Got The Chuck & Fear For My Bearings

What's with all this worry about the Jet mini's bearings? You can replace them if they go out for a small sum and it's not a terribly big job I hear. I bought a Supernova to use on my Jet mini. (I don't think it weighs quite

8 lbs. though.) A Supernova or a Talon might be a better match for your lathe.

Anyway, when I got through reading the manual that came with the chuck, I was afraid to turn the danged lathe on. Then I figured, the manual must have been written by their attorney(s), so they would be able to say that any incident that might possibly happen must have been a failure caused by excessive speed. Corporate liability, I think they call it.

Well, I decided to go ahead and use the chuck sensibly at whatever speeds I felt were necessary. I've had my Jet mini and Supernova chuck for about 4 years and neither has caused me any trouble. I have turned a number of 9

1/4" bowls and I'm still on the original bearings. Pin jaws? What about the 2" standard jaws? I use them at least 75% of the time.

Go ahead and enjoy your new chuck and your lathe. If the stress from worrying about excessive RPM's and bearing loads gets to be too much, you can always trade up to a Oneway 2436 or a Stubby.

Barry

PS Go easy on the speed. Don't try to turn too fast. An awful lot of turning can be done below 1200 RPM's. Sandpaper cuts better and doesn't burn your fingers as quickly. Tool edges don't get as hot. And centrifugal forces on bearings are less.

Charlie,

Don't be too scared of teh skew, exsecially planing with teh long point down. Here is why: You have MOREW control, the tool is closer to the axix of the lathe which makes it easier to direct...it IS more like an extesion of your arm this way.

I've been lucky enough to talk with both turners you mention and see them demonstrating. I find it great to hear your comments about Mike darlow as I fully agree; there is a place for mor details explanations. Unfortunately, many find this too difficult (or don't want to try and understand it). Richard Raffan sure knows his stuff (comes from doing so much production turning in his early days).

Finally, until you try using the skew long point diwn, you'll never appreciate how much more control you have. From my brief experience, you are more likely to get into trouble if you are too cautious..you have to use some force or the wood WILL catch minimally and generate a bigger catch (and trouble).

safe turn>PIcked up the SuperNova2 and the Pin Jaws. Cleaned them

The lawyers are probably setting the RPM's at 680. When I got my first Nova chuck I think it said 800. I have the original Nova and the Supernova. I run both up to 2500 rpm. Me thinks they may be worried about the liability of you getting smacked by a piece of wood if it comes off. I've had several pieces come off at all speeds and the most they ever did was drop down and spin on the floor a bit.

For the slow RPM is safer crowd - aside from bowls coming apart, and they come apart at all speeds, the catches are bigger and nastier at slow speed, the cuts are rougher at slow speed, etc. Crank it up to where you are comfortable and enjoy, and the wood can tolerate - don't try spinning poor or out of balance wood at 2500! If 500 is the max you feel good at, then run at 500. I typically rough around 500 and keep bumping the speed up as it smoothes out until I am in the 1500-2000 range. Pieces are finished by the tool, I rarely have to sand anything. You mention Raffan, ever notice how fast (my guess is 2500+) his lathe is spinning? Notice he uses a variety of chucks? Notice he only gives a swipe with the paper and calls it done?

Practice with the skew. It's my favorite and can be your favorite too. Just takes lots of practice, and speed. Slower RPMs seem to be the nemisis of the skew, at least for me.

The lawyers are probably setting the RPM's at 680. When I got my first Nova chuck I think it said 800. I have the original Nova and the Supernova. I run both up to 2500 rpm. Me thinks they may be worried about the liability of you getting smacked by a piece of wood if it comes off. I've had several pieces come off at all speeds and the most they ever did was drop down and spin on the floor a bit.

For the slow RPM is safer crowd - aside from bowls coming apart, and they come apart at all speeds, the catches are bigger and nastier at slow speed, the cuts are rougher at slow speed, etc. Crank it up to where you are comfortable and enjoy, and the wood can tolerate - don't try spinning poor or out of balance wood at 2500! If 500 is the max you feel good at, then run at 500. I typically rough around 500 and keep bumping the speed up as it smoothes out until I am in the 1500-2000 range. Pieces are finished by the tool, I rarely have to sand anything. You mention Raffan, ever notice how fast (my guess is 2500+) his lathe is spinning? Notice he uses a variety of chucks? Notice he only gives a swipe with the paper and calls it done?

Practice with the skew. It's my favorite and can be your favorite too. Just takes lots of practice, and speed. Slower RPMs seem to be the nemisis of the skew, at least for me.

The lawyers are probably setting the RPM's at 680. When I got my first Nova chuck I think it said 800. I have the original Nova and the Supernova. I run both up to 2500 rpm. Me thinks they may be worried about the liability of you getting smacked by a piece of wood if it comes off. I've had several pieces come off at all speeds and the most they ever did was drop down and spin on the floor a bit.

For the slow RPM is safer crowd - aside from bowls coming apart, and they come apart at all speeds, the catches are bigger and nastier at slow speed, the cuts are rougher at slow speed, etc. Crank it up to where you are comfortable and enjoy, and the wood can tolerate - don't try spinning poor or out of balance wood at 2500! If 500 is the max you feel good at, then run at 500. I typically rough around 500 and keep bumping the speed up as it smoothes out until I am in the 1500-2000 range. Pieces are finished by the tool, I rarely have to sand anything. You mention Raffan, ever notice how fast (my guess is 2500+) his lathe is spinning? Notice he uses a variety of chucks? Notice he only gives a swipe with the paper and calls it done?

Practice with the skew. It's my favorite and can be your favorite too. Just takes lots of practice, and speed. Slower RPMs seem to be the nemisis of the skew, at least for me.

The slower is safer crowd are those of us subject to the laws of physics.

"Chuck" Too bad about those buggy whip factories, eh? ^^^^^^^^^^^^^^^^^^ I don't believe I ever heard of anyone in a buggy being injured for lack of an airbag. Slower IS safer. But, slower is also slower. And, none of us is going to live forever, you know. Take as many chances as you dare, until you get hurt, and then back off a little. ;-)

Too bad about those buggy whip factories, eh?

Too bad about people who have to try to be smart, and succeed only in being smart-alecs.

Energy available to propel a loose chunk, shake the entire piece from the chuck or knock the gouge out of your hand increases with the square of velocity. Simple truth. What's pitiful as that you think it a joke.

It can bite you - hard.

Those who can and will think are well aware that turning is best with the least force applied by the turner. Same holds for the turning.

Huh? Wouldn't that be more like Mass times velocity? (as in a proportional relationship) Maybe the square of the RPM but not the linear velocity.

Steve

1/2 mv^2

..or f=ma

and you cannot push a rope...

Lathe speed should be set on the basis of linear velocity of the surface weighed up against balance of the blank and integrity of the wood.

There are many references that discuss what this speed (inches/second, cm/second, feet/second) should be. As diameter, and hence circumference increases, RPM must be decreased to give the same linear speed of the surface past the tool.

No one that understands the above will ever simply talk in terms of RPM nor follow a table of diameter and RPM without considering other factors.

If the tool is used correctly, the cutting edge has support, and should not catch. The cutting support will increase as speed increases if the turner has presented the tool correctly. From this will follow a better surface finish than if a slow speed was used for fear of a catch (eg Raffan doesn't use 6 grades of paper starting at

80 grit because he has good technique and takes advantage of using an optimum speed. He has also learned that not all timbers are alike and some are better scraped than planed but that is another topic!). If you don't get catches at modest speeds why do you get catches at optimal spreeds? The reason will usually be simple: technique can be improved or poor sharpening of tool leading to less than suitable bevel (=can't obtain required cutting edge support so you get catches).

This isn't rocket science and there are enough references for anyone who is interested (yes, one must actually read, watch and learn) to improve their technique.

Regarding linear velocity calculations... Circumference = 3.1416 x diameter of blank If you multiply circumference by RPM you will have a linear surface speed. eg 1000cm x 24 RPM = 24000cm/min (400cm/second)

If you want to try a recommended linear surface speed, convert it to "distance units" per minute (eg ###cm/minute) and divide it by the circumference (measured in the same distance units).

Example purely for explanation (NOTE; just for explanation): Linear speed = 400cm/second = 24000cm/min Circumference of job1=1000cm : speed = 24 RPM Circumference of job2=10cm : speed = 2400RPM The linear velocity in each case of the timber surfaces is the same.

For safety, approach the calculated speed from the slow side, consider the balance of the blank and the integrity of the wood!

Safe turn>Stephen M wrote:

Hi Alan, Well done, thanks. Your helpful post made me rethink some of my long held verities.

I have assumed that without a sharp tool, wood cannot be turned well. Nothing, not technique, not equipment, not speed, not bevel, not hope and not even fame, can compensate for a dull tool.

I've also assumed that good _turning technique etc. can make a surface that doesn't require beginning with coarser grits, but good _sanding technique doesn't allow skipping coarser sequential grits on a lesser surface.

I thought there were so many variables involved in turning a chunk of wood successfully that engineers, physicists , rocket scientists and the rest of us end up turning empirically and intuititively. It seemed to me that dogmatic assertions and 'always/nevers' about any one variable were more helpful in debate than in turning.

I reckoned that we all suffer catches. Good technique and tooling may keep them infrequent and small, and proper velocity may lessen the consequences, but they happen in the real world of inattention, waving gouges and hidden nails.

Anyway, your discussion provoked thought, not argument. I hope you and others will expand on it. Thanks again.

Turn to Safety, Arch Fortiter

========================= The math is OK, BUT: In your examples, Job 2 would be practical, with a spindle about 1 1/2 inches; Job 1 is a blank over 10 feet in diameter.... anyone here have a lathe that can swing that blank??

Ken Moon Webberville, TX

Glad to see you checked the maths.

It was purely an example...I did say: "Example purely for explanation (NOTE; just for explanation):" so everyone could understand the numbers were just for explanation.

OK, job1 is now job 1a (client had mistakenly advised the size required). Circumference of job1a=100cm : speed = 240 RPM Starting material is a blank of australian cedar from a tree felled in the spring of 1936. It is 95mm thick and has been cut to a circle ofapproximate radius 16cm. The material shows no cracks or knots and is secured to a 200mm faceplate with four short coarse screws. A shallow fruit bowl is the intended endpoint.

Safe turning, Alan

G'day Arch,

I can't disagree with the points you make. My main reason for posting was to refute any suggestion that speed should always be at the low end for safety. Whilst turning at a speed too fast for a given blank is dangerous, I don't believe turning at half the optimum speed is significantly safer and I know the surface finish will probably be poorer.

I suppose the optimum speed for a very experienced turner will generally be higher than that for a novice. However, the novice should always expect to be able to improve and turn safely at higher speeds as experience is gained.

Read, look and listen but always consider it before adopting. If you feel something is dangerous, don't do it. If you are too cautious with your tool presentation you'll probably achieve exactly you fear!

Safe turn>Hi Alan, Well done, thanks.

You haven't refuted a thing. You have demonstrated that you don't understand the laws of physics, and you have a couple of strange turning ideas beyond that.

As stated, more energy is available to the turning at faster speeds. Only a dull tool cuts better at faster speed, or a tool presented to poke and rip rather than cut and peel . Sharp tools cut well at any speed when properly presented. The quality of the cut determines the quality of the surface left behind. Sharpen your jackknife and whittle a bit and see if your best cut happens at higher speed - or your carving tools. See if they don't out-perform your turning tools even at near zero relative velocity. It's the edge that cuts, and the timber that determines the energy required to do the job. Velocity beyond that required to maintain a cut is unnecessary and increases the potential for dismounts, the distance disconnecting pieces may be thrown, and turning pressure on an improperly presented tool.

Do you find it more difficult to make a cut at the bottom of a bowl than at its edge?

I suspect that safe turning, efficient turning, elegant turning and satisfying turning are all so inexorably bound that most of us just refer to optimum turning.

Carried to an absurdity, which we never do, the safest rpm might approach zero, but it's probably not optimum. A velocity approaching the speed of light might not be optimum either, although I heard that strange things might happen.

Given that there are upper velocity limits to _optimum turning any chunk of wood, are there lower velocity limits to _optimum turning that chunk also?

Can you turn too slow? I had thought so, but then I know a little about the physics that purge, but not much about the laws of physics that explain our world.

C' est la guerre! ;)

Turn to Safety, Arch Fortiter