Ultimate base material?

[Stagecraft]

I've moved one of my Bots home after it spent it's entire life in our old shop location.
Seeing as I had to take it apart to move it I thought I'd make any improvements I could while reassembling it in the new location including the addition of a vacuum hold-down system.
The base material (not the spoilboard) previously was .75" Baltic Birch.
Is there anything that others could suggest for better stability through humidity and temperature changes?
Thanks - Boyd

[geneb]

You could use a 3/4" Phelonic(sp?) but the last time I checked, it was $600 for a 4x8 sheet..

g.

[steve_g]

Boyd:
As my shop is only temperature controlled while I’m actually in it, I was experiencing issues with humidity related swelling and shrinking until I went with ¾ inch Baltic Birch. I thought that 1” ABS was the solution until I experienced “plastic creep” over time, resulting in sagging between supports, I can’t speak to the physical characteristics of Phenolic sheet however.

I actually stopped using MDF for my spoil board. Rather than resurface every morning and having it change during the day, I now use ¼” Sintra. When one side gets to bad, I turn it over. Of course that won’t work if you are using vacuum hold down.

Hope this helps…
Steve

[Brady Watson]

I've had great results with Medex moisture resistant MDF for both the support board and the spoilboard. It machines really nicely and is very stable. If I recall correctly, it is made by Sierra Pine. (Yep) http://www.sierrapine.com/index.php?pid=68

If you are not keen on an MDF product for the support board, my suggestion would be MDO plywood. Last I checked you can get up to 1.375" thick for under $100 a 4X8 sheet. It's really nice stuff...I even made a SB table out of the stuff a few years back and it is very stable. I get mine from HarborSales.net (http://www.harborsales.net)

-B

[dlcw]

Boyd,

How extreme are your temperature and humidity swings going to be? If you have huge humidity swings, I don't think anything short of a metal (aluminum probably) plenum is going to work well other then the phenolic plastic that Gene suggested. Either solution is big bucks. I use two layers of 3/4" baltic birch glued together on my 5x8 Alpha (Walle) . The bottom is sealed with 6 coats of shellac and the edges have edgebanding on them. The seams are staggered. Once I cut the plenum channels, flattened and leveled it, I sealed it with 6 coats of shellac.

On to the spoilboard - Started with 1 sheet of 1/2" Truepan, melamine edgebanded and held in place with construction adhesive around the edges and a few places in the field. When that got down to 1/8" (through surfacing evolutions) I glued a new sheet of 1/2" Trupan on top of it and will continue with that approach as I surface through to the original spoilboard (marked with red spray paint in a few places).

The only problem I have with my vacuum holddown is my 2500' altitude where my shop is located. Just can't pull as much vacuum as people closer to sea level can. About 7.5" to 8". Oh well..... :)

[Stagecraft]

Thanks for the replies fellas'
Brady, I hadn't considered Medex...interesting.
Don we're on the west coast and do get substantial variances in both humidity and temperature.
re. Trupan, not a brand name I've heard used much in Canada.
From what I gathered on the intertube it's an mdf type material?
Is it similar to Medite?
Steve, using Sintra as a spoilboard, any issues with excessive static?
- Boyd

[Gary Campbell]

Boyd...
Aluminum, Phenolic and PVC type 1 solid are the 3 best, and most expensive table base materials. All may have their own difficulties when trying to adhere a plenum to the table base. You could machine a plenum in each of them.

Trupan is one of the lightest weight and most porous of the MDF's. As such it is the most susceptable to dimensional change from humidity. It works well for a bleeder/spoil board but not so well as a plenum unless you pour a large amount of heavy bodied sealer on it. The more dense, and especially the moisture resistant MDF's (like Medite, Medex) work OK, but like all wood products, will move with humidity changes.

[steve_g]

Boyd:
I have never had a static issue with any system I’ve tried. Don’t know if that’s dumb luck, or just paying close attention to grounding. I happened to notice today that I actually am using a ¾” sheet of Baltic Birch with a ½ “ sheet on top of that. I hold down the Sintra to the Baltic birch with ½” wide double stick tape every 6”.

Steve