Odd Feature with New Lathe

[SteveW]

Guys,

I was round in a friend's workshop and he showed me a very strange feature of his new and fairly expensive lathe.

Set Up:
1. Using a magnetic base DTI set up on lathe bed just right of bed gap.

2. Set plunger onto headstock casting just behind the head bearing on a flat vertical area and with the plunger horizontal.

3. Note reading.

Then apply cyclic horizontal force against the headstock casting (push/pull across the bed axis at mandrel height).

In my man's case it is possible to get a plus/minus two thou deflection reading.

The supplier says this is normal (WHAT?) and that it would only manifest during high cutting loads (YEA?) and the unit will be well within spec on the final finishing cut (BOLLOCKS!) .

Anyway I repeated the set-up on my old lathe and it's as solid as a rock.

He's also had issues with the mandrel as supplied. In fact everything he buys lately seems to have been thrown together on the Friday afternoon before a major bank holiday. Trouble is it's not just one supplier.

Has anyone got any ideas on this one?

[ron]

Steve
I've a cheap Warco lathe and out of curiosity I tried your experiment, I get no movement at all, solid as a rock, I think the supplier's talking BS, I don't see how a lathe is ever going to be accurate with that amount of flexibility?
Ron

[chameleonrob]

I tryed it on my lathe, which is a 60 year old with a 3.1" centre height, and got +/-3 thou, but on mine there isn't a good place on the head stock for the follower whick probably contributes some of the error. I don't know how much is acceptable but the smaller the lathe (and thus, the smaller the cut) the more pronounced it is likely to become. I have to live with error on mine but it still possible to turn parts to withing 0.5 thou with care.

[SteveW]

Guys,

I feel it necessary to remain circumspect about the supplier/model on this one. My man is likely to be in dispute on this one and it may yet be resolved to his satisfaction.

He knows of one example where there is no movement while the supplier is quoting four other units that exhibit the feature therefore it must be 'normal'.

AFAIK there should be no movement.

[alanstepney]

I cannot see any way that one could turn accurately, with any reasonable cut, if the whole lathe is twisting around as the mood takes it.

[SteveW]

Alan,

From what we can determine the whole lathe (the rest of it) is as solid as a rock. Heave on the tailstock or saddle and nothing budges.

It was first thought to be slack in the head bearing because no one could believe proding the main head casting would cause this apparent movement. It's almost too daft to be what it looks like.

[chameleonrob]

the trick to turning accurately in these conditions is to make sure that the last two cuts are the very nearly same depth of cut, feed and tool condition, it's doable but I really wish I didn't have to.

[davidimurray]

I assume this is the type of lathe where the headstock is bolted to the bed? If so, then has your friend tried tightening up the bolts that hold it down to the bed.?If it is a lathe with the headstock integrated into the bed then there is a fundamental problem with the lathe. Was it supplied with some form of test certificate?

Cheers

Dave

[SteveW]

Dave,

Yep! The headstock is screwed down on to the bed but then so is my lathe and it's solid as is one other known example of this suspect model.

The weird bit is the supplier says it's OK and have examples to support their position.

Under little of no side load, i.e. light cuts, the unit is well within spec.

I should add that my man has had the rep in to look at it and is now in a position of stalemate. I suspect that there will be little idea of what's going on until the unit gets stripped. However, it's a brave man that attacks his brand new lathe in this fashion and the rep wasn't up for it either.

[davidimurray]

Well, first of all it definitely ain't right! I certainly wouldn't consider it fit for the purpose it was made. Just because the manufacturers have others that are the same it doesn't mean that it is right!!!

It sounds as if the headstock has not been correctly fitted/machined to fit the ways. It may be as simple as taking the headstock off and scraping any lumps or bumps off the casting. However, I would suggest continuing to hassle the supplier.

Have you tried smearing a bit of light oil at the headstock to bed interface? Try pushing the headstock around and seeing if the oil is sucked in/pushed out. If it is then you know that there is definitely movement between the headstock/bed.

Keep us posted on how you get on

Cheers

Dave