Off by a Mile

[SeymourDumore]

Hello Semore,

And repeatedly again, my better judgement was correct ...

 

[plastikdreams]

Locating within a tenth with any machine is difficult at best. With a wire machine it's going to take a little trial and error. You especially need to figure out your overburn in the material first and foremost. I estimate overburn of 10 wire in my machine to be 4k, so 2 per side. Material, thickness, epack, and speed can all vary that setting. Even your incoming power can make it vary.

Then there's the recast layer...a whole nother variable.

For instance, I recently cut some tube 2 pieces to be 1.000 long each. I know how our wire cuts and I have programmed this accordingly. 1 came out at 1.00010 the other at 1.00020. I could stone them to 1.00000 but it doesn't matter lol, I could have been 5 under.

I'm surprised Marcus isn't here commenting. He always has great ideas and suggestions.

 

[007Rob]

To the OP: If you're using the start hole to pickup the part, are you sure the hole is on location? A lot of times wire start holes are just drilled and you will need to pickup the outside of the part, if you plan on using a hole for pickup it needs to be a bit more accurate, at least qualified/reamed or finished nicely with an endmill.

Your picture shows a wire block with several parts nested, are you cutting the center hole as well as the outside of the parts?

Is the hole you cut straight after you have wired it?

For a single part you could try picking up the part using your current method and then using the wire take some measurements around the outside of the part to see what you find, if part is picked up on center you should see equal numbers on opposite sides.

As far as picking up parts within .0001" on a wire edm it can be tricky. Since you're using the wire itself to pickup the part, you have variables of wire tension/deflection, the diameter of the wire, conductivity of the pickup face of the part to the table etc so it's not as easy as you might think. Silly things like a sharp corner shaving the wire slightly, or an oily surface giving bad contact can really screw you up.

Within a .0005" is no big deal, but the last couple tenths are not as easy as you might think. My favorite trick for this is to use several tooling holes, if you can use 2 or even better 4 tooling holes you can center and align between them and it helps to reduce some of the variables.

We have also found that if you have a ground diameter that absolutely needs to run dead nuts true within a .0001" to a wired feature it's not a bad idea to leave some material to finish grind after the wire work is done. but ymmv

 

[plastikdreams]

To the OP: If you're using the start hole to pickup the part, are you sure the hole is on location? A lot of times wire start holes are just drilled and you will need to pickup the outside of the part, if you plan on using a hole for pickup it needs to be a bit more accurate, at least qualified/reamed or finished nicely with an endmill.

Your picture shows a wire block with several parts nested, are you cutting the center hole as well as the outside of the parts?

Is the hole you cut straight after you have wired it?

For a single part you could try picking up the part using your current method and then using the wire take some measurements around the outside of the part to see what you find, if part is picked up on center you should see equal numbers on opposite sides.

As far as picking up parts within .0001" on a wire edm it can be tricky. Since you're using the wire itself to pickup the part, you have variables of wire tension/deflection, the diameter of the wire, conductivity of the pickup face of the part to the table etc so it's not as easy as you might think. Silly things like a sharp corner shaving the wire slightly, or an oily surface giving bad contact can really screw you up.

Within a .0005" is no big deal, but the last couple tenths are not as easy as you might think. My favorite trick for this is to use several tooling holes, if you can use 2 or even better 4 tooling holes you can center and align between them and it helps to reduce some of the variables.

We have also found that if you have a ground diameter that absolutely needs to run dead nuts true within a .0001" to a wired feature it's not a bad idea to leave some material to finish grind after the wire work is done. but ymmv

Considering the start hole is .190 I'm guessing they aren't exact lol.

 

[007Rob]

Considering the start hole is .190 I'm guessing they aren't exact lol.

Yeah just realized some of the questions I had were already answered in the earlier replies. For sure .190" sounds a lot like a 3/16 drill that went a bit oversize, but who knows.

Either way, if the center hole needs to be on location after cutting, I would recommend checking the position with the wire after the block is picked up.

Every shop does things a bit different, and if everyone working on a wire block isn't on the same page there's lots of ways things can go wrong. Sometimes people will want you to pick up on a corner and the opposite sides will be unfinished. Other times you will need to center on the outside of the workpiece. And sometimes you will have a specific hole or feature meant for pickup.

Probably worth talking to whoever made up the block to find out what the plan was.

 

[plastikdreams]

When I make a hole for edm pickup it's drilled and reamed so I can get the most accurate pickup, especially if I am burning multiple pieces. The thread holes are just drilled, they don't matter it's just to get the wire threaded...unless you drill the hole too close to the cut and you mark the part lol.

I always lay my thread holes out in cam and use lead in to get to the cut. It's fool proof. If I know there's a risk for a part or piece to drop and cause a shift I put the x,y0 somewhere not getting cut and leave enough to indicate straight (where the original indication was taken).

Wire edm has a lot of tricks and nuances. I've been doing it for a number of years and I know I don't know everything...like taper cuts, I really haven't done many so I'm not as confident. A lot of it is knowing your machine, what it can do, how it does it, and why.

 

[SeymourDumore]

As far as picking up parts within .0001" on a wire edm it can be tricky. Since you're using the wire itself to pickup the part, you have variables of wire tension/deflection, the diameter of the wire, conductivity of the pickup face of the part to the table etc so it's not as easy as you might think. Silly things like a sharp corner shaving the wire slightly, or an oily surface giving bad contact can really screw you up.

Within a .0005" is no big deal, but the last couple tenths are not as easy as you might think. My favorite trick for this is to use several tooling holes, if you can use 2 or even better 4 tooling holes you can center and align between them and it helps to reduce some of the variables.

We have also found that if you have a ground diameter that absolutely needs to run dead nuts true within a .0001" to a wired feature it's not a bad idea to leave some material to finish grind after the wire work is done. but ymmv

Guys

I think we can all agree that a .040" deviation ( heck even a .004" deviation ) is likely due to some silly screwup during the setup or perhaps a mismatch between the program and the actual workpiece.

With all that said.

While I am in no way trying to trivialize the process and requirements of picking up a feature on a wire EDM to be within a .0001, but let's also not make it out to be some colossal feat
restricted only for select members of the Avengers team shall we?
Obviously, milled surfaces or drilled holes as pickup surfaces need not apply, but then again, those jobs certainly do not require such accuracies.
When it does though, you can bet that ALL datum surfaces are properly ground, locating holes are either ground or honed, and all of that are made dead square to the
locating surface which is also ground dead flat BEFORE the EDM process.

As a primarily "bandsaw" shop, I have but a pittance of experience compared to some even here on the PM board, let alone the large portion of the EDM gurus out there, spending their
entire EDM careers in the toolmaking world.
That does not mean I have not done it dozens of times when it was absolutely required that EDM is the very last operation on a fixture, stamping die or a mold base, with the need to
locate to some existing feature that was properly prepared beforehand for the task.

Then of course comes the second half of the equation, which is You and your machine...

 

[newtonsapple]

When I make a hole for edm pickup it's drilled and reamed so I can get the most accurate pickup, especially if I am burning multiple pieces. The thread holes are just drilled, they don't matter it's just to get the wire threaded...unless you drill the hole too close to the cut and you mark the part lol.

I always lay my thread holes out in cam and use lead in to get to the cut. It's fool proof. If I know there's a risk for a part or piece to drop and cause a shift I put the x,y0 somewhere not getting cut and leave enough to indicate straight (where the original indication was taken).

Wire edm has a lot of tricks and nuances. I've been doing it for a number of years and I know I don't know everything...like taper cuts, I really haven't done many so I'm not as confident. A lot of it is knowing your machine, what it can do, how it does it, and why.

Yeah, don't wire away your reference geometry. That's the OP's problem, they can't tell who screwed up. There is no way final inspection is going to be performed relative to the hole that is no longer there!

It generally makes sense to register the part relative to how it will ultimately be inspected. There are sometimes good reasons to not do it that way, but it should always be secondary.

 

[AGMantz]

Replies for: Page 1 of 2
Hello everyone, I'm sorry that I couldn't get back to you guys sooner I had a crazy weekend and didn't have the time to check the forum. Thank you for all the replies and help I'll try and respond to everyone in order. I am very new to this so I'm sorry if I don't understand your question or I sound like a total dummy.

Plastikdreams- Yes I had picked up the first hole as my x,y 0 I then had it cut, move to the next hole, rethread and cut the next profile. Regarding whether it hit the bottom head during cutting I was very careful on stopping it before that happened I used a optional cutoff to ensure that I was around before the part dropped so I don't think that was the issue. It was out in the Y+ direction.

otrlt- I appreciate the kind words I've been trying to take in as much information as I possibly can so I can be reliable on the WEDM. However reading about it is a lot easier than actually pulling it off on the machine myself.

SeymourDumore- I can post the code however it is not short in slightest when outputted it gave me over 7,000 lines for all 8 parts. It feels the need to show every slight movement in x,y as a line. Lmk if you still want to see it.

Plastikdreams-

Reread this, are you picking up on the start hole or the hole in the center of the part?

I am picking up the start hole not the hole in center. The hole in the center isn't touched by me at all in the whole process. The center hole is getting a rod screwed in on it and then fitted to a plastic ejector mold.

SeymourDumore-

If your wire EDM is made within the last 25 years and you cannot reliably locate within .0001 to a feature, then you better give it a good cleaning, you've crashed it a few times or you're just ain't made for the cut! ( pun intended )

I completely agree with you on this I shouldn't be having problems locating to .0001 of a feature, WEDM is fascinatingly accurate and there is no excuse for being .040 off a part. First thing I did after that part came out like that is giving the machine a good wipe down along with a wire alignment and taper-z alignment. As for crashing it I haven't personally crashed it since I got here two months ago(fingers crossed I didn't just jinx myself) but that's not to say that our previous WEDM guy didn't crash it all. At my current state of knowledge I would definitely say I'm not made for the "cut" but that is exactly why I'm on here asking you guys for help and why I've spent plenty of time scouring this forum and other articles for more information. I enjoy WEDM and so I'm going to keep going one step at a time until I figure it out.

-AGMantz

 

[AGMantz]

Replies for Page 2 of 2

Plastikdreams-

You especially need to figure out your overburn in the material first and foremost.

Do you have any good articles on this subject I haven't read about this yet. Otherwise I'm sure I could find some info with a basic google search.

007Rob-

To the OP: If you're using the start hole to pickup the part, are you sure the hole is on location?

I checked the holes with the wire early on after someone suggested the same thing earlier in this post, I did pick ups on them with the wire and then rotating the wire 45 degrees and running it again to make sure the holes were within a tenth. Regarding actual position in terms with the program I will double check. The hole in the center of the part is not being cut just the outside.

My favorite trick for this is to use several tooling holes, if you can use 2 or even better 4 tooling holes you can center and align between them and it helps to reduce some of the variables.

Thank you for the tip! I will definitely try this out on my next available job.

007Rob-

Probably worth talking to whoever made up the block to find out what the plan was.

Was just in conversation with them this morning and they are looking into it as well hopefully we'll get to the bottom of this today.

newtonsapple-

Yeah, don't wire away your reference geometry. That's the OP's problem, they can't tell who screwed up.

I apologize if I got this wrong but the hole is still there... it just now has a .012 line going up to where the wire burned up to the part. I'm pretty sure it can still be used as a way check what went wrong or as reference geometry. Though I might be totally wrong saying that I don't really have the experience to know if its now really screwed up.

-AGMantz
Once again thank you all so much for your replies its been a big help!

 

[Cole2534]

SeymourDumore- I can post the code however it is not short in slightest when outputted it gave me over 7,000 lines for all 8 parts. It feels the need to show every slight movement in x,y as a line. Lmk if you still want to see it.

That's about 100x as many lines as I'd expect for that part in a mill, but I've never run an edm.

Curious to see if that's norm.

Programmed via Mazatrol

 

[AGMantz]

That's about 100x as many lines as I'd expect for that part in a mill, but I've never run an edm.

Curious to see if that's norm.

Programmed via Mazatrol

I'm not sure if that is the norm either and I run WEDM lol. All the other jobs I've done that have multiple parts inside one stock have always been very long so I thought nothing of it when I outputted the NC code. It should be noted though that I do not write my own code I let ESPRIT do that for me after I've finished tooling it out on there.

Quick update on the situation: I haven't cut anymore out of that plate and instead grabbed some scrap metal had someone tidy up the corners real nice and got a brand new design created for me. On this attempt I'm going to pickup the corner instead of a start hole, have it thread in outside of the stock and then burn in through the stock to the part and start cutting. Hopefully this time it'll come out much nicer, if it doesn't the tool maker is going to be at my throat.

 

[SeymourDumore]

I can post the code however it is not short in slightest when outputted it gave me over 7,000 lines for all 8 parts. It feels the need to show every slight movement in x,y as a line. Lmk if you still want to see it.

If those shapes are just rectangles with rounded corners, then I would say something is DEFINITELY wrong with the code!
Looks like you're just doing a one-cut, no skims ( unless I missed something on your image ), so the code should be no more than say 40 lines max for each instance, including wire cuts, threads
ramps and all...

 

[AGMantz]

If those shapes are just rectangles with rounded corners, then I would say something is DEFINITELY wrong with the code!
Looks like you're just doing a one-cut, no skims ( unless I missed something on your image ), so the code should be no more than say 40 lines max for each instance, including wire cuts, threads
ramps and all...

I am doing 1 rough cut 3 skims and then a cut off. It looks like each ID insert has about 830 lines of code but about 800 of them or just slight changes in x,y and u,v.

I'll post some of the beginning of the code below this:
L1
H01 = 0.01120
H02 = 0.00805
H03 = 0.00665
H04 = 0.00615

G62 X0 Y0
G97 X0
G70
G90G92X0Y0
M21
G00 X-.10000 Y.10000
M20
M122 M78
M78

(ROUGH PRIMARY CUT)
Z1=0
Z2=0
Z5=0.57021
E1411 F.236 M90
M80
M82
M84
G92 X-.10000 Y.10000
G41 G01 X-.19095 Y-.19133 U-.04989 V-.04988 H01
X-.18414 Y-.19836 U.00001 V-.00001
X-.17754 Y-.20561 U-.00001 V.00001
X-.17118 Y-.21305 U0 V-.00001
It does a whole bunch of these^ until it gets to the next cut. Hope this gives some insight on why my code is so long.

 

[007Rob]

I am doing 1 rough cut 3 skims and then a cut off. It looks like each ID insert has about 830 lines of code but about 800 of them or just slight changes in x,y and u,v.

I'll post some of the beginning of the code below this:
L1
H01 = 0.01120
H02 = 0.00805
H03 = 0.00665
H04 = 0.00615

G62 X0 Y0
G97 X0
G70
G90G92X0Y0
M21
G00 X-.10000 Y.10000
M20
M122 M78
M78

(ROUGH PRIMARY CUT)
Z1=0
Z2=0
Z5=0.57021
E1411 F.236 M90
M80
M82
M84
G92 X-.10000 Y.10000
G41 G01 X-.19095 Y-.19133 U-.04989 V-.04988 H01
X-.18414 Y-.19836 U.00001 V-.00001
X-.17754 Y-.20561 U-.00001 V.00001
X-.17118 Y-.21305 U0 V-.00001
It does a whole bunch of these^ until it gets to the next cut. Hope this gives some insight on why my code is so long.

That's kind of weird that the code is so long but I'm not sure if it really means anything. Esprit might be outputting points instead of arcs which will make the code a lot longer, but it should be fine.

The weirder thing is all the small U and V moves, does your machine use a probe to align the workplane to the to surface of the workpiece? If so it might just mean the top of your workpiece is ever so slightly out of parallel with the table of the machine.

And goodluck with your next attempt, let us know how it works out!

 

[AGMantz]

That's kind of weird that the code is so long but I'm not sure if it really means anything. Esprit might be outputting points instead of arcs which will make the code a lot longer, but it should be fine.

The weirder thing is all the small U and V moves, does your machine use a probe to align the workplane to the to surface of the workpiece? If so it might just mean the top of your workpiece is ever so slightly out of parallel with the table of the machine.

And goodluck with your next attempt, let us know how it works out!

The U and V movements are their because the ID insert has a 5 degree angle all the way around it. Normally when I'm doing just a normal 2-d cut those small U and V movements are not there.

 

[SeymourDumore]

Holy Crap that code looks ....

I know you can trust Espirit with the code, but Damm that looks UGLY!
Point to point linear segments are OK, but don't see the reason for it nowadays.
Are those blocks with the U and V for your tapered holes? Look pretty darn coarse steps to me.

I don't suppose you can post a slightly larger, dimensioned image of the actual drawing?

 

[007Rob]

The U and V movements are their because the ID insert has a 5 degree angle all the way around it. Normally when I'm doing just a normal 2-d cut those small U and V movements are not there.

Oh yeah that makes sense

 

[plastikdreams]

Im wondering how much is being left to hold on for the multiple passes.

 

[implmex]

Hi AGMantz:
I assume you are making rectangles with a constant radius on the corners...is that correct?
Also, you are keeping the males and throwing away the frame with the female cutouts??

If that is the case, a couple of thoughts spring immediately to mind.

First, others have posted about the desirability of wire cutting the center holes if you want them dead nuts, and they have also posted about the uncertainty around wire pickups.
As was pointed out...it takes very little in the way of dirt or burrs or shaved wire to make a bad pickup and you can really chase your tail trying to get confidence all is as good as it can be.
When every successive pickup is different by a tenth or two it gets hard to know where you really are.
So wiring the hole as well as the outside is an obvious way to eliminate the hassle and uncertainty of wiring to a finished feature...it allows you to make the parts as accurately as the machine is capable of.

The second point is about the code:
Some of you have commented on the length and ugliness of it.
I suspect the part is being programmed without a taper command, but by breaking up the radii into small linear moves in order to get an equal radius top and bottom.
If you just tip the wire over with a taper command and run G02 or G03 in the corners, you won't get a constant radius.

All the CAM software I've tried defaults to small G01 moves and UV displacement commands to manage constant radius tapers, so the code gets huge, and if you look at what has been posted here, that's the pattern that's emerging.

There is another way called "Complex Upper and Lower" in which you stitch the code for the upper profile together with the code for the lower profile, line by line with colons in between.
It will use G02 or G03 for arc moves, and you can use it to make all kinds of weird shapes, including constant radius tapers.
I know of no CAM program that can output this kind of code, so whenever I want to do it, I have to generate the code for the upper path, do the same for the lower path and then put them together manually...a royal PITA but it gives very compact code that's easy to edit.

On a last note, I concur with everyone who's pointing to a setup or basic programming error to account for your unwanted outcome.

Cheers

Marcus
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