Lathe Threading Auto Stop

[zmotorsports]

Nice. Very innovative.

Mike.

 

[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?

 

[Jim Petridis]

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 81874View 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 81875View 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

 

[Jamespvill]

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!

 

[RandyM]

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

 

[Jamespvill]

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!

 

[RandyM]

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:

 

[Jamespvill]

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!

 

[hman]

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!

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).

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.

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!

 

[Jamespvill]

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...

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!