Goofy lathe threading chart

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prfesser

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My South Bend 13x40 lathe is old and has problems so I bought a large "mini lathe" (8.7" x 29.5") to play around with.
1610996500481.png
Change gears are metal not plastic, which is nice. No quick-change gearbox so I have to dive in and manually change some gears for threading, which I fully expected.

Here's the threading chart. Does anyone have any earthly idea what "H" is?? (there are no gears labeled "H")
1610996412079.png


A few unrelated points about this unit, in case anyone's thinking about buying one. The user manual is very thin and provides little useful info (some call this sort of writing "Chinglish"). All graduated dials and the leadscrew are metric. The spindle has a MT#5 and supposedly a 1.50" hole thru; that does NOT mean that 1.50" stock can be fed thru. The internal taper has been ground but the rest of the thru hole is quite rough. No 4-jaw chuck so I bought one separately, and had to drill new mounting holes in the spindle "face", as there are four mounting holes for that chuck but only 3 holes for the included 3-jaw. Weight is under 200 lb so it's not going to be nearly as rigid as a similar size Fox, Grizzly, or other brand of lathe. (I'm going to bolt it to a steel bar to minimize flex.) No threading dial, so threading is tedious: make the first cut, reverse feed without disengaging the half nuts, make next cut, repeat. As you can see from the chart it's rather limited in the English threads it can cut. And the 1.5 hp label is definitely wishful thinking; I doubt it's more than 1/2 hp.

Thanks for any help you can provide on the "H"
Terry
 

Nytrunner

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Hmm, that's a funny one. Could it be H for "High" or L for "Low"? (if yours has a dial with such a setting)
 

mbeels

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Absolutely no idea, but I'm very curious to learn what you find out.

So if you want 0.50 mm linear feed per revolution, you use gears 84, 30, "H", 60, "H", 80 for A,B,C,D,E, &F? Does the meshing work if "H" means "no gear"?
 

jsdemar

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Yes, "H" is spacer. Probably a couple of them came with the lathe.

I've left behind the world of threading on a lathe or muscling taps for larger threads. The new fad is "thread milling" with a threading tool on a mill. My Sherline CNC mini-mill (USA made) handles it nicely *if* I keep the feed rate low.
https://photos.app.goo.gl/tawAgMg1UVyoUPUP7
https://photos.app.goo.gl/XohjJbAg6ZAJbTmVA
However, the tools aren't cheap ($50 to $150 for carbide, depending on thread size). And the CNC programing is tricky.
 

Cape Byron

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哈哈大笑 (hā hā dàxiào) roar with laughter.

Sorry, really no idea but I couldn't resist...

Presumable the spacers are somewhere in the packaging. I never throw it out until I've looked everywhere for weird and wonderful pieces taped down somewhere.
 

prfesser

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I don't recall seeing spacers in the "toolbox" (about the size of a half-loaf of bread) that came with the lathe and had other items in it---change gears, cheap wrenches, auxiliary jaws for the 3jaw, etc.

On the chart the metric threads all have H for gears C and E. But if C and E are removed from the train, it appears that the remaining gears aren't close enough to mesh. I will have to open it up and mess with the gears some.

Thanks to all for your input!

Best -- Terry
 

caveduck

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I'm not familiar with that particular model, but a lot of times the change gears are on arms that can be moved on arcs to accommodate different sized gears. On my HF 7x10 all the spacer bushings were already on the shafts. Some of them can go in front of or behind the gear to control what it engages with. I think they're probably in your machine already.

Thread milling is cool but my machine lacks a spindle encoder (so far).

Change gears can be abolished by doing an electronic leadscrew hack - motor on leadscrew, encoder on lathe spindle, and some Arduino/RasPi hackery. There are vids on YouTube. For bonus points you can do absolutely any thread pitch you want. I've noticed a lot of currently available machines - even large ones - don't go beyond 56 TPI.
 

ttabbal

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It's a spacer. Import machines often write it that way. If you pull off one of the gear sets, you will find an axle, probably with a keyway. The spacers are rings with a matching keyway on my machine, about 3/4" diameter on mine. The arm the gears are attached to usually has a T-slot all the way down so you can space them in a way that will fit. Looking at the chart, yours looks to switch to not using a compound gear stack at a couple of the positions, just single gears. On mine, you loosen a bolt at the bottom and the whole thing pivots to help alignment.

I got real tired of swapping around. It would have been ok if I could have switched from feed to thread without replacing all of them. But my machine didn't work that way. I added the Clough42 ELS and haven't looked back. Tap a couple buttons, and change feed rate or thread pitch.

Never needed more than 56 TPI myself. I think the highest I've gone was 40 TPI. That felt pretty small. :)
 

jsdemar

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Thread milling is cool but my machine lacks a spindle encoder (so far).
The spindle only needs to be free-running to do thread milling. No spindle encoder or sync needed. The tool cuts like any other side-cutting mill bit. The magic is in the CNC helical control of the X-Y-Z movement. The cutter itself has no helical threads on it. For example, a 24 TPI thread mill tool will cut both inside and outside threads for any diameter at 24 TPI. Also right or left threads.

The exception is tapered threads, such NPT. They require a thread mill tool specific to the taper and TPI. But, they aren't ID/OD specific. A 14 TPI NPT cutter will do both 1/2 and 3/4 NPT.
 

caveduck

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Truth. I've been spending too much time thinking about rigid tapping this week.
 
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