I just bought a ~1918 Wade 8A precision toolmakers lathe, and it uses a Wade #8 collet, which is identical to a 5C collet except for a slightly longer length and a different (stronger) buttress thread. They are quite similar, but the Wade collets sell for 50+ dollars each, whereas good 5C collets can be had for just a few dollars a collet in complete sets. All I need is a new drawtube and handwheel assembly, since the lathe already has a spindle nose with the appropriate taper. Does anybody know a source for premade 5C drawtubes that can be cut down to size and fitted with a handwheel?
A longer drawtube can be adapted without cutting it with a shaft collar, roller thrust bearing and shop-made conical centering adapter.
The one I adapted measures 1.365" OD but a split 1-3/8" collar fits fine and has never slipped. The thrust bearing cost about $5. Originally it had plain brass thrust washers and worked reasonably well if I didn't take heavy cuts.
Here is another version:
If you do this to a used drawtube you can remachine either end if it wears out or breaks.
I don't have a problem with building the handwheel assembly, I just don't want to do the ID threading on the collet drawtube itself. Looks like I should be able to find a used or broken part that I can adapt.
A 6-jaw chuck will give less distortion of the drawtube during threading, and if you've got a large enough collet (unlikely, since you are trying to make a drawtube to fit collets to your lathe, and the drawtube is always larger then the maximum collet capacity. :-)
I've not cut threads in the drawtube itself, but I have cut both male and female threads in an extension to a drawtube when I went from
2-1/4x8 spindle nose to L-00 (needed about a 1" extension for that. :-)
Sounds good to me. It just so happens that there is a 8" 6-jaw chuck on the Colchester 15" lathe at work. Our tooling cabinet has a good selection of really large taps, so maybe there is a 1 1/4"-20. I believe the spec for the thread is more complicated than that (I always see it called out as some decimal diameter) but perhaps something will work. I can compare the thread to a new Hardinge collet. Thanks for the advice
The thread OD on my collets measures from 1.220 - 1.230 for Enco to ~1.243 for R-S-B. I made a collet nut for an S&D drill grinding fixture that fits closely on a 1.240 thread. Some of the R-S-B collets are too tight for it.
How would you measure an inside thread to cut it to 1.238"? Cutting out a fixed distance from the ID only works if the tip geometry is correct and your lathe isn't worn. The spreadsheet gearbox chart I made for my old South Bend gives the 29 degree infeed and tip width based on Machinery's Handbook thread data but in practice the last few thousandths are cut-and-try, mainly because I don't regrind the tip for each pitch, especially the internal threading bit. It's about right for 32TPI so it makes coarser pitches undersize if I zero the compound on the blank's surface. If I understand the book correctly, the flat should be 0.00625" wide for an internal 20TPI UN thread.
This is why I suggested using your largest collet thread as a GO gauge.
Don't confuse the thread's nominal size with its major diameter. The major diameter is generally a bit below the nominal with a pretty generous tolerance. For example, the major diameter of a 1.250-20 UN-2A is 1.2486/1.2405.
Well ... pitch diameter is what matters, and there is a way to measure pitch diameters on internal threads somewhat akin to the three-wire method for external threads.
You have a spring wound of an appropriate wire gauge for measuring the pitch involved, and wound to 20 TPI -- but a little over diameter.
You then bend the ends to form a pinch point outside the coil at one end which will cause the diameter of the coil to reduce, so you can put it in the thread to be measured.
Then, you measure the ID of the coil --- probably with something like a tri-mike or something else which can let the spring wire pass out between measuring arms.
You use the same math used with three-wire outside thread measuring to determine how small the hole should be, and from that and your actual measurements you can calculate the actual pitch diameter.
Here is where carbide insert tooling can help you. There are inserts available to cut precise form threads, as well as the more general sharp V ones. You don't have enough stress on a drawbar to need to avoid sharp V bottomed threads, so you can calculate the infeed for the sharp-V threads (straight or angled as you prefer). Note that the angled infeed should be reversed for internal threads -- that is the crank end of the compound towards the headstock instead of the tailstock, but still the 29 (or 29.5) degrees for standard US and metric threads, or half of 55 degrees for Whitworth threads. BTW -- the drawbar and collet for WW and D sized collets use a buttress thread instead of a standard V thread, so the infeed angle for those has to be separately determined.
That is good advice anyway -- that is using the largest *thread* OD, not the largest collet capacity. And if you have things like 3-jaw and 4-jaw chucks mounted on collet shanks, check those as well. My largest is a 3-jaw chuck which I got *after* I made the drawbar extension for my drawbar when converting form 2-1/4x8 threaded spindle nose to L-00 nose.