Metric thread dial obsession (going nowhere)

[Cenedd]

I'd like to be able to cut metric threads on my SC4 without keeping the half-nuts engaged. Why? I'm trying to follow the technique of threading away from the headstock so that I don't (through my own ineptness) over-run the end of the thread. I've tried it with the half-nuts engaged but between winding past the start point and coming back to it (to take up backlash) and then starting the lathe with the tool already engaged, it's a bit painful. Videos of imperial threads where they just throw the half-nut lever as the thread dial comes round make it look so much easier....and I'm jealous
I'm aware that if the thread pitch divides evenly by the lead screw pitch that I can do this without a dial but since my lead screw pitch is 2mm, that only leaves me with 0.25, 0.5 and 2mm pitches that would work. The first two are definitely (at least for me) in tapping territory rather than thread cutting and the last is only useful for M14 and M16.

There are plenty of dials available for the C2 and C3 and I understand I'll need a different gear for different pitches. I found this one that includes 14, 15 and 16 tooth pinions, but it'll be designed for a 1.5mm pitch lead screw. Will it even fit a 2mm pitch lead screw?

If not, presumably the only way to go is to cut my own gear? If so, would it be a 2 Module Cutter No7 I'd need for this? I get that module of a gear = (pcd of gear)/(number of teeth) but don't know how to apply that to a lead screw - so the 2 is a wild guess.

Many thanks,

Gareth

[lakeside53]

You don't need a real "gear".. just a disk with "notches" will work.

A decent design.. The EMCO dial has three notches gears that you engage which ever you need in the lead screw.

https://www.google.com/search?rlz=1C...843b-FyyZJ5QM:

[Erich]

You need a gear with a "circular pitch" of 2 mm. Essentially you need a worm gear designed to work with a 2 mm pitch worm. The number of teeth on said gear is left up to the reader to figure out.

[danlb]

You have a metric lead screw, so I'd suggest buying the threading dial for an SC2 which also has a 2mm pitch lead screw. Only $15 (US) from a european merchant.

http://www.axminster.co.uk/axminster...dicator-600855

I find it interesting that Sieg (maker of your lathe) does not provide a threading dial based on the assertion that it stops quickly enough due to electric braking of the motor.

Dan

[Cenedd]

Thanks Dan. I've seen the Axminster dial but I believe from what I've read, the SC2 has a 1.5mm lead screw. Very happy to be proved wrong here, it'd make my life a little easier! Agreed, it's odd that one isn't available even as an add-on....but neither, it seems, is a carriage stop (I know I don't have a clutch so cannot hit a stop under power and expect it to stop in a 'nice' way but it'd be useful to wind back to as a start point). LMS seem to do one but the carriage and import duty make it prohibitively pricey. Will likely have to make one, but I'm up for being lazy when it doesn't cost much

Lakeside: A disk with notches sounds feasible. Might have to knock something up and see how it fits rather than try to over-think it. The Emco design looks good - would have to modify any design to get around the lead screw cover...but that's another issue.

Erich: Ah, so that sounds like it would rule out a gear designed for a 1.5mm lead screw fitting a 2mm lead screw. It also sounds like it may need a different module of cutter for each different number of teeth. Nothing's ever got a nice simple answer....I must be asking the wrong questions!

Many thanks,
Gareth

[old mart]

Last time I cut a thread away from the chuck, I got a left hand thread, that was ok as I was making screws for a four jaw independent chuck.

[The Artful Bodger]

You might find it easier to make a 'peg wheel' than a gear..



This is the X axis power feed I made for my mill.

[Cenedd]

Old Mart: You have to reverse the spindle too (be careful if you have a screw-on chuck) and have the tool upside down or rear-mounted. Good video here if it's of interest (and apologies if I'm teaching you to suck eggs here): https://www.youtube.com/watch?v=Z-dqOi_z5bk

Artful Bodger: Now that's an interesting idea. Do you have a project page for your power-feed project by any chance? Now I've got my fly cutter working (CBN cheap CCGT from China gives a nice finish on HRS), at 10 minutes per pass, I'm feeling the need for some power feed!

I've ordered 'Screwcutting in the lathe' by Martin Cleeve which I'm told covers the fundamentals of thread dials and the gearing from the ground up. I've a feeling that trying to 'cut and paste' bits of other people's projects without really knowing what I'm doing isn't going to cut it here. Should give me a better idea of how many teeth required on the pinion for different threads and what to mark on the dial.

[IanPendle]

The Martin Cleeve book is a good choice, but having studied it re metric threading dials, they are never going to be as simple or convenient as the those for the imperial system.

The metric version (3mm leadscrew) of the Boxford lathe (a quality UK copy of the Southbend design) uses a sort of double pinion on the bottom of the threading dial's shaft to engage the with the leadscrew. The pinion is one piece, with two different tooth counts (20 and 21 I think - NOT sure!). It uses an intermediate mounting block with two holes, one above the other. Depending which mounting hole you use, either the 20 or 21 tooth pinion teeth engage the leadscrew. This block also has an angle face so that the (straight) pinion teeth engage the leadscrew at the threads helix angle. The Dial has both numbers and letters and you have to consult the supplied chart to see which combination of mounting block hole and dial marking to use for each thread pitch being cut.

I no longer have my Boxford, but there is a Boxford Yahoo group where you could probably find more details - especially the reference sheet for the pitch/dial combinations.

This may give you some ideas, although you would have to do different calculations for a different leadscrew pitch (I think?).

Ian.

[The Artful Bodger]

Artful Bodger: Now that's an interesting idea. Do you have a project page for your power-feed project by any chance? Now I've got my fly cutter working (CBN cheap CCGT from China gives a nice finish on HRS), at 10 minutes per pass, I'm feeling the need for some power feed!

I am sorry there was no project page and no drawings as I built it on the fly. However most of the required detail is in the picture.

The pin wheel is 10mm aluminium plate with the pegs being bits of nails cut and set in epoxy, the worm was turned on my lathe and as you can see the pitch is about 3.5mm. The motor is a high quality electric motor that was salvaged from an old magnetic tape drive from the main frame computer era and the speed is controlled by a PWM circuit I found online although now I think you can buy ready made DC motor speed controllers from China.

The peg wheel is loose on the shaft and has a dog clutch mounted to it, you can see part of the clutch in the picture.

There is a sleeve loose on the shaft with a pin engaged in a key slot in the shaft. The sleeve has a hand wheel at one end and a dog clutch at the other.

I can pull the sleeve to disengage the clutch and use the handwheel to manually more the table feed.

It rattles a bit in use but has not give a bit of trouble in several years.

John

[Paul Alciatore]

I have a background project to design a universal thread dial. One problem part is the needed gear that meshes with the lead screw and I have given it some thought. Before the advent of 3D printers, I thought that the best way to be able to make these gears for any lathe was by using a design like the lantern pinions that have been used in mechanisms like clockworks. These pinions consist of a pulley like wheel with a number of holes drilled at the "tooth" locations. Then a number of round, steel pins are placed in those holes for the actual teeth. There are reasons why this works for clockworks that have to do with the fact that they are driven by springs on the slow end of the gear train. That would no be true for a thread dial, but I reasoned that there is a very low load on these gears, essentially it just turns the dial so there is only the drag of the lubricating oil. So The wear on the gear and on the lead screw would be very small.

I envisioned a purpose built, indexing device that could be set to the angle of the lead screw helix so the holes would be at the proper angle.

In this day of 3D printing, I think this gear could be 3D printed and it should work OK.

Either of these methods should be OK for making a gear for a thread dial. For the metric dials, you could make several and include some kind of quick change feature: a thumb nut, a click-on/click-off detent, a quick removing pin, etc.

BTW, thanks for bringing up the subject. I need to resurrect that project.

[Yondering]

I've tried it with the half-nuts engaged but between winding past the start point and coming back to it (to take up backlash) and then starting the lathe with the tool already engaged, it's a bit painful.

I'm surprised nobody has pointed out that you can cut metric threads AND disengage the half nuts in a fairly simple procedure. You can thread normally, and disengage the half nuts at the end of the thread, but then shut off the lathe immediately. Back the tool out then run the lathe in reverse; when the thread dial reaches the same point again, re-engage the nuts and let it run the carriage back to the starting position. You can disengage the half nuts at that end too, just make sure to use the same process. The general idea here is to use lathe power to rewind the carriage back to the starting position, so the half nuts are always engaged at the same position every time.

It's pretty easy to cut metric threads this way when you get used to it.

[Cenedd]

Yondering: I'd try that but out of the box, there is no thread dial at all and it appears that any that Sieg do make are sized for a 1.5mm lead screw and mine has 2mm. As far as I can tell, 2mm is the least helpful pitch for a leadscrew as it directly matches the least threads and the least useful at that. I intend to cut an M16 thread (2mm pitch) just so I can test it out! (I'd go M14 but the corresponding hole is too big for any taps I have and just too small to take the internal threading tool I have)

Paul: Apologies if I end up causing you any sleepless nights due to not being able to get cog design out of your head....you could always try counting teeth!
3D printing may actually be a possibility - a friend of mine carelessly mentioned that he'd got one! An easily replaceable (just print another) gear in plastic would also be more leadscrew-friendly than metal. Now I just have to work out what to print!

Artful Bodger: Hadn't thought of that. Wonder if I've chucked out all the Ultrium tape drives that were 'useless' and whether the motor would be big enough. Thanks for the info.

Ian: It may even end up easier just to make two or three different units complete with dial and gear and have them on some sort of quick-change mount - a QCTD if you will. (not enough confusing acronyms in the industry already! )

The book has turned up. Amazon were very slow - nearly a whole 12 hours from when I ordered it late at night! It seems good so far but I think it's going to be a hard slog. Worth it to understand what I'm talking about though ....hopefully!

[GadgetBuilder]

Does your lathe have a spindle reverse or must you add that to thread going away from the headstock?

Now that you've got Cleeve's book you might consider a dog clutch rather than a threading dial(s). It handles both metric and imperial sync and is faster than using a threading dial because it syncs in one turn of the spindle. I added a dog clutch based on Cleeve's description to my 7x12, including auto-stop so I can cut to a shoulder towards the headstock with no drama.
See: https://www.youtube.com/watch?v=tWxGEBEjOuk

John

[danlb]

One trick to try when experimenting with tracking threads; Put a fine tip magic marker in the tool holder. Use a clean and smooth steel rod in the chuck. This allows you to "cut" the threads in ink with no danger of crashes. After success you can clean the ink off with a rag and start over.