First real part...parting woes!

Not all QCTPs are created equal. I have a 7x12 and bought the A2Z QCTP from LMS. It is made from aluminum, and I found it really wasn't rigid enough for parting-off. If the parting tool wasn't really sharp it became very difficult to use, showing a tendency to be pulled under the work: not good for one's blood pressure.

The first holder I made for my home-made QCTP was for T-type parting blades. Parting is MUCH easier now.
 
homebrewed said:
Not all QCTPs are created equal. I have a 7x12 and bought the A2Z QCTP from LMS. It is made from aluminum, and I found it really wasn't rigid enough for parting-off. If the parting tool wasn't really sharp it became very difficult to use, showing a tendency to be pulled under the work: not good for one's blood pressure.

The first holder I made for my home-made QCTP was for T-type parting blades. Parting is MUCH easier now.
Click to expand...


Interesting comment re. QCTPs being made of aluminum, I did not realize this.
Would a steel QCTP be better (more rigid)?
Can you recommend a steel QCTP?

Bill
 
When parting so much depends on the material and needless to say the rigidity of your lathe and set up. The pictured lathe is not a good parting off machine for other than thin sections such as tubular pieces or brass and aluminum. Even at that The tool must be set correctly and with maximum rigidity.
Accept it's limitations and don't abuse the machine. It's a nice little machine but it's best friend will be a saw.................Bob
 
I've parted off 2" steel rod on my 618 and got an inch and a half or so into a 4" steel round (chuck back plate). I do all the things suggested above:

t-profile blade - really thin for pieces up to 1" and the next size up for thicker material. Extend the thin one out too far and it'll wander, whereas the thicker one takes more cutting effort

solid tool post

slow rpm and heavy feed. You have to stick in until the tool makes nice curling chips. Too light a feed will cause chatter and crumbly chips.

extra tips:

flood with cutting oil (dark pipe threading oil for steel, WD40 or kerosene for alu), retract every so often to clear chips

step cutting, both length wise and radially. You can use a thin blade and then step it over 1/2 blade width - that creats a wider gullet and less chance of jamming. You can also use a thin blade with minimum stick out to get the cut started, then extend it out of the holder as the cut gets deeper. If it's a decent size piece you can always then swap to a thicker blade.

don't forget that the rpm needs to increase as you get closer to center

Play around with everyones tips and see how it goes. I don't even think about parting anymore unless it's a big piece (and then I'd probably use my horizontal bandsaw), and I've even parted stainless without any problem.
 
Slow the spindle down and use lots of oil. I don't remember where I learned this, but I sharpen the blade by presenting it face-on and tilted up slightly to the grinding wheel, which creates a convex face and allows clearance. I then grind just a small chip break on the top— works for me. I think the tapered blades cause less chatter, too, providing clearance below the cutting point, but you have to have a tapered holder so they'll end up perpendicular. Parting off has become a snap since I added a vfd to my lathe: very easy to get just the right speed on the fly, rather than stopping and taking a guess at configuring belts. Keep at it and don't ever forget your face protection.
 
I really appreciate everyone's comments and insight. I will keep at it and incorporate the concepts you all have mentioned, none of which I incorporated in my original attempt at parting off. If nothing else I dont feel so bad having to resort to using a saw!
 
I do a good deal of parting, thousands of parts per year.

The advantage of power feeding the tool is the constant tool load, it does not vary as if done by hand, if a person operating the handle feels a high load they will often slow the hand feed rate which often ends in tears.

Yes I realize that the tool load changes as the diameter decreases and becomes 0 at the center.
 
Old Rivers said:
Interesting comment re. QCTPs being made of aluminum, I did not realize this.
Would a steel QCTP be better (more rigid)?
Can you recommend a steel QCTP?

Bill
Click to expand...

The A2Z QCTP is made from aluminum. Good name-brand ones should be steel. I'd be very careful when it comes to buying no-name ones from places like banggood etc.
The QCTP I made is a Norman style one, with a steel post. I AM using aluminum tool holders but they are _very_ beefy. I used one to part a piece of 6061 Alu today, no problem at all. Drove the tool in and made nice little donuts of peeled-off aluminum. Plenty of lube of course. I have used it on steel with similar results.
 
The QCTP I bought from LMS is an "all steel construction wedge type." Looked at others and the all steel construction was what sold me on it. It seems rather ridged, the issue I had when parting was the chatter would cause the handle to loosen thus the tool holder would get loose as well.
 
Brian, I have that LMS QCTP,the handle has a slop but it has not caused any problem for me so far, it feels loose with the vibration but the holder remain locked, at least this has been my experience . I Have never been able to lift or remove the tool holder from the post unless I physically unlock it using the handle.
 
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