How to Prevent Chatter.

[jtice]

One of the problems I have when useing my lathe is chatter.
Especially when "Parting" a piece.

The last 2 times I have had to part a 1" dia. piece, I broke my parting tool. /ubbthreads/images/graemlins/frown.gif
I think its due to the tool not cutting properly. And kinda bounces as its trying to cut. Which I guess thats what chatter is.

I had just alittle chatter the other day while boring with a boring bar, but it wasnt too bad.

How do I reduce chatter?
Slower speeds, cut less at a time, more at a time?

Thanks alot for the info.

John

 

[Rothrandir]

reduce vibration, use lube, make sure everything is at the right height, make sure all the angles are correct...

when parting, you need to make sure that the sides don't rub!

set your lathe to the lower gears so you get more torque, and you probably need to plunge faster than you're doing now...

what i do is start out with a parting tool, then pull out the hacksaw and while the lathe is running, i hack away furiously. that goes without saying, be careful.

or you could get a metalcutting bandsaw /ubbthreads/images/graemlins/wink.gif

 

[jtice]

Roth,

I have used lube both times.
The parting bit was shapped properly, with sides not touching.

Lat time I used the lower gears, and I did notice, that when I got brave, and starting plunging alittle more than I ussually do, it would quiet down alittle. BUT... thats when it ends up braking my bit. It will all of a sudden catch, and BAMM!

I hate to admit this, but I have also done the hacksaw trick.
Cuts really fast, and surprisingly, makes a fairly smooth cut.
But, that tends to bounce around alot, and shakes the lathe, and entire workbench.
That cant bee good for the lathes bearings, so I think I am not going to do that anymore.

 

[tvodrd]

Jtice,

How wide a parting tool are you using, and what sort of diameter are you trying to part? When you say "catch, and BAMM!"- been there/done that once and snapped 2 1/4-28's on the holder. You need fairly continuous coolent application. Try a plastic squeeze bottle with a one hole rubber stopper and one of those "acid brushes" through the stopper. It conserves coolant by allowing you to apply it as needed. Hold the brush in the cut while squeezing gently. As to chatter, rigidity is all important. Always part as close to the chuck as practical and with the minimum amount of blade sticking out from the holder. You can also "wiggle" the tool by moving the carriage back and forth to widen the cut slightly and reduce the chance for siezeing.

Parting is such sweet sorrow! /ubbthreads/images/graemlins/icon15.gif

Larry

 

[Chief_Wiggum]

[ QUOTE ]
Parting is such sweet sorrow!

[/ QUOTE ]

ROTFL!

 

[jtice]

Larry,

The parting tool was about 0.055" thick.
First one was thicker.

I was parting about 1" OD bod.

I try to spray it often with lube, but thats not really all that constant.
I will try it with the bottle idea, to try to keep a better continuos flow.

 

[unnerv]

It could also be that your tool is not dead center, possibly a little too low. Also you may need to sharpen the tool, and slow the lathe down. I got a lot of chatter when I 1st started, and it turned out to be a combo of all of the above. I sharpened the tool, then I got a wiggler to find the exact center of the spindle and set all my tools to that hight. I also have a guage made to the exact hight of center so if I put it on the bed rails I can set the tool to that hight and be within a couple thousands from center. Cutting at a lower speed seemed to help to. I do most of my cut off at around 100rpm.

 

[tvodrd]

That sounds good! (Shoulda reread for the 1" dia part.) Your chips should be in little rolled-up curls. Cutter geometry is critical- parting tools are usually zero top rake with some side rake/clearance, and you set it for centerline of the stock. Do you have a link to the blade you are using?

Larry

 

[jtice]

Larry,

Blade is home made, from a tool blank. About 0.055" wide.
I will have to double check to see if the sides are hitting at all, but I dont think they are.

I think the constant lube, and slower speed will help alot.

I also need to check for center.

unnerv,

What is a wiggler?

 

[unnerv]

Here is a link to a wiggler, so you can see what it is and various uses. What I did was mount it in the chuck and spin it. I borrowed a precision block from my father (who is a machinist) that has two triangular blocks that slide against each other (sorry don't know the technical name for it.) The top and bottom of the two peices are exactly parallel. I placed this on the bed under the wiggler and slid the two blocks together until the wiggler stoped wiggling in the chuck. Then I measured the the hight of the block and added 1/2 the size of the wiggler tip. I then had a piece of 1" stainless cut to exactly that height, so I can quickly set my tool hight. I don't have the blocks any longer, but if you wanna see the pic of my guage I can take one tonight.

 

[MoonRise]

Speed, feed rate, lube, rigidity, cutter geometry and set-up. /ubbthreads/images/graemlins/smile.gif

Yeah, chatter is when the tool bounces or chatters as you are machining something. Chatter is usually not good. /ubbthreads/images/graemlins/frown.gif

Speed. Find the right speed for the operation. Sometimes faster helps, sometimes slower is better. And it will vary depending on the material, tooling, and machine used.

Feed, or feed rate. Feed fast enough to have the tool take off a consistent cut. If your set-up allows it, getting a constant and consistent ribbon of material streaming off of the tool tip as you make the parting cut is neat. As long as this big wad of sharp swarf doesn't wrap itself around something and catch, scratch the workpiece, or cut your hands. /ubbthreads/images/graemlins/icon8.gif

Lube is important. Keep a constant flow going so that the tool tip is never cutting dry. The tip about the brush on the squeeze bottle is a good one.

Rigidity in the setup is important. The tool, tool holder, workpiece, and machine should be stiff enough so that they aren't flexing or vibrating during machining operations. Flexing or vibrating could be causing the chatter. Remember to have the least tool overhang out of the tool holder as possible during the machining operation so that you don't have a long lever spring flexing and bouncing in the tool holder. /ubbthreads/images/graemlins/smile.gif

Cutter geometry and set-up are important too. Maybe you didn't grind a chip relief or chip breaker into your tool? Or you don't quite have the cutter set-up so that the cutter TIP is correctly positioned with respect to the stock so that the tip is cutting nicely and the chips can get out of the way?

One inch diameter aluminum -shouldn't- be too bad to part off. Stainless steel is a *****, get the feed/cut rate wrong and you gall or work harden the stock. /ubbthreads/images/graemlins/ohgeez.gif

 

[jtice]

unnerv,

I see what you mean now.
I thought of another way to do this.

Get a piece of AL stock, chuck it, and face it.
When facing, I wont put my little "half assed" shims under my tool bit.
This will leave alittle "tit" on the face, in the center, where the toll isnt touching.
I will then measure to the exact center of that "tit" and make the apropreate thichness shim to get to that level.

I had to shim mine, in order to face properly without leaving that "tit".
This is the same shim I use for parting. But I am thinking now, that maybe its just slightyl too high. /ubbthreads/images/graemlins/icon3.gif

Thanks for all the great tips guys. /ubbthreads/images/graemlins/bowdown.gif

 

[unnerv]

Yeah, that should work. If you have calipers, you can measure the OD of the the "tit" and then halve that. That should give you the amount that you need to raise the tool. I have a QC toolpost , so I can just dial in the hight without shimming. That makes getting the right hight much easier as well as only taking a few seconds to change tools without haveing to worry about correct hight. Also, if you have to be a few thousands high or a few low, for the the cuttoff, a few high would probably be better since when you are low it tends to grab more and you have a better chance of stalling, or breaking the tool. Once you have the correct hight for one tool, use that tool to face off a peice of stock so you have a flat end, then place it one the bed faced side down and scribe a mark on it at the proper tool height. Re chuck, cut off at your mark and reface. This should get you a gauge that is pretty close. You can keep refacing until you have the exact hight you need.

Good luck.

 

[jtice]

unnerv

Wow, I didnt know that QC tool holder would let you change your hieght like that.

I have been meaning to get one.
But I heard that the other one that they have, is better than that one.

What do you think of yours?
What is the sturdyness like, compared to the stock holder?

BTW, what lathe do you have?

 

[unnerv]

I only used the stock holder for a day or two on my Homier 7x12, so I can't really compare, but I have not had any problems with mine at all. Once the cam engages, the dovetails between the two pieces lock up pretty secure. I have taken .060" off the diameter in a single cut (although the finish isn't too pretty) on aluminum without any problems. It seems to be holding up well. It was the best $100 I have spent on accessories. Once you get a QC post, you will never go back. My father has a full sized lathe at his house with a standard tool post, and it kills me to have to center up and shim everything everytime I change the tooling even with his center gauge. The QC post changing a 1 or 2 minute change to a 5 to 10 second change.

 

[unnerv]

Here is a pic of my toolpost and the gauge.

 

[Dan C]

unnerv, your lathe is *entirely* too clean! /ubbthreads/images/graemlins/drool.gif

Dan C

 

[Chief_Wiggum]

Very slick height checker. I got to get around to making one of those.

 

[Rothrandir]

what dan said!

i'm not even going to take a picture of my work area! /ubbthreads/images/graemlins/eek.gif

 

[unnerv]

I clean it every time after I finish using it. It builds up swarf so fast, sometimes I have to clean it a couple of times while using just so there isn't crap all over it geting caught on the parts /ubbthreads/images/graemlins/smile.gif Next time I'll take the pic half way thru my job...

Here is the pic of the whole thing clean

Sorry to hijack the thread. Hope some of this helps with the chatter problems. Keep us updated.