Parting made easy

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: Harold_V, websterz, GlennW

Paulc
Posts: 18
Joined: Fri Oct 18, 2019 2:50 pm

Parting made easy

Post by Paulc » Sun Nov 03, 2019 11:51 am

Many may already know this but I tried a new way ( for me anyway) of parting off a part.
I remembered seeing a YouTube video of someone parting off by having the parting tool upside down and then running the lathe spindle in reverse so I decided to give it a try.
What a difference! Cut thru smoothly, no chatter, no digging in.
This will definitely be my preferred method.

Harold_V
Posts: 17953
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Parting made easy

Post by Harold_V » Mon Nov 04, 2019 2:49 am

Paulc wrote:
Sun Nov 03, 2019 11:51 am
Many may already know this but I tried a new way ( for me anyway) of parting off a part.
I remembered seeing a YouTube video of someone parting off by having the parting tool upside down and then running the lathe spindle in reverse so I decided to give it a try.
What a difference! Cut thru smoothly, no chatter, no digging in.
This will definitely be my preferred method.
Note that this method can be troublesome for folks with threaded spindles.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Russ Hanscom
Posts: 1619
Joined: Wed Mar 15, 2006 11:10 pm
Location: Farmington, NM

Re: Parting made easy

Post by Russ Hanscom » Mon Nov 04, 2019 9:08 am

Commonly done in the british hobby sites with a rear mounted tool post so lathe rotation does not have to be changed, thus no threaded spindle concerns.

curtis cutter
Posts: 426
Joined: Fri May 18, 2012 11:46 pm
Location: Curtis, WA

Re: Parting made easy

Post by curtis cutter » Mon Nov 04, 2019 9:11 am

Can someone help me as to why this method would be superior to what I'll refer to as the "conventional" method?
Gregg
Just let go of it, it will eventually unplug itself.

User avatar
NP317
Posts: 2133
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon

Re: Parting made easy

Post by NP317 » Mon Nov 04, 2019 11:15 am

curtis cutter wrote:
Mon Nov 04, 2019 9:11 am
Can someone help me as to why this method would be superior to what I'll refer to as the "conventional" method?
I second that question.
RussN

RMinMN
Posts: 81
Joined: Tue Jan 02, 2018 8:50 am

Re: Parting made easy

Post by RMinMN » Mon Nov 04, 2019 1:08 pm

In conventional parting if the parting tool digs in it tends to tip the toolpost toward the piece being cut, making the tool dig in more. By moving the parting tool to the rear and upside down, when the parting tool tries to dig into the workpiece the toolpost tends to tip away from the workpiece relieving the dig.

Mr Ron
Posts: 1894
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: Parting made easy

Post by Mr Ron » Mon Nov 04, 2019 1:52 pm

Harold_V wrote:
Mon Nov 04, 2019 2:49 am

Note that this method can be troublesome for folks with threaded spindles.

H
If the work is held in a collet, should not be a problem; right?
Mr.Ron from South Mississippi

John Evans
Posts: 2092
Joined: Tue Jan 20, 2009 9:33 pm
Location: Phoenix ,AZ

Re: Parting made easy

Post by John Evans » Mon Nov 04, 2019 3:03 pm

Right Ron no issue when using a collet as long as the collet is in the spindle and not in some form of threaded on chuck.
www.chaski.com

pete
Posts: 1804
Joined: Tue Feb 10, 2009 6:04 am

Re: Parting made easy

Post by pete » Mon Nov 04, 2019 3:10 pm

As RM said the tool in the rear position will move and tip up and away from the cut. The rear mounted and separate tool holder also doesn't use the flimsy top slide or a QC tool holder most of the smaller machines might have. So the cut off tool is far more stable and locked down much more rigidly. I wish I could re-find the video, but I watched one done in Russian on a heavy 18" + swing good condition eastern European made industrial lathe. He ran numerous tests with indicators showing a great deal more deflection in the lathe parts than one would think possible under no more than average cutting loads. With the tool in the front upside down position it also has to do with how the slides work on a lathe. For them to move no matter how well adjusted the gibs are, there has to be a few thou of clearance even on a brand new machine. With a slightly or highly worn lathe those clearances are obviously a bit more to a lot more. Clearance / wear = chatter. A light weight hobby sized lathe will tend to chatter anyway. It's just not heavy enough to offer much resistance to those higher cutting loads parting off requires. So locking any slide except the cross slide is a good start. Parting off from the front and the tool upside down tends to lift the cross slide due to the cutting forces and/or when the tool digs in and reducing any slide clearance down to zero. The slide tightens up on the dovetail & gib.So the tool then cuts through the chatter as soon as it starts.

Non specialized lathes are designed so the cutting loads are always down and into the heaviest parts of the machine slides, carriage and bed. Quite a few of them in the past and today have T slotted cross slides. So it's easy to use front or rear mounted tooling. The cross section of those T slots isn't very heavy. I've seen a few pictures online where sections of those T slots were ripped out of the machine. My guess was from tools seriously digging in or maybe a hard crash, so reversing the cutting loads needs to be done with some caution. Having a large foot print on the rear mounted tool holder and multiple bolts through the tool holder and into the T nuts is a good idea. Any dig in if it happens you want the tool to break well before the machine parts are going to. If my memory is correct I think the George Thomas designed rear parting off tool holder uses three 3/8" diameter bolts and as large as possible T nuts to hold it down on the rear of the cross slide of the quite small Myford Super 7 lathe. My 11" swing lathe is designed to take 12 mm T bolts on the cross slide, the slot depth is only .480" deep and .700" wide, so each lip on the T slot is barely .115" x.185" thick. In cast iron I think those are pretty weak and would be real easy to damage.

Harold_V
Posts: 17953
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Parting made easy

Post by Harold_V » Mon Nov 04, 2019 4:15 pm

Mr Ron wrote:
Mon Nov 04, 2019 1:52 pm
Harold_V wrote:
Mon Nov 04, 2019 2:49 am

Note that this method can be troublesome for folks with threaded spindles.

H
If the work is held in a collet, should not be a problem; right?
Depends on the collet system. Assuming that the Sjogren type collet chucks are available for threaded spindles, it could still be troublesome. Collets that mount directly in the spindle? Yeah, no problem.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

armscor 1
Posts: 116
Joined: Sun Jun 12, 2016 3:12 am

Re: Parting made easy

Post by armscor 1 » Mon Nov 04, 2019 4:35 pm

I have seen a Lathe destroyed while parting, the operator did not catch the parted off piece and unluckily fell between the chuck jaw and bed, ripped the headstock retaining bolts out of the bed!

pete
Posts: 1804
Joined: Tue Feb 10, 2009 6:04 am

Re: Parting made easy

Post by pete » Mon Nov 04, 2019 4:51 pm

armscor 1 wrote:
Mon Nov 04, 2019 4:35 pm
I have seen a Lathe destroyed while parting, the operator did not catch the parted off piece and unluckily fell between the chuck jaw and bed, ripped the headstock retaining bolts out of the bed!
Yeouch!!!!! a broken out T slot would a real bad day, that's light years past being bad Armscor.

Post Reply