Handy Shop Tips for Plywood

I’ve built several projects over the past 12 years but I really haven’t had much experience working with plywood and other sheet material. With a bathroom reno looming which calls for a new vanity – that’s about to change.

Since I’m also on a mission to make jigs and other shop-related items as I go, I picked up a stack of plywood in varying thicknesses for the purpose. I usually work by myself in my small basement shop, which is too small to manoeuvre large sheets. I’ve discovered some handy tips about plywood such as:

• Shop vs cabinet grade plywood
• Making cutting guides to for use with your circular saw
• Using styrofoam insulation for a cutting pad

This article just scratches the surface on my new adventure into working with plywood.

‘Shop’ grade vs ‘cabinet’ grade plywood

These are terms I’ve heard over the years but I never really had a grip on what they meant and the difference between the two. After a bit of Googling, I pieced together the general descriptions – more or less. At the building centre I found plywood stamped ‘cabinet grade’ which had three core plys and birch veneer on both sides. Like your favourite Doobie Brothers album, it probably has ‘A’ and ‘B’ sides – with a really good side and a slightly less good side.

My understanding of ‘shop grade’ plywood is that it’s (sometimes) cabinet grade that has been downgraded due to various flaws but it has at least 85% useable material. But the less expensive shop grade 3/4" ply that you’ll find at your local big box retailer is more than likely from China  – with all the caveats that go with many other Chinese products. The shop grade material I found had many thin plys (like Baltic Birch) but you could see some really wild variations in the core plys.

Many woodworkers will take a pass on this stuff, citing problems such as uneven plys, de-lamination, voids, etc. Armed with this knowledge, I picked though the stack of shop grade 3/4" ply that was on special and selected a few decent sheets. Time will tell how good a buy this really was – but my mistakes will be less costly than if I was working with the expensive stuff.

Making cutting guides

For years I’ve cobbled together a few clamps and a straight edge to make a cut that I couldn’t do on the table saw for one reason or another. This is inevitably a frustrating experience for various reasons – having to measure the offset from the cut line to find where to clamp the straightedge, not having a straight board, clamps interfering with the cut, you name it.

It’s time to build the proper guides.
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There are a couple of slight variations on these guides but the basics are the same. They’re easy to make and allow you to mark your line, place the edge of the guide on the line and accurately make your cut. Make these cuts with the material good side down to prevent splintering on the good side as the teeth exit. Cut with the good side up on the table saw for the same reason.

It’s a good idea to make two of these  – a 4′ guide for crosscuts and an 8′ guide for ripping. I used some 1/4" fir plywood that I had ‘in stock’ for the bases and 1/2" and 3/4" ply for the fences. A good straight 1 x 4 will work for the fence as well.

Here’s what to do:

• Rip the base at least ten inches wide and the fence about 3 – 4 inches wide.
• Glue or nail the base onto the fence with extra plywood on the cutting side.
• Leave enough plywood behind the fence to use for clamping.
• Check to make sure your saw motor will clear the top of the clamps you’ll use when they’re in position before you attach the fence.
• Once the fence is installed run the saw the length of the guide cutting off the extra.

Since I was working with thin materials (1/2" ply fence – 1/4" ply base) I glued the fence on without mechanical fasteners. I quickly discovered my collection of clamps weren’t deep enough to reach the fence so I had to resort to my "Jed Clamp-it" system (all the heavy objects I could lay my hands on before the glue set). It ain’t pretty but it works.

Once I ripped the guide to width, I applied some paste wax to the sliding surfaces to reduce resistance, but not to the clamping surface left of the fence.

Styrofoam cutting pad

One of the best tips I’ve  found was to use a 2" thick sheet of styrofoam insulation as a pad for cutting large sheets.

I placed the styrofoam insulation on the floor so I could pull the plywood off the stack let it drop flat, landing safely on the foam. Tip – vacuum or sweep the floor first or you’ll have a storm of sawdust and dirt whirling around the shop. First thing I did was cut about three inches off the length of the styrofoam sheet to allow room for the clamps during the initial rip. Set your saw depth for your guide base & material plus a little extra. The 2" thickness allows plenty of depth for the blade.

The real beauty of this arrangement is that the entire sheet is supported by the foam – even after you make the cut. You don’t have to try and support an increasingly heavy and sagging cutoff which can pinch the blade or make you lose your line. I also liked being able to stay next to the saw without over-extending by crawling on top of the plywood as I made the cut.

You’ll notice in the pictures that notches appeared in the side – again for clamps. I eventually decided to cut the sheet crosswise, figuring a 3 foot piece and a 5 foot piece would offer the most flexibility for cutting and storage.