Parting off question

[homebrewed]

What kind of cut off blade holder do you have? Some tilt the blade up, some have the blade flat. This makes a difference in how much relief the front of your blade needs. I bring this up because it sounds like the blade is rubbing, not cutting.

 

[pontiac428]

Parting can be tricky. The good advice here should get you back on track. I'm not sure if it's been mentioned, but finishing the cutting edge(s) of any tool with a hone is a good idea after the grinder. I'll echo the above to check that the back rake matches your material, but this isn't usually a big deal with parting. Lock out your gibs in all but your infeed for rigidity (possibly a big source of chatter). Parting "likes" a higher surface speed than you may be using for general turning, partly because as you approach center surface speed approaches zero. Last, align your tool tip on center. Too high will rub, too low the work will grab and climb your tool.

 

[fishingreg]

What kind of cut off blade holder do you have? Some tilt the blade up, some have the blade flat. This makes a difference in how much relief the front of your blade needs. I bring this up because it sounds like the blade is rubbing, not cutting.

It is one that holds it flat, it has a flat base that the parting blade sits in and a hex screw at that back of the holder that when turned brings down a piece that holds the tool to the bottom and it comes down at kind of an angle to the hex at the back but the tool itself is held level when put in the holder.

 

[T Bredehoft]

One more thought. You reported that the first tool broke, the second would not cut at all, right away.

Is there a possiblity that too high a surface feed dulled the second tool before it could cut? I second the above suggestions, slow your feed way down and crowd the tool into the work. It's scary at first, but you gotta do it.

Sharpen your blade, verify clearance under the cutting edge, verify on center (level with the center tit from facing), hone the cutting edge to make it as sharp as possible, and give it a try.

 

[fishingreg]

One more thought. You reported that the first tool broke, the second would not cut at all, right away.

Is there a possiblity that too high a surface feed dulled the second tool before it could cut? I second the above suggestions, slow your feed way down and crowd the tool into the work. It's scary at first, but you gotta do it.

Sharpen your blade, verify clearance under the cutting edge, verify on center (level with the center tit from facing), hone the cutting edge to make it as sharp as possible, and give it a try.

Yes, the first tool broke, I think it was way too small, after looking at other parting blades that one did not have much meat to it but it did at least cut into the metal before it broke.

Can you explain what you mean by too high of a surface feed? I am hand feeding so on the second blade, I just creeped it up to the metal and gently started making contact. I put cutting fluid on it and I pushed gently but nothing, I pushed a little more and nothing so I threw the towel and and figured I had better ask some questions. I did not try to use the 2nd blade in the grove the first blade made. The 2nd blade is 1/8" wide, the first blade was about 3/32. So I just got my trusty hacksaw out that never fails me and whacked off the first one... (reverted back to my pre-lathe days) I was on a new section of metal with the 2nd blade but same piece of metal just another inch or two down from the first one. Are you thinking I am not pushing hard enough at first and dulling it?

 

[francist]

once I see if I can tell if it is hot rolled or not.

Hot rolled material is pretty easy to spot -- it has the rough, blackened finish on the outside as opposed to the smoother, grey finish typical of cold rolled stock. There is nothing really difficult about parting hot rolled steel itself, but that black surface layer is what takes the edge of your tool right away. If you use it, and I do for turning fairly often, it's beneficial to take a decent enough cut to get underneath that rough oxide surface layer. Once you're past it, no different than anything else really.

What sparked my comment now though was, do you know that what you have is indeed "mild steel" and not something else? We could go round and round trying to tell you how to set up a parting tool only to find out later that you're trying on a piece of stainless or 4140 or something, both of which can work harden pretty quickly making any further effort pure hell, regardless of the tool.

Mystery metal is fine if that's what you want to use, but sometimes it really does complicate things by adding yet another unknown to the equation.

-frank

 

[T Bredehoft]

Can you explain what you mean by too high of a surface feed?

Most cut off blades are High Speed Steel , at best, 90 to 100 surface feet per minute is as fast as High Speed Steel can tolerate. Faster, generates too much heat that dulls the tool. 600 RPM is about as fast as as you can turn 1/2" steel without burning the tool.

Did you perhaps touch the surface of the spinning steel at a faster RPM? That would be a too high surface speed.

 

[fishingreg]

Hot rolled material is pretty easy to spot -- it has the rough, blackened finish on the outside as opposed to the smoother, grey finish typical of cold rolled stock. There is nothing really difficult about parting hot rolled steel itself, but that black surface layer is what takes the edge of your tool right away. If you use it, and I do for turning fairly often, it's beneficial to take a decent enough cut to get underneath that rough oxide surface layer. Once you're past it, no different than anything else really.

What sparked my comment now though was, do you know that what you have is indeed "mild steel" and not something else? We could go round and round trying to tell you how to set up a parting tool only to find out later that you're trying on a piece of stainless or 4140 or something, both of which can work harden pretty quickly making any further effort pure hell, regardless of the tool.

Mystery metal is fine if that's what you want to use, but sometimes it really does complicate things by adding yet another unknown to the equation.

-frank

Thanks Frank, that is a good question, I really don't buy anything other than mild steel for my projects so I assume it is mild steel. I buy some AR500 plate from time to time but this is not plate and I have no reason to buy AR rod. I think this piece actually came just from Home Depot if memory serves, I think I was in a bind one weekend and needed some 1/2" round for something and picked it up there. I can't imagine they have anything other than mild steel unless they have some strange alloy but it welds like normal steel.

That is good to know about the surface of hot rolled. The first cut where I used the smaller blade, I had taken quite a bit more off the outside before parting, I was just playing and getting a little lathe time in. This cut I did not take but a few thou to make sure it was taking a cut all the way around.

I will try to hit a steel supply this weekend and see if I can get some cold rolled mild steel so I know for sure what I am working with.

 

[fishingreg]

Most cut off blades are High Speed Steel , at best, 90 to 100 surface feet per minute is as fast as High Speed Steel can tolerate. Faster, generates too much heat that dulls the tool. 600 RPM is about as fast as as you can turn 1/2" steel without burning the tool.

Did you perhaps touch the surface of the spinning steel at a faster RPM? That would be a too high surface speed.

I was running slow, I tried 205 and 335 RPM and both netted the same results. The tool does not have any off color but I did not jam in it very hard either. As little as it was cutting I am sure the heat would have come on quick if I had pushed it hard.

 

[mikey]

Last, align your tool tip on center. Too high will rub, too low the work will grab and climb your tool.

Greg, look hard at what @pontiac428 says here. Others have said it, too. If the tip of the tool is not dead on center, it will not cut. I know you said you're a precision kind of guy and got it close by eye but I am going to guess that your tool tip is high and it is rubbing. I say its high because if it was low, it would dig in. If it was on center, it would cut. If it is high, it will rub on the relief angle below the cutting edge and it will not cut; it will leave a bright line on the work but it won't cut.

Parting is not rocket science. You need enough relief angle on a tool to allow the edge to cut. The edge needs to be sharp. The tool needs to be perpendicular to the work, and the tip of the tool must be on center. Do all of this and the tool will cut. Your lathe is more than rigid enough to part a 1/2" piece of steel easily.

Make yourself a good height setting gauge that reflects the true centerline of your spindle and use it. It will save you a lot of grief.