Parting off question

[markba633csi]

Your lathe is quite capable, it has to be the tool or the material. You'll get it eventually, or, like me you'll swear off parting for the rest of eternity LOL
Just kidding
Did I mention I hate parting off?

 

[pontiac428]

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.

This is sage advice. I keep a planer gage on my lathe bench that is set to center height. It's so much more precise than eyeballing off of a live center, which has a couple extra elements of uncertainty in addition to a blunted point.

I don't like parting off either. It lets me know how flexy my lathe is. It is counterintuitive to feed into the noise. 1/2" Hot rolled steel bar should be a walk in the park, though, and if you find what's wrong and fix it, you should be parting and grooving your way to funkytown.

 

[fishingreg]

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.

I did see that and have made notes on all the suggestions. It could be I am 10 or 20 thousands high but I faced the end off so I can see center pretty clear and I am very close but I can see how if I am even just a little above center maybe the cutting edge is not touching the material. I can try adjusting that and see what happens.

I will have to youtube a height setting gauge, that is not in my vocabulary yet... It will be now, another note written down...

That's exactly how I feel, this should not be rocket science, people talk about using the same tool for years and if it were this tough, they would not keep a tool in one piece for years... I'll get it, there is something wrong and I have just not found it yet. I might play again tonight when I get home to see if maybe I am a hair high. Thanks for all the help.

 

[benmychree]

a number of wheel that is pink and does nice work on HSS is made by A.P. DeSanno Co (an American brand, the number is RA 80 12 VOS, that is an 80 grit wheel, for rough grinding you'd want a coarser grit, such as 46 or 60.

 

[savarin]

Parting on my 9x20 generic asian lathe was a nightmare and like you I broke many blades.
I could actually see the tool post flex under some cuts so I removed the compound slide and replaced it with a solid plinth.
WOW, parting became a breeze after that.
I use the "T" section blades now in a qctp and also use a diamond hone to touch up the cutting edge before every use.
Just in case you want to go down the solid plinth route heres how I made mine.

Plinth For Qctp On 9 X 20 Lathe

In my never ceasing search for more rigidity in my lathe I decided to make a plinth for the qctp. In its normal configuration I can often see the complete top slide assembly flex slightly. (I think I punish my lathe a bit) After seeing Bill G's plinth I felt it was time to go. I forgot to take...

www.hobby-machinist.com

 

[mikey]

That's exactly how I feel, this should not be rocket science, people talk about using the same tool for years and if it were this tough, they would not keep a tool in one piece for years... I'll get it, there is something wrong and I have just not found it yet. I might play again tonight when I get home to see if maybe I am a hair high. Thanks for all the help.

It is not hard to part on a lathe. While it is true that some lathes are a bit flexy and parting is difficult, that is not the case with a PM1340. The issue is set up or a poorly ground tool.

Grind your tool with a 7 degree relief angle under the edge. Try to grind it square across the front. You will know you have it when you raise an even burr across the front of the tool. Then use a diamond stone to gently knock the burr off. You do this by laying the top of the tool, the flat part, on the stone and pulling back, away from the edge. If you use a good tool, like that AR Warner P2 tool you had, it will last a long time before you need to sharpen it. I re-grind my tool maybe once a year or so and I may re-hone it once every few months. It cuts just fine.

Not to belabor this but you also need to be careful when you install the blade in the tool holder. The blade must be precisely vertical in the tool holder and flush up against the inside of the slot. Many tool holders do not allow this because the top of the blade is wider than the body. The easiest way around this is to use some shims between the body of the blade and the tool holder to space it evenly away so the top of the blade clears. Check this carefully; it makes a big difference.

Contrary to popular belief, you do not need to run at really low speeds to part. You just need to feed fast enough so the tool cuts continuously. This is true of almost all cutting tools - the feed must keep up with the speed or you ruin the tool's edge. If you cannot keep up with the feed then you need to lower the speed ... simple.

I also do not agree that you have to apply a lot of feed pressure to part. A good tool, set correctly, will cut easily. You are looking for a positive resistance to the feed. I mean that you should feel a slight resistance at the hand wheel as you feed in. There should be a nicely curled chip forming and you will feel that push back. Once you get a good chip forming, just maintain that feel of slight resistance and the tool will cut well. Note that a wider blade will cut with more resistance, which is why I personally use the thinnest parting blade that is appropriate for the work. For a 1/2" piece of steel, a P1 or even a P1-N would work fine. The larger the diameter of the work, the wider the tool is supposed to be but I've parted stock up to 1-1/2" OD with a P1-N blade that is only 0.040" thick.

Parting is a routine operation and an important one. You will use it to cut grooves, demarcate cuts and part stuff off. You need to figure out how to do it well on your lathe so don't give up.

 

[jdedmon91]

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?

This sounds like a center hight issue, or a relief on the blade issue. Like I said the only time I have any parting issues is with small diameter stock like 1/4 inch or so. Today I’m working on a spade drill holder and parted 1 1/4 stock with no problem.


Sent from my iPhone using Tapatalk

 

[fishingreg]

Thank you to everyone, I appreciate all the detail. It’s really hard for someone who has never parted a piece off to explain or comprehend pressure and feel type items like that. so thank you all for helping and pointing me in the right direction. I got home today, chucked the piece up closer to the chuck, centered my tool post, and double checked the height. I dropped it down a hair to make sure It was not above center line. I tried it, applied a good bit of pressure and nothing but a shiny line and a lot of squinting from me. So I took the tool down to my pink wheeled chain saw sharpener ( the only non automotive stock grinding wheel I have and I have no stones yet). I ground an edge, went back, put it in and with minimal pressure got a nice rolling chip coming off. I parted several more without any issues. I do not know if it came dull or if I dulled it but it must have been horribly dull. Thanks again to everyone and I have some more homework to do on centering the tool and making something to help me with that. I’m sure I’ll be asking something else basic soon, I’m really enjoying learning and getting some hands on time.

 

[MarkDavis]

Thanks benmychree, made a note of mfg and part number. My little stable of HSS tools has been growing slowly and getting better thanks to many posters on this site.
Thanks to Mikey too! I spend some time lurking on the HSS sharpening thread.

 

[fishingreg]

It is not hard to part on a lathe. While it is true that some lathes are a bit flexy and parting is difficult, that is not the case with a PM1340. The issue is set up or a poorly ground tool.

Grind your tool with a 7 degree relief angle under the edge. Try to grind it square across the front. You will know you have it when you raise an even burr across the front of the tool. Then use a diamond stone to gently knock the burr off. You do this by laying the top of the tool, the flat part, on the stone and pulling back, away from the edge. If you use a good tool, like that AR Warner P2 tool you had, it will last a long time before you need to sharpen it. I re-grind my tool maybe once a year or so and I may re-hone it once every few months. It cuts just fine.

Not to belabor this but you also need to be careful when you install the blade in the tool holder. The blade must be precisely vertical in the tool holder and flush up against the inside of the slot. Many tool holders do not allow this because the top of the blade is wider than the body. The easiest way around this is to use some shims between the body of the blade and the tool holder to space it evenly away so the top of the blade clears. Check this carefully; it makes a big difference.

Contrary to popular belief, you do not need to run at really low speeds to part. You just need to feed fast enough so the tool cuts continuously. This is true of almost all cutting tools - the feed must keep up with the speed or you ruin the tool's edge. If you cannot keep up with the feed then you need to lower the speed ... simple.

I also do not agree that you have to apply a lot of feed pressure to part. A good tool, set correctly, will cut easily. You are looking for a positive resistance to the feed. I mean that you should feel a slight resistance at the hand wheel as you feed in. There should be a nicely curled chip forming and you will feel that push back. Once you get a good chip forming, just maintain that feel of slight resistance and the tool will cut well. Note that a wider blade will cut with more resistance, which is why I personally use the thinnest parting blade that is appropriate for the work. For a 1/2" piece of steel, a P1 or even a P1-N would work fine. The larger the diameter of the work, the wider the tool is supposed to be but I've parted stock up to 1-1/2" OD with a P1-N blade that is only 0.040" thick.

Parting is a routine operation and an important one. You will use it to cut grooves, demarcate cuts and part stuff off. You need to figure out how to do it well on your lathe so don't give up.

Thanks Mikey for the details on sharpening. I need to go shopping and get a stone. I did order a good wheel today for my bench grinder but sounds like the stone will be the finishing touch.