Thread: Your best parting tool

Hello all,

I would in interested in seeing/hearing about what you guys think is the best parting tool, i.e. material, grind etc. At the moment I only have the one that came with the lathe, and all I get is chatter, squealing, and a very torn, untidy looking cut. Despite having the tool sharp, dead centre, and very modest feed rates, the tool still tends to try and dig in.

I will post a pic of it when the camera battery is re-charged. I am mainly interested in steel, and also a bit of brass and aluminium. I have watched videos on youtube and seen beautiful long swarf flying from a very smooth parting tool, so yet again, I have more to learn.

Thanks,

Ned

Originally Posted by iron bark

and very modest feed rates

This may well be part of your problem... Particularly with my carbide parting tool (but also my HSS one), feeding too slow results in a lot of chatter, and not much of a cut. Spindle speed may well be too low too, you don't mention what you're running? I used to attempt to part off at 75rpm (my lathes lowest speed), but now I just use whatever the last turning speed was, and find that works well for me...

Ohh, and I should probably add that I ground some back rake on my HSS parting tool, works beautifully well on aluminium (steel I tend to go straight to the carbide tool most of the time, as my HSS is a bit on the cheap side)...

I agree with J&H, you have to make a cutter cut, if that makes sense. Once chatter starts, you need to get under the uneven surface you have created to cut a nice smooth surface and get those nice long curlys. Sometimes i can make one cut and its as smooth as silk all the way to the center, other times i cannot seem to get the nice cut, no matter what the revs or feed. I use a 2mm iscar insert type blade, 25mm high. I have smashed 3 tips since i had it and it does put you off, but being timid with the feed is really not good for the tool or the cut.
For smaller lathes a rear toolpost with the blade upside down helps, or so i am told, i'm yet to get around to it. One of the biggest advantages i can see is the swarf will fall out of the cut, whereas it can jam in the cut with the traditional method.
Are you locking everything, saddle and slides? I find if i leave the saddle unlocked it makes a huge difference.
Can you remind us of your lathe and post what type of tool you are using, how it is ground, thickness etc?

Are you using lube Ned? On deep cuts it helps if you make a stepped cut to provide some clearance for the side of the tool.
Chris

It seems Hercus lathes were usually supplied to schools and tech colleges with gooseneck type parting tool holders.
I haven't tried one for parting yet, but suspect there was a very good reason for the choice.
I have used a gooseneck tool in a shaper, which worked much better than without it.

Jordan

I found a metal band saw is the go But I use the cobalt blades with my cutter and it is great for steel and brass/alluminium. Not a big fan of carbide and
Pete

Originally Posted by Ueee

Can you remind us of your lathe and post what type of tool you are using, how it is ground, thickness etc?

Sorry for the delay chaps, but I had an unexpected family visit.

I have a HAFCO AL900-A, 300 x 900 capacity with a quick-change toolpost.

The toolholder was with the lathe when I got it, and the cutting tool is 3/32 x 1/2" HSS.
IMG_0475.jpg IMG_0474.jpg

Cheers,

Ned

G'Day Ned,
The most successful parting tool I have used is a simple 2.5 mm wide blade made from a recycled HSS forms cutter blade, I set it dead on 90 degrees with a small square at centre height, power feed @ .08mm/rev @ 200 RPM for steel, 300 RPM for aluminium,bronze & nylon, a squirt of cutting oil for steel, WD 40 for aluminium, hope this helps.
Regards,
Martinp1.JPG

The 1st photo you show is going to be one of your reasons for having a problem.
The side rake (angle going back towards your tool post) should be the other way around,thick at the front and thinning towards the rear.
The way that is showing in your photo would have the tool cutting on the leading edge (face) as well as the sides.

Originally Posted by pipeclay

The 1st photo you show is going to be one of your reasons for having a problem.
The side rake (angle going back towards your tool post) should be the other way around,thick at the front and thinning towards the rear.
The way that is showing in your photo would have the tool cutting on the leading edge (face) as well as the sides.

PC, I think you'll find you are looking at the end relief.

Though the top of the tool looks a little strange. Has it been ground on the top?

Stuart

Thankyou.

Originally Posted by Stustoys

PC, I think you'll find you are looking at the end relief.

Though the top of the tool looks a little strange. Has it been ground on the top?

Stuart

Actually, what looks like a grinding mark on top is just where the tool has been touched accidently against the wheel, and hasn't actually been purposely ground. When setting the tool height. obviously dead on centre is ideal, but if one was to err a little, which is best, slightly high or slightly low. I'm thinking slightly low would be more liable to dig in.

Cheers, Ned

Slightly high and the tool won't cut Ned, it will just rub on the grind, especially when cutting a small dia. It really needs to be spot on for best results. If you are low the tool will move into the cut as the post flexes more than it will if you are on center, and the grind wont stop it. I think thats the other reason a rear toolpost is better for parting, as the post flexes, it flexes up and away from the cut.

Originally Posted by iron bark

Actually, what looks like a grinding mark on top is just where the tool has been touched accidently against the wheel, and hasn't actually been purposely ground.

Ned,
I'm pretty sure you are supposed to grind the top of the tool flat. Check out this excerpt from a South Bend brochure.
Chris

Originally Posted by Ueee

Slightly high and the tool won't cut Ned, it will just rub on the grind, especially when cutting a small dia. It really needs to be spot on for best results. If you are low the tool will move into the cut as the post flexes more than it will if you are on center, and the grind wont stop it. I think thats the other reason a rear toolpost is better for parting, as the post flexes, it flexes up and away from the cut.

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.

Jack,

Thanks, all good info for me to absorb