Holding small acrylic parts

[qwertysimo]

Your vac is *fine* on a well sealed system.

Sounds promissing.

Two or three layers of masking paper on the bottom, vac hold down...
I should add that a vacuum grid and top with ether flow-through properties or just a hole pattern...
Then do the 3 layer method I mentioned, ya know...

Any chance you have some pictures of your method? I have trouble to imagine it - especialy the part with masking paper.
Most common vacuum tables I read about here are table tops with rubber gaskets rings. You mentioned the hole pattern. Do you mean something like this or this? All clear, but the masking paper.


And, thanks to all for your replies.

[HelicopterJohn]

Hi qwertysimo,

Speaking of pictures. If it is not a top secret project, a picture of finished part of what you are trying to make might make it easier for us to look at the completed part and offer better suggestions on how to hold it.

John

[qwertysimo]

Yes, top secret, I have to change all character names in following text... I do not have finished part here, but it should be a medal holder. I made such from wood, now I want acrylic. Basicaly a solid base with notch to hold medal(s). Something like this or this found on net. No bevels, just simple square one.

That masking paper layer between table top and stock sheet, does it serve as sacrificial layer preventing damaging the table top?

[HelicopterJohn]

Hi qwertysimo,

No problem here as I had a top secret crypto clearance. Your design is safe with me. Ha Ha

Just wondering if you are going to cut these individually, or try and cut them from a large sheet. Also how large of a run of parts are your considering.

If ????? you were going to cut them individually and you didn't mind a couple of small holes that could be drilled in the blanks where the coin radius will be cut. You could set up a program to drill the holes in the blanks first. Then make a fixture with pins that go into the holes that just barely penetrate the bottom of your plexiglas blank. Then when you cut the radius for the coin it would not hit the pins in the fixture. You could use two sided tape to hold it to the fixture plate and it would not rotate or try to slip off the fixture providing proper feeds and speeds are utilized.

This probably won't work too well if you are using clear plexiglas as you probably want it to look very clean and neat. Also, at the $5.00 retail price all of this may not be worth the effort.

Also once the items are machined you can flame the edges of the plexiglas to give it a polished professional look. I have made lots of LED Edge Lit Signs and that does make them look nice. BTY I used my shopbot CNC router to machine a fixture out of plexiglas for holding the plexiglas LED sign blanks while engraving the design and cutting the outside profile. I purchase a small GAST vacuum pump off e-bay and it does a good job on holding small items and was not that expensive.

Hope this may have been of some help.

Good luck on your project.

John

[victorofga]

qwertisimo

if your table flat, means exactly follow the tool moving, then you cut barely to the protective paper..
as I mentioned above..

then parts can stay.. but it doesn't mean cutting trough a 3/8 acrylic in one pass will stay.. then you need for the last pass cut trough a thin acrylic yet..
and that what the paper can hold..

[qwertysimo]

No problem here as I had a top secret crypto clearance. Your design is safe with me. Ha Ha

Great, no disclosure risks, I can speak freely now.

No holes in blanks, that would kill the design IMHO. Anyway, aside from specific use of my parts, I am more and more interested in clamping method itself and particulary the vacuum method for holding down small parts utilising a regular shop vac... I count on gfacer´s "nearly 20 years of experience" and hope it will work as expected.

That acrylic edge lit signs - nice!

[qwertysimo]

qwertisimo

if your table flat, means exactly follow the tool moving, then you cut barely to the protective paper..
as I mentioned above..

then parts can stay.. but it doesn't mean cutting trough a 3/8 acrylic in one pass will stay.. then you need for the last pass cut trough a thin acrylic yet..
and that what the paper can hold..

Sure, I will surface the table top.

I miss something very important. What paper are we talking about? "...that what the paper can hold" - how?? You mentioned "protecting paper surface" in your first post. I dont follow : (

[gfacer2]

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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Honestly unless this job is being done free, I'd make up a basic vacuum hold down box. With my brothers suggestion you don't lose vacuum at all from cutting so the vacuum system doesn't need to be great (shopvac).

The time you save will be worth the effort. You need the stickiest mask you can find.

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[victorofga]

oh
im sorry

there are two type of masking for acrylic

one is vynil.. they are better to void them

another is paper masking.. that paper mask sticking enough strong to work with..
most important don't stick trough the papermask, so vacuum hold perfect..

but as I tried to pointing, if you were using some larger bit then you need to leave in acrylic a very small amount for the last cut..
in case small parts

small I mean when the part really just a couple times larger than its thickness.. a larger letter or other shape wont move.. so they can cut to depth in one pass

one more thing important try to choose cast acrylic.... they cuts better than extruded..

[xjdubber]

as far as double sided tap goes, I favor carpet tape, its thick and sticks really well I use it to hold down smaller parts on my router not sure if it will take the force of doing a full depth cut on the acrylic though, but worth a try though.

[gfacer]

The paper masking is also called pre-mask, and you actually want the least sticky that will work for the sizes you have (my smallest pieces do indeed need the stickers I can find)/ premask is the stuff sign guys protect their completed vinyl or printed signs with. 3m spcm-2 is a good place to start. And yes, you shouldn't touch the spoil board at all if it works correctly.

Other tricks, distilled partly from the last few posts. Cut lightly, although a super light last past isn't necessary (could be faster though to do a heavy pass all over and then go back for a light pass all over, but don't use that as a per piece strategy). Using a small bit is a big part of this and may need a finish pass for cosmetics. Cast will cut better, yes.

As for the holes, there are two ways for the suction to get to the top of your table, flowing through something porous like mdf or lightweight mdf or just drill a bunch of holes. MDF should work fine just milling the "skin"off both sides but drill lots of small holes if it doesn't.

Lots of other threads on here about vac tables I'm sure. I'll look at those links of yours and add to this...



This is a typical under grid (from my old machine refurbish project)...the bottom and sides are all sealed up but you can't really see that. Then put a layer of mdf on top, mill the top, flip over, seal all edged, mill again and that should allow the vac to pull through enough. Compared to those links you had, much smaller holes for a table your size, as any problem leaks as much as the hole underneath but getting the pressure differential doesn't need big holes or any holes.

I'll try to post some of my setup sometime.

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[qwertysimo]

victorofga, gface, I am getting the picture now. (thanks for your patience ) Just to be sure:
Is the sole purpose of applying the masking paper to make gap between table surface and stock sheet to avoid cutting the table surface?
That gfacer´s method of using 2 or 3 layers of masking paper insted of one - is to make the gap even bigger?


Cast vs. extruded acrylic - extruded acrylic is easy to flame polish. I have not tried to polish cast acrylic. I will try to cut and polish both.


gfacer, thanks for the picture and notes. I will follow that procedure to get the best possible seal.

xjdubber, thanks, putting carpet tape on my list.

[victorofga]

yes that is a general vacuum table.. and for this need a ""secondary"" sheet, either way a light density board or a drilled board..
the drilled board require smaller vacuum..
since it don't have to force trough air on the light density board..

theres no universal solution..
that's what makes confusing this question...

when I start with channel letters, and cut 12-20 inches letters, there use to be remain the between parts plus the remnant from sheet..
then vacuum is not solution for those small individual parts..

then small screws woth ... 3-4 screw per parts..
when a sheet cost 170 and I can cut of the remnants using screws... then im not really ready to throwing away and starting from new sheets..

a large production shop probably can do.. but I just cant afford to using always a new sheet.

[victorofga]

the several caught my eyes.. and I think a great idea..
now just need sources for :-)

[gfacer]

victorofga, gface, I am getting the picture now. (thanks for your patience ) Just to be sure:
Is the sole purpose of applying the masking paper to make gap between table surface and stock sheet to avoid cutting the table surface?
That gfacer´s method of using 2 or 3 layers of masking paper insted of one - is to make the gap even bigger?


Cast vs. extruded acrylic - extruded acrylic is easy to flame polish. I have not tried to polish cast acrylic. I will try to cut and polish both.


gfacer, thanks for the picture and notes. I will follow that procedure to get the best possible seal.

xjdubber, thanks, putting carpet tape on my list.

It's not really to avoid touching the table so much as keeping a big continuous area to hold down. So, you can drill some holes (or small interior details) that pierce the masking / spoil board and its OK as long as you have enough airflow (vacflow) to compensate. But you don't want to pierce the paper around the individual pieces.

I mention holes as sometimes they need to be about .005" deeper to cut cleanly.



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