Any math (gear ratio) experts out there?

J

jhinze1970

H-M Supporter - Sustaining Member
H-M Platinum Supporter
Joined
May 15, 2018
Messages
15
I'd have a few atlas lathes, all with QCGB. I'd like to be able to cut a 2.4 pitch metric thread..

Anyone know of any formula's that I could use or extrapolate to figure what gear's I could replace the 40t and 48t with and then determine which lever positions to choose to come close? I'm not a math wiz... in fact I'm mathematically challenged.. but would like to learn.

Any help or pointing toward resources would be appreciated
 
2.4 mm pitch is very odd. what do you need it for? 2.5mm is very common for a thread pitch, few if any lathe will have a gear combo to make such a thread at the ready. May need to be made on a cnc.
This is from the new southbend tool room lathe.

1585600360301.png
 
What is the selection of leads of your lead screws of your lathes? Do you have the 120and 127 tooth gear combo? How close must the threads match? can you make do with 10.5 tpi ?
 
1/(2.4*0.03937) = 10.5834 tpi Here is a link for you. https://www.fastenermart.com/understanding-metric-fasteners.html

The manual for the qcgb on my craftsman 12x36 has a list of every thread that can be cut through the gear box. 10.5800 tpi is the closest. Attached is the manual which shows the gears and their positions on page 21.
 

Attachments

  • Atlas10QCgearsetups.pdf
    4.8 MB · Views: 10
Thanks Alexander and Mick(?). I think the 10.5834 might just work, it's 5/16" worth of threads, the error should be almost negligible.
 
Gear selection will vary from one lathe to another. My Grizzly G0602 can cut a 2.400mm thread exactly using a = 40t, b = 36t, and position IB on the gear box.
edit: I do by changing the 48t gear on my input shaft for the gear box with a 40 tooth gear. The input shaft is now rotating 48/40 times as fast so the setup for a 2.0mm thread will now cut 48/48x2.0 = 2.4mm/rev.
 
Last edited:
Cutting a multi-lead metric thread on an inch lathe should prove interesting. Ordinarily, I would use the thread dial to get the proper clocking but that won't be possible cutting metric threads.

A work around would be to thread a small section at the .8mm pitch and use that section to visually set up the threading tool when cutting the 2.4mm pitch. The tool would be set to the .8mm thread and one lead would be cut. Then the tool would be advanced by one thread on the .8mm section and the second lead would be cut. Then it would be repeated for the third lead.

Another way would be to use the compound and do the math. The half nuts would be engaged , the compound and cross feed would be zeroed and the first lead cut. Then the compound returned to zero and would advanced by .0315"(.8mm) if the compound was set parallel to the spindle axis or .0640" (.0315/sin(29.5º) if the compound is set to 29.5º. The compound dial would be rezeroed and the the cross feed brought to touch the major diameter and rezeroed and the second lead cut. The procedure would be repeated for the third lead.
 
If you need a refresher on cutting a multiple thread Mr Pete has an excellent set of videos on how to do it. I just watched them. Here is the first video of the series.
 
Just curious what the perspective on making a custom 3 point HSS cutter head and running it at .8 mm? Sorry if this falls in the stupid questions category. I will forgive anyone that mocks this inquiry.
 
You must log in or register to reply here.
Back
Top