BIG edge jointing problem

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Big in the sense of the boards (timbers?) involved.
I'm trying to edge join the two boards for my bench top. Each board is 80" x 3 1/2" x 7". They're big and I need to join the 3 1/2" edges.
Here's what I've done. - Got the faces flat and square by using long 4" wide strips of plywood screwed to the sides to form a sled. Ran it through the planer to flatten a face, then removed the strips, flipped the board and flattened the opposite face. - planed one rough edge down to mostly flat (so the bit wouldn't have to take a big bite in the next step) then laid the board on its face, screwed one of the straightedges to the face (actually the bottom face so the screw holes will never show) then used a pattern cutting bit (bearing on the top) to true half the thickness of the edge. - Removed the strip, flipped the board and changed to a bearing on the tip bit in the router and rode that bearing against the edge created in the previous step. - I did this to each of the two boards thinking that I would get a nice mating surface. What resulted was not bad, but not the tightness that I was expecting. Would like to get these tighter and some solutions (like adding clamp pressure to draw the boards together during glue up) simply won't work given the size of the boards.
Any ideas?
By the way, I'm going to use a full length 3/4" plywood spling during glue up. Also, the gap on the edge at it's max is about 1/32, although most spots are less or touch flush.
tia,
jc
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On Tue, 24 Jan 2006 19:59:56 GMT, noonenparticular wrote:

So the plywood "straightedge" wasn't so straight.
You might do better using a tablesaw. Screw the plywood strip so it overhangs the opposite edge, and bear against the TS fence with it. This way, the impact of small variations in the plywood will be reduced by the long fence.
--
Art


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So it would seem. I checked it with my straigt edge prior to tightening the 7 screws down, but there was obviously *some* error.... :-(

I thought about this and it should work in theory. Here's the problem I ran into in practice. First, the fence would have to be over 3 1/2" high for the plywood to bear against it. No problem, fasten a tall subfence to it, right? Well yes, but now you have the problem of the mass of the timber pressing sideways against the top of the subfence which is fastened to a short TS fence. The leverage of all that mass will make the subfence flex away from the blade, I'm guess substantially. Secondly, I only have a 10" blade for the table saw which has a max depth of cut of 3 1/4" while the boards are a *strong* 3 1/2. So the blade wouldn't even make a through cut, which would concern me from a safety issue with all that mass against a comparatively flimsy fence.
jc
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On Tue, 24 Jan 2006 20:34:08 GMT, noonenparticular wrote:

Well, a tall TS fence comes in handy for other things. You could make one that is stiff enough for this job. Perhaps in this case its a bolt-on, rather than something that just slips over the existing fence. And if you make the plywood guide wide enough, there will be room at the front and rear of the fence to get a clamp on there, to hold the tall fence in place really well.
As for the blade not making the full thickness, right, I didn't consider that. But you could use your router with a flush trim bit to clean up the last bit.
--
Art


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Art Greenberg wrote:

Not if he uses my CMT flush trim bit that I just discovered is .003 smaller than the 1/2" bearing. I was making table inserts yesterday from a master and found they didn't fit into the recess. I mic'd the bearing at .500 and the bit at .497. That was the tall bottom bearing bit that came with the door making set. Since that one wasn't machined accurately I checked my top bearing bit--perfect. I guess one out of two is better than 0 for 0.
Dave
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David wrote:

I just found that Amana sells a .492 bearing, useful after getting a 1/2" trim bit sharpened.
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noonenparticular wrote:

I think you should be able to use the outside edge of the board against the fence, if it's reasonably straight. It only needs to be straight enough to keep the saw blade from binding -- since you're cutting both boards at once, they'll match up.
Similarly, if you make half-through cuts on both sides, it doesn't matter if they don't match each other perfectly, because the two halves will still match.
Nonetheless, it still seems like a lot of weight and a pretty deep saw cut, and I'd be a little concerned that holding up that much weight and keeping it straight against the fence would be like trying to walk and chew gum at the same time, and I'd end up not holding it quite straight and cause the saw to bind. One could avoid that by using a handheld circular saw (or possibly a router and making lots of passes) against a plywood straightedge instead, I suppose.
...
One possible variant of this idea (specifically, to cut both sides with the same guide at the same time, so that they match regardless of whether the guide is perfectly straight) would be to mount the plywood guide so that your router will just shave a tiny bit off one board, and then clamp the other board a little less than the diameter of the router bit away, so that the router also just shaves a tiny bit off it as well.
If you don't want to cut both at once (which would mean that one's getting cut the "wrong" direction), and you have two router bits of different diameters that would both work for cutting the faces, you can mount the plywood fence on the first board such that the router with the larger cutter will just shave it, and then position the second board so that the router with the smaller cutter will just shave it. Then, take a pass with the smaller cutter to surface the second board, remove the second board, and take a pass with the larger cutter to surface the first board. Or something like that -- if you're following the plywood guide with a roller bearing rather than the router base, then you could use different sizes of rollers for the two passes.
- Brooks
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Brooks Moses wrote:

I just realized that I posted this in the wrong place -- I got noone and Frank's replies mixed up, and thought this was you replying to the idea about cutting both boards at once, which I just realized was Frank's post....
Hope that's not too confusing!
- Brooks
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Brooks Moses wrote:

And now I see that I got noone and Art mixed up when I was writing that.
Sigh. Some days, it just doesn't pay to log in.
- Brooks
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No problem Moses, I'm reading them all
jc aka noonenparticular aka the OP

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Could you mount the two boards with the 1/32 gap as is to a sacficicial piece of plywood (use it as a sled) and rip it right down the joint on the tablesaw? This would remove 3/32 (whatever your ts blade width is) and should remove the gap.
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You're saying to run both boards through at the same time, fastened to the same sacrificial piece, right?
hmmmm..... That may work. Any error on one board is mirrored on the other.....
Thanks Frank. I may give this one a go.
jc
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That's what I was thinking of.
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Frank Ketchum wrote:

I don't know about your TS, buy mine won't cut through 3-1/2" much less that PLUS a sled. <g> (Notice the OP is joining the 3-1/2" edges)
Dave
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just thought of that too, Dave. Maybe if I put the sled on *top* of the pieces...... Still wouldn't get through them both but I could probably handplane the remaining 1/4" down. That way, even if I over planed it, it would be the bottom of the workbench surface and I'd still have 3 1/4" of flush contact glue surfaces on the two pieces.....
jc

just thought of that too, Dave. Maybe if I put the sled on *top* of the pieces...... Still wouldn't get through them both but I could probably handplane the remaining 1/4" down. That way, even if I over planed it, it would be the bottom of the workbench surface and I'd still have 3 1/4" of flush contact glue surfaces on the two pieces.....
jc
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True, but he could cut the majority of the way through and clean up the rest on each board using his router technique he describes in the original post.
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Perhaps the OP can find someone with a 12" TS, or the Ryobi BT3K series--they'll cut to nearly 4"
H
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Wouldn't someone with a 12" table saw also be likely to have a 6" jointer, and wouldn't the jointer be a better solution?
hylourgos wrote:

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H,
I've a 6" jointer, but it's the standard JET 6" and when you take into account the short (for this application) length of the table, the amount of effort it took to keep the timber pushed down on the top and up against the fence was prohibitive. Couldn't get an accurate cut.
Joe

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Isn't is amazing how you can run a board over a device that has a cutterhead flanked by two flat tables and get a board with a crown on the edge?

of
the
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