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Ian Skeldon 225/06/2021 20:45:46
540 forum posts
54 photos

Hi,

Could I ask anyone owning a recently bought Chester Craftsman (or very similar Chester lathe) if you could please measure the diameter of the lead screw and the pitch or TPI and let me know what they are.

Mine was bought very recently from a previous owner who had it for only 18 months, however in that time he has performed some very poor attempts to repair the damage he has done to the leadscrew.

I think I can repair it correctly but have found the leadscrew that is fitted is a little odd and may not be the original one, I can find no documentation to let me know what the dimensions of the original leadscrew should be.

Many thanks in advance.

Ian

Ian Skeldon 225/06/2021 22:12:17
540 forum posts
54 photos

Hi,

Sorry for the second posting but I intended to edit the first and found that I am unable to do so.

Could I ask anyone owning a recently bought Chester Craftsman (or very similar Chester lathe) if you could please measure the diameter of the lead screw and the pitch or TPI and let me know what they are.

Mine was bought very recently from a previous owner who had it for only 18 months, however in that time he has either performed some poor attempts to repair the damage he has done to the leadscrew or the leadscrew is a very poor example of one sent from the factory.

I think I can repair it satisfactorily but have found the leadscrew that is fitted is a little odd and may not be the original one, Mine would appear to be 7/8 diameter and 8 tpi but I can find no documentation to let me know what the dimensions of the original leadscrew should be to confirm if this is the original or a replacement leadscrew.

Many thanks in advance.

Ian

DC31k26/06/2021 07:56:24
556 forum posts
1 photos

Not directly an answer to your question, but please have a look at this thread:

https://www.model-engineer.co.uk/forums/postings.asp?th=140535

It provides downloads to a manual and also some equivalent models sold with a different paint job.

larry phelan 126/06/2021 09:25:55
1079 forum posts
14 photos

Good morning Ian,

I too have a Chester Craftsman lathe and I have just been out to check the leadscrew, which appears to be 7/8",near enough, BUT as far as I know it is 3mm pitch !

I seem to remember checking this some time ago when I was playing around with the threading dial fitting, something I seldom use.

Might be worth while to just count the number of threads on the leadscrew.

Hope this helps, since it,s not a bad little machine.surprise

DC31k26/06/2021 10:07:45
556 forum posts
1 photos
Posted by larry phelan 1 on 26/06/2021 09:25:55:

...as far as I know it is 3mm pitch

Other aspects of the machine will provide strong clues as to whether it is native imperial or metric.

For instance, in what units are the dials (cross, top and tail) graduated?

What are the default thread pitches shown on the screwcutting chart?

Which language requires the translation gear to be used?

What does the leadscrew indicator look like?

Ian Skeldon 226/06/2021 19:59:17
540 forum posts
54 photos

img_20210626_142745.jpgHi,

Thank you for the input gents. I have downloaded the various information available, thanks for the link DC13.

As far as I can determine the leadscrew is either 7/8" dia or 22.05mm so I guess it's 7/8" When it comes to pitch though it does look like it's 3mm pitch or 8 and a bit TPI ?

I have stripped the lathe down completely and chased the leadscrew threads that were rough, I don't want them wearing the nuts out. Further examination was required so I took the carriage apart and straightened out the carriage hand wheel shaft. It now travels down the bed from tail to head nice and silky smooth.

I found screw cut engagement was not reassuring so I stripped out the half nuts, the photos below show (1) how badly the carriage was assembled in manufacture, that screw was put in before the hole for the other screw was drilled, crazy as there is enough room for it to have been drilled where it couldn't interfere with the first screw.

The second photo shows how the screw holding the half nut bronze sleeve to the casting, was just a bit too long so the leadscrew could not be engaged to the full thread depth.

DC13 the dials are both metric and imperial, The default thread pitches are imperial, the leadscrew indicator is just the usual 1 - 4 and a line in between each of the numbers. I am afraid that I don't understand the language translation gear bit?

The grizzley manual says that has a 7/8" leadscrew and 8 TPI, as I say mine has 8 and a little bit per inch.

img_20210626_142846.jpg

DC31k26/06/2021 20:46:52
556 forum posts
1 photos

It is not unheard of for manufacturers to use the same diameter leadscrew on both their metric and imperial machines.

It makes manufacturing and stock-keeping a lot easier.

So it is possible to have 7/8" diameter with a 3mm pitch. Similarly, it is conceivable to have 22mm diameter with 8tpi cut on it.

The translation gear refers to the special gear or pair of gears that allow imperial threads to be cut on a metric machine or metric threads on an imperial machine.

Whichever are the native units of the machine, the geartrains for threads in those units will be simple (e.g. 20tpi on an 8tpi leadscrew needs something that simplifies to 5/2). For threads in the non-native units, the geartrains are more complicated and the numbers do not reduce to simple fractions.

Once you reassemble it, you can confirm the pitch of the leadscrew by measuring how much the carriage moves for say 16 revolutions of the leadscrew. It does not need sophisticated measuring equipment for this: a steel rule will distinguish between 48mm and 50.8mm and a chalk mark will index the rotation angle.

In case you did not find it, the actual manual for the machine is here:

https://www.manualslib.com/manual/1906935/Chester-Craftsman.html#manual

It worries me a little that you say the dials are in both units. If the exploded diagram in the manual is correct, then one set of dial graduations will, at best, be very difficult to use.

Dual reading dials that are easily-usable in both sets of units are available (best known is Gamet dials on Colchesters) but require a few more parts than are shown in the manual.

JasonB26/06/2021 20:55:49
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Moderator
21315 forum posts
2419 photos
1 articles

being American The Grizzley is likely to have been supplied with an imperial leadscrew. UK versions may not.

Best thing to do is when you get it back together see how far it moves with say 20 turns of the leadscrew as that's easier to measure.

regarding the dual dials if they are say 50 or 100 divisions on the imperial scale and 2.5mm on the metric it is likely to be imperial screws. If 2 or 3mm on teh metric and 80 or 120 thou then metric screws. Assuming simple "dual" dials not geared ones.

Howard Lewis27/06/2021 10:32:51
5237 forum posts
13 photos

These Taiwanese lathes were available in Metric and Imperial form. (At one time WARCO offered both forms. )

Your machine sounds to be rather like my Engineers ToolRoom BL12 -24. This is dual dialled, but is basically Metric.

I have always thought of the Chester Craftsman as being a Metric machine, but there is nothing to stop the actual manufacturer producing a hybrid, with a 7/8" x 3 mm Leadscrew, although i would have expected it to be consistently Metric.

Incidentally, 7/8 is 22.225 mm dia , so 22.05 sounds more like a top limit 22 mm, to me.

Your thread cutting chart (Norton gearbox settings ) may also give a clue as to Leadscrew pitch. .

Howard

Ian Skeldon 227/06/2021 14:58:49
540 forum posts
54 photos

Hi,

Thank you everyone for your help. 20 turns of the leadscrew produced a travel of 2 1/2 " so it looks like it is indeed a 7/8 dia by 8 TPI leadscrew. I have now reassembled the lathe and it is much better, half nuts fully engage and stay there. Initially I was concerned by the amount of backlash still in the train and chased that back to the roll pin, fitting a new one has cured that so it looks like it could be a useful machine now that all of those snags are ironed out.

Many thanks again to everyone for their help.

Ian

Howard Lewis28/06/2021 10:47:47
5237 forum posts
13 photos

You have very useful machine there.

How useful you will discover as you use it.

In UK, it is very similar to the Warco BH600 and the ETR BL12-24, having the ability to change from Metric to Imperial screwcutting just by resetting the main Idler Gear..

You have hours, years, of pleasure and usefulness ahead of you!

Howard

old mart28/06/2021 20:47:39
3316 forum posts
203 photos

As there is very little difference between 3mm pitch and 8tpi, you should measure the leadscrew not the nut, and over at least 30 pitches. 8TPI IS 0.125" and 3mm is 0.1181", only 0.0069" difference per pitch.

I just saw your 20=2.5", definately 8tpi.

Edited By old mart on 28/06/2021 20:51:31

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