Threading In Reverse With A Threaded Spindle

[Kevin T]

I've made a few threads recently threading in reverse before it dawned on me... I've got a threaded spindle! I'm wondering how smart that really is on my lathe. Is it safer to use a 5C collet configuration to hold the work? No difference? Which might be prone to more problems? A 2 3/8-6tpi spindle or a 5C collet thread? Is it a non issue for threads smaller than say X diameter? What diameter would that be? Oh ...and always feeding in with compound set to 29.5001 degrees.

 

[CalG]

Snug up the chuck by hand. Thunk!

Then don't worry about it.

or if you are just the worry type, Remove the chuck, evaluate for yourself what it takes to get it to turn.

Get back to us with your experience.

The Hardinge HLV- I had was supplied with a threaded spindle nose configuration. I never worried about any of the tooling coming loose. The Weiler LZ-330 is a threaded spindle, Never a worry.
I have a small three jay in a 5-C threaded adapter that I use frequently on the WADE bench lathe. I NEVER worry about it coming adrift. It takes a good effort to get them off when wanted!

But If I were doing some turning that set up a lot of vibration under heavy load, I would reconsider my methods.

Interrupted cuts being something to avoid. Turn the other way in those instances!

 

[FredC]

Pretty sure I have done it on fine threads also. I have done other things that I questioned later and asked "was that smart"? What ever torque you apply to tighten the chuck it will take more to break it loose. Thread courseness, material toughness, and diameter will determine how much torque is being applied to screw the chuck off. I have never seen a chart with those numbers. With no numbers you are flying blind. One could guess how much torque is being applied by doing a right hand thread and asking yourself if it takes more torque than expected to loosen it. That may be an indication.
Ask what is the worst that could happen if things go south?
Seems like there was a thread many years ago where someone was running in reverse and noticed the chuck coming off and switched to forward to prevent it from coming all the way off. Seems he related it made such a loud thunk when the chuck slammed into the shoulder everyone in the shop turned around to see what happened. If I am remembering right they could not screw it off and were considering machining off the back plate. Do not recall if this was a threading accident or not.

Long answer to say I do not know. I would say you are OK for 1/4-28. 1 inch 8 TPI, no clue.

 

[wood2steel]

Sounds like a good enough reason to me to buy a second lathe.
I do love those L-0 / L-1 spindles! Just keep your head wrapped around that threaded spindle concern. Have heard a story or two about folks having a bit of excitement when they accidentally shifted the power switch in reverse instead of Stop.

 

[crossthread]

Just use plenty of Loctite on the threaded spindle and you shouldn't have any problems.......just kidding.

 

[4GSR]

I've cut hundreds of left hand threads on my 9" SBL over the years. Never once had a problem with the chuck backing off. Just be sure your spindle thread and chuck thread is exceptionally clean, oil the spindle thread, make up chuck on the spindle thread and bump up. Don't jamb the chuck on!!!!! No need for it!!!

A little trick I use occasionally, Take a 10-12" Crescent wrench and leverage on a jaw of your chuck and backup the spindle from turning and give it a slight "bump up" to make sure the chuck won't loosen on you if your worried about it. Now don't make it so tight that you have to fight with it and bust off teeth in you back gearing, that's too much force!

 

[Kevin T]

..."Snug up the chuck by hand. Thunk!"...

..."Interrupted cuts being something to avoid. Turn the other way in those instances!"...

Great mention on the interrupted cuts.
"Thunk" I understand!

..."Ask what is the worst that could happen if things go south?"...

That's the perplexing question that lead me here! lol

..." Just be sure your spindle thread and chuck thread is exceptionally clean, oil the spindle thread, make up chuck on the spindle thread and bump up."...

A little trick I use occasionally, Take a 10-12" Crescent wrench and leverage on a jaw of your chuck and backup the spindle from turning and give it a slight "bump up" to make sure the chuck won't loosen on you if your worried about it. Now don't make it so tight that you have to fight with it and bust off teeth in you back gearing, that's too much force!

I'm pretty good at keeping the spindle and chuck threads clean and lubricated but in support of a good thunk I understand perfectly!

Good trick thanks. My chucks are pretty heavy so when they do seat on a hand spin it is known. I wasn't sure about the reasons behind the evolution of spindle designs but thought maybe...just maybe it was because of my concern here.

I may have never given it a thought except recently I cut a 2 3/8-6 external thread and I wasn't fast enough on the cross side at the end of a pass and caught some fresh material on one of the last passes. I was using an Aloris holder with a P-6 cutter and it and it snapped the end off the cutter! 60 dollar mistake but it was worth the knowledge that there are huge differences in force between cutting a micrometer thread and a spindle master! lol

 

[FredC]

Anyone else remember the account about the chuck coming off and switching to forward to stop it? If it was here on PM it was nearly ten years ago.

 

[Conrad Hoffman]

I vaguely remember the thread. Hey, it's not a problem until it is, and then it can be a big one. If the diameter of the work is small, the risk should be minimal. If larger, you might have a guaranteed failure. Me, I'd use collets if at all possible.

 

[Peter from Holland]

On many machines ,Schaublin and Weiler to mention 2 ,a clamp can be used to keep the chuck on when turning in revers
Attached a picture of one

The sleeves in the flangebody you do not need if it fits properly
Ask me how I know

Peter

 

[Joe Gwinn]

One reason I chose a Clausing 5900 lathe (L00 spindle nose) was precisely so I could operate in reverse, both for threading (so carriage mill move away from headstock or a shoulder), and for parting off without the dig-in-and-break excitement.

 

[richard newman]

I had a wood lathe that I used for sanding and wanted to be able to reverse it quickly. I rigged up a drawbar with a left hand thread that kept things locked up.

 

[JST]

I vaguely remember the thread. Hey, it's not a problem until it is, and then it can be a big one. If the diameter of the work is small, the risk should be minimal. If larger, you might have a guaranteed failure. Me, I'd use collets if at all possible.

Always got away with it.... until the 1 1/2"-8 thread.... that one did get loose. (maybe it was 2 1/8"... not sure)

 

[Kevin T]

Me, I'd use collets if at all possible.

Yeah so that is what I was pondering. Would a snugged up collet mount chuck provide better insurance? It would be a smaller chuck with less mass but does the finer threads and drawing it into the spindle adapter make it a lot safer for the operation?..or less so? Seems like a good thinking mans question.

 

[EPAIII]

Seems like threading in reverse may be a method to try when the chuck is stuck. Make it an interrupted cut if all else fails. Dig in deep.

 

[fusker]

Peter from Holland: Beautiful photo.
I like the caption: Sicherkeitsfutterflansch
Isn't german a lovely language?

fusker

 

[camscan]

Automatic screw machines have a threaded spindle and when cutting a RH thread with a tap or button die run fast left hand slow right hand. I have never seen or heard of a nosecap unscrewing.

 

[UptownSport]

I read the issue comes when reverse is mistakenly selected, then FWD on impulse.
The RPM for correcting a loosening chuck would need to be about 10RPM, or the operator plied with reaction enhancing Scooby Snacks.

How much would these hold ... (Rando seach photo)
I don't believe the LeBlond or Sheldon have such grooves