New to Shopbot

[Keith Crawford]

Hi, I recently purchased a new shopbot 96x48 PRS Alpha and it should arrive in about a week. I need some advice on how to build the table base. So far, my plan is to use 3/4" hardwood plywood, but I can't find it in my area any larger than 4x8 sheets. The reason I want it larger is I want to add some pnuematic cylinders along the x and y axis at the edge of the work area, and I want to mount them thru the 3/4 plywood. Then I plan on using 1/2" thick solid surface material for a plenum, then 3/4 ULDF for a bleeder board. Can I splice pieces of 3/4 plywood together so my base extends past the 4x8 working area? I am not sure if that would weaken the stability of the machine. Any suggestions would be appreciated. Thanks, Mark

[bleeth]

You can splice it. You can also use 5 x 8 melamine or laminated MDF.

[myxpykalix]

If you want to join it together with the intention of someday adding a vacumn to the table you might go to http://projects.100kgarages.com/ and download the "wavy scarfer" and use that to join your plywood.

HOWEVER, if it was me I would reconsider adding material to the 4x8 plywood for the table for this reason. First i'm not sure of the exact width on your table over and above the 96x48 but you are going to need that open space on both sides to be able to clamp material down.

Unless you have some system for hold down mounted within your tabletop you will be using clamps and you will want to have this open space on your sides.

[Keith Crawford]

Yes, I am planning on installing vacuum, thats the reason for the 1/2" acrylic plenum. I only want to add approximately 6" to the width and length to mount the indexers and there should be 13" of extra width between the rails. I was just concerned about rigidity if I didnt use a contiguous sheet. Thanks

[ken_rychlik]

Mark, put a full 4 x 8 sheet in the cutting area and use fillers on both sides. You don't want any flex or moving on the base sheet of the cutting area.

Also if you use prefinished plywood, it won't warp as much.

If you check with a hardwood supplier in your area, you really should be able to purchase 5 x 10 plywood. It's not something you will find at a home depot type of store, but it is very common.

[garyc]

Mark...
A couple things to think about as you plan for your table design.

3/4 MDO is a very stable product and is available in 4 x 10 sheets. I have joined this product using full length splines in the past.

Solid surface material is great for a vac plenum, but may cause difficulties when gluing to the table board and especially to the spoil/bleeder sheet. You may run into a dissimilar materials warping condition if you laminate solid surface to a wood core product.

To get acceptable consistant results with sheetgood cutting the ULDF spoilboard should be fully adhered to the plenum.

[Keith Crawford]

Gary, are you saying if we glue the SS down to 3/4 plywood, we may have stability problems with the plywood? Would it help to attach laminate over the plywood and glue to the laminate?

[garyc]

Mark...
What I am saying is that SS mtl will move very little with humidity change. Plywood will move more. Most SS mfgrs recommend against glueing to a wood panel substrate.

This is similar to putting laminate on 1 side of a panel. You seldom get good results.

[Keith Crawford]

Gary,
Would you recommend that I scrap the SS idea and just us MDF for my plenum? Or would the MDO work under the solid surface plenum? I want to avoid as many issues as possible. I appreciate your help on this, thanks!

[cabnet636]

i would glue 1.5-2
'ss strips (set by the same width apart) on to as solid layer of ss substrate then machine the cross axis to obtain the raised squares. solid surface is generally adhered to non ss material with silicon to allow for movement, it fuses somewhat with its own epoxy