Myford backplate fitting problems

I popped into Chronos today and bought (amongst other things) a part-finished 4 1/4" backplate for a Myford ML7. I intended to machine it tonight but I cannot get it to fully engage on the
spindle; the boss goes on about 1/2 way along the register of the spindle then stops. I used engineer's blue on the register diameter and it's not transferring, so I know that it must be sticking on the threads; I've confirmed this by fitting the backplate on backwards and it does not fully engage all the threads before it gets stuck. I've measured the ID of the backplate threads and found they measure 1.043"; I know the correct dimensions for an external Whitworth thread, but cannot find any reference to the clearance or the minor diameter for an internal Whitworth thread. Can anyone help with what this dimension should be? I was planning to bore through the backplate if the clearance was too small, but I don't know if the thread has been cut to the correct depth; perhaps somebody has a 1 1/8" x 12TPI tap they wouldn't mind loaning out (for beer tokens?) to clean this thread up. Martin
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martin<dot here>whybrow<at here>ntlworld<dot here>com



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on the

spindle
not
I've
fully
1.043";
cannot
internal
too small,

perhaps
(for beer

Martin,
Assuming your spindle thread is undamaged and genuine Myford - then if this backplate was sold as suitable for a Myford surely you should return it as not fit for purpose and give Chronos the opportunity to replace it with one that is. As soon as you start machining it, it ceases to be resonable to expect a replacement.
AWEM
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Martin,
I've bought four of these part machined backplates recently at different shows (not from Chronos) and three had problems including one which was the same as yours. I used a brush to blue the threads on my spindle and confirmed that the thread flanks were interfering in the central portion of the backplate. I set the thing up in the lathe, clocked on the register diameter and rear face and just took a "lick" off the thread with an internal threading tool. Interestingly the tool initially only cut on the central two or three threads which led me to conclude that there was some sort of periodic pitch error with the original thread. I wasn't too worried about the thread fit as from my understanding (limited) the register "should" do all the location with the thread just holding it on.
However, my spindle register is "spot on" and with two of the others I bought there was (in my opinion) excessive clearance on the internal register diameter (.004"), so you might like to check that as well before clearing the thread. As Andrew says they won't be happy to change it if you have already machined it. I didn't so am stuck with the two I have. At the recent Harrogate show I checked several backplate registers from different suppliers and was surprised with the variation I measured. OK my calipers (or technique) are not perfect but they seemed to differ by up to .005" which even allowing a couple of thou for my ham-fisted measurements seems excessive to me. They do seem to work OK but it is one of those "problems" that I can't seem to get out of my head. I have resolved to buy unmachined backplates in future and see if I can do better myself although I would be interested to know if anyone has found a consistent supplier.
Although I didn't buy my backplates from Chronos I do buy a fair bit from them and have only experienced a small problem with one item, they changed it immediately without any issue whatsoever. If you are close enough to pop in then I agree with Andrew that this would certainly be my first recommendation. Obviously, if you can borrow a suitable tap then this will also clear the problem for you.
Best regards
Keith
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Well I measured the backplate more accurately today; the register is 31.80mm which is 1.252", so it's +0.002" which is reasonable. The pitch however is not so good, 6 threads measure 15/32" which equates to 12.8TPI or (more likely) 1.98mm; given the degree of accuracy to which I can measure this it appears to be 2.0mm pitch. I will be taking it back tomorrow, hopefully they'll ignore the traces of blue that remain in the threads. Martin
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31.80mm
it
I went back to Chronos today, they told me that all their backplates are CNC turned so are of the correct thread (!) and that my spindle must be a different thread; apart from the ML2 with a 7/8" thread and the Super 7 Plus with a much larger thread, I was not aware that Myford had ever used a different thread. I had the forethought to take the spindle from my ML4 with me (also 1 1/8" x 12 TPI) and they checked a few more backplates and found they didn't fit; however they then tried a collet chuck (made in Taiwan) and it fitted perfectly (except for the register being the wrong diameter as the ML4 has a 1 1/8" register compared to the ML7's 1 1/4" register). They immediately offered me a refund but that has left me without the backplate I need to mount the spare chuck (which I need to use to complete the job I'm working on). They also told me that if I call on Monday, they can confirm what thread pitch they had the backplates manufactured with (they are UK made for Chronos). This may be worth bearing in mind util they've confirmed that their backplates have the correct thread. Martin
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Ha Ha Ha, I love the assumption that just because they have CNC turned them they must be right.

It seems that once proved wrong they suddenly changed thier tune. I think they have behaved slightly poorly in this instance, and if they are selling a Myford fit backplate they ought to have checked it fitted a Myford lathe before selling it to you. Perhaps a little quality control is called for, instead of blindly trusting the suppliers. I suppose it is a sad reflection that the UK made part didn't fit, wheras the Taiwanese part fitted perfectly -helps explain why manufacturing is in the sad state it is.
Regards
Kevin
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CNC
found
and
the
To be fair to Chronos, they told me that all their backplates would be the same and offered me a refund before they demonstrated that the problem was with their backplates and not with my spindle. I agree with you on the assumption that being CNC machined meant it was correct, without proper inspection any machined part cannot be considered correct as it's not unknown for the programmer to foul up or for the drawings to be wrong (although inspection to drawing doesn't help in that case). Martin -- martin<dot here>whybrow<at here>ntlworld<dot here>com
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Martin
Sorry to hear that your project is held up but at least if I can keep awake your post will save me from picking up a "real bargain" backplate in the next few months or so. I hope they have offered some discount off your next purchase to make up for the additional journey.
It's an "ill wind etc" but I had planned to pop into the Bristol exhibition next weekend to buy the next installment of my "short" shopping list (including a backplate). Prompted by your post I thought I would check to see who else will be there to steal my money only to find out neither Chronos or RDG will be there anyway. Ah well, either an early start to catch Arc Euro Trade or LA Services before they sell out or I suppose I could go without lunch (and Dinner) this week and buy directly from Myford.
It's also interesting how shops' attitudes have changed over the last 25 years from "the customer is always right" to "we are never wrong". I expect that the conversation on Monday will be similar to the one you had today only with Chronos as the customer - I wonder (if it's their suppliers fault), if they will be so understanding?
Hope you find another quickly so that you can progress your project
Best regards Keith
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If you want, I can keep one aside for you.
Ketan Arc Euro Trade
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Ketan Great, I'll call on Monday. Martin
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On Sat, 13 Aug 2005 17:18:51 GMT, "Martin Whybrow"

Get one from Arc Euro, their's are made in China so they have to be better than UK made <bg>
I had a couple of 8" D1-3's off RDG a while ago and they wouldn't fit the tapered register by a long way. They did offer to swap them but as these were also CNC turned in the UK chances are the whole batch was out. Bearing in mind postage wouldn't be cheap on two 8" plates I re machined them.
All it takes is a dummy spindle nose to check, not a lot to ask. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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Slight correction...our backplates for the Myford are currently made in the U.K. too, but made by a different manufacturer from the ones who supply Chronos.
So far, (touch metal), no returns.
Ketan Swali Arc Euro Trade Ltd.
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are
Taiwan)
as
I decided to order 2 backplates, 1 from Arc Eurotrade and 1 from LA Services (The Engineers Emporium). Both arrived today (ordered yesterday); I've measured both and they are identical on all dimensions (as far as I can measure with my digital callipers). I'm guessing they both come from the same supplier or are, at least, turned to the same program or drawing. What Arc don't tell you is that their 4" backplate is actually 4 1/4" so it's perfect for my 4 1/4" chuck. The register on both measures 1.1245" but they fit my spindle perfectly; I'm guessing the error is on the internal jaws of my callipers because the spindle register measures 1.2500". My advice would be to buy from Arc as their price is 1.00 cheaper and their postage charge is a whopping 5.00 less than LA Services. Oh yes, both are correctly threaded and fit the spindle thread smoothly. I spoke to Chronos again today, they confirm that their parts are (supposedly) made with a 1 1/8" 12TPI thread; they haven't yet admitted that their is a problem with their backplates so I would be wary of mail ordering a Myford backplate from them at the moment and if you visit them, take a known good spindle adapter or a spare spindle to check for fit. Martin.
--
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On Tue, 16 Aug 2005 19:56:57 GMT, "Martin Whybrow"

What size was the LA services one?

-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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Services
John The LA Services backplate is also 4 1/4" which is what they advertise it as, Arc advertise theirs as 4". Martin -- martin<dot here>whybrow<at here>ntlworld<dot here>com
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On Sat, 13 Aug 2005 17:31:25 +0100, Kevin Steele wrote:

I suppose it is

I bought an ML7 in 1982 from a chap who bought it from his employers in the early sixties. It came with spindle and backplate which he had never used and I didn't try it until about ten years ago.....backplate wouldn't screw on beyond half way. So Britain's been making duff backplates long before the Taiwanese undercut us.
Ken.
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one
the
but
seem
they
is
CNC
Plus
with
and
the
I
confirmed
I have had a few " strange " :-( machine parts from CNC machines. In every case the CNC has done what it should, but either the work has slipped in it's holder ( my 16 1/2 tooth timing belt pulley :-) ) or the tool has slipped in the holder ( my shaft for an 8 to 12mm tapered key ).
If the plate rotated slightly during machining of the thread, the pitch cut as it slipped will not be to spec and the thread on either end will be out of step. if the ends of the thread will engage O.K. but it locks as it reaches the middle, this is what I suspect has happened.
It often happens when a batch is being run, and the tool blunts slightly increasing the cutting force, causing the work piece to shift under the greater pressure.
--
Jonathan

Barnes's theorem; for every foolproof device
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