Mandrel Warped

cmccarter1 · Post by **cmccarter1** » Mon Apr 18, 2011 3:05 pm

I have turned about a dozen pen and on the lat one it looks like the mandrel has warped as the pen is not centered on the brass tube after turning. I have tried to be careful and not push it too much on the live center but I have to tighten the knurled know fairly tightly to keep the wood from moving when I turn it. Will be ordering a couple of replacements today. Anyone have any suggestions to keep this from happening again. Should I go with the mandrel saver?

chester

nuhobby · Post by **nuhobby** » Mon Apr 18, 2011 4:15 pm

This has been a learning curve for me, too.

One thing to mention before anything else is your type of Live Center. The usual Shopsmith live center is "too pointy" (too acute) to engage fully with the mandrel's dimple. I have intentionally "dulled" the point on my Shopsmith Live Center to help it engage more solidly with the mandrel. Others use a different brand of live-center with a less-acute angle on the point.

Over some months of trial&error (and straightening my mandrel) I got to where I could predict better how the mandrel would act, and how much to tighten the brass nut. Then I finally sprung for a replacement mandrel, and I've been using it very carefully since then, with nice results.

hdtran · Post by **hdtran** » Mon Apr 18, 2011 4:20 pm

Hello, Chester,

Contrary to popular opinion, my opinion is that tightening the knurled knob doesn't cause mandrel warpage. When you tighten the knurled knob, you put more tension on the steel mandrel, and apply compression to the bushings and the wood. Pulling on the steel mandrel should not cause warpage.

Check the following:

Is your mandrel tightly screwed into the headstock adapter?
Remove the mandrel rod from the headstock adapter. Is it nice and straight? (Roll it on a flat surface to check)
Is your tailstock live center properly aligned with the headstock? Don't believe the indicator tick marks on the Shopsmith tailstock! Push the headstock really close to the tailstock, put a chuck w/ a drill into the headstock, and run the headstock out. Does the drill point meet square with the tailstock live center? (Don't ask me how I know this one!!!)

Lastly, you don't need a lot of force pushing the mandrel into the tailstock live center. Just enough to capture the dimple of the mandrel into the point of the live center. Likewise, you don't need to push a sharp gouge very hard. A sharp tool will cut easily.

Best of luck!

hdtran

SDSSmith · Post by **SDSSmith** » Mon Apr 18, 2011 4:27 pm

nuhobby wrote:This has been a learning curve for me, too.

One thing to mention before anything else is your type of Live Center. The usual Shopsmith live center is "too pointy" (too acute) to engage fully with the mandrel's dimple. I have intentionally "dulled" the point on my Shopsmith Live Center to help it engage more solidly with the mandrel. Others use a different brand of live-center with a less-acute angle on the point.

Over some months of trial&error (and straightening my mandrel) I got to where I could predict better how the mandrel would act, and how much to tighten the brass nut. Then I finally sprung for a replacement mandrel, and I've been using it very carefully since then, with nice results.

I use a 60 degree cone style live center with my pen mandrel. I too found the shopsmith live center too pointy and it did not engage the end of the mandrel properly.

terrydowning · Post by **terrydowning** » Mon Apr 18, 2011 5:24 pm

I use the Mandrel Saver form Penn State Industries
http://www.pennstateind.com/store/PKMSTS2.html

No more knurled nut and gentle compression between the tail stock and head stock.