New Chuck won’t screw on

[roy entwistleParticipant @royentwistle24699]

Surely it is better to have the chuck too tight than too slack. At least it can be made to fit. The fit should be on the register not the thread as has already been stated.

[Richard JarvisParticipant @richardjarvis95040]

The Chuck would only go on half a thread, anyway I have sorted it no thanks to RDG who appear to have washed their hands of the problem. After reading Howard’s post it got me thinking as to wether in my dads box of taps and dies I had the relevant tap, but the nearest was 3/4 x12 tpi. So I rolled the chuck on the bench with the tap seating on one edge of the thread and after 1 1/2 hours managed to get the chuck to screw fully on. I had oiled the thread and this clean oil kept turning black, so I presume the root of the thread was full of Iron powder and the tap must have cleaned it out. Thank you very much for all the replies, nowto go and put a dti on it and check for any run out.

Thanks Richard

[Howard LewisParticipant @howardlewis46836]

Your 12 tpi Tap probably took a little off the crest of the thread so that it longer interfered with the root of the thread on the Mandrel.

The main thing is that you have now managed to solve the problem.

Thanks for the feedback

Howard

[Rod RenshawParticipant @rodrenshaw28584]

Richard

Well done you!

Your situation was very much not your fault but your experience may act as a reminder to the rest of us about how important it is to keep the internal threads of chucks and similar fittings really clean.

Rod

[old martParticipant @oldmart]

Well done, you will find that in the real world, the fit is better when it is a bit on the loose side. You should remove the chuck from the backplate and screw the backplate on and off the spindle several times to settle it into place. Then check the runout of the front face outboard of the step and skim that part true if needed. Then refit the chuck.

[Anonymous]

Posted by Richard Jarvis on 21/07/2021 16:50:43:

….. only to be told that they are machined on a myford and then checked on two other spindles to check fit.

Can't for the life of me see why machining the backplate on a Myford would predispose it to fit a Myford.

[not done it yetParticipant @notdoneityet]

Then check the runout of the front face outboard of the step and skim that part true if needed. Then refit the chuck.

Steady on! You’re not suggesting that rdg would get that wrong as well? I am very selective when buying items, so don’t often buy from that source. I would guess that only s small proportion of parts are actually checked at the time of manufacture – and likely no further checks at all (unless a complaint arises? ).

[Richard JarvisParticipant @richardjarvis95040]

Posted by old mart on 24/07/2021 22:25:18:

Well done, you will find that in the real world, the fit is better when it is a bit on the loose side. You should remove the chuck from the backplate and screw the backplate on and off the spindle several times to settle it into place. Then check the runout of the front face outboard of the step and skim that part true if needed. Then refit the chuck.

The chuck fit certainly can’t be described as loose, in fact the thread will definitely be doing the locating. I did put a dti on the circumference of the chuck and found two high spots nearly 180 degrees opposite to each other, I am not sure that’s right,reading it it doesn’t make sense  I will check as you say when I have fastened the lathe back down as I am in the process of lifting it a couple of inches. I wear glasses and my focal point was making me bend down causing back pain.

Edited By Richard Jarvis on 25/07/2021 10:03:13

[Richard JarvisParticipant @richardjarvis95040]

Posted by not done it yet on 25/07/2021 08:52:00:

Then check the runout of the front face outboard of the step and skim that part true if needed. Then refit the chuck.

Steady on! You’re not suggesting that rdg would get that wrong as well? I am very selective when buying items, so don’t often buy from that source. I would guess that only s small proportion of parts are actually checked at the time of manufacture – and likely no further checks at all (unless a complaint arises? ).

But the complaints fall on deaf ears they told me someone else had the same problem as well but when they tried the chuck back at RDG it was ok!. I have bought a few bits from them over the last 18 months but maybe not anymore.

[Graham MeekParticipant @grahammeek88282]

Hi Richard,

Many years ago I had a similar problem with my then new ML 10. The actual register of the Grip-Tru chuck was too small, and that was down to Pratt & Burnerd, they were not cheap, even then.

As regards the supplier checking the thread against another machined part, then this is asking for trouble. Unless the "Inspection Parts" have been checked to see if the threads being used conform to the "Go" and "Not Go" sizes of a Screw Plug Gauge, then this approach is useless. Plus using the Myford spindle as a gauge is checking several conditions at once, and for one thing does nothing to actually check the true size of the Register diameter. The Register diameter on the Spindle, will always be smaller, it has to be to enter the hole. This hole could be 0.25mm or 0.010" oversize and the spindle will still go in. This size of Register would probably not do anything to help the concentricity though.

I suspect from what you have done with your 3/4" tap is restored the correct Crest Radius on the thread. No doubt the Tap, or screw-cutting insert used to produce this thread has become worn on this radius, and this is where the undersize condition actually was. This problem would have been found if a Pukka Screw Thread Gauge was used to check the part. As the "Go" gauge checks the form, pitch and size of the thread. The "Not Go" checks the maximum Effective diameter and looks like a severely Truncated thread, with the top half of the thread ground down to the Max effective diameter.

Lastly, you say you have put a clock on the Chuck. I have seen several posts where a clock has been put on the Body of the chuck. I for one would not expect this diameter to be "true", or "spot on". Nine times out of ten it has only been ground to make it look pretty. This is probably done on a centre-less grinder, and can be anywhere as regards concentricity, as its function is irrelevant to the working of the chuck

Gripping a ground diameter in the chuck jaws is the only safe test for concentricity, as this is where it matters. An old "Gudgeon" or "Wrist" Pin from an internal combustion engine is ideal for this, or a Hardened Dowel Pin.

I hope these notes are of help

Regards

Gray,

Edited By Graham Meek on 25/07/2021 11:43:49

[JAParticipant @ja]

Richard and others

I know how you feel.

I have a very eccentric 3 jaw chuck for my Myford. Thinking I would impove matters I bought a genuine new back plate. It did not fit the lathe so I just put it aside until I had the time and inclination to skim the internal thread with a single point tool.

The time came and I could not find the back plate. Therefore I bought another genuine one which, again, did not fit. At this point I put it all aside, feeling a fool and keeping my thoughts about the new Myford concern to myself.

Does anyone want a genuine Myford big bore back plate that will not fit, for free? When the virus has gone I, myself, might even delivery it for free!

JA

[Martin KyteParticipant @martinkyte99762]

The parallel section of the register can only dictate the limit of concentricity as there must be a clearence. The Thread flanks however are contact faces and so will contre the chuck. If the threads are off and loose then the chuck will be off centre by the clearence of the paraleel part of the register. OK I know I'm splitting hairs and these limits are going to be smaller than the chuck run out anyway. The most important factor is the flange as this sets the centreline of the chuck parallel to the centreline of the spindle.

regards Martin

[old martParticipant @oldmart]

It is always a good idea to check the runout of the backplate when the opportunity arises, especially when it is only fitting properly for the first time. I would bet on the spindle threads being innocent of any faults unless there is visible damage. Unlike most of the experts, I have a choice of 12 items which screw on the threaded spindle of the museums Smart & Brown model A and the register fits are from 0.0005" to 0.020" and as if by magic, they all repeat perfect runout every time. Martin Kyte is one of the few people who understands this.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Richard Jarvis on 21/07/2021 18:45:30:

.

@ old mart,

I thought this was the evidence ^^^

MichaelG.

[Martin KyteParticipant @martinkyte99762]

Posted by old mart on 25/07/2021 14:44:54:

Unlike most of the experts, I have a choice of 12 items which screw on the threaded spindle of the museums Smart & Brown model A and the register fits are from 0.0005" to 0.020" and as if by magic, they all repeat perfect runout every time. Martin Kyte is one of the few people who understands this.

Don't ladle too much praise on me I'm only repeating the words of George Thomas.

regards Martin

[Howard LewisParticipant @howardlewis46836]

With regard to run out of the chuck in either plane, unless the thread is integral with the chuck body, this will be determined by the backplate.

The OD should be a really snug fit in the register in the chuck. (ANY clearance will reduce concentricity. )

The front face of the backplate should be skimmed to clean up, to ensure that is as square as possible to the lathe Mandrel axis.

If we are still pursuing absolute accuracy reliance has to be placed on the jaws holding work absolutely parallel to the register in the chuck body.

The threads will provide a location in the form of two long tapers being brought together..

Howard

[brian jones 11Participant @brianjones11]

I had similar problem with an adapter faceplate 4" od. the thread would start to bind half way along. i didnt want to push it as my chuck – burnerd – slips on easily

wotodo?

a) layout £20 on a plug tap

b) try some fettling with a dremel

c) use a thread boring bar as a scraper (the Myford is 1-1/8"UNF x 12tpi btw so 60deg ok

d) a 3/4" bsf plug tap has the same tpi for a bit of scraping

i spent half hour dremelling and got a working job

but its frustrating and what you can expect with ykw stuff

 

btw Ive got an original 6" faceplate works fine

in the end i didnt use the adapter plate to save money fitting a generic new chuck and blew the kids inheritance on a 125mm 3 jaw ( I desperately need a set of outside jaws) c/w ready made Myford adapter plate from a well known supplier from here

 

Sometimes all the aggravations gets in the ways of doing some real work

 
 

 

 

Edited By brian jones 11 on 27/07/2021 02:59:49

[brian jones 11Participant @brianjones11]

the subject of nose threads generated a lot of hot air

https://www.model-engineer.co.uk/forums/postings.asp?th=122670

The standard BSF/W 1=1/8" thread is 9 and 7 tpi UNF is 12 tpi

e) one trick is to use a 1/2"W ht bolt which as 12 tpi and to cut a slot along it so as to make a set of cutting teeth like a tap, this can be used with some grinding paste to gouge out the thread (old fitters trick to restore damaged threads)

 

1.125

28.75

12

2.117

1.0228

25.979

0.511

1.298

 

https://www.gewinde-normen.de/en/unified-fine-thread.html

Can you believe that Myford would have gone to the considerable expense of commissioning a special thread for the nose, UNF would have been available from america

the chuck is located on the 1.25 shank and on the back face, slight looseness of the thread is expected, what you dont want is a tight fit.

OH well let the Vesuvial fire storm rain down upon my kalbo

Edited By brian jones 11 on 27/07/2021

Edited By brian jones 11 on 27/07/2021 04:08:20

[Howard LewisParticipant @howardlewis46836]

Brian,

The "standard" Myford Mandrel thread is 12 tpi BUT 55 degree WHIT form not 60 degree Unified .

The 12 tpi Whit form dates back to late ML lathes manufactured in the late 1940s (The early MLs used 7/8 x 9 , 7/8 BSW, before moving to 12 tpi, The Series 7 launched in 1947 used 1 1/8 x 121 tpi. )

Even the Taiwanese lathes available until, at least 2004 used Whit form threads for their chucks, (Mine is 2 1/4 x 8 tpi WHIT form! )

Howard

[Martin KyteParticipant @martinkyte99762]

I would think any thread with flat top crests (like unified) would be unsuitable for chuck fitting as the crests would be more prone to damage. The whitworth form with it's rounded crests and valleys would be less prone to damage and picking up and trapping particles of swarf.

regards Martin

[Richard JarvisParticipant @richardjarvis95040]

I tried a dti on the backplate and found about 1 thou runout but the needle was constantly moving due to a bad surface finish. I will try to skim it tomorrow. Hopefully this picture will show the surface.

[brian jones 11Participant @brianjones11]

WOW the machining there shows a ripped finish (perhaps a Covid tool?). Hss should give a nice matt finish, no lube needed assuming grey CI 50 sfm

[brian jones 11Participant @brianjones11]

So Im not so clever either, I just bought an HBM 3 jaw from RDG ready to screw on it said

Well I got most of the way there then it tightened up and wouldnt budge any further about 1.5 turns to go

Still it spins ok and i have got the energy to mess around with a dremel or complain and send it back

I shall live with it and get on with some work

I wonder if I complain they will send me one of their plug taps on loan for a bit of reaming

just makes you wonder do RDG check their stock on a standard nose before they send it out. This is not the first time this has happened – ive seen it reported on this board. Its not beyond reason to expect RDG to carry their own go-no gauge for this rather critical component

Disappointing RDG, but Ill live with it, maybe make a half washer to take up the slack, when ive got nothing on (in this hot weather

The positive bit is my old Burnurd chuck is now sitting happily up on Doreens nose

So there maybe milling ahead

Anyone remember where this other member had trouble and had to return his chuck (not certain it was RDG?)

[JAParticipant @ja]

Do RDG/Myford read these postings? Perhaps they should.

JA

[Richard JarvisParticipant @richardjarvis95040]

Have you checked the machining on the face plate?, I managed to get a better surface finish using a 12mm shank tool with what I think is a brazed tip. I tried a HSS but that left as bad a surface as original, that might be the operator at fault as I had attempted to grind it myself.

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