Parting off question

[fishingreg]

I have just started using my first lathe. I have played with some 1/2” mild steel rod. I have turned 20 or so thousands to true up, I faced, drilled it out about 280 thou, beveled some edges, put a 30 degree bevel on it going into the drilled hole. All that went well considering it was my first attempt at playing. When I got to parting off, it did not go so well. It was a new blade, it was a Arthur Warner blade and holder, I used a thread cutting lube, kept it wet. I ran it about 250 rpm. It did not cut well at all, I applied more pressure, it cut in about 150 thou before the blade broke. I got another type of blade, it’s 1/2” top to bottom, 4” long and the type that has the kind of “T” contour. It did not do any better but I stopped before I applied too much pressure. I forgot to add I only have enough stick out to reach the center of the material. I have it 90 degrees to the material I’m trying to part off and the cutting edge is centered vertically as close as possible. Any ideas what I am doing wrong? How much pressure should I have to apply?

Thanks in advance

 

[MarkDavis]

Parting can be trying.
Square the blade with the work by touching the face with the side of the blade.
Sharp cutting edge with relief is vital.
Spin the work faster, if it's chattering feed the blade faster.
Mild steel can be gummy, sometimes pulling the parting blade out to lube the sides of it help.
Sometimes letting the work cool will help.

 

[fishingreg]

Parting can be trying.
Square the blade with the work by touching the face with the side of the blade.
Sharp cutting edge with relief is vital.
Spin the work faster, if it's chattering feed the blade faster.
Mild steel can be gummy, sometimes pulling the parting blade out to lube the sides of it help.
Sometimes letting the work cool will help.

Thanks, Have squared it off to the work. I don’t think I’ve even gotten to the point of chatter or gummy, I only got 150 thou or so into the first piece I tried to part off. Today I got the new different blade in and tried it but put as much pressure as I felt comfortable with and it did not cut at all, made a tiny grove. The blade has a relief angle, it’s not squared off. It’s a new blade, shouldn’t it come already sharp? The edge feels good but then again, I’m too new to have a clue what a good edge feels like.

 

[MarkDavis]

Look at the top of the tool with a magnifying glass, the corners should be square.
I'm guessing you have the tool height correct at the centerline of the work.
I sharpen mine on an inexpensive 8" bench grinder with a green wheel.
Had to scrap the original stamped steel tool rest, and build one that was square to the wheel, took a couple of tries and a couple of weeks.
The height of the AXA quick change holder sliding on the tool rest brings the cutoff blade up the curve of the wheel so the relief is a curve instead of an angle, but its close to 11 degrees at the cutting edge.
It took quite a bit of grinding to bring the cut off tool to the shape of the wheel, but now I can just make a couple of light passes to touch up the edge.

 

[fishingreg]

Look at the top of the tool with a magnifying glass, the corners should be square.
I'm guessing you have the tool height correct at the centerline of the work.
I sharpen mine on an inexpensive 8" bench grinder with a green wheel.
Had to scrap the original stamped steel tool rest, and build one that was square to the wheel, took a couple of tries and a couple of weeks.
The height of the AXA quick change holder sliding on the tool rest brings the cutoff blade up the curve of the wheel so the relief is a curve instead of an angle, but its close to 11 degrees at the cutting edge.
It took quite a bit of grinding to bring the cut off tool to the shape of the wheel, but now I can just make a couple of light passes to touch up the edge.

Thanks, I will check out the blade under a magnifier. Thanks for the tip on the green wheel. I have a 8” grinder but just have the stock wheels for auto part/tool work. I haven’t tried grinding a tool yet. I will get a green wheel to try. Should I have to apply any more pressure than say facing 15 thou or so to get the parting tool to cut? On videos it looks like it should cut fairly easy. I would think I should be able to let the tool do the cutting and not have to cram it in there.

 

[Janderso]

Parting can be a batch.
My old south bend hated it.
Rigid, rigid is the key.
Make sure all the gibs are tight.
Center the compound over the cross slide.
Sharp cutting tool close to the holder, dead on center of work at 90 degrees.
That’s my two cents.

 

[T Bredehoft]

Cut off as close to the chuck as you can stand. If your 1/2" piece is sticking out three inches and you try to cut off one inch it will not work. It will probably break the tool.

 

[benmychree]

Green wheels are only used to grind carbide, a white, grey or pink wheel will work fine for HSS tools, your problems sound like incorrect tool height (too high) or insufficient front clearance angle. Jeff's answers are also right on. Tom's comments, are also right there.

 

[MarkDavis]

Benmychree,
Please elaborate on best wheels for High Speed Steels, best type and grit.
I bought the green wheel because I thought it was good, it's certainly better than the gray wheel that came on the grinder.
Could be, my perceived "better" is in grit size. My green wheel is finer than the old grey wheel.

 

[fishingreg]

Green wheels are only used to grind carbide, a white, grey or pink wheel will work fine for HSS tools, your problems sound like incorrect tool height (too high) or insufficient front clearance angle. Jeff's answers are also right on. Tom's comments, are also right there.

Thanks for the clarification. I am using HSS so I will grab a couple different wheels while I am at it so I have a selection as I will end up with some carbide as well I am sure..

The clearance angle is factory, i have not ground the tool yet, I did not measure it but it is a visible angle, looks like 5 to 7 degrees. I feel my height is not my issue, I have a tiny spot from facing that I can see is center and I lined it up with that so if I am off center, its only a handful of thousands. Since I can not seem to part, I can't say for sure and I am brand new to using a lathe but quite used to precision type work and I feel confident I am very close to center. T Bredehoft mentioned the work being a few inches out of the chuck will cause me issues, that might be an issue. I do have it probably 2.5 to 3" out where I am trying to part. I would have thought it would at least cut into the work some but that could be an issue I was not aware of. I will try chucking it up closer to see what happens. I just feel like I am trying to cut thick cardboard with a butter knife when I am trying to part, it just kind of makes a shiny ring on the steel but not chips and a minor bit of almost a fine grit it is making from me pushing on it.

Maybe I have a crap parting tool, is there any particular parting tool you recommend? Not so much a type but like an actual model number so I know I get a decent one?