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chatter with form tool at low speed

You're learning by trying, form tools are generally a prick to get dialed in. Most just rough close and finish with a file and emery, there's a big load going on and sometimes the machine just doesn't cope well.
 
@??? It's a Meuser M00L similar to what's shown here:


What model lathe do you have that will take this cut without chattering?


@sfriedberg Yes I have tried putting a land on the edge with a diamond hone. Made no difference. Also chatters the same on 1045 steel. Do you have a lathe that will cut an R.25 without chatter?
 
Just cut one for you.

Lathe Victor 400x750, probably around 1400 kg and super beefy.
Tool old radius end mill, hence the drag lines. No rake, plenty of back clearance.
Not set up at absolutely correct height.
Speed 375 rpm
Brass
Chatter zero
IMG_20240425_111056_MP.jpg
 
Thanks @??? I really appreciate it!

Left work for the day, but will try a setup more like yours tomorrow.
 
I honed the edge with a diamond rat tail until it wouldn't shave my fingernail anymore. No difference.

Can your lathe take this cut without chattering?
Yes. In brass. Hope you can figure it out.
 
I already feel pretty silly about how small the part is for the size of lathe.
Can your lathe take this cut without chattering at a reasonable spindle speed?

Ha. Maybe the lathes.uk site has some old manuals and brochures ? Form tools used to be really common. Look at Sundstrand or Gisholt or maybe Seneca Falls production lathes. For a little 6" chuck machine they are heavier than a Monarch 61. The tool holders are blocks like 4" x 6", the ways are 6" x 3", the feeds are hydraulic, the things are almost solid cast iron, and the tools are sharpened not the same way as normal tools (usually no top rake, not extremely sharp), everything is as short and tight as possible, even a sixteenth of an inch overextended is frowned upon, and they went to great lengths to get free-machining materials. Ledloy.

Up to a point you can use form tools in a regular lathe but all the machining basics count double, and even then you'll need some experimentation to get it working. Don't feel bad, there's no magic button and at some size, you just won't be able to. A normal lathe isn't built for this.
 
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Do you have a lathe that will cut an R.25 without chatter?
I have two, but they both require some dialing in and attention to the cutters to get a clean cut. I don't think of R0.25" as especially challenging. R1" would be another matter. On one of my machines, I'd be strongly inclined to use a skive tool which works tangentially rather than radially.
 
I think check your spindle's radial play, incredible that a machine with pedigree would behave like that. After reading down to post # 23 (???) I went out to the shop & offhand ground a tool bit to 0.25 R, put it on the .......MYFORD ..chucked a bit of 3/4" dia steel (not Ledloy, won't have leaded in the place) & proceeded to turn the form at 400 rpm, hand feeding .. without chatter. Upped the speed to 600 & it 'wanted' to chatter but unintuitively, easing up on feed to 'shaving' rate, averted chatter. Oh, I got about the same finish as ??? because I'd roughed out the radius on the tool quickly with the coarse wheel, 6* clearance, 0* top rake, no subsequent honing or refinement. Possibly the rough grind promoted chip breaking & contributed to no chatter. Have to admit I'd normally drop speed to half 'correct' speed when using a form tool, think I was taught that. Must try it on the Chipmaster but I don't like the chuck overhang on the D1 spindle nose. Once took a handful of 304 swarf, the same Myford had produced off a job at home, into work to show-off to the leading hand. He promptly stuck an inserted tip tool on the Colchester Bantam, set it up for the same DOC & had at a bit of steel .. I'd TOLD him I'd used a knife tool .. I swear the chuck deflected 3/16" before he hit OFF! Biggest fright I've had in my life. The lathe showed no after-effects, but then it was the lowest order machine in the shop of DS&G, Schaublins, Weilers & a Lang. The demo was cancelled.
 
You migh give your tool holder and cross slide a tapping with a 20 oz brass hammer in the direction of cutting forces to see if everything feels solid like a rock, and see that your chuck is marking properly.
If your in feed is with the cross feed you might put a C clamp on your compound.
 
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Exactly. If a Myford can do it there's something drastically wrong with either the OP's technique or his machine, that's the point. Oh, I did try it on the Chipmaster, same tool same metal, superior finish to Myford's at 400rpm, 600, & finally 1000. No chatter at all. Seems D1 is OK. Tried taking a pic, 1st try too small, 2nd try ..'replace battery' . Spare battery .. likewise. I should use that camera more often. Looking forward to posting a first pic.
 
Just cut one for you.

Lathe Victor 400x750, probably around 1400 kg and super beefy.

On 1/2" diameter stock I'm also able to get a good finish as long as I don't dwell:
0.5 diam R.25 RAD.jpg

But, if I go up to 1" stock it chatters no matter what at 320 rpm, and at 2" diameter stock the chatter is kind of scary.

Maybe the lathes.uk site has some old manuals and brochures ?

Brochures for what? Gisholt etc. turret lathes? I have toyed with the idea of getting an old turret lathe. In many ways it would be a good fit for the work I do which is all short chucking stuff. But, all the production oriented features are no good for me. At most I make a few dozen parts in a batch. Usually onesy twosy.

On one of my machines, I'd be strongly inclined to use a skive tool which works tangentially rather than radially.
A skive tool seems like a real hassle for the prototyping. Am I wrong?

I think check your spindle's radial play

Thanks for taking some test cuts. Looking forward to photos.

I pried radially with a 3' bar:
radial_play.jpg
I don't see any play, but I do see elastic deflection. 0.003” displacement with highest comfortable pressure on bar. 0.006” if I put most of my weight on bar.

Prying with the same bar axially between headstock and D1 flange I again see no play, but some elastic deflection. 0.0005-0.0010 with comfortable pull on bar. 0.0015-0.0020 if I put my back into it.

You migh give your tool holder and cross slide a tapping with a 20 oz brass hammer in the direction of cutting forces to see if everything feels solid like a rock, and see that your chuck is marking properly.
If your in feed is with the cross feed you might put a C clamp on your compound.

Feels solid in all directions when struck with a deadblow. Compound is locked with gib.

Invert the tool and feed from behind, as per a rear toolpost.

Is that a technique that actually makes a big difference for you? Having the cutting forces pulling the carriage up off the ways goes against everything I've been told.


I feel like I'm getting mixed messages from this crowd. @EmGo is telling me to use a machine built like a brick outhouse. @swarfless is saying this cut is easy on a light bench lathe. Several others are using phrases like "it needs to be dialed in".

So, is the overall message that form tool chatter is just plain unpredictable?
 
On 1/2" diameter stock I'm also able to get a good finish as long as I don't dwell:
0.5 diam R.25 RAD.jpg

But, if I go up to 1" stock it chatters no matter what at 320 rpm, and at 2" diameter stock the chatter is kind of scary.
The moment is much larger at 2" therefore more force acting on the tool and its assembly
 
Inverting the tool is not a good idea if you are looking to reduce movement, lathes are designed so force is directed down onto the ways. There is always some clearance between the retaining plates on the underside of the carriage and the bottom of the way. Parting off on the back of the job will often show this when you hear the carriage jump and drop onto the way.
 
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Brochures for what? Gisholt etc. turret lathes? I have toyed with the idea of getting an old turret lathe. In many ways it would be a good fit for the work I do which is all short chucking stuff. But, all the production oriented features are no good for me. At most I make a few dozen parts in a batch. Usually onesy twosy.

No, up until the seventies there were things called "production lathes". They aren't turret lathes. They were built for doing mass production, it was all auto cycles but any contours or shapes had to be done with form tools, as they could do L cycles and sometimes threading and some bore stuff that went in, away, out and back - that kind of thing. Form tools were common on those, so the manuals were quite educational on the subject. Not too useful on other things these days but if you're going to use form tools, the same rules still apply.

@EmGo is telling me to use a machine built like a brick outhouse. @swarfless is saying this cut is easy on a light bench lathe.

I'm thinking anyone who says form tools are easy and simple on a light bench lathe has never tried it. Or they think a little 1/16" radius is a "form tool". Whenever you get a large cutting area in contact on any machine, it's not a picnic.

So, is the overall message that form tool chatter is just plain unpredictable?

I think it's pretty predictable - if you get a large area of the tool in the cut, it's going to want to chatter :) true on mills, true on lathes, true on grinders ... what works to stop it, that's always a puzzle. Basic machining practices are important but sometimes it's a challenge no matter what you do.
 
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Thanks @EmGo for the spiritual guidance. I'll try and scare up some manuals for production lathes to get a better feel for how they handled form tools.
 
My turret lathes do handle form tools very well, but then my American Pacemakers do too. Collet and three jaw chucks on the turret lathes both have proven reliable for box turners, collapsing taps, geometric dies etc. that's what they're built for, incredibly large cutter engagement, all at once. So radius form tools are rather trivial..... Usually.

I've also run 1-1/2" cutting tool engagement length with form tools in 1018 steel, flood oil coolant on the Pacemaker. No chatter noticed.
 
On 1/2" diameter stock I'm also able to get a good finish as long as I don't dwell:
View attachment 437408

But, if I go up to 1" stock it chatters no matter what at 320 rpm, and at 2" diameter stock the chatter is kind of scary.
Chatter goes up with diameter? What kind of relief is on the edge of this tool? The fact that 1/2" is ok and 2" chatters like crazy - methinks there might not be enough relief
 








 
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