Thread: homemade cole jaws

Originally Posted by Skew ChiDAMN!!

When Cole jaws break it's simply a case of the moment of inertia requiring a centripetal force to be applied that is greater than the tensile strength of the material.

Otherwise known as centrifugal force

Originally Posted by Jack E

No, Cole jaws breaking is the result of centripetal force being overcome by centrifugal force.

Whether you believe in centrifugal force or not is irrelevant.

It exists,

You can't believe in centripetal force and not centrifugal force as one can't exist without the other.

In fact, you can't "believe" in either, they are proven forces not open to conjecture.

One of the first things taught in Basic Physics or Vector Maths? "Centrifugal Force is a fallacy."

But it's easy to see why the fallacy persists. It's a "lie for children" like explaining a rainbow by comparing it to light refracted through a prism.

Er, just to diverge from this learned debate ...

Joe, thanks for sharing that experience.

Yes, the mag piece was by Betty.

I've been nagging her about getting current AWTs online for purchase. By the time I pay for an individual hardcopy to be posted to Oz it's about 3x the cover price in AUD. But Betty says it's two years away at least.

Originally Posted by Skew ChiDAMN!!

One of the first things taught in Basic Physics or Vector Maths? "Centrifugal Force is a fallacy."

But it's easy to see why the fallacy persists. It's a "lie for children" like explaining a rainbow by comparing it to light refracted through a prism.

Silly me, disagreeing with science.

Perhaps I should become religious so I can learn how the world really works

Well, shucks! Now that the pot has been well and truly stirred, why would I want to sit it out?

"Centrifugal" force served well enough as a perception of reality. But with the space age, and recognition of vector analysis, the mathematics didn't add up. "Centripetal" force was needed in the opposite direction. Then things got anal.

As to the Cole jaws, I haven't done any experiments, but I think the offender is cantilever action on the thin parts at the attachment point, produced by pushing the tool parallel to the lathe axis. And this is where there's the least amount of material, further reduced by attachment holes. Spinning effects probably don't have as much influence. Good timber needs to be about double the thickness of an aluminium pattern for equivalent stiffness; MDF maybe more.

How about photocopies, Ern? For personal use only, of course. Absent that, Google is your friend.

Cheers,
Joe

My guess is that AWT is pretty uncommon downunder Joe. I've not heard any ref to it among forumites or the turning networks in my city. And my local libraries are poor for any kind of WW mag.

Originally Posted by Skew ChiDAMN!!

Not quite...

...There's no other force being applied beyond what YOU are applying. To say that the car is exerting Centrifugal Force back on your finger is wrong... that's like saying a table is exerting force on your finger when you press down on it.

....

Well, I did not intend to buy into the debate, but.....

If there were no opposing force from the table to your finger, your finger would go right through the table and create a hole in it or break the table! In fact, every force has one or more opposing force/s to it.

Regards
Andy

Originally Posted by rsser

My guess is that AWT is pretty uncommon downunder Joe. I've not heard any ref to it among forumites or the turning networks in my city. And my local libraries are poor for any kind of WW mag.

The Public Libraries around here don't stock much on Woodturning either. Apart from the odd Raffan and I'm told they're constantly disappearing off the shelves and may not be restocked in future.

You're buying yours from O/S?

Originally Posted by aak

If there were no opposing force from the table to your finger, your finger would go right through the table and create a hole in it or break the table! In fact, every force has one or more opposing force/s to it.

You're mistaking inertial resistance for force. A force, any force, takes energy to apply. The table isn't using energy... it's simply xferring the force you're applying through the legs into the floor, thus into the Earth. In theory (if you could apply a big enough force) you can move the Earth this way but in reality the table-top or legs would fail under waaay less force than that.

And it's every action has an equal and opposite reaction. Again, a different thing.

Originally Posted by Skew ChiDAMN!!

.....

You're mistaking inertial resistance for force. A force, any force, takes energy to apply. The table isn't using energy... it's simply xferring the force you're applying through the legs into the floor, thus into the Earth. In theory (if you could apply a big enough force) you can move the Earth this way but in reality the table-top or legs would fail under waaay less force than that.

And it's every action has an equal and opposite reaction. Again, a different thing.

When you stop pushing the table top (eg: your arm gets tired) and it flexes back towards to you, That is not force in your opinion, or is it?

By the way, it was you who used the table top example to prove your point. Hence I quoted it. As far as the Earth is concerned, let us not complicate the issue with it. However, I agree that the table top and its legs would fail.

Regards
Andy

....well, I can't resist getting into this one

..........gravity sucks

I thought it pulled?

....

Skew, I've just been ordering the odd AWT from AAW.

Did once have a sub to the UK mag Woodturning, but found later that The Woodsmith brings them in and you can sub with Len.

The local newsagent has the US Woodturning Design at about $17 which is a bit rich.

Originally Posted by Skew ChiDAMN!!

MDF!?!?

PLY!

Or perspex or ally or... almost anything 'cept MDF or chipboard or particleboard! [shudder]

Don't forget that there's not only centripetal/inertial forces at play (there's no such bogeyman as "centrifugal force" ) but there's also lateral forces pushing the jaws towards towards the headstock. eg. any tailstock pressure on the bowl or any lateral pressure you're applying to the tool, etc.

And with cole jaws being as "long" as they are, that's a lot of leverage. It doesn't take much to snap a 1" wide strip of MDF and the jaws aren't that much wider at the chuck end...

MDF is sawdust and glue. Thats it , nothing more.
Its just cardboard !
There is no fiber running along to it to give it strength.
And natural timber , although it has running fibres , has grain , along which it can split.

When making Cole jaws with wood , the only type is plywood .
And suitable ply at that .
Good quality ply of a decent thickness . 10-12 mil. min. , for small jaws , 18-22 for larger ones .

And remember , no matter what the material , keep the speed down.

600 rpm is the recommended max.speed .

Cole Jaws are intended as a light finishing attachment only.

Originally Posted by rsser

Skew, I've just been ordering the odd AWT from AAW.

Did once have a sub to the UK mag Woodturning, but found later that The Woodsmith brings them in and you can sub with Len.

The local newsagent has the US Woodturning Design at about $17 which is a bit rich.

I used to buy UKWT from Len but somehow it seems to me to be 10 years behind the times. Not that that's a bad thing, but I usually only read mags looking for new ideas or concepts.

haven't seen Woodturning Design... might have to peruse your library at the next Ernffest.

Oh... and as for Centrifugal Force, this might explain it better: http://en.wikipedia.org/wiki/Fictitious_forces

I am going to try 3/4 birch ply. Silly question I am sure...perspex? Different name from something I am familiar with?