Metric thread on imperial lathe, without reverse.

[Vernonv]

I guess that you don't have the metric thread cutting gears for your lathe. They came with mine. I am going to have another look at my clutch/brake setup and take some pics. I would like to fix the brake but as the lathe is not really mine anymore I don't plan on spending much time or money. Might be a good idea to have some photos for when it is gone. Wont be far away tho.

No unfortunately the only change gears I got were the standard imperial ones - 30 (spindle), 72 (idler) and 120 (quick change gearbox). I can swap the 72 and the 120 around to give me a few more options. I would love a decent set of change gears, but it's cost prohibitive.

What change gears did you get with yours?

I took a photo of my clutch brake setup, so will post when I have my phone handy.

[Ueee]

What gears are needed Vernon/Dean? And what is the dp?

Ew

[Vernonv]

What gears are needed Vernon/Dean?

Not exactly sure, as I don't know what was available originally, but I guess a 127 would probably be a good starting point.

And what is the dp?

Don't know.

[chambezio]

I am looking forward to see where this thread leads. My 100 (plus) year old metal lathe is German in origin but is set up with the change gears for cutting imperial threads. Because of its age there is no thread dial. So to cut any thread, after you instal the appropriate gears you have to reference the cutting with marks on the chuck and headstock as well as a mark on the lead screw. I cut my first thread 1" X 8TPI using the above method, yes slow and tedious but I got a result. By the way the information is coming in with this thread, I may be able to cut metric threads as well

[Vernonv]

OK, so I got around to testing the clutch with the motor in reverse, and low and behold it works fine ... I'm not sure what strange phenomenon I experienced last time I tried it. Now I just need to locate a change over switch.

Dean, here is a pic of my clutch/brake setup for reference. If you need any more pics/info, let me know.

20131102_082314.jpg

[Ueee]

100% is a lot.

I think I've just done the maths on cutting a 1.5mm pitch on an 8 tpi leadscrew.
Now if I'm right you get exact pick up every 127 pitches(60 turns on the leadscrew). Only 22 of the other turns will the leadscrew be within 36 degrees of TDC with the chuck is at TDC. So granted....... it could be tricky on the fly and at 75rpm... slow.

But this idea might work.
Make up a gage that allows you to move the carriage 7.5" +/-1/32(you just need to be on the correct "turn" of the leadscrew"
Cut your thread, turn the lathe off, open half nuts, move the carriage back 7.5" close halfnuts, cut thread, repeat.

I cant check my maths on the lathe as its metric.

IF the above idea works, another idea you could make up a thread chaser dial with a 60 tooth* gear, wouldn't that let you pick up on the fly?

Granted this wont exactly be fast as you'll effectively be cutting a 7.5" long thread regardless of how much you want.(though you do get quick return unlike full reversal, if the chaser works you wouldn't even be turning the lathe off)

Stuart

p.s. Surely I'm missing something?

0.5 pitch = 2.5" reset
0.25 pitch= 1.25" reset

0.5 pitch = 20 tooth gear
0.25 pitch = 10 tooth gear

p.p.s I've got to be missing something!

No, your dead right. Just did some testing. Of course I have a 4tpi screw, but the distances stay the same, the number of turns is halved....I don't quite get that. I didn't even measure the distances though, I just counted the number of turns of the screw with the counter.

It may only work with a 127 tooth change gear, the math may be different for any other gears.

Pitch of thread to be cut x 127/pitch of leadscrew in metric (ie 3.175). The resulting number is the number of turns of the leadscrew between pick up points. I left the lathe running and just wound the saddle back to the start of the thread and waited for the right amount of numbers to go by, starting as soon as I dissengaged the half nuts. I'd does take a while even at 200rpm.

Cheers,
Ew

[Oldneweng]

I got the 127 tooth gear with my lathe. This is swapped for the 120 tooth gear for metric threading. Pretty standard on a lot of lathes.

My clutch/brake setup looks identical to yours except for one slight difference. You appear to have a lot more thickness of friction material on the brake disk. I have a piece of leather (I think) about 2.5mm thick. What is yours made of do you know?

What gears are needed Vernon/Dean? And what is the dp?

Vernon needs a 127 tooth gear.

Dp. Beyond my current ability to calculate. Have measured the following.

Outer diam 273.05. I used my 12 inch dial caliper for the first time for real!!

Root circle diam 264.414.

127 teeth.

Dean

[Ueee]

12 dp (OD in imp is 10.750", 127+2 gives you the OD of the gear, 129/10.75 is 12), i don't think i have a cutter.
Is that the only gear you need? Mine has 30/35/45/54. All the imp threads are cut with the 30 as the stud gear and the 45 as the gearbox gear. The metric are a combo of all 4, plus the 120/127t gears.

I don't even think i have a lump of steel/CI that big, Vernon if you can find me one (maybe a barbel weight, or weld up a ring and add a hub and spokes like Michael has done before) i'd be more than happy to cut you the gear. I'm sure i could find a 12dp No 2 cutter easy enough.

Cheers,
Ew

PS, the clutch is identical to the Nuttal branded clutches on my shaper and LeBlond lathe. Mine have some sort of black lining, bit like brake pad material, probably asbestos....

[Stustoys]

Hi Ewan,
Thanks, good to hear my maths still works now and then lol

I'd have to think more about "close approximation" change gears. Current thinking is, as long as 127*pitch is closer than say 1/4 the pitch of the leadscrew over the reset distance, you will still get repeat pick up.............not sure.

As your formula show, The pick up points are "Pitch of thread to be cut x 127" so the distance stays the same, just the number of turns changes for different leadscrew TPI

Great idea to use the thread chaser as is.

Its just occurred to me the time would be the same regardless of pitch, even though the reset distance is shorter. 127 turns = 127 turns. Just at finer pitches the leadscrew turns slower over a shorter distance.

Now......... is this any use on a metric leadscrew lathe?

Stuart

[Stustoys]

Hi Ewan,
Thanks, good to hear my maths still works now and then lol

I'd have to think more about "close approximation" change gears. Current thinking is, as long as 127*pitch is closer than say 1/4 the pitch of the leadscrew over the reset distance, you will still get repeat pick up.............not sure.

As your formula show, The pick up points are "Pitch of thread to be cut x 127" so the distance stays the same, just the number of turns changes for different leadscrew TPI

Great idea to use the thread chaser as is.

Its just occurred to me the time would be the same regardless of pitch, even though the reset distance is shorter. 127 turns = 127 turns. Just at finer pitches the leadscrew turns slower over a shorter distance.

Now......... is this any use on a metric leadscrew lathe?

Stuart

[Oldneweng]

12 dp (OD in imp is 10.750", 127+2 gives you the OD of the gear, 129/10.75 is 12), i don't think i have a cutter.
Is that the only gear you need? Mine has 30/35/45/54. All the imp threads are cut with the 30 as the stud gear and the 45 as the gearbox gear. The metric are a combo of all 4, plus the 120/127t gears.

I don't even think i have a lump of steel/CI that big, Vernon if you can find me one (maybe a barbel weight, or weld up a ring and add a hub and spokes like Michael has done before) i'd be more than happy to cut you the gear. I'm sure i could find a 12dp No 2 cutter easy enough.

Cheers,
Ew

PS, the clutch is identical to the Nuttal branded clutches on my shaper and LeBlond lathe. Mine have some sort of black lining, bit like brake pad material, probably asbestos....

You could have told me you wanted the figures in imperial and I wouldn't have converted them.

This is the Gear Train Ewan. 120 tooth at the bottom(Duh). The centre gear adjusts up and to the left to allow for the extra diam. That is all the external gears.

Gear Train.jpg

Dean

[cba_melbourne]

Hi Ewan,
Thanks, good to hear my maths still works now and then lol

I'd have to think more about "close approximation" change gears. Current thinking is, as long as 127*pitch is closer than say 1/4 the pitch of the leadscrew over the reset distance, you will still get repeat pick up.............not sure.

As your formula show, The pick up points are "Pitch of thread to be cut x 127" so the distance stays the same, just the number of turns changes for different leadscrew TPI

Great idea to use the thread chaser as is.

Its just occurred to me the time would be the same regardless of pitch, even though the reset distance is shorter. 127 turns = 127 turns. Just at finer pitches the leadscrew turns slower over a shorter distance.

Now......... is this any use on a metric leadscrew lathe?

Stuart

Stuart, albeit I admire your math skills.... but.... is it not more convenient to leave these half nuts closed until the thread is finished, and turn this non-power-reversing spindle back manually the few turns between passes? Unless you are cutting a longish "allthread" section, it is probably faster turning the spindle back by hand, than it is to open the half nuts and then having to do your maths and rotate the spindle up to 127 turns to find the next sync point. Also consider that if you leave the half nuts closed, you avoid the considerable risk of syncronizing to a "false" (false = looks right but may be slightly off) pick-up point. Chris

[Vernonv]

12 dp

That's what I also worked it out as after Pipeclay gave me the formula via PM.

The other possible issue with getting gears made is the odd star shaped hub, which I would imagine would be a little difficult to replicate.

I'm going through now what gear combinations might be required to be able to create metric threads.

I'll get pics of the brake surfaces and the gear hubs when I get to the shed later.

[Vernonv]

OK, I have been back at the shed. Here are some pics of the brake setup. First one is the metal face, which I think is cast into the assembly cover. The second is of the friction material.

20131103_081219.jpg20131103_081237.jpg

The next set of pics shows the gears and their odd star shaped hub. Is that hard to replicate?
20131103_081547.jpg20131103_081528.jpg

So I've done some calculations on the gears required for metric threads from 0.5 up to 4.5. With the addition of 127, 30 and 35 gears I cover all thread pitches at an error of <0.00001% (a lot are actually spot on). In fact I can drop the 127 and still achieve an error of <1% on most except for 1.25 and 2.5 (any multiples of 1.25) which are <2%.

One thing I have also worked out is that none of the "new" gears would actually need to have the star shaped hub as they are all idler gears - so they could just have a round hole to fit the idler post (see pic above).

[Michael G]

Yes, that star shaped hub will cause some angst. I think I'd be drilling 8 holes on their PCD (bit of layout work required) then boring the main hole and finally finishing up the star with a file or two.
That arrangement is only for keying the 120 to 127 gears together. An alternative may be to make up a new 120t gear as well and use a normal key and sleeve. The fist option is probably slightly less work but will require more hand work than the second.

Michael