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Tips for a panel glue up where the middle wont close up? (lemmy.world)

submitted 4 days ago by inquanto@lemmy.world to c/woodworking@lemmy.ca

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I'm trying to do my very first table top out of hardwood but it proving to be quite the learning curve. I acquired a small benchtop jointer and a lunchbox type thickness planer and I've more or less successfully made my boards. What I'm struggling with now is getting a nice glue up without gaps. My first try turned out so so, and i was afraid i didn't use enough glue so I re ripped the joints with my tracksaw. I think my boards are evenly thick but they seem a bit hourglass shaped if that makes sense. They'reb about 170cm long and they join up on the ends, but there's about a 1mm gap towards the middle on some joints and its too much to squeeze all the gaps together on the panel. I first tried jointing on the benchtop jointer but got horrible results with the small bed. (Could also be lack of skill as this is all new to me). I then went with a tracksaw and parallel guides instead,which is better but still giving me a bit of a gap. So I guess im asking how more experienced woodworkers would proceed.

Would it help to glue up two boards at a time so there's maybe enough strength in the clamps to squeeze the gap shut. Or should i rip the bigger boards down so they all fit upright in the thickness planer and try to get two really parallel sides that way? I have rollers to extend the beds of both the thicknesser and the jointer but have had better results with the thicknesses. Is there something else I'm not thinking of?

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[–] captain_aggravated@sh.itjust.works 6 points 4 days ago (1 children)

Small benchtop jointers can have some limitations with long boards.

The leading edge of the infeed table, the apex of the cutter, and the trailing edge of the outfeed table are three points that describe an arc. Especially if you're using a deeper setting, it's possible that in the middle of the board, it is riding on the two ends of the table and slightly lifting off the table near the cutter, still taking a chip but not at full depth, so it will joint a concave radius into the board. It may be many meters in diameter, and when you bring two of them together it shows 1mm over nearly 2m. This would present as your boards being slightly hourglass shaped as you describe. Also, it's possible the tables of a light duty jointer can sag under the weight of a very large board, exacerbating this problem.

Some things that help when using my benchtop jointer:

Rip the edge on the table saw first to get it straight if saw marked, then take it to the jointer. Using a taper jig as the reference on the fence may help if the board is bowed or otherwise not straight. Your track saw is also a good tool for this.
Set the jointer for a shallow cut. The shallower the cut, the larger that radius becomes. This can reduce but will not eliminate the issue.

Your thickness planer won't help here, because what it will do is take your hourglass shaped boards and make banana shaped boards. You'll go from )( to )). You might could make that work but it's still a problem. I'm also just not a fan of putting boards through a planer on edge without ganging up several.

Rhe most straightforward solution is probably to use a bench plane. This video from Paul Sellers is a great reference for the method. It's either use a hand plane, get a bigger jointer, or try some hacky workaround like use a router and a straight edge. Maybe you can use one of those power hand planers they make with the same techniques as a bench plane but I honestly don't think those are any easier to deal with than a bench plane.

[–] inquanto@lemmy.world 4 points 4 days ago (1 children)

Thanks for the tips, i have some extra boards so maybe i can just practice a bit with the jointer and get a better result, the bench plane also seems like a good option. Though I'm still confused why the tracksaw and parallel guide also gave me the hourglass shape. In the past I used that setup on plywood for similarly long cuts with better results..

[–] captain_aggravated@sh.itjust.works 2 points 4 days ago

Well, one thing to ask is, are the boards actually narrow in the middle, or is the blade of the saw tilting in the middle a bit? Are the jointed edges square to the faces?

[–] DontHurtMe23@lemm.ee 3 points 4 days ago (1 children)

I found a lot of useful stuff from this video from Foureyes, particularly around the 6 minute mark for the in/out method on the jointer. There's also a similar up/down method if you have a table saw.

[–] inquanto@lemmy.world 3 points 4 days ago (2 children)

Thanks I actually used the up down method with the track saw but from my understanding that's more about the board edges not being 90° which seems to nut be an issue when i measure it, but the hourglass shape wouldn't be affected by that right?

[–] captain_aggravated@sh.itjust.works 1 points 3 days ago

The up/down method (or in/out method on a jointer, same idea) is for compensating for any out-of-square condition of the tool.

like, I'm pretty sure my jointer's fence will never be set to 90.000000000000000 degrees to the table. The pre-Trump US office of Weights and Measures couldn't manage it, partially because it's a piece of aluminum almost flexible as my house cat. I'm certainly not going to get it perfect armed with the combination square I keep in my tool belt.

Let's say I get it set to 91.0 degrees. Put one board face into the fence, the other face out of the fence, I'll have cut one of them at 91 degrees and the other at 89. These are complementary angles and together they add up to 180. Paul Sellers planing both boards at the same time achieves a similar effect.

This would compensate for, say, an imperfection in the bevel setting of your tracksaw; if the blade is set to a 90.234572 angle instead of 90.00000, the up/down method will compensate for that. But it won't compensate for, say, if the frame of the track saw isn't perfectly rigid and you apply a little bit of side pressure flexing the foot a little partway through the cut. Track saws are usually better about that than normal circular saws, but still.

Also, did you buy this stock rough and surface it yourself on that jointer and your lunchbox planer? Because surface planing a long board on a benchtop jointer will have the same problems as edge jointing on one. I don't know how flexible your tracksaw's track is but if it conforms even slightly to a twisted board you might get an imperfect cut.

Can you take pictures? It may help with a more definite diagnosis.

[–] DontHurtMe23@lemm.ee 3 points 4 days ago

That's true. The only thing I can think of for getting an hourglass shape would be potentially applying uneven pressure during the cuts. The track saw track should give you a dead straight line, but only if you aren't applying any lateral force during the entire cut.

[–] BradleyUffner@lemmy.world 1 points 4 days ago* (last edited 4 days ago)

For something like that you should dry fit them without glue first, to make sure you jointed true. If they don't line up without glue you need to fix the problem before adding glue.

A gap in the center usually means the outfeed side of your jointer is too low relative to the cutter. It could also be caused by too much downward pressure as you pass over the cutter head.