Parting on the lathe

A

ARM

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Hi Guys
Need some info here, please.
Been trying to part a 50mm BMS round bar and had my 2mm Carbide insert and holder crash boom bang on me ~!@#$%^&*()_
What a disaster
This was quite shocking as the job seemed like progressing quite well. We were feeding merrily merrily and suddenly the earth gave way !!!
We need to know what we did wrong.

We tried our 3mm Carbide insert on another similar-sized project and still could not progress cutting smoothly. The Tool continued vibrating, squealing and still did not cut evenly. Speed here was very slow with coolant flowing nicely. Just gave this project up for the Bandsaw. What a disaster ~!@#$%^&*()_

Lots of obvious questions from this rookie.

Firstly, does the Saddle have to be locked down specially whilst parting ???
Does the Tool have to be exact on centre Axis ???
Won't Setting the Tool below centre line work better ???
Even with nice slow speed and Low Feed why the Chatter, with everything locked down tight ???
With the work drawn even closer to the Chuck, why the heck won't the cut progress smoothly ???
Carbide Inserts were clear on the points - no chips or flaws and still no progress ???
Is it ever possible that a small Tool like the 2mm mounted on a Blade won't cut in a straight line ???

This failure has me fearful of ever tackling such a job again. But then again any project on the Lathe will require Parting at some stage. And we need to overcome our fear first and build confidence to try this again.

Your esteemed inputs will be immensely appreciated and we graciously THANK YOU in anticipation.
LORD BLESS
aRM
 
Parting can be a pain even for the experienced machinist. Everything must be set up just right to avoid a catastrophic crash. Here are a few guidelines to follow to help keep the earth from giving way:


  1. The parting tool must be dead square to the work. Use the side of the chuck or even an indicator to make absolutely sure.
  2. The tip of the tool must be on dead center, not above or below.
  3. Coolant must be on the tool whenever its cutting, that normally means using flood coolant. You can sometimes get by using cutting oil, but don't skimp on it. If the tip of the tool goes dry even for an instant, the chips will weld themselves to the tool and seize. You are familiar with what happens next. :yikes:
  4. The set up be as rigid as possible. That means tool and work overhang must be at an absolute minimum.
  5. The spindle RPM should be roughly half of what you would use for turning. In production situations you can run faster, but for a manual machine, slower will help keep you out of trouble.

Good luck!

Tom
 
Parting, as stated, is a nerve-racking operation, no matter how long you've been machining. I still exercise the old buttocks regularly while parting. I try to do all the above, and check your tool as well. Are you using inserts? Blades? make sure there is plenty of relief and the cut angle is correct for the material you're working with. I always part in manual mode and have had pretty good success parting dry as well. It's slow, but possible.
Good luck and get back on the horse (so to speak).
 
I seldom have any problem parting. Everything needs to be on center and square and locked.

I keep the job reasonable. Don't part deeper than the chips will clear for your tool. Watch the chips as the job progresses as soon as the chips stop moving BACK OUT! it will soon be expensive.

With carbide tooling either use coolant excessively or don't use it at all! Speeds and feeds of carbide can harden the part if coolant is interrupted. With HSS blades constant high sulfur cutting oil low speeds and feeds.

Usually I power feed to part. Less chance of hardening the material due to it not carrying off the heat as it is removed. chicken and egg thing though if everything isn't right and you don't know it, it can get expensive. How would you know just beginning?

Steve
 
AMS, Good info above. Sounds like you had good basic setup. Close to chuck, tool on center, flood coolant, etc.

"We were feeding merrily merrily and suddenly the earth gave way !!!
We need to know what we did wrong."

Perhaps the chips didn't clear, or tool blade got wider than the groove as you went deeper. 25 mm is a deep cut on some machines. I've parted some larger diameter pieces as deep as practical, then finished on the band saw and faced the back side to clean it up.

"Even with nice slow speed and Low Feed why the Chatter"

On my 9 x 20 lathe, I use a 1/16 wide HSS tool. Sometimes I have to feed the parting tool rather hard to get rid of the chatter, more chip load to load the bearings, and manage the way the chip flows. Less pressure just squeals for me.
Another if: carbide usually needs a faster cutting speed RPM to work right. Experimenting will help you find the sweet spot, for feed and speed.

Depending on your lathe, size and condition, 3 mm may be a bit wide for a 50 mm round cutoff.

Just a few more possibilities, to maybe help or confuse you even more.

Ed Hoc
 
Did anyone mention that parting off is/can be one of the most frustrating $@#$^&* things to do - especially on one of the smaller lathes!!:bitingnails:

You mentioned the chatter, and this in itself can be a contributing factor in parting. Chatter usually indicats looseness/slack some where (unfortunately its also more common on smaller less rigid lathes) Check your gibs on the apron, cross and compound slides, the slightest looseness will transmit to the contact point of the cutter bit and give chatter, Snug them down tighter just for the parting job - locking the apron and compound.

My 13" lathe will do parting with seldom a problem, but the 9x20 can give me heartache sometimes.
 
I don't know if it's due to luck or what but I have been using an 0.040" 1/2" parting tool on my A2Z quick change post on my Grizzly mini lathe and it's been great. I've parted up to 2" diameter material thus far (aluminum) and 3/4" stainless.
 
TomG
U have indeed made pertinent practical suggestions which we now see the real need to adhere to stringently.
As ours is a robust 1 metre bed Machine with power feeds, we may have just been mollycoddling it a bit too much !!!
Thanks again for the esteemed input
aRM
 
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