Input a setup for about 150TPI thread on the calculator and experiment from there

Autofeed can give you a good finish

It's also great for roughing down if you have a leadscrew clutch, takes a lot of the drudgery out of the drudgery bits

Hi there, David,

Regarding your lead-screw and auto feed, lubrication is your friend. Also, make sure your lead-screw is rust-free – rust is abrasive.

Regarding the auto feed, the precise value of the pitch is irrelevant, it just needs to be fine. Lay out all your change wheels on the bench in order of size, smallest on the left and largest on the right. Fit the largest on the lead-screw and fit the smallest on the intermediate stud. Fit the next largest on the intermediate stud keyed to the small one already there. Fit the next smallest on the tumbler, fit spacers where necessary and adjust stud and banjo until all the gears mesh. (feed a strip of paper between each pair of meshing gears while tightening the stud and then remove the paper.) If the combination you've chosen won't mesh, swap gears until you get a combination that does. For fine feed, you want small drivers and large drivens.

Check for free rotation, switch on and assess the feed-rate. If it's so slow you fear you'll die of boredom, swap gears to reduce the ratio of the meshing pairs and re-adjust the banjo and studs to restore correct mesh and test again.

It's quite easy to proceed by trial and error until you get a set-up that's OK for the job in hand but do be prepared to get your fingers greasy. (I lubricate my change wheels with spray-on chain oil.)

Best regards,

Swarf, Mostly!