Metric threads on clausing 100

thanks, the plaque turned out better than I expected, I didn’t quite get the size right though, and I wasn’t computer savvy enough to design spots for the screws to go, and on top of it all I snapped a tap off in one of the existing pin holes, cause I thought it would be a good idea to use little screws instead of the drive pins, so I had to move the one hole slightly. I’ll see if I can find the file I made, maybe it will be useful to someone. I tried using one from this forum but I think it was the type of file that made it so I couldn’t use it(again, not computer savvy), but I still used it for the layout. As my plaque was completely missing when I got the lathe.
 
Downunder Bob said:
Hi, The Most accurate way to cut metric threads on an imperial lathe is to use the 127 x 120 tooth gear set. This works very well as 127 is half of 254, so 25.4 mm to the inch exactly, and you can get pretty much all the common metric threads from your norton thread box.

The 127 x 120 tooth gears will fit moist medium and larger lathes, but many smaller lathes have to use an approximation set of gears commonly 63 x 60, and there are others. While the threads produced by these approximation methods are accurate enough for short bolts and nuts, they will produce small errors that add up in longer threads. They are not suitable for making a lead screw for instance.

There are a number of charts available on the web and some here on HM that will help you. Good luck.
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Bob are you sure about the 127/120 combination? I was under the impression it was 127/100. I have a 127 tooth to fit my lathe and am looking around for a 100 tooth gear, but they are spendy. 127/100 combo is a close enough approximation to work on any imperial lead screw but the lesser tooth combinations seem to work out only for certain imperial leadscrew TPIs and are limited to the number of metric pitches they can cut. My Lathe does not have a QC gearbox, only change gears. A QC gearbox may open up more possibilities than I'm aware of.
 
GrayTech said:
Bob are you sure about the 127/120 combination? I was under the impression it was 127/100. I have a 127 tooth to fit my lathe and am looking around for a 100 tooth gear, but they are spendy. 127/100 combo is a close enough approximation to work on any imperial lead screw but the lesser tooth combinations seem to work out only for certain imperial leadscrew TPIs and are limited to the number of metric pitches they can cut. My Lathe does not have a QC gearbox, only change gears. A QC gearbox may open up more possibilities than I'm aware of.
Click to expand...

The 127 x 120 gear set is what came with my lathe, so perhaps it varies depending on other gears in teh train. If you don't have a QCGB then you will have to calculate the full gear chain for each thread pitch that you want, unless you can find a chart for your lathe.

Whatever you use it's 127 gear that does the magic for metric threads. Yes the QCGB does make it easy I can get all the standard metric threads on mine, but as I bought mine new I was able to order it for a specific purpose.
 
Hi i found a webapp to calculate the gear setup. Change the lead screw tpi and you will see what gear is used to get there.

Maybe this helps. I have a 127/100 tooth gear but it has no keyhole it is just an converter gear.

it is under the Clausing 100 thread chart.


Inch Gewinde.gif


Mini lathe change gear calculator

gearcalc.netlify.app gearcalc.netlify.app

1704012838654.png
 
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