4'x8' vacuum table build questions

[dgage]

So its not possible to plug the porous LDF with dust? He was surfacing that spoil board as I read above, so where did that dust go? So I went back and looked at your photos. You have a plenum grid routed in the lower panels fed each by its own piping. On top of each you have a LDF panel held on by what? I am assuming the edges of the LDF is sealed but we are looking for it worked and now it does not thing. I still think dust in the pores or fan blades.

Sorry I didn’t read your previous post clearly on my phone and I should also post about the filter I recommended above. With such small surface area (2-3” pipe covered), I wouldn’t recommend the filter material I suggested stay on for normal usage. It should only be used when making changes to the spoilboard just in case material got into the piping, which is what wmgeorge is concerned about. After ensuring the spoilboard is attached well and the system works, you no longer need the filter material. The spoilboard now acts as one large filter that no trash or dust can get through.

And any machining on top of the table will result in dust that would be handled by the dust collection system and/or swept off after each machining session.

[wmgeorge]

David are you saying its impossible for the LDF pores to plug with the really fine dust from the surfacing process?

Its possible also low or no voltage to the vacuum motors would cause them to not power up 100%. You would need a clamp on amp meter to verify each motor is pulling its load. To bad he is not closer, I have at least two of them I can find right now

[dgage]

David are you saying its impossible for the LDF pores to plug with the really fine dust from the surfacing process?

When surfaced, the LDF is incredibly smooth so there aren’t any pores to plug, just a smooth surface. Microscopically we know there are pores but in practice it is smooth as butter and machined dust stays on the surface and easily visible.

Edited to add: actually, it is hard to seal the MDF. It took many coats of poly to fully seal the edges, and I could tell as there was a noise difference between my “sealed” edges and when I put tape all the way around on the edges. So I had to put more coats of poly on to fully seal the edges. So dust definitely isn’t going to interfere with suction though you wouldn’t want any dust on the surface before putting the plywood down or it wouldn’t seal completely to the table as the dust would hold up the wood leaving a gap for air to enter.

[Gary-Wiant]

Ok so I just got the snow at my house snowblown and the driveway at the shop all plowed out.

I'll start by trying to clear up / answer some of the remarks & questions.

The edges of my LDF spoil board has 4 coats of triple thick polyethylene on the edges.

I would like to find a filter that I could leave in place but wouldn't restrict airflow.

I do not have any check valves on my system. I am waiting on a relief valve to get here so I can install it next week. ( are check valves & relief valves the same thing )

Yes I'm running the filters from Warren. I mounted them once with bolts then when talking to Warren he recommended me using all thread with a nut at the bottom to hold the all thread to the box, then a nut and washer on both sides of the motor flange. My issue is I know the measurement was 2 3/16" but I forgot to write down if the measurement was to the bottom of the flange or to the top of the flange.

The dust just lays on top of the LDF and doesn't embed or get into the LDF.


I went in & did some checking on the vacuum system, here's what I found out.

The first thing I wanted to check was the easiest. See if the LDF is just too porous & just wouldn't hold itself down.

So I turned on 1 motor and the spoil board (surfaced side up) wouldn't draw down so for some reason I decided to flip the spoil board over (surfaced side down) and it sucked it down & I couldn't push it at all. So I flipped the spoil board back over to the original location & nothing. Flipped it back so the surfaced side is down again & it worked again.

My wife said will that hold wood or something on top of it from moving? I had a 4x8 sheet of coroplast laying there so I threw it on top & turned the vacuum on & I couldn't push the coroplast either so I think I'll be good.

I'm thinking of screwing the spoil board down with brass screws my question is does anyone see any issues doing this? I was thinking about counter sinking the screws about a half inch then when I get to those I'll replace the spoil boards. How many screws do I need to use? Should I put a small bead of silicone around the edge & let it set up to make it act like a runner gasket or isn't that needed?

Thank you
Gary

[dgage]

So if I understood correctly, you’ve only surfaced one side of the LDF. The reason for surfacing is to clear any surface glue from the manufacturing process. So I’d put the surfaced side down, turn on the vacuums, and then screw it down if that’s what you’d like to do. Then surface the other side and you should be good to go. And no reason to run the vacuum table while surfacing since you’ve already screwed it down but you definitely want to make sure the table is screwed down and doesn’t move (suck down) when turning on.

And I don’t think you’d need anything around the edge but you’ll need to seal the edge of your top spoilboard too. You’d could put some tape/plastic and glue to the edge if you’d rather not put multiple coats of poly n again,

[Gary-Wiant]

Yes I've only surfaced the one side so far but I will surface the other side once mounted. How many screws do you think I should use on each zone?

Thanks

[routalot]

You don't need many screws.Every fifteen inches or so around the edges ought to be enough.They only need to be deep enough to avoid the amount of tool you expect to have extending below the surface.The purpose of the screws is to prevent the spoilboard moving when the vacuum is turned off and as such they shouldn't see huge forces.It must be a huge relief to have a successful vacuum system.

[wmgeorge]

I think your on track. Brass screws can take a little milling and not hurt anything. Silicone sealer I always us just a little so it can be pried apart without issues. Your set up looks very well done and I am sure its going to make it nice to work with your machine. Glad you got it handled!!

[dgage]

I was going to say 8 inches or so around the perimeter and in the center but routalot is correct in that you just need to make sure it doesn’t shift as when the table turns on, it will pull everything down. The main thing is that the table is tightly screwed down wherever you set table-height or don’t zero the table height without having the vacuum table on.

ALSO, OF BIG IMPORTANCE, NEVER SURFACE THE TABLE WITHOUT THE VAC TABLE TURNED ON OR YOU’LL HAVE AN UNEVEN SURFACE.

[Gary-Wiant]

Thanks Routealot - yes it is a huge relief. This has seemed like the never ending project.

Wmgeorge -Thank you I've tried to be very careful putting this together & making it as precise as I'm able to. I'm excited. I'll put a small bead around the edge just to be safe.

David - 8" is exactly what I was thinking but I see Routealot & your point that I don't need a lot of screws.

My plan is to countersink the screws between 7/16" - 1/2" so I wouldn't hit the heads when I surface the spoil boards. Then when I get down to the screw heads I know it's time for new spoil boards. Do you all think the counter sunk holes will need sealed to keep from leaking?

Anyone that is using a pressure gauge, what amount of pressure should I aim to maintain & does it change with different materials (wood, aluminum, PVC, etc.)?

Thanks
Gary

[wmgeorge]

Gary its actually a vacuum gauge 0-30 Inches. Reminder that 30 inches of vacuum is a 14.7 psig, (nominal) its an absence of atmospheric pressure. When I was doing refrigeration work when we got below 29 inches we switched over to a micron gauge to measure ideally we looked for 500 or below microns.

. Hey where do you live, I am down in central Iowa we only got 2 inches here but other places got 11 inches of snow.

[Gary-Wiant]

Wmgeorge - I've never messed with any of this. Please explain this like you writing the book vacuum gauge for dummies. what number am I looking for?

I live in Northwestern Pa (right off of I-80) we got about 12" over this weekend.

Thanks
Gary

[wmgeorge]

Wmgeorge - I've never messed with any of this. Please explain this like you writing the book vacuum gauge for dummies. what number am I looking for?

I live in Northwestern Pa (right off of I-80) we got about 12" over this weekend.

Thanks
Gary

You can buy those gauges wilthout a problem, my guess you can find them on Amazon. But my estimate and I really do not know for sure but but a vacuum table will not even get close to 15 inches. I hope somebody will chime in that knows.
https://www.amazon.com/2-1-Filled-Va...s%2C164&sr=8-3

[Gary-Wiant]

I ordered & received the Jegs 41008 gauge

[routalot]

Don't get too hung up on numbers for the level of vacuum.You need enough to hold the job in place and obviously the force holding the job in place will increase in line with the area of the piece.For a full 8X4 sheet at 15" of vacuum you would have well over 30,000 lbs acting on the sheet-that won't be going anywhere will it?It is important to keep in mind the distinction between workholding force and a gas tight plumbing system.You will have leakage just from the porosity of the spoilboard and more of it gets exposed as you cut through the sheet you are working with.A high vacuum system doesn't like that sort of leak but the high flow workholding system will be working well.I would be surprised if you ever saw 22 inches of vacuum and you may have a pump that has to have some throughput of air at all times.some systems have a vacuum relief valve to allow for some entry of air if the seal is too good and the pump at risk of damage.Check the data sheet for your pumps perhaps?

[dgage]

I remember reading the DIY vacuums usually pull 6-10” of vacuum though with your 4 motors you should be on the top end of that if not more. The main thing for you is to establish the baseline for your system and location (above sea level). Once you get a good idea for how much vacuum your system pulls with different materials and situations/needs, you use that to determine when you need to turn on/off motors for a given project.

[Kosh]

Maybe a little too late to the discussion, but you have seen this design/approach?

[Gary-Wiant]

KOSH - yes I've seen that video, I'm not sure if you saw my photos of my table design but I have T-slot that boarders my 4 2'x4' zones, which will hopefully give me the best of both worlds.

I was wondering where to run the pressure gauge so I knew where to set the relief valve?

I think this job is literally being a never ending job, I went out to the building to work on attaching the spoil board & out new (less than 2 month old ) Mitsubishi hyper heat mini split wasn't working & my router building was freezing cold so I had to call our HVAC company, they came & looked at it & said a circuit board is out so now I have to wait to see how fast they can get it working & let the metal & plastic all warm back up before I get in there & start ripping & tearing

Thanks
Gary

[wmgeorge]

Gary I just installed one of those mini split HP and since I am a HVAC guy (retired) I did it myself. My son is a service mgr and estimator for a commercial HVAC Co. so I got it wholesale. He says they do not ever have problems with the Mitsubishi units. Mine has been in since October 2018 and so far, so good.

[Gary-Wiant]

Yeah we have had a large Mitsubishi unit in our sign shop for a few years ( it's not a Hyper Heat ) and we haven't had any issues with it. It's my luck & just another thing to keep me from finishing this vacuum table. My brother & I call it Wiant luck, pretty much same as Murphy's law.