Mandrel Tightening

[dmiller]

Being self taught from the forums here. I have a few questions about mandrel tightening.

How tight should it be at:
Point A: (Tight?)
Point B: (Snug enough not to slip?)

and am I correct that the tail stock tightened just until the live center spins..correct?

Here is a picture for reference points.

I am picking up my new 60' live center tonight...so hopefully that will help with my out of round issues. (not ready to buy more parts & tools to do mandrel-less turning.)

 

[low_48]

Yup, tighten A like you would put a router bit in a router, and B just snug. B will tighten all by itself if the blanks spin a little. So check B if the blanks spin so it's not so tight as to cause the arbor move. Making the ends of the blanks square to the tube is actually more critical than the tightening.

 

[turned_for_good]

You pretty well got it right. When tightening up the brass nut, I usdually like mine to where you can turn but if you get a bad catch the blank spins. As far as the live center goes, tighten until it is spinning the same speed as the mandrel and maybe a hair more if you just put your mandrel on the lathe.

 

[marcruby]

Dave -
you have the right idea. Just tighten enough for everything to work. Overtightning can distort the mandrel.

 

[ed4copies]

Dave,

None of those are critical (IME).

Since I have gone "mandrel-less", I have come to realize our bushings are drilled out of center FAR more often than I ever would have imagined. Bring your mandrel down to just a "nub" (shorten with the adjustment at point A on you drawing). Now, put the bushings on and see if they travel "round". I was surprised at the results. Also remember to watch the "shoulders" that support the brass tube, they are SUPPOSED to be traveling ROUND, also.

In my shop, about 20% did not! They are now garbage.

 

[leehljp]

Ed,

I agree with you on the bushings - at least 20% being OOR and garbage.


Dave: AS to the tightening, there is one theory that says that tightening B will be like tightening a string on a guitar and makes it straighter. However, that is not a string and if the tubes are not absolutely 100% squared and the bushings are not absolutely 100% concentric and squared also, the over-tightening will force OOR and end with elliptically turned pens. We are talking about .008 or .009 or so, which become obvious.

In my experience, I learned once that when I over-tightened just a smidgen, I got an OOR, but backed of about 1/8 for a turn on the B nut, the OORs went away.

SO, if looking at it from the guitar string concept, what causes the OOR no matter how tight,- it must come from something not fitting perfectly - and anything more than "snug" causing alignment or OOR problems. "Snug" causes less problems for me. Mr. Experience and Mr. Observation were great teachers for me.

OH, one more thing - There is usually a very fine line between - being snug enough to prevent spinning of the blank when touching a skew or other - versus not being over tight. (I personally use the mandrel-less system 95% of the time now.