Caliper Question (Possibly stupid!)

[David DeCristoforo]

I've been looking at calipers for measuring hollow form walls. I have several of the stainless steel ones and they work well for many things. But I've been trying to work through small openings and the steel calipers do not work in many situations. I keep coming across the ones used by David Ellsworth which are simply bent wire affairs that can easily be made for just about any configuration. The only thing is, I'm unclear on how these are used. The steel ones have two ends and you can read the thickness on one end which is outside of the form. But the wire ones just look like modified "C" shapes. Could someone clarify how to use these?

Thanx
DD

[Harry Robinette]

DD
Try the one's from Veritas tools I got mine from Packard I believe. I use them for HF,bowls,plates about everything I turn can be done with them. They work backwards the spin nut keeps them set and you can open them up to position them and they go back to the size you measured. I love mine.

[Jeffrey J Smith]

The Ellsworth calipers are bent to a known distance between ends, then measure the distance from the outside end to the surface of the HF - the difference is the thickness. Simple, but I find the Veritas calipers to be a little easier. I've got the big ones and they work great on most forms, but if you've got a really long shoulder on a southwest style form, it can be difficult to measure the wall below the shoulder - at the widest part of the HF and below. Ellsworth's idea works great there 'cause you can just bend up whatever you need.

[Ted Calver]

Make sure the points of the wire 'C' are perpendicular to the wall and lightly press the interior point against the form. The gap between the other point and the exterior wall is used to measure the uniformity of the wall thickness. If that gap remains the same at all points on the wall then the thickness is uniform. Variations in the gap reveal variations in wall thickness. Measure the gap between points before inserting in the form and you can then measure the distance from the outside point to the exterior wall and subtract that from the gap measurement to get wall thickness.

[Don Stephan]

This was a GREAT question, a new concept to store in my foggy mind.

[mark ravensdale]

I agree with Harry, the veritas calipers are very good, over the years I have accumulated many different types of calipers but it is my veritas I reach for 95 percent of the time when wanting to check wall thickness on a hollow form, there only down point is the price!!!

[Thom Sturgill]

I made and have been using Ellsworth's design since taking a hands on-with him. I like it much better than any of the other calipers I have used as I use 3/16 wire with rounded ends and it will not scratch the outside finished work. One end is kept straight while the other end curves. by selecting which end you place inside you can check just about any shape and its easy to 'eyeball' the thickness.

[Richard Madden]

For small work like ornaments where measuring through a small (1/2") hole, I use a couple of pieces of wire coat hanger bent to different configurations. The ends are bent leaving a 1" gap. When one end is inside the ornament and the measurement on the outside from wire to wood is 13/16" to 7/8" It's time to stop hollowing.

[David DeCristoforo]

Ah HA! That's the missing piece... measuring! How quaint... I thought I would be done with measuring when I quit building other people's cabinets for them. Now Thom's suggestion... eyeballing... that's for me. So thanks all for clearing this up. I'm off now to my wife's closet to steal some coat hangers...

PS This will also be a great way to locate those pesky little interior ridges and mark their exact location on the outside of the form where I can zero in on their exact location with the laser cannon. Sweet!

[Mike Cruz]

DD, my smart butt response is simply, "Why do you care beyond about 3"...the length of a finger.;) And if you are talking about small openings where only the skinniest of fingers can fit in the holes, who cares?!?!"

But the reality is, I get where you are coming from and why you are asking. Hope you got/get your answer.

[David DeCristoforo]

That's a fair point, Mike. iI's become pretty obvious that the only people who really worry about it are other turners. People I see who are just there to see the work are not that concerned about weather or not the inside is smooth. Especially when there is a small opening. But other turners? Holy cow! It's almost amusing to see a group of white haired old men squinting into tiny holes with flashlights trying to see the inside of a hollow form! Maybe we should start using those little cameras on flex shafts to scan the insides!

In truth, I would like to know that my pieces would stand up to this kind of close inspection. I'm not fanatic about it and normally do not even apply finish to the insides since my main finish these days is wax. I'm just after an even wall thickness and a reasonably "clean" surface.

[Mike Cruz]

Oh, David, I "get" why you asked and why/that you want to know...don't get me wrong! I'm just sayin' that we only need to know about a certain distance in... I've got an idea for you. Somehow place a cutout of a scantily clad pin up on the bottom of the inside of each of your turnings. That way, when turners inspect the inside of your turnings, the walls will NOT be the focus of their interest! :D

[Richard Jones]

"Maybe we should start using those little cameras on flex shafts to scan the insides! "

You mean you don't? :eek:

[Thomas Canfield]

DD, my smart butt response is simply, "Why do you care beyond about 3"...the length of a finger.;) And if you are talking about small openings where only the skinniest of fingers can fit in the holes, who cares?!?!"

But the reality is, I get where you are coming from and why you are asking. Hope you got/get your answer.

I always thought that you need to leave the bottom part of a hollow form "thicker" to add weight for stability. At least that has been my story and I'm sticking to it. I do use the Veritas and found them helpful on both hollow form and also bowls. I won the 17" model when I only had a mini lathe and wondered about trading it, but now with a Powermatic 3520 is is not large enough at times.

[David DeCristoforo]

"I...thought that you need to leave the bottom part of a hollow form "thicker" to add weight..."

I usually try to leave the bottom of the form at about 3/8". But I try for even wall thickness down to that point.

BTW, my wife caught me in the act of purloining the coat hangers. When I told her what I wanted them for, she said I should have just asked for them and that she would have given them to me gladly! Can you believe that? What a great woman! No wonder I have stayed with her for forty years now... what that gal puts up with...!

[Faust M. Ruggiero]

David, My biggest problem with measuring wall thickness when working through a small hole, 1/2" or so is the area from the edge of the hols to the side. I made a bunch of calipers that work for me. They are just two separate bent wires but they do the job. When the calipers are closed the bottom of the wires match in length. A 1/8" wall thickness will cause one wire to stick out 1/8" beyond than the mating wire. I filed little grooves in the wires to tell me they are both on the same plane. The picture should give you the idea. If not, let me know. I make several sizes ranging from 1/2" wide to 2" wide. As I need to measure farther from the hole I move to a wider gauge.
faust248007

[Mike Cruz]

Faust, your T square is out of whack...might want to get that checked. :D

Those are way cool calipers! Not that I would know how to do it, but if they were made out of flat stock, I would imagine that keeping them on the same plane would be easier... Thanks for posting those, Faust!