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+--- Thread: [HELP] Can someone help me to re-gear my lathe? (/thread-4542.html)
Can someone help me to re-gear my lathe? - Dan Boy - 10-01-2023
Hi everyone, I have an old edgwick and theres a lot to love about it. I run my own business and I use this lathe so much for making or modifying motorcycle parts.
There is only one thing I would change and thats the speed of the lead screw. Even when I have it on its slowest setting, its still too fast.
I need help to do this because my knowledge of gears is a little sketchy. Now the idler gear and the driven gear are the same size and the driver gear is real small be comparison.
These are the dimensions as I measure them:-
Driver - 50.6mm OD x 22T
Idler - 143.8 OD x 66T
Driven - 143.8 x 66T
I do totally understand that I will not buy a gear conversion kit for this lathe and I "think" I will need to move the pivot point of the idler gear, which is fine.
I'm not really understanding what "type / size" of gears I have here so I can seek out or have replacements made. Everything will be imperial and that kind of adds another level of complexity for me!
I would really appreciate some help from whoever would like to dig into this conversion.
Thanks, Dan.
RE: Can someone help me to re-gear my lathe? - Highpower - 10-02-2023
Go smaller on the driver gear and/or go larger on the driven gear. A single idler gear only reverses the direction of the driven gear and it will not change the final ratio. Two idler gears of different sizes will change the final ratio but two idlers of the same size will not.
RE: Can someone help me to re-gear my lathe? - Dan Boy - 10-02-2023
Hey Willie, thanks for you informative answer.
RE: Can someone help me to re-gear my lathe? - Pete O - 10-02-2023
Here's a gear pitch calculator that will help you determine what DP your gears are https://evolventdesign.com/pages/blank-calc you'll need to work backwards with that one i.e. guess what your DP probably is (I'd start with 12 just from the photo) and see if the resulting diameter matches the diameter of your gear. Then you can search for a suitable gear or someone to make one (or make them yourself, after all that's one of the 'F' bits in MWFF).
If I may be so brave as to disagree with Willie, on a simple gear train it doesn't matter how many idlers there are- one tooth moves one tooth all the way through the gear train so a 10-tooth drive gear will drive a 100-tooth driven gear at a 1:10 ratio no matter how many idlers are used to take up the distance between them, odd numbers of idlers reverse the rotation and even numbers correct it. (When I was 15 I had an exam question that showed a gear train with about 5 idlers, gave the input RPM and asked the final RPM, I spent ages figuring out every ratio across the train to come up with the final RPM- which was the same as the input RPM with the same gear size! Live and learn.) Different with compound gears like the drive gear at the top of your photo, two gears of different sizes on the same spindle alters the RPM.
Edit: re-read your post and saw the dimensions; your gears are indeed 12DP. Pressure angle is the other parameter but I've been informed (rightly or wrongly?) it is not critical to match it in something as simple as a manual lathe change gear train. To reduce your driven speed, you need a larger driven gear by a factor of whatever speed reduction you want, and an idler of suitable diameter to take up the space between driver and driven.
RE: Can someone help me to re-gear my lathe? - Highpower - 10-02-2023
(10-02-2023, 05:56 PM)Pete O Wrote: If I may be so brave as to disagree with Willie, on a simple gear train it doesn't matter how many idlers there are- one tooth moves one tooth all the way through the gear train so a 10-tooth drive gear will drive a 100-tooth driven gear at a 1:10 ratio no matter how many idlers are used to take up the distance between them, odd numbers of idlers reverse the rotation and even numbers correct it. (When I was 15 I had an exam question that showed a gear train with about 5 idlers, gave the input RPM and asked the final RPM, I spent ages figuring out every ratio across the train to come up with the final RPM- which was the same as the input RPM with the same gear size! Live and learn.) Different with compound gears like the drive gear at the top of your photo, two gears of different sizes on the same spindle alters the RPM.
Right you are Pete. When I see at a change gear set on a lathe I'm already thinking compound gear sets. But then again what's in my head and what comes out of my keyboard doesn't always line up anyway. Good catch. Off to find my dunce hat now...
RE: Can someone help me to re-gear my lathe? - Pete O - 10-03-2023
(10-02-2023, 07:50 PM)Highpower Wrote:
Right you are Pete. When I see at a change gear set on a lathe I'm already thinking compound gear sets. But then again what's in my head and what comes out of my keyboard doesn't always line up anyway. Good catch. Off to find my dunce hat now...
Yeah apologies, first time I've stuck my head in in months and I'm correcting someone.
RE: Can someone help me to re-gear my lathe? - Highpower - 10-03-2023
Nothing to apologize for. I'm glad to see someone posting actually! It's been terribly quiet around here for awhile now.
RE: Can someone help me to re-gear my lathe? - Dan Boy - 10-03-2023
Wow Pete, a very interesting answer and you calculated the DP for me!
OK, so here's the plan. I'll look for a larger gear to replace the driven gear, then I need to find a suitable idler and move its spindle on the arm to suit.
Because I run the lead screw on the slowest setting currently, I have plenty of options to go faster. I think I would like to slow it down by at least half the speed and if that does turn out to be too slow I can just up the speed in the gearbox.
RE: Can someone help me to re-gear my lathe? - Dan Boy - 10-04-2023
So I'm looking at gears and I'm just a little confused how to work out the length / size of the gear train. I know I have a fixed point on the driver gear and a fixed point on the driven gear. I'm happy to relocate the idler gear.
Is there a method of calculation, because I am aware that the gears will mesh together, so that I can come up with three diameters of gears that will match the current length of the train?
RE: Can someone help me to re-gear my lathe? - Dan Boy - 10-04-2023
OK, I think I'm getting somewhere. I drew this up in CAD. I need to measure the one dimension at the bottom and then I can really start to work stuff out. The circles are set to the pitch diameter. I got that information from this website.
https://evolventdesign.com/pages/blank-calc#:~:text=How%20to%20Calculate%20Pitch%20Diameter,diameter%20will%20be%20in%20inches.
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