Clarke CL250M Metric Screw Cutting Gears

[Ian MellorsParticipant @ianmellors72388]

Anyone fitted these?

Tried for hours today to fit them to give a 1mm pitch but the problem is the number of teeth on the Z1 and Z2 combinations mean that the large gear on Z2 cannot fit to the small gear on Z1 before the other gears touch

Pulling my hair out with this.

If anyone has done it a photo of the setup would be a great help

[Ian MellorsParticipant @ianmellors72388]

[Howard LewisParticipant @howardlewis46836]

It might be a good idea to post a photo of your set up, for people like me who are not familiar with the machine. .

1 ) Will swinging the banjo not allow the gears to be positioned to give a correct mesh?

2 ) Will inserting an Idler allow the gear train to mesh correctly?

One or more Idlers will not alter the ratio. The important gears are the Driver and Driven.

Assuming a 1.5 mm pitch Leadscrew you could be looking at a 20T Driver with a 30T on the Leadscrew with one or more Idlers in between.

With just one Idler, you will need to reposition the Tumbler Reverse to ensure that Chuck and Leadscrew rotate in the correction direction to produce a Right Hand thread (If that is what you desire )

Alternatively, if you can fit a second Idler you will not need to use the Tumbler reverse.

Presumably, you are looking foe a 1 mm pitch thread that is larger than 7 mm Coarse, other wise you could use Taps and Dies. Although you can get Taps and Dies for 1 mm pitch Fine threads larger than 7 mm.

Howard

[Ian MellorsParticipant @ianmellors72388]

I'll take some pics later, just put the lathe away and swmbo is putting away Christmas in the same space lol

It's back to stock now, but I can put the two gear sets together to illustrate the problem.

I'm sure I'm missing something obvious

[Brian WoodParticipant @brianwood45127]

Ian,

Do you know what the leadscrew pitch is? It will be either 1.5 mm or 16 TPI

And what change wheels do you have with the lathe? I have looked at the Clarke download for the lathe. The choice seems to be limited to 72, 19, 76, 24 and 90 teeth but you may have others.

With that sort of information it might be possible to work out a gear train

Regards

Brian

[JasonBModerator @jasonb]

You should be able to loosen the pegs that the gears rotate on and slide them along the banjo to allow other sizes to mesh, Banjo pivots so final mesh with spindle gear can be adjusted

[Howard LewisParticipant @howardlewis46836]

In addition to the five gears listed by Brian there is an accessory Metric screw cutting kit Part no. 761074 which appears to contain seven more gears.

The standard gears are a little unusual, where often you find the Tooth Count incrementing by 5T, but there may well be some other very good reason why the standard supply gears have those particular tooth counts. (Possibly a Leadscrew pitch which is, to our eyes, unusual, or some other gear train within the machine. )

Since the spec only mentions Metric screw threads, (No mention of Imperial ) I would assume that the Leadscrew would be a Metric pitch, 1.5 mm probably.

You need to list what gears you have, (if any ) in addition to those listed in the manual, by Brian. The obvious ratios available seem to be 24:72 giving a 3:1 reduction (for a 0.5 mm pitch ) or 19:76 (giving 0.375 mm pitch ) with a 1.5 mm pitch Leadscrew.

Have not given it any thought but others (possibly non standard ) can be arranged by making up a compound Idler and using the 90T it may be possible to arrive at 1 mm pitch. Otherwise, one or more gears from the the Accessory set will be needed to cut a 1 mm pitch, ( 36T driven by the 24T or 60T driving the 90T come to mind, )

What is the train that you are trying to set up?

If you cannot set a suitable train with the gears already in your possession, it MAY be possible to augment with ones from C2 abd C3 mini lathes, which are 1 Module. That is not to say that they would necessarily be an interchangeable fit. Bores or keyways may be different which could mean that a "hybrid" specifically for your machine harder or even impossible to make.

To check your gears, IF they are 1 Module; the OD will be the (Tooth count +2 ) mm., so a 24T gear would be 26 mm diameter, as an example.

For other times, IF mini lathe gears could be used a metal 63T gear is available, which would would allow you to cut acceptably close approximations to Imperial thread pitches.

Brian can go into far greater detail on this than I can. (He has written a book about it )

Howard (Smileys!!!!!!!!!!!! Forgot to include a space )

Edited By Howard Lewis on 09/01/2021 17:31:04

[Brian WoodParticipant @brianwood45127]

Howard,

I have been playing about with other gear sizes. Unfortunately Ian's C1 lathe uses change wheels of 10 mm bore; I had hoped he could extend the range with C2 gears but these are 12 mm bore.

So he is stuck with the gears I listed and the closest he can get to what he wants is 2mm pitch, geared as 24 drives 19. Have assumed a leadscrew pitch of 12 TPI. He could make up a 2:1 reduction with C2 gears, sleeved to run on an intermediate stud and get there that way

Regards

Brian

[Ian MellorsParticipant @ianmellors72388]

Howard is right, I have the 761074 set and the instructions say use the standard 36 tooth on the spindle from the chuck, a 24/42 combination, then a 40/48, then final drive to the lead screw of 45 tooth. The problem I have is the 40/48 which does not leave room for the 48 to mesh with the 24 before the 40 hits the 42….

Edited By Ian Mellors on 09/01/2021 20:57:44

[Ian MellorsParticipant @ianmellors72388]

[Ian MellorsParticipant @ianmellors72388]

You can see I've recorded the standard gearing above the printed table

[Howard LewisParticipant @howardlewis46836]

The way that I read it, the 36 meshes with the 24, the 42 meshes with the 40, and the 48 meshes with the 45 on the Leadscrew.

This gives an overall ratio of 1.68:1, implying a Leadscrew pitch of 1.68 mm (0.0661417 inches.) to cut a 1mm pitch thread.

If the Leadscrew were 1.5 mm pitch, we would be looking for a ratio of 1.5:1 which the 36:24 would give, just needing two simple Idlers to produce a 1 mm pitch Right Hand thread (Assumes the Leadscrew to be a Left Hand thread )

A 15 tpi thread has a pitch 0.06666666.inch. Since the error starts at the fourth place of decimals, this might be close enough? But 15 tpi would be a strange pitch!!!

Or have I got it completely wrong?

Brian, put me out of my misery, please

How far does the Saddle move for one complete revolution of the Leadscrew? That would tell us the pitch of the Leadscrew.

Howard

[Brian WoodParticipant @brianwood45127]

Hello Howard and Ian,

I would love to clarify matters but I am now totally confused. I had no idea there was a second set of gears available nor how they are made up and the chart doesn't help me as I can't get values I trust from it.

It would help a bit if we knew what the leadscrew pitch is. These mini lathes have leadscrew pitches of either 16 TPI or 1.5 mm, not odd values as Howard is struggling with

Regards Brian

[Pete RimmerParticipant @peterimmer30576]

The way I'm reading it, is that Ian finds that he is unable to mesh the 48 of Z2 with the 24 of Z1 without the 40 and 42 fouling each other.

I'm not familiar with the machine but the obvious solution would be to flip Z2 over so that the 40 is on the outside. It would probably require a spacer behind the carrier, and Z3 would also require a spacer so it lines up with the 40T of Z2.

Edited By Pete Rimmer on 10/01/2021 11:56:34

[Howard LewisParticipant @howardlewis46836]

Hello Brian and Ian,

I take consolation that Brian is confused, I most certainly am.

Like Brian, I would have expected a 1.5 mm pitch Leadscrew. In which case I would have set the 36T to drive through two simple idlers, (not compound gears ) to the 24T on the Leadscrew.

To cut a thread with a finer pitch than that of the Leadscrew means that the Leadscrew has to turn slower than the workpiece. So turning the Leadscrew faster than the work, by a ratio of 1.68:1 implies a finer pitch of 0.5952381 mm or 0.0234345 inches for a 1 mm pitch thread. . Both of which are strange numbers for any thread pitch, to my mind.

42:40 is a ratio of 1.05:1, but reversing the 45:48 train gives a ratio of 1.06666667 which does not provide a 1:1 ratio within the idler train

Ian, Please measure how far the saddle moves for one complete revolution of the Leadscrew with the half nut(s ) engaged. This will be a starting point, perhaps.

P S It may be of interest to others to know the tooth counts of the gears in the 761074 Accessory set

Howard

[Ian MellorsParticipant @ianmellors72388]

I'll see if I can work out the lead screw pitch. To put another spanner in the works the standard set that gives 0.05mm/rev are set up as follows:

36 to 72 24 to 76 19 to 90, so the order of the wheels in the table does not necessary correspond to how they are fitted….

[Ian MellorsParticipant @ianmellors72388]

Metric set consists of:

40, 42, 45, 48, 50, 54, 60

[Brian WoodParticipant @brianwood45127]

Hello Ian,

I agree the feed rate you listed fitted up as 36/72 x 24/76 x 19/90 gives 0.05 mm per revolution with a 1.5 mm pitch leadscrew.

However, using exactly the same chart layout ie 36/42 x 24/60 x 40/72 gives a pitch of 0.2857 mm per revolution with a 1.5 mm pitch leadscrew—-clearly NOT 0.5 as the chart says. You can see why I am confused.

If I knew the values of all the gears that are available, and the leadscrew pitch I could attempt to work out an alternative table for you.

In the meantime, this will give you 1.00 mm screw pitch— 36/30 x 40/72 assuming the leadscrew is 1.5 mm pitch and a 30 tooth gear is available

Regards Brian

[Nick Clarke 3Participant @nickclarke3]

This table C1 Imperial Thread Cutting (arceurotrade.co.uk) that I found through an Internet search appears to suggest the leadscrew Pitch is 1.5mm

[Ian MellorsParticipant @ianmellors72388]

Sadly no 30 tooth wheel available. Is it possible that one of the small wheels is not actually used and jyst acts as a spacer? The pegs hold 2 wheels and there are no spacers etc to use in the set

[JasonBModerator @jasonb]

If it is a 1.5mm pitch leadscrew then the chart gives the right ratio but you need a bit of cunning to work it out.

36 on spindle drives the 42 = 0.857

24 is there as a spacer so the 42 does not move about.

42 drives the 48 = 0.875

40 drives the 45 on the lead screw = 0.888

So multiply thos etogether 0.857 x 0.875 x 0888 = 0.666

0.666 x LS pitch of 1.5 = 1

Sketch shows there should be no clash of gears

Edited By JasonB on 10/01/2021 13:32:40

[Ian MellorsParticipant @ianmellors72388]

Nice one! I'll give it a go, still trying to stuff Christmas in the loft (which is where my workshop is too)

[Howard LewisParticipant @howardlewis46836]

Since no 30T is available, could you set up 36::45:60:72, assuming that the Z1 and Z2 studs can be adjusted to accommodate these gears?

You will need to turn up a couple of spacers to go on those studs, to keep all gear meshes in line..

The overall ratio required is 1.5 :1. By virtue of the 36:72 being 2:1 but modified by the 45:60 being 0.75:1 to give 1.5 overall.

If this is successful, I would suggest calculating a table to cut the common Metric pitches using the simplest gear set ups available. It can then be printed and laminated and kept by the lathe for future use. (Ditto if you want to do the same for Imperial, although even with a 63T gear some pitches will not be exact.

You could have hours of fun (and frustration ) making up a spreadsheet for all possible combinations of the gears.

Most of the possible results will probably be non standard pitches, though.

Maybe the quicker method would be to start by calculating the ratio between Mandrel and Leadscrew for the required pitch and then to find combinations of your gears that will produce the required overall ratio.

Brian's book could be a help, although the tooth counts will differ from those that you have.

Possibly, if you wanted to cut Imperial threads of a size that cannot be produced with Taps and Dies, you could buy a 63T gear, and sleeve the 12mm bore down to 10 mm for your C1. Alternatively, you could open up the bore to say 14 or 16 mm and make a thicker walled sleeve to bring it back to 10 mm Although you would ideally need a 4 Jaw independent chuck to ensure that the bore was concentric before you start.

Bear in mind that cutting, say, a 7/8 x 9 tpi thread is going make a C1 grunt unless you are very gentle, because as the standard treads become larger, the depths become larger, calling for more shallow cuts to produce the end result.

Howard

[Howard LewisParticipant @howardlewis46836]

Having just read Jason's post, (written whilst I was thinking and typing ) it is clear that you do need to turn up a couple of spacers so that you can exploit the maximum number of gear combinations to produce the thread pitches, or feed rates that you want.

For pitches of: 0.25 mm the overall ratio is 1:6, 0.5 mm is 1:3, 0.75 mm is 1:2, 1.00 mm is 1:1.5,

1.25 mm is 1:1.2, 1.5 mm is 1:1, 1.75 is 1:0.8571428, and 2 mm 1:0.75

Fine feed, 19:24:76:90 should give a finest feed rate of 0.0666666 mm /rev for a finishing cut.

Howard

[Brian WoodParticipant @brianwood45127]

Jason,

Well done, I hadn't figured on gears being used as spacers, missed it completely

In the meantime I have worked out a greatly simplified chart for all the metric ratios quoted on the machine chart

I can't present a properly drawn out table so Ian will have to construct one for himself from these values

Spindle [W] Driven Driver Leadscrew [Z3] Pitch mm

36 72 40 60 0.5

36 48 40 45 1.0

42 Idler 90 0.7

48 Idler 90 0.8

40 Idler 60 1.25

Regards

Brian

Sorry about the compression, it didn't like the spacing I presented the values in

Edited By Brian Wood on 10/01/2021 15:09:14

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