Clarke CL250M Metric Screw Cutting Gears

[Brian WoodParticipant @brianwood45127]

I didn't bother with the fine feeds, the one that Ian quotes for 0.05mm does calculate correctly

Brian

[Ian MellorsParticipant @ianmellors72388]

Just looked again at the chart on the side of the lathe. Now it's all clear. There's lines joining the gears that are meshed.

 

Edited By JasonB on 10/01/2021 15:39:43

[Howard LewisParticipant @howardlewis46836]

Excellent!

Problem solved, confidence gained and fresh new expanded horizons ahead.

Howard

[Ian MellorsParticipant @ianmellors72388]

Although looking at it the 50 should mesh with the 45 on the 1.25 pitch…..

[Ian MellorsParticipant @ianmellors72388]

So on to the next question. The lathe is by no means a Super 7 that I last cut threads on. It does not have the ability to "drop in" on subsequent cuts so I guess the best way to do it is to stop the motor at the end of each cut, reverse the direction of travel, back the tool off and run back to the start. I'm thinking that the lead screw cannot be disengaged from the drive until the thread is completed?

[JasonBModerator @jasonb]

Posted by Brian Wood on 10/01/2021 15:07:43:

 

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

 

Just a couple of observations

1. this lathe does not have a tumbler reverse so unless you like cutting a lot of Left Hand threads you may need two idlers.

2. Like many of the far eastern lathes the spindle driver, 36T in this case is a larger bore and slips over the spindle within the nuts used to preset the bearings so not something you can change for screw cutting.

3. I can't get 1.25mm pitch from the last line, that gives 1mm pitch 40/60 = 0.666 x 1.5 =1. If available 50 : Idler(s) : 60 would give 1.25mm pitch. 60 : Idler(s) : 72 would also do and looks like you have those gears

Edited By JasonB on 10/01/2021 16:14:33

[JasonBModerator @jasonb]

Posted while I was typing, yes keep the feed engaged and run the motor backwards to take you back to the start with tool withdrawn.

[Brian WoodParticipant @brianwood45127]

Hello Jason,

Thank you for your invaluable checking. You are right of could, a second idler will do the reversing where needed

I didn't know about the bore of the 36 gear although the paper chart lists a 24 in the same position so I assumed, incorrectly it seems, that other gears could be fitted there as required. That adds to the complications

My error completely for 1.25 mm pitch. It should read 50–idler–60; largely academic now but the maths is correct!

Retiring damaged now!!

Regards

Brian

[JasonBModerator @jasonb]

Just to add a bit more damage, the last line of the paper chart will only give 0.1mm/rev if W is 36T

Edited By JasonB on 10/01/2021 16:35:06

[Brian WoodParticipant @brianwood45127]

Maybe Ian could follow the printed chart in the gear cover and dump the misleading piece of paper, it might have saved Howard and myself quite a lot of wasted time.

Regards

Brian

[Ian MellorsParticipant @ianmellors72388]

Many thanks to all who took the trouble to look at this little problem for me, much appreciated. When I first came across it the wife said "ask on a forum" – she was of course right

I also have found this invaluable resource for the future too

[Ian MellorsParticipant @ianmellors72388]

At last an update, managed to do a test thread cut last night, even though it was very cold in the workshop

Not a conventional thread being 10mm o/d (on a bit of spare 10mm stock brass rod) with a 1mm pitch but am very happy that it all works

[Brian WoodParticipant @brianwood45127]

Hello Ian,

It is good when it all comes together as it should isn't it? Thank you for the feedback.

The tread you cut may be unconventional but that is the real value of a lathe in that you can use it to cut any thread pitch you like on any diameter, something that is just not possible with fixed dies.

Regards Brian.

[Ian MellorsParticipant @ianmellors72388]

Posted by Brian Wood on 09/02/2021 09:08:42:

Hello Ian,

It is good when it all comes together as it should isn't it? Thank you for the feedback.

The tread you cut may be unconventional but that is the real value of a lathe in that you can use it to cut any thread pitch you like on any diameter, something that is just not possible with fixed dies.

Regards Brian.

Yes, I'd like to think that old Stewart Walker who taught me to screw cut back in the late 80's is looking down on me smiling

Never tackled an inside thread though …….

[Ian MellorsParticipant @ianmellors72388]

Might see if I can get hold of another gear set for a second 36 tooth, would make swapping between 1mm and 1.25mm pitch a bit easier. as long as the 36 will still fit on the lead screw spindle and mesh OK.

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