Lathe turns convex

Edited By KWIL on 26/01/2012 10:37:55

Thanks all for this info,

This was a very easy fix for my early S7, the wear was on the front face of the short guide, once the strip was fitted and glued in place and the saddle adjusted I am now able to traverse the length of the bed with only a slight tightening at the two ends not bad for a lathe that is 50 years old.

Cyril

Two pages...lol

You can't face flat on a hobby lathe

If you want flat, get a shaper

A lathe is using a revolving unit against an x-y unit, the chances of flat are rubbish

A shaper planes a fixed workpiece

Rocket science it aint

On day 1 as a zero ability shaper user you will see the difference

Edited By Ady1 on 25/10/2012 01:23:23

Ady1, maybe you cannot face flat on a hobby lathe but at least it should not be convex!

Edited By KWIL on 25/10/2012 09:40:31

Ady,

As someone earlier pointed out, lathes should be set up to face fractionally concave in order that mating surfaces do not rock. sometimes 'flat' is not a good idea.  I understand that on Myfords the carriage is set to face concave by 0.001" in 12", so in the 3.5" Max Radius on the lathe  the concavity would be in the region of 0.0003".

Regards

Terry

Edited By Terryd on 25/10/2012 11:19:03

I'm afraid I have the same problem John. It appears that the Chinese don't know about things like that so they make them accurate. Damn inscrutable lot!

Regards

Terry

Edited By Terryd on 25/10/2012 16:03:49

The idea behind a new lathe facing concave is to prolong it's useful life. As it wears it will face concave, then flat and then finally convex which is the least desirable condition.

Tony

My Chinese one wasn't so hot. A thou or so dishing over 3" would have been OK, but 5 thou was too much. I had buy a decent size dovetail cutter, pluck up my courage, and realign the saddle dovetails to get the cross slide more perpendicular to the spindle. During the process, I found that very little on the saddle was square, co-planar or parallel to anything else,

Andy

The idea behind a new lathe facing concave is to prolong it's useful life. As it wears it will face concave, then flat and then finally convex which is the least desirable condition.

So buy an expensive lathe and it only cuts right for 1/3 of it's life? So if you buy a second hand one, make sure it is half way through it's lifespan and maybe it will cut correctly.

Something wrong with that way of thinking.

It's not a way of thinking it's a fact and a properly made lathe will face correctly until it cuts convex. I have only owned a Super 7 but worked on many lathes in industry and I must agree that Myfords are vastly over priced, under powered and short on specification. They are a joy to use and feel nice to the touch but if I ever change my lathe I will seriously look at the far eastern products.

Tony

Money no object

**LINK**

"The spirit of CY is to be outstanding, to be delicacy, and try best to satisfy customers."

You would have to be a bit nieve not to expect an old Myford like any old machine to have a little bit of wear, I know my 1949 ML7 has some.

Even if you consider them overpriced and or underpowered they really have stood the test of time and still have quite a following, myself included.

That said I do rather like the look of some of the modern far eastern lathes and they do seem on the whole very well featured when compared to the Myford, however I wonder as to their longevity as I read of problems with expensive electronic failures, plastic gear train difficulties, bearing failures and poor alignment on machines that in some cases are spanking brand new.

Back to the OP, the previously quoted "rear shear" fix works very well it transformed my old machine.

Regards

Paul

Gentlemen,

I’m reminded of my own experiences with this issue of saddle wear on a Myford. The wear was present on a 1946 ML7 which I bought in about 1965, although I didn’t appreciate the problem until carrying out a deep boring exercise a considerable time later. Only when withdrawing the boring bar did the wear become obvious. The tool tip would dig in as the saddle rotated very slightly ACW.

Others have already mentioned the design weakness in terms of the `narrow guide principle’, and in effect how the shorter part of the saddle guide-way wears more rapidly.

Until I sold my Myford, I always intended to carry out J A Radford’s (NZ) saddle modification, which he did by bringing into effect the much longer (unused) shear face of the saddle. However, my plan to carry out this modification would have to wait until I owned a milling machine, because Mr Radford’s innovation included a small amount of milling.

I got very used to the slight sloppy movement, but the mod never happened.

My point here is that (I think) Mr Radford’s mod (from the ME index) appeared in the following ME magazine :-

Year - 1971

Volume - 137

Issue - 3418

Page - 541

Author - J.A.Radford of New Zealand

Title - Renovating a Myford Lathe (Saddle adjustment)

In my opinion, the changes are worth serious consideration.

Good luck.

Regards,

Sam

Hi Bill,

Eric Whittle made his v8 engine on an old Myford including all of the milling on a vertical slide and I'll never be able to equal that.

Look at it this way. It will not mate if it's convex. A certain amount of concavity is acceptable and as Terryd states three tenths of a thou in 3 and a half inches is well within a gnats wotsit. As the lathe wears it gets better before it gets worse. Longer life before you have to mess with anything.

In addition to all this when Myford grind the bed they purposly introduce a slight vertical hump in the middle by a central hold down bolt. Grind flat, let the bolt off and instant hump. With wear the hump gradually erodes through flat to slightly hollow. This doubles the acceptable life.

It's no different to toolsetting in production, set to cut undersize within tolerance and as the tool wears the turned diameter increases until the upper limit is reached then you have to regrind or these days change the tip.

In any full size job that mattered great pains would be taken to ensure that faces mated flat on flat .

That is what fitters are for !

A lot of this thread just boils down to whether or not the operator knows what he is doing or indeed what he is talking about. Properly set up and maintained a Myford can and has performed very well for many noted figures (and others) in the past. Many continue to do so now.

If you want to buy chinese then do so, they appear to be just as variable as some claim Myfords to be. When Myfords held sway, there was very little else to buy, now you do have a choice. Make it and be satisfied instead of carping about this that and the other.

Who is building a jet engine on a hobby machine?

Michael, the 3 gentlemen you quote are of course no longer with us to defend themselves so we will have to accept your word on what they did or did not say. The truth of the matter is that obviously flatness is the preferred option, then concave and the worst case scenario is convex.

What I will say is that Tubal Cain (the REAL one), GHT, Dennis Chaddock were I believe highly qualified engineers and also extremely skilled and practical machinists etc. In my experience having this combination of skills is not all that common.

Tony