chatter

[MGREEN]

Making a mandrel for a friend, to hold a buffing wheel for buffing
wooden bowls and such.

Stock is 1.250" mystery metal ( mild steel of some kind). 12.5" long.
Mounted in 4jaw with about 4"or 5" hanging out of chuck, dialed in to
a thou or two, turned roughly 3" length to about 7/8".

Then set up the taper attachment and turned a MT#2 on that end
also drilled and tapped to 3/8"-16 for draw bar.

Everything up to this point went well, no surprizes.

Then I removed the 4 jaw, popped in the spindle adaptor sleeve,
inserted the freshly made MT#2 with draw bar and tightened.

Faced off the new end ,center drilled, put my cheapo live center
in the tailstock ,brought that into position, snugged it up.
Now when I take a cut, either light or heavish, with a tool
side cutting or round nosed, on center or a little low, I get
chatter every time. ....Shrug?....
Never had this problem before.
I snugged the crossslide gib, Phase 2 QC tool post with minimum
overhang South Bend 10L lathe flat belt drive, middle step on
3 step pulley .
I think that puts the speed around 470 rpm. 2 thou per rev feed.
HSS hand ground tooling.

What am I doing wrong?
Mike Green

[ptjw7uk]

If your turning at the the centre end I would suspect that as the cause. Even more noticable as no chatter occured when in the four jaw.
I have a polish rotating centre and I thought that I could see it move the other day I will have to invest in something a bit more substantial there a lot of side thrust put on them I have seen inferences that you should use a travelling steady when cutting over a fair distance.

Happy Christmas
Peter

[Carld]

Mike, the only thnig I can think of is an ill fitting taper. Are you sure the taper you cut is a perfect fit? Did you blue the taper and rub it in a factory taper socket?

[John Stevenson]

Just check the fit of the morse taper with a dab of blue or marker pen.
Sounds like it might not be a snug fit and causing a bit of wobble.

One tip is when turning morse tapers is to relieve the centre portion about 1" and then blue and polish to fit.
It's easier to work on with two distinct lands than having to blend a whole length.

Second thing is do you have another centre to try ? as some aren't all they are cracked up to be, even branded ones.
I have a Jacobs one here that's no good on long slender work, it leaves a pattern, but swap to an old Skoda one and it goes away.


[edit] Carl can type faster

.

[oldtiffie]

Adjustable?

Is the pre-load on the live centre thrust bearing adjustable? Is is "slack/loose"?

Chatter may be live centre "bearing noise". Can you remove and examine the bearing/s?

Is there insufficient "end pressure" (from the tail-stock) onto the work-piece? Live centres can stand quite a bit of "load/ing" from the tail-stock.

All other posts are very relevant.

[lane]

Your Taper you turned is not quite right and the center is pulling it out of line and causing chatter.

[MGREEN]

I decided to give it one more try beforedis-mounting the mandrel.
I found this cutter in my drawer;

Gave it a quick hone with a diamond paddle, and it cut very clean with
the part mounted just as it was before but NO chatter!

I put my steady in place on the newly cut surface, drilled and tapped
the end and bored a recess to provide clearance for the washer and
nut that projects out on the inboard side of the cloth buffing wheel.
The stitched center area of the wheel buts up against the
rim on the end of the mandrel.

I turned the mandrel end for end and indicated it back in the 4jaw,
with steady still in place, and checked the fit of the taper.

Everyone was right, the fit was not good, so a little filing and sanding,
I settled for this fit;

I filed smooth the roughly turned spot to the left of the taper.

A shot showing the steady and my carraige stop used to set the depth
of the flat bottomed bore to clear the washer and nut.


Still have to make the hand wheel/nut for the draw bar.
Thanks to all for the insight!
Mike Green

[Carld]

Mike, you need to work on the taper some more. You should try to get at least 80% of the whole circumference and length of the taper making contact.