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Extra large commercial calipier

D

Dennis Weiner

Joined
Jan 3, 2012
Messages
460
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387
Location
New City, NY
Anybody know of a commercially manufactured deep hollowing caliper. I need to measure vase wall thickness on pieces that exceed 28 inches. I own one that can measure 24 inches but it is not narrow enough for vases. I am trying to avoid making one.
 
In prior years I have turned some large diameter forms and I used (2) framing squares bolted together which could be bolted tight to provide a measured distance between the opposing tips of the squares. This works for measuring the outside diameter, for your application if you can find a flat metal circle you can cut it in half and drill a hole in each end and bolt them together. If you can find a proper thickness of aluminum sheet you could mount it on a face plate and use a lathe tool to cut a proper sized flat ring on your wood lathe and fabricate your large caliper. With one sheet of metal you could make a whole set of calipers in different sizes from the rings you cut.
 
Dennis Weiner said:
Anybody know of a commercially manufactured deep hollowing caliper. I need to measure vase wall thickness on pieces that exceed 28 inches. I own one that can measure 24 inches but it is not narrow enough for vases. I am trying to avoid making one.
Click to expand...
Dennis Weiner said:
Anybody know of a commercially manufactured deep hollowing caliper. I need to measure vase wall thickness on pieces that exceed 28 inches. I own one that can measure 24 inches but it is not narrow enough for vases. I am trying to avoid making one.
Click to expand...

You might want to consider side-stepping the issue by investing in a boring bar system with laser or camera guidance.
 
I would agree with both (Dennis and John) of your recommendations if my wall thickness target were 1/4 inch or greater. When my wall is about the same size as the diameter of the laser, I would want to physically confirm thickness. So in my application, I feel the necessity to measure. In some 25 x 8 vases, I may rough the outer shape, hollow, then refine the outside. I may do this in a series of 3 to 6 inch steps until the thickness is reached via internal light color method not laser jig methods. I can not through out my old fashion Calipiers just yet.


So it looks like I’ll have to make my own.
 
Has anyone ever looked into the digital ultrasonic thickness gauges that are available for different industries for measuring the thickness of films, surfaces, materials, vessel walls, etc. Some of these tools are reasonably priced while other ones are extremely expensive based on the required accuracy of measuring task. Usually a small electronic sensor is ran across the surface of the material being measured and a digital display indicates the thickness in a digital display format. We use these types of hand held sensors at several facilities I work at to measure material walls to provide a heads up to replace these systems before they fail.
 
It may not be appropriate to your situation, but it is worth pointing out that either the laser guided bar or the camera guided bar can be re-purposed to act as a very accurate thickness measuring tool. Simply stop the lathe, recalibrate the laser or camera, and move the bar to the position to be measured. At that point the turning can be rotated by hand to see if there is any variation around the circumference. Stopping the lathe eliminates any blurring or change of calibration of the measurement caused by vibration.

There are some important considerations. First, the height of the boring bar supports must be such that the cutting tool is very close to center height. Second, the laser or the camera must be mounted such that they are facing straight down to avoid any parallax error. (With a camera system, small errors in mounting can be calibrated out ahead of time by viewing a target that is directly below the camera and marking that point on the monitor screen.) When calibrating the system, the tip of the tool will be set to that point.

Further comments: With proper choice and adjustment of the laser, you can obtain a very small, but visible dot. In the case of the camera system, it is possible to get considerable magnification of the image if desired. Depending on the cutting tool used, it may be desirable to substitute a different shape of probe for the measurements.
 
Dennis J Gooding said:
It may not be appropriate to your situation, but it is worth pointing out that either the laser guided bar or the camera guided bar can be re-purposed to act as a very accurate thickness measuring tool. Simply stop the lathe, recalibrate the laser or camera, and move the bar to the position to be measured. At that point the turning can be rotated by hand to see if there is any variation around the circumference. Stopping the lathe eliminates any blurring or change of calibration of the measurement caused by vibration.

There are some important considerations. First, the height of the boring bar supports must be such that the cutting tool is very close to center height. Second, the laser or the camera must be mounted such that they are facing straight down to avoid any parallax error. (With a camera system, small errors in mounting can be calibrated out ahead of time by viewing a target that is directly below the camera and marking that point on the monitor screen.) When calibrating the system, the tip of the tool will be set to that point.

Further comments: With proper choice and adjustment of the laser, you can obtain a very small, but visible dot. In the case of the camera system, it is possible to get considerable magnification of the image if desired. Depending on the cutting tool used, it may be desirable to substitute a different shape of probe for the measurements.
Click to expand...

DennisG:

Thanks for that detailed explanation. I recently positioned my boring bar laser to the cutter as you described to determine the bottom of a form. Then proceeded to part it off at a precise point. The laser used as a measurement device works great. In fact, a caliper could not do that with the piece on the lathe. It’s just faster for me to use the old fashion caliper to spot check on certain vessel walls. Laser adjustments take too much time for me to fiddle with when I am in the process of hollowing via the internal lighting - wood color method to determine wall thickness.
A camera system for a 28-30 inch deep vase would be interesting.

Regards,
DennisW
 
You might want to consider Cutter Vision. It's dead on accurate and the software is able to draw a precise wall thickness. And then you can zoom in for a magnified view. The neat thing about it is that you have real time measurements. With a caliper you measure and then cut in the blind and then measure again and on and on.
 
Adjusting the laser is why I started building my own visualizer. You never have to stop to readjust anything just keep on cutting and clearing swarf. A friend who is an electronic engineer tried the Hall effect diodes and several other electronic or magnetic wall thickness devices. The tolerance of when it's on and off was just to great for the accuracy we need. worked pretty well for 1/4 to 3/8" but when you get down to 2mm or 3mm it was just too sloppy. I would love to see the one they are using to measure guitars. They are usually in the 3mm range.
 
The laser hollowing systems are very accurate if set up correctly and ironically that is also a liability. The problem I have with lasers when hollowing tall thin walled vases, especially when they are green, is they can become slightly elliptical as you approach final thickness from drying and wood shrinkage. The laser, regardless of the dot size, is measuring the high point of the elliptical path that appears circular to the human eye while the lathe is spinning. Targeting 1/8" - 1/16" wall thickness is a risky task using a laser system because your vision is being fooled. I don't really know if or when the wood will start to physically change shape in the hollowing process. While taking the risk, I have gone through some pieces using lasers attempting this thickness.
The internal light system works for me obtaining 1/16th thickness. You learn what shade of light is working to achieve the thickness for each piece you do. The moisture content and wood species all influence color. I do not cut, measure, cut and so forth. I may want to measure thickness with a caliper.
@john lucas:
I use my laser for most of my work.
1. Do you think the camera system is less risky in achieving 1/16 thickness that the laser system?
2. When using the Jamison swivel and hunter cutter how many times do you change the angle of the cuter in a bulbous piece.
 
Using a light to judge thickness works very well, but at the same time it can fool you if you don't pay close attention to the change in grain orientation as you progress through a curve.

If you have wood that is warping, you can use Cutter Vision as a thickness gauge by stopping the lathe and slowly rotating the piece by hand to see amount of warp as well as wall thickness and you can magnify the view. And unlike the Visualizer and homemade clones, the cutter is an actual photograph and not a hand sketched outline. Theoretically, you could have a wall thickness down to the camera pixel resolution if you could find wood from the fabled Delirium genus.¹

I don't own Cutter Vision, but I have watched demonstrations at SWAT. It is rather pricey, but it is the "cutting edge" state of the art

A question that I have about turning green wood very thin is knowing that super thin walls are going to continue moving after you have finished turning what is the main objective? Light weight? Minimum Warping? Uniform wall thickness? The challenge?

My experience is once something has been turned very thin, there is no going back later to do any refining of the shape.

¹ The fabled Delirium tree which is yet to be found and studied reportedly doesn't move, warp, flex, nor shrink.
 
Bill Boehme said:
A question that I have about turning green wood very thin is knowing that super thin walls are going to continue moving after you have finished turning what is the main objective? Light weight? Minimum Warping? Uniform wall thickness? The challenge?
Click to expand...
According to David Ellsworth his reason for such thin walls is to let the vessel warp into its own organic contours impossible to acheive otherwise. If I ever got the skill to turn that thin that would be the foremost reason in my mind to do it.
 
Bill Boehme said:
Using a light to judge thickness works very well, but at the same time it can fool you if you don't pay close attention to the change in grain orientation as you progress through a curve.

If you have wood that is warping, you can use Cutter Vision as a thickness gauge by stopping the lathe and slowly rotating the piece by hand to see amount of warp as well as wall thickness and you can magnify the view. And unlike the Visualizer and homemade clones, the cutter is an actual photograph and not a hand sketched outline. Theoretically, you could have a wall thickness down to the camera pixel resolution if you could find wood from the fabled Delirium genus.¹

I don't own Cutter Vision, but I have watched demonstrations at SWAT. It is rather pricey, but it is the "cutting edge" state of the art

A question that I have about turning green wood very thin is knowing that super thin walls are going to continue moving after you have finished turning what is the main objective? Light weight? Minimum Warping? Uniform wall thickness? The challenge?

My experience is once something has been turned very thin, there is no going back later to do any refining of the shape.

¹ The fabled Delirium tree which is yet to be found and studied reportedly doesn't move, warp, flex, nor shrink.
Click to expand...
It maybe interesting to note, that while using the light-thickness method and nearing final wall thickness the shadow of the cuter outline can be seen and used as a visual aid during the final finishing cuts. No need to use any other aid to view the position of the cuter. Of course this is only true if the wood spieces, grain orientation, moisture content and form shape all cooperate in wood translucency. You gotta pick your battles with this method. For me, Knot free/straight grain wood works best.

I can stop the lathe and rotate the piece and view different shades of light when the piece is going out of round. When turning the lathe on, I see the illusion of combined light colors blended as one. In this case, being fooled actually helps me see the average wall thickness.

============================================================================
I’m not certain if your question highlighted above in blue was rhetorical? I turn very thin as a want-need. I-need to turn very thin because I want to. Others have artistic goals. How does a pierced piece look with a 1/4 inch wall vs 1/16 wall? Artistic Creativity may find license “ in warpness” and non uniform thickness. I must caution you about the Woodturning Police. :)

I’m having difficulty with changing text color. Not sure if it’s my iPod or forium software so I will post other thoughts later.
 
Several years ago I watched Johannes Michelsen demonstrate turning a hat about 1/16" thin using a light to judge thickness. It was impressive to see a real master work. He gave me the hat for letting him use my lathe. I definitely got the better part of that deal.

I wasn't trying to be a woodturning policeman. I turn very thin basket illusion pieces.
 
Just a question from the naive--why is it so important to hollow a vase or other object so thinly--I really want to know?
 
It's not. John Jordan once said, turn something thin and then get over it. Most vessels should be turned thin enough to feel good in the hands for the size they are, and thin enough to dry and not crack. Of course that was before piercing. Piercing is very hard to do on woods 1/4" thick. Very slow and burns up your bits. They need to be 1/8" or less and often thinner looks better after the piercing. For vessels that aren't pierced too thin can sometimes be a dissadvantage. I had one piece that I turned extremely thin, as much about showing off skill as anything. I was proud of it. People hated it. It felt too fragile. Of course that's in my market. Obviously pierced work actually is fragile and it sells well in other venues.
 
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