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?
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:
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.
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..
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?