Of change gears and QC gearboxes

Virtually every modern lathe above 7 inches swing has a quick change gearbox. When trying to get a pitch not listed on the feed/threading
chart the options are limited compared a lathe equipped with a full set of change gears. Since I have the CNC option odd thread leads are easy to do. But there are many times that I have a setup in the CNC that I don't want to disturb so a one off part then has to wait a while. I am considering putting CNC on a manual lathe and just switching between manual and CNC. But I'd also like to know what others do when faced with the odd lead, QC gearbox problem. Cheers, Eric
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snip

I have a random assortment of change gears (some home made) for my Logan.
I can swap these out in the gear train that feeds the QC gearbox and change the gearbox's ratios.
I usually just swap the gear on the gearbox (usually 48) with the new gear. If I put a 54 tooth gear there and set the levers for 24tpi (1/2 of 48) it cuts a thread of 27tpi (1/2 of 54).
Paul K. Dickman
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snipped-for-privacy@whidbey.com wrote:

You mean I can feel smug that my Smithy is a piece of crap?
I just made a chart with all possible combinations of the (manual) change gears supplied with the thing. There's something like 80000 different combinations, many of which are redundant, many of which are extremely oddball, but many of which are rational, commonly used threads (like 40TPI, which was my immediate need, and 56TPI, ala 2-56).
I gotta find a way to sort the list now, to pick out the useful inch and metric threads, the 'best choice' of the redundant ones, and to depreciate the oddball ones.
--

Tim Wescott
Wescott Design Services
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Redundant ones are for broken tooth in 'that wheel' - use redundant ratio.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
Tim Wescott wrote:

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Download Marv Klotz's program change.exe and edit the config file for the gears that you have:-
http://www.myvirtualnetwork.com/mklotz/files/change.zip
As to the OP. Manual lathes should have a banjo at the end even if they've got a QC gearbox. Both of mine do and it has proved useful for threads that the designers weren't aware of/bothered with.
Mark Rand RTFM
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Thanks to those who replied to my QC gearbox post. It seems to me that I'm going to have to figure out which gears I'll need that will work with the gearing in the quick change system. Then modify the banjo to accept the new gearing. Even though I have the CNC lathe it will be easier a lot of the time for one off parts to just use custom gearing solutions. Even though it means some time spent up front making the lathe able to accept the non-standard gears. Cheers, Eric
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