lathe query

[lubbing5cherubs]

Hi I have a lathe query. I made a pill box that I posted in the pen section so some may of seen it but I have a question. I thought my mandrel was bent so I order a new mandrel because all my pens have been getting diveted. Well now I just turned this small container and it got the divets too. See just under the knob on the lid. What causes them??:confused:
https://www.woodworkforums.com/attach...chmentid=32458

Thanks Toni

[RETIRED]

Vibration in the timber or lathe. Tools not sharp enough. Lathe speed too slow. Incorrect application of the tool. Incorrect tool used for job.

Just a few reasons for you Toni.

[RETIRED]

PS Tool rest vibrating because of length.

[Skew ChiDAMN!!]

That's called chatter, Toni.

It can be caused by several different things, but basically it's the end of the tool vibrating in time with the lathe RPM.

Among the causes are: too much tool overhanging the tool-rest (most likely), thin tools that "flex" (any tool less than 1cm thick when taking big cuts), working at the end of a long tool-rest (ie. the tool-rest is vibrating), very thin wood (so the wood is vibrating... most common inside thin bowls & goblets), etc, etc.

How to stop it? Always keep the tool-rest as close as possible to the part you're cutting. Sharp tools and fine shear-scraping cuts. Try not to work at the very end of a long rest. In the case of thin bowls/goblets, a finger on the other side to help damp out the vibration.

One of these days I won't need a whole page to answer one of your questions... I'm dying for the day when I can say "Dunno. Go ask BDar or Ern."

Mind you, sometimes I deliberately want that sort of effect and I've made myself a tool to do it evey time! :eek: You can see the effect in the base of a goblet I broke here (and how I salvaged it here. Gotta admit, it turned out a lot better than I'd planned. )

Edit: beaten to the post by ! LOL!

[Hickory]

That's called chatter, Toni.

It can be caused by several different things, but basically it's the end of the tool vibrating in time with the lathe RPM.

Among the causes are: too much tool overhanging the tool-rest (most likely), thin tools that "flex" (any tool less than 1cm thick when taking big cuts), working at the end of a long tool-rest (ie. the tool-rest is vibrating), very thin wood (so the wood is vibrating... most common inside thin bowls & goblets), etc, etc.

How to stop it? Always keep the tool-rest as close as possible to the part you're cutting. Sharp tools and fine shear-scraping cuts. Try not to work at the very end of a long rest. In the case of thin bowls/goblets, a finger on the other side to help damp out the vibration.

The Skew man be pretty much in line with the What & How not to.... I agree. A couple of other points to try might be tool rest height. On outside turning, Raise the cut and the "timber" scrapes across the bevel making a lighter cut area and decreases the vibration. When I had students with difficulty in their turning, I often had them raise the toolrest which lightens the cut for them. That is IF you have the rest in correct position, etc.


If all else fails, blame the lathe.... bad bearings can also create a chatter as the spindle shaft is allowed to move laterally inside the head. One of my lathes is an old lathe with Bronze bushings and they often wear out and some chatter will begin, this is one way of telling me they need replacing. If you are having the problem with other fixtures and such, and you are doing all the right things, look into examining the wear on your lathe.

[lubbing5cherubs]

[quote=Skew ChiDAMN!!;392195]Try not to work at the very end of a long rest. In the case of thin bowls/goblets, a finger on the other side to help damp out the vibration.

YOU WON'T CUT YOUR FINGER???

One of these days I won't need a whole page to answer one of your questions... I'm dying for the day when I can say "Dunno. Go ask BDar or Ern."

YEAH RIGHT.. I KNOW I HAVE A QUESTION I KNOW YOU CAN ANSWER ME BECAUSE YOUR BRAIN WIRED TO WOOD AND IT ARGUMENT..LOL

Mind you, sometimes I deliberately want that sort of effect and I've made myself a tool to do it evey time! :eek: You can see the effect in the base of a goblet I broke here (and how I salvaged it here. Gotta admit, it turned out a lot better than I'd planned. )

NICE I love that goblet save


Toni

[lubbing5cherubs]

thank you Hickory
Toni

[Skew ChiDAMN!!]

A couple of other points to try might be tool rest height. On outside turning, Raise the cut and the "timber" scrapes across the bevel making a lighter cut area and decreases the vibration.

You may've put your finger on it, Hickory. Another look at the pic & I can see the chatter's in a "spiral" pattern, so if Toni was using a scraper she either had one side off the rest or was cutting below centre...

If all else fails, blame the lathe.... bad bearings can also create a chatter as the spindle shaft is allowed to move laterally inside the head.

I glossed over that with "etc., etc." Toni's Leda is still pretty new, so hopefully she won't encounter those problems for some time yet.

YOU WON'T CUT YOUR FINGER???

Not unless you do something stupid, like cut all the way through the wood. Actually, when I'm turning bowls and goblets really thinly, I find that with my finger on the other side I can feel how thin the wood is (it's sort of like feeling through thick paper) and it makes it easier for me to turn the walls to an even thickness!

Mind you, slow and careful is still the order of the day. I'd rather keep my fingers just as they are.