Foam: glue-cut or cut-glue

[mcfunkeymonkey]

In the process of glueing 2' foam to the ply of my benchwork on my L-shaped switching layout.
Already did one leg, a 24"x83" rectangle:

 

The other "leg" is 18" then narrows down to 12".
I have a 2'x8' piece of foam.
Should I trace the outline, cut the foam, and then glue to the ply?
Or glue the foam, with the back & sides very square, THEN trim off the excess in front.

I can see plus/minus for both.  Glueing first will allow to use the ply underneath as a straightedge for the knife, plus leverage to snap after scoring bottom & top.

Any thoughts?

(btw, the benchwork will sit back in the corner when done. After I get the foam on I can screw in the fascia and push it back against the wall.)

Thanks & cheers!
--Mark

 

[dgwinup]

The quickest and easiest is to glue first, cut later.  The plywood becomes a template.  Unfortunately, you will have to cut from underneath to use the plywood as a template.  I don't think I'd cut and snap the foam.  The edge may not come out very smooth.

If you can cut the foam first, it may turn out to be neater and more accurate.  I think I'd use a large sheet of paper to make a template from the plywood.  Use the paper template to mark and cut the foam.  I've used brown wrapping paper that's readily available and is strong enough to withstand a lot of handling.

Hope this helps.

Darrell, quiet...for now

[Allegheny2-6-6-6]

 From my limited knowledge of working with this stuff I would say clamp the foam to the table by placing something flat over the surface so as not to leave dents in it and then cut it out in place. #1: if you make a mistake you just unclamp it and start over, not having to deal with the glue mess etc. #2 it seems like it will be easier to work on the bench work it's self then on the floor or saw horses. I have this problem as I am retrofitting foam in certin spots where I had never intended it to be but have found that it's advantageous for me to use it. So cutting long piece on the florr and then fitting it in place is becomng a real pain. What are you gutting it with a hot knife, wire foam cutter or a saw blade. I hate the mess this stuff makes so I have the shop vac running and let the nozzel sit right next to where I'm cutting so most of the stuff is sucked up as soon as it's cut.

[Medina1128]

What's worked best for me was to temporarily hold the foam in place, mark it, cut it, then glue into place ( I use acrylic latex caulk). This is for the bottom layer only. After the bottom layer has set up, I stack the foam and glue it into place. As each layer sets up, I cut it to rough shape, then trim to final shape with a wire brush (or surfoam if that's what you have). In either case, you DO have a shop-vac, right?

[Doc in CT]

 Another question: are you going for a square edge or contour (to reduce the table top look)?  Seems to me tracing the outline and cutting foam before gluing would make the contour approach easier, especially with hot wire cutter (no vacuum but lot's of ventilation).