Auto disengaging the thread lever

Ken_Shea · Sep 5, 2006

Well I spent about 3 or 4 hours today attempting to fabricate some form of mechanical auto disengage for the lathe thread engage lever. Just about had it to, except I overlooked the fact that this lever needs to be suddenly disengaged.

Question, can anyone explain how this is done on lathes that are so equipped.

I am thinking either solenoid or air cyl.

Thanks
Ken

Forrest Addy · Sep 5, 2006

Use an over-center spring. Engaging the lever cocks the spring and you start threading. A stop that trips the lever causes the spring to suddenly disengage the half nut.

Procede with caution so all components work properly before you move on to cutting threads for real.

Mike C. · Sep 5, 2006

And most lathes with threading stops are true toolroom lathes with reverse to leadscrew. The stop only knocks the leadscrew into neutral, leaving the half nuts engaged. You STILL have to back the crossfeed out manually if you do not want a relief groove behind the last thread.

On a toolroom lathe, you set your stops on both ends of the thread. Fwd leadscrew and thread to the stop, back out, rev to the other stop at the start of the thread, in on the crossfeed, advance compound, and back into fwd. REAL fast threading.

matt_isserstedt · Sep 5, 2006

The Monarch 10EE has a form of this called Electric Leadscrew Reverse.

The basic gist is there are 2 stop pins (adjustable) on a 3rd rod parallel to the leadscrew and feedrod.

The spindle will stop at either one within a couple revs depending on speed, so as mentioned you can simply close the half-nuts and then zip back and forth with the compound making chasing passes, leave the cross-slide alone. The difference is that the entire machine stops and the half-nuts are still engaged.

I still like a relief groove though

Ken_Shea · Sep 5, 2006

For the most part I do see what (not how) they are doing on the originally equipped models now.

The over center spring is probably a doable option to consider although it might just be easier to get quicker on the lever.

Thanks much for the input
Ken

rke[pler · Sep 5, 2006

I worked on one that was pneumatic. Every time it hit the stop it sounded like a gunshot, scared the hell outta you the first time it went.

Matt - on the 10EE ELSR use you still have to use the cross slide threading stop, retracting the tool before reversing the spindle. What you don't have to do is to play with the halfnuts.

donie · Sep 5, 2006

Probably best to learn how to cut threads rather then rigging a gizmo to do it.
I can see no use for such a contraption.

4GSR · Sep 5, 2006

You have a use for it if you are cutting 4 pitch threads and have to pull out 3/8" from a shoulder at 200 RPM on a part around 6-1/2" diameter!!

Lehmann Lathes has been building air kickouts for their lathes since the late 50's. They even had a air cylinder hooked up the cross slide to pull the threading tool out of the cut when the half nuts disengeged! Not sure if they had a device that engage the rapid traverse to return the carriage to the start of the thread, that would be neat.

Dad built a solinoid kickout to disengage the half nuts on his 9" South Bend Lathe many years ago.

Ken_Shea · Sep 5, 2006

I well know how to thread Donie,
Ken hit the nail on the head with his statement.

This gizmo would not thread it would stop the threading

Even a 8 pitch thread up to a shoulder is a crap shoot for me.

Every time it hit the stop it sounded like a gunshot, scared the hell outta you the first time it went
Now that would be fun for those loitering onlookers

Greeno · Sep 5, 2006

What sort of lathe?
Jim

Pete28 · Sep 5, 2006

We hooked up a 2" diameter Bimba air cylinder, about 4" stroke, to the foot bar that shuts off the motor and brakes the spindle to a stop. No flow control, just wide open through a solenoid valve.....actuated by a lever arm limit switch....tripped by the advancing carriage. Darn thing stopped on a dime, repeatably. Could stop it turning, threading, any operation. Just had to be careful when going back for another cut because the tool was still in the work when the machine stopped.

MitsTech · Sep 5, 2006

That has to be very hard on all of the bushings etc. for the halfnut.

If you need to thread up to a shoulder without leaving a "ring", put the tool in upside down, set the machine spindle to reverse, start it at the shoulder, engage the half nut, turn the spindle spindle on, and crank in the compound at the same time. It will leave a small taper into the thread, but when the hell are you ever going to run a nut right into a shoulder anyway?

Ken_Shea · Sep 5, 2006

Jim (Greeno),
It is manufactured by Prince under the MSC Industrial Name, made in Taiwan. I was surprised to see they still sell them as I purchased this unit over 15 years ago, although delivered at less then 1/2 the current price.
http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1803094&PMT4NO=0

I think the solenoid may be the easiest solution, but the air cylinder setup is interesting.

Ken, As you are able to recall, did your dad's system on the SB 9" work out well ?

Ken

Ken_Shea · Sep 5, 2006

but when the hell are you ever going to run a nut right into a shoulder anyway?

I am not sure the "attitude" of that statement but presuming it is civil and not some look down your critical nose statement..... I do not have need to turn a thread up to the shoulder, what I have difficulty in doing, in a repeatable manner, is dis-engaging the thread lever at a specific point when doing TPI of 10 or less before it hits the shoulder.

MitsTech · Sep 6, 2006

Entirely civil. Nuts/threaded holes typicly have a lead in or chamfer that so the mating thread has no requirement to go exactly into the shoulder. I completly understood your question, and even offered a soloution.

mikerr · Sep 6, 2006

Ken_Shea, not sure if I have missed the plot but there is an article "An Automatic Carriage Stop for Thread Cutting" in Home Shop Machinist May/June 2005. Page 18.

Rgds

Michael

Doozer · Sep 6, 2006

The article was crap. Bad design. It slowly drags the half nuts open. Will lead to stripped half nuts. As said before, you need a cocking trigger mechanism, to assure rapid withdrawl of the half nuts or clutch. The air cylinder sounds like a good rapid disengagement way to go. Also, look at a Bridgeport cocking mechanism for a good example.
--Doozer

Greeno · Sep 6, 2006

As an add on, the air cylinder sounds the most promising and the simplest set up. It's another damn hose ti trip over, rip off or collect crud.

Inverting the tool and threading outwards is a really neat solution with no unpaid work to do. It all depends on how much critical length threading you have to do.

Regards, Jim.

Ken_Shea · Sep 6, 2006

Inverting the tool could at times be helpful, never thought of it until MitsTech mentioned it, good idea.

JST · Sep 6, 2006

Logan offered what looks like an over-center mechanism for their machines with the "automatic (full-feed) apron. I have thought about it since.

But, so far, I have been teaching myself the hand-eye co-ordination to back out the crosslide and hit the half-nuts. So far so good, leaves a nice finish.

But I would NOT like to do that under the circumstances Ken_Shea mentioned.... Thread milling anyone?

Auto disengaging the thread lever

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