Parting

[Ray C]

I gather several folks do this and believe there are some tooling setups to do it. For the life of me, I don't understand why it would be any better. Instead of a piece that wants to climb on top of the cutter, now you have a cutter that wants to climb on top of the piece. I must be misunderstanding something -but anyhow, simple parting and grooving "the old fashioned way" isn't all that terrible...


Ray

I just remembered something my 'mentor' taught me: He made a tool holder that fit on the backside of the saddle for parting. He said that because the tool would 'lift' the part couldn't climb onto the parting blade. I thought it made perfect sense at the time.

As I have a slotted crosslide, making something like this shouldn't be a problem. Anyone see any problems with this idea?

Bill

 

[TomS]

I've done a lot of parting in my life as a machinist and the key is, as others have said, having a rigid setup and the parting tool on center. Other keys to success are the correct speed, some tend to part off too slow, use plenty of cutting oil, and the parting tool must be absolutely parallel with the cross slide travel. Even a slight misalignment of the parting tool will cause problems, i.e. one side of the parting tool will drag. This creates side force that results in poor surface finish, parts that are not flat, and broken parting tools. Care in your setup will result in quality parts. How do I know this? Just yesterday I made a .015" thick thrust washer that was about 1-1/2" OD by 1/2" ID. The surface finish on the parting tool side was as smooth as the side I faced with a turning tool and the thickness was uniform across the 1/2" cross section.

Hope this helps.

Tom S

 

[wrmiller]

I gather several folks do this and believe there are some tooling setups to do it. For the life of me, I don't understand why it would be any better. Instead of a piece that wants to climb on top of the cutter, now you have a cutter that wants to climb on top of the piece. I must be misunderstanding something -but anyhow, simple parting and grooving "the old fashioned way" isn't all that terrible...


Ray

If my memory is correct, with the parting tool on the backside of the part, when the tool loads, it actually backs away from the part, making it impossible for the part to 'climb onto' the parting tool.

Bill

 

[yugami]

I just remembered something my 'mentor' taught me: He made a tool holder that fit on the backside of the saddle for parting. He said that because the tool would 'lift' the part couldn't climb onto the parting blade. I thought it made perfect sense at the time.

As I have a slotted crosslide, making something like this shouldn't be a problem. Anyone see any problems with this idea?

http://statecollegecentral.com/metallathe/MLA-6.html

 

[lrsglory]

Hey, I need to know others experience with parting hard material, say H-13. I have a couple of HSS blade type parting tools that work pretty good on plastic, aluminum and mild steel, and recently purchased one of the grizzly kits that had the carbide inserted parting tool which is pretty nice, BUT, I still have a terrible time parting H13 material. It takes forever, and I'm not producing any "chips" per say, but only dust. I've heard different opinions on how to set the tool height. Do you set dead center, or slightly above, or slightly under? What works for you?

Larry Smith here: After all I'm 66 and should be entitled to an opinion. Here's mine. I apprenticed in a die and stamping dept. for 5 years. Did everything you could do to compound and progressive dies. to repair and keep them running. They wouldn't let us build, but every new die they bought came back to the toolroom 30 minutes after it was set for repair and modification to get it to work. Go figure. You get a real good education on how not to build a die. A ton of work was done on grinders. I could almost take as much material off on a grinder as the average machinist could remove on a mill ie.making die sections. etc. Point, left there to work in a toolroom for a major jack mfg co. First few days on the job I was boring out a 6 inch round piece with a tragically undersize boring bar. Boss comes in , see's setup. proceeds to rip me up and down. Called me everything in the book. I almost quit. His famous quote, don't send a boy to do a mans job. Referring to bar, not me. Hands me a big bar and says get it done. Ok. Next time he comes in I'm trying to part off a 3 inch pc. All the problems I'm reading about. Looks at the setup, asks if I'm done with the end. Pulls it out of the chuck, takes it over to the saw, wacks off the other end. hands it to me and says, face it off a mile a minute and get to me , I need it. Point. don't part unless its the only way available. I had a large old Reed Prentice lathe and I could face off a depth of 1/2 inch, mile a minute. Why part ? They got bar machines for that. Another point. Surface speed. FPM. You may start at the correct surface feet, but halfway thru your at the wrong speed. The only solution is stop, jack the rpm up, and start again. Was never an answer for me. engine lathe only. The piece doesn't have to be indicated in, as long as the axis of the part matches the chuck. kinda like turning a cam shaft. looks goofy but it works. Watch a NC turning center, or listen , as one parts something off. hear the rpm keep increasing till it drops off. Another way to possibly skin that cat.

 

[ScrapMetal]

If my memory is correct, with the parting tool on the backside of the part, when the tool loads, it actually backs away from the part, making it impossible for the part to 'climb onto' the parting tool.

Bill

Seems to me it would be much simpler to use a tool holder designed to "swing away" from the work that attaches normally. The concept has been around for quite some time. Here's a pic of an Armstrong "anti-chatter" parting tool:



-Ron

 

[Ray C]

I'm pretty much on Larry Smith's side of the fence... I don't part unless it's absolutely needed. Once in a while you need to section a piece without removing it from the chuck or else you lose your center. Only then do I part a piece; otherwise, it goes in the bandsaw. As mentioned, I also use the parting tool to dig a shoulder or groove maybe 30 or 40 thou deep. I do that quite a bit and it works well.


Ray

 

[epanzella]

I don't have a bandsaw, so I have to part off fairly often. On the occasions when I do have trouble, it was because on a deep cut I didn't take the time to make sure the parting tool was absolutely 90 degrees to the piece being cut and the extra side drag towards the end of the cut breaks the tool. I used to have an old Logan that would not part steel no matter what I did. I finally cured the problem by eliminating the compound slide altogether and made a tool post that mounted directly to the cross slide. A fringe benefit was that nearly all lathe operations improved with the added rigidity. The exception was threading. Without the compound my threads were always kinda grubby looking but they worked OK.

 

[GK1918]

I'm not that crazy about it myself but once in a while, it's worth the hassle. Mainly though, I use it for shoulder grooving for external threading which only goes 30-40 thou deep.


Ray

Ray; One of the main things we do is threading, so much we had to work all day Sat & Sun. for Monday. And I hate production work or my back hates it.
The job is 5/8 bronze with double end 11tpi. in range of 12" to 28" long. My first thoughts are; 4jaw chuck is out, 3 jaw is junk, has to be done on
centers. So the GK 1918 will center drill one end & campher, flip it do the same thing, thats all that lathe will do. Now it goes to my Model A I love it.
to thread between centers. Back to the post. correct or not I dont care, as my compound is set to 29.5 I stick the parting
tool in it, and do a releif cut for the depth I have to go or close, it doesnt care! Im thinking if this is to be steady work, I think I'll have to break down,
for a quick change for the GK thats big bucks then my son can do the centers champhers and releif cuts. one less thing I have to do.
I hate to be long winded or whine, kick in the buck, Sat. after 75% done customer comes in and now wants one side threaded to 3 Inches. If anyone
knows whats involved with adding on to a perfect thread with a releif cut?? just ask my back; there went Sundays lawn mowing. And then I had a
brain fart! Have a new one of those saw blade craftsman clocks Chrismas present, new, stuck it behind lathe. zero it, and I got it down to nine
min. dead start to finish (for one side) cheap time clock. hey good idea a real time clock conclusion; for this, no need to be perpendicular parting
a releif cut for threading.

 

[Chuck K]

I used to hate parting and I always blamed my problems on the lathe I was using. Looking back on it, the lathe had some bearing on it but there was a lot of user error involved too. I agree with all that has been said about centering and aligning the tool, speeds and feeds, and oil. For me the most important factor is the tool. I always use hss. I have several different thickness and length tools ground. The deeper I have to go the wider the blade will be. I usually set it on power feed so my hands are free to keep a steady drip of oil on the cut. Having said that....whenever it's practical I use the bandsaw.

Chuck