Parting off

Ed Hoc

Ed Hoc

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Hi Guys. Parting seems to give some people a lot of trouble. Yes it's tricky and takes some practice but here's how I do it. I have a HF 9X20 lathe, Phase 2 QCTP hobby size (I took it off my 7X12 lathe).
Photo 1: The blade I use is from Travers Tool. "P"Type High Speed Steel Cut-Off Blade
Dimensions 1/16"; x 1/2"; x 4-1/2" Item # 55-202-510. Wider tools will chatter more. I believe the key is that the top is hollow ground. That is to say the top of the blade has a concave shape that curves the chip narrower and it flows out of the slot easily. The T Shape has lots of clearance on the sides. I've tried a couple other brands but this one works well on my 9X20 and my 7X12. I had to modify my holder to fit the T shape of the tool.
Photo 2: Make sure the tool is parallel with the face of the part. Very important. The part is turned 2.0"; OD and bored 1.0" ID. Low carbon HR steel. The bore running true make things easier when you break thru. Tool only long as necessary out of the holder.
Photo 3: On my 9X20 lathe. 120 RPM . I used a center with a washer to give support to the part, I'm not holding by alot and I'm cutting pretty far from the chuck. Ideally I would be less than 1/8" from chuck even if it means turning the part around. Not possible with this piece, and a small chuck. Sometimes I use a center even if close to chuck or with a larger part as needed. Your setup needs to be rigid.
Started grooving. I use water soluble coolant applied with acid brush.
If I get chatter then : Feed a little harder, but don't go crazy. I know it's hard but proper chip load is important. Check center make sure it's tight. Check speed (slower or faster there's a "sweet spot" RPM). The chips come out like clock springs when you get a little deeper. Keep that coolant coming. Flood would be great but I'm not set up for that.
Photo 4: The finished cut, I kept the center tight all the way thru. Having the bore run true is good, then the cut-off part just stops turning, I try to switch off the spindle quickly but don't panic. With a little practice you can feel the tool pressure go soft you know it's about to break thru, you can back off the center then if you like.
Keys to remember: close to chuck; rigid setup; narrow tool; short tool length; good grip in chuck; coolant or other cutting oil; proper RPM; proper chip load.
Yes it can be done, a little practice and you'll have it. Sorry guys I don't do video I'm on dial-up.
Good Luck.

Ed Hoc



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I think the main fear of parting comes from the minilathes. Or, more properly, the improper setup of those lathes. If they aren't adjusted correctly (and most from the factory are not, in my experience) than they are far too loose. Looseness equals chatter, digging in and broken things. Just one snapped off parting blade is enough to scare off a newbie. I know it nearly was for me.

I readjusted the saddle on my minilathe a short while ago, and using my experience gained in the past couple of years was able to get it tuned up the way it should have been. Parted off a piece of 2.0 diameter CRS with absolutely no fuss and no problems this weekend. Just a year ago I would have been using a hacksaw because parting was so scary, even on aluminum.

I encourage the use of a carriage lock, and tightening up the carriage gibs. Huge difference.
 
And, if your carriage is total toast, try parting off upside down with the machine in reverse.
 
Ed,
I really did appreciate that post. I'm very new at this lathe thang, :) and parting is one of the operations that is giving me a little trouble. I've viewed a few videos and read all I could find on parting. In doing so, I've come up with a couple of questions. Tubalcaine, in the mrpete videos warns against trying to part hot rolled steel as being to difficult to do well. He also says that you shouldn't use a center, just to let the parted off piece fall loose. Are these just differences of opinion, or am I missing something here?
After your comments on the parting tool holder, I understand why my AXA type tool holder doesn't hold the parting tool as it should. Maybe a little modification would be in order, huh?
Tim,,,
 
Use of a center depends on the diameter of the part. If, when parting, the part is going to bend away and flop around, use a center with light pressure. A larger part like Ed shows shouldn't need a center unless it is sticking out quite a ways. In his case, I might use a center just because it is sticking out so far.

Some people use a pin stuck into a small part when making washers and such to catch the part before it drops into the swarf.
 
Incidently, LMS has parting blades on sale this week for 5 bucks. Sale ends Tuesday night, so get one if you need it.

I have always been of the mindset that it's better to grind my own tools. The resoning is, so that I learn what works and what doesn't. But, since I switched to the QCTP and a purchased parting blade, I have had much more success in parting off than before. I save the hand ground tools for grooving.
 
I figured some of you old hands would help out with some more tips. It helps to get everything working for you not against you. Each machine is different and each machinist will have his own twist on parting off. Just have to sort it out on your own machine, depending on circumstance. Main thing is a RIGID setup. How many of you can cut 1/8" per side on a turn or face with a mini lathe? Even 1/16" per side? Not me! Now plunge a 1/8" wide groove. ya right

Paddy, & nctox, my toolpost is sized for the 7X12 lathe 'hobby size'. It's a bit smaller than AXA. The parting blade holder is modified for the T shaped blade. I miilled clearance for the wider top and 'Trued Up' the clamping areas. Blade 1/16" X 1/2" X 4-1/2". Part number listed in original post. Yes I tried the tapered and straight side blades, they gave me fits! This one works great for me.

rleete, nctox, mayhem, Sometimes I use a center, Sometimes not, Sometimes I've used the rod in the tail drill chuck to catch the washers as they fall. It all depends...

Keep trying fellas. it can be done . good luck and fel free to ask more qustions as they arise.

Ed
 
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Placed my first order from LMS when I saw these blades on sale and I gotta say I'm thrilled with the service! Ordered 2 blades on Thursday, had it shipped first class mail, paid $2.75 (actual shipping cost) and had them placed in my grubby hands in Minnesota about 11AM Monday!! ::thumbzup:: Me and the friendly postman even chatted about what great service that was!! Modified my AXA holder tonight and can't wait to lop some slices off tomorrow! Todd
 
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