Line Boring with Through Bits

A discussion of bit choice for a line boring block. Can you do all your boring with through bits? June 16, 2014

Question (WOODWEB Member) :
I have a small drill block for line boring and thinking of loading it with all through bits. About 1/3 of my boring is through bore. What are the pros and cons?

Forum Responses
(Cabinetmaking Forum)
From Contributor H:
If only 1/3 is through, I would load with brad points. You can go through with brad points with a backer board without too many issues.

From contributor F:
The through bits should cut cleaner for those cuts, however you'll need to be careful you go deep enough for the non-through. You don't want to end up with shallow holes your shelf pins won't fully seat in, and you don't want through holes for shelf pins either. I only have one through bit on my drilling machine for confirmat screws so it always go fully through. Maybe a few test runs are in order?

From contributor H:
I use all through bits on my machine even if the hole is only half drill without a negative issue.

From contributor L:
We also use all through bits on our router. All our material is 3/4" so even when the holes are only on one side there is plenty of room without going all the way through. Test whatever you are thinking of using. If you are backing up with a router spoilboard a dowel bit will likely cause a chip-out when used as a through bore.

From contributor D:
On a nested base CNC router with a spoilboard you can use brad point bits. They drill a nice, clean through hole without damaging the spoil board or any chipping on the part. We have drilled a bazillion of them over the last two years on our machine. Through bits will drill too far into the spoil board and the spoilboard will need to be resurfaced more often and remove more material each time.

From contributor L:
No need to worry about the little V pockets left by the through bits, they don't connect to the outside world! No path for the vacuum to escape. I'm not familiar with brad point bits for a router? We use dowel bits for doweling and through bore for line bore, or other appropriate uses. Cylinder bits like the typical 35mm hinge bits will work for clean through boring, only if your spoil board is tight to the work, as in no prior grooves. Perhaps you could slow the Z-axis feed enough to not push out the melamine face when it is not backed up.