Vacuum table advice

[TMerritt]

Hi guys, first post here. I've spent the past couple days reading through this forum on vacuum table set-ups and I think I have an idea of what I want to do now, but I'd like to run it by you guys and get some input, and also ask a couple questions. This is a great forum for DIY vacuum table knowledge, I haven't found more in depth info anywhere else on the web, so let me say thanks for that!

The work:

The table is going to be a 48"x48" working area setup. I will be cutting PTFE in 48"x48" sheets and cutting them into various basic shapes. Mostly circles and rectangles of varying sizes. Maximum thickness of these sheets will be 3/16" but the majority will be 1/4". Many of these pieces will be small, as in 9 sq inches or even a little less sometimes. Generally they will be rectangles ranging from 8" x 3/4" up to 2" x 20" for the smaller pieces. The larger pieces I'm less concerned with because they will generally be 100 sq inches or more and rectangular or circular.

I will also be doing some engraving on this table, but that will be a solid sheet of thin stainless or aluminum which I will then shear into size after the fact, so probably not much of a concern as far as table requirements go?

The table:

I'm planning on building a universal set-up with a 3/4" ultralight spoiler. The plenum, I'm still deciding on the pattern. I'm thinking .5" to .75" channels with 4 zones. I plan on using two lighthouse motors (or similar) and building a housing for them and running 2" PVC to the zones with one motor running two zones each. I will run individual shut offs for each zone for more fine control over the vacuum.

The questions:

What size channels in the plenum would be better for what I'm looking to do?

Can I just use cheap 2" PVC ball valve shut offs? I'm curious as to why every one opts for the much more expensive guillotine style valves.

I see a lot of people use MDF for the plenum and coat with watered down wood glue a few times to prevent leaks. What about using fiberglass resin?

What motors should I run for this job? I don't have much of a budget, maybe $500 for everything give or take. I do have access to 240v near my table. There's a lot of options and I'm not sure what will suit my needs the best. I'm guessing more CFM the better with a spoiler board set-up.

Has anyone ever used transfer tape to mask off areas of the table that aren't being used? If I have to cut a piece of scrap or something on one zone and need to mask off the area around that zone, would that be a viable option, is what I'm asking.

[TMerritt]

Thoughts on this motor here?

[Kyle Stapleton]

We use the 2" pvc ball valves they work just fine.
I do not see your universal vac table holding those little parts in place (Generally they will be rectangles ranging from 8" x 3/4" up to 2" x 20" for the smaller pieces )

[TMerritt]

We use the 2" pvc ball valves they work just fine.
I do not see your universal vac table holding those little parts in place (Generally they will be rectangles ranging from 8" x 3/4" up to 2" x 20" for the smaller pieces )

No? What needs to be changed about the table? Should I go with 4 motors, using 1 per zone maybe?

Also thanks on the confirmation of using ball valves.

[ntraub01]

We opted for the 2" brass ball valves. They were a bit stiff at first but they have a large, durable handle on them and are much easier to turn than the PVC valves we've had experience with in the past. Yes, more expensive but you can find them on ebay which makes them more affordable. T

he ONE big thing you MUST do is pipe in a free air bypass for any vacuum motor you use. We initially opted to NOT install a bypass and it wasn't more than a couple of hours of use before our 2 - $2500 vacuum motors were suffering from heat soak. Yes, you want maximum vacuum BUT you also need to allow the motors to breath and cool down. Shutting them down won't fix the problem it will only compound it.

Be careful to provide enough air circulation around the motors to assist in keeping them cool. Our motors are mounted to the floor under our table without any enclosure and we still find it necessary (comforting) to put an 20" fan blowing across the two of them during warmer weather.

I agree with Kyle that holding down a 8" x 3/4" piece of material is going to be difficult. If you use a small diameter bit to minimize the material loss, play with the order of which you cut parts (smallest to largest) AND you adjust your vac table while the machine cuts the parts to focus the vacuum you MAY be able to the material without it shifting. I would honestly suggest using a thin ATG tape which you could easily remove after cutting to ensure you don't have a failure. You could also make more zones to be able to focus your vacuum efforts into a smaller space?? You wouldn't need to split your entire table into smaller zones but say the front two get split in half and you know that if you are going to cut the smaller pieces they need to be positioned in those zones and cut first before you cut larger pieces.

Just my thoughts.

Welcome to the forum. There is a lot of experience in this forum and we all tend to be very respectable of each other's input and encouraging in our struggles. Keep asking questions and keep learning!

[TMerritt]

Thank you, glad to be here. So far this place has been the wealth of info I was looking for. I'm currently going back through the archives and reading anything I can find on tables.

I like the idea of brass valves for durability over PVC, I will look into those. I appreciate the suggestion.

I was thinking of making a bleeder system that I can adjust with valving, let me know what you think. The plan is, as I make more cuts through my material, I can close off the bleeder so that I get more vacuum out of the system while the system doesn't starve for airflow to keep cool. Basically instead of having a static bleeder leak, I can adjust it as needed to keep maximum vacuum at the table while also keeping the cooling requirements met. This would require constant monitoring, so maybe it's not 100% feasible, but I've got an infrared temp gun and was thinking of doing some testing with it. I'd imagine on cheaper motors like I would like to get that cooling would be more critical to the success of them staying alive as long as possible so I may also look into some sort of homemade water to air cooling set-up. I've got plenty of old radiators and condensers I can play with. Provided I can get a suitable way to draw heat out of the motor and into the piping for that. Either way, cooling will be a top priority next to maximum vacuum at the spoiler board.

I'm completely new to CNC and am figuring it all out as I go. This includes tooling. So I'm hoping that I can use an 1/8" tool (or smaller) to cut my pieces out, but that is an area I have done minimal research as of this time, so I have no idea. Speed really isn't a factor here, so if it would be best to use a small tool with multiple passes, that can be done no problem. And would I be wrong in assuming that in that scenario, less load on the cutter would also translate into less force on the work piece, allowing less chance of movement of the piece while routing?

That was the plan also, to turn off areas of the table that are already cut and focus the vacuum on remaining areas of the table as the toolpath progresses. In that instance, would it make sense to cut the larger pieces out first and then the smaller pieces last with the vacuum focused entirely on them at that point? My original plan is to break up the 48" table surface into 4 equal quarters. I've got no problem breaking it down further if that will help me meet my goals on a budget. MDF and PVC are a lot cheaper than these big blowers/pumps, lol. The tape idea is last resort. The PTFE I'm cutting needs to be very clean and free of residue. The one side is acid etched from the manufacturer to promote adhesion to the final product and the other side needs to be clean and smooth. These parts are going in bridge bearings that we manufacture in house. This teflon actually sees hundreds of thousands of lbs, to millions of lbs of force once put into operation, and is bonded in place with an adhesive. So I'd like to avoid using two sided tape on either side for fear of contaminating the surfaces with residue before they actually bond it to the bearing. If I have to, I have to. But I'm sure going to exhaust a lot of other options before I go down that road, hah.

[TMerritt]

Also, when looking at motors, is there a specific CFM at a specific inches of vacuum (or range of the two) that I should be looking for. Like for example the motor I linked earlier has 7in(H20) at 143CFM, 57 in at 95CFM, 145in at 0CFM ect. Where in those charts is the best place to focus on? From what I understand, CFM is more of a concern with a universal table than other styles, so I'm just trying to get some hard data on what I should be looking for.

[TMerritt]

Editing that last message because I found a converter for water to mercury for figures that make more sense to me now because all the data I've read must have been in inches of mercury. That motor has .51in at 143CFM, 7.36 at 50CFM (hopefully this is close to the magic number I'm looking for), 4.2in at 95CFM, and 10.6 at 0CFM.