All,
I'm glad we have "counter-point" (pun?) responses to my post! We only benefit from differing opinions and observations. The mandrels; two were from PSI - one was the MT1 collet setup, and the other the threaded headstock adapter. I bought the collet setup after not liking the threaded model because I know threads make very poor centers because they are rarely straight and concentric to the shaft. I'm speaking of the threads on the mandrel shaft where it threaded into the headstock adapter. At .250 diameter and sticking out 3/4", even supported by a tailstock, it's very hard to thread stock such there is no deflection and the threads remain true in total indicator runout to the shaft. Especially since there is no shoulder on the shaft for the threading insert to exit the cut - which relieves the tool pressure. With no shoulder the insert necessarily touchs a larger surface area at the end of each pass - which tends to deflect the shaft among other undesirable things. So a collet, assuming it is ground concentric ID/OD, is far superior to holding a shaft true to the spindle taper than a thread screwed into an adapter could ever be.
One mandrel was from my local wood store where I compared the Delta and Jet, it was made in China, but didn't look like either of the PSI mandrels. Another from the same store was a mandrel that looked suspiciously like the pSI mandrel setup. You are right.. probably eevrything is made by two or three suppliers. Two more were ones I looked at in the Denver WoodCraft store. One was a copy of the PSI (or same one branded differently). It was sold under another name. The other was branded "American Turner Systems", which is the one I bought. Made in Indiana (it didn't say what town). But it WAS properly machined in my opinion. It had less than .003 inches TIR and was much harder than any Chinese version. It had a beautiful centerdrill feature on the tailstock end of the shaft. No burrs, no chatter, no material smudging. Just done right, the American way.
I've attached a centerdrill gif. The one I liked and bought had a profile that looked like this, the drill diameter was clean and truly reflected this profile. The others all looked like they were done with an 82 degree included angle drill, and not a very sharp one at that. In the bottom of the PSI mandrel that came with their "starter kit" (threaded headstock adapter), the cone went to a surface, then a positive "bump" of material came back upwards near the center. This feature was caused by a chipped or damaged tool. I've seen careless lathe operators make thousands of parts with damaged tools and not notice it. This also happens on unattended screw machines. Anywho, you can see how the minor (drill) diameter, if deep enough, leaves room for most any LC pointed tip - regardless of angle. The problem comes when we have no minor diameter for the point to clear. Do you gents have this profile in the tailstock end of the mandrel you use? If not, you're letting an inferior product affect your outcome.
Randy, it's all good; I never personalize statements of skill, so I don't know about being a good or bad machinist; it depends on the tolerances, the capability of the machine, and the consistency of the material. A good machinist is one capable of meeting the expected quality and standards with at least two of the caveats being true. In the last 10 years this would not consistently describe my abilities because I spend almost all my time on the engineering side. So you may be right. I hope I always accurately describe what I observe. And my observation is we have a pile of Chinese crap to choose from. [
] I think that's an accurate observation, yes? [
]
Gregg
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