What Type of Parting Blade?

[woodchucker]

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:
View attachment 386721

I didn't see an answer to your post before it was hijacked.
Question, did you already buy the shars holder above?
if so, what type of blade does it take? a P blade is a blade with a small T top,
Mine is a simple chineese AXA holder as well. It takes 1/2"(H) x 3/32"(T) x 4-1/2"(L) blades. They are Tapered from top to bottom to relieve the cutting edge.

It works, and works quite well. There are carbide parting blades and you'll need a different tool holder for them.
There are two main types.
A blade that you wedge an insert into. It needs a special tool holder to hold the blade, it's a block that clamps on the blade, and fits into the holder with a tab that sticks out and you tighten in a normal axa holder.
The other type is a regular holder, that you clamp the insert into. This has a limited depth that it can part.

if you purchased the block you referenced, just buy the HSS or Cobalt blade for it.

If you start with HSS or Cobalt you will be able to do 90-95% of the parting. Only very hard will HSS not work for... Cobalt might ..
Parting is not hard, although when I was first learning I had a few disasters. One, I didn't use a TS on a long piece, and it jumped on top of my tool and crashed. You want to be on Center. slightly high on big piece will work, until you get close, then it won't cut anymore.
TOO LOW with the tool and you will most certainly have a problem. The part will try to ride up on top of the tool, and it will get ugly quick... like I just described with too long.

if you have a long part, use a center until you get close to the end. When you get close on a long long part, you need to remove the TS at the end, or loosen the pressure slightly. you also need to capture the piece right when it's coming off so it doesn't bind on the spinning part in the chuck and parting tool at once.

when parting ALWAYS make sure your parting tool is 90 to the ways. I do this by taking a 123 block and holding it against my chuck and squaring my axa holder and tighten it down, then remove the 123 block. if you are not square you will have a problem parting.

When doing a deep parting , start with the least stick out, move it out when you are no longer able to advance the tool. You need to recenter the tool at that point.. most of the blade holders hold at an angle.

I center with a scale against the piece and the tool. if the scale is straight up and down, I'm in the zone..

I know I spent a lot of time on process rather than tool... if you need more let me know.

 

[benmychree]

One thing that I have found with my very vintage Monarch Jr. 9" lathe is that when parting with the tool overhanging the front of the cross slide is that digging in happens, when I move the tool holder to the right not overhanging the cross slide, it works fine, or as fine as parting gets under normal circumstances, I use Tapmagic for cutting fluid.

 

[karlsangree]

I didn't see an answer to your post before it was hijacked.
Question, did you already buy the shars holder above?

Thanks woodchucker and all who replied. Yes, the Shars QCTP came with a parting blade holder. Based on the comments in this thread, I ordered two blades: a P3S 1/8" x 4 1/2", and a P2 3/32" x 4 1/2". I'll give them a try and just learn what works best for me by using them. I went back and watch parting videos by Quinn Dunki (blondiehacks) and Joe Pieczynski and with the tips in this thread, I'm ready to give it a go.

Thanks again to all who replied.

 

[woodchucker]

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.

sounds like you are already too low if it is digging in deep.
Have you tried bumping a scale against the part and holding the cutting edge of the parting blade against the scale. It should be straight up and down?

 

[T Bredehoft]

Karl, new the hobby, put your wedge type tool holder square to the chuck, and keep it there. I see people turning them to get a different cutting angle. They work best when you know they are square.

As you develop skill you will learn to grind HSS tools at the correct angle, no turning your holder. Square with the chuck will automatically keep your cut off and threading tools at the right angle. I use a 1 2 3 block to set it square, with the tool mount not tight to the compound, (but snug) put the 1 2 3 block between the face of your chuck and the mount. put a bit of presure on the saddle to snug the holder against the 1 2 3 bock and tighten down the holder. You're good to go.

Edit: correct improper word

 

[karlsangree]

put your wedge type tool holder square to the chuck, and keep it there. I see people turning them to get a different cutting angle. They work best when you know they are square.

I was just wondering about that. I've seen a lot of variations but now that you mention it, the pro machinists like Keith from Cutting Edge Engineering, Adam Booth, and Joe Pieczynski always seem to have theirs square to the chuck.