Threading speed?

[Steffin T]

If doing a relief area at the end of the thread, what is the proper way to make the relief so that it has a clean and finished appearance? As an example, if I needed to place a relief, prior to threading, approximately 1.5" up from the end of the tube, which tool should be used to get a "clean" start/finish to the relief?

Thank you.

[J Tiers]

Threading fast and doing the "flying pull-out" is classy, can be required in industry, etc, etc.

When working for your own benefit, there is no other particular reason for doing it. I do tend to do it, but that does not mean you need to. It isn't worth costing yourself money in busted parts etc.

As far as speed and cut quality...... Quite often, the speed you need for good cut quality based on speed is going to be a speed that will make the thread go by in a blur..... it is often much less than practical, you are not a CNC. So, while true, and even applicable, it may not matter much.

Tool grind is going to help...... the typical flat top threading tool "plows" off material, it does not cut. So it throws up a big 'furrow", and that changes little until you are really screaming speed-wise.

Grinds (not easy to do) that for instance give a horizontal edge but a positive rake, with a valley down the middle of the tool, can make a big difference in cut quality at lower speeds. There are other ways also. People did cut threads with carbon steel tools on old slow lathes, you know, and they did not have to put up with threads that look like they were cut by a dull squirrel tooth.

[stevec]

Have you done any work for the defense system (government)? If so, you understand that if a groove is not specified, it can't exist. That's part of the discipline of being a machinist, and not an engineer, where parts MUST be built per print---and you often are not afforded the luxury of an undercut. Besides, a skilled machinist has no need for one. He can pull out as required.

Harold

Gee, I thought I said "If design permits" and thank you for declaring that I am not a skilled machinist

[seal killer]

All--

I have wondered about this very thing (threading to a shoulder). This is a very valuable "thread" for me.

Practicing using a relief groove sounds good to me, as does using PVC. These are new ideas for me and I appreciate them.

--Bill

[Harold_V]

Have you done any work for the defense system (government)? If so, you understand that if a groove is not specified, it can't exist. That's part of the discipline of being a machinist, and not an engineer, where parts MUST be built per print---and you often are not afforded the luxury of an undercut. Besides, a skilled machinist has no need for one. He can pull out as required.

Harold

Gee, I thought I said "If design permits"

Yep, you did---but it's important for others to understand that, assuming you find yourself in the position of doing work for others, you are not at liberty to alter designs. Might work for hobby application, which this forum addresses primarily, but there are also commercial machinists that visit this forum---with the distinct possibility that they have never been in a situation where they are not at liberty to alter designs.

and thank you for declaring that I am not a skilled machinist

Sorry--but I didn't say that. I simply stated that qualified machinists don't have issues with that operation. I did not judge you, nor your talents. That's not what I do here---what I do is try to present factual information------if it does not agree with your assessment, that's unfortunate, but my comments are not intended to be personal in nature. It's a fact--skilled machinists don't have an issue with pulling out. If they did, they wouldn't be skilled machinists. I'm sure you can do it, just like the rest of us do it.

Harold

[schwabw]

Even more basic than pulling out, I am still trying to figure out how to reliably engage the half nuts at the right time; to get started, I'm just practicing engaging on a particular number on the dial. Either I am being too timid with the lever, or I need more practice to lead it correctly.

Sometimes when I engage as intended, the half nuts will disengage a short distance later. That adds to my suspicion that I am being wimpy, however good my intentions might be (don't want to tear up a nice lathe).

Suggestions?

Bill

[GlennW]

It's possible that brushing a little way oil on the leadscrew may help the half nut to engage easier.

Have you tried engaging them with the lathe stopped so you get a feel for how much the lever should move. Rock the cariage handwheel back and forth slightly as you engage them and put some pressure on the lever until you feel the lever formly stop. This should give you an idea of the pressure needed on the lever and the amount of motion needed to seat the half nut.

It is important to get the same engagement depth on the lever/nut each pass when threading or the tool will not track in the thread properly.

I would also run the carriage back and forth for most of the bed length under power with the half nuts to "wear" (for lack of a better word) the nuts in as they have not had much use. Choose a slower spindle speed for this so you don't crash anything!

You should also get used to giving the lever a good pull when disengaging, as being timid on the disengagement may not always work out!

I have an older Asian lathe, and it is very notchy feeling on the half nut engagement, which I don't care for.

[mechanicalmagic]

I am still trying to figure out how to reliably engage the half nuts at the right time; to get started, I'm just practicing engaging on a particular number on the dial. Either I am being too timid with the lever, or I need more practice to lead it correctly.

Sometimes when I engage as intended, the half nuts will disengage a short distance later. That adds to my suspicion that I am being wimpy, however good my intentions might be (don't want to tear up a nice lathe).

Suggestions?

When I first got my lathe I hated the half nut engagement. (I have been single pointing threads for a few decades, so I knew it wasn't me.) Upon closer inspection;
My half nut engaged slightly before the line on the thread dial. No by much, but enough to mess up my timing.
It was very easy to change the thickness of the spacer between the carriage and the thread dial. Now it pops in dead on the line, I'm a happy camper.

Dave J

[Harold_V]

Do not be timid about opening half nuts. You can do no harm by being firm and fast----but if you miss your queue and the tool hits the shoulder, you risk not being able to open them at all.

Closing half nuts abruptly when they are not aligned can cause the carriage to propel by the friction of the nuts closing on the major diameter of the screw---so it's always a good idea to start the cut a small distance away from the part in case you misjudge. Alternately, with the spindle running, I often propel the carriage by hand towards the tailstock to bring up the desired line on the threading dial quicker---at which time I engage the half nuts. That also buys you time in case you miss the mark.

With experience, threading becomes routine. One is far better served to face the task and get some experience than to avoid the process. Once mastered, I promise you, you'll wonder just what had worried you. This comment from a guy that has mild dyslexia----yet can chase threads effortlessly.

Harold

[BadDog]

When I'm ready to disengage, I pull the lever "with authority". Not jerking or otherwise risking damage, but I have taken to threading rather more aggressively than most (DoC and speed), and while it is not really difficult to disengage, it's not a light fingered timid moment.

As for engaging, particularly at the speeds I tend to use, I've developed a sort of "anticipation" technique. Just a moment before the mark aligns, I engage somewhat gently and quickly so I feel it come up on the crests of the screw as they continue to go by. Just a tiny moment later, as the mark aligns I'm already applying more firm pressure so they slide readily into the groove as it aligns. Seems to work well enough.

I also clean the lead screw threads along the range that will be used by using a comparably sized nylon cord looped 180* around and allowed to traverse under power down the length where the half nuts will travel. [Obligatory warning - hold the ends between finger tips in such a way it can NOT pull you in!] Once it is basically pristinely clean, I use an acid brush wet with Way Oil and let that ride along the same range to wet it with lube. Keeps everything working smoothly and reliably with minimal wear (not that I will ever wear out the half nuts on my lathe, they are the size of my fist and about 3" long!).