getting precise cuts with the lathe

[ariz]

I'm timidly going back to my hobby, building model engines (do you remember that I had stopped the work on the Scuderi engine a while ago?)
a couple of days ago I was cutting a piece of steel on the lathe and noticed that on a lenght of about 120 mm for a diameter of 35 mm I had a difference of 1-2/10 mm in diameter from end to end (35,2 at one end, 35,3-35,4 at the other)

so I started to think, consider, imagine... till I reach the conclusion that I need to rebuild the lathe
it is a VERY old lathe, 80 years old, Boley 4L screwcutting lathe

browsing the web and Ebay, I found this auction:
http://cgi.ebay.it/910mm-R-J-H-Cast-Iron-Ground-STRAIGHT-EDGE-Unused_W0QQitemZ170385546577QQcmdZViewItemQQptZUK_Home_Garden_PowerTools_SM?hash=item27abc51d51&_trksid=p3286.c0.m14
and was going to buy the item to control the scraping of the ways of the lathe

fortunately, I posponed the purchase to verify first the lathe setting
after an hour of fine adjustment with DTI I was able to obtain an error of 0,02 - 0,03 mm in the same conditions above, and even better with more care in setting up the work

well, I saved about 200 $ on the straight edge, and more if I count the other necessary tools to rebuild the lathe
and a lot of time and frustrations without knowing if I really could had been able to do a right work
it would have been a real mistake to start this adventure! ???

but a question remains... I noticed that every little change in the setup has a great consequence in the accuracy of the setup
in my tailstock, also shut the lever that blocks the spindle causes a movement of the DI of several 1/100 mm
and many other parts react in the same manner
so, to maintain the accuracy, is it necessary to check with a DI every stock after that it has been fixed in the lathe? an annoiyng practise, isn't it?
or my old lathe is really too much sensitive to these factors?

thank you

 

[Blogwitch]

Ariz,

You are coming across what all people who restore these old machines have trouble with.

That is wear in all joints. Most probably not enough to allow the parts to rock about, but just enough to allow deflection when it is tightened up. You will also find that these old machines were never really built to the same exacting standards we have today, materials weren't as good as are available now, screw threading was a lot more crude etc.

It all depends on how much of a restoration you want to do, and whether you are willing to modify or remake parts to get the machine up to a modern day standard. Or leave it in it's 'wobbly' state and enjoy it for what it is. A machine that will turn metal, and if you get used to how things work together on it, compensate for it's lacking precision, and maybe produce some fine, but not super accurate work.

Over quite a few years, I gradually restored an old Atlas lathe while it was still being used as the main shop lathe, twiddling with bits when time allowed. It was a labour of love, and I eventually got it where it was as good as any modern day lathe. Then it went to it's new keeper, while I got in a modern square box.

But I can guarantee, the new guardian should have no complaints about the great work it can turn out. It should be good for another 70 years if looked after.

Your thought has to be, just how good do you want an 80 year old lathe to be, and how much time and effort do you want to put into it?

Blogs

 

[jonesie]

alot depends on how much time you want to spend on getting something to turn round and straight if time is no issue then you can do the DI routine by if time is then i would do alittle rebuild at a time and also maybe someone local can help with lending the tools to do it, or do some of the rebuild for you at a good cost ,as times are slow and they might be glad to get the work.me i would to the rebuild and save the extra monkeying around .jonesie

 

[ariz]

thanks for the reply Blogs, jonesie
Bogs I understand what you're saying and agree completely
it is an old, old machine, and it is simply impossible that wear wasn't present on it
fortunately its last owner (a mechanical engeneer) had changed the main spindle bearing in the headstock, so the spindle has 0 runout also today
but all the other parts are not so good

I can live with these limits, but obviously I would prefer a more precise machine
but I love this lathe, it has some features that are of great utility

so the dilemma is: rebuild or new lathe?

jonesie I could have enough time to rebuild it, what is missing is the spirit to start such a difficult task (tools apart)


well, I will eventually keep an eye around to see if I can get a bargain on an almost new lathe, but more probably I'll keep my lathe for quite a while (maybe 1 year or so) and then I'll buy a new lathe

 

[jonesie]

ariz the time issue also refers to how much time you want to spent on getting you part to run true, you just might be able to add some shims to take up some off the slop or if you can turn with a center you can adjust the tailstock. i to am looking for a good old used lathe but they are not easy to come by right now. we have had alot of small toolshops go out of business around here but have not been able to find a good old small lathe.jonesie