Parting tool chatter

[lathe nut]

Tim, I have a 1220XL, they are good machines, they have a heavier cross slide and compound that a lot of the lathes of this day and time, I got mine from a fellow that had a three jaw, four jaw chuck and a load of tooling he wanted to sell it fast and I made a good deal, just needed another lathe they are all so happy in the shop together.

 

[lathe nut]

Tim, just found the picture it was at a yard sale, I probably have 200 taps and dies but those in the picture are left hand ones, how cool.

 

[RM-MN]

Absolutely.

And sharpen your parting blade regularly. I have a USA made high cobalt HSS blade in an Aloris style holder that presents the blade at 7 degrees (I think) from horizontal. So the back-rake is built in. All I have to do is give the front face of the blade a light touch on the grinder and it good to go. It's amazing how a light sharpen can turn a parting-off horror show into an easy job.

I have a mini-lathe with (as explained by someone else) the rigidity of a wet noodle but I can part off quite well with the sharp blade but I use a diamond honing stick as it needs to be sharper than what my grinder can do. Honing all my cutters is essential with this lathe.

 

[OrangeAlpine]

Well I'm up and running with no chatter, but another evil has jumped out. The tool wants to dig in. I'm very slowly feeding by hand, while the tool is cutting cleanly it will suddenly dig in, taking a heavy cut. The tool is still on center. I'm thinking that adjusting the tool to be under center would help. But I'd rather eliminate the cause.

Bill

 

[jack620]

I'm very slowly feeding by hand, while the tool is cutting cleanly it will suddenly dig in, taking a heavy cut.

what material are you parting Bill?

 

[OrangeAlpine]

Mystery metal steel. It machines nicely but is not leaded.

Bill

 

[awake]

It may be a symptom of some lack of rigidity, but I have learned that on my well-worn lathe, when parting some materials, I have to feed in, then give it a moment to "digest' the bite - it continues to cut, and may pull out quite a bit, even though I'm not feeding. Then, before chatter starts, it is time to feed some more.

And some materials just seem to be problematic no matter what - at which point, I take the part out of the lathe and transfer it to the bandsaw!

 

[OrangeAlpine]

"I take the part out of the lathe and transfer it to the bandsaw!"

Been there, hate to do that!
Bill

 

[awake]

I hear that! But when it becomes clear that sooner or later something is going to break, long before the material in question is going to be parted successfully ...

 

[SmithDoor]

Just look at the hook on band saw blade. This is what is need on cut off blade.

Just watch videos of screw machines. Look closely at the blade.
If can find old book Brown and Sharp screw machines it will a disk type cut off with lots of rake.
Back band saw blade look.

Dave

"I take the part out of the lathe and transfer it to the bandsaw!"

Been there, hate to do that!
Bill

 

[BaronJ]

Well I'm up and running with no chatter, but another evil has jumped out. The tool wants to dig in. I'm very slowly feeding by hand, while the tool is cutting cleanly it will suddenly dig in, taking a heavy cut. The tool is still on center. I'm thinking that adjusting the tool to be under center would help. But I'd rather eliminate the cause.

Bill

Hi Bill,

Sudden dig ins can be caused by play in the cross slide lead screw, but a much less obvious cause particularly parting aluminum is build up on the cutting edge. Which is also why its a must to use some lubrication that will stop material sticking to the cutting edge.

WD40 is good for alloys, though I use paraffin or diesel oil.

 

[SmithDoor]

Hi Bill,

Sudden dig ins can be caused by play in the cross slide lead screw, but a much less obvious cause particularly parting aluminum is build up on the cutting edge. Which is also why its a must to use some lubrication that will stop material sticking to the cutting edge.

WD40 is good for alloys, though I use paraffin or diesel oil.

All screws have play or you can not move the screw.
After the screw wears in middle now try moving the screw to ends.

Now without roller bearing the could use a cutoff tools without chatter.

The time that seen no backlash screws in on mills.
But this was per loaded type screws using hydraulic cylinder and was only used for climb milling.

Dave

 

[SmithDoor]

This most interesting part of cut off tools is most do not want to grind a hook in top of the blade. But will stop using the blade ungrounded.

Dave

 

[goldstar31]

This most interesting part of cut off tools is most not want to grind a hook in top of the blade. But will stop using the blade ungrounded.

Dave

This is all discussed in 12 pages( yes 12) in G/H.Thomas's ' book 'Model Engineer's Workshop Manual.
He inclined the Parting off tool at 7 degrees which, inverted does not require a hook. Of course grinding a hook on a parting tool makes a mess of the quite expensive tool and takes a long time to regrind on top and bottom.
Actually, I've just reground a parting tool with this hooked configuration. It came from a box of someone else's rejects.
The maths between the two is roughly, 0.0088 x the diameter of the grinding wheel in inches x the degrees required with the andwer in nthe height or depth of from the centre of the grinding spindle.
Professor Dennis Chaddock simply produced the chart in his Quorn book- assuming the his readers were none too bright.

Anyway, I fitted a Quorn spindle into spindle holder on a Kennet tool and cutter grinder( the forerunner of the Worden which I am starting to make. I noted that Thomas suggested a soft while Aloxite wheel wheras the one that I got was a 60 grit one. Having said all that, I created almost a mirror surface for cutting.
Err, uhm, I'm making an arbor to go on my Mark 1 Quorn to diamond swop for the final honing.

Hope this clarifies things somewhat.

 

[SmithDoor]

My Aloris #7 UNIVERSAL PARTING BLADE HOLDER has 4° angle. Which I think would have the correct angle for cutoff blade. It works on very few metals at that angle.
There no way to adjust the angle. So back to grinding.
At less I had background in screw machines to know the angle.

I do believe this gives a false angle to everyone.

I have even design a holder for 15° that fit the Aloris tool post.

Dave

This is all discussed in 12 pages( yes 12) in G/H.Thomas's ' book 'Model Engineer's Workshop Manual.
He inclined the Parting off tool at 7 degrees which, inverted does not require a hook. Of course grinding a hook on a parting tool makes a mess of the quite expensive tool and takes a long time to regrind on top and bottom.
Actually, I've just reground a parting tool with this hooked configuration. It came from a box of someone else's rejects.
The maths between the two is roughly, 0.0088 x the diameter of the grinding wheel in inches x the degrees required with the andwer in nthe height or depth of from the centre of the grinding spindle.
Professor Dennis Chaddock simply produced the chart in his Quorn book- assuming the his readers were none too bright.

Anyway, I fitted a Quorn spindle into spindle holder on a Kennet tool and cutter grinder( the forerunner of the Worden which I am starting to make. I noted that Thomas suggested a soft while Aloxite wheel wheras the one that I got was a 60 grit one. Having said all that, I created almost a mirror surface for cutting.
Err, uhm, I'm making an arbor to go on my Mark 1 Quorn to diamond swop for the final honing.

Hope this clarifies things somewhat.

 

[goldstar31]

My Aloris #7 UNIVERSAL PARTING BLADE HOLDER has 4° angle. Which I think would have the correct angle for cutoff blade. It works on very few metals at that angle.
There no way to adjust the angle. So back to grinding.
At less I had background in screw machines to know the angle.

I do believe this gives a false angle to everyone.

I have even design a holder for 15° that fit the Aloris tool post.

Dave

I'm not into QCTP and as you mention an Aloris( whatever that is when it's at home) but my maths suggests that 4 degrees is an angle suitable for carbide tools.
No Dave, I DID research into cutting acoustic tiles made from spun rockwool- but that was in the 50's.
I'd just got out of 'battledress' and wanted a few coins. Surprisingly, most of the Masonic Halls still have suspended ceilings with them.

I hope that I will not be 'blackballed'

So mote it be

Norman

 

[SmithDoor]

I try carbide too.
Looks great on paper
I try on A36 and DOM tubing
I found A36 and DOM like about 15° to 20° angle, it will cut like butter.

I did not like wasting cutoff blades but had to do the work.
Let put this I started use band saw then to Turret lathe. Lot band saw blades.

Dave

I'm not into QCTP and as you mention an Aloris( whatever that is when it's at home) but my maths suggests that 4 degrees is an angle suitable for carbide tools.
No Dave, I DID research into cutting acoustic tiles made from spun rockwool- but that was in the 50's.
I'd just got out of 'battledress' and wanted a few coins. Surprisingly, most of the Masonic Halls still have suspended ceilings with them.

I hope that I will not be 'blackballed'

So mote it be

Norman

 

[jack620]

My Aloris #7 UNIVERSAL PARTING BLADE HOLDER has 4° angle. Which I think would have the correct angle for cutoff blade. It works on very few metals at that angle.

You must be doing something wrong. I have the same toolholder with a very good quality 2mm parting blade fitted. Since adding the new blade I have no trouble parting any metal now. That includes titanium.

This blade: T-Type Cut-Off Blades H.S.S. | Somma Tool Company
The 5/64” cobalt version.

Keep it sharp, keep the lube up, keep the feed up.

I agree with Norman. You shouldn’t need to grind a hook in a parting blade.

 

[SmithDoor]

I purchased a book from Brown and Sharp screw machine from the 1920's.
It gave the table for cutoff tools and metals.
After read the book had more problems using a cutoff tool.
The two worst metals that I work with was A36 a DOM tubing

PS .
First it was 9N making the parts later it was Turret lathe. Very long days.
Finally made parts on A25 screw machine just stand back and watch.

You must be doing something wrong. I have the same toolholder with a very good quality 2mm parting blade fitted. Since adding the new blade I have no trouble parting any metal now. That includes titanium.

Keep it sharp, keep the lube up, keep the feed up.

I agree with Goldstar. You shouldn’t need to grind a hook in a parting blade.

 

[jack620]

The two worst metals that I work with was A36 a DOM tubing

OK. A36 is listed as structural steel, so I would expect it to be ugly to part-off. And DOM tubing has a welded seem. I haven't tried parting it, but I imagine the weld would provide an interruption to the cut, being harder than the rest of the tube. I can see that introducing chatter.