Cut Off Blade Grinding...?

[EmilioG]

Emilio, if you go with HSS/cobalt blades, I suggest the P-type blades. This tool is built like a girder; it is very stiff and has a 5 degree side relief on each side to reduce binding in the cut. I sharpen mine similar to UlmaDoc except that I use a 7 degree nose relief and grind it flat across the face. Either way, his or mine, works and you should try both ways and see which works best for you. I use a 7 degree relief angle because I found it to be the best compromise when parting anything for which a HSS blade is appropriate. And yes, I ground and tested multiple angles to find my preferred angle. That doesn't mean it is right; it just means its right for me.

I also have an Aloris AXA-71 that takes GTN-3 inserts. This is huge blade (1.5" tall X 0.120" wide) that actually works well but the narrowest insert it takes is 1/8" wide. I use it when I cut harder stuff and have had no issues with it but there are smaller, narrower versions of this type of insert that I think would work better. Iscar makes more modern insert geometries; worth a look.

I also have an Aloris AXA-7 that will take HSS blades and smaller/narrower inserted blades. I don't like this tool much but it works okay if you get the blade perfectly vertical.

Sharpening a HSS tool is simple. Get the blade vertical in a tool holder, lay the holder on the side and rub the front of the tool against a sharpening stone while following the front relief angle. I prefer diamond stones but that is a personal preference. I stroke the blade only in the downward direction to avoid the tip from digging into the stone (which I have done all too many times). A few passes is sufficient to remove grinding marks and a pass or two on top to remove the burr and the tool is ready for use.

HSS parting tools need to be very sharp and used precisely on the centerline of the work and precisely perpendicular to the work. When parting from the front, keep your blade extension to a minimum. When parting from the rear, blade extension is not a major concern. When the tool cuts well, it only takes a slight positive feed to keep it cutting. That is, you should feel a slight positive resistance to the feed. Try to keep the feed consistent and the tool should part with no issues if the lathe is tight. In my experience, speeds should be whatever allows you to keep up a positive feed rate. Works for me anyway.

This is all good but I still can't see exactly where these relief grinds are made. I need a simple diagram or photo of the where the grinds are supposed to be. I don't mean to be thick, I just want to understand exactly where and how much. I have P type MoMax blades, HSS. Still looking for cobalt P type MoMax cut off tools. Thanks so much, everyone.

 

[Rooster]

The relief is at the front of the blade, that's the only place you need to grind.

 

[Chipper5783]

How do I grind a HSS cut off blade and prep it for cutting steel? Do you just grind and hone the front part or do you also put a radius on one side?
Any diagrams or photos available? I've seen differing opinions. I need help on this. Also, can someone recommend a good cut off blade holder that uses inserts?
ThinBit?
Tool: Cleveland MoMax HSS cut off blades.

Lots of good suggestions above. I struggled with several different HSS blades, tried lots of different grinds - I still frequently had trouble parting off. I went to a carbide insert blade and it was like magic - I could part nearly anything with no problem at all.

I have gone back and tried one of the HSS blades again - now it works fine too! I really don't know what I am doing differently, but paying attention to the details, gained a bit more experience. Parting is no longer an issue.

Keep asking questions here and try it out for yourself. Not all the suggestions will work for you, but you'll improve - after a while you'll wonder what the problem was.

 

[EmilioG]

Here's a good video that I found by my friend Tom

 

[petertha]

That video pretty much sums up my experience & primary tool of choice. I use inserts too. The edges last longer in tough material, they need a bit more oomph but some make very nice chips when they are feeding properly.

About the only thing I can volunteer is when people grind a slight angle to one side of HSS in order to part one side off a bit earlier drop yield less of a nub. My feeling (somewhat unsubstantiated) is that this should be very slight. Too much angle can cause the blade to want to yaw off track in thicker, tougher or gummier metal... which is exactly where you don't want this happening. Any extra friction, especially non-symmetrical is not desirable. Notice in the video he ground it square & when all set up properly made a very clean part with no drama & negligible/no nib.

Parting large diameter thin washers in some plastics like UHMW is real interesting. They appear to cut effortlessly, no undue cutting temperature, 90-deg tool... but tended to come out slightly irregular like 'potato chipped'. Haven't figured that one out yet. Internal stress relief? I ended up parting them slightly oversize & faced them with adhesive backed faceplate. If anyone has some ideas on this. I'd like to hear.

Here is another vid with interesting perspective on parting bronze & those type alloys.

 

[mikey]

This is all good but I still can't see exactly where these relief grinds are made. I need a simple diagram or photo of the where the grinds are supposed to be. I don't mean to be thick, I just want to understand exactly where and how much. I have P type MoMax blades, HSS. Still looking for cobalt P type MoMax cut off tools. Thanks so much, everyone.

Like Rooster said, grind it at the end:



This is a typical P-type blade. You can see the 5 degree side relief angles. The front relief here is 10 degrees; I prefer 7 degrees - stronger, lasts a long time and cuts very clean.

 

[ddickey]

T type on the left. B type on the right.

 

[Rooster]

After watching the video EmilioG put up it's clear whats needed for easy parting. Sharp, center height, squared and a $60,000 Hardinge.

 

[EmilioG]

Thank you Gentlemen. Those diagrams are a tremendous help. I only have 3 parting blades and I would hate to ruin them.
AFA parting a thin washer, I've never done this. If they are coming out wavy or not symetrical/flat, what would cause that?
Is there a trick to parting off thin sections? Thin slicing?

 

[mikey]

No trick, Emilio. Dial in the cut and part it off. I've made shims/washers a few thou thick with no issues.