Does anyone have a suggestion for a supplier where I may get a 45 tooth change-wheel for my Mitchell lathe. I have measured my other change-wheels and they are all 11DP with a pressure angle of 14.5 degrees, 1 inch wide with a 1 inch diameter bore and 0.25 x 0.125 keyway.
The standard suppliers I have tried only seem to offer 20 degree PA and even sized DP's.
I am not too fussed about the bore and width as I can modify the bore and would probably get away with a narrower gear wheel.
Boston Gear do 14.5 degree gears, but they don't list 11DP - only 10 and 12 - I haven't come across an odd size before. Although they are States based they have UK distributors. I recall this came up in an earlier thread which you'll probably find by searching the newsgroup, but all their stuff is listed via their website. Are you sure these are
11DP ? Whenever I measure gears I end up with some strange inbetween number. I think generally you round up. Maybe you can offer up your gears against a known 10 or 12DP at one of the Boston Gear distributors if there is any doubt.
I was thinking the same thing about 11DP. Can you post a few OD's and tooth numbers so we can check. They might even be that so they were a proprietary part, at 1" wide they must be a decent sized gear. I have a drawer full of older change wheels, many off dividing head trains and one of these may do if we can determine sizes.
I've got 11dp cutters, nos 2 & 3 in 14.5 deg, if you're really stuck I could make you a gear or maybe make some arrangement for you to borrow (hire ) the cutter.
Cheers
Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Thanks for all your suggestions, I have measured the diameter of the change wheels that came with the lathe, they are however an incomplete set when compared to the threading charts attached to the lathe gearbox.
The diameter of the 57t and 63t may be a little bit out as there are no teeth directly opposite each other (so a best guess).
I would be grateful if someone could check my calcs that they are 11DP.
Measuring the pressure angle I found difficult, I took one of the larger wheels and with a straight edge projected as best I could the angle of one tooth to the opposite side of the gear, then measured the angle between the projected line and a diameter taken from the root of the same tooth, I got something like 13 or 14 degrees so assume it is a standard 14.5 degree, it seemed well off 20 degrees so unlikely to be that.
Incidentally, I need a 45t gear wheel in order to cut 1.5mm pitch threads, the lathe setup suggested uses the 20tpi gearbox setting modified with a compound gear train of 45/60 and 63/40. The leadscrew is 0.25 inch pitch. Any help you can offer much appreciated.
The only suggestion I have that won't cost lots of money is Ivan Law's gear cutting book and the manufacture of some gear cutters. This is what I may well be doing for the 22DP stub form gears for My Hardinge project. Of course, John may come up with something from his box of bits!
Thank you for the offer of cutter hire or making a 45t gear for me. Can I put this on hold for a bit as Russell has come up with a cunning alternative, using a 60/80 gear setup rather than 45/60. I will check to see if these sizes will go onto the quadrant of my lathe first as I already have an 80t gear. Will report back if I may on results obtained.
The suggestion by Russell to use a 60/80 tooth gear pair rather than follow the thread chart suggestion of 45/60 has worked a treat - a bit of a tight squeeze to get the 80t on the idler pin and avoid hitting things it shouldn't, but all is well.
Many thanks to all for their suggestions and offers of help.
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