Running a Myford in Reverse?

[Martin King 2Participant @martinking2]

Hi All,

i have quite a few small knurled thumbscrews to make with a 3/16 x 24 thread.

I now have the correct dies from Tracy Tools but would also like to have a go at screw cutting in reverse a la Joe Pie on YouTube.

I am aware that the Myford S7 has a screw on spindle and the dangers therein but wonder if anyone has come up with a way of safely locking the chuck to prevent it coming off in reverse running?

Cheers, Martin

[Martin King 2Participant @martinking2]

[John BaronParticipant @johnbaron31275]

Hello Martin,

I too have a Myford S7 with a screw on chuck ! I have never had a problem with it unscrewing whilst threading in reverse. In fact I try to do all my threading away from the chuck. It is also the best way to do internal threads as well.

I do know of one chap that managed to unscrew his chuck, but that was his mistake trying to part off from the front with the tool upside down, jamming the blade in the cut.

A properly tightened chuck should not cause a problem.

A note on jammed chucks: Always make sure that the threads and register are scrupulously cleaned and oiled each time you change the chuck. It doesn't take much to cause a jamb !

[Martin KyteParticipant @martinkyte99762]

The thing about screwcutting in reverse is that in general the diameter of the work is small. It's torque 'wot unscrews the chuck so on a small radius you can get away with quite a large cutting force.

regards Martin

[John HaineParticipant @johnhaine32865]

On the big bore Myford there is a vee groove just behind the register into which a set screw on the backplate can engage to prevent the chuck unscrewing very much and falling off. IIRC it is not recommended that this is tightened fully as it may push the chuck out of alignment. Is this not present on the standard spindle?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 11/02/2021 09:59:21:

On the big bore Myford there is a vee groove just behind the register into which a set screw on the backplate can engage to prevent the chuck unscrewing very much and falling off. IIRC it is not recommended that this is tightened fully as it may push the chuck out of alignment. Is this not present on the standard spindle?

.
< with a pedant alert >

Yes, it is not present on the standard spindle

MichaelG.

Edited By Michael Gilligan on 11/02/2021 10:09:56

[egaParticipant @ega]

I understand that the big bore's vee groove/set screw is intended as an emergency safety measure and, presumably, if it comes into play the work may have been spoilt by the slight loosening of the chuck?

OT:

Is "yes" the grammatically correct answer to a negative question in English (as it is in French)?

[Clive HartlandParticipant @clivehartland94829]

I see that the chuck locking problem has come up again, there are chucks with a locking ring behind the chuck. This is simple collar with an Allen key screw which tightens the chuck collar againsthe the spindle.

All Schaublin chucks had this facility and it is so simple.

I would fotograph mine but it is such a faff to enter the pic. into the album.

[OldironParticipant @oldiron]

Posted by Clive Hartland on 11/02/2021 11:05:03:

I would fotograph mine but it is such a faff to enter the pic. into the album.

personally I do not see why it is a faff at all.

Click green"album" link at top of page/edit album info/add photos/browse to photo, select & upload. It takes less than 30 seconds to do. I just uploaded the picture of my snow drops in 20 seconds to my album.

regards

[egaParticipant @ega]

Posted by Clive Hartland on 11/02/2021 11:05:03:

I see that the chuck locking problem has come up again, there are chucks with a locking ring behind the chuck. This is simple collar with an Allen key screw which tightens the chuck collar againsthe the spindle.

All Schaublin chucks had this facility and it is so simple.

I would fotograph mine but it is such a faff to enter the pic. into the album.

Would such an arrangement be possible on an S7?

[Martin King 2Participant @martinking2]

Thanks guys,

I am assuming that if one is in back gear at low rpm for threading anyway the potential for a problem is much reduced;

Is anyone aware of "upside down" HSS threading tools being available or does one have to make their own? Something I am very bad at doing

Cheers, Martin

[GeorgineerParticipant @georgineer]

Posted by ega on 11/02/2021 10:48:22:

Is "yes" the grammatically correct answer to a negative question in English (as it is in French)?

My schoolboy French from 55 years ago tells me that one would answer 'si' rather than 'oui' in this case. Sort of 'Yes but no'. I don't believe English has an equivalent.

I have seen a modification to lock the Myford chuck to the mandrel thread, and memory says it is a screw in the collar of the backplate, with a soft pad to press against the mandrel thread or possibly the register. Regrettably, memory doesn't tell me where I saw it.

George B.

[John HinkleyParticipant @johnhinkley26699]

Posted by Georgineer on 11/02/2021 11:59:10:

My schoolboy French from 55 years ago tells me that one would answer 'si' rather than 'oui' in this case. Sort of 'Yes but no'. I don't believe English has an equivalent.

I think Matt Lucas' character, "Vikki", in "Little Britain", covered that one, with "Yeah-but! No-but!"

John

 

Edited By John Hinkley on 11/02/2021 12:09:17

[Martin ConnellyParticipant @martinconnelly55370]

I don't think you need yes or no. The rest of the answer is sufficient on its own.

Martin C

[John HaineParticipant @johnhaine32865]

Posted by Martin King 2 on 11/02/2021 11:43:35:

Thanks guys,

…….

Is anyone aware of "upside down" HSS threading tools being available or does one have to make their own? Something I am very bad at doing

Cheers, Martin

Use an internal threading tool "behind" the work, lathe in reverse?

[JasonBModerator @jasonb]

That's how I do it just the standard internal tool held behind the work.

Depending on size of work you could also use a collet (one that goes into the taper) as that won't unscrew

[peak4Participant @peak4]

Jason's is one obvious solution with a collet in the taper, directly or via an ER chuck or similar, but what sort of conventional chuck do you use?
My method precludes the use of long bar stock but seems to work well enough>

My 4 jaw is a Pratt Burnerd style slimline, fitted to a separate backplate.
The hole through the backplate is a smaller than the hole through the throat of the chuck, so I just add a washer and some threaded rod as a draw-bar.

For my Griptru, there is a gap between the front stub/register on the front of the backplate, and the back of the internal recess in the chuck.
Again I use a washer/draw-bar, but this time, I've modified the washer.
I've tapered the outside diameter, as well as cutting a pair of flats on it that fit the threaded bore of the backplate.
This means that I can slide the washer up at an angle through the threaded hole in the backplate, and then it catches and locates OK when squared up.

Bill

[Howard LewisParticipant @howardlewis46836]

If you make or buy a Rear Toolpost, you could use a normal threading tool, "right way up" with the lathe running inn reverse.

You don't need a special "upside down" tool. As long as any tool is mounted with the cutting edge on the centre line, and has correct clearance angles, it will cut.

Parting off is better with the tool mounted upside down in a rear toolpost., and the lathe running forwards.

I have parted off with an inverted tool in a rear tool post for 17 years on this lathe and many with the predecessor ML7, finding it a less problematic method.

HTH

Howard

[Nick HughesParticipant @nickhughes97026]

An option I used:-

The ensuing discussion was here:- https://www.model-engineer.co.uk/forums/postings.asp?th=142307

Edited By Nick Hughes on 11/02/2021 15:35:07

[Mike PooleParticipant @mikepoole82104]

I remember reading about a solution to retain the screw on chuck for reverse running but I think the through hole was sacrificed while it was fitted. It was most likely in MEW some years ago.

Mike

[old martParticipant @oldmart]

The Atlas 12 x 24 which we are getting into running order has a screw on spindle mount similar to the Boxford and, slightly bigger than Myford. When I decided to add a 160mm three jaw chuck, the chuck body had enough metal in it to enable the bore to be increased to just about 1 3/4". The spindle thread is 1 1/2", so a drawbar with a flanged end 1.74" diameter would stop the backplate from unscrewing if reverse was used. This has the drawback of blocking the spindle bore.

As already mentioned, threading in reverse using a left handed threading tool to produce a right hand thread allows you to thread away from the chuck. Usually slow speeds are used and the forces are not great enough to be in much danger of unscrewing the chuck. I would loosen and retighten the chuck firmly before doing this tye of work.

I made a much more sophisticated locking system for the Smart & Brown model A, which doesn't block the spindle, but nobody on this forum was interested in the design.

[SillyOldDufferModerator @sillyoldduffer]

I'm on the cautious side when it comes to Health and Safety, but I suggest there's a big difference between taking heavy cuts in blissful ignorance the chuck might unscrew and light threading whilst fully alert to the risk. In the first case the surprise causes an accident, in the second the careful operator is watching for trouble and can disengage.

And a common problem with screw-on chucks is they stick so firmly lathes are damaged trying to get them off!

Dave

[John BaronParticipant @johnbaron31275]

Posted by SillyOldDuffer on 11/02/2021 17:33:02:

And a common problem with screw-on chucks is they stick so firmly lathes are damaged trying to get them off!

Dave

That is why I made a statement about keeping the threads and register scrupulously clean and well lubricated.

It takes very very little in the way of dust, dirt or other debris to jam the threads.

[Chris CrewParticipant @chriscrew66644]

As regards 'upside-down' screw-cutting tools I am just trying to clarify in my own mind exactly what this means as regards screw-cutting. I always cut internal threads on the rear-face of the bore with the tool inverted but it is still a standard screw-cutting tool. This method has several advantages : – a) you can use the set-over top-slide method which puts less stress on a necessarily slender screw-cutting tool when cutting small internal threads. b) you don't have to remember to withdraw the tool in the opposite direction to cutting external threads. c) you can actually see what is happening in the bore to a certain extent.

Even if you were cutting left-hand threads it is only the side-rake angle that has to be reversed if you grind screw-cutting tools with side-rake for using the set-over top-slide method, otherwise just grind top-rake and use the tool for both right and left hand threads. Always cut left-handers with the tool moving away from the chuck and the lathe rotating conventionally. It would be difficult to cut left-hand threads with the top-slide set over for moving away from the chuck in any event. A screw-on chuck, as on the Myford or Boxford type lathes, will always unscrew unless specially secured. I have had a chuck fly off when I accidentally knocked the Dewhurst switch lever over and threw the Myford into reverse.

I have an Ainjest rapid threader on a Student and its an absolute godsend when screw-cutting so I was considering making and fitting either the Radford or Cleeve device to knock out the half-nuts on the Myford but I am yet to decide if these devices will knock out the half-nuts fast or precisely enough. I think they should.

[John BaronParticipant @johnbaron31275]

Hi Chris, Guys,

[quote]A screw-on chuck, as on the Myford or Boxford type lathes, will always unscrew unless specially secured. I have had a chuck fly off when I accidentally knocked the Dewhurst switch lever over and threw the Myford into reverse.[/quote]

This can only happen on a machine with a three phase motor ! Switching to reverse whilst running forward will not stop the motor, it will just keep running. The single phase motor speed has to slow down enough for the centrifugal switch to drop out reconnecting the start winding.

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