Understanding the screw cutting gearbox in an engineer's metal lathe

[@Hellawacked]

Great explanation

[@georgegeorgakopoulos5956]

I will try with your calculator. I want to get a first pass with 10mm or 2"-1/2tpi,and then i will advance the tool 5mm with the top slide to get the second start.

[@petermcneill80]

Hello, I’m probably basically not clever enough to be discussing this subject but I’m interested. Iv not used a boxford , my Smart + Brown model A imperial lathe has a screw cutting gear box of a similar style to the 1 shown in your video. It has A,B,C and 1-9 with a very user friendly brass chart plate marked a-c verticaly + 1-9 horizontally to give a good selection of tpi settings which iv used with good results. I’m not 100% clear how or rather when I’d use your program is it to allow me to calculate how to cut metric pitches on my imperial lathe ? Iv not got any additional gears

[@Evan-e-cent]

@@paradiselost9946 and Peter: Yes the idea of the program is to do all those calculations for you and suggest a gear train and gearbox setting that will give the thread you want. It makes life easier when you want a thread that is not on your table. That may be when you want to turn a metric thread on an imperial lathe (or an imperial thread on a metric lathe). It can also be handy if you have a non-standard set of change gears. When it comes to metric threads on your imperial lathe you can get an exact conversion with the 127/100 compound pair. The reason is that 127 x 2 =254 and the conversion factor is 25.4 mm in one inch. However, you mentioned that you do not have these special gears. In that case you may be able to get a pretty good approximation to the metric thread you want, using the gears you already have. What the program does is try every possible gear ratio, and in some cases there are millions of ways you could put them together and it really isn't practical to do it by hand. It tried out every combination, but ony displays the ones that have a small percentage error. Actually, you choose the percentage error you are willing to tolerate (eg 2%), and it only displays gear combinations that have less error. It even sorts then so the lowest errors are listed first. It can be surprising how many results it finds, especially when you have a gearbox and a reasonable number of change gears. This particular video explains a lot of stuff that you don't really need, but some people have asked for it. If you would like your Smart and Brown lathe added to RideTheGearTrain I would be happy to add it for you. I will be away for a while but should be able to get it done quite soon. I need a photo of the gear table, the pitch /TPI of the leadscrew, and the "Standard Gear Train" that is normally used with the gearbox table. Meanwhile you could try running RideTheGearTrain. Click step 10.Custom Gearbox, enter the data, and then copy and paste the URL web site address into an email and send it to me. My email address is listed on the program. I look forward to hearing from you. The Smart and BRown is a copy of the South Bend lathe like mine.

[@Evan-e-cent]

@@paradiselost9946 I didn't hear any more about your progress with the Smart and Brown Model A lathe. I would like to add it to RideTheGearTrain dot com. You can contact me using the email address on the program if you like.

[@paradiselost9946]

@@Evan-e-cent i never said i had one, i was just advising OP on how to go about figuring out their own thread conversions... sorry. wrong person... the OP does have one though?

[@georgegeorgakopoulos5956]

Hello. Is it possible to generate a 10mm or a 2-1/2tpi on a boxford A with 8tpi leadscrew? I want to rescue a friend's bench vice with a worn out nut. This nut has trapezoidal double start thread,Φ26*5mm,or,1"-5tpi. Thank you in advance,very nice videos.

[@Evan-e-cent]

Yes, this is exactly what my online computer program, RideTheGearTrain dot com, is designed to do. The program knows the gear ratios of the gearbox in the Boxford A lathe. When choosing a lathe gearbox scroll down to find imperial Norton. Just follow the instructions and email me if you have any difficulty. I don't know exactly how you measured 2.5 TPI. Cutting a multistart thread is a special case. If you measure the distance between one thread and the next and decide it is 2.5 TPI (apparent pitch = 1/2.5 = 0.4 inches) then you would cut the thread with double that pitch (0.4 x 2 = 0.8 inch pitch or 1.25 TPI. Whether you can produce the required pitch will depend on what change gears you have for the gear train. With this program you enter the gears you own and it calculates what gear train to use. If you need to obtain an extra gear, you can enter it into the list to try it out. Calculating metric threads is quite simple with the program too, but you must not disengage the half nuts from the leadscrew between cuts. Instead run the motor backwards, or turn it backwards by hand. There are more details in th program's help file and there is a help button in the main menu.

[@Evan-e-cent]

RideTheGearTrain now displays the maximum and minimum pitch possible with your set of gears. An information box called MAXIMUM AND MINIMUM VALUES appears after the results.

[@roccowyatt7237]

Promo'SM