Machining Metric Threads on the South Bend lathe -- For Two Dollars??? Part One

[@NancyTrogman]

Noodled around with your spreadsheet. Great tool. I found that adding lines to calculate using 5.5 and 5.75 TPI really helped for a few of the entries. Thanks for the video and spreadsheet

[@TheBuildist]

Fantastic. I'm glad it's useful! Everyone has to"adjust"the spreadsheet for their lathe. How many teeth their factory bull gear is, and what exact TPI entries their gearbox can be set for. I don't know how many people really get the gist of this process. But at least you and I do! :-)

[@potechopz]

lol @ 02:34 Thanks for the video. I learned a lot and subscribed. I look forward to more!

[@34tab]

Thank you so much. So I cut 32 tpi on my ancient lathe- (CANADIAN MACHINERY CORP) and yes it is metric 0.8. However the stud gear on my lathe has 21 teeth. I can machine stud gears but I don't which ones I need . Can you help me ? thanks

[@TheBuildist]

Looking at the excel spreadsheet linked in the description section, I set the "factory ,stud gear" to 21 tpi, and looking in the righthand grid, the closest match to "0.8" is with a 29 tooth stud gear, and the QC gearbox set to 44 TPI. That'll produce a metric ".797186" thread, which is off by .0035% I'm presuming your QC gearbox can do a 44tpi thread, if so, you need a 29 tooth stud gear.

[@34tab]

@@TheBuildist thanks

[@johnstrange6799]

Enjoyed the video. Thanks.

[@dizzolve]

that's an interesting tool post. What is it

[@TheBuildist]

It's a Norman patent tool post. It was one of my first machining projects. The tool holders themselves are made from a scrap pieces of 1 in thick forged steel, sawed from a cap/plug for 8-in flanged pipe. This site explains the concept pretty well:. www.bazmonaut.com/machines/hobbymat-prazi-md65-lathe/norman-patent-toolpost/

[@stevecallachor]

A metric thread of 0.8 millimetre pitch is a unicorn. You can make it but you will never find it used anywhere in the S. I. Universe. Stephen

[@TheBuildist]

So there's no point in having that entry in the chart? What a shame! That's the only one that the stock stud gear can cut!

[@stevecallachor]

To cut proper metric threads you need a gear with 127 teeth and one with 100 teeth. You can reduce this to 63 teeth and 50 teeth but you lose accuracy to keep the overall gear set compact. Over 10 to 15 threads this doesn't matter but if you were to cut something like a lead screw you could be in deep merde. Stephan again.

[@TheBuildist]

@Steve Callachor You're right, of course. For something like a lead screw, this method would be a poor choice. But for the vast majority of threads, (bolts and nuts and fittings) 99.4% or higher accuracy is just fine. For instance, if you use this method to thread a 6 inch long M20x1.5 metric bolt, your total accumulated error over the course of 6 inches of threads is less than 3 thousandths of an inch. (27.5 microns per thread, about 101 threads over 6 inches) That's undetectable in use for general fasteners and fittings.

[@phineasj.whoopee3301]

M5 x .8 is standard

[@kieranh2005]

@@stevecallachor 80/63 transposing gear is the more common reduced size one, and is REALLY close. 47/37 also works for almost all applications.

[@c.j.1089]

Are you sure that's HDPE?

[@TheBuildist]

If you watch to the end of part 2, you'll know for sure. :-)