Uneven table top joints

[Michael Furey]

I'm edge gluing my boards while also using a biscuit cutter to help with the alignment of the joints across the top. Most of the areas come out nice and flush after I join them, however there's always a few spots that seem to raise up a little bit and are not perfectly flush. I usually end up having to sand it down to make it even. I thought the point of the biscuit cutter was more for the alignment of the boards (in making table tops) rather than the strength which comes from the glue. Why is this happening? Am I not using enough biscuits? Some of the boards are not perfectly flat, they have a slight bow. Do I need to use more biscuits to when I have boards like that? I do put them through the planet but sometimes the board as a whole is bowed sometimes just slightly where I can bend it straight with my hands. On say an 8ft table I will use 5 or 6 biscuits per joint. I have a feeling I need more. Any advice is appreciated.

[Lee Schierer]

When working with bowed lumber start tightening your clamps at the center of the length and align the boards. Then work toward the ends one clamp at a time aligning the top surface. This method will help eliminate the misalignment. Biscuits help with alignment, but they aren't a perfect solution. Personally I don't use them.

[glenn bradley]

The planer gives you parallel faces but, as you have seen, does not flatten material; that's a jointer's job. Certainly using flat square milled material is the best solution. If you have to force things into position, sub-optimal results are generally the rule.

Biscuits will help with alignment of flat square stock but, the fit is not such that will force material into position. The method Lee recommends will help. Edge gluing two boards with this method and letting them set, then adding one more board at a time may also help. However, if the stock is not flat, the end result may still not be what you're after.

[Joe Jensen]

The key is flat stock. Once I added a planer to my shop and started only buying rough sawn wood I haven't had to use biscuits or anything to align boards for glue up.

[Matt Day]

In addition to what was said above, you have to use the biscuit joiner appropriately as well so the slots are consistent. And make sure the biscuits fit snugly. Cheap ones seem to vary quite a bit in thickness and do not make a tight fit.

[Matt Day]

The key is flat stock. Once I added a planer to my shop and started only buying rough sawn wood I haven't had to use biscuits or anything to align boards for glue up.

I am guessing you already had a jointer. Just having a planer of course would not give you flat parallel stock.

[Prashun Patel]

Even Dominos don't result in perfectly flat joints usually. Both biscuit joiners and Domino mortisers rely on your hand pressure to keep the tool perfectly flat and perfectly square to the face. That's a tall order on long edges.

On rare instances (ironically with a 9 foot slab glue up) I've had the joints come together perfectly with a Domino, but most times, there is a tiny lip.

The best way I've found to flat glue ups is using cauls across the face. Of course, this also requires that your edges are perfectly s4s.