Parting tool blues......

J

jGEE

Guest
Someone tell me to quit trying to use a parting tool please. Should i just give up or is there a secret?

I mostly work with aluminum round stock 3/4" to 1-3/4". Tonite i'm making some aluminum bushings for my action wrench and needed to part off a few pieces of 1-5/8". First one i used my porta band but then i wanted to try and make some nice cuts with my parting tool - is that even dooable/possible??

I got the cut chattering so bad i about wrecked my neighbors lathe across the street!~!~ All i can make is chips... What is the proper swarf? i'm looking for.. chips -a nice curly shaving or what please.

If it is possible could anyone show a pic of how to grind the tool and what is the approach angle, center, above center , where is the cut made? I'm about ready to use a hatchet for a parting tool, lol.
I would appreciate any help, thanks- joe:)
 
I rarely use one, but when I do I run the lathe very slow about 40 rpm and feed by hand to get small curls. You have to be very careful when it gets colse to the bore if you are cutting material with a hole in it. Trying to run the lathe at any higher speed has always resulted in serious chatter for me, as you said.

Gary
 
I am in the Machine Shop Business. My men use parting tools on a regular basis. We use a lot of 303 stainless in 3 inch diameter to make pins for steering systems in tug boats, we just use a carbide insert parting tool at about 300 RPM to part the sections off rather than sawing them.

Usually, you can trace parting tool problems back to the rigidity of the machine. If the machine is up to the task, then proper clearance is the key. You want a parting tool to have just enough clearance so it will cut, but not so much as it will try to dig in. Getting the tool just right on center is also criticle.

If your machine is a little lax in rigidity, you will have to slow things down untill the surface feet are below the capabilities of the machine. ........jackie





As you have already found out, shaving build up on the tool is a big problem with aluminum, especially plain old 6061.. Goofy as this sounds, the best cutting fluid that we have found when parting aluminum is WD-40. ............jackie
 
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Well that is one thing for sure, i think i started at about 450 in speed and kept going up in RPMS! Ok next go around the lowest i have is 72 rpms and i'll give that a try.
Jackie i am guilty of my machine not being rigid enough, I am having to make some compromises at this time.
Can't wait to try lower rpms -i'm not surprised everything i do is always backwards first! thanks guys! joe
 
slowest speed on my machine is 90...and i do use a parting tool. bbl steel, alum, ss. i set the tool straight and center..not above or below. hand feed and lube.keep the tool as short as required to make the cut.

mike in co
 
I have absolutely no problem parting off steel or alum. This is with my Grizzly 4003G and the parting tool setup that Grizzly sells. I did grind some side rake and some rake at the business end of the blade. This may be your problem, the cutting surface has to be the widest part of the tool both in the horizontal plane and the vertical plane.

I sometimes have to set the cutting edge a little low instead of centered. Also make sure you have the blade square to the cut or if cutting at an angle have the blade perfectly inline with the compound. I'm usually parting off alum at 220 to 360 rpm and steel at the machine's lowest rpm.
 
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WOW!! I was still set up from 1am this morning -i went out to my 'skunk wurks right now and just had to try! Mike with your comment on "center", i checked where i was -have one of those cheap "v notch" center finder with a level built in- i was high with my cutting tool!
Exact same set up from last nite, piece was still in the machine. Slowed my machine down to 72 rpms and centered my tool and i was freeking shocked! i've had my "china cheepie" for almost 2 years now and have never been able to part anything.

I got nice 6 to 10 inch long nice curls -no chatter!!!!!!!!!!!! I could not believe it, perfect cut! I have tried at least 20 times in the last year or so to part something and never worked, always chips and chatter! I honestly was ready to chunk my parting tools!~ Then brainstorm last nite was to ask you guys, just never thought to ask before!!

Everything i have learned about a lathe has been right here. I really appreciate the help!!! I'm typing this and still amazed what a dumb *** i am, lol. I'm happy happy happy- thanks guys!! joe
 
When parting or turning the OD you can't be high. When turning the ID you can't be low.

You need to really think about this and know in your mind what is happening at the cut if you are high. This will help you have a deeper understanding of machining.
 
J,

I use parting tools everyday as I manufacture alot of vintage H/D, Indian, Merkel, and JAP motorcycle parts. The "secret" is ditch the blade and (cry once) and get an inserted tool.

That statement is almost certain to ruffle feathers on this board. It isn't meant in a disrespectful tone or to suggest that insert tooling is the only way to make good parts. What it will do though is launch you into the 20th century so that your time is spent making the parts you need instead of having to learn a craft that isn't (as you've discovered) as simple as it would initially seem. Grinding tooling from HSS stock isn't difficult once you know how. The learning curve can be a real biche though.

I'm saying this not to insult anyone's intelligence, ability, experience, or anything else. I'm saying it because the manufacturing community has discovered that its a cost savings to use an inserted tool made from carbide that costs around $20.00 and produces hundreds/thousands of parts vs paying someone a healthy wage for thier experience to precisely grind a tool from steel that might make it for 50-100 parts before needing to be reconditioned.

A typical holder runs about 100-150 dollars. A pack of ten inserts will set you back around 200 bucks. If a guy stalks ebay he can save a few bucks on the total. A pack of ten inserts should last a hobbiest at home around 10 years. (seriously) unless he's making gun parts from inconnel or 6AL 4V.

If you elect to go this route, it then becomes a function of RPM and feedrate. If the tool chatters (assuming your tool post is solid, the cross slide of the machine is in good shape, and the spindle runs tight) you either increase the feed or slow the RPM. (sometimes both) Use an aluminum cutting fluid to avoid chip weld and go for broke. In a pinch kerosene works pretty dern good for a cutting fluid on AL. Just be careful with the fire hazard potential. NEVER use it on titanium. When it work hardens it tends to produce sparks and they turn a shop into a 4th of July experience you'll never forget.

Good luck on your project and again, hope this didn't offend anyone.

C
 
Chad thanks for your suggestion. I read all your post and they a very neat to say the least!! I enjoy seeing what you do!!
You have forgotten what it is like to be a novice. Your at +10 and i'm only at .5, lol. Before i got my -well it ain't even a lathe to you (harbor freight) i was using a file and a side grinder for my machine work!!

To me, "I got 'er going on" now that i can use my parting tool, heck i was using my porta-band before!! thanks for the advise though and thanks to everyone else... i can't wait to tell my buddies I'm a machinist now, lol!! joe
 
If you use a cutoff wheel or a dremel to grind a groove in the top surface of the parting blade, parallel to the blade, it will cause the chip to roll inward like an insert. Check a picture of an insert to get an idea of the groove.
 
I used to have trouble with parting but I kept at it and have it pretty well figured out now. Lots of little things can add up to make it easier and better.

More tips, some already given and some different:

Use a parting blade that is tapered - slightly wider at the top - so there is enough clearance on the rest of the tool. You can grind clearance but its better to buy the blade with the clearance built in. You only have one grind to worry about then.

Buy a good quality parting blade. Harder tougher material only costs a few dollars more.

Extend only enough tool to make the part - no more overhang than you need.

Make sure the blade is perfectly perpendicular to the work and parallel to the cross feed axis.

Lock everything down tight. You are locking the carriage bolt - right??

Aloris style tool holders can be more rigid than a rocker, especially for parting and you don't have to re-set to center every time you use it.

Grind and stone the cutting edge as perfectly as you can.

Use plenty of oil -- continously.

Use a center in the tailstock to support the work even when you think the part is plenty rigid. Back it well off before the part is cut fully.

Don't be chicken - feed it in smooooth and keep the speed up.

When everything is right it'll cut fast, making chips and not a big curling ribbon.

I'd really like to have an inserted parting tool but that will come when there's spare money. I am sure Chad and Jackie are right but its pretty expensive compared to a $30 parting blade.
 
I realize that you might have a hard time beliveing this, but......
When you are geting chatter in a parting operation, feed it faster.
If possible, have a bottle of cool tool in one hand and drip it right in to the parting cut.
Slow rpms, fast feed, it works.
Try a few practice cuts and you will see
 
my best Parting tool is an insert tool by Iscar I can have moderate rpms, but I have found my best parting cuts come from a slower powered feed, slow but steady, I also use a little wd-40 as needed. The powered feed is when my parting got better.

Paul
 
I do quite a bit of parting each day and rigidity and tool height are the most important things to pay attention too.
My parting cuts aren't deep, up to approx 4.5mm, but the diameter is from 220 mm to 330mm OD, I use a carbide insert tool and run at 210 RPM, when I teach other people to do the parting cuts most feed the tool in too slow. I always used to have trouble parting 100mm OD stainless shafts, clearing the chip was the problem so power feed didn't work too well..............Ian
 
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