Thread: Your best parting tool

Originally Posted by iron bark

Yes, and for that reason I had a good look at Eccentric Engineerings parting tool which works from the rear, but unfortunately my lathe has a screw on type chuck.

If you used the BTF tool holder in a rear toolpost the lathe would be running forward.

Stuart

You can use any parting tool in a rear toolpost, you just turn it upside down.
The back rake Martin has also provides side clearance due to the blade's taper, you just have to make sure the rake is ground back as far as the deepest cut you will make.

Originally Posted by iron bark

Martin, Thanks. From the pic it looks like the top of the tool is ground to produce a back rake. Roughly what angle is this? Just out of interest, what is a forms cutter blade?

Cheers,

Ned

I would DEFINATELY grind your tool to have a decent back rake like that, and you'll probably find many of your problems gone! I would be guessing that on your lathe, that tool is mostly just rubbing against the metal, and flexing your toolpost and carriage when you attempt to feed it in.. Looking at your tool holder, the top edge of the blade runs uphill from the cutting edge, which makes it negative rake... Negative rake tooling is generally used on much more rigid and powerful machines than you have, and the tool tends to sort of 'push' the metal off the surface, while positive rake tends to shave the metal off (requiring less HP and rigidity). For most applications with your lathe, you should get the best results with positive rake tooling (although some brittle materials like brass can apparently benefit from negative rake - I haven't experimented with that one yet). Worth noting that my parting tool holders (both the carbide and HSS ones) presents the tool as positive rake, and my machine is much the same size and weight as yours (AL335).

Originally Posted by Ueee

You can use any parting tool in a rear toolpost, you just turn it upside down.

But the BTF parting tool from Eccentric Engineerings is already upside down.... so to speak.
Stuart

But with back-rake on a parting tool, every time you touch up the front edge of the tool on the grinder, don't you lower the cutting edge slightly? This means you need to raise the tool slightly to bring it back to centre height. Not a problem if you have a QCTP, but if you have a toolholder like Ned's (and mine) you need to increase the shimming under the holder. Otherwise you need to grind all of the raked area away and start again. Have I got that right?

G'Day Ned,
Many years ago when I was struggling with a gutless Myford lathe I learnt to ignore text book angles and increase rake until the tool actually cut, the angles on the parting tool are front rake 25 degrees, back rake 12 degrees giving an included angle of 37 degrees presented to the work, and yes, the tool height needs a touch up when the tool is sharpened, hopefully the photo shows the tool a little more clearly.
Back in the olden days before laser printers, high speed impact printers produced most computer output, the fan folded paper was run through a forms cutter which removed the sprocketed edges and the perforated strip between sheets. The cutter blades were beautiful quality German HSS, but could only be sharpened a few times before being discarded, and being a card carrying pack rat I accumulated a few and have found the material handy for the occasional weird cutting tool.
Regards,
Martinp2.JPG

I get away with a P&N HSS cut off blade in a rear tool post on my bitty Hercus. No top rake means it's always exactly on centre. Cuts 1214 like butter, 4140 causes a bit of groaning. I wouldn't mind having a go at using a carbide insert cut off tool but that would involve a new tool post. One day maybe.

BT

Hi,

"I wouldn't mind having a go at using a carbide insert cut off tool but that would involve a new tool post. One day maybe."

I have a carbide cut off tool on my Hercus 260 3/4 HP, 2mm Blade from Glanze UK, wasn't really worth it. The tool itself seems flimsy and likely to break (which it hasn't but I always worry it will). Depending on the material, I get different finishes - MS not so good - Bright Bar better. I've tried different feeds and centre heights to no avail, just depends on the day.

I will soon be trying a HSS Cut off tool on a rear mounted toolpost.

Ben

Originally Posted by bwal74

Hi,

"I wouldn't mind having a go at using a carbide insert cut off tool but that would involve a new tool post. One day maybe."

I have a carbide cut off tool on my Hercus 260 3/4 HP, 2mm Blade from Glanze UK, wasn't really worth it. The tool itself seems flimsy and likely to break (which it hasn't but I always worry it will). Depending on the material, I get different finishes - MS not so good - Bright Bar better. I've tried different feeds and centre heights to no avail, just depends on the day.

I will soon be trying a HSS Cut off tool on a rear mounted toolpost.

Ben

Ben
Ive got a rear mounted (Inverted) parting off tool set up in the Hercus 260 & it works well.
The parting off tool portion is .110" wide with back & side relief & no top rake. Its ground from a solid piece of HSS 3/8th" square.
It can part off 1 1/4" dia BMS 1020 steel, which is the stuff I mainly use, very well. I always clamp or lock the saddle when parting off.
Another advantage of the rear inverted mounted parting tool, is the self clearing ability of the tool.
The cutting chips do not tend to crowd the cutting groove as in front mounted parting tools, as they fall away with gravity.
Cutting oil straight or soluble is always applied, & a slightly slower speed, than normal machining, is generaly used.
These have been my findings.
regards
Bruce

I've stayed out of this because there's been SO much written about the subject, and a quick search will provide endless reading. But one angle is rarely mentioned. This is a quote from Beckley23 of Practical Machinist fame. I'm sure he wouldn't mind it being repeated. The original is here: Another New Toy - Page 6

30 something years ago when this was still a hobby, I learned a valuable lesson that has stayed with me, in fact it is SOP in my shop. Whenever I buy a "new" lathe, the carriage and cross slide gets checked out and scraped if necessary. This is all about the ability to cut/part off successfully. When I was young and dumb, I was trying to cut off in an Atlas 6" lathe, which was essentially brand new. I wasn't having any success at all. I asked a machinist friend if he could help. He took one look at the lathe, used it a bit, and said it needed scraping in. I asked about scraping, and he gave me a very brief description. It went over my head. A while later I bought a 9" South Bend and Connelly's book "Machine Tool Reconditioning". I didn't know what MTR was about, but I read and reread the book and various sections several times until I felt that this was something I could do. I reworked the carriage on the SB, fortunately it wasn't in bad shape, made a square tool post for it, and tried cutting off. What an eye opener, no problems. I quickly found the limits of the SB, and as long as I worked within those limits, no problems. I then took another look at the Atlas, and noticed as I was in feeding, there were oil drops/bubbles coming from under the cross slide. I took the cross slide apart and spotted it on the surface plate, and only 3 corners barely had any blueing. I scraped the entire cross slide assembly as well as the carriage slides, reassembled the lathe, made a square toolpost and tried cutting off. Another eye opener. I had tried all the remedies that we've read about here and on HSM. Not one of them worked, and yet I keep reading the same crap, all these years later. I guess nobody has investigated the root cause of the problem, rigidity, nor cares too. Scraping is not the total answer to the cutting off problems, but it is the biggest contributor to success, IMO. I have never been able to consistently grind a cut off blade, and still can't, which is the next biggest problem, but I solved that problem with inserts. I've told a modified version of this story a couple of times in the BBS's, but I guess it's not the easy way. My friends get on me about my workup procedures, and I explain my reasoning, but all I get are rolled eyes, and "hell, just put it back together and make chips". One of them is/was a machine shop owner, he told me his machinists couldn't cut off, so they just cut the parts long on the saw, and go from there. He came into my shop one day while I cutting off, and was amazed to see the results. I told him the same story. He had bought all new machines, and his machinists couldn't cut off. Go figure. I've moved on since the Atlas and South Bend, and these Monarchs, Pacemakers, L&S's, etc, etc., are in a different class. I don't think I would have too many problems using the machines as received, but I'm not interested in problems after the machine is up and running. Harry

Bryan,

Thanks for putting that article on the forum. I was about to reply that I have tried most suggestions offered, and whilst they are appreciated, don't seem to fix my problem.

I am reasonably happy with the concept of proper sharpening, and tool angle/height etc, but the consistent problem I now have is chatter. I will go back and try locking down the carriage, and also check to see if I can pick up any movement elsewhere in the machine whilst trying to part off.

It is very frustrating to be able to cut, drill, thread etc, and then have trouble with the last bit i.e. parting.

I am actually trying to part off some 30mm dia. steel which has a 6.8mm hole drilled through the centre, in order to make some new height adjustment nuts for my QCTP, but the chatter is really giving me the sh!ts.

Cheers, Ned

Hi All
Why don't just turn the parting tool upside down, run lathe backwards, all grabbing and digging in don't happens, just make sure sure chuck is tightly secured

Welcome to the forum Tore
Rear parting was discussed briefly in this thread
https://www.woodworkforums.com/f65/pa...-tools-160704/
Apart from the additional problem if you have a screw on chuck (which some of the guys do), I can't see that running a front mounted tool in reverse offers any great advantage over a rear mounted parting tool. Depending on the condition and age of your lathe a rear mounted tool has a range of impact on parting ability.

Michael

I use Sandvik 151.2-21.30 blade with R151.2-300-5E Inserts in a Glanze (i think it was) holder (sandvik one doesnt fit in my QCTP). (or L151.2-300 depending on whether i want a pip left on the workpiece in the chuck, or the parted off piece)

I flood coolant, run the lathe at about 60rpm and all is front mounted.

Dead on center. Feed in until it touches, then increase feed in rate slightly. You get a sweet spot where it just curls off MS beautifully. If you go to quick it digs in, if you back off too much it rubs and stops cutting. Takes a bit of practice, but you get used to the feed rate required from how the chips are coming off.

The thing that I find gives me most help in getting the chips curling is lube/coolant.

The sandvik inserts are shaped so the chips curl in on themselves on either side to stop jamming (a 3mm parting off insert will produce chips that are about 2.8mm wide (for example.... numbers made up to make the point)). They curl into about a 5-10mm round nugget and then line up on the top of the tool and are slowly pushed out from the gap that is being cut. No big long curls of swarf to worry about, just these little tight curls popping out.

Holders and inserts can be picked up for a reasonable price on ebay.