New Chuck won’t screw on

[Richard JarvisParticipant @richardjarvis95040]

Posted by JA on 28/07/2021 12:56:21:

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

JA

Well they did not answer my last correspondence seven days ago so I decided to have a go myself with help from the group.

[brian jones 11Participant @brianjones11]

Well Richard, it seems ive caught your nose problem myself with a new 5" RDG 3jaw "screw on chuck" that does complete the travel.

This is so annoying as the thread doesnt have to be an interference fit. The chuck is located on the shank shoulder (1.25dia) and the back face. the thread merely clamps the surfaces together

I have lashed out on a plug tap from chronos and hope I will solve the problem @ £14. If it works I will put the tap back up for sale here, Maybe the tap can be passed around and help others in distress

I cant live with a half fitted chuck, never knowing when it might move

When I have solved the problem and regained my normally mild mannered composure, RDG will feel the hot breath of my displeasure at their carelessness and a demand for compensation. All will be duly reported here

[duncan webster 1Participant @duncanwebster1]

If one buys something and it's not fit for purpose, send it back. Any attempt at rectifying it, buying a tap for instance, will void any warranty, and anyway why should you be put to the expense of a tap.

one advantage of ebay/paypal is the no quibble return

Edited By duncan webster on 28/07/2021 18:36:04

[not done it yetParticipant @notdoneityet]

Posted by duncan webster on 28/07/2021 18:34:47:

If one buys something and it's not fit for purpose, send it back. Any attempt at rectifying it, buying a tap for instance, will void any warranty, and anyway why should you be put to the expense of a tap.

one advantage of ebay/paypal is the no quibble return

Edited By duncan webster on 28/07/2021 18:36:04

As well as ebay, I would recommend everyone to ask for (or even demand) a receipt for expensive goods at exhibitions, etc. I’ve heard more than enough stories of poor items not being accepted as sourced from stalls – RDG not excluded in that – although I cannot remember the particular item(s) involved.

[FlywheelParticipant @flywheel]

I had a similar problem with backplates some years ago, at the time I purchased a set of taps 1-1/8 x 12 tpi BSF made by Draper, these have served me well over the years in sorting out faulty backplates. The spindle nose thread is 55 degrees and most certainly NOT 60 degrees.

I am based in South Yorkshire and if anyone who lives in my neck of the woods has any problems with backplates or chucks etc please message me and you will be welcome to come and use the taps to sort out your problems

[clivelParticipant @clivel]

I don't think that the problem is unique to RDG chucks.

My secondhand ML7 came with a Burnerd 3 jaw chuck which was mounted on the spindle, as well as a Myford catch-plate and faceplate.

A few weeks later I purchased a secondhand 4 jaw Pratt Burnerd chuck in good condition. I was horrified when I first tried it to find that it would only go on about a quarter of the way before getting stuck.

Trying the catch-plate and faceplate for the first time neither would go on all the way. I was convinced that there must be a problem with the mandrel nose. But I then spent some time with a small brass brush and some strips of brass making absolutely sure that all threads were as clean as possible. Yet, although this improved the fit, none except the 3 jaw chuck which was originally fitted would seat all the way.

In desperation, I ordered a Myford spindle tap from Chronos – shipping to Canada was more expensive than the tap.
I first tried it on the catch-plate, and although I didn't see any filings when I ran the tap through, afterwards it was a perfect fit. Same with the 4 jaw and the faceplate after receiving the same treatment.

Clive

[brian jones 11Participant @brianjones11]

It seems that this Myford nose design is fundamentally flawed and will always be of potential for trouble on new parts

You see 1/2 thou oversize and all is sweet, but 1/2 thou undersize, whole pile of grief

you would expect RDG to run a plug tap through its adapter plates (made in india?)before selling them

is that too much to expect?

 

As for sending stuff back, not that easy for some living away from the now disappearing post offices, and there is the likelihood of getting another back with the same (unchecked problem – as I remembred reading from another post – lost in time, only on the third try did he get one that worked

thats a lot of grief

I will just engineer my way out of the problem = its what Myfordians do

btw just to show we are not alone

https://www.model-engineer.co.uk/forums/postings.asp?th=52289

Edited By brian jones 11 on 29/07/2021 12:00:15

[Michael GilliganParticipant @michaelgilligan61133]

Posted by brian jones 11 on 29/07/2021 01:46:35:

It seems that this Myford nose design is fundamentally flawed and will always be of potential for trouble on new parts

You see 1/2 thou oversize and all is sweet, but 1/2 thou undersize, whole pile of grief

[…]

.

I think that’s a little harsh, Brian

The same basic design has served well on many machines.

What seems to have been lost is the necesssary attention to detail in manufacturing.

.

As John Ruskin is alleged to have put it:

There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.

MichaelG.

[FlywheelParticipant @flywheel]

These are the taps that I purchased for sorting out the myford backplate threads,

when I dug them out of the shed they where not Draper has I thought but made by Garvin and are Whitworth not BSF (apologies for the error in my earlier post)

I have checked on the Garvin website but sadly they are no longer listed

Peter

[Andrew TinsleyParticipant @andrewtinsley63637]

A friend of mine purchased 3 Myford back plates from RDG at a reduced price (via Ebay), which were described as faulty. They all fitted the Myford spindle , with no problems.

As you seem to have problems with anything you have bought, my money is that your spindle is at fault. If that is not the case then why not buy a "Myford" tap from Tracy Tools and be done with it. For less than £20 you have a solution and everyone can relax.

Andrew.

[SillyOldDufferModerator @sillyoldduffer]

Posted by brian jones 11 on 29/07/2021 01:46:35:

It seems that this Myford nose design is fundamentally flawed and will always be of potential for trouble on new parts

…

Compromise rather than flaw. Threading the spindle and backplate is cheap to do and allows chucks to be changed quickly, most of the time, ahem. Disadvantages, the threads are vulnerable to damage and dirt; they are likely to jamb if not regularly loosened, and the chuck is likely to come off if the lathe is run in reverse. Can't give top marks to a design that won't unscrew when its supposed to, and comes off when its wanted to hold.

A slightly more expensive alternative is the flange/bolt system used by most Far Eastern hobby lathes. This arrangement has no critical threads to damage or keep clean and is positively fixed in forward and reverse. On the downside: slightly more overhang; takes longer to change (3 nuts), and because there's not much room to manoeuvrer it pays to have slim fingers.

Of the two I prefer the flange system (I have small hands), but when quick change is necessary the professionals reject both and cough up for one of the cam-lock or other better systems.

Don't expect professional features at hobby prices – it leads to disappointment! To my mind unnecessary too: all I need is a machine that does what I want, and although Myford and Far Eastern lathes have multiple disadvantages, they're a good fit to most amateur and small workshop needs. On the subject of expectations why assume the new backplate is faulty when the lathe's spindle thread might have had a hard life? In engineering it's best not to assume anything – measure twice, cut once.

Dave

[JAParticipant @ja]

As mentioned earlier, my difficulty is with backplates for a "Big Bore" Myford which I have, in the past, considered skimming the threads with a single point tool.

I now realise using a tap would be much easier. The thread is M42.5 x 2mm and Tracy Tools do not stock that size tap. Such a tap, that will only be lightly used just a few times, cannot be difficult to make. I estimate that 3" of 1.75" diameter silver steel would cost around £25. The only problem could be the heat treatment which would require a proper furnace. This is not a project for the near future.

JA

[brian jones 11Participant @brianjones11]

Posted by Howard Lewis on 25/07/2021 21:23:22:

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

Are you suggesting the spindle thread is deliberately tapered slightly

it might explain my conjecture about a Myford secret fudge

I cant do measurement myself just now, waiting on plug tap but perhaps someone with a newish ML7 can measure his nose thread to see if it has a secret taper

[Howard LewisParticipant @howardlewis46836]

I am am not suggesting that the thread is tapered along its length, far from it!

That technique is used on pipework to facilitate sealing.

The usual object is to produce a thread which is parallel on diameter, without root / crest interference.

(Which is why Whitworth form threads have rounded tops and roots, while Unified are truncated to produce a flat top, or root. )

If you look at any thread form, it is a taper, usually on both sides. (Whitworth, Unified, Metric, BA, Acme, trapezoidal etc. )

Go back to basic mechanics.

Think of a chamfer, immediately backed by an undercut, on a huge diameter, so that the circumference is long,

Take it off and wrap it around a bar, to form a helix like a spring, and you have a thread. In that case, one with one vertical side, That would be a buttress thread.

Forcing two tapers together should provide a location, which is why we use Morse or R8 tapers, for instance.

Threads produce a large clamping force because of the mechanical advantage that they deliver. Rotating a nut involves a long distance travel for the end of the spanner, (Effort ) for small linear movement ( Load ).

(Using a long crowbar as a lever, is another example of a mechanical advantage. )

That is why they are used for clamps, such as nuts and bolts, extractors, (such as bearing pullers ), and car jacks.

The ability to change a large circumferential travel into a small linear travel is what is used in the micrometer to measure small distances..

HTH

Howard

[brian jones 11Participant @brianjones11]

q

The thread is M42.5 x 2mm

uq

what is that?

[EmgeeParticipant @emgee]

Posted by brian jones 11 on 29/07/2021 19:25:19:

q

The thread is M42.5 x 2mm

uq

what is that?

I would say that thread is non standard if metric, good list of Metric Fine thread details at this link.

**LINK**

Emgee

[JAParticipant @ja]

I suspect the backplates for the "Big Bore" lathe were cut with a single point tool and originally finished with a factory made tap. During the change of ownership the tap went AWOL or its importance was no recognised. Using just the single point tool could produce a slightly tapered thread.

JA

[duncan webster 1Participant @duncanwebster1]

But any reasonable inspection would have go/nogo gauges for both the location diameter and the thread. Problem with a lot of importers is that they use the customer as the inspector.

And I don't see why using a single point tool gives a tapered thread. Load on tip doesn't change, overhang doesn't change as the tool advances along the bed.

[brian jones 11Participant @brianjones11]

iso 724 shows a metric extra fine thread, M42 x 2

 

https://shop4fasteners.co.uk/metric-fine-pitch-straight-flute-taps-m42-x-2-0-second.html

 

a mere £124, bargain

 

sound like you need to get your OD right first, then check the root of the female and start doing some calcs its a 60 deg form

 

use the 3 wire method when you think your close

**LINK**

 

 

more info on big bore conversion

https://www.model-engineer.co.uk/forums/postings.asp?th=138053

Edited By brian jones 11 on 29/07/2021 20:51:03

[Ian HewsonParticipant @ianhewson99641]

Sounds like someone should check Myford site for facts before opening his mouth!

[brian jones 11Participant @brianjones11]

OMG I stand corrected Myford actually do make a non standard M42.5 x 2 threaded spindle

Can anyone enlighten me on why such a peculiar system was chosen. Was it some dirty means by marketing men to corner their market

My loyalty to Myford brand severely dented.

[not done it yetParticipant @notdoneityet]

The thread is M42.5 x 2mm

Is it metric? Is the thread-form really truly metric? Or is it 1 2/3” of Whitworth form with 79 thous pitch – 12.7 tpi (so tenuously related to the metric value for 1/2” (in mm)?

It would not surprise me.

[JasonBModerator @jasonb]

Why change loyalty now, it's not as though what you have on your machine is a common "standard" size

1 1/8" x 12 Whit are unlikely to be found on a fixing or pipe. As they are not Whit Fine, Whit coarse or Whit pipe threads

There are many metric threads of what may seem odd diameters but they almost all tend to use the common pitches

[Anonymous]

Posted by JasonB on 30/07/2021 07:14:52:

………..but they almost all tend to use the common pitches

Good thing the word 'almost' was used.

I've just made some parts for a guitar for a friend of a friend. One part had an internal thread – M3 no problem, except an M3 tap didn't fit. Try 4-40UNC, also didn't fit. A clue is that the guitar was made in Japan. Turns out the thread was M3x0.6; an old French standard, but is also a current Japanese JIS standard. Fortunately I was able to buy a NOS tap on Ebay.

Last year I did a small PCB layout including a D-type connector. The mating equipment (also made in Japan) used M2.6 for the D-type screwlocks rather than the near universal 4-40UNC, or less common M3. So I had to make a set of M2.6 to 4-40UNC adaptors.

Andrew

[JasonBModerator @jasonb]

Though 0.6mm is a Standard pitch for M3.5, I was thinking more along the lines of M39 x 26tpi camera lenses as being an "uncommon" pitch for metric.

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