Got a fixture idea, need some advice (PLEASE)

Thanks in advance unless everyone ignores me then screw off...joking

Here's the theoretical part... a 5-6" long round graphite rod, with tapers on it. very simple geometry. Imagine the tip is .010 diameter with a 3 degree angle that changes to a 2 degree angle at a diameter of .150, then goes on the rest of the way at the

2 degrees. Basically 2 tapers on a round shaft. Simple enough.

But a real pain in the azz to manufacture. Currently I grind them, manually, or cnc. Sometimes I do a lathe operation in the mill with the electrode in the spindle and a lathe bit on the table. All these things work fine, till we get to the .010 diameter tip hanging out 5" made out of graphite. of course this operation is more complex due to the needed +-.0001 diameter and a max of .0004-.0005 tir on the tip.

If you havn't imangined it yet, all these operations cause deflection of the flexable graphite sticking out 5"-6" at such a thin diameter. The idea I want to really try is using a wire edm machine and copper electrodes, and turn and burn the part. Problem with that is we have 2 wire machines and 2 operators who have no intention of trying that. Added to that problem is they havn't dropped a slug in years, so basically those 2 machines will never be open for R and D.

So...here's my alternative fixture:

On this web page is a herman smidt fixture we bought a few years back...we are talking kick azz quality. One tenth all day long.

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Now, imagine that fixture up on parrallels or whatever to get the allen wrench hole on the side that drives the dies lined up with a 4th axis on a mill. Then, instead of the 3 pins it uses to hold the part, they become the cutters. Take carbide pins and maybe edm a dome in the top of them to create a cutting edge that can be infinitely indexed.

Now, to operate it would be to simply load the pickup bushing herman smidt provides and pickup the center of the fixture. Touch the electrode on top and you are ready to go. Programming would be relatively simple, figure how much an angle drops for how much infeed.

example: 3 degrees, 1 inch deep

N1 G91 Z-.002 A.009 F1. N3 GOTO 1 (500 times)

(note..the A was a guess, I would need to measure the actual fixture to see the feed rate ratio to rotation).

What I'm looking for from this group is things like why it wouldn't work, or better ways to make it, or the real thing I'd like to see, something ALREADY invented out there.

Please dont say pencil sharpener. It's just not funny anymore.

Reply to
vinny
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Do it in a Tsugami.

Reply to
John R. Carroll

Can't you turn or grind it between centers? Cut one end off and last finish the .010" tip! Simple! JS

v> Thanks in advance unless everyone ignores me then screw off...joking >

Reply to
Protagonist

tried it. When you cut it off the tir goes bananas. .001-.002 or worse.

Reply to
vinny

I went to the site and checked it out. I'm not sure how that would change anything, Iv'e tried it on a lathe, even with coolant just in case it helped. But... Can the thing have a tool on both sides of the part? That might work? Can't use a support easily, it's graphite and has a tiny tip. Besides, when the tip is .010 (lots of times down to .003) a single point tool wont work, the stuff is too flexible.

Reply to
vinny

Actually, the tip sticks thru the part, usually .030 or whatever you can get away with, so the length isn't critical. If I could cut it off, that would be good enough.

Reply to
vinny

=20 I would try creep grinding/turning the full profile in one sweep on a CNC grinder with a 1A1 profile wheel running a few degrees horizontal to the centerline. This would keep radial deflection to pratically zero. A 1/2" or maybe 3/4" graphite rod should be stiff enough, even with 5" hanging out.=20

We often do this when we need to grind small, long & thin parts. If the parts are too long or thin we use a steady-rest which "follow" the wheel. This way we can grind i.e. a 0.025 x 2" core with multiple steps. Don't know how "dead" graphite is, though, might have a problem holding the TIR. =20

I guess the parts are for EDM'ing hot-runners of some sorts? If so, why not use a free cutting copper alloy and have them made on a Tsugami like John suggest.=20

--=20

-JN-

Reply to
J. Nielsen

Like Steve suggested, run that puppy on a Swiss.

The headstock on a Swiss feeds the material through a guide bushing. You can position your cutting tool about .050 away from the guide bushing that supports the barstock, and feed the material into the tool. Since your tool is so close to the guide bushing, there is no chance of material deflection. Therefore greatly reducing any TIR problems because of length to diameter issues.

Since your trying to hold +/-.0001, the feed would have to be pretty slow, and I'd probably take it easy on the RPM's as well. I only have a 4" stroke on my 5-axis Swiss, so I couldn't make them, but someone with a larger machine could probably spit those long skinny parts out in a little over a minute.

The time will vary greatly depending on RPM. I was thinking 8000, but then, I don't know squat about graphite.=20

Matt

Reply to
Matt Stawicki

I had an old Davenport & I am an old geezer, most cams are off the self but for this job they would have to be modified a little . Run OIL . Chucker use, load 5 pcs... couldn,t use an old geezer for that, maybe an illegal?

Reply to
Why

Vinny,

What quantities?

Since your other methods have not produced acceptable results, it may be less expensive in the long run if you sent it out to a Centerless Profile Grinding Job Shop. This is a quick and easy job for a centerless profile grinder, preferably one with CNC dressers.

The style machine would be the Cincinnati Centerless Grinder that has the regulating wheel supporting the entire part. Not the type grinders that are little more than an OD grinder with a "centerless" attachment holding one end of the part rather than supporting the diameters being ground.

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(photo)

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(video of fully automated centerless)

Superior makes and sells 2 axis cnc dressers for the type centerless I am talking about. They make attachments for both grinding and regulating wheel dressers.

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them for a centerless profile grinding job shop or search the web.

Tom

Reply to
brewertr

Like Steve suggested, run that puppy on a Swiss.

The headstock on a Swiss feeds the material through a guide bushing. You can position your cutting tool about .050 away from the guide bushing that supports the barstock, and feed the material into the tool. Since your tool is so close to the guide bushing, there is no chance of material deflection. Therefore greatly reducing any TIR problems because of length to diameter issues.

Since your trying to hold +/-.0001, the feed would have to be pretty slow, and I'd probably take it easy on the RPM's as well. I only have a 4" stroke on my 5-axis Swiss, so I couldn't make them, but someone with a larger machine could probably spit those long skinny parts out in a little over a minute.

The time will vary greatly depending on RPM. I was thinking 8000, but then, I don't know squat about graphite.

Matt

hmmmm, you guys are giving me some good ideas! We have lots of gun drills, lots of bushings, I could rig one up to cut for a test. But, the graphite? I wonder how smooth it would feed thru the bushing? I was thinking, a cutter behind the bushing would size the stock for the bushing, then, the cutting of the trode will happen on the outside of the bushing.

damn, where's my pencil! thanks.

Reply to
vinny

Have it supplied to you centerless ground. There isn't anything new about what you want to do and there is a very good reason for the low TIR. I was doing these types of syringes in the mid 90's and was also the first to succesfully produce tipless plunger syringe assemblies. If they aren't extremely round when you mold them the plungers leak, which is no good in a disposable drug delivery system that's prefilled. Screws up the dosing and makes an unsanitary mess.

Reply to
John R. Carroll

========== As you are already grinding these, what you may need is a better grinder.

This just showed up in my email.

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Most likely you won't want to buy one for just this job, but some one in your area may have and be looking for some work to start paying back their loan.

Anyone in the group used one or something like it?

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Reply to
F. George McDuffee

"vinny" wrote in news:fqm8g7$ma$ snipped-for-privacy@aioe.org:

In a Swiss screw machine the bar is chucked in a collet and fed through a bushing by the headstock which slides along the Z-axis. The turning tools are generally fixed in "Z" and move along the X and Y axes. Your turning tool is set 1mm in front of the bushing so you are cutting right at your support. You turn in one pass. I've turned a 0.0005" diameter by 1/2" long in BeCu just to see if it could be done. It can. That's 1,000 times the diameter in length. No additional support was used.

I've run graphite rod in a Swiss before and there are a couple of issues. First you'll have a long remnant. Probably 5-7" long. You also have to have a spindle liner that's fairly close to the bar diameter. Bar whip will crack the graphite rod. Third, to hold the tolerances you need, you'll need to start with a centerless ground rod.

Reply to
D Murphy

So cut out the middle man (you) and centerless grind the part to finish dim's....

Tom

Reply to
brewertr

Well Ok but EDMS will provide centerless ground round stock as a catalogue item. I think I know now why Vinny is working nights. LOL

Reply to
John R. Carroll

F. George McDuffee wrote in news: snipped-for-privacy@4ax.com:

Sure.

(It's the same machine)

Weldon imports/supports/modifies the Tsugami grinding machine(s). The punch grinder is the G18 fitted with C-axis and a bunch of really cool software that Weldon wrote. It's so easy to use I bet they could even train Cliff to grind punches on it.

The bigger machines (1632, Phoenix, etc,) are all built by Weldon right in York. The little grinders are Tsugami under the sheet metal. Weldon does the controls, automation, and anything special for the customers application. Weldon is a great company with some really talented people. I've seen some remarkable applications and specials that they've built.

Reply to
D Murphy

snipped-for-privacy@aol.com wrote in news: snipped-for-privacy@4ax.com:

I suppose if you have all day vs. a minute or less. Through feed grinding a bar is fairly quick and simple. Crush grinding down to a ten thou diaamter is a whole other deal. Not to mention the stress centerless grinding induces into the part and the resulting spring and TIR issues.

Reply to
D Murphy

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ROFLMAO! Spit up some prefectly good coffee. You owe me a keyboard!

Reply to
Matt Stawicki

I am on night's because I don't fit in. I'm not in a mold shop, I'm in a machine shop. (slaves)

ANY kind of blanking up of graphite is a major waste of time. The worst is when the boss of a shop decides he's gonna save money by forcing everyone to use the graphite in the waste pile. How much graphite does 75 bucks an hour buy in 3 hours of blanking?

Reply to
vinny

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