Parting-off

[JAParticipant @ja]

On my Myford I use a rear mounted tool post with the parting off tool mounted up side down (chuck running in the usual direction). As long as a cut is being taken in a positive manner (without dithering) there are no problems. I did use the power cross feed, again without any problems, but ceased after being told on this forum that it was a real NO-NO. I note that Jason uses power cross feed.

I have a rear tool post on my Cowell whose chuck screws onto the headstock shaft. However, as yet, I have only used the normal toolpost for parting off.

Geo. H. Thomas used forced diagrams to explain why a rear tool post worked. They made absolutely no sense. I note the comments about the possiblity of lifting the carriage etc but I think the drop out of swarf from the kerf (thanks for the new word) is very important especially after looking at how quickly it filled up with bronze chippings with the Cowell.

I find parting off to a hole very much easier than to solid. Also I always try to use a rod up any such bore, from the tailstock, to catch the parted off item. I once had a largish item fall between the bed and four jaw chuck. Fortunately nothing was hurt.

So, for me, use rear tool post on Cowell and power cross feed on Myford.

JA

[noel shelleyParticipant @noelshelley55608]

As Andrew has said, Cut Off Slide, Myford made 2, a screw operated one (which I have ) and a Lever Operated one (more common). They were clamped to the bed in the required position and wound across to cut off. They were part of the repetition gear that turned a Myford into a production lathe. There were 2 capstans available, a cross slide mounted one or the very expensive bed mounted Proper capstan, add the lever operated collet chuck and your away ! Noel.

[peak4Participant @peak4]

Thinking purely Myford 7 here, another reasons I suspect some folk find a rear toolpost advantageous for parting with an inverted cutter;

You are pulling the tool towards you using the opposite side of the feed nut, using the distant end of the feedscrew, and the least worn farthest end of the top slide dovetails.
You are loading the dovetails upwards which reduces the possibility of vertical movement, as well as increasing the front to back friction.
All of this makes the setup slightly more rigid and less likely to allow a dig-in of the cutter.
It’s also loading a different area of the main bronze cone bearing on a Super 7, or a different section of the softer bearings on an ML7.

Bill

[Howard LewisParticipant @howardlewis46836]

For what my comments are worth.

The object is finish up with a 12mm long ring, with a 28 mm bore.

My imclination for such a job on a Myford would be to saw off a piece of raw material, say 15b mm long.

Ideally on a bandsaw, with the vice suitably packed to hold the material; otherwise a lot of hard work with a hacksaw.

The resulting piece can then be faced, and drilled / bored out, before being reversed in the chuck to face to length.

Parting off works much better with the tool inverted in a rear toolpost, but parting off 75 mm diameter stainless protruding 50mm sounds like a challenge.

As already said, if you di decide to part off, keep up a slow steady feed, don’t rush, but don’t let the tool rub.

Good luck

Howard

[old martParticipant @oldmart]

Having a rear inverted parting off tool in a suitably stiff mount and rear locking for the saddle (carriage) helps greatly with the stiffness, particularly as theordinary toolpost and compound are eliminated. Gravity helps with swarf removal and the screw threaded spindle is still running forwards. Any hole in the workpiece makes the depth of cut less and the stickout of the parting off tool should be the minimum to achieve the thickness to be cut.

When I made a solid block for industrial blades, 26 and 32mm to fit the Smart & Brown model A at the museum, it was bolted directly to the cross slide with 4x 8mm SHCS after first removing the cross slide to make sure the threaded holes did not get in the way of anything. The photo shows a 32mm x 3mm Kyocera blade fitted, the top half can be turned round to hold 26mm blades from 1.6, 2, and 3mm widths.

[Chris CrewParticipant @chriscrew66644]

Don’t ‘peck’ at it, be bold, a good steady feed in with plenty of suds/coolant and use a freshly sharpened tool – easy if you use ‘traditional’ tooling. Rigidity, as others have stated, in both work and tool holding is key so use the 4-jaw to hold larger work if it is at all possible. If you need to reposition your hand on the cross-slide screw, then back-off the tool half a turn, reposition your hand and start the cut over again. You are not being tested, nobody is going to reprimand you if your parting fails first time because you are the boss in your own workshop. The worst you can do is ‘ping’ the parting blade if it happens to dig-in, takes about 2 – mins to sort out with an ‘Eclipse’ type blade in a J&S holder. Can’t say anything about this ‘new fangled’ tipped tooling for parting because I have never used it and don’t intend to as I have a way of working that works for me 95% of the time, but I will accept it may not do for others.

[JasonB]

On JasonB Said:

On SillyOldDuffer Said

 

I consider it ‘best practice’ to minimise rigidity before parting-off,

That’s where you are going wrong, it would be better to MAXIMISE rigidity.

Have you not got power cross feed on your 280?

Oh no, one of those typos we’ve been discussing in another thread got in!   Of course it should say MAXIMISE, as one would expect in a post that starts ‘Successful parting-off, I think, depends mostly on rigidity. ‘

Yes indeed my 280 has power cross-feed, which is why I said: ‘The same machine and set-up parts-off reliably when I step back and let the powered cross-slide do the job, chatter almost unknown.’

Dave

 

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