Handy tip on holding down thin sheets of material.

[EL34]

A sheet of 1/16" thick fiberglass being held down to a wood base using Krylon Easy-Tack



Here's a link to a larger image
http://www.el34world.com/Misc/Cnc/images/IMG_1497.jpg

It can be tough to hold a sheet of material absolutely flat while you cut out shapes.
I have tried super glue, clamps, etc and nothing really worked well.

1/32" thick copper clad Printed circuit board material was the most difficult to cut because I am only cutting .005" deep to remove the copper foil and 1/32" is very thin. If the sheet is warped, which they always are, you don't get a nice cut.

Another problem is that the sheet will rattle around as you start to cut out pieces and the sheet has less and less material. If the sheet rattles around too much it will break the 1/32" diameter endmill I use on very fine PC board material.

I guess some companies use vacuum tables that will suck a sheet of material down to the CNC base, but that's not an option for most home CNC guys.

I always thought that some sort of very thin and light spray glue might work and so I went in search of a product. I found a few products on the web by 3M and other companies that looked good.
I ended up using Krylon Easy-Tack with great results.




Krylon Easy-Tack is a repositionable adhesive that is clear and sprays on super thin.
It has worked out great so far on the thin sheet type materials I use.
The label on the can states that you can use it on just about every material including paper, and you can reposition the material easily. It has made cutting thin sheets of material on my CNC very easy.

I wasn't sure what to use to clean off the glue after you have cut a sheet of material so I tried mineral spirits.
Mineral spirits seemed to clean Easy-Tack off the wood backings I use and the material sheets but it left just a bit of residue because it seems to melt the glue.

The can says just to wash your hands with soap and water and so I tested that.
I was able to clean off all residue on fiberglass sheets with just warm soapy water.

Note that the spray cans I got from Joann fabric were 5.5oz. The part number is 7021 on my 5.5oz cans.

Here's a link to Joann fabrics which had the best price I could find on the web.
http://www.joann.com/joann/catalog.jsp?CATID=cat3270&PRODID=prd33862

Hope this tips helps

[Jeff_Birt]

That's a great idea. I've used light duty double sided tape for holding PCB material flat before but never thought abut using a spray adhesive. I use a light duty spray adhesive at work for holding paper patterns on sheet metal. I'll try it out for this application and post the brand name if it works well. (Sometimes some brands are more easily available in certain areas.)

[EL34]

Thanks Jeff,
yeah, other brands may work also.
The key is having a super thin tacky glue that also lets the two parts come apart easily.
Also, not leaving a heavy glue residue on the the two surafces is another important point.

see ya

[revwarguy]

Good post!  I have the problem, so a post like this just makes my day.  Thanks!

[EL34]

excellent.
I'd like to hear how this works out for folks after you give it a go.

[EL34]

Glue update

In order to start with a super flat surface, I took a 3/4" thick particle board shelf piece and then milled the top surface flat with a 3/4" straight wood router bit.

I glued down a 8" x 8" sheet of 1/32" one sided copper clad board.
I Layed another board on top of the sandwich and then set a propane tank on the stack for weigh, to make sure everything was mashed down really flat and that the copper board did not spring up.

I forgot about the sheet for a week.  
Anywho, I just started cutting some parts on the sheet yesterday. The sheet has to be a couple weeks old by now.

The parts did not release from the backer board super easy because the glue had dried pretty good.
The glue was still very tacky, but it had firmed up way more that using it the same day, as in my first test.
Since my backing board was a particle board, some of the wood particles stuck to the back of the copper board parts.
I poured a little bit of mineral spirits into a container and threw the parts in for a soak.
The glue residue wiped right off fairly easy after wiping them with a cloth.

I have to find a better backing board material. One that the glue will stick to, but does not have loose particles.
I have sheets of HDPE here, which would be perfect, but HDPE is very slippery and the glue may not stick to it.
Have to run an experiment.

One nice thing that I was able to do, using the glued down copper sheet.
I was able to run all the parts without using tabs!!!
The parts required no sanding and had a nice finish without the tabs.

[EL34]

Here's an update on the backer boards material I now use to cookie cut sheets of small parts.

I am now using 1/2" or 3/4" HDPE as my backing surface.
It machines like butter.
I machine it flat using a larger diameter router bit.
The Krylon glue sticks to it great.
It does not leave any particles behind like a wood backer board.
After pulling the thin parts off the HDPE, you can just wipe it down with mineral spirits to clean the glue off
The small parts that I cookie cut get soaked in mineral spirits for a couple minutes after being pulled off the HDPE backer sheet. The Krylon glue comes right off the parts very easily.

It is working so well that I now do not use tabs on the parts, only the glue.
This cuts way down on parts clean up time.

I have gone through several cans of glue so far.
This process is working out very well.

[EL34]

Another update
I have been using easy tack on sheets of material for a couple years now and it is still working out great.

As long as your backing material (HDPE sheets in my case) is clean and flat, you get excellent results with no holding tabs.

[Bubba]

Great idea. Thanks for sharing.

[EL34]

The nice thing about Easy tack is that it is a super thin film of glue.
It is not like contact cement or heavy glues that have thickness and lumps that can distort the material shape
It is also very easy to reposition the item if you need to.

I use this method to cut 1/32" thick copper clad PC board sheets

You just spray a thin film on both surfaces, wait a few minutes and then stick them together.
I like to wait an hour or so before cutting the sheets
If you start cutting very small parts too soon, the glue is still too soft
If the parts is larger and has more surface area, you can start cutting as soon as you stick the two parts together.

A rag with mineral spirits or a soaking tray with mineral spirits removes the glue very easily.

[GeorgeRace]

I don't know if this will help, but, I have a friend who CNC cuts PCB's and he uses a piece of stone like counter top material that was a laser cutout from a sink opening.  It is about 24 X 30, weighs about 40 pounds, and he claims is flat within a few tenths anywhere on the piece.  He says what he got was ground on the back and ground and polished on the top.  Even better he said it was free as the company doing the cut out just tosses it out.   He also uses some kind of a spray on adhesive, did not say what the brand was.  Companies that sell counter tops can probably give you the location of their supplier who makes these "stone" custom cut counter tops.

[Imagining]

Use a heat gun set on low to reactivate the glue if the glue has set for a long time.

This also works to get those pesky adhesive tags off.

[EL34]

I cut very thin 1/32 inch thick copper clad circuit board material
I rip big sheets into 8 x 8 inch squares

There is no way to cut the copper traces accurately unless that ultra thin board is glued down
Or, a vacuum table may be able to do it properly.

On thicker sheets of pcb material, it is probably possible to clamp at the edges

Use a heat gun set on low to reactivate the glue if the has set for a long time.

Good tip
I just cut a few small pcb's .74 inch diameter on an old sheet that had been glued up maybe 6 months ago.
The pieces came off with no problem using a ultra thin blade to lift them
So I guess Easy Tack does not set up rock hard
Have to try the heat gun trick if I ever use a sheet that old again.

[Alan45]

Another method more suited to milling thin sheet metal objects is to use a cyanoacralate glue, one of the permanent type Loctites or similar. These will release when heated to around 200 C. They can be applied to a backing sheet, the object to be milled is attached and milling can commence within a few minutes.

[lloydsp]

Alan,
I've found that a flexible epoxy is better if there are any interrupted cuts or heavy ones to be done.  The brittle glues can release with enough vibration.

For light work, even double-stick tape works fine.

Mostly, though, I plan my work for hold-down holes in waste areas, and bolt the pieces down to a waste sheet.
Although I'm sure folks like them (and I need them occasionally), I just despise "holding tabs" and the extra work and ugly artifacts they leave.

LLoyd