Cure Those Parting Off Problems

[JasonBModerator @jasonb]

This popped up this morning seems to cure the need for a rear stool post…………….

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

https://www.facebook.com/reel/2784251771739609

[Bo’sunParticipant @bosun58570]

Don’t you mean “pooped-up”?

[Alan JacksonParticipant @alanjackson47790]

Using  that and a constant steady feed should avoid serious chatter.

[JourneymanParticipant @journeyman]

Should make parting very convenient.

John

[Clive FosterParticipant @clivefoster55965]

It’s the constant steady feed that defeats most folk. Hand feeding its far too easy to overdo things making oversize chips that easily jam. Doesn’t help that far too many folk get frightened into working low speed in back gear. Which takes forever.

Takes a certain nerve to wind up the speed, wind down the feed and leave it to the machine.

The most important thing is that the chip be thin enough so that if one does jam it’s not too tight to clear next time round. If it doesn’t clear the work will start climbing over the tool drawing it into the job, deepening the effective cut rapidly escalating the problem until either the drive stalls or something breaks. Because rear toolposts put the feed screw in tension rather than the conventional compression the draw in problem is greatly reduced. Little chance of stretching a 1/2″ or so diameter screw but working in compression with a couple of inches or more unsupported it can easily bend off line touch as it tries to go off line. Doesn’t help that many machines, Boxford and SouthBennd for example have a an inch or so necked down to core diameter before the thread starts. Clearly reducing stiffness

Professionals run fast with very low feed so the chip can escape but that needs lubrication and coolant for a part of any size you are not to burn up the tool by overspending on the outside diameter.

The carbide insert advantage is two fold. Firstly it can run faster and secondly the concave to folds the chip so it is narrower than the slot significantly reducing the risk of jamming.

If you fancy a neat version of the “LooLuber” but don’t want to do all the making take look at teh motorcycle chain lubrication systems. Import knock offs of the Nemo handlebar mounted device are nicely anodised and can be had for £20 (ish). Screw cap pressurises the oil.  Add needle valve and you are done.

Clive

[EmgeeParticipant @emgee]

Guess you swivel the brushhead around when traversing.

Emgee

[DalboyParticipant @dalboy]

That will stop the “P**s poor performance”

[noel shelleyParticipant @noelshelley55608]

Painless parting – what a relief ! Noel.

[duncan webster 1Participant @duncanwebster1]

I thought that was the bog standard way of doing it.

[Neil LickfoldParticipant @neillickfold44316]

Most problems with parting and deep grooving occur from the slides being too loose, or the stock is held in a worn chuck, 3 jaw or 4 jaw.

My coolant bottle has the red crc can tube poking through the top. It has about a 1mm hole through it, and allows for a controlled amount of fluid out of it. Being about 2mm in diameter, it sits nicely over the grooving parting tools.

I don’t wind continuously to the centre. I go about 1mm deep, 2mm diameter back out a little to force the break on the chip and wind back in. My feedrate is about a thou or 0.03mm or so per rev. I go slower at the very centre.

Start with the highest rpm for the material at full diameter with a little more coolant /oil for the beginning.

Something I need to make up is a hands free oiler.

[Nigel Graham 2Participant @nigelgraham2]

Another point when using HSS parting blades is to grind the front at right-angles to the sides.

Grinding at an angle – an old dodge supposedly minimising the pip left on the work or the stock – makes the chip wider than the kerf, so more likely to jam.

[duncan webster 1Participant @duncanwebster1]

Grinding the tip at an angle also pushes if off to one side if its long and thin. Results in a conical surface (if you’re lucky) or a broken tool. If going in deep what I was taught was to go in say 1/2 inch, back out, move over 10 thou, go in 1 inch (ie an extra 1/2 inch) back out, move back to original position, and so on. The kerf is then wider than the chip for most of it’s depth. As others have said, steady positive feed, don’t pussy foot around

None of this worked on my old ML7, the QCCut holder helped, but I often had the resort to hacksaw.

 

[Mark RandParticipant @markrand96270]

To Clive’s comment about the rear toolpost putting the feedscrew in tension, I would suggest that some lathes would put it in tension, but others would put it in compression for the same activity (I speak only from knowledge of Myford and Hardinge in my shed).

However:- With the rear toolpost, when the load increases the tool levers away from the work, with the front toolpost it is levered in. I suspect that that is the advantage of rear toolposts on ‘flexible’ lathes.

I find that carbide parting off inserts work well due to their shape making the chip less wide than the slot, but note that Mr Geo. H. Thomas recommended grinding a ‘V’ groove in the top of HSS parting blades to achieve the same effect.

[Howard LewisParticipant @howardlewis46836]

If one can be fitted (Purchased or nade) a rear toolpost avoids may problems with parting off. On the ML7, mine started liife a sa poece of 2″ x 2″ box section, and the end product revolusionised parting off.

On my present lathe, the rear toolpost is a 75 mm square, four way one, using the same 3/32″ tapered HSS blade, at fairly low speed.  Now I am so brave that I use power feed, of about 0.075mm per rev, usually with a drip feed of soluble oil. Problems are rare , even when parting 50 mm M S bar.

Plenty of lubrication is big help, as is a slow steady feed!

Howard

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