Shank diameter and wall thickness vs derlin tenon size?

[brownred]

Was wondering if there was a rule of thumb with tenon size and wall thickness?

I was working on my second pipe last night. I turned and drilled the stummel "shank diameter was .580 and 5/16 mortise" and it looked good. Then I turned the stem to the approx. shank size then drilled and inserted the 5/16 derlin tenon.
Then when I put stummel on the stem to turn stem and shank together to get them the same diameters the shank cracked.

The first pipe was done the exact same way with a shank of .550 and it didn't crack.

Is it safe to assume the second brair was bad and cracked or was I just lucky on the first pipe?

Is there a minimum shank size and shank wall thickness for certain size tenons?

I want to get 1/4 derlin for tenons, do you still use a 5/32 draft hole with a 1/4 tenon?

Thanks

[NathanA]

I doubt if the briar was bad if there was no visible flaw. If I am doing the math in my head right the walls of your shank are less than an 1/8 and if your stem is a tight fit breakage is certainly possible. In addition to the 1/4 delrin you can also use the 3/16 stainless steel tubing that is used with bamboo if you want to do really thin shanks.

[d.huber]

I want to get 1/4 derlin for tenons, do you still use a 5/32 draft hole with a 1/4 tenon?

Yes.

Hope this helps.