Vacuum hold down fixture for cnc router.

[machiningfool]

I have a need to cut .040 styrene plastic on my cnc router and divised this simple but effective vacuum hold down fixture, works well. Bob.

[Al8236]

Or could he have just taped it down? I would have liked to have seen trying to pick it up without the vacuum turned on.

[Peter Sanders]

I expect he would be able to pick it up exactly the same way WITHOUT the vacuum cleaner on, as the packing tap would hold down the plastic very well!

[Frank S]

A 6 & a 1/2 minute video about nothing.. after tapping the plastic down of course he's not going to lift it off the vacuum box. unless his whole point wasn't so much to demonstrate that it held it on but held it flat against the wooden top keeping the plastic sheet flat so he could route what ever design he needed in th eplastic. In that case then he probably has achieved his goal

[machiningfool]

Well, Peter Sanders, If just taping it would have done the job, I wouldn't need a vacuum fixture. 5 minjutes into the video when I turn on the shop vac. look closely and you can see the plastic move down about 1/8th of an inch, holding it solidly against the fixture. Taping around the frame has nothing to do with holding the plastic down directly, as the reason is to make a seal, so the there will be no leakage of air, so that the vacuum will hold the plastic down. I suggest you critics out there, try your design first, before you knock someone's design. There can be no movement up and down when cutting allowing the blade to exit the plastic without lifting it, as the blade will try to lift the plastic if not held down, and also the vacuum will keep it from racking from side to side, so obviously you haven't tried to cut thin plastic with great accuracy, so your expectations are wrong. Bob.

[Frank S]

That's more in lines with what I thought the vacuum fixture was for. it was probably the block of wood glued to the plastic in an effort to demonstrate how the vacuum was working that caused the stir. Large aircraft manufactures use vacuum tables to hold huge sheets of aluminum down for milling

[machiningfool]

Yes, you are correct. The 2x4 was just so that I could get a hold of it to show that there was no movement off of the fixture, hence the blade would not stick to the plastic and lift it. Bob.

[machiningfool]

Yes, you are correct. The 2x4 was just so that I could get a hold of it to show that there was no movement off of the fixture, hence the blade would not stick to the plastic and lift it. Bob.

[joneb]

I've built a very similar vacuum table originally for vacuum forming plastic sheet, but soon realized how useful it would be for holding down thin plywood for cutting out intricate parts. I use inch square wood for the outside sandwiched between 18mm mdf with a few bits of the 1" glued in the middle to prevent sagging . I then made a adapter to fit the vacuum hose and drill the holes in a about 3/4" apart. Any hole that hit the supports I just re drill at a angle.
Using thick mdf allows for skimming the surface should it get marked.
If the work is not as big as the table I use thin plastic sheet to cover the unused hole (plastic bag).
If the cutouts cover a few holes they will stay in place while the the remaining cutting takes place but the cutting order is important outside last. bits of plastic bag can be placed over exposed holes but be careful they don't get caught in cutter.
One important point is that most vacs need air to pass through them for cooling and have cutouts to prevent overheating. I use a Dyson which has a bypass valve if the vacuum gets to much.
And most important don't forget to switch on vac before starting cutting.
John

[machiningfool]

I will keep all of your pointers in mind, thanks for the hints, Bob.