Parting tool chatter

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OrangeAlpine

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What causes it? I've made a very rigid parting tool holder that mounts directly on the compound and makes a very rigid setup. Usually works like a dream, but sometimes get chatter. It really seems to be a random event as it comes and goes with the same setup. Sometimes touching up the tool helps, but not always. The tool is spang on center and flat on top. I've tried varying the grind angle, sometimes it helps, usually does not. When it does smooth the cut, the next cut may chatter. Using a .090" wide blade. Chatter starts the moment the tool touches the part.

Using a WWII era HSS blade.

Any suggestions?

Bill
 

stevehuckss396

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I usually reduce the speed of the spindle. Sometimes getting below 100rpm on some metal and well above 500rpm on others. If I get chatter my go to solution is less rpm
 

WOB

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A rigid toolholder is not a cure for a flexible compound/cross slide arrangement. The best you can do is make sure the tool holder is centered on the compound to cross slide pivot axis, minimize tool overhang, sharp tool, and tighten the compound gibs. Try setting the tool a little above center so that when it flexes down in the cut it approaches center. Starting on center allows the tool to flex down and away from the cut, reducing engagement setting up a chatter situation. Always use power cross feed when parting to maintain constant pressure on the tool.

WOB
 

fabricator

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It's all about the rigidity of the entire saddle assembly. The machine size and mass has a lot to do with it also as does the material being parted.
 

SmithDoor

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There one other trick is put around 7° on the front of cutter .
This will give a cleaner cut off. If everything is right there will tip and end of the cut.
I have trick in download section under cutters

Dave
 

goldstar31

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I'm using a rear mounted parting tool blade, projecting an 1" to part off round mild steel bar 2" in diameter but am using it as a lathe tool proper as my front tool is set to cut a chamfer in a bit of 3/4" round bar- down to 1/2" round at one end and the rear tool to reduce the stock to 0.3125". Both ends are going to be tapped. The thin end- with a female 2BA thread and the thicker end M6 female .

It's for the forerunner to the Worden grinder- called the Kennet. Lubrication? Good old lard lard oil.
Ironically, both tools were by the same guy as wrote and designed the GHT Rear parting tool.

Basically, i'm merely following 'the book'

Norman
 

SmithDoor

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I use very thin blades
It gives better cut and less chatter The down side is the blade may brake if move the carriage

Dave

I'm using a rear mounted parting tool blade, projecting an 1" to part off round mild steel bar 2" in diameter but am using it as a lathe tool proper as my front tool is set to cut a chamfer in a bit of 3/4" round bar- down to 1/2" round at one end and the rear tool to reduce the stock to 0.3125". Both ends are going to be tapped. The thin end- with a female 2BA thread and the thicker end M6 female .

It's for the forerunner to the Worden grinder- called the Kennet. Lubrication? Good old lard lard oil.
Ironically, both tools were by the same guy as wrote and designed the GHT Rear parting tool.

Basically, i'm merely following 'the book'

Norman
 

Fred Madsen

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First, I am using a mini lathe and have experienced all of the above problems. My "solution " was to turn the tool upside down and run the lathe lathe in reverse. Remember that the cutting edge of the tool is now just slightly above the C/L. Try this and experiment with the height adjustment.
Please let me know if this has helped you?
P.S. My speed depends on the material and what I am prepared to suffer in breakages, (remember I am using a mini lathe).
 

goldstar31

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I have two 'mini lathes. a Myford Super 7 with a gear box and power crossfeed- which will swing ( just) 7 inches across the shears and a SiegC4 with no gear box but will swing 8 inches- and no gap like the ML7

I have only broken one thin blade and that was on a then clapped out other ML7B- now reconditioned and sold for the newer machine.

Years ago, I made a GHT Thomas rear parting tool and it is on the new-er Myford. Again, it will go on the Sieg( as will almost ALL my Myford bits from years back- and now.

The TWO most obvious answers are the probability of a worn or or badly adjusted lathe.
The other is parting off from the front.

For the umpteenth time, a front mounted parting tool will 'go into cut' whereas a rear mounted and inverted and the lathe running normally will lift "out of cut' and avoids breakage etc.

Actually, the much vaunted and coveted Myford Super7's saddle is weaker than the Sieg C4.
As has been explained times without number, once one has bought a Myford which is not cheap, buying the appropriate books by expert owners is relatively inexpensive.

Instead of rushing off to seek a an internet course - from whoever fancies themselves as an expert, it is better to read, learn and inwardly digest.

Something to think about- and try?

Norman
 

Steamchick

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Wierd.. reversing the lathe and using the tool upside-down! The saddle is designed to be "more rigid" in normal mode... In reverse the gib-strip and taper slide loading is reversed.... but maybe this induces more friction with the changed leading and thus damps-out the chatter?
Not something I will try, as after setting the saddle and cross slides correctly my chatter dissapeared. I do not have a power feed (luxury) but 2-handed feed is good (55 years practice?). Don't wind with the handle, work the circular disc of the feed handle hand-over-hand to keep the feed constant and slow, and you should learn to feel good cutting. And slow the speed of the work. While I may be machining at hundreds of rpm, I probably part at 1/2 to 1/3 speed. The material being removed instead of being say 10 this wide is 100 thou wide when parting, slow as the cross sectional area of the cut is related to the work you can do, the feed-rate must be 1/10th of your normal facing speed. Also, the cutting speed reduces as the diameter of cut reduces, so you must slow down the feed, or speed up the rotation as the diameter of cut reduces. SHARP TOOLS are a must, with text book relief. Chatter suggests the tool is too flexible when everything else is good. Shorten the overhang to minimum required.
Enjoy!
 

Steamchick

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I agree other comments - and I am one of those authors of "Internet advice" but not an expert machinist. Just an engineer with a bit of machining experience. Please teach me anything where my advice is off-line.
Ta!
 

Fred Madsen

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Wierd.. reversing the lathe and using the tool upside-down! The saddle is designed to be "more rigid" in normal mode... In reverse the gib-strip and taper slide loading is reversed.... but maybe this induces more friction with the changed leading and thus damps-out the chatter?
Not something I will try, as after setting the saddle and cross slides correctly my chatter dissapeared. I do not have a power feed (luxury) but 2-handed feed is good (55 years practice?). Don't wind with the handle, work the circular disc of the feed handle hand-over-hand to keep the feed constant and slow, and you should learn to feel good cutting. And slow the speed of the work. While I may be machining at hundreds of rpm, I probably part at 1/2 to 1/3 speed. The material being removed instead of being say 10 this wide is 100 thou wide when parting, slow as the cross sectional area of the cut is related to the work you can do, the feed-rate must be 1/10th of your normal facing speed. Also, the cutting speed reduces as the diameter of cut reduces, so you must slow down the feed, or speed up the rotation as the diameter of cut reduces. SHARP TOOLS are a must, with text book relief. Chatter suggests the tool is too flexible when everything else is good. Shorten the overhang to minimum required.
Enjoy!
 

Peter Twissell

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As stated several times above, rigidity of the whole setup is key. This is not just the toolholder, cross slide and saddle, but also the whole machine, spindle bearings, chuck and the workpiece itself.
Sometimes it is possible to reduce or eliminate chatter just by changing speed. Everything has a natural frequency and if the frequency of your setup is close to the spindle speed, chatter is more likely.
Beware of suggestions to run in reverse - if you have a screw-on chuck, it is a disaster waiting to happen.
 

tornitore45

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Slow the RPM/Feet-per-Minute considerably below the regular turning and
(I know this is controversial) keep the tool an hair lower.
 

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