make·it spin around and shoot green stuff·from·a trade show booth).

I assume you want these mini mills for PCB cutting on the "Community Milling Machine"?

Ken Gracey
Parallax, Inc.

Jon Williams

For those wondering why Ken is machining bases for crystal skulls, visit our new Parallax EFX group web site -- we're having lots of fun with BASIC Stamps over there, and you can see a short video of the crystal skull in action.

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Jon Williams
Applications Engineer, Parallax

Newzed

Thanks for the pointer, Ken.· As a matter of fact, I bought the MF70 Micro mill I was telling yiu about.· It came Friday and I have been busy figuring out best to use it.· The X-Y-Z axes all have little handwheels, are they are a bit harder to turn than I thought they would be.· I'm going to have a tough time finding a stepper motor that will handle the torque, plus I haven't the vaguest idea how I'm going to connect the stepper to the axes.· Right now every thing is manual - one turn of the X-Y handwheel moves the table .0393 inches.· I've been making special clamps out of 1/2" thick Lexan which work quite well.· I routed out a channel on the bottom of each one .125 wide and .040 deep.· This channel receives one edge of my little PC board.· I made a special fixture which the Lexan outside edge slides·up against to keep the Lexan perfectly square with the X travel.· The smallest cutter I have is a little .032 ball cutter which is not perfectly round on the bottom - it has sort of a "rounded" point.· I have been able to cut slots with that about .020 wide but the Z adjustment is very critical.· That is why I was looking for something around .025.· I'd like to see if I can make a rather crude PC board which will hold a 595 and a 2803 so I can build up the ccircuit to drive a stepper using Jon's Demp program.· When I say crude, I'm not joking - all pads are .065 square and the lands are .060 wide!!· All I have to do is route a .025 isolation gap between everything.

I also made an edge guide for my Dremel drill so I can drill holes for the chips in a straight line.· I'll use .035 holes so if the vertical spacing is a little bit off I can still plug the chip socket into the holes.

Don't laugh, my friend - I gotta start somewhere.· Right now I'm going to J & L and see if I can find a .025 cutter.

The engraving you did - did you program all that into your CNC?

Sid

Newzed

Forgot to ask, Ken - which would be best for trying to make a PC board - 2 flute or 4 flute.· They are the same price.

Sid

Bean

Sid,
For our LPKF PCB milling machine at work we use bits from "Think and Tinker".
www.thinkandtinker.com
Bean.

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"SX-Video·Module" Now available from Parallax for only $28.95

http://www.parallax.com/detail.asp?product_id=30012

Product web site: www.sxvm.com

"What's the difference between ignorance and apathy ?"
"I don't know, and I don't care."
·

Newzed

Bean, that cutter with the 60 degree tip looks like the perfect tool for trace isolation.· Is that the one you use?

Sid

Newzed

OUCH!!· They have a $50.00 minimum

Any chance I could buy a couple from you?

Sid

Forrest

You can buy a 10 piece set of .036 inch, 3 flute resharpened end mills for $12.95 at www.drillbitcity.com/catalogue/special_tools.asp?Pt=2&St=&Sc=
Just click thru the pages of specials until you find it.

Ken Gracey

Sid,

Two or four flute - your choice. Multi-flute mills are often used for finishing work. You will increase the feed rate at the same RPM with four flute mills.

As for attaching steppers to the mill, I'd recommend you use a mini drive belt/gear system. Don't bother attaching the steppers for a direct-drive setup - it's going to cause missed steps and probably too high of a step/distance.

Also, it's best to use the largest cutter you can for a particular job. If you're plunge cutting PCB material, step up to a larger mill diameter. That small machine probably can't provide the RPM needed to effectively use a small end mill, not to mention that the finish is better with a larger cutting tool.

Yes, the logo was programmed in CNC. Trying to do that manually would take all day. One wrong move and bamm! the whole piece is trashed. The engraving process with CNC took only five minutes per base.

Ken Gracey
Parallax, Inc.

StarMan

An old machinist once told me that 2 flute cutters were best for softer materials like aluminum and plastics and 4 flute cutters were best for hard stuff like steel, etc.

As Ken mentioned, speeds and feeds should be adjusted accordingly.· Since you got your own mill, I'm guessing you will be doing a lot more machining.· I suggest you invest in a Machinery's Handbook.· Last time I bought one they were about $50.· That was before Amazon existed.

And... I guess great minds think alike.....ha.· I've been working on skull lighting of my own.· I'll be doing it with slow changing RGB leds.· I ordered a [url=mailto:BS@SX]BS2SX[/url]·kit from ebay and I'm going to try to control the LEDs with Bean's PWM program.

PLJack

Newzed said...
The X-Y-Z axes all have little handwheels, are they are a bit harder to turn than I thought they would be.
Sid

Thought you might want to read this.

Proxxon Conversion
www.indoor.flyer.co.uk/millingmachine.htm

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Jack

Newzed

Russell, I just went out and ran a little backlash test on the MF70.· i rotated the Y hand wheel several turns CW, stopping on 0.· I ran my cutter in about 1/2", then backed it out.· I turned the Y handweel three turns in the CCW direction, the three turns back, stopping on 0.· I ran the cutter in again and it looked like it was dead on.· I moved the Y hadwheel 1 division - .002" -· and ran the cutter in again.· I could definitely see the jog in the cutter slot, so whatever the backlash is, it is much, much less than .002".· I'll give you .0005".· Of course the mill is brand-new.· I would expect the backlash to increase a tad as the machine wears.

Sid

pjv

Hello Sid;

I'm not sure I understand your test. I thought that backlash was the amount of combined "slop" in the lead screw nuts and lead screw end bearings. By your description I can't understand how you measured the backlash to be much less than 2 thou. Normally I would expect this to be done with dial gauges.

Furthermore, as far as estimating small distances are concerned, it is very difficult to "eyeball" them. In my experience, to even see 1 thou distances really requires magnification of 5X or more; and half a thou? well I just can't imagine.

In our shop we need to machine holes in castings positioned to an accuracy of one third of one thou with our CNC machine, and at times it can take an expert machinist one whole day just to set things up right. The deflection alone in small cutters can easily be several thou, and precision measurement is no simple task. Our ability to certifyably read a hole center to the half a thou precision you speak of requires a $15,000 instrument.

Cheers,

Peter (pjv)

Newzed

Peter, I'm sure you are more knowledgeable than I, but I have always thought that backlash was the positional eror that occcurs if you move the leadscrew X turns CW, then X turns CCW.· In other words, the difference in where you started and where you finished would be the backlash.

I was using a 5X magnification headband, and was really comparing the difference in the slot to 0 offset and .002 offset.· The .002 offset I could easily see - I could see no difference in the 0 offset, 0 offset being moving the Y table two turns CW, then 2 turns CCW.

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

·

bobledoux

With the limited torque found on stepper motors you might want to loosen the gibs on the ways to reduce force required to turn the handscrews.

Newzed

And just what, pray tell, are the "gibs"??????????????

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

·

Russ Ferguson

Steve Bedair's web site has information on tuning up a lathe and talks about the gibs.
http://www.bedair.org/Gib/Gib.html

Ken Gracey

Sid,

Gibs are normally molded from a composite material and they fit between the two dovetail ways. Their purpose is to make final adjustment on machine tool dovetails to compensate for tolerances and wear. They're usually thin and have an angle cut on both sides to match your ways. Gibs can usually be adjusted·to eliminate slop, which is all but impossible to avoid with a lead screw and brass nuts (the alternative is ball screws and bearings).

Peter is telling you that you can not measure backlash with the eye. To measure backlash in a single direction you need to put a dial indicator on a magnetic base against the vise or something else mounted on the mill. Turn the handles of the mill one direction to see the dial indicator move - maybe a 1/4" distance. Next,·turn the handle the opposite way to back the part off of the dial indicator. Take note of the distance you turn the handle prior to seeing the dial indicator move.·The amount of handle movement (manually in·this·case) is your backlash. If your handle turns 20 times for an inch and this test required a quarter of a turn, then your backlash is 0.0125". Once you've got a grip on this value then you can build the backlash compensation into your projects. Stepper control software can build in some "wasted steps" each time it needs to reverse direction. Measure it several times to check for consistency, too.

At least this is how I measure backlash. If·I posted my explanation on a machinist forum I'd find out I'm all wrong.·My point is you need·a dial indicator. Go to·www.littlemachineshop.com and get one of their Phase II indicators. These are cheap (price and quality) and good enough for what you are doing.

Ken Gracey
Parallax, Inc.

pjv

Hello Sid;

I was not understanding how you were making your measurement without dial gauges of some sort. I have not seen any "rulers" with graduations fine enough to measure the distance between holes, altough an optical loupe with an appropriate reticle could do a credible job for very short distances.

I just wanted the forum readers to be aware that certifyable precision measurement is not a trivial task, and deflection in cutters can certainly give an unspecified error of several thou.

I like Ken's explanation of backlash measurement.

I know I love the precision of our CNC which has a position resolution of one tenth of one thou. Although the actual placement accuracy over its 24 inch table travel is quite a bit poorer than that eventhough it uses a programmable look-up table for correction along its travel. I guess it is really hard (expensive) to grind lead screws of any significant length with such precision, never mind temperature effects....... one tenth of a thou is REALLY small.

Have fun with your new machine!

Peter (pjv)

StarMan

I machine a fair amount of stuff by hand.· Nothing of high precision, though.· The·method I try to use is to approach all positions on a work piece·from the same direction.·

If you are moving to a position that is in an opposite direction from your positive direction of travel, go past that position by an amount greater than your backlash and then return to the desired position.· This works well for hole patterns.· It's more difficult for 2 dimensional milled sections.



Chris I.