Musing about things I had assumed I knew, but didn't.

"Arch" wrote: 3. When the headstock end of a long heavy blank held with tail support is balanced with counterweights adjusted on a steel plate, is the entire length of the long blank now in balance. (ie. do I need to balance both ends of a long heavy blank?) ^^^^^^^^^^^^^^ I know this one, so I will answer. The *other* number 3, and the others as well, will have to come from those with better info.

If you balance a long, unbalanced piece at by adding all the weights at one end, you achieve "static balance." The piece will stay where you stop it, and not fall/rotate to lower its center of gravity. However, if the ends are differently out of balance, you have "dynamic unbalance." The two ends will try to behave independently of each other when spinning, and you get a tilting, end-to-end vibration.

One of the books I own suggest removing the spur center, and pounding it into the wood, and then inserting it back into the headstock.

Certainly sounds like a safer approach.

I think it was the Tage Frid book on Shaping.

I have read that this is not a good idea and that the spur center should be removed and tapped in off the lathe.

the head casting is the cause of the 'braking effect' of over tightening the tail center?

My guess would be yes but now I have a question. Why do you tighten the tailstock that tight?

In my experience, no, at least I don't think so, at least I never noticed a diference.

Hi Arch, where have you been ?? kind of missed you on the rcw.

Arch wrote:

Just depending here as always, shaft thickness between bearings and length, length of overhang, but filling the shaft with a fitting taper will certainly increase the stiffness of that shaft, MO

Bearings and bearings are like wood and wood, all kinds and not the same, there are many configurations and/or combinations of bearings, not to mention qualities. However if the right kind of bearing of good quality is used I wouldn't be afraid to wallop a chunk of wood onto a spur center wood, the steel will win that handily. Now running the lathe while HEAVY pressure is put upon them is another story, we have now steel wearing against steel, and the lubrication film could very well be insufficient and overheating and damage could then occur, so yes you can use pressure, but if the bearings heat up a lot, take some pressure off and/or slow down. MO

Like Leo L said, you might have static balance, but that's not dynamic balance, to which I would like to add, that if you have rigged up a piece of wood and got it statically balanced and you now think you can rev. it up, the dynamics are there in full force, and you better be aware of that, it can do a lot of damage in a hurry, so keep it down.

I'm not to sure about this one Arch, vibration is more like a resonance, and probably a dynamically induced imbalance, changing with speeds used, I don't think rotating the headstock will, but could make a difference, like I said I'm not sure.

This is more a thing of who got the upper hand in making drill bits and the drill chucks, with their own proprietary taper, best way to prevent slippage is a clean and precise fit, MO

I don't follow you here Arch, the metal crystal structure and the kind of other alloys/metals in there make for the carbon steel to generally be able to be sharpened to a finer/narrow edge, This to the best of my knowledge. I worked with it, never made it.

Haven't got a clue Arch, maybe it's something like what hurts most, I hit it or it hits me.

1 I believe that a tubular shaft is about 80% as strong as a solid shaft.

2 hammering on bearing is a bad practice unless you plan on replacing the bearing.

3.2 The Nova head stock sits on a ring about 8 inches across the pin you tighten lock down the head stock pulls down in the center of this ring so it does not care how you turn it.

5 How often do you want to sharpen? The softer the steel the more you will sharpen.

6 When you suddenly kill the power to the control unit it will cut the current to the motor. DC motors make good generators the energy stored in the rotating shaft and the magnetic field around the motor will be returned to the motor controller. the current running the motor had built a large magnetic field around the motor if the current should suddenly stop the magnetic field will collapse the energy from this field will be collected by the coils of the motor. There is a lot of energy stored in that field, this energy will find away to complete its circuit throw the path of least resistance. The higher the resistance the higher the voltage will go, should the voltage become high enough it will break throw the insulation in the motors coils and damage them. The designer of the motor control made some plan for this catastrophic event, testing this plan is about as smart as testing the air bags in your car.

Electronic controls are great but they can and do sometime fail. Let's assume you left a 40 pound blank on the lathe a few hours later a thunder storm rolls throw and the motor control fails to a full speed condition, how big is the hole in the wall?

Walt A

Hi Arch,

I've done a little judicious snipping to skip the things I don't know about to hit this one-

First part, I'd guess that the MT does a better job of preventing mating parts from rotating. More surface area = more holding power.

Next, ever seen a machinist's Bohr blocks? If you haven't, they are two blocks with perfectly flat surfaces that hold together with no adhisive or fasteners. This is because the machined surfaces are so precise that they allow the two pieces to sit so closely together that the atoms in each can swap electrons (and possibly other forces, I'm not an expert on the subject by any means)

In a perfect world, the mating surfaces between the MT or JT and it's mating socket should work on a similar principle. Granted, most of them have some dings and nicks, so it's not going to be quite the same, but getting it close must be good enough. Allowing the two parts to rust introduces a failure point that should not be there- that doesn't mean it doesn't work in application, but the best way to get the full performance is to make sure both the taper and the socket are perfectly smooth and shiny. To help things stay rust-free, a little oil goes a long way, and also adds to the bond between the two mating parts.

As far as "tightening" goes, I've always fully opened chucks, then inserted the JT, and put the assembly into a vise. Seems to work well enough, and you're not pounding the guts out of your chuck.

Adequately answered.

The bearings are designed to work against an axial load, loading at 90 degrees is bad for them. Hammering is worse.

Also not sure if the

Betting the bearings at the headstock are _much_ better than the ones in the live center. Look there for drag.

I reread the answer, and it still does not make sense to me. If I taper the bottom of a bowl blank, it doesn't start oscillating, so any physics are going to be so subtle as to be meaningless. It is mv squared, after all, and for balance _Delta_ (difference) is the appropriate mass. What makes sense is to get as much unneeded wood out of the way at the bandsaw as possible.

Keeping things short minimizes the effect of runout error. Side loads - see above - ar not what tapers are about. Clean, unlubricated is what you want, just as the directions have it.

Malleability counts in turning the burr. Of course, the more easily it's turned up, the more easily it can turn down. No burr is really required with the piece in motion, just an edge on your HSS will do.

Betting it matters not. Probably a shunt besides the braking for the generated DC.

Always interesting to get an explanation and then test it. Hopefully these are better than hypotheses.

"George" wrote: The bearings are designed to work against an *axial* load, (clip) ^^^^^^^^^^^^^^^ Did you mean to say "radial?"

Ayup, dicandpurpular to the axis of rotation.

"George" wrote: Ayup, dicandpurpular to the axis of rotation. ^^^^^^^^^^^^^^^^ Herst a wort? (Do you speak any Yiddish?)

Arch one addition here, regular ball bearings are not designed for axial trust, but you don't have to go to spherical or tapered roll bearings hat need preload on them, there are torrington or angular load ball bearings, specifically designed for loading in both directions, I put a link in here for you to peruse if you like. They would be exactly the kind of bearings for most wood lathes. MO

Have fun and take care Leo Van Der Loo

The JTs that the chucks mount on are Jacobs tapers, not Jarno. The Jarno tapers are long tapers very similar to Morse tapers.

The Jarno tapers are easier to machine than the Morse as they all have a .600" per foot taper. The Morse tapers are around the same, but vary for each size.

A Jacobs taper will hold very well if it is installed correctly. Perfectly clean surfaces, free from burrs, is often enough. To get them tighter, heat the female part in an oven and then drive in the male arbor.

Here is a link to a good table of tapers:

John Martin

Thanks John for that link, some really interesting stuff on there.

Have fun and take care Leo Van Der Loo

John wrote:

Thank you all for your information and insights. I learned something from each of you and I hope some other woodturner learned something he/she didn't know. There are many things related to our craft that we don't know that we don't know. :)

Turn to Safety, Arch Fortiter