Broke a parting tool

I made a tool holder just for parting. I followed a video from Winky's Workshop adapted for my Norman style QCTP. The tool holder rests on the base. This is as solid as it can get it. Since making this I have not had any problems with parting. Parting has become just another task instead of a challenge.

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I have an Enco 12x36, 1000lb. Parting usually goes OK for me, but I am always adjusting to avoid chatter. Peak rigidity is key. Minimize chuck stickout, use a tailstock live center whenever possible, keep the tool short. Wide blades chatter more due to the higher cutting forces, but thin can snap if going too deep. Tool alignment is important too!

I've found lately that a medium speed, 300-600 rpm, and feeding the tool faster than you think gets the cut done with no chatter. Once chatter starts it is hard to stop since the tool rubs over the ridges from the previous pass and has vibrations induced. Again, a hefty enough feed can help. Also a heavy tapping oil is my go-to for parting.
 
Rigidity and alignment are key. Cut as close to the chuck as possible. Lock everything down except for the cross feed. Minimize stickout as much as possible. One trick is to make sure the blade is held properly. the blades can be T shaped or slanted. Put a shim on the lower side to get the blade held vertically in the holder. I cut on a slow speed but once you get it, feed agressively to get the chip going. I used to cut timid and slow and didn't produce a good chip. I have had several blades shatter. Parting is the one operation where I wear safety glasses and a face shield. you must have both! I also have a coolant feed on my lathe that I feed cutting fluid rather than coolant. That lubricant helps tremendously. If you get lazy and forget any one of these things that affect rigidity, the tool will bite you. (I am not a production shop so I don't need coolant. I only use the lube feed when I part. I used to dip a brush but for parting but I found that was best. I use the brush for normal turning etc...) Sharp tooling is essential. You must grind and hone in my opinion. Center height is critical although I cheat on the high side slightly at times. Low is no good. Hope that helps.
 
Rigidity is the key, swap the compound for a solid plinth, if you have one set up a dial indicator to the top of the parting blade and watch it deflect as you start cutting.
I also diamond hone my parting blades before every use.
 
The most important factor I've learned in parting is that the cutting edge must be sharp and everything should be nailed down as solidly as possible before aligning the cutting edge on the center line. I actually part with the blade perhaps .001 below the center line (it seems to work better. and make absolutely certain the parting tool is at a perfect right angle to the material I'm parting. Then, with everything solidly in place, my lubrication is continuous and my feed as constant and steady as possible. Any noise, I stop to identify the source. Cutting tool too long; cutting angle too steep or too shallow (bind on the long axis of the parting tool) speed too fast or too slow. I still break a tool once in a while. But it happens with less frequency that it did when I first attempted the task.
 
mickri said:
I made a tool holder just for parting. I followed a video from Winky's Workshop adapted for my Norman style QCTP. The tool holder rests on the base. This is as solid as it can get it. Since making this I have not had any problems with parting. Parting has become just another task instead of a challenge.

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Parting tools function better if they have back rake, your holder does not provide that.
 
If you do parting off, you will break blades, a fact of life in any machine shop, but it does get better with time and experience; being timid with speed and feed will cause more problems than the opposite approach.
 
While my holder doesn't provide for back rake there is about 3* of back rake ground on the blade. The blade came with the back rake ground on the blade. Might need more than than. Seems to work so far. Thanks for the suggestion.
 
I had plenty of problems parting on my old 10” Logan, and too often would finish the last part of the cut with a hacksaw.

Parting got a LOT easier with the 2500 pound Takisawa, and pretty much resolved when I was given an Aloris #71 blade, and
I made an adapter to mount it in a CXA holder. The blade is about 1.5” tall and uses GTN-3 inserts. Mikey gave me some tutorial support and now I can power feed through 2.5” steel rounds, pointing a koolmist mister at it and standing out of the way of the blue chips that come off. I align the blade with a dial indicator, a la Joe Pie. Occasionally an insert chips, so possibly buying the cheapest eBay stuff I can find is not a perfect strategy. But I have lots of them. :)
 
,I learned about parting watching automatic screw machines,
Rule 1. make a curling chip, not shavings
Rule 2. It's just metal and has no friends in the shop
Rule 3. lots and lots of cutting oil put on the tool tip
Rule 4. Push the tool in, no sissy crap, get the speed up
 
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