Milling Machine Vertical Spindle?

Slightly Naive question perhaps but I might be missing something. I've had occasion to check two vertical milling machines recently (one today) and it struck me as strange that the spindle of both seem to lean in slightly towards the column i.e. if you were flycutting a flat top surface to a block, the block would be fractionally thinner on the side towards the operator (I assume). We're only talking a lean representing a couple of thou over four or five inches but are machines built this way? Both are quality machines who have had the vertical face where the swivelling head bolts checked for squareness with the table and they're both spot on yet as soon as you reattach the head and fit a test bar into the quill, the bar measures as 'tucking under' slightly. There is no crud trapped between any working faces nor in the spindle. The test bar is accurate and rotates without any noticeable wobble and there is no movement even with the firmest tugging.

The logical conclusion is that the rear face of the head is not square with the quill. Is this deliberate like arranging for a lathe to cut very slightly concave across a faceplate or poor manufacturing tolerances? My initial reaction is to want to shim the joint to make the spindle vertical to the table when checked against a precision square or angle plate.

Edited By Chris Trice on 12/04/2013 00:57:47

... Oh, and all things clampable were tightened and gib strips were meticulous adjusted to lose all play.

Chris,

Roughly; what size & weight are these machines ?

e.g. Floor standing, or bench mounted ?

MichaelG.

Chris,

In his Test Chart for Vertical Milling Machines

Schlesinger describes this alignment as ...

Column: Vertical adjustment of cutter slide square with work table in plane through longitudinal axis of machine (table rising towards the front side)

He gives a Permissible Error of 0 to 0.02 per 300mm

Your own requirements may differ, but Schesinger is a good point of reference.

MichaelG.

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Ref: page 48 of

Testing Machine Tools, by Dr. Georg Schlesinger

Seventh Edition [1966], revised by F. Koenigsberger

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Here is a brief biography of our hero.

Edited By Michael Gilligan on 12/04/2013 09:22:05

Well, it's way over that. If you put a test bar in the spindle socket and offer up an angle plate, you can see the spindle isn't square to the table. Yes, the test bar is parallel, the angle plate square and turning the spindle makes no difference. One is a Myford VMC, the other a Rishton, both floor mounted on their own stands. I'm guessing not but I'll ask anyway, presumably there is no way of adjusting the position of the bearings in the head block of the Rishton is the worse of the two? It seems to be the head where the error is. I know there isn't with the Myford and although the Myford was only a smidge out, I improvised a turned shim that varied in thickness from side to side. Neither machine has seen a lot of use. I admit I'm a bit OCD about obtaining Schaublin tolerances.

Edited By Chris Trice on 12/04/2013 18:59:12

Does anyone have a table of the lathe and milling machine limits?

English Wikipedia doen't even have a page on the good doctor (their German page says he came to Loughborough in 1936, and a google search suggests he may have been on the Nazi's wanted list).

There don't appear to be any digital versions of the book, even though it is over 60 years old - google books seems to be running out of free books and replacing them with links to sellers

Neil

Looking at the design of the VMC there are several parts that would have to be spot on to ensure accuracy. It looks like the whole head assembly rotates and a actual gnat's wisker on the mating faces of the flanges would thow it out. Try calculating the accuacy needed in these parts. Assuming it turns out to be surgicly clean you might hazard a guess the horizontal bar isn't absolutely straight and try rotating it. If that doesn't help try reassembling it 180 degrees around. That might make the tilt the other way.
I would think the way to correct it would be to scrape the flange the head rotates on.

Between the table and spindle there are I think 7 interfaces that would hvae to be spot on to ensure zero error. In practice that would be impractically expensive so I expect them to rely on random variations in one part to be balanced by an opposite random variation in the other parts. Mostly it works (it certainly works in electrical equipment) but of course sometimes it doesn't.

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Neil,

I have just put "schlesinger testing machine tools" [without the quotes] into Google Search.

The third hit appears to be for a torrent download of a recent edition.

Personally; I would not risk it ... but it does appear that there is a PDF out there somewhere.

MichaelG.

I have the book.

In fact mine came from Myfords together a with a load of Russian text books on machine design.

Obviously didn't read it when they did the VMC ?

I have put the first couple of pages up in my photo album.

Bit ironic that two of the mainstays of British machine tools have exactly the same problem that the Chinese mills have been slated for for years.

I have repeatedly asked if anyone has ever checked this good old British iron and now it appears that they are all / were built to a price.

Edited By John Stevenson on 13/04/2013 00:24:40

Though the Rishton was of UK manufacture, I believe that the Myford VMC was bought in from Taiwan.

Looking at pics of Rishton millers,nearly all the weight of the head and motor seems to be forward of the column, which might cause the head to "nod" a little. Be interesting to know if it gets more and more out of tram as the head is raised.

Andy

Edited By Andyf on 13/04/2013 00:52:03

Very true, they were brought in from taiwan but reworked by Myfords hence the hike in price.

Chris must have had a Friday morning one as they never worked Friday afternoon.

You can download a PDF extract illustrating Schlesinger limits applicable to vertical milling machines from here:

Note — Tinyupload is a free on-line document archive that operates in the same way as Photobucket does for images. When the Tinyupload splash screen appears, clicking on the link given will start the PDF download.

Joe

Edited By joegib on 13/04/2013 06:53:34

Edited By John Stevenson on 13/04/2013 15:36:22

Yeeeach that tinyupload site seems to be riddled with crapware. don't click just through it .

I cancelled it after a couple of pages of crap and it still tried to shovell its malware into my computer so I had to use task manager to crash the program. Make sure you know how to do this before you start.

Even then it left me with a page full of 'free games apps' - you have seen the news last night about that stuff.
If you have kids put that site into the blocked URLs in your router.

Thanks for the head-up Bazyle.

I'm very cautious of torrent sites.

We have 'family protection' which is a bit of a pain sometimes (wouldn't let me translate a German Wikipedia page, and it won't let me bring out airgun targets) but it has stopped me having to reset my daughter's laptop to factory settings every couple of weeks, and it's prevented this computer from havinga near-death experience so far. A few settings on the router too.

Neil

In light of Bazyle's comments can an Admin/Mod arrange for the link in my post at 06:52:59 to be deleted/disabled please?

I am sorry if that link caused problems for users. I'm not sure what has happened here — the link works OK for me and the Norton and McAfee Website review pages give this site a clean bill of health. Nor can I see any chat on the Web suggesting the site is subject to malware.

Joe

Link disabled checked and hosted here.

http://www.stevenson-engineers.co.uk/files/Schlesinger_Vertical_Milling_Machine_Limits.pdf

Edited By John Stevenson on 13/04/2013 15:39:02

Does anyone have a table of the lathe and milling machine limits?

You will struggle to find them "free" - they are usually National Standards (BS, EN, ISO, DIN etc.) and all are sold, not made freely available.

And the relevant authorities know how to charge !

BS ISO 1984-2:2001
Test conditions for manually controlled milling machines with table of fixed height. Testing of the accuracy. Machines with vertical spindle costs £140 from the BSI

I know I have a couple of lathe alignment charts (Harrison & Gildemeister) at work for manual machines, but not sure if I have one for the XYZ turret mill ( the only manual mill in the works) - I'll have a look on Monday.

Quite a few of the older machine tool fitters I worked with used to quote a "rule of thumb" for alignments of "1 thou per foot" - this may have been applicable to the larger manual machines built in the '60s & '70s (the fitters came variously from the likes of Asquith, Butler, Churchill Redman, Crawford Swift etc.- pretty well all of the machine tool builders that used to proliferate in the Halifax area), but that was somewhat more relaxed than the standards required for the CNC machines that my former employer used to rebuild/retrofit, where less than 1/2 a thou per foot was more usual.

Nigel B.

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Nicely done, John

MichaelG.

Thanks John

Neil

I was most interested to read the comments about the Rishton milling machine as some years ago I made the mistake of buying one. (new) Believing at the time that British must be best and perhaps slightly beguiled by the fact that it was made by a company described as precision engineers I spent rather a lot of money to be very dissappointed. The spindle was out of truth to the table. I'd bought it from a reputable dealer who came and had a look, agreed it was rather poor and offered to either refund my money or get me a replacement. As, of course, British engineering was absolutely the very best in the world I assumed mine was maybe a Friday afternoon job and opted for a replacement. This came and though an improvement was still not right. I complained again and again the dealer called, agreed with me and said he'd discuss it with the MD of the manufacturers. He subsequently reported back to me the MD's response. "What's he expect, a Bridgeport." A further replacement wasn't on the cards so rather than a refund I decided to make the best of it. There wasn't a lot about at the time in the way of small milling machines, I do recall the Emco FB and some clones of same. I was however never able to get the head to move correctly up and down the column, which was a necessary requirement given the lack of fine feed on the quill. I still remember with some anguish my desperation in trying to bore a cylinder on the machine. Although it wasn't purchased from Myfords (Beeston) I did subsequently have the oportunity to discuss it with a Myfords fitter who'd had experience of them and he'd also found appropriate head adjustment barely possible. The head was either loose or stuck. I wouldn't fault the base and table but as for the head and column..............well. With increasing fustration it had to go and I eventually got a Myford (Beeston) VMB. I've found this a super machine and I wouldn't part with it. I've never understood why there didn't appear to have been a greater take up of them by people such as myself without space for a large machine. I'm convinced a milling machine really needs a dovetailed column rather than a round one. I've also got a small X1 machine which came from Arc-Euro and that has also afforded me every satisfaction. Athough it's tiny I'd never swap it for a Rishton.

Well many stories have a moral and this is no exception. History shows us that mankind has a tendency to look back to some golden age and British Engineering was one of them. Yes, a lot of it was golden and still is but there's always been the mediocre and poorly designed and still is. The philosophy often seemed to be "barely good enough will do". I remember reading on an earlier posting some criticism of Raglan Milling machines by someone who'd been involved in their manufacture. So in essence one should be wary of deriding all Chinese and Indian products. There's good and bad, just as there were and are in those of British manufacture. In conclusion do a bit of googling re Moore& Wright combination squares. I was surprised.

Michael

I have two Rishton CNC mills, got them as a breeding pair but they are either queer or been talking to next door's panda.