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Clark CL430 question on threads

Need to know pitch of leadscrew

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fastdave24/05/2020 15:24:43
18 forum posts

need newbie help (that's the way it feels).

I have owned and used this machine for about a dozen years, an it hasn't failed me - I built the Milling cutter chuck and made a test bar from Harold Hall's wee book - Lathework - a complete course fairly early on, and have done numerous projects with it.

The latest, was to create an adaptor (some of you may know - for what?) which would be 18 x 2.5 to M33 x 3.5.

I discovered to my horror, after purchasing the smaller diameter set of taps, that the 'ole 430 wouldn't cut 3.5 - it only went up to 3.0.

I am struggling with basic arithmetical errors, and knowing it is data dependent, I need to know the pitch of the leadscrew for the 430, which I don't seem to be able to find anywhere - this is essential for future use, and I need to know if there is any way I can make this lathe cut 3.5 pitch - in my head I think I can, but all is pointing to the restriction of the leadscrew.

Can anyone help?

I am looking into another lathe, and fancying a Boxford, Myford or Colchester, but transport is my big problem, and I would struggle if it had no metric ability.


Howard Lewis24/05/2020 17:22:51
3272 forum posts
2 photos

Has ther 430 a handle on the leadscrew?

If it has, you can measure the pitch. Give the handle a couple of turns, with the half nuts engaged, to take out any backlash.

Set a DTI against the Saddle,

Rotate the handle, in the same direct, for one or more complete turns.

The DTI reading, divided by the number of turns should tell you the pitch of the Leadscrew.

Say 1 turn moves the Saddle 0.125" Leadscrew pitch = 8 tpi, or if Metric, 3 mm

If you are lucky, you will have a DTI which uses the same units as the pitch of the Leadscrew. If not then you will need to use a calculator to convert from Imperial to Metric, or vice versa.

If you have any doubts, repeat the exercise, but do ensure that the movement is always in the same direction, to avoid any discrepancies caused by backlash.



Martin Connelly24/05/2020 17:32:50
1369 forum posts
159 photos

The bigger the pitch the further the carriage has to go per revolution of the spindle. The restriction may be due to the requirement for higher power or higher forces through the gears to produce this thread. Hand mandrels can help with the power required but I have seen some suggestions that hand turning the leadscrew is the best way to cut large pitch threads on a low power lathe.

Martin C

Les Jones 124/05/2020 18:09:44
2130 forum posts
146 photos

If it gives a change wheel setup for any thread you should be able to work out the leadscrew pitch. If you can't work it out post the information here ant there will be may members that can work out the leadscrew pitch.


Howard Lewis24/05/2020 18:16:15
3272 forum posts
2 photos

If the pitch required is coarser than that of the Leadscrew, it means that the leadscrew has to turn faster than the spindle. (Mandrel ).

So if you turn the Leadscrew handle, it is effectively geared down to rotate the Mandrel, Whereas the Mandrel has to drive the Leadcsrew faster, so imposing a greater load on the gear train.

Just picking numbers out of the air, say you wanted to produce a 4 mm pitch with a 2 mm pitch Leadscrew..

The Leadscrew would have to turn twice as fast as the Mandrel. So turning the Leadscrew Handle will involve half the effort of the mandrel doing bthe driving.

Mandrel driving the Leadscrew is a ratio is 1:2. Leadscrew driving Mandrel is a ratio of 2:1, so less load on the gear train.

A 3.5 mm pitch would require a 3 mm pitch Leadscrew to turn 1.166666' times faster than the Mandrel, or 1.0583333times faster if the Leadscrew is 8 tpi (0.125" pitch )



Martin Connelly24/05/2020 18:40:34
1369 forum posts
159 photos

I've looked at the manual and the gears supplied with the machine. The nearest you can get with the supplied gears is 3.2mm pitch. To get to 3.5mm pitch you need a 70 tooth gear to replace the 60 tooth gear in the 3mm setup. I don't know where you could get one of these gears or if the gear train with the 70 tooth gear in will be possible to assemble. The gears should be 63, 32-70, 30 (A, BC combination, D) with the lever to the right. You don't need to know the leadscrew thread to work this out. 70/60 is the same as 3.5/3.

Martin C

old mart24/05/2020 20:37:40
1771 forum posts
138 photos

It should have 1.75mm pitch available, as that is a common one (12mm metric coarse), so you need to find a way of doubling the speed from that which will give 3.5mm pitch.

fastdave24/05/2020 20:39:44
18 forum posts

Many thanks, all of you - I'm beginning to get the hang of this. Dave

Martin Connelly24/05/2020 20:52:39
1369 forum posts
159 photos

The gears for 1.75mm pitch are 60 and 49 drivers and 36 and 32 driven. To change this to 3.5mm pitch would require 120 instead of 60 or 98 instead of 49 or 18 instead of 36 or 16 instead of 32. Non of these sizes are included with the lathe, the supplied ones range from 27 to 63.120 and 98 may be too large for the available space. 16 and 18 may be too small for the gear shafts. That's why a 70 tooth wheel seems the best option to try. It requires finding the mod or DP of the existing gears to be calculated but should be something that can be bought from HPC or other supplier.

Martin C

fastdave04/06/2020 16:29:36
18 forum posts

Absolutely helpful - learning curve decreasing. Dave.

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