# Will I lose my screwed on chuck if I convert my lathe motor to reverse?



## Dranreb (Feb 12, 2013)

I see a lot of Atlas lathes with drum switches fitted, I would like to hear of users experiences whilst using them in reverse.

Is it worth the bother to fit one?

Bernard


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## swatson144 (Feb 12, 2013)

My lathes reverse (both with screw on chucks). I never use the feature except perhaps when threading metric.

Steve


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## pdentrem (Feb 12, 2013)

I never had it happen on my Atlas, but usually I was threading and therefore slow speeds.
Pierre


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## Dranreb (Feb 12, 2013)

pdentrem said:


> I never had it happen on my Atlas, but usually I was threading and therefore slow speeds.
> Pierre





swatson144 said:


> My lathes reverse (both with screw on chucks). I never use the feature except perhaps when threading metric.
> 
> Steve



Yes, I am thinking my only use would for be metric threading, I suppose it would be safe using collets (which I don't have) so most likely too much bother, as I have a crank that I put on the lead screw if I need to thread metric.

Replies appreciated

Bernard


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## wa5cab (Feb 12, 2013)

My machine also reverses but I don't think that I would use it with a part held in a chuck except maybe to back out a tap or back off a die.  

But just out of curiosity because two have mentioned it, why would you use reverse if threading metric?

Robert D


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## kd4gij (Feb 12, 2013)

When metric threading with a sae lead screw the threads won't match the marks on the thread dial. so you can't dissingage the half nuts while cutting the threads.


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## wa5cab (Feb 12, 2013)

Oh, that's right.  I had forgotten about that.

R


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## VSAncona (Feb 12, 2013)

kd4gij said:


> When metric threading with a sae lead screw the threads won't match the marks on the thread dial. so you can't dissingage the half nuts while cutting the threads.



Sorry if this is a dumb question, but why can't you just back the tool bit out and reverse the lead screw direction without disengaging the half nuts?


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## pdentrem (Feb 12, 2013)

The reason is a metric lathe has a metric leadscrew and the threading dial may have 10 positions, while. SAE lathe has a SAE leadscrew and the dial has 4 or 8 positions. The leadscrew on the SAE will never line back up to the original start position due to the ratios do not match.

So the other way to look at it, is the metric lathe cutting SAE threads, you can not disengage the half nuts neither.
Pierre 

I will try to finish a better explanation for this.


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## wa5cab (Feb 12, 2013)

Disengaging the tumbler gears does essentially the same thing as disengaging the halfnuts.  You lose the locked angular relation between the lead screw and the spindle.  Plus if you don't disengage the half nuts, the only way to move the carriage is to turn the lead screw anyway.  Which is what the motor running in reverse does.

Robert D.



VSAncona said:


> Sorry if this is a dumb question, but why can't you just back the tool bit out and reverse the lead screw direction without disengaging the half nuts?


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## pdentrem (Feb 12, 2013)

I found many references to metric vs SAE threads. Using google books I did a search for "Chasing metric threads with inch thread lead screws", there is an article by one of the trade magazines. I got a lot of hits.

Moving a bit away from the original question but related to the threading and half nuts discussion. One should also look at dog clutch. Gadgetbuilder's mini lathe website has a page on this topic and a more recent article on modelengineeringwebsite.com has a build for the common Grizzly and others Asian lathe products.
Pierre


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## Dranreb (Feb 13, 2013)

Dranreb said:


> Yes, I am thinking my only use would for be metric threading, I suppose it would be safe using collets (which I don't have) so most likely too much bother, as I have a crank that I put on the lead screw if I need to thread metric.



The more experienced ones amongst you may have noticed the onset of brain fade in the last bit of my post....:nuts:     

I made that crank for my first Atlas so I could traverse the carriage when the rack gear case was broken, of course it would not work for metric threading (which I haven't tried yet) the crank would have to be on the back of the spindle!

sorry if this caused any confusion...

Bernard


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## jedel (Feb 14, 2013)

I have a three phase motor on my lathe which works fine for a break,I always jam the chuck while screwing it on and have had no loosening problems. Just saying!


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## wa5cab (Feb 14, 2013)

Jedel,

I always snap my chucks the last quarter to eighth of a turn while tightening.  And have a heavy duty 3/4 HP motor on the machine (instant start for sure).  I've never had a chuck come loose when reversing.  However, I still wouldn't risk cutting in reverse.  

Robert D.


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## kd4gij (Feb 14, 2013)

I do run by lathe in reverse when boring to a shoulder.:yikes: Just take lighter cuts and be carfull. Never had the chuck come lose. I do have my back plate drilled for a spanner wrench so it is on tight.


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## rdhem2 (Aug 19, 2014)

_*NO         *_Old wives looking for a tail to chase!!!!!!!!!!!!!!!   Do it all the time with my Logan.


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