Holding small acrylic parts

[qwertysimo]

Hi,

I need to part 1/3" thick stock acrylic sheet into 2x2" rectangular parts using a router (no laser cutting). The only requirement is full thick (single pass) outside profile finishing operation on all four sides for each individual part. I am not sure how to hold down the small parts.

I have browsed this forum and found many holding methods like tabs, clamps, onion skin, vacuum, press fit dies, magnets, hot glue, spray adhesives, double sided tapes, vices or custom jigs.
I like the double side tape the most so far. I can place tape over the spoil board, stick the acrylic sheet, perform multi-pass roughing operation to create a "grid", followed by light finnishig operation. (Regardless of unpleasantly unclamping the parts and cleaning the table, based on tape quality.)

Can this work? Any other tips and tricks?


Thank you.

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[bill south]

I've used double sided tape for acrylic in the past and had some success and a couple of failures. My advise would be to make sure the surfaces the tape is to stick to is clean and dry. I actually put a base of clamped acrylic on my table as a spoil board and use it to assure good adhesion for the tape.
Good luck.
Bill

[gfacer]

Two or three layers of masking paper on the bottom, vac hold down.....obviously you need good table condition and consistent height, but that job would a piece of cake for me, I've done .375" x .75" parts for years that way. Having said that, if just squares, I would never do it on the cnc, all table saws and table mount routers would be quicker and better.

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[qwertysimo]

Thanks Bill.

gfacer, I have no vacuum hold down system available and getting one is out of my budget now. That will not be "just squares", there will be other operations done, hence the cnc approach. I cut acrylic using table saw before...

[georgineer]

I make a lot of small acrylic parts using double-sided tape, and the best I've found is by Techsoft (techsoft.co.uk - no connection) which is made to their own formulation for this purpose. All such tapes will allow small parts to move, which can affect accuracy, and it is not uncommon for it to let the part go during the separation cut, which wrecks the part and spells doom for small cutters. I agree with all that has been said about flat, dry and clean surfaces, and would add that it is worth warming things to improve adhesion if your workshop is cold.

If you are planning a finish cut after the part has been cut free from the stock sheet (not clear from your description) double-sided tape will not hold it still enough for an accurate cut, though there is a way round it by rough-cutting almost through then doing the separation and finish cut in one. There is also the fact that the separation cut mashes up the tape, and spreads a horrible mess of adhesive, tape substrate and swarf along the edge of the workpiece and up the cutter blade.

You would be safer with a vacuum holder if you can arrange it, though I agree with gfacer that for squares a table saw would be better.

George

[fixtureman1]

If the mask is on the acrylic or mask it. Then screw down a flat piece of material spray it with 3M supper 77 and spray the masked acrylic and stick it down. do your cutting and then peel the parts up

[qwertysimo]

If the mask is on the acrylic or mask it. Then screw down a flat piece of material spray it with 3M supper 77 and spray the masked acrylic and stick it down. do your cutting and then peel the parts up

The acrylic has masking film. I wonder - how to clean spoil board from 77 residuum. I have not tried it never before. Any tip?

[qwertysimo]

If you are planning a finish cut after the part has been cut free from the stock sheet (not clear from your description) double-sided tape will not hold it still enough for an accurate cut, though there is a way round it by rough-cutting almost through then doing the separation and finish cut in one.

Yes, my idea is to use roughing operations to cut free individual parts - maybe the last operation will remove very thin layer left by previous ops, not making big pressure on part.
Now I should have many separated parts sticked to spoil board.
I expect and hope that the light finishing cut will not move parts...

"Separation and finish cut in one" might help in terms that the individual part will be more or less attached to stock sheet while cutting... I will try this!

There is also the fact that the separation cut mashes up the tape, and spreads a horrible mess of adhesive, tape substrate and swarf along the edge of the workpiece and up the cutter blade.

Unless I make "tape patches" to hold each part individualy that will arrise from rough cutting... Patches should be a bit smaller than part of course.


In other words, I think of creating a jig - spoil board similiar to a vacuum table surface, with grid of channels that make quare studs, slightly smaller than 2x2". I want to stick a tape patch to each stud. Then put stock sheet on it and cut... Blue is the tape:



Cutter blade would never touch any glue - whether from DS tape or spray adhesive layer on protective film...
If this works, I definitely do not mind preparation and cleaning afterwards...
What do you think?

[qwertysimo]

...spray it with 3M supper 77 and spray the masked acrylic...

I could spray 77 on studs instead of placing DS tape. If I do not spray the protective film on acrylic sheet, would 77 still firmly hold the sheet? This way the cutter would not touch the glue... I mean, is it mandatory to spray 77 on both parts of a join?

[qwertysimo]

I could do another jig - paper with 2x2" cutout grid - for applying 77 to acrylic sheet´ protective film and then to precisly place the sheet on cutting jig to match studs...

What would provide better hold down - DS tape or 77?

[awerby]

I don't understand why you want to use a router to do this. If all you're doing is slicing this sheet of acrylic up into rectangles (or squares, if they're 2" x 2"), why not just use a table saw? It would be faster, and probably do a better job. Get a blade intended for plastic, cut strips, and cut the strips into pieces the right length. No need to stick it down to anything.

If you want to do machining operations on the parts, do that first, when it's all one sheet and easier to hold onto (vacuum would be best) and then take it to the saw.

[gfacer]

Your approach in posts 8 and 9 should work, and which is better is probably depends on the tape, #77 either works or doesn't, but lots of variety of tape. It is nice to avoid the adhesive but may be less of a problem for using the 77 over tapes. A lot of set up and probably still some pieces will come loose.

With the tape everything method (ie masking paper), you have a light adhesive (so not too much to gum things up later) that you get to apply good pressure to first, rather than say spraying on a spoilboard and tapping the sheet down.

I should add that a vacuum grid and top with ether flow-through properties or just a hole pattern, combined with a shop vac, would be enough to use my method under vac pressure. You don't need a lot as the vacuum isn't developing leaks. I run almost all my smallest parts on a 48x39 table with one shopvac as vac source....with tape around the edges too.

[fixtureman1]

I don't spray my spoil board but another piece like coroplas or scrap sintra and screw that down to my spoil board.

[victorofga]

exactly...

creating a ""square wave "" toolpath , after the first row when router advanced to second row, screw down it like a clamp,
then cut, then repeat..

driving in one screw per part takes less time, than cleaning the gummy glue residue and biting off nails waiting when parts will releasing itself causing the real mess, flying around in the shop....

also with a good table worth to cut twice.. and second small pass just cut barely to the protecting paper surface... and parts are staying..

[qwertysimo]

awerby, I want to get the best possible edge finish from router bit because some of the small parts might be glued or flame polished. I have a circular saw blade for plastics - cuts very nice, no chiping, but there are always blade marks visible.I tried saw before and I hope that router approach will make things easier in spite of the longer preparation.

gfacer, the shopvac - what I have is this Metabo vacuum cleaner. Would it be suitable for holding purposes? I dont think so.

[gfacer]

Your link had all models of that brand and I don't know the table size you are working with, but if the vac hold is a) suitable for cleaning the shop your have and b) generates suction similar to shop vac (ie good vac running well) then it should work.

Really, if the leaks are handled then it hardly matters how big the vac is.

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[qwertysimo]

Strange, that link opens my specific model in my browser... Nevermind, you can search for Metabo ASR 35. Or, simply, it´specs say 1400 W or 1.9 HP, 248/3.6 hPa (mbar).

[gfacer]

And how big is your table?

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[qwertysimo]

I am in process of building my router. It will be around 3x2 ft.

[gfacer]

Thanks Bill.

gfacer, I have no vacuum hold down system available and getting one is out of my budget now. That will not be "just squares", there will be other operations done, hence the cnc approach. I cut acrylic using table saw before...

Uhm, that sure implied your table was finished, as adding a vac table is about $20 in mdf and sealer. Your vac is *fine* on a well sealed system. So make a bolt on vac grid plate, seal it, put the top on and seal the edges, machine flat every time you mount it, as flatness is key.

Then do the 3 layer method I mentioned, ya know, if you want to make you life easy and build on nearly 20 years of experience.

(Edited to not be an ass)
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