[dzsflw]

I have what is probably a simple question that I'm guessing someone here can answer. If this should be asked in a different subforum, let me know.

I have a Benchtop Pro 2424. It has currently a 3/4 MDF spoilboard mounted onto the standard aluminum table, and that spoilboard has a grid of threaded holes. This normally works great for what I do with the machine, but I have a project in which vacuum would be much more convenient. I was considering trying a simple removeable vacuum table, in the sealed MDF plenum and MDF bleeder board style. I can cover all of the unused area when cutting. I am out of space, money, and sound capacity, so I'm going to try using a Fein vacuum with it. I realize that's not ideal, but I'm going to do it anyway.

My question is: does the bleeder board need to be glued to the plenum? What I'd really like to do is NOT glue it to the plenum, so that I can bolt the plenum itself to the existing threaded spoilboard and still be able to remove the whole setup easily when I want to not use it. It seems like vacuum should hold the bleeder board in place, assuming the top is entirely covered either with the work piece or dams, but it also seems like a lot of people glue them on.

If it IS necessary to glue the bleeder onto the plenum, would it be a viable option to put access holes through the bleeder so I can get to the bolts in the plenum? Maybe as long as they're covered or sealed up when vac is on it's ok?

Anyone have any experience or suggestions about this?

dzsflw

[routalot]

It might not be exactly the item you need but these-or something very similar-have been very useful to me over the years https://www.toolpost.co.uk/product/m-power-u-mach-kit . The bottom has a neoprene gasket that holds the whole assembly down when a vacuum is applied.The ball valves in the top only open when covered by a workpiece.You might have to build a special to suit your machine and the size of the piece you are working on,but I offer it as a possible solution.

[ger21]

You can route a groove around the perimeter and use a rubber seal, and keep the spoilboard loose. You may want to use some dowel pins in the spoilboard to keep it from sliding around.

[Gary-Wiant]

Dzsflw - I built a 4'x8' vacuum table for my Pro4896 & it works great. I used 4 motors 122178-18 from this site https://www.centralvacuummotor.com/shopbot.htm if I was you I would use 2 just to make sure everything stays put. I placed a sheet of 1" MDF on the aluminum frame then I used a sheet of 1" ex-cel if as my plenum. I routed my grid with a 3/8" ball nose about 5/8" deep attached to my vacuum through the bottom of the table via 2" PVC. I have a gate for each zone and a seperate gate and power switch for each motor. I then use LDF (Low Density Fiberboard) on top as a spoil board that the vacuum will pull vacuum through. I put several coats of triple polyurthane on the edges then placed the spoil board on the plenum, turned on the vacuum surfaced the first side flipped it over ran a toolpath to drill & countersink mounting holes then I used brass screws to permanently mount the spoil board to the plenum turn the vacuum back on and surface the top & you are done. I did a grid of t-slot around the perimeter and through the centers so I can clamp down items that are not good to use the vacuum on. If you or anyone else interested in seeing my toolpaths shoot me a PM with your email address.

Good luck
Gary

[Gary-Wiant]

I did not use any rubber gaskets for mine

[dzsflw]

Thanks for the input folks, gives me lots of great things to consider. I'm working on the design now and will update with whatever I come up with.

[wmgeorge]

Thanks for the input folks, gives me lots of great things to consider. I'm working on the design now and will update with whatever I come up with.

I build a small portable 24x24 vac table and it holds down fine with a new Shop Vac, the 6 Hp one with the 2 inch hose. Its documented on here within the past 3 months. The only thing I would change as I would use 1/8 hole size peg board instead the 1/4 (I think I used) hole size.

I just edited my other post and its directly above this one.

[dzsflw]

Thought I'd follow up here for future readers, although the outcome is disappointing. I did a small-scale test with a 12"x12" 3/4" thick MDF plenum with a grid of grooves and a vacuum port in the bottom, sealed with poly, with a 1/2 mdf spoilboard (with the outer layer skimmed off both sides), powered by a Fein Turbo. I could not reliably hold the material I need to hold, which is various hardwood edge-glued panels between 3/4" and 1" thick. The problem seems to be flatness related. At this time of year, in this area, it's tough to keep any unfinished wood within 1/64" of flat for more than a couple of hours, and it's not logistically feasible for me to surface everything immediately before CNC.

Stuff that was very flat or a little flexible held down quite well, though.

I'm thinking about trying out a vacuum pod-type situation instead. I figure gaskets might be the key to overcoming wood movement induced unflatness.

[routalot]

Did you look closely at the item in the link I posted earlier?You may have missed that it has a sealing gasket on the base as well as a umber of zones on the top surface which only become activated when the workpiece covers them and the neoprene gasket effectively gives you vacuum pods.

[ger21]

Flatness of material is extremely important for holding parts. We have two 10HP vacuum pumps ($15,000+), and if boards aren't flat, we can't hold them down.

Any hardwoods should be surfaced on a jointer to get them flat before trying to hold them down.

[dzsflw]

Did you look closely at the item in the link I posted earlier?You may have missed that it has a sealing gasket on the base as well as a umber of zones on the top surface which only become activated when the workpiece covers them and the neoprene gasket effectively gives you vacuum pods.

I did, yes, and thanks for pointing that out. I hadn't seen that particular unit before, but that's exactly the type of thing I'm considering trying.

[dzsflw]

Flatness of material is extremely important for holding parts. We have two 10HP vacuum pumps ($15,000+), and if boards aren't flat, we can't hold them down.

Any hardwoods should be surfaced on a jointer to get them flat before trying to hold them down.

Sadly my 24" jointer is on the fritz right now. Ha! Seriously, though, given my space and situation I have to prep several pieces of stock in batches and use them over the course of a day or two, during which time they become no longer flat enough. At some point if the situation warrants I might look into options to surface (or surface again) just before usage. It certainly would make several things easier.