Thickness gauge

[Frank&Earnest]

After discussing the benefit of laser jigs for estimating the thickness of the wall of vessels while turning, I have done a bit of research on the existing mechanical gauges on the market.

Could not find much, but they all seem to be based on setting a fixed thickness between the measuring point and the cutter, which has substantial problems well known by the hollowing experts. The current way of attempting to mitigate these problems is to make the measuring point flexible so it can move sideways if there is a catch.

I am thinking of addressing the problem by changing the way of looking at the thickness measurement: make it variable but constantly monitored. This allows a design similar to a car's shock absorber, which should avoid the dangers involved in turning with a fixed point in the way.

By looking at the lines engraved on the measuring rod while the cutter proceeds along the inside wall, the turner can skim the surface at the best cutting depth and, if necessary, come back for further passes until the desired thickness is achieved.

Two questions:
- has this been tried before? I have not found any precedent, but that does not mean that there isn't any;
- any problems beside those of the fixed point solutions I should be aware of before building a prototype?

Any advice gratefully accepted.

[RETIRED]

- any problems beside those of the fixed point solutions I should be aware of before building a prototype?





The force comes from above and it will not react quick enough.

149278

[Frank&Earnest]

Thanks. This raises more questions... :-

1 - Does this mean that it has been tried and it did not work or are you expecting that on the basis of your expertise?

2 - By force do you mean the pressure exerted vertically by the rotation of the timber against the point of the rod?

3 - Is the force exerted horizontally by pushing the cutter forward likely to compound or counteract 2?

Could be a one word answer to each question, but please allow for my thickness... :wink:

[Tim the Timber Turner]

I agree with .:2tsup:

This is a disaster waiting to happen.:C

It wouldn't react quick enough.

It could pull the cuter into the work and cause an uncontrollable dig in.

At the very minimum you would need a rotating ball in contact with the outside of the vessel.

A laser is the way to go.

If you want a 10mm wall thickness then you offset the laser 10mm and when the pointer drops off the outside of the vessel, Bingo you have 10mm. couldn't be easier, safe, very accurate (within 0.5mm with care), very simple, not much skill required to operate.

I like to work on the KISS principle, never make things more complicated than they need to be.

My 2 bobs worth.

Cheers

Tim

[RETIRED]

What Tim said.

[Frank&Earnest]

Fair enough. I can't see the mechanical reasons for your assessment, but I accept your experienced opinion.

[NeilS]

I complete the outside of my pieces (to polished stage) before working on the inside.

Putting aside any judgments on whether it would work safely or not, any mechanical contact device, even a rubber covered wheel, is going to mark the outside surface.

I hate having to go back and to repair what has already been completed.

So, don't think this device would suit the way I work.

.

[Frank&Earnest]

Yes, I think this is the crux of the matter: conceptually I see the forces involved to be much weaker than what you (plural) know by experience they are in reality. It's all academic anyway, given that the laser system has proven to be better. How long did it take for this innovation to be accepted? :D

[RETIRED]

A nano second.:D

[joe greiner]

A nano second.:D
A little longer than that, I think. A predecessor consisted of a piece of spring steel flexed below the equator, and carried by an outrigger attached to the rig. When the designated thickness had been achieved, the steel finger flipped up to the equator. Both it, and the laser, as well as your gauge, suffer from a parallax effect in sloping sides: the thickness measured is along a radius, not the thickness itself. When you set the laser, you can compensate for various positions along the cross section, including undercut rims.

Best of all, the laser doesn't mark the outside, so there's no need for refinishing.

Cheers,
Joe

[Skew ChiDAMN!!]

Both it, and the laser, as well as your gauge, suffer from a parallax effect in sloping sides: the thickness measured is along a radius, not the thickness itself. When you set the laser, you can compensate for various positions along the cross section, including undercut rims.

I'm waiting - although not with bated breath :U - for the day when I can buy a laser that creates an adjustable radius circle rather than a single dot.

With the cutting tip at the origin, you could use the appropriate tangent of the circle as your guide, thus avoiding parallax errors. (Well... to a large degree, anyway. The cutting edge isn't a point so there's always going to be some error, but it can be reduced significantly.)

Might need more than a 5MW laser to generate something visible, though. :think:

[Frank&Earnest]

This is another problem that I tend to dismiss, theoretically, because the cutting rim of a round cutter and the diametre of the spherical end of the measuring rod are circles and their tangent point is a point *. If these points are both on the symmetry axis of the measuring rod, to ensure even thickness that axis must remain at all times perpendicular to the external profile of the turned object. Because the measuring rod is perpendicular to the axis of the hollowing tool, provided there is sufficient distance between the point of the cutter and the shaft and between the shaft and the holder (parallel to it) of the measuring rod, keeping it in the correct position depends only on the skill of the user. Visual control would be much easier looking at a straight rod than at a speck of light. Or you could install a pair of sonars to constantly monitor perpendicularity...:D


* which is also the reason why I am perplexed about 's comment: the force is not applied to a point above the rod that would create a lever effect counteracting the movement of the spring.

[Ed Reiss]

if you guys persist in keeping up with all this space rocket enginneering talk, I'll just have to mosey over to the neighborhood pub till it's out of your system. BYE:q:D:D

[RETIRED]

Ed, I don't blame you.:-

Frank. You have a rotating piece of timber. The force is downward. A mechanical pointer if aligned with the cutting tip will also not allow the tip to cut because the cutter must precede the pointer thereby putting all measurements up the creek without a paddle or canoe..

Think about it. Nuff said from me too.

[hughie]

T'm waiting - although not with bated breath :U - for the day when I can buy a laser that creates an adjustable radius circle rather than a single dot.

Might be closer than you think :U there are focusable lasers on the market

YouTube - Focusable 100mw titanium green laser pointers

[RETIRED]

Might be closer than you think :U there are focusable lasers on the market

YouTube - Focusable 100mw titanium green laser pointers (http://www.youtube.com/watch?v=5XBXJ5qR_9I)Hmmm. You could dry your timber at the same time as turning it. :cool::D

[joe greiner]

* which is also the reason why I am perplexed about 's comment: the force is not applied to a point above the rod that would create a lever effect counteracting the movement of the spring.

The downward force isn't exactly where drew it, but the effect is the same, i.e. it produces a lever effect and a bias on the gauge. Consider when you make pencil marks for laying out a spindle shape, and spin the piece to trace them all around for visibility when turning, by pressing the pencil against the piece. The force you feel in your fingers is the same to be felt by the gauge. Similar with the older spring steel doodads.

And it ain't rocket science, Ed.

Some brain surgeons gathered to discuss a challenging operation. After they found a simple solution, one of them said, "Well, it isn't exactly brain surgery, y'know. . . Oh, yeah, I guess it is.":D

Cheers,
Joe

[Frank&Earnest]

The downward force isn't exactly where drew it, but the effect is the same, i.e. it produces a lever effect and a bias on the gauge. Consider when you make pencil marks for laying out a spindle shape, and spin the piece to trace them all around for visibility when turning, by pressing the pencil against the piece. The force you feel in your fingers is the same to be felt by the gauge. Similar with the older spring steel doodads.

And it ain't rocket science, Ed.

Some brain surgeons gathered to discuss a challenging operation. After they found a simple solution, one of them said, "Well, it isn't exactly brain surgery, y'know. . . Oh, yeah, I guess it is.":D

Cheers,
Joe

Yep, it ain't. :D I am aware of what you say, Joe, but have you tried marking with the pencil held radially and noticed the difference? :wink:

Anyway, I am not a physicist and I can't talk by experience, so I am not in a position to make any forceful assertions. I will shut up now and if one day I'll have the will and the time to actually make one for the hell of it, I'll find out the hard way. :)

I know enough about geometry to be comfortable with what I said about consistent thickness, though.

[Ed Reiss]

Might be closer than you think :U there are focusable lasers on the market



hmmmmm...coming in the near future? - The Ci Laser Easy Rougher

[Ed Reiss]

The downward force isn't exactly where drew it, but the effect is the same, i.e. it produces a lever effect and a bias on the gauge. Consider when you make pencil marks for laying out a spindle shape, and spin the piece to trace them all around for visibility when turning, by pressing the pencil against the piece. The force you feel in your fingers is the same to be felt by the gauge. Similar with the older spring steel doodads.

And it ain't rocket science, Ed.

Some brain surgeons gathered to discuss a challenging operation. After they found a simple solution, one of them said, "Well, it isn't exactly brain surgery, y'know. . . Oh, yeah, I guess it is.":D

Cheers,
Joe

...for some of us it is :doh::D