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Mortise in Birch-Ply?

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Forum topic by BustedClock posted 06-30-2011 10:36 PM 2596 views 0 times favorited 2 replies Add to Favorites Watch
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BustedClock

112 posts in 1988 days


06-30-2011 10:36 PM

Topic tags/keywords: question

I’m trying to make a stand-up computer station that sits on top of a regular cube-farm desk. I’m a noob at wood-working and thought this would be relatively simple (looks don’t really count in this instance). I was thinking of a 2X2 red oak… frame I guess you’d call it—four legs with 1X2 stretchers, with a baltic-birch plywood top.

I started by trying to cut mortises in the top, and the project immediately went south. After laying out the lines for the mortises, I used a hole-saw to cut out the waste, then tried to use a jig-saw to cut the holes square. I guess most of you already know what happened: the birch layer chipped like crazy, the holes weren’t square or smooth, trying to chisel the holes looked even worse, and no amount of wood rasp plus elbow grease would clean things up. Where did I go wrong? Or, perhaps the better question, did I do anything right?

Thanks.

-- Hey, I'm usually right twice a day! Except where they use 24 hour clocks.


2 replies so far

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crank49

3981 posts in 2437 days


#1 posted 07-01-2011 12:14 AM

Was this true baltic birch or birch ply from a big box store? The former should hold up fairly well, the latter will barely make it home before coming apart. Big box stores have lowered the standard to a point all they sell is worthlless junk. One exception, and I can’t explain it, is the AC grade sandply with exterior glue coming from south america.

I’m not sure I have my head wrapped around what you are describing but, if I understand, you want to cut a tennon on the top of a leg and insert it into a mortise in the plywood top? And in trying to cut your mortise it tore your plywood apart?

I built my work bench like that, but my top was 4 layers of sandply laminated together, I cut the mortises in three layers before I laminated them, There was no mortise in the top layer. I used a very good Bosch blade in my jigsaw and had the saw set for minimum orbit with a zero clearance shoe on the saw’s foot. This made a clean hole, no tearout. After laminating all my layers together I used a sharp chisel to trim and clean up the mortises. With plywood you have to have very sharp tools or it won’t work. I’m talking scary sharp. So sharp you could cut the end of your finger off and not feel it. Don’t ask me how I know.

If you are dealing with a single layer top I assume you are trying to make a through tennon. That might be hard to do without de-lamination. Mine were not through tennons, the top layer had no mortise. I had closed mortises and poured epoxy in them before I drove the leg tennons home. The epoxy bonded all the parts together so nothing has ever de-laminated.

Hope this helps and is not to confusing.

And welcome to Lumber Jocks. I just now noticed you’re new here.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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BustedClock

112 posts in 1988 days


#2 posted 07-01-2011 04:13 PM

Crank49,

Thank you for the welcome. I did a web-search trying to find an answer and LumberJocks was one of the first results. I’m enjoying exploring the site and looking at the pictures.

You describe the situation exactly—ply from an orange big box store, single layer top with through tenons, and sharp but probably not scary sharp chisels. The other color big box store has some 20X48 panels composed of edge-glued 1X6 pine. I think I’ll give that a try—after working on my chisels some more ;-)

Thanks for the info.

-- Hey, I'm usually right twice a day! Except where they use 24 hour clocks.

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