I had a difficult time parting 3” 1080 round bar that almost turned dangerous.

 

I watched that video a few days ago, good info, I have had mixed results when parting on a lathe.

 

Best result is a 7° to 15° rake angle .
I have cut thousands of parts in a lathe.
That angle the give is to little to make a good cut in most steel.

Dave

 

Thank you. I like that. I have always dreaded parting off.
I don't want to make one, but I hope I can find one somewhere for my AXA holder.
cg

 

Hmmm,, I think my toolholder set came with a "T" blade holder,, probably not the "spring" type.

I must have 30 or more of those "T" type blades, various heights, various thicknesses, none have ever been used as a cutting tool.
I never used them on a lathe,,
(Most of them came in the drawer of an old metal lathe I acquired)

Instead, they make PERFECT parallel bars,, spacers for holding parts in a milling vise,, etc.
I think most of them are the 8% cobalt,, not that my use needs cobalt!! LOL!!

The guy that I got the lathe off of told me he used them as cutting tools, instead of regular HSS tools.
I don't know, I ain't much of a lathe operator,,

 

We had a real nice carbide insert parting tool in the shop where I worked that did a good job 99% of the time.
I think one of the biggest issues with a High speed steel blade is that the sides need to be clearenced a little bit. aand lots & lots of cutting oil.

 

This was the original design from another guy.

https://youtu.be/s9qcd5-wj3c?si=jAcUzyemlSqRUQZE

https://youtu.be/p93bUqpdWMg?si=8shbTvEYivLlH_Pk

It's easier to make, and works well. Something more for just getting on to making parts, instead of spending a ton of time on making the tool.

The chatter when the blade starts to cut is unnerving.........BUT THE CUT DOESN'T CRASH THE LATHE. That's the amazing part. Usually when you hear this chatter, a failure is generally not far behind. This tool makes noise for a bit, then smooths out.

 

I guess it depends on how much material you need to remove and frequency of use. I have used 3/8 sq hss bits. Shaped to Remove 1/8" wide material. No special tool holder. I can part 1 inch stock.

 

Have you tried a high quality carbide insert parting blade, Sam?

I have a kennametal A2 blade with a load of NOS ebay inserts. It's great. Most of the time I part stuff off completely dry, no issues at all. Bigger stuff I'll use flood coolant, or if I need a good finish on the back side.

I think lathe rigidity plays a part (!) in parting off successfully no matter what blade type you use. A big solid lathe has less chatter issues than a small flexy one, or a worn out one. I see guys in UK complaining about parting off issues all the time, and they seem to be using very old lathes with very worn beds, or small chinese types.

That, and people don't use parting blades properly, they tickle the job instead of feeding it in positively. The geometry on a carbide parting tip means it needs a proper feed of material in order to form the swarf and evacuate it properly.

 

And that my friend is the problem. My lathe is of the 1300ish# variety. Long on aspirations..........short on muscle. It chatters when you look crosseyed at it.:laugh:

That's what impressed me about the tool. The guys using them had little Atlas type lathes.

Mine will either attempt to stall, spinning the material in the chuck.............or the workpiece will start to climb over the blade into my lap. No matter what speed. I will admit that I'm a bit timid about feed rates, but that's my nature. One attempt at power feed was enough to set the record straight:laugh:

The lathe is still tight. The spindle is tight..........ought to be......I had to rebuild it if you recall(fresh out of the crate). .00015 runout at the taper IIRC.

All I have to do is pick up a parting tool, and the lathe goes View attachment wave-finger.gif

 

The best results I’ve had with parting tools was after I
ground a small relief on top of the tool, giving it a small
curved depression right behind the tip. It makes the chip
curl up tight and reduces tool pressure. Unfortunately tool
also needs to be ground more frequently because top rake
is excessive.

 

This is the same style as the carbide blade I used at work.
By far the best cutter I used on stainless.

The other thing I've noticed is that regardless of material, power feed set to take a decent chip works the best for me.

One other note, any machine that has "excessive" spindle play is nearly impossible to get consistent results for me.

That youtube guy Abom has had similar experiences that went away after spindle head service.

 

I part in the lathe day in day out.

It is one of the hardest things to learn the feed rate when parting as it changes several times as you get closer to center. I never power feed when parting.

I have driven in too hard and brought the lathe to a sudden violent stop a few times but been lucky. The worst was exploding the parting blade one time not so long ago which sucked. Sometimes you get so used to it you drive a little hard and if part is getting hot and blade not especially sharp or lack of lube it can dig in suddenly and hook.

The feed is most like you would feed a drill bit into the material. You just want to ensure you are always taking off material and you can feel it when you are pushing to fast/hard.

Look in my swarf can and there are many clock springs in there from parting just about every part it produces.

 

I part in the lathe day in day out.

It is one of the hardest...
... you can feel it when you are pushing to fast/hard.

Look in my swarf can and there are many clock springs in there from parting just about every part it produces.

Particularly when those are pretty yellow brass, bright aluminum, or multicolored (grey to purple) steel, when stretched out they can make interesting ornaments for Christmas trees.

 

Too much speed and too little feed are proponents for chatter, BUT the feed doesn't always relate whe parting.

 

Wow! Great video! I am new to machining, and other than plastic and alum, parting suks! LOL Unfortunately, I do not have nearly the skills to make one of those tool holders.

 

Parting takes a tight machine with no backlash and good tooling with lots of good lubricant and proper tool height & proper speeds & feed rates, and even then it's a BITCH at times, one problem is that the surface speed decreases as the cut diameter decreases. We had an awesome little insert parting tool, I don't even remember what brand or anything, but even it would grab. A high speed steel parting tool works ok on brass

 

I thought surface speed decreases as the diameter gets smaller???

I just parted a hunk of hex brass just shy of 2", and it was a dream with HSS. However, I tried it on settling and ended up throwing it in the cold saw! Haha I didn't know until this morning, when I watched youtube, that oil or coolant is necessary. My lathe is actually like new, so it should be plenty tight. I am so glad it didn't grab the steel. I would not have been expecting that.

 

Surface speed decreases as diameter decreases, I think you misread my post. You haven't lived until you've broken a high speed cutoff tool in the cut.

 

I had a 3" diameter part climb the cut off tool. Not fun!

 

When parting, the tool has to be absolutely dead on perpendicular to the workpiece. It also helps to lock the carriage to the ways if you have a carriage lock on your lathe. Have the gibs on the cross and compound properly adjusted as well. There's no replacement for displacement. Some lathes just don't have the mass and rigidity to consistently part.