WEDM high concentricity bore, ER collet or vise?

Been working in the same machine shop for 3 years, and we have this one part we struggle with.

We have to finish a bore to within .0005 TIR to and OD that varies by .0005-.002 regularly.

Currently we are using a custom cut v-block style clamp to hold it, as we also cut various slots around the outside of the part.

The slots around the outside have a .005+/- range so they are super easy.

My question, would a ER style collet work or would a much more expensive 3 jaw self centering vise linked below be worth the $4k cost?

Or do you guys have another idea?

Stainless Steel Precision Three Jaw Chuck – Square .020” – 1” Capacity - BTDSQ - Hermann Schmidt Precision Workholding

nlancaster said:

Been working in the same machine shop for 3 years, and we have this one part we struggle with.

We have to finish a bore to within .0005 TIR to and OD that varies by .0005-.002 regularly.

Currently we are using a custom cut v-block style clamp to hold it, as we also cut various slots around the outside of the part.

The slots around the outside have a .005+/- range so they are super easy.

My question, would a ER style collet work or would a much more expensive 3 jaw self centering vise linked below be worth the $4k cost?

Or do you guys have another idea?

Stainless Steel Precision Three Jaw Chuck – Square .020” – 1” Capacity - BTDSQ - Hermann Schmidt Precision Workholding

Click to expand...

I've had the same struggles with some parts, bit the bullet an bought the Hermann Schmidt Three Jaw Chuck. As long as your stock is good an round, this fixture has been worth it.

Id just use a Grinding vise, I hold better than .0005 regularly with them.

Bore a pilot hole when turning the od, then pick up pilot on each part?

Part is 1.5 inches long and thru hole final size is only .1504, lathe operators swear they cannot bore a hole that long and only .140-.145 size.

Put a .125 hole through it, or smaller. You should only need a hole .012 to thread 10 wire through.

Hi nlancaster:
I know the Hermann Schmidt stuff is very good, but I've still done best by wiring a custom holder from a scrap block and using an expansion/contraction clamp to spread it so my part will slip in.
The thing with the Hermann Schmidt is that you still have to pick it up with the wire, and the accuracy of the pickup will depend on a bunch of things that are hard to control within tenths.
With a custom holder you KNOW where the center is because you wired it, and then didn't move it so if you get the size right, the orientation is close to perfect.
I put a relief slot into the fixture to make one side flexible and then use the spreader clamp to spread the fixture just enough to slip in the part.
Then I cinch up the clamp and cut my part.
I can get it within a tenth or two without having to try to pick up the part, or a chuck, and I know it's not tilted off axis relative to the wire too.

Sadly, for once I cannot find a good photo of the whole setup to show you, but here's one of the clamp I use.

It's pretty simple; the bottom screw pinches the two round stems together and the top screw spreads them.
So my custom fixture has the main bore, a split, a relief slot and the two sockets to fit the clamp wired into them all in one setup.

The fixture bore is wired to exact size and the other features are wired in with just a roughing cut (no need for accuracy except for the main bore).
The clamp is dropped into its sockets and the top screw is tightened to spread the fixture.
The part is slid in and the top screw is relaxed again.
Then the bottom screw is nipped just enough that the part can't move.

Last the part is wire cut using the same origin.
I've never been disappointed with this method and it has the virtue of cheapness too.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Drill it and ream it with carbide drill and reamer no problem
Don


Sent from my iPhone using Tapatalk Pro

nlancaster said:

Been working in the same machine shop for 3 years, and we have this one part we struggle with.

We have to finish a bore to within .0005 TIR to and OD that varies by .0005-.002 regularly.

Currently we are using a custom cut v-block style clamp to hold it, as we also cut various slots around the outside of the part.

The slots around the outside have a .005+/- range so they are super easy.

My question, would a ER style collet work or would a much more expensive 3 jaw self centering vise linked below be worth the $4k cost?

Or do you guys have another idea?

Stainless Steel Precision Three Jaw Chuck – Square .020” – 1” Capacity - BTDSQ - Hermann Schmidt Precision Workholding

Click to expand...

I have the Hschmidt fixture. I am able to square the wire to it, use the gage rings to pick up once, then run all day. It holds .0005 concentricity no problem. The parts do need to have a good OD to repeat though.

We have a custom holder already, issue is when the OD varies .001-.002 the concentricity suffers. And yes we have asked the lathe guys to hold it to less then .001 tolerance, and they either won't or can't. We do make several hundred of these at a time every few months.

The vise I linked claims to hold to .0001 even with OD variations, that is what is making me think it will solve our issues.

Hi again nlancaster:
OK, given your constraints, you will be well served by the Hermann Schmidt chuck.
As I said in my previous post, it is a very nice device...accurate, repeatable, designed for the environment etc etc.
I don't think you can go wrong with it, with the caveat that humanrobot points out in post # 9.

By contrast, the ER chuck solution is going to be a PITA on a few fronts:
First, you need to make a holder for it...not a show stopper but a minor nuisance.
Second, unless you can find stainless collets and a stainless body it's going to be rusted to ratshit pretty quickly.
Third, you're always dealing with a bunch of bits and pieces; the collet and the collet nut, and the wrench, and the part itself.
Fourth you can't hold the height easily, especially if the part diameters are all over the map, so you risk clipping the lower flushing nozzle every time you clamp an undersize part and it drops down too far as you clamp it.

However, as humanrobot commented, if the parts aren't cylindrical, if they're rougher than guts, if they are lousy with burrs, the super HS chuck won't help enough to matter.

So you might have to dope slap the turning department if they can't (or more likely can't be bothered to) hold a reasonable diameter tolerance or finish on the chucking surface.
It's not like you're asking the earth here, so do what you need to do, get noisy if you must, and bring the blank parts into a state where they can be used efficiently by the wire EDM department.

Once you've achieved that, hitting your concentricity tolerance won't be an issue, and the chuck will be a super convenient way to get there.
I'll be jealous when you get one, so make sure to gloat on here with pictures

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Marcus,

The Lathe guys turn out a great finish on the parts, just the OD of .300 varies +/- .001 no matter what they seem to do. And that variation moves the total concentricity on the current clamping method as it is basically a vblock vise on both sides with a fixed jaw. We made a huge improvement too it last year when we were making a new fixture, and I suggested one screw with a flexure on the otherside, repeatability went way up.

you need to sub out the turning part, then you can reject out of size parts that will not work edm efficiently

Could you hold the part by the back edge to expose more of the part and pick up with the wire on the od of the part to find the true center with a 3 point pick up.
Just thinking.
Don


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D Nelson said:

Could you hold the part by the back edge to expose more of the part and pick up with the wire on the od of the part to find the true center with a 3 point pick up.
Just thinking.
Don


Sent from my iPhone using Tapatalk Pro

Click to expand...

This is on the right track but you really want 4 points of contact 90° from each other, then also be able to rotate the pickup 45° and retake the points. This will give you a pretty good picture of what you are working with.

Do you indicate vertical runout?

Hi D Nelson:
You asked "Could you hold the part by the back edge to expose more of the part and pick up with the wire on the od of the part to find the true center with a 3 point pick up.
Just thinking.
Don"

The problem with picking up on the wire is that there are three main things you must have in order to get a chance at a good pickup.

First, the part must be accurately positioned in the XZ and YZ planes.
If it's tipped even a little bit you'll never know it without clocking it in and your wire touches will be wrong , because the wire finds the point of first contact and calls that the edge of the part, even if it's more like the corner of the part in reality.

Second. the touch off faces must be geometrically very good: very smooth, burr free, and flats have to be flat, cylinders have to be cylindrical etc etc.

Third, you must have good places available to touch: the process of hanging the part into the worktank so the lower head can travel freely under the part and the upper head can travel freely over the part often makes the edges inaccessible to wire touches, especially ones distributed over enough of the periphery of the part to make meaningful touches.
You're almost always grabbing some part of the periphery of the part unless you are cutting a plate shape that's capable of being clamped directly to the machine table with enough hanging out into the worktank that you can reach everything without plowing the lower head into the table or running out of travel for machines that have a built in NO-GO zone near the table(s).​

All of those things, (never mind the problems getting a touch with wet or dirty parts) make picking up edges a sometimes frustrating exercise in uncertainty, so a good fixture that is repeatable once verified is super useful.
The Hermann Schmidt chuck is a great choice when you can't guarantee that all parts are virtually identical in diameter, but you still have to get your features into the middle of them within close limits.

So the protocol is to pick up the fixture as best you can, load one, wire it, check it and adjust accordingly.
Now you can just wire all your remaining batch with confidence you're within a tenth or two from part to part even with variable diameters.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Yeah, can't pick up the OD of the barrel as there is a larger section of the part that has a looser tolerance for concentricity.

Along with all the issues of true verticality.

with the Herman Schmidt three jaw mounted to a 3R Adjustable base, I can chuck up a dowel pin of the right size and use a TDI to dial in verticality.
Then insert the HS bushing of appropriate size to find true center of the chuck.
Burn the first part, and verify and adjust as needed.
Once done should get as perfect as possible parts for the rest of the run.

If all the parts are different one setup will probably not work...gonna have to indicate them all. You said they runout between .0005-.002. That's a long way off to hold .0005 tir.

nlancaster said:

Yeah, can't pick up the OD of the barrel as there is a larger section of the part that has a looser tolerance for concentricity.

Along with all the issues of true verticality.

with the Herman Schmidt three jaw mounted to a 3R Adjustable base, I can chuck up a dowel pin of the right size and use a TDI to dial in verticality.
Then insert the HS bushing of appropriate size to find true center of the chuck.
Burn the first part, and verify and adjust as needed.
Once done should get as perfect as possible parts for the rest of the run.

Click to expand...

If you end up with the Herman fixture, I use a 3 or 4N-M torque wrench to help with repeatability.

The herman 3jaw vise is a self centering vise. claims to hold .0002 with OD variances.