The problem you each of you describe with mandrel is that the mandrel can be just as much User caused as well as a mandrel problem itself. Everyone looks for the magic bullet cause when there is in fact two or three causes simultaneously or that we move from one cause and fix it and then cause a second problem.
The problem more than anything else is that most of us do not want to admit that WE are the problem.
Below:
MP = Mechanical Problem
UP = User Problem
Number of DIFFERENT Mandrel Problems:
1. Mandrel actually bent (or more precise Bowed)
MP
2. Tail stock too tight, which causes Bow
UP
3. Usually 4 bushings or 3 in a few cases and either 1 or several bushing
holes are off center.
MP
4. Blank not squared properly.
UP
5. Mandrel nut too tight on even a squared blank. (Big and strong hands may feel like it is barely tight but still too much.
UP
6. Mandrel nut too loose. (Small and weaker hands are not tightening enough. Rarer but does happen.)
UP
7. Not using a 60° live center
UP/MP
8. Head - tail stock not aligned.
MP
9. Tail stock not locked down properly.
UP/MP
10. Bushings do not fit properly in the tubes. Should slide in with very slight pressure, not fall in. Those that "fall in" will allow too much movement and sets up eccentric turned blanks.
MP
11. Too much hand pressure on the chisel causing mandrel flex. This is greatly amplified with loose bushing fitting into the tube.
UP
12. Finish problems with:
- A. CA lifting when bushings separate;
UP
- B. Bushings glued sticking;
UP
- C. Busing Dust on wood.
UP
- D. Dull spots due to too much sanding pressure causing mandrel flex, Out Of Round bushings/ Bent Mandrel, loose bushing fittings, too tight or too loose tail stock, or non 60° live center.
UP/MP
Number of problems with TBC
1. Bushing Holes Off Center (OC) when used to start the rounding process. (Some people with lots of experience don't use bushings even from the beginning, thereby eliminating this problem.)
MP
2. Continued use of OC bushings down to size. (Problems of OC bushings can and will be corrected with light touches and turning when bushings are removed.)
MP/UP
3. Bushings too loose at startup. (But self correcting once bushings removed.)
MP
4. UnSquared blanks.
UP
5. Improper pressure: too much will ream brass; too little will not allow one to turn, so this one will be self evident and quickly corrected.
UP
6. Too much pressure on the chisel creates catches and aggressive cutting more than out of round/eccentric and chatter.
UP
7. Head Stock/Tail Stock alignment.
MP
8. Tail Stock not locked down properly.
UP
ON the above, it is easy to see that the mandrel does present more complications in getting a great turn.
In addition, it takes several more steps to use a mandrel than TBC. Still some people prefer to do both blanks at the same time on a two part pen.
Steps explained here:
http://www.penturners.org/forum/f14/truning-without-mandrel-7319/index2.html
There may be more and a few of these are much more rare than others. It should be noted that MOST of these were not a problem in the early days because the early adapters were keen observers and natural trouble shooters on the mechanics of their lathe machines and knew what to look for when a problem arose. They also knew their machines enough to know about alignment and tightness to the point that these problems did not crop up with them. Squareness was also a non-issue. This is all a part of experience and knowing the machine and mechanics as well as the end product wanted. To the more experienced, the product is a journey, not a destination.
