To Glue or Not To Glue...

[jTr]

Vac Table - currently using a 5 zone vac table setup. Have used the "pallet" method of applying trupan = vac grid cut into platen layer - 1/6" vac gasket inlaid around zone borders and and simply place individual sealed-edge pieces of bleeder ultralight trupan style mdf on each grid section. This was done to establish a vacuum zone sytem to focus vac on smaller workpieces and allow for inlay of aluminum hold down track, as seen numerous times in photos on the forum. I need to keep it divided as such, even though I've found I do not use the Aluminum hold down tracks. Wooden dowels have been used as indexers and to prevent slipping of the trupan "pallets" as workpieces are slid on/off the table.

Problem: Trupan is curling - badly.
Current short term solution: countersunk screws to hold snug to vac grid layer
:eek: BIG NO NO :eek:

Long term solution: Glue new layer of trupan to vac grid?

Unable to get a true flat surface - run surfacer and vac at same time in hopes of snugging bleeder layer tight - still uneven, regardless that I've got screws applied every 24" = once workpiece is placed on table, inaccuracies creep in because now arched pieces of trupan are pulled snug to table since workpiece weight and sealing properties of workpiece are now pushing down on table. = uneven thickness in pocket cuts and frayed ply edges.

This is not a fatal issue as far as producing usable parts, but would like to tune this out of the setup in order to acheive more predictable, exacting results.

Am feeling I missed or misunderstood a vital step in vac table setup - Can anyone else with similar setup clue me in on how to remedy this?

Thanks!
jeff

[jerry_stanek]

I cut my spoil board into 24x48 pieces. I have a 4 zone vacuum and I cut a 6mm groove between the zones and glued in 6mm sintra strips to split each zone up. I glued the spoil boards down and have very little problem keeping it level.

[knight_toolworks]

I cut my spoil board into 24x48 pieces. I have a 4 zone vacuum and I cut a 6mm groove between the zones and glued in 6mm sintra strips to split each zone up. I glued the spoil boards down and have very little problem keeping it level.
No need for the sintra just use yellow glue on the inside cuts that's what I do.

[Brady Watson]

You don't want or need any 'gaskets' around the perimeter, aside from maybe foil tape. You should have enough CFM to overcome that little bit of leakage. Gasketing is only really necessary when you get into high Hg" pumps that don't make a lot of CFM.

Screws are okay around the perimeter as long as they are countersunk. Increase frequency to 8-12" along X and throw 5 or 6 screws in the Y. This is where the Kreg ones work well. The 1" ones are perfect.

Glue is OK too around perimeter AND a few dots in the middle. Whatever you do to the edges, ya gotta do to the middle anytime you are setting up a vacuum jig etc. Otherwise it will be convex or concave. You don't want to over-do it with the glue because you want to make sure it bleeds and doesn't get sealed off.

-B

[dlcw]

Jeff, when I put down my 3/4" trupan spoilboard on my plenum, I used white chalk to "glue it down". I cut individual pieces of trupan to fit each of my zones and then edgebanded each piece. This eliminated vacuum leakage from zone to zone. The chalk also significantly reduced or eliminated vacuum leakage from zone to zone and around the parameter. Within each zone, I would put little buttons of chalk on the areas between some of the channels and this keeps the spoilboard flat. When I surface down to about 1/8" spoilboard left, I cut new pieces the same size as the original pieces of trupan, edge band them and chalk them in place.

I've recently started using 1/8" MDF as a layer between my real spoilboard and the material I'm cutting. For all my 4x8 sheet material work, I cut into this 1/8" piece and not the actual spoilboard. At $2.10 for a 1/8" sheet it is well worth it considering my current spoilboard has now lasted thru about 10 cutting jobs and I have not had to surface it, because of cutting in to it, one time (I have surfaced it once to make sure it is still flat and true). I can run 4 sheets per side of the 1/8" stuff before having to flip it over and use the other side for 4 more sheets. Adding $6 or $8 to the price of a job is nothing compared to down time, to resurface the table spoilboard and replace it often.

[Brady Watson]

Donny - I think you meant 'caulk', not 'chalk' - right? Or did you mean chalk...if so, that's a new one I'd like to hear about.

-B

[dlcw]

Donny - I think you meant 'caulk', not 'chalk' - right? Or did you mean chalk...if so, that's a new one I'd like to hear about.

-B

You're right Brady - sometimes my fingers go faster then my brain (wait, most of the time they go faster then my brain :rolleyes:). True signs of getting old. :eek:

[jTr]

Gasketing is only really necessary when you get into high Hg" pumps that don't make a lot of CFM.
-B

Thanks Brady - seem's I overdid it with the gasket tape, as I'm currently utilizing a gang of lighthouse motors.

Don, I think once you release your self-sealing adhesive chalk on the market, you can retire in comfort.;)
- Unable to obtain 1/8", but think I'll have my supplier throw on a sheet of .25" mdf for tomorrow's truck - if I shave both faces, I think that may work similarly well - great idea!
How do you avoid the nusiance of it sliding around - simply duct tape edges?

Thanks guys!
jeff

[dlcw]

Jeff -

The 1/8" MDF "sticks" pretty well to the main spoilboard. I have 2 X=axis "pins" and one Y-axis pin for position material to be cut. The 1/8" sheets fit right against these pins and don't move around much. Once the vacuum goes on, it's going nowhere. I don't place anything between the main spoilboard and the 1/8" MDF sheets. There is very little CFM loss thru the 1/8" sheet.

[jTr]

Great -
Thanks again, Don - can't wait to give it a try.

jeff

[myxpykalix]

Jeff if you feel like you must have screws to hold down your bleeder board then go get some nylons ones like that hold your toilet seat down. If you hit those (and eventually you will) the only thing that gets damaged is the screw/bolt

[ron_moorehead]

Hi Don,

I was wondering where you got your Trupan in Washington.

[bleeth]

Don's a lucky guy. Living in Washington state it is incredible the variety of product that many lumber yards carry there that most of the rest of the countries suppliers don't. I so miss being able to go down to Crosscut Hardwoods and also have Compton's only a block away!

[dlcw]

ROn,

I live over by Spokane and I get my 3/4" Trupan at Specialty Forest Products. They have a branch somewhere on the left side of the state also because they run trucks back and forth.

[twelchPTM]

Jeff - when we first got out bot set up it seemed like no mater what I did the spoildboard would not stay flat. So much so that I ripped of the entire table top and started over, After I cut my plenum board I sorayed it down with a glue/water mixture to seal the board and ensure vacuum only went throught my bleeder board. I glued the bleeder board down with a small bead of glue around the edge of the board and around the edge of each zone, imediatly after placing the bleeder board down I turned on the vacuum and covered the bleeder with a sheet of plastic to suck it down good and tight.
That all being said and done I realized that mdf by nature is a bit unstable and I can still find variation in my table if i look for it but it is .002" or less so unless I am running something that requires super precision i don't let it bug me. (I lie, it bugs the ever loving-**** out of me but I have learned to deal with it). I do keep some mdf blanks around so I can surface that flat for ocassions that require it saving me from having to surface the entire table.

[dlcw]

When you are fastening (gluing) your spoilboard down, are you apply glue around the edges as well as several of the little islands in the plenum that the air channels create?

I've not had any warping, twisting and bending problems because I put a little dab of caulk on several of these little islands, in each zone, when putting the spoil board down. Works great.

[gundog]

When I did my spoilboard I glued it down in the high spots and around the edge of all the zones my spoilboard is one piece and it has worked great no warping. I sealed the perimeter edge with varnish.

Mike