# Asking the amazing collective intelligence of HM



## dbb-the-bruce (May 14, 2021)

I've been using my desktop CNC to cut copper sheet patterns that are then folded into geometric shapes (small 1" boxes etc). My experience is that it's hard to find a good way to secure thin stock options of supper glue or double sided tape are pretty much it. The copper is is dead soft and .03 thick.

The tape works but cutting through into it gums up the end mill, it's also easy to bend up the soft copper trying to remove it when done. Gluing alone also has issues.

So I ended up gluing the copper to some thing ( .020 ) plastic sheet and then taping the plastic to the bed. This has worked out phenomenally well! A razor blade is enough to work a corner of the finished  copper off the plastic enough that I can then use a credit card to pop it off. After that pealing the plastic and tape up is pretty easy.

The plastic base layer gives me something to cut into that the end mill doesn't mind at all. So this is really a winning approach.

-ACCEPT-  The plastic sheet I'm using is really a car dealer plate filler and I'm just about out of it!!

I think the reason this plastic works so well is that one side is smooth (the side with the logo on it that faces out) and the back side has a very slight texture on it. I'm sure that stuff is really cheap and meant for printing signage (like plate fillers) on.

Can anyone help me identify a source of this plastic sheeting? Not sure what kind of plastic it is. Soft white and flexible. Thickness is .020 Inch and one side is smooth.

The picture shows the very slight texture on the back non-smooth side. I think this texture really helps when gluing the plastic to the copper.




Thanks!


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## derfatdutchman (May 14, 2021)

Check with local sign shops they may be able to tell you what the material is. Hardware stores usually stock pre-printed signs (for sale, for rent, etc) they are printed on plastic, take a sample of what you have so you can compare.


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## francist (May 14, 2021)

Sounds like polystyrene, maybe. Available in a few thicknesses, sign shop as said previously would be a good source unless you have a dedicated plastics supplier in your town (we do). Not sure on the texture though, I think most of it comes smooth both sides.


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## Nogoingback (May 14, 2021)

I don't know about the .020" part, but hobby shops sell packages of thin white plastic sheet
for modelers.


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## dbb-the-bruce (May 14, 2021)

Thanks everyone. 
I think the first cheapest and quickest idea was to hit the hardware store and look for plastic signs. Sign shop is a good idea if I can find one nearby. The thing is I kinda want to look at the stuff rather than buy it blind off the net.


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## Aaron_W (May 14, 2021)

Plastruct, Midwest and Evergreen are the big suppliers of styrene for hobby shops. They offer all kinds of different sheets, with a variety of textures available.

Hardware store plastic For Sale signs are the popular source of styrene sheet for modelers on a budget, but you are limited in selection.


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## Bi11Hudson (May 15, 2021)

I have a similar problem, setting up brass sheet and shim stock for milling. I use a plastic that comes from the "big box" stores. Clear but not plexi or polycarbonate. They call it "styrene" but I'm not so sure that's what it is. But it comes in 4 x 8 foot sheets and I use a lot of it for windows and machine covers and what-have-you. About 2mm thick. Often bent in gentle curves with a hot air gun. Current cost is unknown, I've had mine for a while, and acquired it in a "horse trade".

For a "one time" or trial use, hobby shop sheet stock would work, but is horribly expensive for regular work. The "license plate" stock sounds sort of thin. As would be the hardware store "For Sale" signs. I use political signs and realtor's signs of 1/16 inch thick size that have been collected when I'm out on scrounging runs. They're polystyrene, usually white, cut easily, and as scrounge quite cheap. Just the cost of time and fuel. . .  Model builders do a lot of scrounging runs. . .

There is a plastics dealer locally where cut-offs and other scraps of acrylics and polycarbonates can be purchased by the pound. As a "source", they are handy. But the grades are precious to me for other projects so don't get used for disposables unless there is a need for some specific characteristic. I use a lot of plastics for electrical insulating material.

The hardware store signs could be doubled up to get thicker stock. But that gets into a lot of "non-productive" labor and the possibility of air bubbles (thicknesses) between sheets. A dumpster behind a real estate office would be a better source. Especially one that has changed personell recently. Grocery stores are another good source for thicker shapes, but not so good for sheet stock. Good scrounging is an art of sorts, it takes time and awareness to get good at it.

.


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## Boswell (May 15, 2021)

Another approach might be a vacuum table. could could even make a sacrificial top out of MDF with enough holes to allow the vacuum but not so many that it would be hard to replace after you cut it up too much to work. If you over depth cuts were not too deep you might even be able to "Patch" the MDF with RTV or silicon a few times.


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## 7milesup (May 15, 2021)

Not sure how big your CNC is but here is some food for thought...
I set up a large CNC machine for a friend of mine.  It is a Shop Sabre with a 5ftx11ft cutting area.  It has zones for vacuum hold down.  We use MDF as THE hold down.  No holes are drilled through the MFD. The vacuum permeates its way right through the MDF and holds down whatever you place on the table, as long as it is not porous.  The edges of the MDF should be sealed; duct tape or similar is fine.  This system eliminates all need for mechanical hold downs.  
We utilize two 5hp vacuum pumps, so it is not a small set up.  A hobby sized CNC could probably get by with a vacuum pump that they use for vacuuming out air conditioning systems or similar.


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## Larry$ (May 15, 2021)

Like Boswell said, try vacuum.
Even a shop Vac can pull fairly decent Vacuum. Vacuum is a widely used method in CNC woodworking. We've got a 40HP pump on our 5x10 router. We use 3/4" MDF for spoil boards. After they get too chewed up they get surfaced by a 4" router bit made for the purpose.  If you use MDF seal the edges so they don't leak too much. Fastening blocking at work edges will help prevent side movement. If you are doing repetitive work make dedicated fixtures with more of the surface cut away. If you have small parts that can come loose use tabbing where a small, thin "tab" is left connecting parts. Manually remove them after machining.


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## homebrewed (May 19, 2021)

The polystyrene sheets I've bought over the years have a slick side and a textured side.


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