View Full Version : Chinese Threading Torture

11-25-2009, 01:07 AM
Like water torture, only you pay for the privilege.

Seriously, I'm seeing a lot of Chinese lathes advertised in the 12-13" class, like this Hafco and the PM1236 with these strange 4-knob gearboxes. The problem is, the boxes aren't really inch, and not conveniently metric. They seem to be designed primarily to make you wish you'd bought a 12x36 with a Norton gearbox, like my G4003.


So, for instance, if you look closely at this threading chart, what it's saying is that:

1. You need a slew of change gears to access all the columns on the inch box, and there are two ranges that also require gear changes.

2. The box seems to be more adapted for metric threads, but even in that case, there are two ranges requiring different gear configurations. Remember, this is driving an inch leadscrew.

A basic two-stage Norton gearbox is almost perfectly adapted for one standard and requires change gears only to cut the other. Since the threading standard chosen presumably meets the basic "use case" of the lathe, you'd think that gear changes would be relatively infrequent. But what you have here is basically a change gear lathe with easy feed changes. You'll be changing gears all the time just to deal with the 24T/48T changover between inch ranges.

Some 13" lathes come with 2-knob, 2-lever equivalents that are almost equally illogical in their design.

Other than having an enclosed oil bath, can someone please explain how this is not a dreadful setback in the state of metalworking? :)

11-25-2009, 02:22 AM
I haven't looked at it yet, but I agree it's dreadful. What you can add to the confusion and ridiculousness is that the leadscrew is probably - what's the word for it- screwed. I tested a machine that wouldn't advance the carriage by the same amount for a given rotation of the dial. It had a horrible periodic error- and it was new.

Ok, I just looked at it. It's worse than I thought. Looks like a total nightmare to operate.

Paul Alciatore
11-25-2009, 02:56 AM
Get a used South Bend.

11-25-2009, 03:15 AM
I have this lathe and the only good thing I can say about it is the corsest feed on the 'fine' feed range is usally course enough for roughing, and its easy to change feed speeds while its running (Never spindle speeds! the feed gearbox has 0 momentium and is usally low speed so shifting it on the fly isent that nasty, Also the feed direction lever seems to shift gears that move way to fast to shift on the fly)
However most imperial threads are 24:48 or 48:24 so its not that bad, you basicly have a 'fine' and 'course' threading range, and the change gears are just for the odd pitch the gearbox could'nt easily do.
Unfrotualy I learned the 24:48 combo in my lathe doesnt fit in metric and actualy has to be replaced with the 26:52 gears, but same diff.

I have considered adding some sorta optical encoder/stepper motor insted of the gears so I could have automatic 1:2 and 2:1 ratio shifting on press of a button. Or just replace the whole threading gearbox with electronics.

11-25-2009, 03:46 AM
Given the choice between no lathe and the Hafco, I would have to pick the Hafco.

A difficult to use lathe is better than none at all.

If you want difficult, try doing precision work on a worn out lathe.

11-25-2009, 04:13 AM
Odd that.

I was in MachineryHouse aka Hare and Forbes aka HafCo near me in OZ only last week.

I had a good look at that lathe - or similar - and I thought it looked pretty good for the money:

I don't like "inch" lathes as we are "Metric" in OZ and I changed to metric years ago -and I ain't goin' back!!

I didn't realise or see that the one I looked at was "inch" and had an inch lead-screw - but I could live with it. I'd insist on metric if it were me.

I neither run nor seen it run, but based on my experience with HafCo stuff (lots) I'd be prepared to give it a go.

I have no problem with 4>6>8>+ (well - not quite) gear-box levers/settings nor can I see me doing too many change gear changes The top range settings on the setting levers without changing change gears is 0.054">0.003"/rev which should cover most turning jobs. With a change of two gears and re-setting up the change gear back-lash I get the lower panel with a feed/rev range of 0.013">0.001" - which I'd use only rarely.

Looking at the threading dial chart, my guess is that the lead-screw is 1/8" pitch and the threading-dial has 24 teeth. That dial is well set out.

The biggest PITA with metric threading dials - on metric lead-screws - is the number of different-tooth gears that are required for threading dials once you move outside the "standard/tabulated" range for the particular lathe and lead-screw combination. But they are quick and easy enough to make sufficiently well to do the job.

4 gear lever shifts is not bad for the range of speeds. It only takes a minute - or less. The "you beaut" OZ-made "Macson" (by McPherson, Melbourne) had all of that as well as some Dean Smith & Grace and similar others. If you really want to see complicated mult-shift per cycle gear changes - try a big turret or capstan lathe. I do like the lowest speed as many Chinese lathes low speed is too high for me.

The threading range of 4>60tpi is pretty good.

I don't see a 127 tooth gear for metric threads - it is a "connected pair" and if done well enough would suffice.

"Norton" QC gear-boxes are like exposed external head-stock gear-trains -and belt-driven back-gear trains - all of which just keep grinding away with little care or attention in some pretty gritty and abrasive environments. I'd go for gears enclosed in an oiled box - every time.

But I do take the OP's concerns seriously.

11-25-2009, 04:15 AM
Get a used South Bend.

He is not in the US...

11-25-2009, 04:29 AM
Hmmm, wonder if the EMCO they copied was an imperial one with a set of Metric change wheels or vicky verky, same saga as the 1,2,3 blocks with strange hole sizes??

Regards Ian.

11-25-2009, 07:14 AM
Yeah, a lot of these imports are Maxwell Support lathes: "Would you believe it has a quick change gearbox".

I have seen worse. That one at least allows you to do the common machine screw sizes and all the UNF/UNEF sizes for large screws. The large UNC sizes require a different change gear setting and a couple perverse common large UNC sizes need their own combinations.

With the 24/48 gear combination, you can do the standard machine screw threads 24, 32, 40, 48, and 56 plus 1/4-20, 5/16-18, 3/8-16 and all of the fractional UNF sizes except 1/4-28 UNF and all of the UNEF sizes. For bolts larger than 3/8-16, you have to swap those to gears to the 48/24 combination which will handle UNC 7/16-14, 9/16-12, 3/4-10, 7/8-9, and 1-8.

For UNC 1/2-13 UNC and UNC 5/8-11, you need weird gears, the 22 and 26. 13tpi and 11tpi are two digit prime numbers with nothing in common with other common UNC sizes.

For tiny 64tpi and 80tpi machine screws, you are screwed.; those are outside the range of the lathe.

Two other change gear combinations (which use the same pair of gears) cover all of the standard metric sizes except 0.25mm (101.6tpi), 0.35mm,(72.57tpi), and 5.5mm (4.6tpi). For those you are screwed, too.

On some of the chinese lathes that size and smaller, you can't even go from doing 6-32, 8-32, and 10-32 to 4-40 without swapping out change gears.
Look at the Grizzly 0602 (two knob job). The only gear combination where both knobs are halfway useful is the a=36 b=40 where you can choose 10, 12, 20,24, 40, and 48tpi but you gotta swap gears to get to 8/16/32tpi.
Your knobs give you 1/2/4 and 5/6/7 ratio selections. And by the thread
chart, only that one setting lets you use at least two settings on each knob. However, part of this may be due to the idiot who came up with the thread chart who made you swap gears to an otherwise useless combination to get the 14/28/56 sizes which are probably available just by setting one of the knobs to "III" (multiply by 7, only used on metric on the charts) from the 10/12/20/24/48/48 setting. But you are still stuck getting to 8/16/32 because the 5/6/7 knob lacks a "4" setting.

The lathe you pictured has one numbered knob that does 4,4.5,5,7, and a mystery fifth setting that isn't used on any chart put is probably 6. The lettered knob used in metric also has a 4, 4.5, 5, 6, 7 progression. and the I/II knob is 1/2. So, I suspect if you made up your own chart, you could get some more thread sizes without changing the change gears. And if you swapped out some of the gears inside the gearbox you could get more useful sizes without resorting to change gears. In fact, with 24,Z=48 gear tooth combination, I suspect you can get 12, 15, 16, 18, 20,21,24,27,28,30,32,36,40,48,and 56TPI using only the knobs.

I think the knob settings give the following ratios: multiply the three values together, then mulitply by 2/3 in the 24,Z=48 configuration:
{ 4, "D" },
{ 4.5, "C"},
{ 5, "B"},
{ 6, "A"},
{ 7, "E"}

{ 4, "2" },
{ 4.5, "3"},
{ 5, "4"},
{ 6, "5"},
{ 7, "1"}

{ 1, "MII" },
{ 2, "MI" }

I can't read the gear markings on the threads metrc pitches or the feeds/inch
or feeds/mm tables in the pic. I am guessng there is a 127 and 100tpi gear sandwiched between the 48 and 24 pitch.

On an old south bend quick change, you can do all the standard inch sizes; metric - well, that requires swapping something like a 127 tooth gear.

11-25-2009, 07:15 AM
I've got a HAFCO AL-960B and it has a standard Norton box. The lathe is superb to use, much better than the Myford ML-7 which it replaced. Threads from 4 tpi to 112 tpi. I agree that the other types of gearboxes are painfully limited.


My dad made up a sheet which shows many other threads which can be cut with the lathe, if anyone else has the same lathe I'll see if I can dig it up.

11-25-2009, 07:54 AM
I wonder how hard it would be to add a 'quick tumbler' 1:2/2:1 mod to the 1236 lathe, much like how the small lathes sometimes get a mod for easy carriage reverse

Still really tempting to try that optical encoder->stepper idea, could probley be very smooth since its a direct 2:1 or 1:2 ratio... just slap a small UC inbeween... let the mass of the spindle be your ramp up/down. mmm.

11-25-2009, 10:04 AM
He is not in the US...

Actually, I am. The HAFCO was just the best shot of the whole chart that I've found, but the PM1236 (sold in the US) is just the same, as are a bunch of others.

I've had a G4003 for years. Same basic lathe with a Norton gearbox. It works basically like the Taiwanese 12x36 that someone showed.

The basic flaw here,IMHO, is not the number of basic ratios available for multiplication. A lot of enclosed non-universal gearboxes won't do 13 tpi natively, for instance. It's really the hi-low division on the box, which is set so that you're guaranteed to change gears often. I see that even some of the Colchester-Harrison lathes have a hi-low division in their universal gearboxes. In those cases, though, only the coarsest pitches are going to require a change-over.

It might seem, as Click-and-Clack would say, that this thing is "totally unencumbered by the design process." More likely, someone at Shanghai #5 Lathe Gearbox Factory decided to produce an oil bath gearbox that could go on lathes destined for any market, as some sort of economy measure. Given limited space in the box, something had to go. In this case, that was operator sanity.

BTW, while Chinese/Taiwanese lathes may aesthetically knock off Emco, I don't think this gearbox even apes any of their designs. The current Emco gearboxes are 2- and 3- knobs only.

11-25-2009, 11:50 AM
the 4th knob on the 12x36 selects beween feed rod and lead screw, so your not even wearing out the lead screws support bearings when not threading.

11-25-2009, 12:35 PM
I've got a HAFCO AL-960B and it has a standard Norton box. The lathe is superb to use, much better than the Myford ML-7 which it replaced. Threads from 4 tpi to 112 tpi. I agree that the other types of gearboxes are painfully limited.


My dad made up a sheet which shows many other threads which can be cut with the lathe, if anyone else has the same lathe I'll see if I can dig it up.

My 1994 Enco 13 X 40 has this same type of gearing. It's got an inch leadscrew which is all I ever use for threads. It has two slide handles that move to change threading gears. I also have 8 or 9 change gears for metric and unusual threads.

It's very easy to use and works very well.

Don Young
11-25-2009, 10:40 PM
A real Norton-type metric gearbox as used by South Bend reverses the 1-8 section of the box so that the cone gears are drivers rather than drivens. This makes the threads coarser with the larger gears so that a 4-5-6 gear sequence can give you 1mm,1.25mm, and 1.5mm instead of 1mm, 0.8mm, and 0.666667mm as you would get with the cone gears as drivens. Some European lathes such as the TOS basically do this as well, reversing the feed through part of the gear train. I suspect an inch gearbox could be fairly easily installed in reverse on the right end of the feedscrew to do the same thing. You would have to do some rearranging of the gears in the left side so they would still make the threads finer instead of coarser. One of my "round tuit" projects that CNC may make redundant.

11-26-2009, 02:45 AM
The following table shows all the possible TPI's and metric mm pitches for this sort of lathe with the following change gears: 22, 24, 26, 38, 44, 48, 52

Standard Inch Thread Sizes

Change Change Change Change Gear Gear
Gear1 Gear2 Gear3 Gear4 M-Range Letter Number TPI
48 127 127 24 II A 2 4
48 127 127 24 II A 3 4.5
48 127 127 24 II A 4 5
48 127 127 22 II C 3 5.5
48 127 127 24 II A 1 6
48 127 127 26 II C 3 6.5
48 127 127 24 II A 5 7
48 127 127 24 II B 4 7.5
48 127 127 24 II C 1 8
48 127 127 24 I A 3 9
48 127 127 38 II C 3 9.5
48 127 127 24 I A 4 10
48 127 127 24 II B 5 10.5
48 127 127 22 I C 3 11
48 127 127 24 I B 2 12
48 127 127 26 I C 3 13
48 127 127 24 I A 5 14
48 127 127 24 I B 4 15
48 127 127 24 I C 1 16
48 127 127 24 I B 1 18
48 127 127 38 I C 3 19
24 127 127 48 II A 4 20
48 127 127 24 I B 5 21
24 127 127 44 II A 1 22
24 127 127 48 II B 2 24
24 127 127 52 II C 3 26
24 127 127 48 II B 3 27
24 127 127 48 II A 5 28
24 127 127 48 II B 4 30
24 127 127 48 I A 2 32
24 127 127 48 I A 3 36
24 127 127 38 I E 5 38
24 127 127 52 I A 3 39
24 127 127 48 I A 4 40
24 127 127 44 I C 3 44
22 127 127 44 I B 2 48
24 127 127 52 I C 3 52
24 127 127 48 I B 3 54
24 127 127 44 I B 4 55
22 127 127 44 I A 5 56
24 127 127 48 I B 4 60
24 127 127 48 I B 1 72

Standard Metric Thread Sizes

Change Change Change Change Gear Gear Pitch
Gear1 Gear2 Gear3 Gear4 M-Range Letter Number (mm)
24 127 120 48 I B 4 0.4
24 127 120 48 I C 4 0.45
24 127 120 48 I B 2 0.5
24 127 120 48 I A 4 0.6
24 127 120 48 I E 4 0.7
24 127 120 48 I A 2 0.75
24 127 120 48 II B 4 0.8
24 127 120 48 II C 4 0.9
24 127 120 48 II B 2 1
24 127 120 48 II A 4 1.2
24 127 120 48 II D 2 1.25
24 127 120 48 II E 4 1.4
24 127 120 48 II A 2 1.5
24 127 120 48 II E 2 1.75
48 127 120 24 I C 4 1.8
48 127 120 24 I B 2 2
48 127 120 24 I C 2 2.25
48 127 120 24 I A 4 2.4
48 127 120 24 I D 2 2.5
48 127 120 24 I E 4 2.8
48 127 120 24 I A 2 3
48 127 120 24 II B 4 3.2
48 127 120 24 I E 2 3.5
48 127 120 24 II C 4 3.6
48 127 120 24 II C 3 4
48 127 120 24 II C 2 4.5
48 127 120 24 II A 4 4.8
48 127 120 24 II D 2 5
48 127 120 24 II E 4 5.6
48 127 120 24 II A 2 6
52 127 120 24 II A 2 6.5
48 127 120 24 II E 2 7

It can also do a several hundred other pitches that work out to very odd TPI's and Pitches, some of which are very close to something useful.

It can't do 17 TPI, but can do either 16.9333 or 17.01818
It can't do 23 TPI, but can do either 22.9895 or 23.0303

The Artful Bodger
11-26-2009, 04:01 AM
My CQ6230a-1 (sold in New Zealand with a 'Morgan' brand stick on label) has a metric lead screw and cuts metric threads without too much head scratching and no gear changing except if changing between the fine and the coarse end of the range.

Imperial threads require require gear changes.

Being a newby I have not yet mastered the threading dial which was supplied with 3 pinions. I have read that different pinions are required for different ranges of metric threads because of the way metric threads are defined, but I do not really know.:rolleyes:

11-26-2009, 04:40 AM

See my post at:

Read these in conjunction. It should explain the need for multiple threading dial "chaser gears" when cutting metric threads on a metric lathe:




The Artful Bodger
11-26-2009, 03:25 PM
Thanks Oldtiffie, I will read through that all, nowadays it seems I must read every new subject several times before the concepts get firmly embedded!