OldTools Archive
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262363 | Erik Levin | 2017‑05‑26 | Yankee brace 2101a pad thread |
A question for which I have been unable to find an answer in the archive (though I limited myself to 3 hours...): What is the nominal thread for attachment of the pad? I have a couple examples that all are in the ballpark of 0.810"-12, or 0.810"-11-1/2, or.... The less than three complete threads do not give a good measure, and the originals that I have are rough enough that all measure between 11-1/2 and 12 pitch using traveling microscope and parallel wires. My objective is to make a proper tap, since I have two Stanley era with barf- smelling plastic pads in need of replacement, and I have a threading demo to do with some students. But, as the replacement pads will be in wood, being off will lead to eventual failure, even with only 2-1/2 threads engaged. *** This message was sent from a convenience email service, and the reply address(es) may not match the originating address |
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262364 | george@g... | 2017‑05‑26 | Re: Yankee brace 2101a pad thread |
Erik Levin asked: > A question ...): > What is the nominal thread for attachment of the pad? I have a couple > examples that all are in the ballpark of 0.810"-12, or 0.810"-11-1/2, > or.... The less than three complete threads do not give a good measure, > and the originals that I have are rough enough that all measure between > 11-1/2 and 12 pitch using traveling microscope and parallel wires. > My objective is to make ... replacement pads will be in wood, being off > will lead to eventual failure, even with only 2-1/2 threads engaged. There is one ideal way of doing this, and that is to make a plaster cast of the male threads on the remaining (?) quill (s) and then to find a Wade Bench Profiling Machine: >> http://www.lathes.co.uk/wade-bench-profiler/img0.jpg I have the all-apart original made by the American Watch Tool Company which I got from Phil Lathrop many years ago, and for which I now have an incentive to get it up and running. There is one severely bent lever which I can replicate, rather than try to straighten, which is doomed to failure unless I first make a replacement. Not any time soon, though. The bench profiler works with a stylus or follower that is kept against a model part by said lever, which controls the travels of a cutter in the main spindle with a one-to-one lever arrangement. Alas, it does not do mirror images ... hence the need for a plaster cast. The cutter and follower each need a vee shape just like the thread profile, which ought to be easy to find or make. The bench profiler was mainly used to make a great many copies of the frames of pocket watches, and one could shape the basic profile as well as spot all the holes to be later drilled & tapped, for screws or jewels. One might cobble together a wooden model of such a machine with a high speed grinder as the prime mover ... or build an auxiliary spindle for a lathe driven one-to-one by equal size pulleys and a Vee belt, and then use a follower coupled stiffly to said high speed grinder. The follower will be pressed against the front side of the quill's male thread, while the cutter will bear against the rear side of the female thread-in-waiting, using the cross-feed slide (without any feed screw) to serve as the rigid coupler. The lathe must turn very slowly while the operator's left hand traverses the carriage and the right hand keeps the follower in contact with the male thread. For a right hand thread with the spindles turning counterclockwise, both threads travel right-to-left, but it's the front side of the male thread and the rear side of the female thread. However, the opposite sides of both move the same way ... so the threads will have the same hand. Whew. George Langford, cutting & running in SE PA |
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262365 | Kirk Eppler <eppler.kirk@g...> | 2017‑05‑26 | Re: Yankee brace 2101a pad thread |
On Fri, May 26, 2017 at 2:08 PM, |
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262366 | Erik Levin | 2017‑05‑26 | Re: Yankee brace 2101a pad thread |
George replied: >There is one ideal way of doing this, and that is to make a plaster >cast of the male threads on the remaining (?) quill (s) and then to find >a Wade Bench Profiling Machine: As much as I would love another machine, I do not see a profile machine on my horizon. If all else fails, I may use this as an opportunity to make a thread tracer for the small lathe. Part of the difficulty is that the flank angle isn't the same to either side, being about 50 degrees on one side and about 55 on the other, for an included angle of about 75 degrees (again, not consistent from point to point. Come on, Stanley. It is steel, not chewing gum). Given that the design is post turn of the 20th century, I would guess that it is some reasonable nominal pitch, even if it isn't a standard machine thread. It just comes in at less than 12TPI and greater than 11-1/2TPI on both braces, any position I measure, any method (thread gauge, traveling microscope, over parallel wires, direct scale). I even pulled out the oddball scales for comparison (true point and pica rule among them. No clear match. I no longer have access to a CMM (really? who besides me would think of using a CMM for this?) though that would be the cats meow for this. Oh well. Given the short timeframe I have if I want to make my demo useful, I may just go with 12TPI and see how the pads hold up, but I would really like to make the tool so it is useful to others, as I am likely to have a lifetime need of two brace pads. *** This message was sent from a convenience email service, and the reply address(es) may not match the originating address |
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262368 | Erik Levin | 2017‑05‑26 | Re: Yankee brace 2101a pad thread |
Kirk opined: >Do the threads really have to be "that" precise? Seems to me that most of >the braces I have taken apart have had smaller screws holding the main >screw in place (stop the turning of the pad). 11-1/2 vs 12 should be a >trivial difference. I tend to get fixated on details like this. Probably the threads don't need to be that precise (wood moves, after all) but an accurate nominal minimizes the chance of misfit or failure given the variation in the parts I have in hand and other parts that may be seen in the future. >How about filing a sharp edge on the leading edge of your screw, and just >work it back and forth into an appropriately sized hole in the new pad. That may be the final endpoint. I am still looking at this project for use in my threading demo. As to the lumberyard, I have the wood on hand. A really nice chunk of curley maple from a tree i helped a friend take down several years ago. Truely lovely. *** This message was sent from a convenience email service, and the reply address(es) may not match the originating address |
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262385 | Erik Levin | 2017‑06‑02 | Re: Yankee brace 2101a pad thread |
Well, after a bit of digging, thinking, measuring, and comparing, I came to the conclusion that the thread on this brace is just plain odd. I tried fitting a hole tapped with a 13/16-12 tap (60 deg thread, 0.812 dia) and no go, and it appeared to be the pitch rather than the thread included angle, but I am not sure. Tried another Stanley pad with the same two screw setup and the threads were close but no match. Still seem to be between 11-1/2 and 12TPI. So, I made the new pad, bored the center to 0.795-ish, let the thread smoosh itself in very lightly, and the two wood screws do the primary holding. If I get the incentive, I may burn a few electrons on the CNC machine and make up test pieces at 11-1/2, 11-3/4, and 12TPI to see what the best fit is, but first, I need to make (or, perish the thought, buy) a thread milling tool suitable for the thread pitch... Looks and feels great. I love maple. *** This message was sent from a convenience email service, and the reply address(es) may not match the originating address |
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