Sick Of Lathe Change Gears, Made A Quick Cange Gear Box

I did shoot a few quick videos of the gearbox whon I got it running.
It's potato quality, but it is by request..
It moved surprisingly quick at the coarsest setting, 2mm/rpm. Bit of a quiet panic there for a while.
Next I tried the very slowest setting.
And an in-between-one.

So, it actually works.. There is a bit of tweaking left to do. The mount isn't at all rigid yet and there's a few things to do on the gearbox itself, like drilling and tapping holes for a gear cover on the left side (wich will incidentally keep the tumbler bearing and idler shaft from wriggling out).
Then there's of course paint and labeling the positions of the tumblers, and printing out a sheet of combinations for various threads and feeds.
I had to modify the locating pins in the tumblers as well as the holes they went into. In my first attempt I used a centerdrill for the holes and had cut a 60 degree taper on the point of the pin, thinking that this would be plenty strong enough to hold the gears in mesh. They of course came right out as soon as any load was present so I drill the holes out straight through and turned the points into pegs instead. Much better.
 
I'm adding the calculations I've made for the various thread possibilities. It's three sets based on a 25, 35 and 50 teeth gear driving a 127 for metric or 100 for imperial. Leadscrew is 4tpi.
I think I've got pretty much all threads covered.

I'm going to think about how to replace the banjo with a quick change setup as well, but I don't think I'll be changing gears that much anymore. The 35 is pretty much only needed for 1,75mm and 0,7mm.
50 will be noisier but cover coarser threads.

Edit:
I missed the 30 tooth. Thats needed as well.
 

Attachments

  • gearcalclathe25.pdf
    20.1 KB · Views: 18
  • gearcalclathe35.pdf
    20.3 KB · Views: 8
  • gearcalclathe50.pdf
    20.1 KB · Views: 7
  • gearcalclathe30.pdf
    20.8 KB · Views: 9
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That is quite an accomplishment! Very well done!
 
That is so cool that you did that from scratch!


Steve Shannon, P.E.
 
Thanks for the praise guys! It's finally in place, but It took me literally a week of patient tinkering to get it fitted properly to the lathe. I had to make a new bearing block for the leadscrew tailstock end with a ball bearing and a thrust bearing just to be able to repeatably shim and align it. I also had to take the apron off and shim the cast part that holds the keyed gear that rides along and transmits power to the crosslide feed since that was crooked and caused lots of binding. Once that was sorted it was a never ending job of measuring, adjusting and sighting to get it all lined up, but now it feels great.
It has surprisingly little backlash, and I've now used it to cut the first thread, a rather unexciting M30*1 for a boring head I'm working on for the mill.
Lubed up with chainsaw oil and with the cover on it's actually kind of quiet now. The reverse gears in the headstock makes most of the noise now.
 
That is a thing of beauty. You have done some really nice detailing on it and the function seems like it will work perfectly. Very impressed!
 
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