Milling Cutter Run-out - advice needed

I've just got my first milling machine up and running. It's a Dore-Westbury which I've been restoring/improving for the last 3 or 4
years.
The TIR on the spindle, measured using a DTI either on the external Myford chuck register, or on the inside of the MT2 taper socket, is just under a thou. This doesn't seem too bad (to me)
My question is what run-out is acceptable on a cutter?
I ask because I'm finding that on my machine it can be anywhere between 0 and 3 thou, the variability coming from how I fit my Modeloy milling chuck into the spindle, and how I fit the cutter into the chuck.
I'm tearing out what little hair I have left trying to get consistent results. Am I wasting my time?
All advice from the old hands much appreciated
Mike
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snipped-for-privacy@virgin.net wrote:

Mike, hi, I have to declare straight away that I am no expert on milling but I thought I would post a few experiences just to see if we can stimulate some advice from the better informed.
Just out of interest I measured the runout on the 3MT spindle of my RF25 mill, to be honest it is almost unmeasurable but at a guess something like .0002". I only got this after a really good clean and degrease of the socket which as far as I can see is undamaged; with the uncleaned spindle I was getting figures of .0005" or so.
When using an Osborne screwed collet chuck and a variety of cutters I got figures of between zero and .003". The best figures were obtained with Presto/Clarkson/SKF cutters. The cheap import cutters I have are all within .0015" and the .003" was a cheap long shank dovetail cutter. Again to get any repeatable results everything had to be very clean and I have not yet cracked how to ensure the centre locator is properly positioned. I have cracked more than one small diameter endmill by screwing it in too far.
When using a Vertex ER32 system (20 micron spec) the figures were better but this is a new system compared to a 30 year old Osborn. I also tried the ER32 with some new drill blanks and got consistent results all within .0005" so they are all well within the 20 micron spec. Best results were with the collet holding the max size it could ie a 6-7mm collet holding a 7mm drill blank.
To be honest although these figures are interesting they don't mean a great deal. In use the chucks are never that clean and I have not experienced any problems milling with the import cutters which appear to be the worst, in fact I thought they all cut fairly well and have recommended them to several friends who also use them without problem. I have experience problems with the dovetail cutter which very obviously cuts on one side when trying to take a fine finishing cut.
I'm not sure if this helps at all Mike but with a bit of luck someone with more experience will come along and tell us what we should be getting.
Best regards
Keith
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jontom snipped-for-privacy@hotmail.com wrote:

Thanks Keith, much appreciated. Good of you to carry out these tests.
Having spent some more time checking my set up, I've convinced myself that the axis of the morse taper in my machine spindle is slightly tilted with respect to the axis of the spindle. This error adds or subtracts to the errors in the chuck and cutter, resulting in the variation I'm seeing.
So the question now is whether to live with the run-out of up to 3 thou, or to attempt to re-machine the spindle to improve the Morse taper accuracy.
Thanks again
Mike
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IIRC the Dore Westbury was a kit of parts to make at home, so you have two possibities, either it was wrongly machined by the P.O. or it has had a bash at some time that has given the spindle a 'permanent offset'. Probably worth giving the spindle a very close examination, and consider making a new one. The runout should be imperceptable as the bearing seatings and taper should have all been machined at one set up ensuring concentricity. Ultra high precision spindles would have the socket ground spinning on the actual bearings to be finally used in the machine.
That said, there isn't a milling machine in existance without some runout, and all milling cutters will have a tooth that cuts first if only by a small margin. Take consolation that it will be the first to wear down <G>
AWEM
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wrote:

Mike
If you contact the company below, I'm sure you'll get some sound advice. MES no longer make the DW due to the low cost of Eastern imports, but you'll get to the benefit of the designer of the later Mk2 version.
Steve MODEL ENGINEERING SERVICES
PIPWORTH FARM
PIPWORTH LANE
ECKINGTON
SHEFFIELD
S21 4EY
Phone +44 (0)1246 433218
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snipped-for-privacy@virgin.net wrote:

Mike, many (many) years ago I attempted to make a small bench top mill using various parts I had about. Having machined the spindle on an old Colchester Student I had trouble getting a decent internal finish on the 2MT socket. Although as far as I could measure it ran true I just couldn't settle with the awfull looking finish. Someone lent me a 2MT reamer "just to clean it up" and assured me it would follow the bored taper. I attacked the spindle with that and it never ran true again, I eventually remade the spindle and learnt to live with the internal finish.
These days and assuming the spindle outer diameter is true and the spindle is not bent I might be tempted to set up a small grinder in the tool post and grind the internal taper. Run the lathe at top speed and use the top slide if it has sufficient travel to get the correct taper. It takes a little trial and error to set the top slide "just so" but I've done it on a small 1MT spindle for a high speed drilling machine and after a couple of attempts I got good coverage when tested with a 1MT drill and engineers blue. The machine is not finished so I can't tell you if it has been completely satisfactory. I spent a lot of time setting the spindle up in the 4 jaw to run "spot on" and I bet I didn't remove more than a couple of thou in total. While I was lucky that my lathe spindle was large enough to take the drill spindle I suppose if it isn't you could always set it up with the fixed steady and do the same thing, just a bit more fiddly.
As Andrew says and Adrian shows, there will always be a little run out, If the machine is doing what you need I'd be tempted to carry on using it. Of course this a case of "do as I say not as I do" with me because if I've spotted something that I'm not happy with I just have to get it right. I can't help myself even though I have a pile of experiences where the trouble to fix something was far worse than the perceived problem. Anyway, good luck whatever you decide to do.
Best regards
Keith
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On 23 Sep 2006 16:45:39 -0700, jontom snipped-for-privacy@hotmail.com wrote:

I built a Dore many years ago and from what I remember you could get the spindle pre bored and reamed to MT2 or do it yourself. MES then hired out a double ended MT2 plug so you could fit this direct into the headstock spindle of an ML7 or similar, centre the end and then turn the bearing diameters all at this setting so it ran true.
. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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jontom snipped-for-privacy@hotmail.com wrote:

I'm likewise no expert, but I do have the same Dore-Westbury (Mk 1). I've measured the TIR at just under 2 thou on the register or in the taper, rising to about 5 thou on a cutter in an end-mill holder. So at least yours is better than mine !
-adrian
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Adrian Godwin wrote:

Many thanks to all who replied for the helpful comments.
Like Keith, once I know somthing is wrong I feel compelled to fix it. However, I've had a similar bad experience in the past when trying to "improve" a dodgy Morse taper socket (I made it worse, not better!), so I think I will try to live with the error.
I take comfort from Adrian's measurements on his own DW. Maybe mine, a very early Mk1 machine, isn't so bad after all.
Mike
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