Straight-in threading question

[Lucky Shooter]

I've tried straight-in threading after reading some recent posts.

I did this with the half-nut engaged all the time and didn't change the compound setting.

My question is----do we need to back the tool tip out of the threads before reversing the spindle ?

Is it bad practice to leave the tool tip in place while reversing the spindle ?

I ask because generally there is a reason for what we do.

Thanks for any opinions.

A. Weldy

 

[urbanrifleman]

Honestly my only question would be "why"? Why full time half nut engagement?

 

[gunsandgunsmithing]

Yes, if you don't back it out before reversing, it'll very likely chip or break the insert...or worse, if any slack in the machine. It could bugger the threads as well. Just back it out. I'm with Bradley, why not disengage the half nut?

 

[paperpuncher]

Honestly my only question would be "why"? Why full time half nut engagement?

One reason would be if doing a metric thread with an imperial lead screw I find the easiest way to do it is leave the nut engaged. I actually prefer to thread leaving the half nut engaged for all threading when practical. My machine has a electrical brake and a clutch so I simply back out the tool and reverse the spindle This inst practical for long threads as it takes too long to back up but for short threads like a tenon I prefer it. I find it much faster than waiting for the threading dial to come around YMMV

 

[SKWERLZ]

Definitely back out.

 

[urbanrifleman]

One reason would be if doing a metric thread with an imperial lead screw I find the easiest way to do it is leave the nut engaged. I actually prefer to thread leaving the half nut engaged for all threading when practical. My machine has a electrical brake and a clutch so I simply back out the tool and reverse the spindle This inst practical for long threads as it takes too long to back up but for short threads like a tenon I prefer it. I find it much faster than waiting for the threading dial to come around YMMV

My standard modern has a clutch that stops the chuck immediately. It's one of the features of a standard modern.

 

[AccelR8]

I've tried straight-in threading after reading some recent posts.

I did this with the half-nut engaged all the time and didn't change the compound setting.

My question is----do we need to back the tool tip out of the threads before reversing the spindle ?

Is it bad practice to leave the tool tip in place while reversing the spindle ?

I ask because generally there is a reason for what we do.

Thanks for any opinions.

A. Weldy

While I've never done it that way from what I know (and I certainly don't know everything) you are going to have lash in the spindle gear box and in the half nut/lead screw and this will create trouble when reversing. I would think you have to back the tool out.

 

[gunsandgunsmithing]

My standard modern has a clutch that stops the chuck immediately. It's one of the features of a standard modern.

Yep. Just don't do that with a thread on type chuck/spindle.

 

[hpshooter]

Honestly my only question would be "why"? Why full time half nut engagement?

If you don't have a threading dial and never learned how to catch a thread or if you are cutting metric threads on an imperial lathe. Back the tool out when reversing the carriage.

Paperpuncher beat me to the draw!

 

[Lucky Shooter]

The prime reason for not disengaging the half-nut was to turn the spindle
by hand to thread close to the tenon shoulder without a relief groove.

My main concern was the effect on thread quality with the second
---reverse---pass of the tool tip.

Mike, I did reverse the spindle enough to remove the backlash.

Thanks for the replies----I appreciate the voices of experience.

A. Weldy

 

[Sniperhandle]

Honestly my only question would be "why"? Why full time half nut engagement?

Because most lathes have a leadscrew that is inch, Like say an 8 TPI leadscrew, You have to leave the half nut engaged if you are doing Metric threads.

And to answer the other posters question, Yes always back the threading tool out before you reverse the lathe back to start threading again.

 

[gunsandgunsmithing]

Yes, when doing metric threads on most machines is a reason for leaving the half nut engaged. I don't think the op stated what he was threading for. Seems like he would've said so, if he was threading metric threads when he was asked why he was doing it that way.

 

[shortgrass]

Because most lathes have a leadscrew that is inch, Like say an 8 TPI leadscrew, You have to leave the half nut engaged if you are doing Metric threads.

And to answer the other posters question, Yes always back the threading tool out before you reverse the lathe back to start threading again.

You do not have to leave the half nut engaged if you are doing metric threads! This is a simple solution to allow you to disengage the half nut at the end of the cut. Works every time! I was shown this method in the late 70s by the 'lead man' in a job shop I was working. This explains the method probably better than I could. The part that explains it is near/at the bottom of the page. http://www.conradhoffman.com/metricthreading.htm

 

[shortgrass]

My question is----do we need to back the tool tip out of the threads before reversing the spindle ?

Is it bad practice to leave the tool tip in place while reversing the spindle ?



Thanks for any opinions.

A. Weldy

Yes, back the tool from the work, it is bad practice not to. The tool rubs, and not much can dull a tool quicker than allowing the tool to rub.

 

[jackieschmidt]

In this case, a self demonstration might be the best answer to the OP’s question.

Take a piece of steel. Take a threading tool and set your lathe to cut threads. Thread the piece for about an inch.

without disengaging the half nut and pulling the tool out, reverse the machine.

The mess it makes will answer all of your questions.

 

[Sniperhandle]

You do not have to leave the half nut engaged if you are doing metric threads! This is a simple solution to allow you to disengage the half nut at the end of the cut. Works every time! I was shown this method in the late 70s by the 'lead man' in a job shop I was working. This explains the method probably better than I could. The part that explains it is near/at the bottom of the page. http://www.conradhoffman.com/metricthreading.htm

Leaving it engaged is the way I was shown. In Precision Matthews Manual it also says, Half nut must stay engaged.

If I get time I will read the article you linked, I am sure there are many ways to skin the metric cat, I will stick with what I know for now.

 

[LVLAaron]

The short version; You can disengage the half nut, but you have to re-engage the same spot on your thread dial. Instead of waiting for the dial to go all the way around, just reverse the lathe to get to your spot.

That will work. The author talks about this under the context of needing to thread up to a shoulder, where you'd need to quickly disengage and back out.

 

[urbanrifleman]

I suppose if there is no shoulder to slam into, not disengaging would not be a big deal.

For metric threads.

I would still want to practice that.

 

[jackieschmidt]

A thread relief is a great help in avoiding the shoulder.

If you are having to cut a metric thread to a shoulder and cannot disengage the half nut, my best advice would be to practice and get proficient at this sort of thing before attempting it on a important item.

At my shop, I do not turn men loose with jobs that they are not comfortable in performing at their skill level. That is when it becomes a teaching session.

 

[shortgrass]

The short version; You can disengage the half nut, but you have to re-engage the same spot on your thread dial. Instead of waiting for the dial to go all the way around, just reverse the lathe to get to your spot.

That will work. The author talks about this under the context of needing to thread up to a shoulder, where you'd need to quickly disengage and back out.

You're da** right it'll work! Over the years I've cut hundreds of metric threads, on many different makes, models and vintages of lathes that have inch lead screws. I've seen operators manuals that say not to dis-engage the split nut when threading metric. I guess they put that in print for those who can' seem to wrap their heads around how a gear train works, and why this method does work . You still have to change out to the proper gears for the metric pitch (or move the shift lever to the proper position for metric). But it allows you to thread to the shoulder easily.