Myford question

[phillip burbankParticipant @phillipburbank45787]

Hello every one my first post on here, so please excuse my ignorance, but here goes.

I hope that this is in the right forum if not sorry.

What is the spindle bore of a Myford ML7, small bore and big bore.

I'm trying to identify which one it is.

Is there a difference is the outer dia, I.E. are the chucks interchangeable without having to change the backplate. I recently aquired this current machine, I have had a Myford before, a super 7 b pxf, but the chucks came with it, so totally in the dark.

Thans in advance everyone.

[phillip burbankParticipant @phillipburbank45787]

Spindle bore

[Brian WoodParticipant @brianwood45127]

Hello Phillip,

Welcome to the forum.

I can't answer part 2 of your question on a big bore Myford, the standard S7 has a bore of 16 mm.

Regards

Brian

[DiogenesIIParticipant @diogenesii]

If it's an ML7 I'm fairly certain will be a small bore, using a standard myford 1 1/8" thread, the Big Bore S7 is a 40-something mm metric size spindle nose – the backplates & mountings are totally different and not interchangeable, to the best of my knowledge – maybe someone can confirm..

[noel shelleyParticipant @noelshelley55608]

I don't think there was a big bore Ml7 it's bore is 5/8" ! and welcome aboard ! Noel.

[egaParticipant @ega]

Brian Wood:

I have a feeling that the S7 bore has varied slightly – I don't think mine will accept 16mm (or even 5/8"!).

[Nick Clarke 3Participant @nickclarke3]

Posted by ega on 12/11/2021 17:17:01:

Brian Wood:

I have a feeling that the S7 bore has varied slightly – I don't think mine will accept 16mm (or even 5/8"!).

As Brian has suggested I too have heard that it has varied over time – however the early documentation says it is 19/32"

[GreensandsParticipant @greensands]

In general the bore size of a Myford Super 7 spindle will not accept 5/8" bar stock, a fact which I have always found to be very frustrating. However, I do recall having a conversation with Chis Moores some years ago at an exhibition where he told me that subject to individual inspection Myford did offer a special machining service to carry out the reboring operation stressing the fact that it would not be possible to do on every unit. Hope this helps.

[Thor 🇳🇴Participant @thor]

The big bore Super 7 Plus has a M42.5 x 2 mm pitch nose and a 4 Morse taper socket and will pass a 1" bar.

Thor

[Brian WoodParticipant @brianwood45127]

I quote from my own experience. It is a tight fit but my ML7R will pass 16 mm

Brian

[Harry WilkesParticipant @harrywilkes58467]

Welcome to the forum

H

[egaParticipant @ega]

Posted by Greensands on 12/11/2021 17:42:33:

In general the bore size of a Myford Super 7 spindle will not accept 5/8" bar stock, a fact which I have always found to be very frustrating. However, I do recall having a conversation with Chis Moores some years ago at an exhibition where he told me that subject to individual inspection Myford did offer a special machining service to carry out the reboring operation stressing the fact that it would not be possible to do on every unit. Hope this helps.

It sounds as though later production Sevens had a slightly larger bore and that smaller bore owners would not be advised simply to enlarge their spindles to 16mm by drilling from the tailstock (also, I believe the taper is hardened).

[Brian WoodParticipant @brianwood45127]

ega,

The spindle bore is not hardened

[Mike CrossfieldParticipant @mikecrossfield92481]

The maximum bore size in the small bore 7 series lathes is limited by the MT2 dimensions. The small end of a standard MT2 taper is .572 inch diameter, which is roughly 14.5 mm. The MT2 taper is .050 per inch, so if the bore is opened up to .625 (5/8 inch), roughly 16 mm, you lose about an inch of the taper. This seems to have been done on some late machines, but on my early ML7(long gone) and Super 7 the minimum bore is less than 15mm, though beyond the end of the morse taper the bore opens up to more like 16mm. Same story on the late model Speed 10 I had at one time.

Mike

[egaParticipant @ega]

Posted by Brian Wood on 13/11/2021 11:07:48:

ega,

The spindle bore is not hardened

Brian

Thanks for confirming this. What I had in mind, however, was that attempting to open up the bore at the tail end of the hardened taper could be problematic; no doubt a carbide-tipped tool would help but as Mike Crossfield points out some of the taper would be lost – not necessarily a major problem, of course.

The varying size of the bore becomes apparent to those who make J A Radford's stop bars; the major diameter of his Super Seven spindle was 0.621" and the smaller end near the chuck 0.580".

JAR was not averse to modifying his Myford, notable with respect to the narrow guide of the saddle, a modification whose principle was I understand later adopted by the makers.

[Howard LewisParticipant @howardlewis46836]

My memory of my ML7 was that the taper was 2 MT so that anything much larger than 1/2" was unlikely to pass through the spindle.

This was one of my reasons for moving to a larger machine!

Being a coward, I would be wary of enlarging the bore, for fear of the thinner wall weakening the spindle and degrading rigidity and accuracy. No doubt, the Spindle OD and 2 MT taper were considered to the best compromise of strength and facility within the cost target for the machine, in its intended market..

Getting it wrong might be a very expensive error!

Howard

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