Latest and greatest - Spoil board prep for vac table

[aschutsky]

Hi all,

So over the past month or two I've read through nearly ALL of the threads I could find on here centered around setup and preparation of the vaccum table. It seems that opinions vary and have even evolved quite a bit over the past few years. I've set up my new (to me) PRTAlpha machine now which is up and running. Yesterday I've got most of the plumbing done from the table to the manifold and now I'm on to preparing the spoilboard.

I ordered and now received what I was told was "Trupan" Ultralight MDF, but there are no markings on the edges so I will assume it is just normal UL MDF. It is indeed much lighter than the normal MDF I'm used to working with though. :)
My questions remain:

-I'm planning this evening to begin sealing the edges of the spoilboard with a 50/50 mix of water and Titebond wood glue. I was NOT planning to do any sealing of the grid/vac surface, should I seal this as well? The previous owner installed "trim" around the entire grid perimeter which I assume would seal it pretty well.

-The latest opinions I've seen were to NOT use silicon around the edges and between zones of the grid since this potentially creates an opportunity for an uneven surface. Is this still correct/accurate? I was simply going to clamp the spoil board down and let the tool drill the holes and pockets and fasten every 16" or so around the perimeter.

I would welcome any additional input as well.

Thanks everyone! Can't wait to start my first project - an enclosure for my 'blackbox' housing 4 of the lighthouse 240V motors. :D

[aschutsky]

Some pictures for fun - including mockup of manifold (given to me from prior owner) and piping position. I had some fun freeing up those valves yesterday. :)


http://i164.photobucket.com/albums/u12/aschutsky/2BEDA946-86A2-4DC0-B165-9657C32A6CD7_zpsjuj5rocx.jpg
http://i164.photobucket.com/albums/u12/aschutsky/EE67992F-6F46-4EC9-8A68-1144688D400C_zps9uteoyer.jpg

[jTr]

- Seal the grid with same mix - 60/40 glue to H20. I used shellac on mine for speed of application - 2-3 coats. This will help prevent vacuum from bleeding through the bottom and edges of the grid layer.
- When applying the ultralight, I would put a drop of glue (full strength) on each of those grid flats and along the divider ribs where the ultralight meets the grid layer, and get a helper so you can simply drop that sheet on with as little shifting/aligning as you can. Throw a sheet of painter's plastic over the trupan. Fire it up and let the vac table clamp the bleeder to the grid for an hour or so to set up.
- Be sure to hit the perimeter with that glue mix to seal the edge, as you originally intended.

Screws should be avoided, as after they are removed, they still have created irregular areas of compression in the material - humidity swings can cause those areas to misbehave.

When the bleeder/breather layer is finally skinned down to the last .25-.375 inch, you can simply surface it away and repeat the process. If treated carefully, it will be a year or so between bleeder replacements, and a lot longer before you'll skim enough off that grid layer to warrant any action there.

Jeff

[aschutsky]

Hi Jeff,

If you're gluing the entire spoilboard to the grid, what do you do when/if the grid needs to be removed from the table?

[myxpykalix]

I glued my spoilboard to my plenum and am now down to about an 1/8th inch left so i'm going to just shave it all off and reapply.

When i first started i didn't want to glue it down and instead i drilled holes and bolted it down but was told that it would balloon up in the center.
When i did bolt it down instead of using regular nuts and bolts i went and bought several nylon toilet lids bolts and nuts and used them instead.

I seem to recall that i got that ballooning effect so i removed all bolts and glued around the perimeters of the different zones (I have 4) with 2 feins and a manifold and that seemed to work good. I did use a silicone caulk around the edges also.
Brady seems to be the "Yoda" on this subject (notice i didn't say Obe Wan for obvious reasons:D) so just do what he says...."Do or do not...there is no try":D
just kidding B:rolleyes:

[aschutsky]

Thanks Jack. Is silicone a viable option vs. glue? I'm just wondering if I need to remove the spoilboard for some reason it would be nice not to have to machine it all off before doing so.

[jTr]

If you're gluing the entire spoilboard to the grid, what do you do when/if the grid needs to be removed from the table?

Jack did a good job of clarifying that part.

As to using silicone in hopes of the ability to remove spoil board - I'd like to address the concept of reversibility:

- First year or so, I used a "palletized" approach to utilizing the bleeder layer.That way I could remove/replace individual sections if need be, thereby conserving the expensive, hard to come by ultralight sheets. Bought slotted aluminum channeling and made a 4 section grid to have the option of using t-bolt hold downs for irregular/solid wood processing. I'm sure you've seen pics of this approach in your research. It proved to be a constant fight to keep the individual sections of ultralight down / flat / sealed, etc. As they got thinner, the individual pieces of ultralight really began curling, to a point I had to use screws to hold flat, and was constantly removing/replacing duct tape around edges to keep them all sealed where they met with the aluminum channel recesses. Not to mention, every time a plywood through cut passed over that 1.5" gap over the aluminum channels, there was inevitably some tearing and loose fibers to contend with.

- A year ago, I removed the aluminum extrusions, filled in the grooves by gluing in solid stock, and used described method in my first post to attach what currently is in use. I've never been happier - consistency of depth of cuts in sheet goods, particularly with dado and related joinery operations is much more accurate. Vacuum hold down power is significantly better, due to the nature of a "permanent" fixing of the bleeder layer, which eliminated a lot of vacuum loss due to leakage that a "reversible" approach inherently brings to the table(no pun intended:rolleyes:)

Yes, I still process just as much solid stock, even though I've eliminated the t-bolt slots. I am primarily a custom furniture maker, but process a fair volume of plywood for furniture as well as kitchen and bath cabinets.

Don't mean to dictate or contradict other's methodology, simply wanted to share my approach in hopes it may help you avoid the year or so of frustration and mediocre vac performance I experienced. Ultimately, the type of work you do will dictate the optimal approach for your processes.

Best of luck!

Jeff

[aschutsky]

Thanks Jeff. It sounds like gluing all surfaces together is the ideal approach when it comes to a full, even seal. Now I've got to figure out a clamping strategy that will allow me to cut my enclosure for my LH motors before the vac table is ready. Seems like I will need that done before I can glue it down and use the vac to seal everything together. :cool:

[jerry_stanek]

What I did was cut my spoil board in 4 pieces and used a piece of 6 mm pvc between. That way you could use 1 vac to suck down a piece while it is drying.

[aschutsky]

What I did was cut my spoil board in 4 pieces and used a piece of 6 mm pvc between. That way you could use 1 vac to suck down a piece while it is drying.

Not a bad idea Jerry, thanks. Couldn't I just do the same thing - Hook one up of my vacs without enclosure directly to the vac manifold, but without cutting up the spoilboard into sections? Without any leakage the single vac should suffice, right?

[jerry_stanek]

Yes that would work remember to machine one side of the spoil board then flip it when you glue it down. Also though a full sheet on top as the spoil board is being glued down that way you get a good seal.