Tall and Angled Parts Tips

[AGMantz]

Hey all, I've just been given a heads up that in the near future I am going to be cutting some lifter pockets(unfortunately I don't know all the specifics of the job yet). From what I do know about these and what our previous wire guy has on his computer in the most extreme cases it'll be about a 25 degree angle and up to 12 inches high. We have a Mits MV4800 and I know it is more than possible to cut things like this in our machines, but I can't help be worried about these as I have read things start to get tricky when your faced with tall parts and bigger angles.

First off, I understand that I'll probably need to change out my flush cups and guides so I can actually get to that angle(lmk if there is anything else I should be changing out.) But when faced with tall parts at steeper angles I assume the wire might "warp" in the middle while it is cutting leaving me with a not so straight cut. Is there any way to reduce the chances of this happening i.e changing some settings on the machine? I'd also like to know from those who cut similar things like this if there is anything I should look out for before or during the cut to help reduce the chances of a bad cut? This is my first time cutting something this tall as well as at this much of an angle so any tips or tricks you guys have would be greatly appreciated!

Many Thanks
-AGMantz

(I have done some digging on this forum to get some extra knowledge on the topic but most of the threads were from a few years ago so I am curious to see if you all have learned any new tricks since then.)

 

[Luke.kerbey]

What accuracies are you expecting?

 

[implmex]

Hi AGMantz:
I've cut a fair number of lifter pockets and here's my take on it.

First thing is you have to keep your expectations within reason...angled burning, especially tall angled burning, even more especially, large angles are very much harder to get right than vertical burning.
The take home is that you have to decide which parts to care about more and which you can relax a bit about.

In most instances, what happens at the ejector plate end of the pocket matters less than what happens at the parting surface end of the pocket...so you focus the best part of your attention there, and try to get that bit right.
For this reason I always did two things:
1) I'd program and set up so the parting surface was on top; that way I could interrogate my pocket location more easily because I could reach it.
2) I'd make my mold plate very square and interrogate my plate size accurately so I could measure from the edges of the block with rolls to establish where I was.

Next, the overwhelming numbers of lifter pockets were for parallel sided lifters, and the lifters were going to be made on the mill and fitted with the surface grinder.
This meant that getting the pocket walls straight and parallel was more important than getting it exactly to size, and since the pocket walls were sliding surfaces, a good, but not exceptional finish was important to help retain a bit of grease.

In those instances where the lifters were going to be tapered, (typically for super "flashy" materials like Nylon or Santoprene), the finish had to be better since it was going to be relied on as a sealing surface.

Next there is the "How to get there".
Taper burning requires a few different things from upright burning, one of the principal ones is that your wire hardness and wire tension matter in a whole new way.
You can control to some extent where a finish burn will take off material along the length of the burned surface by manipulating the tension...it's instructive to do so during a test burn just to see how much it will matter on your machine and at what sort of angles it will begin to matter a lot.

Ditto for wire temper...since the wire must wrap around the donut shaped holes in the wire guides as soon as you tilt the wire, the intimacy with which that occurs depends on the hardness of the wire and the tension.
This affects both the accuracy of the burn's position, and the flatness of the surfaces you make...hard wires describe a sinusoidal shape unless you jack the tension way up, and that inaccuracy is worst right close to the wire guides where you are trying to get it accurate.
How bad it gets is also dependent on the angle of the burn.

The third thing is the fidelity of the angle you get compared to the angle you program.
If it MUST be dead nuts accurate, you will benefit greatly from doing test burns on scrap pieces first and interrogating them, then adjusting the programming before you commit to the mold plates.

I hear all kinds of bullshit from wire EDM makers flaunting how accurately they can make tall taper cuts at big angles.
All I can say is "Yeah...right" ; and I am so skeptical because there are so many variables at play, all of which get worse as soon as you tilt the wire and run it through donut shaped guides.

So my informal rule of thumb is: if you can cut to a tenth with the wire upright, you will do well to cut within a thou when the wire is tilted more than 10 degrees or so.

Next you have to pay attention to the flushing...when the wire is upright it's already hard enough on tall workpieces...tilt it and it gets infinitely worse.
Aggressive tapers make this much worse...bigger flush cup orifices, a more tortuous path for the water, and the bad effect high flushing pressure has on wire flutter.
Balancing all this is experience driven...you have to fuck around with it until you figure out where the balance point is for your machine on your cut.

For this reason, some operators leave an extra couple of thou on a roughing cut: that way they are sure to have enough to clean up. but it all takes longer too.

The last bit as you have pointed out, is that you need to set up the machine for your cuts...flush cups may have to be changed, guides may have to be changed, different tech files may be needed etc etc.

Cheers

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

 

[plastikdreams]

Edit, nevermind

 

[AGMantz]

Hi AGMantz:
I've cut a fair number of lifter pockets and here's my take on it.

This... This right here is why I love this forum. Thanks a ton Implmex, since I've been told about this job all I've heard from other people in the shop is how important it is for me to cut these accurately on the wire. I was planning on doing some test cuts to feel out how this is going to cut on my machines but before this I really had no idea what I should be looking for or attempting to mess with. Once again, thank you for sharing your experiences and knowledge with me, I feel a lot better about taking these on now!

Regards,
-AGMantz

 

[implmex]

Hi again AGMantz:
You're most welcome, and I'm glad I was able to ramp down the intimidation factor a bit.

Something you might wish to bring into your mindset about all this, is that you have to stay realistic about what you're making...much of the hype around moldmaking is exaggerated for effect.
Some is not, of course, and the whole trick getting comfortable working on these expensive parts is to understand what will happen if there's a misadventure, and how bad it has to get before it's life threatening.
So it's worthwhile to understand the build well enough to be able to point to the features you're responsible for and say to yourself..."I really have to care about this part of it....that part, not so much".

In the case of your lifters, often times but not always, the position of the obtuse edge at the parting line and the position of the sides have to be much more accurate than the position of the acute edge at the parting line.

So you concentrate on getting those three sides as close as you can, and then worry about the fourth side in order to bring the pocket to final dimension on the angled faces.

The vertical sides are easy to both cut and interrogate for fidelity to the print...the angled faces not so much.

So you look at the mold design and figure out what matters most.
Then you find a way to get those bits accurate and to measure them so you are confident they're where they're supposed to be.

As I said above, often times you can use rolls to measure where you are on angled faces...I've often stuffed gauge blocks down the pocket and then pushed a roll up against the gauge block stack to find the intersection of a lifter pocket wall and the parting surface.

Some times you have to get a bit tricky to find a good way to measure..I've made blocks I can shove in the lifter pocket and then touch off on the block with the wire to find out where I am without having to measure from the outside of the workpiece.
I've used a gauge block stack, a roll and a CAD program for the same objective.
This is super handy to have in your back pocket when you can't make the workpiece nice and square for some reason...often because it's a mold base and is just too damned big to set up on the surface grinder.

So break your problem down and have a strategy for measuring it before you begin to cut.
It will make the whole exercise a lot less intimidating.

A last thought...resist the urge to hurry on work like this, even if your boss or co-workers are trying to goad you.
All can be legitimately told to fuck right off until you are damned well good and ready to give them the finished work.
This is hard stuff to do well...the last thing you need is some asshole pressuring you.

Cheers

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

 

[AGMantz]

Hi again AGMantz:
You're most welcome, and I'm glad I was able to ramp down the intimidation factor a bit.

The last paragraph gave me the biggest shit grin ever so thanks for that lol.

I've messed up enough smaller cheap jobs in my first two weeks of trying to figure out how to run these damn WEDMs that I've weeded out some of my beginner mistakes(granted I'm sure I'm still making tons of small mistakes I don't realize yet). But as jobs get more complicated so do the setups. These lifter pockets will probably be one of the more difficult things I'll ever have to wire here so if by some miracle I can pull this off I'll be feeling pretty good.

I would definitely say though I am/was most worried about the set up process for these things. One of my biggest issues I have right now is figuring out all the little in and outs of setting up parts accurately to prepare for cutting. I have only been in this field for about 3 months and though my knowledge in the field is growing it is still lack luster at best. Though your thorough explanation of how you go about setting them up gives me a pretty good idea on how I can do it, now it is just a matter of me pulling it off.

Once again thanks for the information,
-AGMantz

 

[implmex]

Hi again AGMantz:
Try this for an exercise:
Make a rectangular block say 5" x 5" x 1" thick, ground to size and as square as you can make it.
Poke 5 wire start holes into it; one in the middle, and one each at the cardinal points say 1.5" from the center.

Now stuff it in a wire vise (assuming you have one) set it up on the machine; get it perfectly square and level within a tenth or so.

Now pick it up with the wire touching off on all four edges and find the center as accurately as you can.

Program it to make an upright center round bore and four ten degree angled square pockets at those cardinal points, big enough that you can put a gauge block stack down them.

Wire the center bore to a nominal size so you can just push a gauge pin down it.

Wire the pockets at 12:00 and 6:00 by just tilting the wire and using the origin you wired the center bore from, going entirely by reading and tweaking nothing except the pocket size (by changing the wire offsets until you get them to size).

Now take the 9:00 and 3:00 pockets and rough them by reading.
Do a first skim and shove a gauge block stack down each.
Drop a roll against the gauge blocks and then gauge off the roll either with a depth mike or with another gauge block stack out to the edge of the part.
Noodle around with it. tweaking the positions until you get it as close as you can measure....centered and in the correct spot.
Wire those to the same size as the other pockets.
Mark each pocket with a Sharpie so you know which is which.

Now rip the whole works back off the machine and interrogate them with the best measuring gear your company can provide.
See whether you got where you pretended you were going and keep track of the results.
See if you're actually centered in the block with your round bore, see if your angles are what you programmed them to, and see if you got the pockets where you wanted them.

You will learn a LOT from this simple exercise.
It might take you a day's worth of screwing around, but it will tell you a lot about your wire, and a lot about how good you are at touching off, measuring, and all the other stuff I've been babbling about.

If you get it dead nuts on the first try, pat yourself firmly on the back...you deserve it!
If you don't, you can start thinking about where it didn't go so good and why.

Cheers

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

 

[plastikdreams]

Hi again AGMantz:
Try this for an exercise:
Make a rectangular block say 5" x 5" x 1" thick, ground to size and as square as you can make it.
Poke 5 wire start holes into it; one in the middle, and one each at the cardinal points say 1.5" from the center.

Now stuff it in a wire vise (assuming you have one) set it up on the machine; get it perfectly square and level within a tenth or so.

Now pick it up with the wire touching off on all four edges and find the center as accurately as you can.

Program it to make an upright center round bore and four ten degree angled square pockets at those cardinal points, big enough that you can put a gauge block stack down them.

Wire the center bore to a nominal size so you can just push a gauge pin down it.

Wire the pockets at 12:00 and 6:00 by just tilting the wire and using the origin you wired the center bore from, going entirely by reading and tweaking nothing except the pocket size (by changing the wire offsets until you get them to size).

Now take the 9:00 and 3:00 pockets and rough them by reading.
Do a first skim and shove a gauge block stack down each.
Drop a roll against the gauge blocks and then gauge off the roll either with a depth mike or with another gauge block stack out to the edge of the part.
Noodle around with it. tweaking the positions until you get it as close as you can measure....centered and in the correct spot.
Wire those to the same size as the other pockets.
Mark each pocket with a Sharpie so you know which is which.

Now rip the whole works back off the machine and interrogate them with the best measuring gear your company can provide.
See whether you got where you pretended you were going and keep track of the results.
See if you're actually centered in the block with your round bore, see if your angles are what you programmed them to, and see if you got the pockets where you wanted them.

You will learn a LOT from this simple exercise.
It might take you a day's worth of screwing around, but it will tell you a lot about your wire, and a lot about how good you are at touching off, measuring, and all the other stuff I've been babbling about.

If you get it dead nuts on the first try, pat yourself firmly on the back...you deserve it!
If you don't, you can start thinking about where it didn't go so good and why.

Cheers

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

Can we get a setup print for this

 

[implmex]

Hi plastikdreams:
Were you thinking of something like this?


Here's the roll measurement details:



Cheers

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

 

[plastikdreams]

Great now I'm gonna have to try it some day...lol

 

[AGMantz]

Hi again AGMantz:
Try this for an exercise:
Make a rectangular block say 5" x 5" x 1" thick, ground to size and as square as you can make it.

Well I see no reason not to try this, this is great idea for newcomers and those who have been operating for awhile. In addition to running this little exercise I get to cut out a mock lifter pocket. Though height wise it pales in comparison to what I'll be cutting when I get the actual lifter pocket job it'll be nice to see what cutting on a 15 and 20 degree angle feels like. I am actually pretty excited to see how it comes out with all the information I've received. It'll be a big confidence booster if I can get the location and angles right on this mock run, then all I'll have to worry about is the actual height of the part and how that'll affect everything.

Regards,
-AGMantz

 

[Luke.kerbey]

Hi plastikdreams:
Were you thinking of something like this?
View attachment 342706

Here's the roll measurement details:

View attachment 342707

Cheers

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

I really like that idea. I’ve got a taper software on our machine so seems a good exercise. I like the pre-ground piece that can be used to check touching off accuracy. But could it be done by cutting the holes and squares first then cutting the peripheral out after wards?

You can then check the angled faces against parallel/ perpendicular wired faces instead of pre ground faces, the cutting dynamics will be different so may create different inaccuracies to take it to account?

 

[implmex]

Hi Luke:
Part of the idea with this exercise is to establish whether a touch off on each edge will center the part accurately.
If the outside contour is wire cut in the same setup too, you will never know whether you are any good at touching off, nor will you know how much you are out by.

So I specified the block should be ground so it's square with the sides exactly the same length.
That's easy to do and it doesn't matter what size they are, just that they're the same.
When the OP pushes a gauge pin into the center bore, he can find out how good he was easily just by flipping the block on edge on the surface plate and putting a tenths clock on the pin.
Because the clock deviation is twice the error with this metrology, it gets really obvious really quickly, how fiddly it can be to get a clean touch.

Similarly, he can shove a gauge block stack into each lifter bore, lay a roll into the corner and clock the roll to see how good the machine does just going by the numbers versus how good he can get if he fiddles it to make it as close as he can with the measuring methods he's free to use while the block is still on the machine.

As you well know, sometimes the hard part is putting the shape where it's supposed to go, not making the shape itself a specific size.
Trying to do accurate metrology in the work tank can be daunting...I want him to experience that so he can learn what the problems are.

All this will inform him of the limitations in a really obvious way on a block he can throw away afterward, or re-cut if he wants to try something different.
It mimics what he's going to have to do every time he has to cut lifter bores; especially if he has to cut them into some honkin' big P-20 mold where he can't just do maneuvers to make his life easier (like just re-cut the outsides of the block to bring everything into center after he's cut all the inside stuff, or wire them into an insert and then just grind them into the middle).

You and I had to learn all this doing jobs, fucking them up and eating Humble Pie.
Hopefully he can avoid some of that pain.

Cheers

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

 

[plastikdreams]

I have wire capabilities on my mastercam but I've never used it...this would be a good way to test it out...on overtime Sunday

Ok so now can we get that in a parasolid file

 

[implmex]

Hi plastkdreams:
Where should I send it to?

Cheers

Marcus