Stem/shank gap after bending...

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JMG
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Stem/shank gap after bending...

Post by JMG »

I'm having trouble with the stem/shank junction. Everything starts off great, nary even the tiniest sliver of space between the two...until, I heat and bend my stems. Once I do this I'm ending up with a very slight gap between the stem and shank. Nothing major at all, but certainly not something I want.

Any ideas/advice?
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sandahlpipe
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Re: Stem/shank gap after bending...

Post by sandahlpipe »

Make sure you have a perfect fit before the bend and be careful not to heat the tenon and stem face. If your stem is fitting too loose, bending can create a gap where none was before.
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caskwith
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Re: Stem/shank gap after bending...

Post by caskwith »

Where are you holding the stem/shank when you do the bending?
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Re: Stem/shank gap after bending...

Post by JMG »

I tend to hand the stem at the button and the stummel...I bend it while in the shank. Am I doing it wrong?
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Re: Stem/shank gap after bending...

Post by NathanA »

Is the gap equal on all sides or just on the top of the shank from pulling down on the stem?

If you have a gap after bending on just one side you can usually eliminate it by holding the shank face to a piece of sandpaper on a perfectly flat piece of something (I use a granite tile) and pull the shank over the sandpaper with the high side where there is no light gap as the leading edge. The leading edge will have slightly more material taken off and that should fix it. It might take a few passes. If you have to take too many passes you might have to shorten up the tenon.
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Tyler
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Re: Stem/shank gap after bending...

Post by Tyler »

Or, if the gap is heat related, heat the tenon and it will go back to straight.

Do you apply a lot of force to bend?
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Re: Stem/shank gap after bending...

Post by JMG »

Tyler wrote:Or, if the gap is heat related, heat the tenon and it will go back to straight.

Do you apply a lot of force to bend?
No, not too much force. I heat the stem with a heat gun until they are fairly pliable. Also, I'm using delrin tenons.
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Tyler
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Re: Stem/shank gap after bending...

Post by Tyler »

JMG wrote:
Tyler wrote:Or, if the gap is heat related, heat the tenon and it will go back to straight.

Do you apply a lot of force to bend?
No, not too much force. I heat the stem with a heat gun until they are fairly pliable. Also, I'm using delrin tenons.
I was going to ask about delrin. You might be heating the epoxy too much, then pulling the delrin out of alignment,
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Re: Stem/shank gap after bending...

Post by LatakiaLover »

Put your heat gun in a base/vise/holder of some sort, so it's pointing as close to straight up as the holder allows.

Put a leather work glove on BOTH hands.

Using your strong hand, hold the pipe AT the shank/stem junction when both heating AND bending.

Do NOT use a heat gun's "high" setting to bend. Too much too fast doesn't work, and might destroy the stem by bubbling the surface.

During heating, the glove will act as a heat shield for the base of the stem, keeping tenon and shank temps down. During bending, the clamping action will hold things in alignment (apply an extra bit of grip pressure when bending).

If a tight hold results in some surface pebbling after everything has cooled, turn the gun to high and "flash heat" the affected portion by holding the rough spot in the heat stream FOR NO LONGER THAN ONE SECOND, at a distance of about one inch from the nozzle. Check surface, repeat as necessary. Done right, any pebbling/depressions will pop back out without drama.
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Re: Stem/shank gap after bending...

Post by JMG »

George I question your knowlege with pipes. How csn I be sure you know ehat you're talking about?

Thanks for all the info bud. I eill give this a try on the next one.
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W.Pastuch
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Re: Stem/shank gap after bending...

Post by W.Pastuch »

I've had this problem with thick shanked pipes with a tapered mouthpiece (like the author shape). You need quite a lot of heat to get the mouthpiece to bend and it's easy to overheat the tenon in the process. If the tenon becomes too warm it will bend from the pressure applied to the mouthpiece, thus creating a gap between the shank and stem faces. (I don't know how delrin reacts to heat, but if it's glued in it the heat might also affect the glue joint).
My solution is to make the tenon as thick as possible on thick shanked bent pipes, or even better, make a reinforcement from stainless steel inside the tenon- you can then heat and bend a thick mouthpiece without any risk of bending the tenon as well.
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Re: Stem/shank gap after bending...

Post by caskwith »

Hmm very odd, I use the same method as pretty much everyone has described and I have never had this problem that I can recall. I warm the stem holding the bowl with the heat gun on high (sorry George) then grip the stem just past the shank junction and bend it using gloves and set it under the running tap. I always use 6mm delrin tenons on any size pipe, no problems.
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Re: Stem/shank gap after bending...

Post by LatakiaLover »

caskwith wrote:I warm the stem holding the bowl with the heat gun on high (sorry George)
I guess it depends on the make and model of gun. Mine is over 1000 degrees when set on high, and will boil the surface of acrylic in an astonishingly short time.

People should definitely experiment with their own gear, starting on the low side and working upward. Losing 3-4 hours of work in a flash sucks.
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JMG
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Re: Stem/shank gap after bending...

Post by JMG »

From all you guys have written I think my problem lies in the fact that I either don't hold the pipe at the stem/shank junction at all, or at least too loosely when actually applying the bend. I will try to reinforce that spot on the next pipe I make. I really appreciate all the help guys.

Now, I just have to wait 3 weeks to make another pipe...traveling, traveling, traveling. Starting our "goodbye" rounds before heading back overseas in March.
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Re: Stem/shank gap after bending...

Post by LatakiaLover »

W.Pastuch wrote:I've had this problem with thick shanked pipes with a tapered mouthpiece (like the author shape). You need quite a lot of heat to get the mouthpiece to bend and it's easy to overheat the tenon in the process. If the tenon becomes too warm it will bend from the pressure applied to the mouthpiece, thus creating a gap between the shank and stem faces.
Exactly so.

Here's something close to a worst case scenario... the stem is short, tapered, over an inch in diameter at the base, and the customer wanted the new one in acrylic: :shock:

(I didn't use a stainless "tenon rigidity sleeve" like Pastuch suggests---just gloves, patience, and held the joint tightly when applying pressure---but might next time. It's a good idea.)


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Re: Stem/shank gap after bending...

Post by kamkiel »

I really like the new stem you made for that pipe! I have two very amatuer questions I'd like to ask though. What is the purpose of the p-lip, and is there any special reason for the tenon to have the step in it?
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Re: Stem/shank gap after bending...

Post by LatakiaLover »

kamkiel wrote:What is the purpose of the p-lip, and is there any special reason for the tenon to have the step in it?
-- It's a 19th century patented design which is still in production because people still like it enough there's a market for it. The main feature that Peterson's focuses on in adverts & promotional materials is how the smoke stream is angled upwards away from the smokers tongue.

-- There's not necessarily any purpose to tenon steps in general, but I HAVE encountered instances where the length of the step (meaning how far past the contact area of the tenon the reduced diameter portion extended into a pipe's "dead air" space, such as Peterson's condensation chamber) made a night & day difference regarding wetness finding its way up the stem's airway. Still trying to figure THAT one out, lol.
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Re: Stem/shank gap after bending...

Post by Oakbear »

That new stem is lovely George, such an improvement!

Maybe a newb question, but does everyone insert the tenon into the shank to bend? If i have a thick stem i tend to bend it on it's own, making sure there is no pressure on the tenon and stem/shank junction. I'll wait for it to cool then fit it and tweak as needed. Am i missing something?
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Re: Stem/shank gap after bending...

Post by LatakiaLover »

Oakbear ---

On a stem as short and thick as the one in the pic where the bend starts AT the stem/shank junction, not having the shank to hold would introduce other problems. Holding it tightly enough to get leverage could make it egg-shaped, for example, and if you DID touch the tenon it would take very little pressure to knock it out of alignment. If the latter happened, even if you let it "return to straight" with gentle heating, having it go back to PERFECTLY straight would probably not happen. Then you'd be stuck either trying to tweak it by trial and error (and still maybe never get it), or re-face the shank, which is extremely difficult to do by hand as well as time consuming. It only takes a couple thousandths off to create a light gap, and gaps are magnified by shank diameter.

It's easier and less risky (in percentage terms) to do both together in such cases, in my experience.
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caskwith
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Re: Stem/shank gap after bending...

Post by caskwith »

LatakiaLover wrote:
caskwith wrote:I warm the stem holding the bowl with the heat gun on high (sorry George)
I guess it depends on the make and model of gun. Mine is over 1000 degrees when set on high, and will boil the surface of acrylic in an astonishingly short time.

People should definitely experiment with their own gear, starting on the low side and working upward. Losing 3-4 hours of work in a flash sucks.

That's a good point, I don't know the temp of my gun but might not be that hot. Also experience plays a lot into it, I have bent hundreds of stems using this gun, I know where to hold the pipe and how to move it. It probably helps as well that Polyester doesn't bubble if you get it too hot. It will snap though if you get the temp wrong so again practise is the key here.
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