What Type of Parting Blade?

[karlsangree]

Newbie alert!

I am brand new to machining and recently purchased a 1942 South Bend Heavy 10. I converted the tool post from the original rocker/lantern style to a Shars AXA wedge type.

I really need some help selecting the parting blades for it. I foolishly thought to myself, "Just go to Amazon and order a couple." However, I didn't realize there were so many sizes and styles, and now I'm confused. Amazon has widths from 1/16" to 1/4", lengths in 3", 4". 4 1/2", 5", and 6", and styles that I have no clue about such as P1, P1N, P2, P3S, P3W, P5, P5X, and P6 and all those styles come in either HSS or Cobalt, and in Cobalt, there is 5% and 8%.

Amazon's choice (not that I put a lot of stock in that) is a 1/8" x 1/2" x 4-1/2" 5% Cobalt P3S Style.

I'm so confused... Any help would be much appreciated.

Shar's universal AXA parting blade holder:

 

[mmcmdl]

Keep it simple . An Iscar holder can be used in any size toolholder and will accommadate multiple blades as well as insert blades .

 

[Ulma Doctor]

I’m partial to M42 cobalt parting blades
I turn stainless constantly, the cobalt blade works wonders
I like 1/8” thick for most operations, but i have thinner and thicker blades for different jobs

 

[Bob Korves]

Before ordering one, find the height range possible with the your tool holder and tool mounted on your lathe. You need to have the cutting edge close to the center line of the part to cut properly. Have some additional area with the tool holder/blade combination for reaching different depths of cut with the cutting edge on center with the work. Shimming up the tool holder to the working height can lead to a less solid mounting...

 

[Pescadora]

Before ordering one, find the height range possible with the your tool holder and tool mounted on your lathe. You need to have the cutting edge close to the center line of the part to cut properly. Have some additional area with the tool holder/blade combination for reaching different depths of cut with the cutting edge on center with the work. Shimming up the tool holder to the working height can lead to a less solid mounting...

Two years now with the 1030V and PM30, but parting is still something that never goes quite right. All is well at first. Feeding carefully, adjusting RPM. Slow approach. Chips clearing out. But when it gets down to the skinny? Without fail, jams, stalls the motor. I have to back out, reset and come in slowly to pop off the wedge and then make a bit more progress before it happens again. After 3-4 instances, out of the chuck, into the vise and hacksaw the part off.

HSS 3/32 blade, backed into the tool holder for minimum clearance. Cutting edge at center of part. Must be something I do not know. Which would not surprise me, being a mill man more than a lathe man.

Here's a small hydraulic cylinder I'm making for a special project. 1018 cold roll. 1.25" diameter out of 1.50 bar. Got the part-off diameter down to about .600 before troubles began. Quit and did the hacksaw thing around .400. Too bad, I wanted a smooth end back there.

 

[FOMOGO]

Another option for lighter machines is parting from the rear. There have been threads on that here. Mike

 

[MrWhoopee]

Did you get the AXA set with parting blade holder? Moving the clamping wedge from maximum to minimum will give you the height range. Taller blades are more rigid. I have a setup similar to yours ('63 Heavy 10 with AXA wedge post). I use a P2 blade, which is 3/32 wide. I am able to part regularly without drama or chatter, 20 years in the trade might have something to do with it. Since parting is done a low speeds, the grade of HSS is probably not critical.

The keys to parting are a sharp blade that is square to the spindle and on center (very slightly below is ok, but not above center) with minimum stick-out and plenty of cutting oil down in the groove. The trick is feeding at a rate that produces a nice curl. Beginners tend to be nervous, feeding tenuously and backing out at the first sign of chatter. This is exactly wrong. When it starts to chatter, increase the feed rate. Chatter is caused by the tool loading downward then springing back up repeatedly. The answer is to apply enough load that it can't spring back up.

 

[Pescadora]

[plenty of cutting oil down in the groove. The trick is feeding at a rate that produces a nice curl. Beginners tend to be nervous, feeding tenuously and backing out at the first sign of chatter. This is exactly wrong. When it starts to chatter, increase the feed rate. Chatter is caused by the tool loading downward then springing back up repeatedly. The answer is to apply enough load that it can't spring back up.]

That pretty much describes my approach. My blade is 3/4" x 3/32 and I do back it into the AXA blade holder leaving about .050 clearance from the holder with the part is cut off.

But I had always believed my problem was being too aggressive on the feed. So that's not it, but square to the spindle might be a hint. From memory, the blade has an upward cant. I've been approaching with the upper edge at mid-part height, IE, with the cutting edge of the blade at the same height as the center of the rotating part. It is clear to me that the tool is digging in, loading up, flexing downward and peeling off a chip much too deep, thereby stalling the motor. It also seems that when it flexes downward, the tip then cuts deeper. Maybe a lower approach? Maybe I'm still too high initially. When the cutting edge flexes downward, it seems it should pull away from the center of rotation, not dig deeper. Those were my thoughts on the drive home last night. Good discussion right here.

Low speeds - ? Having a variable lathe, I tend to seek best speed while working. I believe I was spinning about 380ish on this part. I typically operate this lathe in low range.

Feed rate: by hand or by engaging the cross slide feed? Never tried that. Always did it by hand, which is terribly variable.

Making a mental note to check the parting tool tip sharpness

Thanks for all the hints.

 

[Bob Korves]

I have found that keeping the tool feeding under good pressure, without backing off if possible, usually achieves the best parting job, with the least change of how the cut is proceeding. The last thing I want to do is back off the tool until the entire cut is done. First, study feeds and speeds that are appropriate to your lathe, your work, and your tooling, and then just do it. Power feed, if you are tooled up for it, is usually the best method, with hand on the lever to stop the feed if necessary. If no power feed, get your brain in that mode and start cranking...

 

[Bob Korves]

I have found that keeping the tool feeding under good pressure, without backing off if possible, usually achieves the best parting job, with the least change of how the cut is proceeding. The last thing I want to do is back off the tool until the entire cut is done. First, study feeds and speeds that are appropriate to your lathe, your work, and your tooling, and then just do it. Power feed, if you are tooled up for it, is usually the best method, with hand on the lever to stop the feed if necessary. If no power feed, get your brain in that mode and start cranking...