MYFORD SUPER 7 TELESCOPIC CROSS SLIDE FEEDSCREW
By Graham Meek

When using the taper turning attachment on the Myford Super 7 lathe the instructions are that the cross slide feedscrew bracket be detached and allowed to hang on the feedscrew, usually upside down. After a couple of times using this method I was not happy with the feedscrew bracket just hanging there on the feedscrew, the set up had all the potential of an accident waiting to happen.

Anything dropped and impacting on the feedscrew bracket is going to potentially bend the feedscrew. Similarly the sleeve of a smock coat could quite easily catch the ball handle and again bend the feed screw. Admittedly this is not such a problem with the power cross feed models due to the larger diameter feedscrew thread but one still has the task of realigning the feedscrew bracket at the end of the session, which is not always an easy task.

These first sessions with the taper turning attachment was about the time that George Thomas was describing his modifications to the Myford cross slide micrometer collars in Model Engineer, details of these improvements can be found in The Model Engineers Workshop Manual by GHT, chapter 15, page 164.

Reading through the articles as they were being published I thought it would be a good idea to add the needle roller bearings to my own lathe. Thus a spare ball handle, feedscrew bracket and feedscrew were ordered from Myford’s, in the meantime a start was made on the new feedscrew bearing and collar that would eventually take the needle roller bearings.

As I was about to drill and ream the 9.54mm or 3/8” bore the penny dropped, rather than Loctite the feedscrew into this bore, what if the feedscrew could telescope inside this bore then the need to dismantle the feedscrew bracket during taper turning would be unnecessary.

A Woodruff key in the feedscrew and a keyway in the 3/8” bore would ensure a positive drive from the ball handle to the feedscrew, the whole assembly being retained by an M6 capscrew fitted where Myford’s chrome slotted ball handle retaining screw normally resided.

To use the taper turning attachment in future this would simply mean slackening off the M6 by 30 long capscrew, or removing it completely, then by turning the ball handle a couple of turns clockwise there is instantly play in the system to allow the cross slide to float under the influence of the taper turning attachment. The taper machining cuts still have to be put on using the topslide as before, which incidentally can be set at a fairly shallow angle to make use of some very fine adjustments towards the final stages of producing the taper.

I regret to say I have not taken any photographs to include with this article as the lathe in question was passed on many years ago when I acquired my Emco Maximat Super 11, the only photograph I do have is a Polaroid and does not come out very well when scanned. It was only recently when having a long overdue tidying up session in the workshop following my retirement that the original ball point sketch came to light. Therefore, the reader who is contemplating adding this to his or her Myford would be well advised to read the articles by GHT mentioned earlier as the modification is primarily George’s, I have just added a refinement.

My modification retains a friction setting dial, this can be arranged by using the nip on an O-ring as the friction medium or the reader could do as I did and make a friction spring similar to that used on GHT Versatile Dividing head to provide friction for the sector arms. Details of such a spring can be found in Fig 22, detail 34 on page 81 of Dividing and Graduating, of course the outside diameter will need reducing. Not knowing which way the reader might opt to go these dimensions are marked thus (*) in the drawing for the modifications to the ball handle. Obviously the centre dial locking arrangement favoured by GHT in his article on the lathe micrometer dials cannot be used with this setup.

The reader will notice from the drawings that overall length of the new feedscrew bearing also carries a (*). The reason for this is initially the feedscrew bearing needs to be produced slightly oversize on length, as does the 12mm long spacer. When the feedscrew modifications have been completed the feedscrew bearing is fitted to the feedscrew and

the 12mm spacer with some Loctite 603 on the outside diameter dropped in the bore all is locked up with an M6 Capscrew, a final check is made to ensure the feedscrew bearing is hard up against the shoulder of the feedscrew and all is left to set. Needless to say the amount of Loctite used needs to be minimal, as we do not want to end up with the feedscrew permanently attached as well. When all is set and I usually leave these things overnight, a light facing cut over the end of the feedscrew bearing and spacer to bring both faces flush while establishing the 21mm dimension.

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