Combination Spoil Board Design

[rink]

Good afternoon, everyone.
Sorry for this long post. I’m considering spoil board design options and have some questions about vacuum tables. I’m hoping to upgrade to a larger CNC but don’t want to take the plunge until I’ve worked out some of the supporting aspects.

I know there are several people here with expertise in this topic and it seems like we cover a pretty broad assortment of questions on this forum. But if it’s the wrong place to ask these questions, please point me in the right direction.

On my small CNC (work area 12”x13”), I’ve used a vacuum table consisting of a bottom piece of MDF with slots milled in a 1” grid pattern as a plenum, and a top piece of MDF with holes drilled to align with the plenum slots, powered by a small shopvac. Recently, instead of the vacuum table, I’m using a piece of MDF with EZ-Lok threaded inserts in a 1” grid pattern. I use nylon hex bolts to secure workpieces with home-made slotted wooden clamps. Both methods have pros and cons.

I’d like to design a vacuum table that also includes threaded inserts. I’ve read about vacuum tables where there are no holes in the top spoil board, but the smooth finished surface of the MDF is simply skimmed off and then the vacuum takes place across the entire surface of the MDF. Some questions:

1. Is skimming off the smooth MDF surface necessary?
2. Does the skimmed MDF, without any holes, provide adequate suction?
3. If I drilled holes in the MDF top piece (the skimmed surface piece) aligned to NOT be above the plenum slots…could I install threaded inserts there, without losing any suction?
4. On my hole-based vacuum table, I always had to cover all the open holes in order to get adequate suction under the workpiece itself. Is the same true of the skimmed MDF design?
5. I won’t be using a shopvac. Would a small single-stage rotary vane vacuum pump be sufficient for this purpose? Like something used for car AC maintenance?

Thanks for being patient with me. Over several years, I've found no better place to learn than this forum!

Thx, rink.

[martin54]

Not an expert but here are my thoughts, the surface of MDF is sealed so that is why people skim the surface, you will need to surface the spoilboard anyway when it was fitted on the CNC.

if people are using this method then I guess it works but I would think you need some serious vac pumps to suck through the material & give suitable hold down.
I wouldn't think the inserts will make to much difference but then it might depend how many.
Air will take the easiest path so I would imagine you would have to cover any areas that won't be covered by your stock material unless again you have some serious kit Even large industrial machines have zones so you can shut off areas of the bed that aren't covered.
I am guessing you will still need the right type of vac pump & something along the lines of what is used on other CNC machines, a lot will depend on what sort of size this new machine is going to be

Just to add with this sort of system it's not about high pressure it's more about air flow, you can hold a board down with a few inches of vacuum as long as there is enough airflow to maintain it

[IslaWW]

There is a lot of information regarding vacuum systems on CNC machines on the web, some of it is even true.

Answers:
1) Yes, top and bottom before it is installed. Most heavy and almost all big box MDF wont work well
2) Yes, much better than when holes are drilled (of any size)
3) Yes, unless the inserts are sealed, they will leak
4) Yes, you should always cover the unused portion of a zone that has vacuum flowing
5) AC type (Hi Vac, low volume) wont work with a spoilboard, they will work with gasketed fixtures tho.

Some info: https://www.camheads.org/forum/new-cnc- ... out-vacuum

[adze_cnc]

1. yes with anecdote

I needed to temporarily store 6 sheets of 3/4" MDF so I placed them on the bed of our machine on top of our existing 3/4" waste board and 1/4" protective barrier between plenum and waste board. That's 5.5 inches of MDF. I fired up our vacuum pump and a sheet of paper was held firm. A 1/4" sheet of MDF not so firm but it did provide some shear resistance.

4. covering unused areas to improve suction—what I've found useful are those "butcher curtain" strips (4 or 6 inch wide) https://www.curtain-and-divider.com/but ... -curtains/

[wilkigr]

You may want to take a look at CNCNutz on Youtube. Peter did 4 videos on is various vacuum table designs, with a lot of testing of each one.

[TomGB]

Someone should make and sell a few size models out of high density plastic that you could bolt down to your deck. Include various adapter options to connect to vacuums or pumps. You could lay a piece of pre-skimmed MDF on top for a waste board. Maybe even the CNC makers should include it as a deck top option. I'd pay a little extra to have that already included.

[ohiolyons]

You may want to take a look at CNCNutz on Youtube. Peter did 4 videos on is various vacuum table designs, with a lot of testing of each one.

Watch these videos from CNC Nutz if you haven't already, great testing, not just his opinion.

[rink]

Good morning.
Thanks, everyone, for the guidance. This gives me a lot to think about. And I’m familiar with CNCNutz, and will watch those videos.

I expect to have some more, maybe more specific, questions.

Thx, rink.

[martin54]

Good morning.
Thanks, everyone, for the guidance. This gives me a lot to think about. And I’m familiar with CNCNutz, and will watch those videos.

I expect to have some more, maybe more specific, questions.

Thx, rink.

Gary's your man he's the expert here for your more specific questions

I have made vacuum pucks & jigs for certain projects but don't have a general Vacuum hold down method. I went down the route of making gasketed fixtures mainly because I already had everything I needed for that sort of method so my only outlay was time

Oh & I can probably help if you want to go down the route of using steam

[rink]

Gary's your man he's the expert here for your more specific questions

Yes, sir.
I’ve read a lot of Gary’s posts on this forum, as well as yours and a few of the other obvious experts. I was hoping several of y’all would chime in. I’m really happy with the responses and the insights.

I’ve been following this forum for several years, and I’m amazed at how much I’ve learned from you guys. The experience and expertise among this group is deep.

Thx, rink.