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First real part...parting woes!

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BrianT

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#1
Been awhile since posting so I thought Id share the first actual part I made on a lathe that actually will serve a purpose...drawbar spacer for the Atlas 618. IMAG0141.jpg
Everything went well until I decided to try to part off, way too much chatter. I have the qctp from LMS and the blade type cutoff tool that fit in the tool holder. I will read up on the parting issue as I know there is much info here on this. I already understand I was running too fast to part off. I've only had this lathe running for a couple weeks so overall I was happy with the outcome. So thanks to all who contribute their knowledge here, without that I do not think I would have gotten this far so quickly. Any recommendation on alternative parting tools I would be interested to hear.

Lastly here is the 618, got it 2 years ago in a box of pieces and finally got it running with all the help offered here. IMAG0145.jpg
 

junkcollector

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#2
Parting with a small lathe just plain sucks .
I use the t type parting blades and they work pretty good .
A lot less chatter , at least with my g0602 I get a lot less chatter .
I still can't reliably part anything over 1.5" diameter in steel .
Keep the tool sharp and be a little aggressive to keep underneath the chatter might help some to .
I bought a bandsaw just so I could keep parting to a minimum because it sucks :)
 

BrianT

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#3
Thanks for the info. I will get some of the t-type. I was using a generic plain blade from an assortment pack. I ended up sawing the end off and faced that end. With all the chatter I was getting the tool post got loose and things just got worse from there...so the t-type is worth a try...
 

T Bredehoft

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#4
Don't forget, croud the blade into the work. It's scary at first, but the only way to go.
 

BrianT

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Don't forget, croud the blade into the work. It's scary at first, but the only way to go.
Does "croud" mean kind of forcing? I was forcing it some, kind of afraid to try it again as I dont want to damage anything and that was the direction it was going to go. I was at the same speed I faced/turned at when I tried parting which is one problem I believe. I also had the cut off blade extended much further than it likely should have been. Everything else went so well I just went to part off with out lots of thought.
 

Ken from ontario

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#6
I also use a bandsaw when I can or should I say whenever it's more practical even though I can use the parting tool I made for my mini lathe but with a bandsaw there's less drama and it's quick.
 

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#7
Greeting's Brian, i have the same wonderful lathe. All i do is put it in back gear and it works great. Blade must be on center height and snug up all gibs.
 

Bob Korves

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#8
If parting goes bad, just stop and hacksaw through the remainder of the cut, then face the part smooth. Chatter is caused by looseness and lack of rigidity, make sure everything that slides is adjusted for snug fits and everything that can be locked down is locked down. See if that helps...
 

westerner

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#9
Don't forget, croud the blade into the work. It's scary at first, but the only way to go.
Blade must be on center height and snug up all gibs
Brian, I feel your pain. My lathe is your lathe's big brother, quite worn. The chatter was scary! Very recently, I decided to follow the advice of Mr. Bredehoft and others here, and just PART THE DANG THING OFF. Good sharp tool, as thin as you can find, square and centered, minimal overhang. Then, WIND THAT SUCKER IN! You will find a feed rate that minimizes or eliminates the chatter, but it is MUCH, MUCH faster than you think is possible. After the first time I did this, I was in disbelief! So I moved over, and did it again, just for fun. And that was so much fun, I did it again!
 

ericc

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#10
One needs to have some common sense when doing the "croud" thing. If it is chatter, that can be helped by increasing the feed rate. If the tool is grabbing, this can lead to a crash and broken and flying pieces. I have encountered both situations, and it is hard to tell the difference. One good way is to find a nominal parting feed rate and make sure that you don't exceed it too much. For example, 0.002" per rev. If the spindle speed is 200 rpm, this translates to 0.4" per minute. You may try bumping this up to 0.005" per rev, which would be 1" per minute. Do not increase it to 10" per minute (1" in 6 seconds) just because someone tells you to cram in the tool. There is something wrong. Probably something is loose, and if you cram the tool in at this fast feed rate, even though "fast feeds are good", something could break.
 

homebrewed

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#11
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.
 

Old Rivers

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#12
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.

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
 

bhigdog

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#13
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
 

mattthemuppet2

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#14
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.
 

poplarhouse

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#15
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.
 

BrianT

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#16
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!
 

P. Waller

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#17
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.
 

homebrewed

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#18
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
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.
 

BrianT

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#19
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.
 

Ken from ontario

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#20
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.
 

BrianT

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#21
Ken, you are right about the handle having some slop and that is likely the main movement I saw from the chatter. So yes the tool holder remained secure from what I could tell.
 
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