Power Feed to Make Threads (English or metric threads) Curiosity

[RJSakowski]

By the way, I do use my lathes to wind coils. I find that I usually do this at extremely slow speeds so as to keep the wire nice and neat. But I usually guide the wire by hand.

I wind coils by hand as well. Sometimes though, you want to lay down a coil that doesn't have close spaced windings. It also would be useful if you wanted to wind non overlapping, close spaced windings in multiple layers.

 

[JimDawson]

Sounds like its time for a CNC lathe conversion

Extra credit: Convert a manual lathe without disturbing any of the manual functions and be able to switch between CNC/manual operation in under a minute.

 

[7milesup]

With using the power feed, wouldn't you have to leave it engaged, stop the lathe, reverse and repeat? Not sure what you would be gaining, but then again I am a complete novice when it comes to threading.

 

[Christianstark]

I’m not sure, but I do not believe the straight gear teeth on my 1340 lathe bed are involute. I would think that may be enough to ruin some finer threads, but I’m a novice.

 

[mikey]

Wait ... what? You want to use power feed instead of the leadscrew to cut threads ... why? The gearing for thread cutting is tied to the gearing on the leadscrew to give you the correct pitch. While the power feed is also tied to the gearing, the ratio is not the same as the leadscrew so you will not have accurate pitch results. Moreover, the thread dial indicator does not function if the leadscrew is not used so how are you going to time your cuts?

I must be missing something here so color me dumb but I don't get where you're going with this.

 

[cwilliamrose]

I have done odd ball threads on my Emco V13 lathe. The plate on the machine only addresses the most common pitches. I made a spreadsheet to search out other possibilities. There are a couple of customizible tools available to do the search using computer power rather than patience and a bunch of manual iterations. This started for me needing to cut 3.3333 TPI threads which was not on the plate but was possible with the right combination of change gears.

 

[mikey]

I have done odd ball threads on my Emco V13 lathe. The plate on the machine only addresses the most common pitches. I made a spreadsheet to search out other possibilities. There are a couple of customizible tools available to do the search using computer power rather than patience and a bunch of manual iterations. This started for me needing to cut 3.3333 TPI threads which was not on the plate but was possible with the right combination of change gears.

Yes, many threds can be calculated but did you use power feed or the lead screw to cut it?

 

[cwilliamrose]

I used the lead screw. I agree with those other comments regarding it being impractical to thread with the power feed -- unless you can do it in one pass. Not sure about the backlash part of the question but it could be a problem too.

 

[RJSakowski]

Sounds like its time for a CNC lathe conversion

Extra credit: Convert a manual lathe without disturbing any of the manual functions and be able to switch between CNC/manual operation in under a minute.

I thought about a CNC lathe but I like the hands on machining. In fact, most of my lathe work doesn't even involve using power feed. Old habits die hard.

I should point out that if/when I need the capability of a CNC lathe, I can use my CNC mill as a vertical lathe. True, I don't have through spindle capability and turning is limited to about 9" and I don't have spindle sync but for most needs, it would suffice.

 

[B2]

Thanks folks, Good comments and appreciated. I'll respond to them a bit below.

Extra credit: Convert a manual lathe without disturbing any of the manual functions and be able to switch between CNC/manual operation in under a minute.

Hi Jim, Yes, I once saw a U-Tube video where some one had done this. It looked cool. But then I lost the link so have to search for it again. Sometime.

With using the power feed, wouldn't you have to leave it engaged, stop the lathe, reverse and repeat?

Yes, 7mileup. You would want to leave it engaged. The reason for doing it might be that one could get TPI values which are not available other wise. On my PM1440GT, and including the change gears that come with it that amounts to about 1500 additional TPI values (It is possible there are some redundancies.). Without the change gears there are 16 possible feeds and so TPI additional values.

I’m not sure, but I do not believe the straight gear teeth on my 1340 lathe bed are involute. I would think that may be enough to ruin some finer threads, but I’m a novice.

Hi Christian,
I am not for sure what the effect of the different kinds of teeth on the lathe bed would have. Anyway, if you keep the feed lever engaged, back out the tool a bit, and backed up the apron, put the tool back to a cutting position, and go again... I would think the results would be repeatable. This is what some folks advocate when using the proximity stop approach. However, maybe the Feed threads are not always uniform? I would think that the fact that the 1/2 nut grips multiple lead screw threads that it tends to reduce backlash and cutting resistance, as well as other possible clamping issues. I am not an expert on threading, but sometime I will try this out and just see if it is repeatable. On my old South Bend where I need to replace the 1/2 nut along with a bunch of other rebuilding, I can hardly cut a thread anyway. (The lead screw on it seems to be in very good condition.)

This started for me needing to cut 3.3333 TPI

Hi CWilliam,

Cool, so there is sometimes a need for rather unique TPI values.

Using the spread sheet tool that I have been working on I find that there are several external gear setting where I can get 3.3333 or 3.33?? threads. ??=> other digits. But you cannot get either of those with the 60/30 external gears that are normally used on the PM1440GT. The tool is nice as it generates all possible TPI values for all possible gear settings as well as all possible external gears that I possess into a table. Then I have a macro command that will search for almost anything you request for in the way of TPI. It appears that there are 5 possible unique gear and lever combinations out of the 6144 possible combinations of gears and settings to get the 3.33?? values. The PM1440GT has 16 fundamental TPIs that can be reached with the main gear box, then it can generate times 4 possible factors of 2 of these. So that yields 64 possible threads without changing an external gear. Suppose you have inserted external gears, like 65T/30T, 69T/28T, 60T/28T, 60T/35T, or 60T/42T which are not the more common 60T/30T gears of the 1440 where you would cut a 24TPI .... and you wanted to cut it without taking the cover off and removing gears. Would it not be nice to just change the gear box levers and get the standard thread? What gear settings do you use? Just search for 3.33?? in the tool and you find either 24.000 or 24.00?? for each of the external gears I just mentioned. The Power Feed values just make more entries to that search. The PM1330GT manual says that you cannot get to the 13.0000 TPI with the standard 60T/30T external gears. However, I have found that there are 60T/28T, 60T/30T, 60T/35T, and 60T/42T combinations will get the exact 13.0000 TPI value. If you are willing to drop the preciseness to 13.0??? then I find 9 unique settings. Even the standard 60T/30T yields 13.0909 TPI which is with in 1%. Maybe the manual should have said that, but maybe the author did not know?

if/when I need the capability of a CNC lathe, I can use my CNC mill as a vertical lathe.

Yes, I prefer to use my lathe by hand too, but I do find that if I want a really smooth surface the power feed does a better job of making the cuts uniform. This seems to be especially true on soft materials like brass. My CNC mill has enough backlash that the circle cuts are not really round! Also the final surface always has cutter marks. The nice think about that CNC lathe video was that you could effectively turn the CNC off and it worked like a manual lathe.

Dave L.