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Several times I have cut a mortise into a shank with a typical drill bit and find that the tenon (cut with VF tenon cutter) catches or hangs at certain points in the mortise as it is inserted.

I can't tell if this is a mortise issue or an issue with the tenon cutter but sanding the tenon does not seem to improve things and sometimes seems to make it worse.

I watched a video this morning where a well known pipe maker drilled the mortise hole and then used what I'm guessing is a reamer.

Can anyone explain why he did this and if there is a chance it might help with the problem I've run into?

If so, do you buy the same size reamer as the diameter of the drill bit used to cut the mortise?

Thanks,

George

Reaming the mortise is standard among the higher end makers.

The reason is drill bits cut only on their end which leaves the sides of a hole fuzzy with torn wood fibers, while a reamer is dull on the end but sharp on the sides so leave a smoother hole.

Since you can't drill a hole with a parallel-sided reamer, you must first create "most of" the hole with a drill bit, then enlarge it slightly with a reamer. A few thousandths larger than the drill bit is all that's necessary.

The type of reamer you want is called a "chucking reamer". Either the spiral fluted or straight fluted model will work, but the spiral type leaves a slightly smoother surface because it slices instead of chops.

Was it my video?

Like LL says, and I'll add. Decide on a few tenon sizes you will use and then find a drill bit, whether it be letter, number or fractional, that is a few thousandths smaller than your chosen tenon size, use said drill first and then follow up with the chucking reamer.

This is really good info guys. Thanks for sharing it!

A reamer doesn't just make the hole the correct size, it also makes it round. A standard twist drill bit doesn't drill a round hole, if it's ground off centre it usually drills an oval hole but even if it's well ground it actually drills a triangular hole. A reamer makes the hole perfectly circular.

Good info as usual guys. I think it is time for a reamer. I really think the problem I described would be solved, or at least improved, with one. When it happens it is almost unsolvable. If I sand the tenon to the point where it doesn't catch and hang it becomes too small. Not sure why it happens some times and not others. Possibly the grain of the wood. Possibly the giant pile of not-so-new drill bits I grab out of with no consistency.

Doug535 wrote: ↑Wed Dec 11, 2019 4:31 pm Like LL says, and I'll add. Decide on a few tenon sizes you will use and then find a drill bit, whether it be letter, number or fractional, that is a few thousandths smaller than your chosen tenon size, use said drill first and then follow up with the chucking reamer.

I've got to do this. I normally use the VF tenon cutter and cut the tenon to an arbitrary size then find a drill bit that approximates it by trial and error on scrap wood. I either need to set the tenon cutter at a specific size and leave it or start doing more delrin tenons. So far I've done two delrin tenons and they work well with one specific (and new) drill bit.

caskwith wrote: ↑Wed Dec 11, 2019 4:26 pm Was it my video?

No it was Former making a billiards. But, I have watched quite a few of your videos.

Also, I notice that reamers are not cheap. So I don't want to do this by trial and error. Does anyone have a standard delrin tenon size + drill bit + reamer combo that you'd be willing to share that works for most applications?

George

n80 wrote: ↑Wed Dec 11, 2019 6:08 pm Also, I notice that reamers are not cheap. So I don't want to do this by trial and error. Does anyone have a standard delrin tenon size + drill bit + reamer combo that you'd be willing to share that works for most applications?

George

I found them anywhere from $8 up to $50.

I would only ever buy $50 ones.

I find that the chucking reamer leaves a pattern of paralell grooves in the mortise. The may be a chatter effect due to the speed at which I am running my drill press. I made my own bit patterned on the spoon bit principle with a single cutting edge. This seems to give a smoother mortise.
Docaitch

DocAitch wrote: ↑Thu Dec 12, 2019 12:25 am This may be a chatter effect due to the speed at which I am running my drill press.

Anything slower than 50,000 rpm, well... though that wouldn't be wrong, exactly, you're missing a lot of fun.

One trick you can try is something I learned from a machinist several-many years ago - take a stone (or diamond hone) and just knock off the corners of the cutting edge way out at the outer diameter of the drill. BUT, start with a good, quality drill bit that is uncoated (bright uncoated HSS only). This helps reduce any radial grooves made by that very sharp corner of the cutting edge where it transitions to the side, forces the bit to follow the tip, and can even help keep it straight as you drill. Also - use the shortest drill bit you possibly can (mine are about 2" long) to reduce flex, torquing, and resulting wander.

I use reamers for everything in metal, but in briar (and other woods) I have not found them to be necessary.

Thanks Kurt. Good tip.

As an aside, I've never used a reamer.
But then again, I'm from Africa.