Running a Myford S7 in Reverse

[peak4Participant @peak4]

Posted by Mitch Lees on 11/02/2022 20:56:05:

Peak4,

thanks for that insight. My Pratt Burnard Chuck has a bore the same as the spindle and so I cannot fit a washer for a draw bar. ……………..

I am now in the process of making a spindle handle, but I want to incorporate a through bore so that if I do decide to change chucks and have a draw bar, I can use it with the handle.

thanks for the help

mitch

Mitch, re the handle/drawbar thing, I'm not sure you would really need to use both at the same time, as, by design, everything will be happening slowly.

Is your PB chuck on of the Myford threaded ones, or is it on a backplate.
If the latter, there's nothing to stop you temporarily removing the chuck, turning a recess on the front of the backplate, and then reassembling.
A washer with trimmed opposite sides, will then slide up the bore, and drop into the recess you've just made.

Bill

[Mitch Lees 1Participant @mitchlees1]

Bill,

you are right, and it will be easier to make the handle without bothering with the through bore. My 4 jaw is the threaded version without back plate, but the 3 jaw does have a back plate. I had not considered boring a recess in the back plate because I did not think I could get the washer in without separating the assembly each time. Although I will probably not bother with the draw bar for now, I may machine the recess anyway and experiment with filing flats on the washer and inserting it as you say. I suppose there are always solutions! A lot cheaper than buying a new Chuck. Than you, Mitch.

[HopperParticipant @hopper]

Posted by peak4 on 11/02/2022 20:08:21:

There's other reasons for running the Myford backwards as well as screwcutting.

When I picked up a part built Quorn, I needed to re-cut the taper in the main spindle.
I set the whole spindle tube up in a couple of fixes steadies, so the spindle ran in its own bearings.
The taper was re-cut to get it central again, correcting the original builder's error; The top slide was in the normal position and used conventionally with a boring tool.

Whilst the top slide was set over, it made sense to turn up more arbors for the grinding wheels.
Yes I could have cut the tapers conventionally, with the tool at the front of the work, but that would mean the thin end would be at the chuck, and I couldn't easily turn the taper, parallel portion and the thread on the thin end, all at the same setting.

By running the lathe in reverse, I could cut on the back of the workpiece, have the thick end at the chuck, turn the parallel section(s) and also add the thread at the end with a Herbert die head, and everything was guaranteed concentric.

….

Bill

Could you not have cut on the back of the job, but turned the toolbit upside down and run the lathe in the forward direction? IE like a rear parting tool.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Mitch Lees on 07/02/2022 18:47:29:

I want to have a go at screw cutting on my Super 7 and it seems that by running the lathe in reverse I can cut away from the chuck – hopefully less stressful! However, I have read that the chuck can unscrew with disasterous consequences! …

Power threading away from the chuck is wonderful because you can cut at top-speed without any risk of smashing into the headstock or the spinning chuck. Unfortunately the technique is risky on lathes fitted with a simple screw-on chuck because the forces tend to undo it, which spoils the thread, and might even cause the chuck to fall off.

All machine tools have limitations, and screw-on chucks are one of Myford's! Although they work well in most circumstances:

1. Chucks can jamb so tightly that owners often damage the lathe trying to get them off. Avoid over-tightening by regularly loosening the chuck and don't use the machine heavily for years without checking the chuck, or allow rust, or the oil to gum up in the threads!
2. The lathe can't be used willy-nilly in reverse! Has to be driven with due care and attention. But reverse cutting can be done provided the operator resists the urge to hack metal at full throttle, and checks the chuck is still secure every so often.

I'd only consider modifying a Myford for guaranteed safe reverse threading if a lot of threading had to be done in a hurry. For occasional work, it's easier to slow down and thread carefully. In the forward direction avoid crashing the carriage, in reverse don't cut so hard that the chuck unscrews.

Modifying the chuck and spindle mechanically is one option, an Electronic Leadscrew is another. Or admit the Myford is a poor choice for this particular application and replace it with a lathe fitted with a bolt-on or cam-lock chuck.

Dave

[peak4Participant @peak4]

Posted by Hopper on 12/02/2022 11:24:18:

Posted by peak4 on 11/02/2022 20:08:21:

………………
By running the lathe in reverse, I could cut on the back of the workpiece, have the thick end at the chuck, turn the parallel section(s) and also add the thread at the end with a Herbert die head, and everything was guaranteed concentric.

….

Bill

Could you not have cut on the back of the job, but turned the toolbit upside down and run the lathe in the forward direction? IE like a rear parting tool.

Certainly yes, and from what I can recall, I did look at that, but because of tool and toolholder sizes, I would have had to raise the QD holder too far up the Dickson style toolpost, such that I couldn't clamp it properly.

I'm sure I could have found a much smaller bit of HSS, rather than the carbide insert I used, but just thought running backwards was easier overall.

Horses for courses I guess, since I prefer not to skin cats.

Bill

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