Crazy Threads...

ok. so i set back up to metric to 1.5mm and tried to use the threading dial. i used #2 each pass for three passes. it cut a totally different location each pass. not just a thou or two infront of the previous, but a complete different spot....
 
I would ignore the threading dial and just not open the half nuts until the job is done. This is the way I cut metric threads on my Imperial lathe. It is a pain to stop, retract the tool, reverse the motor to reset the carriage and start again but that is the only way I can think to maintain the timing in your situation.
Pierre
 
I concur. but someone asked me to try it again, so I did.
 
Well now it seems absolutely clear that the 14 tooth gear on the thread dial should not work and actually does not work in either Imperial or metric. I'm starting to wish your lathe could talk.
 
For a 16 tooth thread dial gear, you may be able to use a gear from a different manufacturer. For an 8 tpi lead screw, the pitch diameter should be the same for any lathe. You may have to modify the bore by boring out or adding a bushing and possibly a keyway but that will be easier than cutting the gear.
 
Tozguy said:
Well now it seems absolutely clear that the 14 tooth gear on the thread dial should not work and actually does not work in either Imperial or metric. I'm starting to wish your lathe could talk.
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I'm starting to wish I saved a bit more money and bought one of the other lathes I was looking at...
 
pdentrem said:
I would ignore the threading dial and just not open the half nuts until the job is done. This is the way I cut metric threads on my Imperial lathe. It is a pain to stop, retract the tool, reverse the motor to reset the carriage and start again but that is the only way I can think to maintain the timing in your situation.
Pierre
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Hukshawn said:
I concur. but someone asked me to try it again, so I did.
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There is a way to use the threading dial. Tom Lipton from OxTool did a video on it.

It allows an Imperial threading dial to be used for cutting metric threads. Basically, you use one mark on the thread dial. You would engage the half nuts as normally done. When you reach the end of the pass, disengage the half nuts,shut the lathe off and back the tool out. Then reverse the lathe and engage the half nuts when your mark on the threading dial is aligned again. This restores the synchronization to where it was prior the disengaging the half nuts. (make sure that you catch the mark one the same revolution). When the carriage has moved to far enough to set up another pass, shut the lathe off and advance your tool for the next cut. Make sure that you moved far enough to the right to take up the lash in the gear train and lead screw.

You still have to run the lathe in reverse to set up another pass but this allows you to thread to a shoulder without worrying about the lathe coasting to a stop.
 
I'll give that a watch later tonight.
I always thread in back gears so the lathe stops pretty fast.
 
Hukshawn said:
also, i did recount all the gears in the train and compared them to the diagram, as far as the diagram is concerned, they are correct...
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I don't think you can rely on the diagram. I think you have to count teeth and do the arithmetic.
 
Metric threading dials are crazy. The 14 tooth gear that’s on the dial now is one of a set of 5 interchangeable gears that usually come with a metric threading dial. See post #100 in this thread. (no pun intended)

Tom
 
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