Tool chatter

[thezetecman]

I have a real problem with tool chatter when I use a flat or parting off shaped tool.
The tool tip is set to work centre height.
The tools chatter as soon as i start to cut at all speeds.

I have a new chuck with run out less than 0.03mm

i can not see any movement in the compound slide or the cross slide but there is quite a lot of backlash in the cross slide screw. Do you think this is the cause?

The head stock bearing sounds very smooth.

Other cuts tool shapes produce a very good finish similar to the finish I got on the new work lathe.

Thanks in advance for your help

 

[DickDastardly40]

I don't know if this will help with your problem but chatter IME is often caused by poor rigidity. I always part by hand rather than power feed and always use coolant to flush the chips

My tips for parting: (pardon pun)

Ensure the job is securely in the chuck, nipped up tight.
If the job allows support with a live centre in the tailstock.
Try to get your cross slide and compound gibs as snug as possible.
Have minimal overhang of the tool from the toolpost
Part as close to the chuck as possible.
Try to maintain light even pressure on the cut to prevent any backlash in the crossslide allowing the tool to move 'backwards'.

As ever I hope others chime in with stuff I've overlooked.

A rear toolpost with an upsidedown tool, if your lathe has provision, anecdotally is supposed to make parting easier. I believe it is because the chips fall away and the job cannot ride over the tool.

As ever hope this is of use.

Al

 

[SignalFailure]

If it's a HSS tool why not try relieving the end very slightly (in plan view) such that the cuting edge isn't quite parallel to the work? I've found that more rather than less speed works better (on my mini-lathe) whereas others say directly the opposite!

 

[Florian]

Have you got any photo of your tool? Maybe just with the job you are working at?
It can depend on different things:

1. material
2. quality of the parting tool (hss isn't just hss)
3. clearance angles, cutting angle
4. distance to the chuck
5. diameter of the workpiece

Maybe you can try to tighten the slide a little for parting off.

Florian

 

[Jadecy]

I've had this problem at different times on my 9x20 cutting fins in cast iron. Rigidity definitely plays a big role. If you have a small lathe you may want to enhance your cross feed mount to make it more rigid for this type of operation. Sometimes I have better results when the tool is just slightly below center. I always feed faster than I think I should to keep the tool cutting and not skimming the surface. I always use plenty of WD40 or some other light spray lubricant especially when parting aluminum.

 

[georgeseal]

Al,
A word of caution live center is alright for starting a cut but must never be used for the finish cut. It will bind and all sorts of things get broken. :'(

I used to have problems with cut off. The tool that came with my 12" X 36" lathe was a little more than 0.125 wide. :-\I have switched to a T type that is 0.040 wide and this has helped tremendously. ;D

 

[Metal Mickey]

I'm not sure I am on the right path with this chatter question, but if I have any chatter when turning I reduce the speed of the lathe until it stops (not the lathe!(I have a variable speed lathe)).

If its parting off then I always part off using a slow speed and I make more than one cut. For example I go in until it seems to be cutting less well, then I come out and make another cut along side it to the same depth, then going back to the original cut. This seems to stop the parting off tool from binding as it goes in.

Using this method I have parted off successfully some large diameter pieces. I do the same with both hard and soft metals.

I will be putting a parting off tool on the other side of the top slide and upside down to see how this works.

 

[rickharris]

I have to confess NOT to be a parting off expert - Indeed i seem to have had all the problems everyone else has in doing this effectively but a couple of observations:

When parting off the diameter of the work is getting smaller and smaller - quite dramatically - To maintain tan even surface speed the chuck speed should go up as you approach the centre.

Out CNC lathe parts off at a frighteningly, (to me) speed, but seems to handle it OK.

I often resort to a hacksaw - and then clean up the cut end - Maybe this is admitting defeat.

Our bigger and more rigid lathe at school parts off MUCH better than my mini lathe.

 

[DickDastardly40]

Al,
A word of caution live center is alright for starting a cut but must never be used for the finish cut. It will bind and all sorts of things get broken. :'(

I've never had a problem even parting large stuff (very large), however caution is everything and thanks for noting it. If the part is large I'd keep the centre in until the last possible moment.

 

[Bogstandard]

This has all been discussed on here before. But unfortunatley I can't find the link.

A little tip for those that have smaller machines, reduce the width of the tool to around 1/16" to 3/32" and set it a few thou high. By setting it slightly high, when it starts to cut and the tool and lathe are flexing, the tool will end up at the correct position and cut as it should. It is a matter of trial and error.
No matter what anyone says, the correct method has to be found for your specific machine to take into account the way it works.

Be ruthless, take no prisoners and go for it. If you break a tool, make another one and try again. Don't play about with it.

Once you get your feeds and speeds plus tool heights, all things will drop into place and you should have no further troubles.

On my old machine I could just put the tool in, wack a piece of material in the chuck and part it off under powered cross feed.

[ame]http://uk.youtube.com/watch?v=aS6Ct502S7g[/ame]

Once I have found the settings for my new machine, I can guarantee I will be able to do the same thing.

John

 

[rake60]

On my second attempt at Jan Ridder's flame licker I had a miserable time
cutting the grooves for the cooling fins.
For that project the material was cast iron, and the thin HSS parting tool
was just rattling the whole shop.
After trying everything that made sense, I went to the opposite extreme.
I increased the spindle speed to 600RPM and cranked it straight in to depth.
It cut great! I did burn up the tip of the tool up twice, and had to regrind it.
I had to expect that using HSS at those speeds on cast.

But it DID work well for me.

Rick

 

[dave e]

I might have missed it, but I don't think anyone has mentioned feed rate. When I started, I was making the mistake of feeding too slowly and chatter was miserable. Back when Bog orignally posted his video, it inspired me to try turning up the speed on the lathe and feeding the tool more agressively. On my lathe at least, that was the trick.

Dave

 

[rake60]

As rickharris already mentioned, watching a CNC machine part off a finished piece is
a little frightening, at least for the very first piece of the order.

The program tells the machine to run that parting tool at 220Sfm.
It goes to a final diameter of .150" At that diameter 220Sfm is 5600RPM
Now the speed is limited by whatever maximum you put into the program.
Parting off a 2" diameter piece I'd personally set that limit at 1200RPM.
Even at that speed, watching those numbers on the position screen flip by
faster and faster as the tool approaches that .150 diameter creates some
"pucker power"

The tool comes back up out of the cut, you open the machine up and
with one hand easily snap the finished part off the bar of stock.

EASY!
Still, sometimes I think I'm getting too OLD for that kind of excitement! :-\

Rick

 

[Powder keg]

In the shop I'm in, The biggest problem machinist's have is parting. (As far as running the machine) 95% of the time the speed and feed is way to slow. I'll show them how. and all will be good again. When I first started as a machinist, they didn't talk much about parting. I struggled a but to, for a few years. We hired a guy that was good at parting and I paid attention. I've seen him part 4" shaft under power with no trouble He told me the guy he learned it from did 6" shaft all the time.

You need to have your tool square to the lathe.

You need to have your lathe's gibs adjusted right. They can't be to loose.

You need to have your work supported with a live center if it's hanging out very far. I've done this for years and have never had a center in the end of my part cause any kind of trouble.

You need to have the speed and feed right. Figure out what your speed is supposed to be. It will probably be way faster than you think it's supposed to be.

Run coolant of some sort. At home, I use a pump can.

Remember this is fun. Play around on a scrap piece until you figure it out. Get good at it. It will be worth it in the long run.

Have a great day!!!

Wes

 

[sparky961]

The tool comes back up out of the cut, you open the machine up and
with one hand easily snap the finished part off the bar of stock.

I've always ran the parting tool all of the way until the piece falls off. I usually place a towel underneath the chuck and table prior to starting things in order to catch the part. Seems to me that leaving a bit of it still attached is a much better idea.

-Sparky

 

[tmuir]

Can't really add much as my experience is limitted and so far I've only parted off fairly small stuff but what made the biggest difference for me was when I got out my Dial Indicator and used that to ensure my parting tool was exactly square to the work.