Parting on the TH42, kinda proud of myself!

[great white]

Parting has always been a hit or miss thing for me.

HSS or carbide tooling.

But today, I think I got 'er dialed in.

I needed to part a 3" round piece of mild steel with a 1.5" dia hole in it. I figured there was no way my old soldier was going to handle it. But I needed it done, so I set out to part it off.

I pulled my HSS parting blade and gave it a touch up on the grinder, just to make sure it was as sharp as it could be. I adjusted it to center using my tailstock pointer. Adjusted it to half the stick out needed to cut the 1.5" depth (about 3/4"), so it would be as rigid as possible as I got a feel for the cut. Square the cutter to the work. Belt pulleys to the largest on the spindle, smallest on the drive. Engage back gears. Dial the Spindle RPM down to 45 RPM and the DC motor was spinning good and fast because of the pulley choice. Grab my oil can and start pumping it into the blade/work interface.

Nope. Chatter. Bad chatter. That make your spine hurt type of chatter. Feed rate does nothing. Dial the RPM down to 40 rpm.

Nope. Some chatter. Still uncomfortably loud and waaaay too buzzy Dial down to 30 rpm.

Mostly curls. Infrequent chatter. Much better than before. Tools aren't falling off the lathe bench now.

So increase feed rate and pump more oil.

Curls!



They start off nice and loose, but start to roll on themselves as the cutter runs deeper into the work and there's less clearance for them to drop away:



Then I run out of depth on my first tool stick out setting.

Now I think to myself; this is going to get interesting. I have to double the amount of stick out, which means a big loss in rigidity and a possible risk of my ever present parting nemesis: teeth rattling chatter.

So I adjust the cutter, make sure it's still centered, grab the oil can (take a deep breath) and plunge into the existing cut:



Going pretty good! With the reducing diameter, I start raising the RPM to try and keep my SFPM constant. I get it up to 40 RPM, which should be around the right SFPM for 3" of steel. Still curling nicely and now the Baldor motor is even happier with more airflow and more intertia.

And then, finally:



Oh yeah baby! That was satisfying!

I can't believe I just parted a 3" dia steel chunk with HSS on my old TH42 without chattering or screaming metal. I'm betting I'm pretty close to the outer capabilities of my Atlas though. That chunk seems pretty big to me to part on a TH42.

Here's the part I needed to make:



It's the beginning of a bellcrank for a shift linkage I'm making for my tractor. The bearing is a light press fit in the housing.

So, I'm not going to say I've got parting completely nailed down, but this was a pretty big milestone for me.

This might have been a small task for some people, but for me...well...I'm going to enjoy this little victory and go enjoy a fresh cup of hot tea!

 

[Moderatemixed]

I am struggling with parting off with my Atlas QC42. I had been using HSS cutoff blades and getting squeals and vibration enough to wake the dead. So I bought the Aloris Carbide Insert cutoff blade and inserts for my QCTP...... still no better, and I’m cutting aluminum. Tomorrow I will head down to the shop and give “slower” a chance. Thanks for the “wake up” back to feeds and speeds. Cheers.


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[great white]

I am struggling with parting off with my Atlas QC42. I had been using HSS cutoff blades and getting squeals and vibration enough to wake the dead. So I bought the Aloris Carbide Insert cutoff blade and inserts for my QCTP...... still no better, and I’m cutting aluminum. Tomorrow I will head down to the shop and give “slower” a chance. Thanks for the “wake up” back to feeds and speeds. Cheers.


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For me, SFPM has been the most important variable I've had to get right. Keep in mind the diameter of your work piece and how it effects SFPM. I measure spindle RPM and calculate what my SFPM is for the diameter, then adjust my cutting accordingly (IE: spindle RPM and feed). It's not about "slower", its about SFPM. At least it has been for me.

The last part in the equation for me is oil. As in: you need lots of it. At least I always do. I'm actually considering making up a "drip feeder" of some sort that I can position over my parting tools. Holding the oil can while trying to manage feed rate sucks.

Good luck.

 

[Meta Key]

Parting has always been a hit or miss thing for me.
...........snip................
This might have been a small task for some people, but for me...well...I'm going to enjoy this little victory and go enjoy a fresh cup of hot tea!

Lots of good advice about parting being given. I, OTOH, will advise the use of Taylor's of Harrogate. Excellent tea; well deserved...

MetaKey

 

[Moderatemixed]

Great White....... you are a full on genius. I put the lathe in back gears, made sure my speed was right, oiled the hell out of it with Aluminum specific cutting oil and began parting...... and NO DIFFERENCE. It was chattering and vibrating like hell. I’m an airline pilot “by trade” so I decided to “run the checklist”. Tool was centered (precisely), speed was set, exactly. I was in back gears, QCTP locked, cross slide locked, success guaranteed. Damn I thought, what am I doing wrong? Goodness knows that I have spent the money to have the “right” equipment...... so in distain I switched the “beggar” back on, oiled it and tried again, no change. So I plunged that part in tool into the material with “****** off” as my fuel...... and oh my goodness to my surprise the chatter instantly stopped, and the most BEAUTIFUL chips began to form...... I parted that piece off like I was “in the business”. They don’t call it “FEEDS and speeds” because only speeds are important. My feed rate was wrong, and once I got that straight, well, the results were amazing. I got into machining because I have a profound respect for what goes into the “creation” of the tools that I use daily, and which allow me to both make a living and to do so safely. It is with that respect that I humbly learn every moment I am in my shop, and appreciate every step of the learning process. Thanks to all who contribute on this forum and who have done so in this thread, and to Great White for starting this string. Cheers everyone.

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[great white]

Great White....... you are a full on genius. I put the lathe in back gears, made sure my speed was right, oiled the hell out of it with Aluminum specific cutting oil and began parting...... and NO DIFFERENCE. It was chattering and vibrating like hell. I’m an airline pilot “by trade” so I decided to “run the checklist”. Tool was centered (precisely), speed was set, exactly. I was in back gears, QCTP locked, cross slide locked, success guaranteed. Damn I thought, what am I doing wrong? Goodness knows that I have spent the money to have the “right” equipment...... so in distain I switched the “beggar” back on, oiled it and tried again, no change. So I plunged that part in tool into the material with “****** off” as my fuel...... and oh my goodness to my surprise the chatter instantly stopped, and the most BEAUTIFUL chips began to form...... I parted that piece off like I was “in the business”. They don’t call it “FEEDS and speeds” because only speeds are important. My feed rate was wrong, and once I got that straight, well, the results were amazing. I got into machining because I have a profound respect for what goes into the “creation” of the tools that I use daily, and which allow me to both make a living and to do so safely. It is with that respect that I humbly learn every moment I am in my shop, and appreciate every step of the learning process. Thanks to all who contribute on this forum and who have done so in this thread, and to Great White for starting this string. Cheers everyone.

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Small world. I'm a flight Engineer, formerly Aircraft Mechanic....

 

[Moderatemixed]

Awesome.


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