Chatter - Grrrrrrrr! :(

[warreng8170]

OK guys, hopefully you can help me out here. I am starting to have issues with chatter in the center of full-length blanks. The latest round was really frustrating. I was trying to round out one of my recent cast blanks and the chatter was worse than ever. The blank was 5.25 long. As you can see from the photos the ends are fine, but the center has extreme chatter marks. It was so bad that it was causing chip-out in the blank.

I have tried the bowl gouge, spindle gouge, scraper, skew (all sharpened to the best of my ability) and even my woodchuck pen pro with a fresh edge. I've tried sharp angles, shallow angles, light cuts and heavy cuts. Nothing makes a difference.

As you can see in the last picture, a half-blank turns nice and smooth but that doesn't help me out when I want to turn a Zen or Long-click.

BTW, this happens with wood as well, just not quite as noticable. Any ideas????

 

[DozerMite]

Move your toolrest closer. Is there any flex? Where does your tool touch the blank?

 

[Andrew_K99]

How much pressure are you putting on the tail stock? Might they be bending under the pressure?

 

[srf1114]

Maybe a much lighter touch in the middle? the ends have support that keep the blank from flexing, the middles have no support. Even a tiny flex could cause this.

 

[Dalecamino]

Warren, you're not the only one with this problem. I get the same thing. If I recall, the last time, I checked to make sure the Woodchuck blade was touching in the center of the blank and, moved the tool rest closer. Also didn't use much pressure in the center. It seemed to help. I don't have any turning planned for a few days so, I'll have to watch for your reports. Thanks for bringing this up here.

 

[Drstrangefart]

I have had to learn my way through the exact same thing. It took me a ton of practice and finding the magic combination of sharpening angle, and holding my tools just right. A few coats of medium CA can backfill those chipouts.

 

[Ruby pen turning]

I have this happen all the time. I think when you/me are turning a blank from square to round the ends cannot move but the center flexes. This happens on fresher blanks for me usually. I do also think pressure from the tail stock may bow it also. You might try using your skew holding it firm so it does not bounce in and out every time you hit peaks and valley`s .

 

[warreng8170]

Thanks for all the suggestions. A few things: I've tried the tool rest at multiple distances with no luck. Also, as for light cuts, if they were any lighter I wouldn't be touching the blank! I was cutting so light that what was coming off could barely be considered "fuzz".

My vote for most likely suggestion is too much tail stock pressure. I am cranking it pretty good to keep the blank spinning when I put the tool to it. I'll try another blank tomorrow and see if I can get better results.

 

[Ruby pen turning]

I meant to say firm pressure on the tool rest so it doesn't bounce in and out so it knocks off the peeks.

 

[G1Pens]

Tail stock should have just enough pressure for the live center to turn. I usually start the lathe with the tailstock just barely touching and then tighten it up just enough th get the live center turning. I then turn it off lock the tailstock and set the tool rest then fire it up and get to work

 

[JeffT]

Thanks for starting this thread... I am having the same problem to some extent. One thing that has worked is to turn between centers which, because of much less length, is more rigid. You would have to really try to make the work piece flex. YMMV.

Thanks for all the other good answers. This site is a GREAT resource!

Jeff

 

[robutacion]

I believe the problem comes from the tail stock being too tight. I may not make any difference with a short blank but long blanks, will most certainly force the blank to bounce due to the slight curve the over tight tail stock causes.

The reason why most are having this same problem is due to the fact that, the TBC live and dead 60° centers, made with the harden and polished steal, doesn't have much "grip" to make the brass tubes glued in the blanks, to spin "firmly" with only a light touch that becomes a lot more an issue the longer the blank is so, the first reaction is to put some extra pressure in the tail stock. That is what is causing the problem...!

There will be many ways one could add something to the live center cone to increase the grip and not compromising accuracy, I use an O'ring (various sizes depending of the brass tube size) on the live center tip, there is, where the brass tube and the cone meet. The O'ring has to be the correct size to work, in this case, the O'ring diameter is about the size of the brass tube diameter. You know when you've got the correct size when you insert the O'ring on the live center cone tip and bring the blank, already with the brass tube glued and with the gentle hand pressure you see the O'ring ALMOST go inside the tube, as due to the conical shape of the live center, by the time you bring the tail stock to the other side of the blank, a very gentle pressure is all you need to get the O'ring to lock in the brass tube, making a gentle but firm grip to turn without spinning...!

This stops any center wobbling on the center of longer blanks, well, it did to me...!

Cheers
George

 

[Russianwolf]

Couple questions....


Is that a solid blank? I looks like the centers aren't far enough in for it to be a tubed blank.

What kind of lathe is that?


I did have this issue early on with my first lathe. The issue for me was my first lathe had a cracked bed and would flex slightly as I was turning. So check to make sure the headstock and tailstock are mating tightly with the bed and that there is no way for anything to flex as you are turning. Check the spindle on both headstock and tailstock to make sure that they aren't allowing the piece to move away as you are cutting.

Chatter marks are made in two ways. (1) The piece is moving back as you start cutting and then rocking back in when it hits the limit it can travel, then back out as the cutting gets deeper again, etc. etc. (2) the tool is flexing in the same way as the piece is in number 1. That's why chatter tools are made of thin material, to allow them to flex.

 

[warreng8170]

George did a good job of explaining what the problem is. The 60 degree TBC live center doesn't create enough friction on it's own to keep the blank spinning so I was putting too much pressure on the tailstock to create friction on the live center.

I'm thinking this might be a good solution.

http://www.pennstateind.com/store/LCENTSS11.html

1/2 crown should be small enought to avoid hitting. I don't round down below 5/8.

 

[Andrew_K99]

You could also drill a small pilot hole to allow the live center to go in further. I'll do this when rounding over blanks before drilling them.

AK

 

[GColeman]

When this happens to my turnings I use a underhand grip and support the blank with the fingers of my left hand. I also use a skew flat as a scraper, (I know sacrilegious right?) to fine tune before sanding. The underhand grip also lets me feel imperfections with my fingers that I can't see.

 

[Dalecamino]

George did a good job of explaining what the problem is. The 60 degree TBC live center doesn't create enough friction on it's own to keep the blank spinning so I was putting too much pressure on the tailstock to create friction on the live center.

I'm thinking this might be a good solution.

http://www.pennstateind.com/store/LCENTSS11.html

1/2 crown should be small enought to avoid hitting. I don't round down below 5/8.

Do you think this will solve the issue? I use a 3/8 spur with 4 blades so I can get down to 1/2" Maybe I should try this one. Thanks Warren.