Metric Threads

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pollardd

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Hello Again,
l'm still getting familiar with my new old lathe.
I have a V 42 without a quick change gear box.
( I haven't found a manual yet)

Inside the change gear cover I notice the chart that describes all the different gear combinations.
To my surprise down the bottom I see metric pitches listed.
With the lead screw being 8tpi how does any combination of gears convert this to metric?
How does the star wheel (chasing dial) work for a metric thread?
in the good old days we used to just leave the clasp nut engaged and back the machine up to make another pass when cutting threads.

Im drawing on stuff I learned 30 years ago so I could be a bit rusty :)

How does metric thread cutting work?
David
 
The threading dial will NOT work for metric. Since the lathe lead screw has inch threads, ie 8 tpi, you have to keep the half nuts closed for the whole time you are cutting metric threads. You have to manually reverse the lathe and rewind the carriage back to the start position within reason and feed the tool in and cut the next pass, repeat until done. The same applies in reverse. If one has a metric leadscrew and dial set, the half nuts are not openned until finished when making inch threads.

To get the metric threads you will note that the 52 and 44 tooth gears are used in some combination in all those setups.
Pierre
 

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pdentrem said:
The threading dial will NOT work for metric. Since the lathe lead screw has inch threads, ie 8 tpi, you have to keep the half nuts closed for the whole time you are cutting metric threads. You have to manually reverse the lathe and rewind the carriage back to the start position within reason and feed the tool in and cut the next pass, repeat until done. The same applies in reverse. If one has a metric leadscrew and dial set, the half nuts are not openned until finished when making inch threads.

To get the metric threads you will note that the 52 and 44 tooth gears are used in some combination in all those setups.
Pierre
Click to expand...
While it's true you don't want to lose the engagement on your leadscrew, you can disengage the halfnuts at the end of your cut while stopping your machine immediately after. Then back out your tool, reverse the direction and reengage the halfnuts at the same mark on your threading dial. It doesn't speed up the process any, but it does allow you to thread up to a shoulder without the concern of crashing while your machine spins down.

Chuck
 
Chuck K said:
While it's true you don't want to lose the engagement on your leadscrew, you can disengage the halfnuts at the end of your cut while stopping your machine immediately after. Then back out your tool, reverse the direction and reengage the halfnuts at the same mark on your threading dial. It doesn't speed up the process any, but it does allow you to thread up to a shoulder without the concern of crashing while your machine spins down.

Chuck
Click to expand...

I have seen that on different sites, but not had the chance to try it that way yet.
Pierre
 
I cut some metric threads for the first time last week. I disengaged the half nuts each time and then reversed the direction and reengaged the half nuts. It worked fine, but it does take a lot longer than cutting standard threads. I don't see myself cutting metric threads very often so I guess it isn't a big deal. At least I have the option to do metric when necessary.

Chuck
 
Thanks for the great response guys.
I guess that means my memory isn't to bad. :)

I just didn't know what to do without a reverse gear. I never thought to wind the machine backwards by hand.
I will only ever need to do it if I'm making a one off special for something I can't get off the shelf somewhere.
So time is not a big deal.

Stay tuned more questions to come :)

David
 
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