# Crashing a micrometer stop?



## graham-xrf (Nov 9, 2019)

It seems obvious to me, but I take it that "micrometer carriage stop" and "threading" are not concepts that should ever feature in the same sentence. My search does not yield anything much about power feed crashes involving hard stops.

Of course, the survival sense in the bones is yelling that, if you are threading, you pay attention, and let go with the lead screw half-nuts pretty darn smartly, or start from the left end!

So how often do we hear of a lathe driving the carriage into a micrometer stop - or for that matter, into any other part of the lathe? Has anyone ever simultaneously reworked their chuck and toolpost?

This is just background to me thinking that a limit switch arrangement might be used to stop things if the saddle gets to places it should not go. I also am imagining that a micrometer carriage stop might reasonably have a 2-stage feature which would push on some arrangement on the apron to automatically take out the power feed (stage#1) while still allowing the carriage to be manually moved a little further up to the intended mechanical stop (stage#2).

OK - so I am somewhat a beginner. Maybe the fancier lathes have something that does this?


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## Chuck K (Nov 9, 2019)

As you said, I wouldn't use a micrometer stop while threading, but I use them regularly while turning. It's really not hard to disengage the feed before crashing. After you've done it for a while you find that you're comfortable enough to almost kiss the stop before disengaging the feed.  I do use feed screw stops while threading, but I have an old Hendey that has feed screw stops.


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## GL (Nov 9, 2019)

You are correct in many places of your thread.  Carriage stops limit travel to a shoulder, manually.  Some lathes have cams that disengage travel.  Some VFD systems have a proximity switch built in to shut the lathe down at the stop and can be very accurate.  Skill can get you close, but driving into a stop should be avoided.  Some have clutches that will ratchet on normal feed, but would go out of time on a thread - but you have to set the tension on the clutch and there is a balance between carriage drive for a cut and the stop that causes damage to gears ans such.


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## ttabbal (Nov 9, 2019)

If you can thread away from the chuck, the stop is extremely useful. Makes setting up the next pass much faster.


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## mmcmdl (Nov 9, 2019)

Over time you won't need a stop . It just becomes easier with experience .


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## mksj (Nov 9, 2019)

You would not use a micrometer stop for threading, the leadscrew has no clutch mechanism so crashing it would = damage. Leadscrew has a shear pin that should break with a hard crash, but you could bend the rod, break the half nut, or other damage. Even if it had a clutch, you would loose the registration with the thread if its position changed relative to the spindle. If turning to a shoulder using the feed then some people will use the feed rod clutch to stop the carriage. Not routinely done and I recall someone discussing the forces exerted and they were high. Higher level/cost machines have disengagement stops for the carriage feed that operate within the carriage. I set the micrometer carriage stop as a hard stop more so to prevent the carriage/cutter crashing into the chuck which often results in significant damage. I also use electronic stopping which has its merits/accuracy but is more difficult to implement and is very different then a mechanical stop system.

The micrometer stop is not used as a hard stop for threading.  So plan on disengaging manually and only use the micrometer stop more as a safety device, with the exception of using the feed shaft that has a clutch, which is not the de-facto. Even in the with a feed clutch, I do not know of anybody that routinely uses it in this manner. On the higher end lathes the feed shaft clutch tension can be adjusted with a knob, and some have different forms of limit switches.


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## mikey (Nov 10, 2019)

A "micrometer stop" is actually intended as a precision end point when boring or cutting to a shoulder in a turning operation. You feed until you get close and then disengage power feed and feed manually until you gently contact the carriage stop. This gets you your precision depth. 

Stops are not really intended as a substitute for a brain. Likewise, on lathes that have clutches at the end of feed rods, they are not a substitute for proper technique; they are there in case of a crash so you don't destroy your gear train. You might destroy your chuck, tool, tool post and maybe your compound but the rest of the lathe should survive, hopefully.

The guys are right. We either learn to disengage half nuts on time when threading or we learn to thread out, away from the chuck. Limit switches are another option but with just a bit of practice you brain is actually quite good enough, I think.


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## graham-xrf (Nov 10, 2019)

My thanks to all of you. It helps a lot to get the words of experience!
mksj - thanks for the pictures.
Chuck K - I get distracted. Curious about what a Hendy looked like, I ended up reading their history, which comes with lots of links to great photographs, from 1871 through to 1950s when Hendy were taken apart by a corporate raider.

I have acqured two 9" South Bends for bargain silly ££, a 9C and a 9A, both in reasonable underlying condition.  The 9A is in a total stripped down state, the present activity being to give it the kind of cleanup and maintenance it now deserves.

I came across a YouTube video of a micrometer carriage stop being made, and also I spotted one for sale on eBay. For the present, there is much more important stuff to get right, but one day, I will likely add a micrometer stop to at least one of them.


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## eeler1 (Nov 11, 2019)

What they said.  Undercuts or threading away from the chuck work well if you can do it.

If you must, for some reason, use a carriage stop while threading, you can shut the machine off as you approach the end of the thread, then crank the spindle by hand till you get to the end, leaving the half nuts engaged.   I’ve done it this way when I couldn’t undercut the end of the thread.  Had to make a crank handle for the outbound end of the spindle.


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## graham-xrf (Nov 11, 2019)

eeler1 said:


> If you must, for some reason, use a carriage stop while threading, you can shut the machine off as you approach the end of the thread, then crank the spindle by hand till you get to the end, leaving the half nuts engaged.   I’ve done it this way when I couldn’t undercut the end of the thread.  Had to make a crank handle for the outbound end of the spindle.


eeler1: Thanks for the handy work-around. At my level of experience, I was just looking at a (micrometer stop), and my mind was playing out the scenario. I get it that it takes serious mis-attention for a crash to happen. The actual need should be minimal. Threads do not usually need to get made right up to a shoulder. There is usually at least one turn's worth of inner diameter cut before one is truly out of space, and if it needs to be accurate and repeatable, then sure, let us use a stop - and approach it manually.

I am guessing that bad stuff happening from inadvertently having the leadscrew drive the carriage into an unfortunate situation must happen sometimes, and not only into a micrometer stop - but maybe not so often!


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## Janderso (Nov 11, 2019)

I think we are all a bit respectful of the "crash" potential while threading. I know I am.
I learned by incident that I have the clutch in the apron almost exactly like the picture mksj posted.
I was threading and got to the end or under cut section and the thread or half nut lever was stuck.
The QCTP hit the chuck outside the jaws so I didn't have a bad crash. Thanks to the clutch I had very little damage.
I stepped on the brake almost immediately.
After reviewing what happened, my under cut was not adequate in size or depth.
Lesson learned.


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## mikey (Nov 11, 2019)

Graham, the single biggest aid to threading comfortably and safely is practice. Your half nuts will disengage instantly and the saddle will stop instantly the moment you move the lever, you'll see. 

Whenever possible, a thread relief that is 2-3 threads wide is recommended. The depth of this relief is about 0.005" deeper than the minimum diameter of the thread. This relief is usually more than enough to stop in time provided you are not threading at insane speeds. You will learn to pick a spot where the tip of the tool just enters the thread relief and your hand will kick the half nuts out of engagement and the saddle will stop at the instant you do. With repetition, this movement will become subconscious and you won't need to even think about it much. 

I joked a bit about using your "brain" in my previous response but it really is true. You will find that with enough practice, screw cutting on the lathe is a fun, stress-free activity. You don't need a carriage stop; you simply need to stay focused. Try not to worry too much about it - you will do just fine.


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## Chuck K (Nov 11, 2019)

The 9A is fun to cut threads on.  Here's a pic from last weekend.  I needed a bolt for the carriage lock that would hold the wrench that also fits the feed reverse.  The machine had an allen head bolt when I got it.  So I would have to look for the allen wrench as well as the wrench that fits the feed reverse. Now it will be right in front of me.  The machine didn't have a thread dial either. This one seems to work until the right one comes down the pike.  I'm no pro at threading but I have fun doing it.


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## graham-xrf (Nov 12, 2019)

Chuck K said:


> The 9A is fun to cut threads on.  Here's a pic from last weekend.


Woah Chuck.. Most excellent pictures!
I can see TWO machines in there, the one behind clearly a bigger, more beefy sort.
Great idea for the carriage lock. I can understand how easy it is to always be hunting down the right Allen wrench.
 I have sets of Allen key wrenches, one a full set in a plastic case having both metric and imperial, and a couple of those plastic storage bins where goes all others I rescue or tidy up. I attach the right size Allen key to certain tools so I don't have to go hunting for them. The circular saw has a special storage place for it's wrench, etc.

Of those that get muddled together, the attempt to separate metric from imperial did not work well. Some I have put little printed labels on, covered with transparent sticky tape (cellulose?). Others have dabs of colour coded paint, and some have colour coded heatshrink idents miss-applied from electrical cable marking kit. Since I acquired the South Bend(s), I have had to get used to 3/8" and 1/2" and 9/16" etc. all over again. Last I used those units was in a previous century - a previous millennium even! It's going to take some patient sorting and a caliper to separate the imperial Allens from the metric. They all look much the same!

I take it you also have a mill, to make the square head on your lock-bolt.


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## graham-xrf (Nov 12, 2019)

mikey said:


> Graham, the single biggest aid to threading comfortably and safely is practice. Your half nuts will disengage instantly and the saddle will stop instantly the moment you move the lever, you'll see.


 I am totally looking forward to getting to the point I can get some of the "practice" working the half-nuts lever. Right now I am up to the armpits in iron stuff part-way through adventures with paint stripper, wire brushes, and yuk little heaps of tear-off paper towels that I am sure are becoming a fire hazard! I seem to spend a large fraction of "messing with machines" time  just cleaning up after me. When I have the parts in fit condition to assemble, I will post more. I wanted to be taking photos of the stripdown detail, but one Samsung Galaxy7 nearly ended up in the dirty paraffin solvent! I need stuff like that so I know how to put it together again.


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## Chuck K (Nov 12, 2019)

I take it you also have a mill, to make the square head on your lock-bolt.
[/QUOTE]
You have to have a $5000.00 mill if you want to make a $5.00 bolt.  LOL


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## MrWhoopee (Nov 13, 2019)

mksj said:


> View attachment 305499



Hey, I recognize that apron, that's a Clausing Colchester. Did a lot of crazy high speed threading on one of those.


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