Vacuum Tables - Need Opinions for Machining Acrylic
I've been a member for a while now, ended up getting a XZero Raptor with a 23" x 40" working area and t-slot table and I've been using that for my home based business (dedicated garage workshop) for a few years now.
I'm looking at making things more efficient and I've been wanting to make a vacuum table or maybe buying one. I'm mostly using 1/8" diameter bits and I'm usually cutting into ACM (Aluminum Composite Material - Dibond, etc.) and acrylic. I may do thin aluminum (< 1/8" thick) in the future.
It seems that the best solution for the ACM is to have a "bleeder" type vacuum table - I would section it off into 2 areas. 1 area with dimensions matching the thicker acrylic that I cut/engrave. The second section would cover the rest of the working area. I would likely use 2 shop vacs or Lighthouse vacuum motors, one for each section - with everything running I may need to get an electrician to run some wire but I will likely get an electrician anyways as working in the garage in the winter is a bit torturous and a 220VAC heater would make working in there less miserable especially after the garage doors are insulated. The ACM I tend to cut through but it usually holds well together via chip packing and I'm doing larger pieces (I will cut a 4' x 8' in half and feed it through the machine section by section).
I am a bit concerned about suction power for the acrylic however as it may sometimes have a slight bow in it. As the acrylic is always 19" x 24", I've been thinking of having threaded inserts for the 4 corners as well just to help minimize side to side motion - I would drill holes in the corners then use machine screws in addition to the vacuum. Currently I've been using a thick plywood spoilboard with 25+ Kreg screws. Each time I machine the acrylic, in addition to everything else, I have to rearrange the screw holes and I pre-drill with the CNC and increase the size on the acrylic with a hand drill. Then I screw everything down. This time tends to add up. I do not need to cut through however, I leave a thin layer of material. When cutting out the pieces I use pre-mask (typically used in signage for covering/protecting decals) and flip over the material. I have to indexing pins matching indexing holes in the acrylic and I line those up. I then use about 1/3rd of the screws but I still need to screw things down. After that use an engraving bit to finish cutting everything out. The pre-mask and screws work well enough to hold things together for my needs but I imagine a proper vacuum table would save me quite a bit of time. For this I think a vacuum grid (with rubber gasket) would work better. It sounds ridiculous to me but I'm considering having a separate aluminum vacuum table for the acrylic on top of the larger 2-section vacuum table, this would only be necessary if the holding force is not enough to keep the acrylic in place. This would likely be purchased and I would have some sort of indexing system to fix the vacuum grid in the same place while being removable.
I'm not too concerned about Z clearance as I work almost exclusively with sheet materials so it's OK that I lose some Z height with a couple vacuum tables. I would design space for aluminum T-slots to be attached to the 2-section vacuum table for clamping flexibility. Any opinions on whether I would have issues with a bleeder type vacuum table on my 19" x 24" acrylic? Again I am mainly machining with 1/8" bits. My goal is to cut setup time. Thanks in advance!
Re: Vacuum Tables - Need Opinions for Machining Acrylic
For your acrylic works, consider combining the vacuum ideas along with a fixture jig for your blank work pieces.
What I mean by that is use the vacuum to hold your acrylic flat but mount the blank sheets within a pocketed (or elbow type) fixture to provide the X, Y co-ordinate alignments you mention. You mentioned locating pins, this involves drilling to get the work piece aligned whereas the pocketed/elbow fixture avoids these steps. You have your X,Y zeros at (say) one corner. You can then either use that as a reference or use an offset for X and Y to use a center starting point for two-sided jobs.
I can also highly recommend the use of a spring loaded engraving tool such as the one available from Spring Engraving Tool
This helps overcome irregularities in work surface to tool height differences.
I ordered one about a week ago and tried it yesterday for some acrylic engraving with exceptionally good results on the first go! Very impressed!!
Vacuum Tables - Need Opinions for Machining Acrylic
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