Lathe setup question

I recently bought an MT3 parallel setup bar from Chronos and used it to setup my Boxford AUD at the weekend. I'd just levelled it and was
chuffed to find there seems to be essentially no out-of-parallel error in the lathe slides.
If I traverse the saddle with a um reading dti on the side of the bar there is only about .003mm ( a tenth of a thou) total runout in the whole 125mm length of the bar. Turning the mandrel by hand with the dti at the far end gave similar readings.
With the dti set on top of the bar I got a much worse reading of around .04mm (1.5 thou) with the lathe mandrel pointing upwards towards the tailstock. I did some elementary trig and it seems that should have essentially no effect on accuracy (except perhaps on tiny turned diameters) and I wondered what the opinion of the group is on this misalignment ?
Is there a way of adjusting this out on a Boxford, or should I just forget about it ? Or are all lathes set up with the headstock pointing upwards for some obscure reason akin to the one relating to facing always being a smidgen concave ?
Thanks,
Mike Davies
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Hello Mike
Others will be better qualified than me to answer this as I tend to ramble on a bit too enthusiastically sometimes without always thinking things through:) However I thought I'd mention what I had to do on my original chinese lathes to level them before I sent them back for good. I couldn't level them properly just bolting them down to the supplied tray/stand as it kept distorting too much, both under the weight (not too heavy at 125kgs) and also because of the flimsy stand construction which would move every time the wind changed direction. Every time I shimmed a foot and re-checked it the reading had no correlation to the adjustment I had just made.
I had a piece of 3/4" plate from work which had been surface ground on both faces, and when cut in 2 was the perfect size to go under the single-piece foot castings. Once this was in place shimming to take the twist out was a doddle, although I had to pack the foot at the rear of the headstock end by 0.032" (0.8mm) to achieve this. HTH
Peter
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It's unlikely the head is out of alignment with the bed to any significant degree, Mike. The most likely explanation is bed wear. If you're putting a clock on top of the test bar and traversing the saddle to check along the length of it, you'll be moving the saddle into the most wear prone area of the bed. As the saddle moves into the dip the clock will appear to show the test bar is rising, when in fact it's really the saddle that's descending.
-Neil F.
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I would normally agree that this would be a likely cause, but in this case I really don't think it's the problem. The lathe has basically not seen any work at all despite being 20 years old : the chip tray is still completely covered in the original paint and although there are the odd signs of dropped chucks from its previous (minimal) school use I really believe there is no wear at all. I know feedscrews are easily replaced, and so are deceptive as an indication of useage, but there is basically no backlash at all in any of them.
As I said in my post, vertical misalignment ought (if trigonometry is any guide) not to be a problem in terms of accuracy. I just wondered if there is any way of adjusting it out on a Boxford ? The cabinet is pretty stiff (to the extent that when levelling it there was no bed twist at a point in time when I only had 3 of the 4 adjustable feet fitted) so I can't just adjust the mounting feet under the cabinet.
Of course I could try putting shims between the tailstock end lathe foot and the cabinet, does anyone think this would work ? Or should I just ignore the whole thing ? The only thing that stops me doing just that is the fact that there seems to be basically no lateral misalignment and it somehow jars with this thou-and-a-half vertical misalignment :-/
Thanks to you both for the advice,
Mike
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Mike,
I will be in a similar position to you as I have recently purchase an AUD. I was considering the same set-up bar as you have but wondere if the investment was worthwhile. The manual says to turn up a bar o at least 1", machine a couple of collars about 4" apart then check fo equal sizes. I was going to use that method along with an engineer level to get it all correct. What's the concensus? They also mention that if the levelling has been done correctly an there is still a problem the headstock could have been disturbed. I can be loosened and slid to and fro on the bed and retightened. The final leveling done either by jacks under the tailstock end of the be or that end of the cabinet. BTW, have you used solid adjustable feet under the cabinet or anti vibration mounts? I was considering the later to limit noise but a concerned that the accuracy could be effected. Looking forward to any comments, Ro
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Dunno about a consensus but istm that you're in a bit of a chicken and egg situation when it comes to setting up a lathe without some kind of pre-made test bar. I bought the Chronos one because it seemed reasonably cheap, my engineers' level is a 6 inch one bought second hand and is not really sensitive enough. If you have a MT test bar at least you're guaranteed not to be wasting your time measuring chuck runnout or anything other than bed-spindle misalignment. Always assuming the bar's a good 'un...

This is probably good advice but I'm too scared I'll make it worse to try it...

Anti-vibs. They don't seem to have any affect on either noise or accuracy, but they did make the lathe easy to level. As a bonus, the external coolant system will now fit under the cabinet.
Cheers,
Mike
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Mike,
I didn't consider the influence of the chuck. I'm returning t machine tools after rather a long lay-off. It's those sort of thing one forgets!
I'm off to Chronus on Friday's open day so I will probably come awa with a test bar. They are on the Christmas offers list.
Any pointers to what size and manufacturer of the feet? I want som for my little Centec mill as well.
Ro
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Probably worth it if you can't borrow one from somewhere

I've got these ones on my Boxford 5" : <http://www.gmt.gb.com/pages/products/machinefeet/pages/8-1.html type AMF1013 soft,
and these on my Warco VMC : <http://www.silvaflame.com/page900.htm type 220001.
There doesn't seem to be any difference in performance but the Silvaflame ones were cheaper, have more adjustment (important if you have a very sloping floor as I do for the mill) and are taller at minimum height (could be a pro or a con according to your circumstances).
The types above have 12mm hold-down bolts, but obviously you will need to pick a size compatible with your machine's fixing arrangements.
Cheers,
Mike
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