Sacrificial layer for vacuum chuck?

[Vvmvbb]

Looking for some help, fellas

We need to set up a vacuum chuck to machine some credit card size pieces of COC plastic from 6"x6" 1mm thick stock (COC machines a lot like acrylic).

We need to mill some shallow ~3mm wide grooves, drill a couple of 1mm holes, and cut the perimeter. Miller is a ShopBot.

A chuck like this should do it (I already have a suitable vacuum pump):

http://www.mscdirect.com/product/08492068

Question is: is there a sacrificial layer that can go between the piece and the chuck that preserves the vacuum force and let's me cut through the piece without hitting the chuck?

Thanks in advance!

 

[Vegaman_Dan]

Sounds like a job for a piece of plexiglass or lexan.

 

[Kevin54]

In all my years of machining, I have neve seen a sacrificial piece from the get go. You have to make the piece yourself to put down, and the holes will have to line up with the holes on the vacuum chuck. What you would need to do is put your sacrificial piece down with double sided tape so it stay in place and your holes would stay in alignment. You could use a piece of plastic, or a piece of aluminum, or even a piece of thin ground steel. All will stay put with good double sided tape between the chuck and the sacrificial piece. You will have to make sure you deburr the SP after the first piece you rund, then you should be good to go after that.

 

[larry_g]

We used to use silicone clad aluminium plate to make vacuum chucks. Lay out your vacuum channels to hold the unmilled portion of the part and the Si will mill away where your cutting. Drill the AL for air passages to direct the vacuum to the proper areas. I would also suggest that you use a 2 way switch that switches between vacuum and air pressure to the chuck. When switch from vacuum to air you clean the chuck and prevent swarf from being sucked into the passages.

lg
no neat sig line

 

[lametec]

I'm with lg. Why use a table if you're going to put a SP in between anyway? Just make the SP the vacuum chuck.

 

[Kevin54]

I'm with lg. Why use a table if you're going to put a SP in between anyway? Just make the SP the vacuum chuck.

I may be wrong, but I think the reason he wants a SP is because he has to go through the pieces he's working on and doesn't want to put mill cuts into the vacuum chuck. If it were me, I wouldn't want to cut into the chuck either.

 

[cnc-me]

Woodworking industry uses MDF, don't think that will work for what you want though.
Why don't you just forget about using that chuck and make a vacuum fixture out of aluminum or thick plastic. Might be able to help you out with the plastic.
Do you often hold parts using vacuum?

 

[larry_g]

I may be wrong, but I think the reason he wants a SP is because he has to go through the pieces he's working on and doesn't want to put mill cuts into the vacuum chuck. If it were me, I wouldn't want to cut into the chuck either.

Kevin
My point is that he does not need that chuck. For all the work to make the sacrificial plate to go on the VC a custom plate can be made with the addition of a couple of passageways.

lg
no neat sig line.

 

[Vvmvbb]

Thanks, all!

I may be wrong, but I think the reason he wants a SP is because he has to go through the pieces he's working on and doesn't want to put mill cuts into the vacuum chuck. If it were me, I wouldn't want to cut into the chuck either.

Yeah, that's it. I'll laser cut some acrylic if needed to work with the part. Or maybe something softer if I need that to get a better seal.

Was hoping to find something general purpose, though.
Datron has something.

Spoke to them on the phone and they say they sell sheets of stuff. Multiple kinds. But I was on the street on my cell, so I figured I'd just find it on their site. But I can't. So another call on Tuesday.

Woodworking industry uses MDF, don't think that will work for what you want though.
Why don't you just forget about using that chuck and make a vacuum fixture out of aluminum or thick plastic. Might be able to help you out with the plastic.
Do you often hold parts using vacuum?

No never before. I only need a few dozen of these parts, but life's too short to scrape adhesive off the parts all day. Part will ultimately be molded and these are just to de-risk the design some before going to mold. We spent the afternoon trying a few home brew rigs. Definitely some tricks to it, I'll no doubt be able to get good results, but I don't want this to be too big project.

 

[finley31]

Sounds like you already have a solution, but just sharing some input from someone who uses a vacuum table every day. I have used mdf to hold sheets of aluminum, teflon, lexan, and G10 (what I cut everyday). Both sides get a skim cut over the surface to face them them the suction through it is incredible. I have made template spoilboards before though to hold some production parts that had holes in them like you are talking about, and it works fine, especially if the parts are all the same and your suction holes line up right under your part that will be cut out. I have also found using compression or downcut style end mills works best when cutting on a vacuum table. It keeps down pressure on the workpiece so it doesn't lift up off the table.

 

[cnc-me]

Sounds like you already have a solution, but just sharing some input from someone who uses a vacuum table every day. I have used mdf to hold sheets of aluminum, teflon, lexan, and G10 (what I cut everyday). Both sides get a skim cut over the surface to face them them the suction through it is incredible. I have made template spoilboards before though to hold some production parts that had holes in them like you are talking about, and it works fine, especially if the parts are all the same and your suction holes line up right under your part that will be cut out. I have also found using compression or downcut style end mills works best when cutting on a vacuum table. It keeps down pressure on the workpiece so it doesn't lift up off the table.

Vacuum works well for many parts, unfortunately it ***** electricity almost as much as it does air, depending how many leaks you have and the size of the pump(s). We have gone to screw clamps over vacuum for some things when the clamps are not in the way.

 

[kbs2244]

I thought double sided tape kind of put vacum chucks at the back of the shelf for low volume stuff.

 

[Kevin54]

I thought double sided tape kind of put vacum chucks at the back of the shelf for low volume stuff.

The one bad thing about using double sided tape for the parts theirself is the fact that when you go to take them off of the tape, you can risk doing damage to the part you just made as far as dents in the part from prying it off, or worse yet, breaking the part itself.

 

[Vvmvbb]

The one bad thing about using double sided tape for the parts theirself is the fact that when you go to take them off of the tape, you can risk doing damage to the part you just made as far as dents in the part from prying it off, or worse yet, breaking the part itself.

Yeah, double sided adhesive is what we are using now and it's a nightmare for these thin parts. Cuts are great and quick, but releasing and cleaning the part without damage is a complete quagmire.

I plan to try the Command adhesive at some point, but right now vacuum seems like it will be best.

 

[Regnar]

Even with perfect vacuum you are only looking at 432 pnds of downward force. You will have to use a down cut spiral bit and block the sides so it doesn't slide. If it was me I would go out and buy some shelf liner and attach it to you material. Then use 3m spray adhesive to glue it to a sacrificial piece and screw that piece to the table.

 

[spooler41]

Just replace your vac vice top plate with a piece of 3/8' or 1/2" Lexan,drilled the same as the steel top. When it's too beat up ,replace it again then you will have a virgin steel to
use when there is no danger of cut through.

......................Jack

 

[Vvmvbb]

Even with perfect vacuum you are only looking at 432 pnds of downward force. You will have to use a down cut spiral bit and block the sides so it doesn't slide. If it was me I would go out and buy some shelf liner and attach it to you material. Then use 3m spray adhesive to glue it to a sacrificial piece and screw that piece to the table.

Thanks so much for the tip. Shelf liner has been working so well that we're not even thinking of vacuum these days.

And thanks for all the other tips, fellas. I bet they'll all come in handy eventually!

 

[Regnar]

Glad it worked out for you. I use it all the time to cut aluminum, plexi and veneers on my machine. I like that it is cheap to and doesn't leave a sticky residue.