# Lathe Threading Auto Stop



## Jamespvill

Hello Gentlemen! 

I've got a project coming up soon that is going to require a few hundred internal threads done that are fairly long. I'm not the biggest fan of rushing to disengage the halfnut milliseconds before it goes crashing into a shoulder at high speeds. And this is even worse with internal threads as and lathe owner knows. So here is my solution! A simple automated carriage stop.

[video=youtube;-Riiep0c64o]https://www.youtube.com/watch?v=-Riiep0c64o[/video]

If there is any interest I can post a full write up on the "build". It's essentially just a simply trigger, Luckily I know my guns! )

Anywho...Enjoy!


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## hman

Jamespvill said:


> If there is any interest I can post a full write up on the "build". It's essentially just a simply trigger, Luckily I know my guns! )




You betcha!

And thanks for what you've already demonstrated in the video!


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## tertiaryjim

Great idea! 
Very nicely built. 
Enjoyed the video. Even watched it twice.
Thanks for sharing.

Now some one will want to know if it's negative, positive, or neutral.


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## RandyM

Yeah, no holding back now. We need all the details.


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## Fabrickator

That's great.  The other day I was doing some internal boring and thought about setting up a shut down switch like on my power table feed on the mill.


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## Kevinb71

Nice Idea! Let's see/hear some more details.


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## 12bolts

Nice work and nice and simple to boot!
Do you have the free end of the fixed pushrod supported at all, its a bit difficult to tell behind the crossfeed handle?

cheers Phil


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## JXg76

That's a great idea, nice setup


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## Jamespvill

12bolts said:


> Nice work and nice and simple to boot!
> Do you have the free end of the fixed pushrod supported at all, its a bit difficult to tell behind the crossfeed handle?
> 
> cheers Phil



Hey Phil,

There is no additional support for the pushrod besides where it it attached to the ways. I would imagine that adding some more support for it would increase the accuracy of where it stops. The pushrod itself it 3/8" so it's fairly rigid.


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## Jamespvill

Hello Gentlemen! 

After punching out a few dozen threads today, I'm happily surprised at how well this carriage stop works. I'll gladly post a few more details and information about the mechanism. 

First a more close-up video of the mechanism (is that the right term?) itself:

[video=youtube;rY6YHA4upRU]https://www.youtube.com/watch?v=rY6YHA4upRU[/video]

Here are a few stills of it engaged and disengaged.





The toughest part of making this is retrofitting it to your lathe and finding clearance for it, but after you lay everything out, it smooth sailing.

First and most importantly is to find where your pivot pin will go, this should be a place where the pushrod can get the most leverage. So halfway is just about perfect, but your lathe will determine this more. 

Next you need to build a "trigger" this is the item that pivots on the pivot pin and is pushed by the pushrod (finger). After that is on then it's time to find the best location and orientation for the "sear" or the piece that it attached to the half nut lever. From there is simply fitting and filing to see where everything latches together properly but also disengages smoothly. 

I used drill rod for the pin on the "trigger" and O1 tool steel for the "sear" both of which were heat treated and polished on the contacting surfaces. 

After that then it's time for springs! One on the rear of the "trigger" to keep it always trying to engage and one on the half nut lever to keep it always wanting to disengage. I'm not too fond of the current spring setup for the lever, it looks a little goofy for my liking. 



Finally it's time to build your pushrod or "finger" and means of attaching it to your lathe. I chose to attach it to my ways. If I would have had wider aluminum bar then I would have opted for that, but I only had 1/2" so I went with that. 





I'm probably going to add a threaded rod through the aluminum block so I can stabilize it against the gearbox behind it in an attempt to diminish all of the flex. The rod is a 3/8" piece that I'm probably also going to add some sort of stabilizing function to towards the end of it. 

Besides that, It should be apparent in the original video that it stops in just about the same place each time, which is really all I can ask for!

Thanks for your interest gentlemen, I would like to hear what you would have done differently!


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## zmotorsports

Nice.  Very innovative.

Mike.


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## Hawkeye

Thanks for sharing that. I had to run down to the shop to see what I'd have to do to add it. A bit different on my Storebro, since it has the mirror-image layout (half-nuts on the left).

Would a tension spring in the top half of the trigger work to replace the compression spring at the bottom?


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## Jim Petridis

Jamespvill said:


> Hello Gentlemen!
> 
> After punching out a few dozen threads today, I'm happily surprised at how well this carriage stop works. I'll gladly post a few more details and information about the mechanism.
> 
> First a more close-up video of the mechanism (is that the right term?) itself:
> 
> [video=youtube;rY6YHA4upRU]https://www.youtube.com/watch?v=rY6YHA4upRU[/video]
> 
> Here are a few stills of it engaged and disengaged.
> 
> View attachment 81874
> View attachment 81873
> 
> 
> The toughest part of making this is retrofitting it to your lathe and finding clearance for it, but after you lay everything out, it smooth sailing.
> 
> First and most importantly is to find where your pivot pin will go, this should be a place where the pushrod can get the most leverage. So halfway is just about perfect, but your lathe will determine this more.
> 
> Next you need to build a "trigger" this is the item that pivots on the pivot pin and is pushed by the pushrod (finger). After that is on then it's time to find the best location and orientation for the "sear" or the piece that it attached to the half nut lever. From there is simply fitting and filing to see where everything latches together properly but also disengages smoothly.
> 
> I used drill rod for the pin on the "trigger" and O1 tool steel for the "sear" both of which were heat treated and polished on the contacting surfaces.
> 
> After that then it's time for springs! One on the rear of the "trigger" to keep it always trying to engage and on on the half nut lever to keep it always wanting to disengage. I'm not too fond of the current spring setup for the lever, it looks a little goofy for my liking.
> View attachment 81877
> 
> 
> Finally it's time to build your pushrod or "finger" and means of attaching it to your lathe. I chose to attach it to my ways. If I would have had wider aluminum bar then I would have opted for that, but I only had 1/2" so I went with that.
> 
> View attachment 81875
> View attachment 81876
> 
> 
> I'm probably going to add a threaded rod through the aluminum block so I can stabilize it against the gearbox behind it in an attempt to diminish all of the flex. The rod is a 3/8" piece that I'm probably also going to add some sort of stabilizing function to towards the end of it.
> 
> Besides that, It should be apparent in the original video that it stops in just about the same place each time, which is really all I can ask for!
> 
> Thanks for your interest gentlemen, I would like to hear what you would have done differently!



Very smart idea James! Every one should built an attachment like this. Thanks for sharing it with us


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## Jamespvill

Hawkeye said:


> Would a tension spring in the top half of the trigger work to replace the compression spring at the bottom?



Certainly! As long as the trigger is being directed towards the "sear" at all times then your good to go. And as you stated, it really depends on how it fits in on your lathe.  A torsion spring would probably be the most low profile and best option. I would have went torsion but I don't have thick enough music wire to wind up the appropriate spring. And in all honesty, you don't exactly need the spring either. You could just flick it under the sear each time if you want. But i'm lazy and want it as automatic as possible!


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## RandyM

Nice job James! How do you lock it out when not in use?


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## Jamespvill

RandyM said:


> Nice job James! How do you lock it out when not in use?



Thanks! 

When it's not in use I simply pull the pushrod out of it's fixture. The whole mechanism remains disengaged after it's triggered so theres no worry that it will reengage. 

Now I just have to figure out how to make it work for my automatic feed too!


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## RandyM

Jamespvill said:


> Thanks!
> 
> When it's not in use I simply pull the pushrod out of it's fixture. The whole mechanism remains disengaged after it's triggered so theres no worry that it will reengage.



Bear with the slow old guy here, but I must be missing something. How does it remain disengaged with the springs controlling engagement. You can not use the powered feed without it locking in the on position. :think1:


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## Jamespvill

RandyM said:


> Bear with the slow old guy here, but I must be missing something. How does it remain disengaged with the springs controlling engagement. You can not use the powered feed without it locking in the on position. :think1:




Keep in mind my only experience with lathes is ones made after the year of 2011! On my lathe, threading is engaged via the halfnut, while power feed is engaged through the use of the powerfeed lever. 

As for the mechanism being disengaged; after the trigger trips the sear the trigger rests on top of the sear with the lever disengaged. Then to reengage one must push the lever down which forces the trigger out of the way and when it can get under the sear, it reengages. 

Hopefully I hit on what you were asking. I would suggest watching the video, but I'm sure you already have! Let me know if it still needs clarifying!


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## hman

Jamespvill said:


> Thanks for your interest gentlemen, I would like to hear what you would have done differently!



Of course you realize that, now that you've published, EVERYBODY is gonna be an expert!:rofl:

That said, I really appreciate your concept, and applaud your success with the first iteration.  You got 'er done, and she worked!




Jamespvill said:


> I'm not too fond of the current spring setup for the lever, it looks a little goofy for my liking.



That was kinda going to be my only concern.  It looks almost like you JBWelded the aluminum spring anchor to the underside of the feed lever housing.  I'd worry about two things - either knocking the spring anchor off accidentally, or the compression spring going "sprang" and coming off one end or the other.  If (FOOEY - WHEN) I add one of these to my lathe, I'll try to stay with extension springs.  They're easier to anchor positively.  You might consider changing to an extension spring - either anchored to the right (below the half nut lever base) or left (to the top of the feed lever mount).



Jamespvill said:


> Finally it's time to build your pushrod or "finger" and means of attaching it to your lathe. I chose to attach it to my ways. If I would have had wider aluminum bar then I would have opted for that, but I only had 1/2" so I went with that.





Jamespvill said:


> I'm probably going to add a threaded rod through the aluminum block so I can stabilize it against the gearbox behind it in an attempt to diminish all of the flex. The rod is a 3/8" piece that I'm probably also going to add some sort of stabilizing function to towards the end of it.



Question here - it looks like the aluminum bar attaches with a short steel bar below the ways, but no fasteners are in evidence.  Are they at the underside? 

As for flex, I do tend to agree that a mounting bar wider than 1/2" might have been desirable.  The threded rod should help.  You might also consider turning a "hub" for the pushrod, and attaching it to the bar.  This should keep the rod aimed toward the proper place.  Or else, mount a guide to the left edge of the carriage.  I doubt you'd ever have to make a thread longer than the width of the carriage, so it's unlikely the rod would disengage from the guide in use.  And as you mentioned, you remove the pushrod completely when not threading.

Again, it's a great design overall, and even if you don't tweak anything, it's a winner!  Thanks!


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## Jamespvill

hman said:


> That was kinda going to be my only concern.  It looks almost like you JBWelded the aluminum spring anchor to the underside of the feed lever housing.  I'd worry about two things - either knocking the spring anchor off accidentally, or the compression spring going "sprang" and coming off one end or the other.



Actually, It's even less impressive than JB weld, it's hot glue! I just so happened to have a piece of threaded aluminum bar that I threaded undersized so I threw that on as a "temporary" piece...Of course we all know how temporary tends to become permanent if it never fails! Fortunately, the spring is always compressed to a degree even when disengaged, so I'm hoping it never comes flying off. But the hot glue will surely fail sooner or later...



hman said:


> Question here - it looks like the aluminum bar attaches with a short steel bar below the ways, but no fasteners are in evidence.  Are they at the underside?



You are correct, there are two 10-32 set screws that hold everything together down there. They are just countersunk out of sight. I hope you can get one on your lathe soon so I can compare and make improvements on mine!


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## scrollsawer61

Thanks for showing your innovated idea.

Barry


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## Micke S

Great idea and clever solution :thumbsup:


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## rafe

That is a good one, Thanks for putting it up.


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## ogberi

Sir, simply awesome.   Let me count the ways, 

#1.  It's home made.  No $400 "Synergistic Synchronized Positive Thread Depth AutoFeed Disengagement version 12.4" made of space age alloys with coolant-repellent finish there!  Nope.  If you didn't cobble that together with scraps, I'll watch someone else eat my hat!

#2.  It works.  It's simplicity at it's finest.  Low parts count, easily sourced materials, no complex machining involved.  

#3.  It's removable.  Yes, it'll leave a few holes here and there.  What good is a machine if you can't modify it?  I'm sorry, but my Taig has spoiled the heck out of me with T slots *everywhere*.  If I designed a lathe, it'd be square, blocky,and *covered* with T slots and tapped holes.  Want to mount a threading-auto-disengage-widget?  Surprise!  Convenient T slots and tapped holes within reach!   Are you listening, Import Machine Makers?!   At the very least, give us flat, square (machined is okay!) surfaces all over.  We'll drill and tap, just leave enough meat for it! 

#4.  It's single-purpose.  It disengages the half nut.  It doesn't slice bread, cook your dinner, tuck you in and tell you a story.  It disengages the half nut, and then sits there staring at you.   I'm a firm believer in a tool that does *one* job well, vs a tool that does a few dozen things half-a**ed.  

#5. It shows your cleverness.  That mechanism is clever.  No doubt about it.  You had a problem, and you solved it very handily.  Without resorting to a Rube Goldberg apparatus to do so.  Well done.  

Good luck with the job!  At least one problem with it is now solved.  Time to start planning how to solve the next one!


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## Jamespvill

Thanks for the kind words gentlemen!

I've had this on for a little over three months and it hasn't failed yet. My DRO tells me that it usually stops within a thousandths or two on either side, which is acceptable by my standards!

I was actually contacted by a fellow who's going to publish this method in his book with a few of my pictures. Not sure weather he wants me to share which book or his name, so I'll keep it quite for now

ogberi, thanks for the 5 ways of it being awesome, I am humbled by the list! And it was made from everything out of the scrap bin, the only purchased item was the main return spring for the handle. 

The best part is that my hot glued piece of aluminum that retains the sear spring is still holding up. I wouldn't say I'm proud of it, but I have a tendency of making temporary things permanent until they fail.


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## randyjaco

I made this a few years back. It works OK, but I would bet that the addition of a spring would make it much better.

Randy


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## Franko

Very clever gizmo, James.


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## wayne.inspain

I made a variation of this yesterday, it works fantastic!! cut a 12mm long thread in a 14mm blind hole no run off, first internal thread I have ever done.
Just needed a stop collar on the telescopic rod


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## dickda1

Jamespvill said:


> Hello Gentlemen!
> 
> After punching out a few dozen threads today, I'm happily surprised at how well this carriage stop works. I'll gladly post a few more details and information about the mechanism.
> 
> First a more close-up video of the mechanism (is that the right term?) itself:
> 
> [video=youtube;rY6YHA4upRU]
> 
> 
> 
> 
> Here are a few stills of it engaged and disengaged.
> 
> View attachment 81874
> View attachment 81873
> 
> 
> The toughest part of making this is retrofitting it to your lathe and finding clearance for it, but after you lay everything out, it smooth sailing.
> 
> First and most importantly is to find where your pivot pin will go, this should be a place where the pushrod can get the most leverage. So halfway is just about perfect, but your lathe will determine this more.
> 
> Next you need to build a "trigger" this is the item that pivots on the pivot pin and is pushed by the pushrod (finger). After that is on then it's time to find the best location and orientation for the "sear" or the piece that it attached to the half nut lever. From there is simply fitting and filing to see where everything latches together properly but also disengages smoothly.
> 
> I used drill rod for the pin on the "trigger" and O1 tool steel for the "sear" both of which were heat treated and polished on the contacting surfaces.
> 
> After that then it's time for springs! One on the rear of the "trigger" to keep it always trying to engage and one on the half nut lever to keep it always wanting to disengage. I'm not too fond of the current spring setup for the lever, it looks a little goofy for my liking.
> View attachment 81877
> 
> 
> Finally it's time to build your pushrod or "finger" and means of attaching it to your lathe. I chose to attach it to my ways. If I would have had wider aluminum bar then I would have opted for that, but I only had 1/2" so I went with that.
> 
> View attachment 81875
> View attachment 81876
> 
> 
> I'm probably going to add a threaded rod through the aluminum block so I can stabilize it against the gearbox behind it in an attempt to diminish all of the flex. The rod is a 3/8" piece that I'm probably also going to add some sort of stabilizing function to towards the end of it.
> 
> Besides that, It should be apparent in the original video that it stops in just about the same place each time, which is really all I can ask for!
> 
> Thanks for your interest gentlemen, I would like to hear what you would have done differently!
> 
> View attachment 81873
> View attachment 81874
> View attachment 81875
> View attachment 81876
> View attachment 81877


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## Silverbullet

Lots of LATHES , turret LATHES have push off buttons built into the carriage . Most use a trigger with springs . We use to set them up so we could run three machines sometimes depending on the parts. Old Knox manufacturing made all kinds of valves stems on the LATHES bodies inflates and mill lapping machines all running every day . I miss the shop but don't miss the labor. Nice job on your push off. I'm going to make one but I'm also adding a roller switch to kill the power . Never trust anything completely.


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## T Bredehoft

I'm no gunsmith, so triggers aren't part of my repertoire. I got to thinking about this, came up with a lever on the engagement handle, operated by a push rod (with roller bearing on the end) to disengage the feed on my MK2. It took me  all weekend to whittle it out. I'd planned on eventually adding a threaded ring adjustment, may yet do that.  If you look close you can see the aluminum collar I applied to the engagement handle, held on by  5 5-40 set screws. 



It ought to work for threading and feed. It seems to  stop within a couple of thou.


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## hman

Reading this and other threads, as well as (who was it)'s excellent thread about the gear box technique (also written up in HSM or MW), I've been wondering if there weren't a simpler method of achieving a quick stop when threading.  After having installed a 3 phase motor and VFD with braking resistor on my 12x24 lathe, I've been impressed by how quickly it can come to a stop.  I have the stop time set to ½ second, and could probably go even lower.  Couple this with a measurement I did quite a number of years ago, indicating that a microswitch's operating point is reproducible within about .001" to .002", I offer the following "wild hair" for your consideration:

Attach a microswitch to something like a feed stop bracket, that can be positioned along the ways and locked in place.  Wire the microswitch into the VFD controls, so that it activates the stop.  With the lathe off, run the carriage to where the threading tool is in the relief groove.  Position the microswitch to activate at this point.  Now back off the cross slide, run the carriage to the start point of the thread, advance the cross and/or compound as required, and start hit the start button on the VFD.

If my wild hair is valid, the lathe will make a threading cut and stop when the tool is in the groove.  Then back off the cross, reposition the carriage, reset the tool, and repeat the process.  

Consider this a target on the wall.  You're all invited to start throwing darts at it!  I really don't want to try this unless it passes the smell test.


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## homemadetools

Nice build! We featured it in a recent newsletter, properly credited to you and Hobby-Machinist.com of course. Looks like you guys just reached over 100 homemade tools that we've indexed. I hope we've been able to send you lots of visitors. Well done.


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## Canobi

hman said:


> Reading this and other threads, as well as (who was it)'s excellent thread about the gear box technique (also written up in HSM or MW), I've been wondering if there weren't a simpler method of achieving a quick stop when threading.  After having installed a 3 phase motor and VFD with braking resistor on my 12x24 lathe, I've been impressed by how quickly it can come to a stop.  I have the stop time set to ½ second, and could probably go even lower.  Couple this with a measurement I did quite a number of years ago, indicating that a microswitch's operating point is reproducible within about .001" to .002", I offer the following "wild hair" for your consideration:
> 
> Attach a microswitch to something like a feed stop bracket, that can be positioned along the ways and locked in place.  Wire the microswitch into the VFD controls, so that it activates the stop.  With the lathe off, run the carriage to where the threading tool is in the relief groove.  Position the microswitch to activate at this point.  Now back off the cross slide, run the carriage to the start point of the thread, advance the cross and/or compound as required, and start hit the start button on the VFD.
> 
> If my wild hair is valid, the lathe will make a threading cut and stop when the tool is in the groove.  Then back off the cross, reposition the carriage, reset the tool, and repeat the process.
> 
> Consider this a target on the wall.  You're all invited to start throwing darts at it!  I really don't want to try this unless it passes the smell test.




I have an old Grayson lathe which is very shy on features so I've been thinking along the same lines as I have a bunch of inverters (I work at Invertek Drives UK). I'm new to machining but have an almost lifelong electronics background so my plan is to add at least five switches and a trim pot for analogue speed control.

Essentially I'm just going to get creative with a bunch of paddle, momentary and latching switches to use with the manual start/stop/forward/reverse to control the carriage.

Once I get it all figured out I'll make a new thread and post easy to follow wiring diagrams and make a short vid of the system in action. In all honesty though, I can't say when this will happen exactly as I'm in the middle of fixing up a Mk1 Dore Westbury mill I recently acquired but it will happen...


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## Canobi

I finally got time to concentrate on the VFD saddle control, so the thread is now up:
http://www.hobby-machinist.com/threads/fun-with-a-vfd-lathe-stops-and-auto-traverse.63072/

I must say though, as much as the VFD will come into play for turning and threading, a half nut disengagement mechanism is definitely on my hit list of things to make, though there's not much real estate on my lathe for fixing things to, so I'm also looking into using a long throw solonoid actuator as it will allow for a much more compact mechanism.


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## tertiaryjim

T Bredehoft said:


> I'm no gunsmith, so triggers aren't part of my repertoire. I got to thinking about this, came up with a lever on the engagement handle, operated by a push rod (with roller bearing on the end) to disengage the feed on my MK2. It took me  all weekend to whittle it out. I'd planned on eventually adding a threaded ring adjustment, may yet do that.  If you look close you can see the aluminum collar I applied to the engagement handle, held on by  5 5-40 set screws.
> View attachment 226287
> 
> 
> It ought to work for threading and feed. It seems to  stop within a couple of thou.



Tom
The half nut lever closes or spreads the half nut so if it's opened slowly there will be a variance in the thread pitch.
Thats why a trigger is used to open it quickly at the end of a run.


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## T Bredehoft

tertiaryjim said:


> Thats why a trigger is used


I threaded a dozen aluminum pieces,it stopped close enough to the same place on each piece that I couldn't visually see a difference. It may not work as well in steel.


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## tertiaryjim

Sorry Tom
I guess I didn't make myself clear.
While the engagement will release at the same point the graduall release will
allow the the threads of half nut and lead screw to retard .
They will engage on a different point because the thread is following the thread face 
like slipping down a wedge. This will cause a varience in the lead of the thread.


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## T Bredehoft

tertiaryjim said:


> This will cause a varience in the lead of the thread.



Gotcha, Jim. For my purpose it works well. The thread at the end of the pieces I'm working (this job) are not required to be correct, the piece gets a plastic cap screwed on. If I need it I can put a groove there for it to stop in.


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