Mandrel bent questions.

[hanau]

I just got my Tool rest and dial Indicator mount from Rick.(good fast service from rick)
I have been having a lot of problems with my blanks not turning completed round.
had problems with one side always being higher at the bushing.
I check my Head stock and get a measurement of Barley any movement at the mandrel when it goes in the headstock.

Then move down about half way down the mandrel I get about .003

Then at the live center on the tail stock I get just shy of .001

Appears all my mandrels are bent. So I am going to have to see about replacing them, tomorrow at woodcraft.

I have 2 that screw into the MT part of the mandrel and I have 1 that is adjustable that slides thru the MT part of the mandrel.

Should I see if i can buy new shafts at woodcraft or should I just purchase all new mandrels?

Also on the Live center do I need to replace it. I just got it last year but finally brought it into the shop last week and used it for the first time.

 

[D.Oliver]

You can straighten the mandrels. I just mark it with a sharpie and then tap it with a ball pean hammer. Recheck and tap accordingly.

 

[its_virgil]

How tight is the tailstock's live center against the mandrel? Running true on both ends and way off at the center tends to make me think the mandrel is bowed from too much live center pressure on the end of the mandrel.
Do a good turn daily!
Don

 

[Whaler]

I just got my Tool rest and dial Indicator mount from Rick.(good fast service from rick)
I have been having a lot of problems with my blanks not turning completed round.
had problems with one side always being higher at the bushing.
I check my Head stock and get a measurement of Barley any movement at the mandrel when it goes in the headstock.

Then move down about half way down the mandrel I get about .003

Then at the live center on the tail stock I get just shy of .001

Appears all my mandrels are bent. So I am going to have to see about replacing them, tomorrow at woodcraft.

I have 2 that screw into the MT part of the mandrel and I have 1 that is adjustable that slides thru the MT part of the mandrel.

Should I see if i can buy new shafts at woodcraft or should I just purchase all new mandrels?

Also on the Live center do I need to replace it. I just got it last year but finally brought it into the shop last week and used it for the first time.

I threw away all of my mandrels several years ago and started turning between centers. That solved all of my out of round problems due to bent mandrels. With this method you can even skip the bushings and use calipers.

 

[hanau]

I have over tighten them in the past most likely.

I will try to straighten one of them.


Turning between centers? have a recommendation for the drive in center?

 

[JohnGreco]

I have over tighten them in the past most likely.

I will try to straighten one of them.


Turning between centers? have a recommendation for the drive in center?

John Goodin has these in MT 1 and 2: MT2 dead center Carbide tip [MT2DC-CAR_TIP-NO_MOD] - $18.50 : Penturners Products!

I just started turning between centers using bushings from his site and am ready to toss the mandrel...I just can't see going back to it after this method.

 

[johnnycnc]

John,
Your mandrel isn't necessarily bent from what you are checking.
There are several minute things that can cause the numbers you are getting, and for an out of the box, "working" mandrel setup... your numbers aren't too bad, in my experience.
I've fiddled with a lot of run-out checks on every part of penturning lathe setups over several years time.

Here are some pointers;
1. check at the headstock side, not only on the Morse adapter,
but on the shaft itself too. this is important because there is an "interface" of the mandrel to adapter there and may not be the same as the adapter itself.
And the mandrel is what you depend on directly.
2.relax the live center pressure when you check the mandrel closer to that end, too much to dive into deeply here, but tailstock alignment is a factor.
You want to "isolate the mandrel" and check IT, at this point.
3.check your live center point for wear and damage, it's pretty common where the mandrel seats on the point and can cause grief.
4. the probable cause, from my turning experience with equipment like you are using, of the out of round or one side higher than the other,
is the bushings.
they don't fit well in the tubes and allow center-line offsets of the barrel to bushing diameters.
try Scotch tape on the smaller diameter of the bushings to shim them up to fit snugger in the tubes. sounds dumb, yes. but at least try it.
this will help you isolate your issue.

(*disclaimer; yes a lot of you know I'm a purely between centers kind of guy,
but I started and turned a lot of pens on a mandrel using the same type equipment that is in question here in this post.
There is a lot to learn about mandrels, and set-up tuning as well!).

 

[MarkD]

I pitched the mandrels and got "turn between center" bushings from JohnnyCnC. What a difference!!! Penturners Products!

 

[randyrls]

I just got my Tool rest and dial Indicator mount from Rick.(good fast service from rick)
I have been having a lot of problems with my blanks not turning completed round.

Should I see if i can buy new shafts at woodcraft or should I just purchase all new mandrels?

John; The Dial Indicator is your best bet to find out what is going on.

John's Goodin's suggestion to check the shaft at the headstock is a good one.

Your checks of the mandrel are a good start, but only a start.

Next take the pen bushings you had problems with and bare tubes for the same kit. Mount these just tight enough to keep them in place and repeat the checks on the bushings, and on the tubes. Now mount blanks as you normally do with a normal tightness on the mandrel nut. Measure the bushings again, especially in the middle.

Unfortunately, pen bushings are often off-center, out-of-round, or eccentric. Any where there is a connection from one part to the next, tolerance is an issue. Tolerances can either cancel each other out, or reinforce each other. Between centers turning eliminates about 5 or 6 connections, and so is less subject to tolerance issues.

If the original mandrels came from Woodcraft, you can replace just the shafts, but I would make the measurements to find out where you are having the problem before getting things you may not need.

I once thought that I had bent mandrels, but discovered that I was not finishing the blank ends exactly square to the tube. When I tightened the mandrel nut, the angles on the blanks "pulled" the mandrel out of true.

 

[hanau]

I replaced the shaft and they came out better and noticed about a .001 variance on the Dial indicator with the new shafts.