Just How Accurate Is A Modern Colchester Lathe

malmac

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I understand that the Colchester Lathe is still considered a bit of an industry standard for quality and accuracy.

Can't justify buying a Colchester lather but would like some data on there accuracy specs if anyone is willing/able to share.

Planning to buy a good quality Taiwanese lathe and would like to compare the accuracy between the machines - to see what I am potentially missing out on.

It is true that there are some really super accurate Taiwanese machines - Cyclematic (on one machine spindle runout of .00125mm) - but somewhere below that are some machines with more modest but still desirable levels of accuracy - that is where I am looking.

Any advice is welcome and appreciated.

Mal
Australia
 
I wouldn't get too hung up on the specs. You can still make good parts with tight tolerances on a worn out machine.
 
Orental machines just need some help to make them ok.
 
The accuracy of parts made on a lathe is mainly due to the operator. Same idea holds for many other tasks. The cheapy import lathes, will readily give a pretty average competence home machinist guy dimensional accuracies of better than 0.01 mm.

The more expensive machines give you about 99% the same result, just faster and with a bit less fussing.

Cholchester has made many good machines, but for the most part, the resulting components won't be any different from a mid level Asian import.

My suggestion is that you don't sweat the brand top much.
 
I am sure you guys are right - just wanted to get my head around relative accuracy per cost.

I am looking at two lathes - one has a centre line runout of .015mm and the comparison lathe has a centre line runout of .008

That means the second lathe has a more precise action by .007mm - how much is that improvement worth????
Also how do those figures compare to an industry standard Colchester lathe?

Mal
 
Thanks Chipper

I am willing to accept that I am not a hot shot machinest. However if I am going to upgrade my lathe I would like to buy the best one I can afford and know why I am paying the extra dosh.

Guess I also like the effect that using precise tools and equipment give me.

When I work on the old bikes I like to build special tools which means I can do the specific job in a calm and controlled space. I experience a pleasure from using a precise piece of equipment - but I do realise that experience really does make a world of difference.

Thanks for your response.

Mal
 
I'd say those figures are derived from a sampling of their production machines and are based on two primary factors. First and probably foremost would be the bearing quality. It seems to me that this is the easiest way for machine builders to save substantially in their build cost, and they take advantage of that. The other basic contributor to that specification would simply be their own in-house machining practice, in particular the precision of their spindle grinding. That could be ultimately be because of their poor quality grinders, their average operator's accepted performance, or perish the thought, their original design intents and limits. Unfortunately, there is no way to know. You might get a monday morning machine and it be right at, or even out of the spec furnished. Or you may get one where the boss is watching the grinder operator closely right after a threat to their job.....and get one near spot on. Then in both cases, in the end it depends on what the QC department decides to let ship. Or perhaps even checks before shipping. You might just look at it as a gamble, with the odds more in your favor the more you gamble.

All that aside, I have an Acer Dynamic series that I bought new in '97 I believe. I've not mistreated it, never wrecked it.....and I'd say it is every bit as accurate as it was on day one. I regularly work in tolerances less than 0.0005 and have no problem cutting to it, and not having to paper it in. I have no affiliation with them other than a satisfied customer. I have other lathes, so it's unlikely I'll be buying another in the future (other than a couple of smaller Rivetts I am looking at), but should I need another, Acer would be high on the list.
 
If you look at some of the Taiwanese lathes, such as the PM1340GT, the guaranteed spindle nose TIR is +/- 0.0001" 0r 0.0025mm. I have measured mine, and it is better than this spec., and I would expect similar quality in better built lathes. You do not need to spend big $ to get there. It is all a bit ethereal at the end of the day, when you factor the TIR of a standard scroll chuck is usually around 0.002-0.004" for the better ones, a set-tru is about 0.0004", otherwise use a independent chuck. This also changes over the clamping range and then you have the accuracy of the Jaw clamping and parallelism to the Z axis. A heavier lathe will have less axial deflection and allow deeper cuts, but at the end of the day one should easily be able to get dimensional accuracy of 0.0005" or better on most of these lathes in the size you are considering. With the lathe it is mostly the operator that determines the accuracy of the final product, assuming the lathe is in good condition. You want a lathe that will fit the scope/size of your work and of good quality and features you need, but there is a point of diminishing return chasing the numbers.
 
The spindle on my Chinese built Kent USA KLS-1340A is right at .0002" of runout. Goodbye, alibi! To get .0002" accuracy on actual work requires some careful fussing and tweaking when using any lathe. Ultimate lathe accuracy does not really do much for the results of your work, though better machine quality does tend to keep the machine's inherent accuracy in place for a longer time frame with less adjustment and repairs.

I laugh out loud when I see the test report sheets for Asian machines. For the price they are pushing them out the door for, there can be little real, careful inspection of the accuracy and quality of the machines. What it is, it is, and those test reports are almost certainly pencil whipped into being. The numbers reported are usually right at the tolerance limits, with a few entries a bit better. It is mostly a waste of time and money doing it at all, those completed machines are going out the door if they look like all the components are installed. Employees do what it takes to keep their jobs, and keeping production going out the door tends to work toward that end better than taking fussy measurements, sidelining marginal product, and refusing to write down the expected numbers, in most factories making things that stay in the earth's atmosphere...
 
In the big picture, a lathe is a lathe and it makes round things. The operator of the lathe decides how round the things are, for the most part! And I’m not trying to give credit to import machines. Only that the talent of the operator could be the deciding factor for part accuracy.
 
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