Eric The Viking
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- 19 Jan 2010
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In some areas, I would expect a spiral to be worse, slightly (but better overall).
The trouble with the router method is that, however you design the jig, There will be somewhere where the bit is pushing the fibres out into empty space, rather than cutting them. You can arrange a tablesaw blade so this only happens on one side (if backed by a zero-clearance/sacrificial board that problem is fixed, too).
I did a bit of YouTube searching yesterday: every industrial box joint machine I found used saw blade/dado cutters (or a spindle-moulder, but same cutter design). I couldn't find any industrial systems with a router(s) as the basis.
I find this slightly frustrating, having put quite a lot of effort into trying to get the router table thing to work well a few years back, but I have to admit defeat, insofar as it can't be both quick and clean simultaneously.
If you use sacrificial stock both sides (The fence being one side), it should work well (and probably doesn't need a spiral bit, either), but without that, there will be tearout (probably reduced by a spiral cutter tho). If the inside of the finished box doesn't matter (and they often don't), then that side should face away from the fence. Also, when cutting the "b" form (the second half of the joint), you need to either keep the "a" form on the peg, or put a similar sacrifical piece in to replace it, to avoid really impressive tearout on the edge of the "b" piece on that side -- it's not enough just to use the "a" piece to get position while you clamp the "b" stock on the fence.
One thing I didn't try, which ought to make a big difference, was knife marking the bottoms of the slots (and round the outside edge of the "b" piece). I think if you sever the outermost fibres properly, you make things a lot easier for the cutter.
The trouble with the router method is that, however you design the jig, There will be somewhere where the bit is pushing the fibres out into empty space, rather than cutting them. You can arrange a tablesaw blade so this only happens on one side (if backed by a zero-clearance/sacrificial board that problem is fixed, too).
I did a bit of YouTube searching yesterday: every industrial box joint machine I found used saw blade/dado cutters (or a spindle-moulder, but same cutter design). I couldn't find any industrial systems with a router(s) as the basis.
I find this slightly frustrating, having put quite a lot of effort into trying to get the router table thing to work well a few years back, but I have to admit defeat, insofar as it can't be both quick and clean simultaneously.
If you use sacrificial stock both sides (The fence being one side), it should work well (and probably doesn't need a spiral bit, either), but without that, there will be tearout (probably reduced by a spiral cutter tho). If the inside of the finished box doesn't matter (and they often don't), then that side should face away from the fence. Also, when cutting the "b" form (the second half of the joint), you need to either keep the "a" form on the peg, or put a similar sacrifical piece in to replace it, to avoid really impressive tearout on the edge of the "b" piece on that side -- it's not enough just to use the "a" piece to get position while you clamp the "b" stock on the fence.
One thing I didn't try, which ought to make a big difference, was knife marking the bottoms of the slots (and round the outside edge of the "b" piece). I think if you sever the outermost fibres properly, you make things a lot easier for the cutter.
