Do you have some hints for parting off?

[HMF]

Hey Guys,

What can you do to prevent breaking bits while parting off?

I have seen these suggestions:

- tool dead on center. Cutoff tool need to be exactly 90 deg to the work or it will bind the tool.
- tool as thin as possible (minimum length of cutter edge engaged in workpiece)
- correct cutting fluid (NOT a lubricant, must a be cutting fluid), use cutting oil to reduce friction and galling (sticking metal)
- correct speed and feed
- setup as rigid as possible.
- quick change toolpost rather than williams holder/lantern toolpost
- minimum extension of workpiece from chuck or collet
- gibs on machine snugged down
- carriage locked down during cut"
- Use a live center.
- American HSS parting blades like those made by Empire work better than the China made ones. http://www.micro100.com/inch/t_v_blades_brazed.html
- A nick in the center of the top of the blade will cause the chip to curl up on the sides, there by lessening the chance for it to become caught between the side of the blade and the work.
- Parting blades need to be sharpened when they are new from the factory and every so often when you are using them.
- Parting on a bigger lathe is easier
- when parting try to start at the highest speed for the size of the work and try to feed more slowly as you get towards the center.
- minimum front clearance
- power feed at it's slowest setting, if you have the feed and speed right, parting with the cross feed under power is better than by hand.
- do not have the tool stick out too much.
- after cutting depth of 2x width of blade, back out move over 0.010" and continue cut deeper. keep moving over left and right sides of cut wider so a 0.093" wide blade is in a 0.103" or wider groove.


[video=youtube;82LtUTBmxwQ]http://www.youtube.com/watch?v=82LtUTBmxwQ[/video]


[video=youtube;w0N6K9y2i2M]http://www.youtube.com/watch?v=w0N6K9y2i2M[/video]


[video=youtube;PgS5GFQXSQo]http://www.youtube.com/watch?v=PgS5GFQXSQo[/video]



Do you guys have any other suggestions for success parting off?

Thanks,

Nelson

 

[8ntsane]

I must admit, I never had any luck parting off when I had a 12X37 import lathe. I had the qctp, spent all kinds of money buying different HSS blades, but at best it was a hit and miss deal.
With the import lathe, I had better success parting with the rear tool post mount, with the machine run in revese. For the guys with screw on chucks, you better flip the blade over, and run in forward. Coolant does help alot, as the heat goes up, thats when it seems to grab the blade and snap it off. I found that the sulferized cutting oil was the best for parting, but maybe thats just me?

Blades,, I found thinner blades worked better for me, I seemed to mess up more of the 1/8 blades than all others.
Feeding the tool in under power, holy crap, what a night mare!
That never worked for me. I snapped off more blades than I ever care to remember doing that, regardless of the feed.
So any time I parted, I feed in by hand. That way if I could feel the slightest bit of roughness, I would pull out,and more cutting oil, and check to see how hot the blade was. if the blade was hot, the work piece being cut was too.

As Tubal Cain has mentioned, the heavy machines do get away with alot more. My current lathe at 4000 pounds parts off like easy street. hand fed, under power and all. I can even use those 1/8 blades that were sittin around for yrs. For me, I still use the elcheapo blades, but have a very ridgid machine now. I guess that does make a fair bit of differance.

Cutting a nick on the top, I didnt see any change, but could be me again. Making sure the blade had releif, thicker at the top, that makes a huge differance. I did run across that with cheapo blades, they measured the same top, and bottom.

Sharp blades are a must, and the only thing Ive noticed with a sharpening job is, if you get the cutting edge to a angle, the chips seem to flow over to one side, then that familular sound,snap.! So that does make a differance when sharpening your tool. If it cut pretty good out of the box, and now its not doing so well after the re sharpening, best to go back and have alook at that.

Just few of my thoughts

Paul 8)

 

[8ntsane]

Paul,

What lathe do you have that weighs 4000lbs?
Ed

That would be a 1941 Sidney , its called a 14X30, but swings 17 3/8 in front of the carriage, and swing 10 inch dia over the carriage. It not a gap bed either. Built in the middle of hell back in war time. These guys were made to remove lots of metal, in a hurry. The manual claims 4200lbs

Paul

 

[Tony Wells]

.....

Hey Guys,

What can you do to prevent breaking bits while parting off?

I have seen these suggestions:

- tool dead on center. Cutoff tool need to be exactly 90 deg to the work or it will bind the tool. Agreed on being perpendicular, but run the tool 0.005/0.010 below center to reduce tool pressure.

- tool as thin as possible (minimum length of cutter edge engaged in workpiece) Agreed

- correct cutting fluid (NOT a lubricant, must a be cutting fluid), use cutting oil to reduce friction and galling (sticking metal) Agreed, more or less

- correct speed and feed Agreed

- setup as rigid as possible. Agreed

- quick change toolpost rather than williams holder/lantern toolpost Agreed

- minimum extension of workpiece from chuck or collet Agreed

- gibs on machine snugged down .No tighter than normal

- carriage locked down during cut Agreed

- Use a live center. For what? J/K...As long as you regulate the pressure, use of a center is fine until the part is ready to drop. Then retract the center and provide a catch means for the part.

- American HSS parting blades like those made by Empire work better than the China made ones. http://www.micro100.com/inch/t_v_blades_brazed.html In general, micro100 is good carbide, but I have not compared these.

- A nick in the center of the top of the blade will cause the chip to curl up on the sides, there by lessening the chance for it to become caught between the side of the blade and the work. Possible, but be aware that the geometry is changed by this. A similar idea is common on inserted part off tools to reduce the width of the chip curl, and prevent scrubbing on the parted faces, and minimize chip jamming, by allowing the curl to ride up and out of the groove.

- Parting blades need to be sharpened when they are new from the factory and every so often when you are using them. HSS blades, yes. Inserts, no.

- Parting on a bigger lathe is easier .Generally yes, all other considerations aside.

- when parting try to start at the highest speed for the size of the work and try to feed more slowly as you get towards the center. Select speed based on mid-radius. The sacrifice is on the beginning and ending diameters. Change feed to compensate if hand feeding.

- minimum front clearance. Material dependent, somewhat, although a low clearance provides greater edge strength.

- power feed at it's slowest setting, if you have the feed and speed right, parting with the cross feed under power is better than by hand. Agreed. Consistent feed produces a predicable, and hence controllable chip.

- do not have the tool stick out too much. If you're on a manual, and doing a one-off, choke up on the blade at first, perhaps only a 1/2". Then, as you go, dial out and extend the reach a bit at a time. Of course, this only applies to large diameter part off jobs, like 3"+, depending on the lathe itself and how it handles vibration, etc.

- after cutting depth of 2x width of blade, back out move over 0.010" and continue cut deeper. keep moving over left and right sides of cut wider so a 0.093" wide blade is in a 0.103" or wider groove. No, you lose support needed on the flank of the tool to keep a straight cut

 

[Frank Ford]

My suggestions -

Indeed, follow those guidelines. For parting of large diameters, consider running the parting tool in, say up to a half inch, and then use that groove to guide your band saw to finish the rest of the cutting.

Step A:



Step B:



My Sharp Hardinge clone is a pretty stout lathe for 11" swing, but when I try to part 2" steel, I get nervous. By contrast, I used a well worn Clausing Colchester 15" at TechShop and it parted 3-1/2" cold rolled with absolute ease. Rigidity is the deal. That and mass. Mass and rigidity are the deal. And a good sharp too. Mass, rigidity, and a good sharp tool are the deal. And, nice red uniforms. Nobody expects the Spanish Inquisition. . .

As with all techniques, I think it's easy to get into over-studying it. My favorite way to learn is to get some basic info and then give it a try, using common sense and good safe behavior. An old time machinist once told me, "Forget about feeds and speeds - learn to read the chips, listen and get the feel for how the machine and tool are cutting." For sure, I've broken more than my share of parting blades, but each time I've done it, a lesson sinks in. . .

 

[sasquatch]

Good informative topic, and i always enjoy Tubal Cains teaching capabilities.

 

[Goldstar31]

Whilst I run a ancient and somwhat worn small lathe- a Myford Super 7, I have no problems with parting off.
Quite simply, the late George H Thomas wrote an article in Model Engineer in Volume 142 and it became embodied in his Model Engineers Workshop Manual.
Much of the principle will be seen by refering to HemmingwayKits who sells many of his designs as kits.
However the Rear Parting Tool is fitted to the rear of the saddle and the HSS tool inverted at centre height at an angle of 7 degrees to the work. The lathe is run forwards and the parting tool is firmly clamped.

George- in his pedantic but non waffleway, specified that the 'top' of the blade should have a 140 degree kerf ground along its 'top' and a 140 degree positive edge on the cutting edge for the best results.

OK, I have a very refined tool and cutter grinder to do such things but in practice, neither seems necessary to part up to 2" diameter in mild steel ar 350 rpm.

Recently, I have cutting a mountain of spare washers for my Clarkson T&C from a rusty old bit of 1" round and simply lubricating the kerf with a lard oil.
The only snag is that the job is so quick that the curled swarf clogs the space between the inverted tool and the lathe saddle.

Frankly, if one stops and reads the words and music from the real gurus like Thomas, there isn't a problem.

Thomas was the man who developed how to make division plates with a ONE hole division plate. I followed that as well!

Apologies but the subject has been explained and explained- and for a few coins for a book , no one seems to take the least bit notice.

Rant over

Norman

 

[Loggerhogger]

I have had good luck with the tool slightly lower than center. Use low spindle speed, (backgear) and use lots of cutting oil

 

[knifer-one]

i have a bxa sized holder for cut off tools The slot is not quite 3/4 inches high. can I use a 11/16 or 5/8 or 1/2 inch blade in it?

 

[jghm]

In the last hour I figured out how to part successfully! (Chatter city before that) My parting tool wasn't level. It was lower at the work piece. I couldn't level and center it with the toolpost wedge in. By removing the wedge instant chatter free smooth cuts. It is now just a tad below center but works great. Finally!!! BTW, my lathe is a SB 9"
John