Just How Accurate Is A Modern Colchester Lathe

[malmac]

An interesting discussion. I have a cheap 1340 Chinese lathe and have found accuracy to be one challenge and quality of build another. So as I have been considering an upgrade I have obviously looked at the experience I have had to date (which I freely admit is modest) is influencing my decision making. I also have a chinese mill which is good up to a point - but if I was changing that (which I don't see happening) I would be looking for rigidity and accuracy as well - the size of the machines I have seem really good - just attempting to quantify accuracy and quality before I part with any more dollars.

Thanks to everyone for your input to date.

Mal

 

[mksj]

I agree with you on your experience with the Chinese machines that you are discussing. One reason why I do not plan on buying any future machines from China, and am in the process of purchasing a Taiwanese mill.

I have attached a brochure from Kent USA precision lathes, but these lathes seem very close to the ERL and RML lathe models available through different vendors around the world. Tolerances are as follows:
PARALLELISM:
Headstock Alignment
0.0006"/12" (V)
0.0006"/12" (H)
Longitudinal Bedways
0.0006"/40"
Center Line of Spindle
with Carriage Motion
0.0004"/12"
Center Line of Tailstock
with Carriage Motion
0.0006"/12"

SQUARENESS:
Center Line of Spindle
with Cross Slide Motion
0.0006"/12"

RUNOUT:
Spindle Nose
0.0002"
Spindle Flange
0.0004"

That is about as good as it gets, and these are usually maximum allowances. There are so many other factors that affect precision lathe turning, that these specs are impressive and I would expect these machines to be quite rigid.

 

[Bob Korves]

Bottom line to me is that you can buy quality and mass in lathes and milling machines, but you cannot buy accurate work. That has to come from within the machinist. Much of it is repeatability. I can do some really accurate work -- sometimes. But not consistently. Lots of experience and practice, and keeping work practices and standards high, will gradually but noticeably improve the quest for consistently accurate results. That quest is mostly in the machinist, not in the machines -- as I see things.

All of us can improve our machines by adjusting the gibs, checking the geometry and adjusting it as needed, and keeping things properly lubed. The world's best mill still needs to be accurately trammed to make nice parts.

 

[malmac]

Hi Mksj

Thank you for the brochure. I think we are looking at the same lathe.

Looks the same to me. When I work out how to attach a pdf file I will share with you the precision data sheet I have been supplied with this machine and also a slightly more economical machine (also from Taiwan).

I also have an accuracy data sheet for this machine as a comparison.

There is another factor that I am considering is also upfront sales assistance - Whitelaw is very good in this area. Also hoping they will remain as helpful after the lathe is potentially supplied and I need that rare commodity "after sales service".

Mal
Australia

 

[Tony Wells]

To me those are Left Hander's lathes. The carriage handwheel is on the wrong side. I have run a lathe like that, but sure seemed awkward. Chips slapping around will make you hesitate to grab that operating handle too. Just me, perhaps....but I wouldn't have either of them.

 

[mksj]

To me those are Left Hander's lathes.

Great call, I missed that, assumed they are all the same, but you are correct and I wouldn't want the half-nut lever on the left side of the carriage. Never seen that before. Like the carriage hand wheel guard on the kent RML shown. On the precision note, I was just turning some 3.5"x 12" stock down, wobbled at the end, but turned very nicely and was better than 0.001" to spec. when done. As long as you do not remove it from the chuck you would be fine.

 

[malmac]

Hi Mksj

So do you already have this lathe you have posted the image of?


Mal

 

[mksj]

PM1340GT, http://www.machinetoolonline.com/PM1340T.html
Added a VFD and a number of other modifications. Does everything I need it to do, a number of individuals in this forum own this lathe. I originally was seriously looking at the ERL 1340 and 1440 models, but the budget just wasn't there.
Mark

 

[malmac]

Yes I hear you on the budget side. Wrestling with my do vs don't muscles as we speak. Will keep you posted.


Regards


Mal

 

[Kiwi]

Isn't Colchester (Group 600) also now made in Taiwan I know that some of them were assembled in England in the early days of the Group 600 from my understanding the tolerance claims are from the average of special assembled machines which can be different from production machines but not by much