Author Topic: Workholding thin stock on CNC  (Read 223 times)

Offline maury

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Workholding thin stock on CNC
« on: September 07, 2018, 10:28:59 PM »
I need to make some parts on my CNC with thin 303 stainless steel. Normally, I solder the stock to a steel square tube, but solder won't stock to 303. has anyone done this or can offer suggestions as to how to solve the problem?

Thanks,
maury
"The trouble with socialism is that you eventually run out of other people's money."... Margaret Thatcher

Offline RonGinger

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Re: Workholding thin stock on CNC
« Reply #1 on: September 07, 2018, 10:51:19 PM »
I saw this on the NYCCNC you tube channel. It sounds nuts but I have done it now several times and it works well.

Cover the back of the piece of SS with blue painters masking tape. Cover the mill table where the part will go with blue painters masking tape. Spread a few drops of super glue- CA- on the tape and press the SS down on the table. The glue holds the tape faces together.

I was skeptical, but it works great with brass sheet. When you pull it up the glue seems to rip, but the tape comes off the table and the part cleanly.

Offline Dave Otto

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Re: Workholding thin stock on CNC
« Reply #2 on: September 07, 2018, 11:04:21 PM »
How thin?

Offline maury

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Re: Workholding thin stock on CNC
« Reply #3 on: September 07, 2018, 11:20:14 PM »
Ron, Dave, you may have just saved my butt. I'll give this a try tomorrow. The stock is .125. but it needs to be faced down to about .085 before the profile is done. The problem I have run into in the past with taping metal to a substrate is it heats up and migrates. We'll see.

I'm still interested in any other suggestions anyone may have. I'll post the results for others. 303 is a great metal for small parts on a model because of it's rust resistance, and it's easy machinability.
maury
"The trouble with socialism is that you eventually run out of other people's money."... Margaret Thatcher

Offline Dave Otto

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Re: Workholding thin stock on CNC
« Reply #4 on: September 08, 2018, 12:08:13 AM »
It may go banana on you when you thin it down. 

Start out with a piece big enough that you can get some toe clamps on it and still have enough room to mill all the way around your part. Also the stock needs to be large enough so the cutter doesn't break through on the edges. Clamp it down to a fixture plate and rough out your profile leaving .02" on the bottom, Z-.065. Then do a finish cut on your part at the same Z -.065 value. Then drop down and and cut to Z-.080 to Z-.082. Now you can remove the stock from the machine and then remove the part from the stock. With just a little clean up, you have a finished part.

The reason to do a finish cut at Z-.065 is when you remove that last 15 or so thou from the bottom, your cutter isn't trying to push your part around.

I use this technique often and it works quite well; and you don't have to worry about your tape turning loose. I use double sided tape too, it just depends on the job.

Attached is a picture of a copper job that I run with tape. I leave .002 on the bottom and you can see that it does break free some spots. but the little bars usually stay put.

Dave

Offline maury

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Re: Workholding thin stock on CNC
« Reply #5 on: September 08, 2018, 08:02:00 PM »
Ron, Dave, thanks for the ideas. I slept on this last night, and decided to make yet another clamping system. I make them with parts I made from previous ones to save work and increase utility.

I have always been plagued with problems machining thin stock ans have been just too lazy to solve the problem. I think this new tooling will help. I used a 5" piece of 2" thick wall square tubing, squared it up, and made a hole pattern. The neat thing is I can always add more holes. I made a new edge clamp, but I can also use standard clamps from my other systems. Holes are 8-32.

It only took a couple of hours to make.

maury
"The trouble with socialism is that you eventually run out of other people's money."... Margaret Thatcher