Threading on a "slow to stop" lathe

First, turn a "land" at the point where you wish the threads to stop. Make the diameter just at, or a couple-thou under the minor diameter of the thread.

IF you have a threading dial, and don't have to reverse your lathe to get back to the start of the threads --

When the tool enters the land, disengage the longitudinal feed (halfnuts), then stop the lathe with the tool still in the land.

Watching carefully, you can stop in a land barely more than one thread pitch wide.

If you don't have a threading dial, be right quick on the cross-feed, and back the tool out rapidly when it hits the land. Then stop the lathe, reverse, etc.,etc..

LLoyd

Thanks. What about simply reversing the lathe, would that not keep the bit exactly where it needs to be on the thread?

Jim

NO! Backlash will have it all over the place. Ken.

Shut the lathe off early and let it cruise to near the end of the threading section and finally move it by hand to the proper stopping point. That's one way to do the job.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Stopping? Why are you stopping during threading? Blink blink?

You put a long shank dial indicator on the ways below or next to the headstock, and when you reach where you want to be..you disengage the half nut handle, back off the compound two turns, hand feed back to the hard stop you put to start from, and repeat as needed. The spindle never gets shut off until you are ready to remove the work from the chuck.

Threading up to a shoulder is nearly ...nearly impossible with these types of lathes, but you should be able to come pretty darned close if you are turning slow enough. Always plan for a bit of relief at the end of your thread if running up to a shoulder.

Gunner

"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown

I know one fella who made a crank that gets shoved into the spindle from the backside just for this purpose. Does the last few turns by hand, thus stopping at any given point is a snap.

Cuz' a lot of the 3-in-1's like my older Smithy don' have half-nuts and cant be retro'd so its not an option.

================================================================= Standard US practice is to simultaneously withdraw the tool using the cross slide and snap the half nut out of engagement with the lead screw. This required a good deal of practice and concentration.

The longitudinal slide is then cranked back to the starting position, the cross slide cranked back to its starting position [a thread stop is very hand here] and the cut deepened with the compound [top slide in the UK] set at ½ the included thread angle. This puts the cutting almost entirely on the tailstock side of the cutting tool [assuming a RH thread]. This avoids a very wide chip that tends to result in chatter and having two chips meeting in the center of the tool causing jams. This also gives the affect of positive rake because you are moving into the work toward the headstock. Some very good machinists suggest setting the compound slide a few degrees less than ½ the included thread angle to give a burnishing action to the side of the thread away from the headstock and the added contact is stated to reduce chatter. I have not found this necessary.

There is an accessory [actually a necessity] called a "thread indicator" which is a small gear that engages the lead screw. The gear turns a dial with a number of lines that indicate the position of the half-nut relative to the lead screw. Pick any one of the moving lines and snap the half nut in when the fixed and moving index marks are aligned. I suggest using a magic marker to highlight which moving line you are using.

Note: This works as long as you are using an inch leadscrew to cut inch threads or a metric leadscrew to cut metric threads.

I suggest that you buy some of the older lathe books such as Milne's Machine Shop Methods [c.1944] see

If you will send me an email with a valid address, I will send you a scan in pdf of the section of an atlas craftsman lathe manual that covers threading.

Hope this helps.

Perhaps the most common reason (for those of us with half-nuts on our lathes) is the cutting of metric threads (which account for 95% of my threading operations).

- Michael

Which would that be? Someone here was looking for a Sheldon manual. I did not see it on Lindsey's site.

Rex

============== Lindsay's web site is somewhat tricky to navigate as the hyperlinks are not clear [at least to me] From home click on great machine shop books the machine shop then running a regal lathe at the bottom of the first [real] paragraph you can click on how to run a southbend lathe ... and another page with the Sheldon, southbend and Colvin info will come up.

If you don't want to go through all of this see

Very good.

Did you catch that, Al?

- - Rex Burkheimer WM Automotive Fort Worth TX

F. George McDuffee wrote:

I thought we were talking about real lathes?

Gunner, ducking and running

"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown

Metric???? Only them damned furriners use that Metric stuff. When I want to do metric..I simply change that little knob on the HLV-H to metric.

Gunner

"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown

That lathe looks like a bastardised version of a a Clausing Model 106, which had 17" between centers. The carriage/apron and headstock look the same but the QC gear box is different than what I see in an old brochure. The QC difference I see could just be camera angle & perspective, though.

Apparently some (all?) the Model 100 series lathes came with a friction clutch/brake, which could certainly be useful to you.

You really ought to spend a few bucks and get a manual from Clausing. It would probably run you $10 to $25, plus postage.

Mike

I did Rex, thank you!

AL

I want to thank everyone who participated. I will give your techniques a try soon.

Set your cross slide so that the crank is oriented in a way that mashing down on the handle will back the tool out. Once you get to where you need to stop, spin the cross slide handle a couple of turns to back the tool off. While you're backing out the tool (or after it's backed out) disengage the half nuts. If you consistently come to your zero mark from one direction every time you should place the tool in the same physical location each time with no backlash errors. I was told that I should do both actions (back out and disengage half nuts) simultaneously, but I found that to be a pain to get right consistently and disengaging the half nut before backing out tended to break tools in later passes, whereas the other way around did no damage and terminated the thread aesthetically. So, for me, it's back out the cross feed, then disengage the half nuts, reposition everything for the next pass. Repeat until done. The lathe I learned with also had to coast to a stop, and when in low gears it could literally take a minute or so to come to a halt. I just kept it running throughout the threading process.