Parting off question

T Bredehoft said:
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.
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Thanks, I will give that a shot, I am out about 2.5-3" but it had no issues facing or turning so I did not consider it might have issues parting.
 
fishingreg said:
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
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All the advice is good. The key thing is rigidity, I have not many parting issues, I do use inserts parting tools, in fact their Banggood on top of that. I don’t part under 1/2 inch diameter because of part flex. Also I use GTN 3 inserts for the same reason rigidity. IHMO the heavier thicker the blade that increases rigidity. So if you need a custom holder to do that you need to do it. I’m attaching two videos one of mine where I made a one piece block fit my insert set up, the second one is a YouTube creator who made a block to hold a large blade to attach to the compound.


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When parting you should have your blade as close to the chuck as possible to try and elevate any flex.
For a regular straight parting blade I have good luck with grinding a little hook on the cutting edge. Along with a angle on the cutting edge not a square edge. Pic below.
image.jpg
As for a T style which I use on my larger lathe. I use a 6” wheel to put curvature to the business end of the blade slightly. Every time I use the blade I touch up to make sure the blade is sharp. Once you start the plunge do not stop keep the curls coming and lube often. Always lock which ever axis not being used.
 
Thanks Jdedmon91, I watched the videos, if rigidity was my issue would I notice some flex, jumping, or something? It appears to be smooth, no jerking, jumping, shaking or anything, just no cutting at all. Just a lot of rubbing and making a nice shiny line but thats about it. Do you notice any movement when it is not rigid or does it just refuse to cut? The first parting blade I did get to cut some but then it broke. That one I do think broke due to rigidity, it is a Arthur R Warner and had its own holder which the holder seemed good but the blade was really small and only about 1/4" top to bottom and about 3/32" wide so I don't think the blade itself was very rigid. The blade I have now is 1/2" top to bottom and 1/8" wide but maybe super dull even though it is new?
 
Cadillac said:
When parting you should have your blade as close to the chuck as possible to try and elevate any flex.
For a regular straight parting blade I have good luck with grinding a little hook on the cutting edge. Along with a angle on the cutting edge not a square edge. Pic below.
View attachment 298091
As for a T style which I use on my larger lathe. I use a 6” wheel to put curvature to the business end of the blade slightly. Every time I use the blade I touch up to make sure the blade is sharp. Once you start the plunge do not stop keep the curls coming and lube often. Always lock which ever axis not being used.
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I am guilty of not pushing too hard so needless to say I have not continued to plunge. I kind of did on the first blade but it was a smaller blade and broke but at least it did start to cut, this one has not started to cut so I have not felt comfortable cranking down on the wheel, I just can't imagine that would end well. After all the videos I have watched and its a lot, I suspect maybe my blade is really dull. I will get a pink or white wheel and attempt to sharpen it and go from there. There has to be something fundamental wrong since it does not really remove any metal at all. In every video I watch when the parting blade engages the metal, it makes chips and starts to cut, I am not getting that at this moment. Now my hacksaw had no problem but it was not very straight...
 
Another thing is to use the minimum stick out of the tool from its holder, and the closer you can locate the part to the chuck jaws, the better. If as you say, the tool is on center, the problem likely lies with the front clearance angle. It would be better to have the tool slightly below center than slightly above center. You asked about specific grinding wheel specifications, I will get back with that, but buy American, brands such as Norton.
 
Your blade is dull; the blade may be new, but not necessarily ready to use. You should get chips as soon as it touches the work.
What size/type of lathe do you have? On small lathes, parting can be nearly impossible due to rigidity issues and backlash
Try using the slowest speed the lathe will go- use backgears if you have them
Tighten the gibs as much as possible while still allowing movement
You might try mounting the tool upside down at the rear of the carriage and feeding toward you- sometimes this works when all else fails
ps I hate parting off almost as much as I hate running a table saw
 
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I was watching some more videos and heard Tubalcain mention do not bother trying to part off hot rolled steel. This could very well be hot rolled. Could that be my issue and I need to get another piece to play with?
 
turn slow and feed hard - you should be getting nice curls coming off the top of your parting tool. If you're getting shavings, splinters or dust, plus it's making a hell of a racket, you're turning too fast (most likely) or feeding too slow (less likely). If your tool isn't exactly perpendicular or is thin'n'whippy then it can wander and cut at an angle, causing a jam or belt slip. good idea to retract the tool every so often, clean out the slow, apply some more oil. If it cuts on the side as you feed it back in, the blade is cutting at an angle.
 
markba633csi said:
Your blade is dull; the blade may be new, but not necessarily ready to use. You should get chips as soon as it touches the work.
What size/type of lathe do you have? On small lathes, parting can be nearly impossible due to rigidity issues and backlash
Try using the slowest speed the lathe will go- use backgears if you have them
Tighten the gibs as much as possible while still allowing movement
You might try mounting the tool upside down at the rear of the carriage and feeding toward you- sometimes this works when all else fails
ps I hate parting off almost as much as I hate running a table saw
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It being dull is what I am leaning towards or what I have might be hot rolled steel, I really don't know its just some I had around from an old welding project. One video said don't bother trying to part off hot rolled steel, just take it to the band saw. I need to probably make sure of what I am playing around with so I don't confuse myself worse if there is something to trying to part off hot rolled.

As far as the lathe it is a PM 1340GT so it should be able to part off ok I would hope... I might need to tighten the gibs a little but everything feels really solid minus maybe I need to be closer to the chuck which I will try once I see if I can tell if it is hot rolled or not.
 
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