I have a few broken tenons on some very ice pipes. I used to sedn them out to be fixed. Since I have made several stems from scratch I figured I could insert Delrin myself. I am have a problem gripping odd shaped stems in the 4 jaw. I have a set of pin gauges and find one that fits in the air hole and tried chuck the stem until the pin runs true. I have several stems that I can not get to run true no matter how I try. ANy one have a solution?
max
Replacing a broken tenon
It's tough to chuck finished stems up because they're all generally tapered to some extent. They tend to slip out of the chuck while spinning and go off-center or, worse, they can shatter while you're working on them. Someone may have an answer for you in regards to doing this on a lathe. I have not a clue as I haven't figured out how to do this myself.
However, if you have a drill press, you may look at investing in a pen maker's vise. Here's a link to one: link
This will allow you to chuck up those stems and drill them true.
However, if you have a drill press, you may look at investing in a pen maker's vise. Here's a link to one: link
This will allow you to chuck up those stems and drill them true.
I'm only speculating on a solution here, since I haven't tried it personally...
Perhaps you can chuck up a drill bit just slightly larger than the airway hole size in the tenon. Then hand feed the tenon end to the bit, using the tailstock with a dead center to help guide you. Do not use the tailstock pressure to feed the stem into the bit, just to help guide. Hold the stem tightly and be careful that the bit doesn't catch and grab the stem and drill deeper than you want it. Progressively use a larger bit until you reach the diameter of your delrin.
Perhaps you can chuck up a drill bit just slightly larger than the airway hole size in the tenon. Then hand feed the tenon end to the bit, using the tailstock with a dead center to help guide you. Do not use the tailstock pressure to feed the stem into the bit, just to help guide. Hold the stem tightly and be careful that the bit doesn't catch and grab the stem and drill deeper than you want it. Progressively use a larger bit until you reach the diameter of your delrin.
I've been thinking about this. Spinning the stem on a pin gauge works just fine so long as the airhole is centered in the tenon and square to the face. The ones that aren't, the easiest thing to do would be to make a new stem. If that can't be done, you've got one reliable point of reference -- the stem face, with, it is hoped, enough of a stub of a tenon to locate a new one. Here's what I'd do if I had to do it. I'd chuck up a piece of brass or mild steel. I'd face it, center drill, and drill a 1/8" hole maybe an inch deep. I'd make sure a 1/8" center drill (extra long) would slide in the hole, not too tight, not too loose. Then I'd drill maybe 1/8" deep exactly the diameter of the old tenon, deeper if there's more of the tenon stub remaining. I'd part off that inch of stock. That would now be a drill guide. I'd spin the 1/8" center drill in the lathe, using a collet or drill chuck so as not to whack my knuckles, hold the stem very firmly against the face of the drill guide you just made, and guide the whole mess onto the center drill. The tenon stub will be centered and kept from scooting to the side by the pocket you made, the center drill will be relatively square to the stem face, and the stiff center drill will hopefully override the existing cockeyed air hole. You can go 1/4" deep with this first drill. Depending on how far off the air hole *was*, you might need a second guide for a larger center drill, or you might be able to go right to the size of the tenon, but you'd want to make another guide. Center drills come in different sizes, it would be handy if one happened to match your replacement tenon material. If this happened to work and you did a lot of this sort of thing and accumulated a set of these bits and guides, it might turn out to be faster and more accurate than the pin gauges.
Cumbersome, yes, but remember that the stem face is your one reliable index surface, so you have to use it as a guide one way or another. I suppose you could put the stem in some sort of swivel vise on a drill press or milling machine and use a dial indicator in the quill to indicate the face and adjust it square and centered to the drill, but that could take all day. Better just to make a new stem.
Edit: If I were serious about this I'd make the guides for center drills from oil-impregnated bronze bushing stock. I'd use a little oil, too, when drilling the stems. Guides for regular drill bits I'd make from A2 steel and harden if necessary, or from pre-heat-treated stainless. The latter isn't much fun to machine, but would eliminate the possibility of warpage from hardening. That's to make a lasting tool, for a onesy-twosey deal it doesn't matter what you make it from.
Cumbersome, yes, but remember that the stem face is your one reliable index surface, so you have to use it as a guide one way or another. I suppose you could put the stem in some sort of swivel vise on a drill press or milling machine and use a dial indicator in the quill to indicate the face and adjust it square and centered to the drill, but that could take all day. Better just to make a new stem.
Edit: If I were serious about this I'd make the guides for center drills from oil-impregnated bronze bushing stock. I'd use a little oil, too, when drilling the stems. Guides for regular drill bits I'd make from A2 steel and harden if necessary, or from pre-heat-treated stainless. The latter isn't much fun to machine, but would eliminate the possibility of warpage from hardening. That's to make a lasting tool, for a onesy-twosey deal it doesn't matter what you make it from.
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LatakiaLover
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Yeah, Max, this one's a pig alright. As Jack said, the issue goes beyond just chucking up a weird shape, it's that the air hole isn't necessarily centered within the tenon, and the tenon is almost never centered within the shank. A new tenon must go exactly where the old one was AND be axially aligned.
If the air hole isn't centered in the old tenon, don't forget that means the new Delin tenon's air hole then won't line up with the one in the stem. More goofy/messy reaming and drilling is then required.
When I have customers request this procedure, all I can do is explain the difficulties and promise I'll give it my best shot. That there is a significant chance the new stem won't align perfectly, and etc. Doing this procedure perfectly and reliably would require some sort of 3-axis, micro-adjustable clamping fixture for stems, laser alignment (shudder), and super sharp, super rigid Forstner bits that wouldn't deflect when drilling through/alongside old holes.
If the air hole isn't centered in the old tenon, don't forget that means the new Delin tenon's air hole then won't line up with the one in the stem. More goofy/messy reaming and drilling is then required.
When I have customers request this procedure, all I can do is explain the difficulties and promise I'll give it my best shot. That there is a significant chance the new stem won't align perfectly, and etc. Doing this procedure perfectly and reliably would require some sort of 3-axis, micro-adjustable clamping fixture for stems, laser alignment (shudder), and super sharp, super rigid Forstner bits that wouldn't deflect when drilling through/alongside old holes.
UFOs must be real. There's no other explanation for cats.
For the airhole mismatch, running a tapered drill bit up the Delrin tenon once it's glued ought to do the trick. Eh, it's a bent stem? Bummer.
George, you don't need all that laser alignment stuff. Here's another idea. Make a tube--aluminum, let's say, some kind of fairly round and straight stuff, with a flat bottom, maybe an inch and a half deep. Put it on a mandrel to drill a hole exactly the old tenon size exactly in the center. Make a clamping jig with a locating hole for the tube and something to exert a little force straight down -- an arbor press would work great so long as you didn't crank on it, maybe a little shot bag on the handle. Get a Brownell's Acraglas Gel glass bedding kit. Coat the stem with the epoxy release agent, clamp it in the jig inside the tube so that it is perfectly straight, the face of the stem flat against the bottom of the tube. Fill the tube with epoxy. When it cures, you can chuck the stem in a lathe, no problem. Face off the bottom of the tube and take a thou to square up the old stem, center drill and drill your hole for the new tenon, glue it in, chuck it back up, center drill and run your tapered drill on up to mesh the airholes. Cut a slit down the side of the mold and pop the epoxy off. Yep, this one is a pain in the tuckus, too, but it uses the stem face as a reference and also gives you a chance to make sure the tenon and stem face are square, at least to each other. Might the stem be a fraction of a degree off, due to the difficulty of exerting force exactly on the axis of the old tenon. Well, yeeeees. This is a setup exercise for me, I can't imagine a pipe and stem worth this much trouble in the first place, even a handcut new stem could be done in the time it would take to set up and machine the mold. But then, maybe you could find something common that would work, like half a spent shotgun shell. Chuck up, center drill and drill out the primer pocket to the tenon size, and proceed. The bottom might not be perfectly flat, but it's a thought.
George, you don't need all that laser alignment stuff. Here's another idea. Make a tube--aluminum, let's say, some kind of fairly round and straight stuff, with a flat bottom, maybe an inch and a half deep. Put it on a mandrel to drill a hole exactly the old tenon size exactly in the center. Make a clamping jig with a locating hole for the tube and something to exert a little force straight down -- an arbor press would work great so long as you didn't crank on it, maybe a little shot bag on the handle. Get a Brownell's Acraglas Gel glass bedding kit. Coat the stem with the epoxy release agent, clamp it in the jig inside the tube so that it is perfectly straight, the face of the stem flat against the bottom of the tube. Fill the tube with epoxy. When it cures, you can chuck the stem in a lathe, no problem. Face off the bottom of the tube and take a thou to square up the old stem, center drill and drill your hole for the new tenon, glue it in, chuck it back up, center drill and run your tapered drill on up to mesh the airholes. Cut a slit down the side of the mold and pop the epoxy off. Yep, this one is a pain in the tuckus, too, but it uses the stem face as a reference and also gives you a chance to make sure the tenon and stem face are square, at least to each other. Might the stem be a fraction of a degree off, due to the difficulty of exerting force exactly on the axis of the old tenon. Well, yeeeees. This is a setup exercise for me, I can't imagine a pipe and stem worth this much trouble in the first place, even a handcut new stem could be done in the time it would take to set up and machine the mold. But then, maybe you could find something common that would work, like half a spent shotgun shell. Chuck up, center drill and drill out the primer pocket to the tenon size, and proceed. The bottom might not be perfectly flat, but it's a thought.
Maybe it's not so difficult as long as the airhole remains perpendicular to the stem face at least the depth of delrin to be imbedded. I don't know the rule, but I drill 1/2 inch or a little less into the stem face. I think most airholes would be perpendicular for that length at least, but depending on how the stem is made. Cut off any bit of broken tenon as flush as possible with the stem face. With a handled hand jacobs chuck, carefully ream the airhole with a drill bit a small fraction larger than the airhole to the proper depth. The airhole should act as a guide for the drill bit, so be loose, easy, and 'use the force'. Repeat with incrementally larger bits until you get to the proper diameter for the pre-drilled delrin insert. After the epoxy dries, hand ream the airhole through the new delrin tenon just past the depth of the insert, or as suggested if there is misalignment with the existing airhole, use a tapered bit a bit further. The end result may not be perfect, but it won't take so long that you'll never do it.
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LatakiaLover
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If you use the existing hole as a guide, hole misalignment shouldn't occur. The rest of your description is spot on---pretty much the only practical way to do it, in fact. With practice and good natural feel, such hand operations can be done more accurately than adjustments can be made to a vise/drillpress setup anyway. (Even with an X-Y table, axial alignment is still a beast.)kbadkar wrote:The airhole should act as a guide for the drill bit ... if there is misalignment with the existing airhole, use a tapered bit a bit further.
The gotcha with the whole business is how rarely the air hole truly is centered relative to the outside of the old tenon, at the base of the old tenon. Sure seems like it would be, but it's usually off. I've seen no small number of pipes where it was WAY off. No mystery, the maker just used a tenon cutter without a guide pin.
I agree with pretty much everyone who has tried this ugly little business that while it is a fall-down-easy way to obtain a functional fix, it's a low-percentage way to get a collector-grade precise one. Worth trying, of course, to salvage an original stem from a true collectable, but when that isn't the case just replacing the thing is far easier.
Something not even touched on in this discussion is sizing Delrin to fit precisely in the existing mortise, too. More headaches in store there, too.
UFOs must be real. There's no other explanation for cats.
Regarding the airhole, right, the OP was asking about pipes where you spin the stem on a pin and it's out of whack.LatakiaLover wrote:kbadkar wrote:SNIP
Something not even touched on in this discussion is sizing Delrin to fit precisely in the existing mortise, too. More headaches in store there, too.
Delrin turns very nicely, the replacement tenon just needs to be made from oversize stock. Very sharp tool bit exactly on center, turn before drilling to keep as much stiffness as possible. Live center if necessary, keep close to the chuck to reduce flexing. Very light power feed helps, high rpm gives better finish. You can make the hole in the stem either larger or smaller than the tenon, doesn't matter, just turn smaller diameter first.