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Shank size and tenon length
Posted: Thu Aug 19, 2010 9:15 pm
by TRS
A couple of my first pipes have developed cracked shanks. One of them had a chunk crack away on top, the other one split down the middle on the bottom. I wanted slimmer pipes so on both of these I went from my usual 5/8 shank to 1/2 inch. The tenons are 5/16. I have an old Savinelli billiard that has a 1/2 inch shank and a 5/16 tenon and it seems quite sound. The difference is that my tenons on these early attempts ended up being about 3/8 inch long, whereas the Savinelli's is closer to 5/8 inch long. Is the extra length keeping more stress off of the end of the shank/mortise? Should I just graduate to skinnier tenons if I'm doing a skinnier shank? Thanks
Tim
Re: Shank size and tenon length
Posted: Thu Aug 19, 2010 10:51 pm
by Sasquatch
Beatus, what a longer tenon does is gives you more surface area between the tenon and the mortise walls. Basic physics equations apply here, and what it means is that if you want a tenon to "grip" you need a certain amount of friction. You can generate this by using a tenon 1/8" long and making it press the sides really hard (= cracked shank) or 1" long and hardly pressing the sides at all, for the same "feel". Obviously, niether of those makes any sense at all, but that's why you see a fairly long tenon where possible - it allows a tight feeling fit without applying pressure to the shank.
I've had pretty good luck on some fairly thing "Bing" style pipes with somewhat exaggerated tenon length - 3/4" or longer. They slide in easy, but park well, and don't exert much outward pressure on the shank.
Re: Shank size and tenon length
Posted: Thu Aug 19, 2010 11:22 pm
by TRS
Thanks Sasquatch. Heh, the Savinelli in question is, in fact, a Bing's Favorite; ugly as sin, but it was free, so.....
Re: Shank size and tenon length
Posted: Fri Aug 20, 2010 9:49 am
by KurtHuhn
For thinner shanks I've settled on a long 1/4" tenon. A 5/16" tenon seems too big for thinner shanks without banding of some kind.
Re: Shank size and tenon length
Posted: Fri Aug 20, 2010 2:45 pm
by TRS
KurtHuhn wrote:For thinner shanks I've settled on a long 1/4" tenon. A 5/16" tenon seems too big for thinner shanks without banding of some kind.
Yeah, I think I'm going to order a bigger variety of sizes of Delrin from Mcmaster this time around....give me some more elbow room for customifying my tenons.