An alternative to parting-off

Standard inserts have a flat cutting edge at the front, even though there is a shaped groove behind.

Neil.

And as neil says, it needs to be just high enough to stop it eating inserts. This is going to be different on a Hardinge than an ML7 (mine are , at least!).

Basically, if it's working properly, leave it. If you get a chipped insert at the end of the cut, the solution is to raise the tool an RCH.

In some industries, especially CNC production, there are people whose job is tool setting.

A quick google shows a CNC tool setter can earn £25 - £30 a hour, that's nearly £60-K a year before overtime... I bet you have to be within a thou to earn that!

Neil

Do tell me how many people have a lathe capable of not having a tangible deflection at the parting tip? OK, I usually set tool height by facing to no pip, but that counts for nothing with a length of parting tool hanging out from its holder, let alone the forces on the rest of the machine as it loads up, particularly the older machines such as mine (OK, it’s only 5 decades, or so, since it was made). I can still part off successfully, knowing full well that deflection from a theoretical centre height setting is occurring and changing as the cut continues.

Until there was an extra toolpost, fitted (almost) permanently at the back of the long(er) slotted cross slide on the Raglan 5” (compared to the LJ) I didn’t bother too much with parting off. Yes, sometimes things got difficult but never insurmountable. The biggest advantage of the extra fitted toolpost is that it doesn’t need squaring up as often.

Some time ago I got an optical centre finder, it was on sale at the time. It has many useful functions, two of which are centre finding (that's a surprise!) and tool height setting, simply stick it in the tailstock chuck, and you can see the tool in scary detail. To my mind better than all the gauges, tools etc.

cheers

Bill

Regarding parting off and centre height, (I haven’t discovered yer how to add a quote) thanks for the explanation, that will explain why I chipped a new tip on first use parting off with a new fixed height toolpost, I discovered the tip was just below centre and it went bang! Now been adjusted with a bonded shim under it to get it to centre height.

I agree about cheeped tips as well, I was having great tifficulty with a the next tip, it grumbled when in use on my S7; a lot of force to get it cutting but then it went ok once cutting started. Close examination revealed the top of the tool was flat so it had no back rake. changing the tip for a top brand and instant success. I’d messed about for an age adjusting the spindle end thrust, (tightened it, but now Iv had to loosen it again, too tight it got hot and squeeaked) and all gibs were adjusted( they didn’t really need it). So with the second new tip things changed to service as normal. I had a back post, but sold it when I got the tipped holder as there was no problem from the front working. I didn’t like the back post, it magde using the die holder difficult, and it needed a lot of care to ensure it was clear of the chuck. And it seemed to add a lot of Xslide handle turning to get it in the correct position but with the fixed post tool changing is fast and easy.

It was on indeed.com, but surprise, surprise, when I looked this morning the job has gone!

Still some at £15 an hour or 'negotiable'.

But my original point wasn't the salary so much as there are plenty of skilled jobs out there setting CNC tools to high levels of accuracy.

Neil

Hi Bill,

What sort of accuracy can be achieved with the optical centre finder? I've never used one.

Thinking on it a bit your method would only work on my Boxford if I allowed for the fact that my tailstock is sitting a couple of thou low due to wear on the base. I must get around to shimming it up.

Steve.

Thanks, Oldiron, for these tips from the horse's mouth; it is indeed interesting to compare them with opinions on the thread (always remembering that the author is concerned with industrial applications).

From the number of Posts generated by the above subject,it seems I was right when I said that many of us have problems parting off [OK,some dont,as we know ].

Front post,back post,door post ,goalpost,you name it,above center,below center,even off center !

It seems that what works for one is dead meat for another,and as for setting the tool height to a thou ????,wishful thinking for most of us,who can just about see the tool,never mind the tip !

It has been very enlightening reading the different views and one does learn something from them and helps to point out where one might be going wrong. We,at the bottom of the heap,will just have to try a bit harder,since we have a long way to go,if some of the claims are to be believed.

PS The vision of a lump of 10" round whizzing around is SCARY to say the least ! not that I doubt it has been done.

Did someone else part off 18" in the good old days ? Brave men !

I hadn't realised that this thread had prompted such discussion. (I don't seem to get notifications)

Anyway, as it turns out I am 100% serious about this, and I used the attachment this very evening to finish the cut through some 4" Meehanite bar.

I am sure that it is possible to part much bigger stuff but it does get proportionately more difficult as the tool extension gets greater. I have done some big stuff, but it only takes a moment of inattention or for one of the metal nautiluses to get wedged and you are looking around for another parting tool blade.

My current parting-off tool is an insert-type which takes 2mm tips, but it isn't the blade type, it is one of the more solid ones from P H Horn. **LINK** It does a lovely job, but only goes so deep. I machined a blank Multifix block from Create Tool to match the T-shaped interface.

As for the suggestion of taking the work to the saw rather than the inverse: The three-jaw chuck makes a much better job of holding short round stock than the bandsaw base does.

Hi Steve,

In absolute terms I don't know, however the magnification is sufficient to make tiny changes to tool height to be VERY obvious. So, having used it (Opt Ctr Finder) more than 10 years, I'm very comfortable with setting it just below the horizontal line visible in the viewfinder, so I'm guessing that it's 0.015 to 0.02mm below. Tool height setting is now a very consistent process. After setting it's very gratifying to find that the tool parts off very cleanly, with no noticeable centre pip....except on cast iron, of course, which is a law unto itself!!

Mine is a Chinese one which was on sale at ENCO in the US, it certainly wasn't what I'd call cheap but it was priced way below what I've seen European retailing for. It's not often that you see multi use bits of kit!!

cheers

Bill

Regarding tool height setting. When I was working out how to calibrate tools and store offsets on my CNC lathe conversion I realised that making sure every tool was at the centre height was important. For example if you turn a piece with a tool and you are turning to a different diameter to the one at which the offsets were calibrated, an error is introduced if the tool is not at centre height and you turn to a different diameter assuming the offsets are correct. In particular if for example you set the tool to a 6 mm gauge, when you try to accurately turn to a larger diameter without stopping, measuring and taking a bit more off, you find you've turned off too much. I now set tool height using a digital height gauge which at least resolves to 0.001" and try to set to that accuracy for each tool. It takes a lot longer but I have more confidence in getting consistent results.

For centre-height settting, these are pretty and make good christmas presents:

https://www.machine-dro.co.uk/edge-technology-speedy-lathe-gauge.html

Edited By Andy Pugh on 09/11/2018 14:57:39