Cutting off parting

[drsportster]

Still having trouble cutting off on lathe .I bought one of the little carbide holder but tools snap or pop out of the holder being a pain in the butt. I often hacksaw it off then reface the rough cut , how do you cut off smoothly and efficiently I have been using a hacksaw for some years now,

 

[timcasbolt]

It's very difficult to do parting off on a lathe because of the backlash in the cross slide screw. The softer the material, the worse it is. Whenever possible I do like you and cut the piece off on a bandsaw or some other method. When I have no choice, I make sure the blade is perpendicular to the spindle, set on center as perfect as possible, and sneak up on it very slowly.

 

[wore out]

Still having trouble cutting off on lathe .I bought one of the little carbide holder but tools snap or pop out of the holder being a pain in the butt. I often hacksaw it off then reface the rough cut , how do you cut off smoothly and efficiently I have been using a hacksaw for some years now,

For some jobs I use a hand-held bandsaw to cut off parts still mounted in the lathe.

 

[Butch(OH)]

As was said parting is probably the hardest thing to learn on a lathe. There is plenty enough guidance on line for how to set up and part on a lathe so I'm only going to hit the high spots.
Flimsy/light duty lathes and setups are very difficult to part. Gummy materials like hot roll cannot be parted on light duty equipment.
Do everything you can to make the setup as ridged as possible. Lock the compound down. Lock the carriage. Shorten the blade to being just long enough to reach center. Keep the parting line as close to the chuck as you can. You cannot work out away from the chuck more than a couple inches except with a very ridged lathe in free matching materials of large diameter. Proper tool center is vital and varies with how ridged your machine is. Lots of of a top notch cutting oil is needed. SFM should be about 50-60% of turning SFM in most cases. Gummy materials such as the hot roll sold at hardware stores cannot be parted on a flimsy lathe and not on a good lathe unless the setup and feed is perfect.
The only people who have not crashed tooling and parts when learning how to part on a lathe are the one who have never run one,,,and the liars club. Even after you have figured it out you will still need to keep spare blades and inserts handy.

 

[BarnyardEngineering]

Parting with a small lathe is touchy due to lack of rigidity.

Here's a playlist of a guy who made an innovative parting setup for his small lathe. The tool is on the REAR of the lathe so instead of pushing down, it's pulling up. He explains how it works.

https://www.youtube.com/playlist?list=PLbPzkHRZCQB8TSYAQ0eoPKWHs9HJ2Qldu

 

[Jim PA]

One of the most common problems is having the cutoff tool above center. When it is above center, some portion of the tool is pushing metal and not cutting. .010 lower would leave a .020 stub on the part but give you less tool breakage. Too far below center and the part will try to ride up over the tool causing chatter. Cutting a gummy material will require positive rake with a chip breaker incorporated into the tool to prevent stringing. Harder good quality steels a negative rake tool will break a nice C shaped chip with the proper feed rate. Also, the cutoff tool must be straight, so the sides of the tool are nor rubbing into the part, that is why a cutoff tool is wider at the tip to provide side clearance. A solid setup is mandatory. Good luck!

 

[BarnyardEngineering]

One of the most common problems is having the cutoff tool above center. When it is above center, some portion of the tool is pushing metal and not cutting. .010 lower would leave a .020 stub on the part but give you less tool breakage. Too far below center and the part will try to ride up over the tool causing chatter. Cutting a gummy material will require positive rake with a chip breaker incorporated into the tool to prevent stringing. Harder good quality steels a negative rake tool will break a nice C shaped chip with the proper feed rate. Also, the cutoff tool must be straight, so the sides of the tool are nor rubbing into the part, that is why a cutoff tool is wider at the tip to provide side clearance. A solid setup is mandatory. Good luck!

That's where the reverse parting tool has an advantage. Instead of the part riding up on the tool, the tool rides up on the part, flexing instead of breaking.

 

[Mike(NEOhio)]

A lot depends on how tight your machine is. I found feeding the cross slide works better than hand feeding. Use the slowest feed rate you have, .001-.002/rev. and keep the tool dead center with plenty of lube. Grind the tool tip about a 10 deg. angle, point to toward the piece being cut off. A very thin chip will curl and not build up on the tool.

 

[wp6529]

As has been noted, a port-a-band type saw is your friend. For most work, even if you get a parting tool setup perfectly you will still need to finish the parted item anyway so port-a-band and setup for the finish and save time and frustration. Worry about parting for real production work only.

 

[drsportster]

Wore out and wp I like your Porta-band saw idea .I have a shelf under the lathe that could hold that To everyone else thanks for the tips I will heed the advice !

 

[farmersamm]

I will NOT do any parting on my spaghetti like lathe. It just won't handle anything but bronze.

If I ever get off my butt.........gonna make one of these.

Armstrong made a parting tool that was the bee's knees for parting on small lathes. It "unloads" when tool pressure gets too high, or the workpiece tries to climb over the tool.

This fella went through a bunch of iterations to come up with a final solution. I'VE ONLY INCLUDED A VIDEO THAT WAS AT THE BEGINNING OF THE PROCESS.............AND ONE AT THE END OF THE PROCESS.

Old school worked then, and works now.

 

[Ray,IN]

Spent years working in a tool-room, now a retired tool-maker. The single most important thing is to have the parting blade exactly centered on the work and parallel with the chuck face. Under-center causes the blade to jump into the work, over-center means you are pushing the material as much as cutting. Neither is desirable.
Our lathes were used units from the main Westinghouse plant in Philly when our plant was built in 1956. We never replaced them, and they still worked good in 1999 when the plant closed.
Sharp tools cut best, but don't last long at excessive SFM.
I never liked the split-holder, IMO it introduced vibrations into the cutting action.

 

[gears]

I typically use your hacksaw method- even on Titanium... I like the band saw idea, next time I will try that. All that fussing with exact angles, rake, .010 , perpendicular.... who has time for that!?

 

[Pete in Holland MI]

I cut off on my 1922 South Bend from time to time. What I learned in high school shop class was to grind a sharp tool, use a high speed steel parting blade in the proper holder, part close to the chuck, turn the lathe really slow, keep the cut wet with oil, and slowly hand feed, watching your chip.

 

[farmersamm]

Spent years working in a tool-room, now a retired tool-maker. The single most important thing is to have the parting blade exactly centered on the work and parallel with the chuck face. Under-center causes the blade to jump into the work, over-center means you are pushing the material as much as cutting. Neither is desirable.
Our lathes were used units from the main Westinghouse plant in Philly when our plant was built in 1956. We never replaced them, and they still worked good in 1999 when the plant closed.
Sharp tools cut best, but don't last long at excessive SFM.
I never liked the split-holder, IMO it introduced vibrations into the cutting action.

Assuming these probably ran in a lantern style toolholder, do you think the vibration was inherent to the tool post? Or, was it simply the spring action?

 

[Ray,IN]

Assuming these probably ran in a lantern style toolholder, do you think the vibration was inherent to the tool post? Or, was it simply the spring action?

Spring action of holder; I had straight holders that didn't pickup vibrations. I used a 4-way solid post. Been retired for 25 years so I'm having to wake up my memory bank.
I centered my parting tool by using my pocket scale. I ran the slide in until the tool would hold the scale exactly vertical, then tightened the holding screws. I had a small box of shims I had made to raise the holder when necessary.
Still have my toolboxes filled with now-obsolete tools. Everything today must meet ISO certifications; digital instead of vernier scale. I kept track of tool expenses, last tally was over $17,000, now they're just obsolete tools to look at.
This reminded me of watching a How It's Made show today. They had a segment about mold-making for glassware. The narrator said there weren't many toolmakers/moldmakers left today, most everything was made by computerized machines.