Myford Super 7 with ‘Big Bore Conversion’

[Nick HulmeParticipant @nickhulme30114]

Posted by John Haine on 05/04/2020 14:08:49:

why on earth they didn't just make it ER40 in the first place I don't know.

John Stevenson suggested a native ER40 headstock would be the best option for the Super 7, I think Myford were just making a point of ignoring him and common sense by finally employing the MT3 design which one of their employees had come up with in the 1960s or 1970s.
Perhaps the "New Myford" will go with ER40 sometime in the middle of this century!

Edited By Nick Hulme on 05/04/2020 14:23:42

[Paul Smith 37Participant @paulsmith37]

I thought you could get an MT4 to MT2 adaptor? This one

[Howard LewisParticipant @howardlewis46836]

On the face of it, holding a MT sleeve in an ER collet is merely involving another possible source of error.

Although would it be as great as using a 4MT / 3MT sleeve?

I have to use a 5MT / 3MT sleeve in my mandrel, and am unaware of problems.

Maybe that's what comes of not looking for them!

Howard

[Derek GrantParticipant @derekgrant67792]

Hello all you Myford experts!! I have been exploring the Bigger Bore question regarding the Super7. I need 25mm clear borein the spindle and would appreciate any help you can give. Please be gentle with me

Regards Derek.

[Paul Smith 37Participant @paulsmith37]

Posted by Derek Grant on 05/04/2020 21:01:15:

Hello all you Myford experts!! I have been exploring the Bigger Bore question regarding the Super7. I need 25mm clear borein the spindle and would appreciate any help you can give. Please be gentle with me

Regards Derek.

Well so far ive gleaned there were two manufacturers of the big bore spindle headstock, one was Roy Milner who has packed up doing them, and theres Myford themself, who are closed due to the Corona and i dont know wether or not they will supply said big bore spindle headstock on its own as a kit. Regs Pauly

[Mike PooleParticipant @mikepoole82104]

I doubt it would be practical to build a big bore headstock from parts, it would be a long and expensive shopping list. It would make more sense to part exchange your current machine for a big bore I would think.

Mike

[Nick HulmeParticipant @nickhulme30114]

Posted by Mike Poole on 06/04/2020 23:03:41:

I doubt it would be practical to build a big bore headstock from parts, it would be a long and expensive shopping list. It would make more sense to part exchange your current machine for a big bore I would think.

Mike

That's what Roy Milner did, with most of the parts being taken from the headstock being converted, no new gears or pulleys were used.

[Paul Smith 37Participant @paulsmith37]

I just wish it were documented somewhere.

[Mike PooleParticipant @mikepoole82104]

I have seen some pics of Roy’s conversion, a talented engineer no doubt. I think the smallest sheave of the cone pulley is lost so I would think the back gear would need a couple of new gears and the gear that drives the screw cutting train would need to be larger, the chuck backplates will need remachining or replacing, the tumbler reverse for the leadscrew will need work also. It’s not a trivial task to undertake if you wish to copy Roy’s solution. Nearly every part of the Myford big bore headstock is different from the standard bore machine.

Mike

[mariano diazParticipant @marianodiaz48581]

Hi; can someone please point me to were I can see pictures of Roy's big bore conversion? I would like to do it as well, but first because Im intending to make the new spindle (4340 nitrided) and with a different taper, I would like to see if I would have to make gears as well..

Regards

Mariano

[Andrew Moyes 1Participant @andrewmoyes1]

Posted by Michael Gilligan on 22/09/2018 08:53:24:

Posted by Alan Waddington 2 on 21/09/2018 23:51:06:

Seems like a great idea, how can large bearings be inferior to a smaller plain bush ? ……..

.

The general concept of this conversion sounds excellent, but I have a 'back of the mind' recollection that Myford [Beeston] opined that such a conversion was impractical, because the headstock casting was too small for it.

Things change [including bearing designs]: So It would be very interesting to know what bearings, and what adjustment mechanism, are being used here.

MichaelG.

If I recall correctly, when I studied the photos posted by Roy Milner on eBay, it was apparent that he used his own casting for the headstock, confirming what Michael quoted here. The shape of the casting around the pulley and in front of the backgears was different to standard. Also, the enlarged gear on the back end of the spindle (38T on my Beeston big bore machine) means the fourth gear (after the two tumbler gears) has to be enlarged to 38T too in order to preserve the 1:1 gear ratio for screwcutting. That changes the tumbler lever geometry too. So a conversion will not be easy.

Andrew M

Edited By Andrew Moyes 1 on 29/06/2021 08:36:18

[mariano diazParticipant @marianodiaz48581]

Thanks Andrew, Like I say I have never seen any close up pictures os a Super7 with a big bore, At the moment , after purchasing a Super7 headstock for replacement of my Spindle and bearings damaged ML7 , the Idea is to start up with the old ml7 headstock , making a spindle and bearings similar in shape as the Super7 , with the hole now being about 17? mm , I intend to make it at least 20.5 , and for that I will need to line bore , the existing bearing locations, and yes , maybe alter the geometry of the tumbler..

I have a fully equipped workshop including a Colchester Student 1800, Bridgeport knee mill, and universal T&C…

Why do I bother with making a big bore Mod in a Myford , when I have a 38mm Colchester? , well , I think that it’s the challenge,

sorry for the rant

mariano

[peak4Participant @peak4]

Roy has one for sale on eBay at the moment.
https://www.ebay.co.uk/itm/174681228852?hash=item28abd00634:g:cTMAAOSwR5lgTO02

A little while ago someone, probably Roy, had an eBay listing, priced at £1 where one could show an interest before he made a new batch.

Bill

[Chris CrewParticipant @chriscrew66644]

I have visited the workshop of Roy Milner, nr. Lincoln, when I collected a Myford S7 cross-slide from him that I won on eBay. I am not qualified enough to comment on the technical attributes of his big-bore conversions, but simply by observation of his work and the finished examples of his converted lathes, I have to say the products I observed looked absolutely superb.

In fact, had I not had the Maitresse de Maison in tow, I would have been tempted to buy the long-bed example he was selling at the time on the spot. Only the fear of a severe reprimand prevented me from doing so.

Edited By Chris Crew on 30/06/2021 13:27:43

[old martParticipant @oldmart]

The whole spindle must be bigger diameter, as the common Myford spindle thread is 1 1/8" which is 31.75mm.

[mariano diazParticipant @marianodiaz48581]

Posted by peak4 on 29/06/2021 21:15:22:

Roy has one for sale on eBay at the moment.
https://www.ebay.co.uk/itm/174681228852?hash=item28abd00634:g:cTMAAOSwR5lgTO02

A little while ago someone, probably Roy, had an eBay listing, priced at £1 where one could show an interest before he made a new batch.

Bill

Thank you , but Im in Australia, and it will be uneconomic to get it shipped to here…

regards

Mariano

[mariano diazParticipant @marianodiaz48581]

Posted by Chris Crew on 30/06/2021 13:26:48:

I have visited the workshop of Roy Milner, nr. Lincoln, when I collected a Myford S7 cross-slide from him that I won on eBay. I am not qualified enough to comment on the technical attributes of his big-bore conversions, but simply by observation of his work and the finished examples of his converted lathes, I have to say the products I observed looked absolutely superb.

In fact, had I not had the Maitresse de Maison in tow, I would have been tempted to buy the long-bed example he was selling at the time on the spot. Only the fear of a severe reprimand prevented me from doing so.

Edited By Chris Crew on 30/06/2021 13:27:43

Lincoln? my nephew parents live there. Perhaps when the situation normalise , and we be able to travel I may go to visit him, and try to contact Roy , to see what is de difference , and appreciate his skills levels..

I dont like the Myford m42.5×2 spindle thread (I realise that it maybe there together with the grove in the location diameter, to try to stop the chucks from being unscrewed , but in my opinion they should have used a better and more modern way of chuck location

stay safe

Mariano

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