Thread: Your best parting tool

Here's an old Atlas flyer on parting tools:

Originally Posted by TKO;1582571[ATTACH=CONFIG

243347[/ATTACH] this is my way with no problems Eddie

The nice thing about the inclined blade is you don't need to grind side clearances. That's a steep angle you've got there - I had one that was only 7 degrees from horizontal.

Jordan

Hi nadroj,, you are quite right its a steep angle, the blade in the holder now is used for cutting up plastic and it is on its last legs ,but saves using a good blade which has a more vertical front clearance.The rear blade is for cutting off BA 10 and 12 nuts,from
square Brass or Steel,after drilling ready for tapping, the front cut off tool was shown to me by a retired engineer.and i have never looked back with the cut off problem,

Eddie

Thanks all of you blokes for the valuable input on parting off.
It got me chasing after better methods.
I have parted off dozens of pieces, using different tool angles, speeds, & feed rates, lubes in an attempt to improve things.
The parting tool I use is ground from a solid piece of 3/8" square & is identical to what Jack 620 from the Atlas book shows. (See post above). That is, no top rake & 8 degree front rake with relief as outlined.
Its mounted in the rear toolpost of my Hercus 260.
Works well on dias up to 1.5" or 40mm dia.
Please see photo of 3 point steady set up. This gives a very rigid support, & parting off is easy with little waste, as in a chuck mounted workpiece.
The very worst parting off tool, is the straight one shown in the photo. I noticed "Tubal Cain" in the USA videos does not recommend this design & that has been my finding.
Once again thanks to all.
regards
Bruce

Thanks for the info Bruce. Now I just need to find a slotted cross-slide for my Hercus 260. I know you can buy castings and machine your own, but I feel that's a bit beyond me at the moment.

Originally Posted by jack620

Thanks for the info Bruce. Now I just need to find a slotted cross-slide for my Hercus 260. I know you can buy castings and machine your own, but I feel that's a bit beyond me at the moment.

Perhaps give Hercus a phone call, they may have some old stock. or try Mal at "Australian Metalworking Hobbyist" in Melb. He has a good range of Hercus parts or will chase one up for you.
It would be a big job to try & make an Extended Cross Slide.
regards
Bruce

Hello to all
I hope you don't mind me chiming in.
I joined this forum for my interest in woodworking.
I am a self employed toolmaker with 25 years exp.

There are many things which affect how a tool will cut, especially a parting tool.

From the pic of the tool in the first post
The tool is tapered from top to bottom to allow for side clearance. You need to watch that the tool is vertical. This is hard to do as it's tapered.
Check the side clearance on both sides to ensure that the angle is the same both sides.
There is also a double angle on the top of the blade which assists in clamping the tool central. You cannot cut with this.
There has been discussions here in regard to pos and neg rake angles. you most often see neg on carbide tools used in reasonably rigid machines.
For you HSS blades you need pos rake on the top. If you look at TKO's tool in the second last pic, it needs to look something like that, maybe not quite as savage on the top rake. There is really no need to have it at an angle like that. They are used that way to allow you to reset the tool on center height when the tool is sharpened. If it is used flat you will need to shim the holder to recenter after sharpening. It should still work though up to .5 mm below center height. That allows for quite a bit of sharpening. If you can imagine the bottom 1/3 of a pea sitting below the top of the blade, you would be pretty close. The chips will also follow this form and curl up into a coil.

The rake or clearance angle on the front of the tool is largely irrelevant,( provided it is dead center) it only affects the achievable feed rate. Having said that something between 5 and 10 degrees is the norm.

The biggest factors that affect a HSS parting blade are coolant and spindle speed. Coolant is a must ( especially for a deep cut ) A well sharpened tool used with coolant should last a long time. Excessive spindle speed will kill a HSS tool. In a perfect world the spindle speed would be variable to allow for the dia change. It's a balance from the starting dia and zero dia.

Finally when looking at any cutting tool, have a good look at a drill bit. A good look. They cut perfectly and the design and dynamics are well founded.

Regards

Andrew

At home use a plain parting tool holder with sucess not rake I just set it on center height .At work we use a sandvik carbide parting tool with a 110 rpm soindle speed and a .75MM feedrate We can achieve mirror finishes.

Originally Posted by jack620

need to find a slotted cross-slide for my Hercus 260. I know you can buy castings and machine your own, but I feel that's a bit beyond me at the moment.

You can buy a finished Boxford slotted cross slide that fits the Hercus. The same one fits both Hercus 9 inch and 260.

Jordan

Today BT Bob asked me to try some parting off using the rear mounted HSS toolbit on some tougher 4140 steel he submitted to me a while back.
Remembering that with parting off....
Rigidity
Rigidity
& Rigidity are all important factors to remember.
So I set up the short workpiece in the Hercus 260 with a centre to support it, as I did not want the piece popping out of the chuck & doing damage.
Set the direct & variable, belt drive on the lathe to "what looked right" & locked the carriage.
And away we went.
It cut beautifully, the HSS toolbit is the same piece I have used for years.
No top rake, a front clearance of 8 degrees & rear relief of a few thou.
Lubricant used was a straight cutting oil,(Soluble without the added water) applied with an oil can.
Tried "Tap Magic" it too was excellent.
Feed rate, by feel, by hand.
Speed was checked by a Tachometer & it was 300 RPM or 80 feet per min a bit higher than what I would normally part off a tough steel like 4140. Using HSS.
Photos of the operations are shown together with the surface fiinish of the parts.
Mention has been made of top rake vs positive rake, & this varies as to the lathe type.
For a lighter lathe like the Hercus 260 no top rake seems to work well.
A top rake seems to make the tool "grab" (confirmed with a number of users on a USA sight)
This toolbit parting tool is the same configuration & geometry,I have used for the past 20 yrs or so.
It works fine on my lathe.
regards
Bruce

Thanks Jordan- I'll look into that.

Bruce, I'll talk to Hercus and also to Mal. BTW- Mal is in Sydney.

Chris

Originally Posted by Abratool

For a lighter lathe like the Hercus 260 no top rake seems to work well.
A top rake seems to make the tool "grab" (confirmed with a number of users on a USA sight)

Yep, I tried it on my 260 and the machine almost disassembled itself.
Thanks for posting Bruce. It always good to have info that is specific to your own lathe.

You could always try adapting your present Cross slide to take a rear tool post or if you access to a mill you could have a go at making your own.

Nice job pipeclay. I don't have access to a real mill. I only have my lathe milling attachment. The adaptor on the standard cross-slide is a good idea. I could make one of those with my milling attachment. Is yours steel or cast iron? Either way, what grade of metal?