segments

android · Post by **android** » Thu May 29, 2008 1:39 pm

when you guys use segments or bands on your stems, are they generally glued into place before drilling or is the tenon elongated and the bands slipped over or what?

thanks.

Frank · Post by **Frank** » Thu May 29, 2008 1:53 pm

Either way is a matter of personal choice, but slipping and gluing them over an elongated tenon will give a much stronger joint. I actually prefer to make a double tenon for the end piece, when possible, so that no joint is visible at the tenon.

Post by **KurtHuhn** » Thu May 29, 2008 1:58 pm

Since I use Delrin for my tenons, I just epoxy an extra long piece into the stem and slip the ring over that.

Frank · Post by **Frank** » Thu May 29, 2008 5:06 pm

Detailed instructions of the Kurt method: http://pipedia.org/index.php?title=Using_Delrin_Tenons

android · Post by **android** » Thu May 29, 2008 11:43 pm

wow, thanksf for that link... it helped immensely. I've another question, what is the exact purpose of the tapered bit for the airhole? and is it ok to just use a normal 5/32?

Frank · Post by **Frank** » Fri May 30, 2008 2:54 am

android wrote:I've another question, what is the exact purpose of the tapered bit for the airhole? and is it ok to just use a normal 5/32?

In order to get an even taper to the outside of the stem, you need to taper the inside airway, especially if you make a saddle stem.
Also, you need a gradual change in airway diameter. If you use a straight bit, you will have a sudden change in airway diameter from 5/32" to approx 1/16" about 1" from the button.
Also, at the point of diameter change, you will create a very weak area in the stem, since it will be closest to the surface, plus have a very sharp inside angle.

Hard to put into words, but you should get the gist of it. My advice: use a tapered bit, not a straight bit.

android · Post by **android** » Fri May 30, 2008 10:16 am

i think you put it into words perfectly. makes plenty of sense. thanks.

kkendall · Post by **kkendall** » Fri May 30, 2008 12:38 pm

Frank wrote:... If you use a straight bit, you will have a sudden change in airway diameter from 5/32" to approx 1/16" about 1" from the button.
Also, at the point of diameter change, you will create a very weak area in the stem, since it will be closest to the surface, plus have a very sharp inside angle.

2 things, it makes the wall thinner at that point (bite through).
Plus it creates a 'stress riser'... that means it's a weak point that adds and potential for failure (break/crack) right at the point where the diameter drops down to the smaller diameter.

Stresses along a gradual taper distributes loads across the entire cross section. When that cross section has a sharp change in direction, those stresses pile up at that point (stress riser).

That is also why it is kind of important to have a small radius at the base of the tenon. This obviously doesn't apply when using delrin tenon, but when you cut the tenon from the stem material itself, a radius at the base of the tenon helps to reduce the stress riser at that point.

hazmat · Post by **hazmat** » Fri May 30, 2008 1:56 pm

kkendall wrote:
That is also why it is kind of important to have a small radius at the base of the tenon. This obviously doesn't apply when using delrin tenon, but when you cut the tenon from the stem material itself, a radius at the base of the tenon helps to reduce the stress riser at that point.

I cannot for the life of me etch-a-sketch one of these things on a stem when I'm cutting a tenon. I've ruined more blanks doing this than I did trying to learn how to handcut a stem. Any thoughts?? Or is it just something you have to get used to doing?

RadDavis · Post by **RadDavis** » Fri May 30, 2008 2:03 pm

Grind a tiny 45 or so angle at the point of your cutting tool. Then it's cut automatically when you cut your tenon.

Rad

hazmat · Post by **hazmat** » Fri May 30, 2008 2:06 pm

Thanks, Rad.

I am smart...s-m-r-t...I mean s-m-a-r-r-t