Extending the range of calipers

[volodar]

¨The sagitta, ED (marked S in the diagram) is the distance from the chord to the circle's circumference¨

Marv, in your diagram, the sagitta, marked S is the line segment EC, not ED (ED is half the chord BD, not the sagitta). Too lazy to check the rest of the math (too late, too much wine), so assume r and d expressions - and results correct within YMMV.

[mklotz]

¨The sagitta, ED (marked S in the diagram) is the distance from the chord to the circle's circumference¨

Marv, in your diagram, the sagitta, marked S is the line segment EC, not ED (ED is half the chord BD, not the sagitta). Too lazy to check the rest of the math (too late, too much wine), so assume r and d expressions - and results correct within YMMV.

Thanks for pointing it out. I must have been half asleep when I proofread that. It's fixed now.

[Toolmaker51]

I'm going to experiment with this, using parallel-jawed calipers. It shouldn't make a difference mathematically, but mechanically I wonder how relieved [pointed] outside jaws of a normal caliper interface in comparison.
I've detected variance before relying on Starrett master verniers as final word over digitals, those instances when only a caliper was available. It's far easier detecting proper contact perpendicular to cylinders or flat parallel sides, vice a narrow 'bite' of angled models. Overall, spherical contact is most effective

I'll perch caliper's spine on a pair of 1-2-3 blocks to establish that plane, easy part. The calculation could take me a week.
I need to figure a large radius, seat of a missing bandsaw table pivot, a 36" machine. It will take Tony Foale's version to measure. It's about 5"Ø, and dang near 180°. Have plenty of tooling balls, but no two in same configuration.

In lieu of that, will try a good-sized smaller cylinder and 3 gauge pins, starting with two of same size, third as a feeler. I expect greasing them, and a little manipulation so they 'find' centerline axis. Am I on the right track? Sounds like easy trig for a solution.
What attracts me here, the weight of sample will assure appropriate contact, quite close to the real thing, minus actual table. It is too big for casual handling, at about 34" square and 2.5" thick. Once the new cylinder is made, milling a flat, bolt holes and dowels will finish it off.

[tonyfoale]

I'll perch caliper's spine on a pair of 1-2-3 blocks to establish that plane, easy part. The calculation could take me a week.
I need to figure a large radius, seat of a missing bandsaw table pivot, a 36" machine. It will take Tony Foale's version to measure. It's about 5"Ø, and dang near 180°.

What I made is pretty simple and very quick to make. You don't even have to do any calcs. I uploaded a bit of software to do the heavy lifting.

[Toolmaker51]

What I made is pretty simple and very quick to make. You don't even have to do any calcs. I uploaded a bit of software to do the heavy lifting.

Absolutely intend duplicating your device. I'll cut a paper template to estimate spread of contacts and length needed for indicator stem, though using a depth mic in a reamed hole might help. When I depth radii, a ball or rod makes an ideal seat.
As goal's equivalent of a slip fit, with the saw and running lathe separated by 70 miles, certainty is an issue. There's ways to address a few thou' under by shimming. I'd trust blue spring stock to not gall under load. Over-size not so easily, unless I hold off separating work piece from spud being chucked. The shoe, being so 180° will reject less than correct fit.

Now, as to your software capable of heavy lifting; has it a winch attached?
Lol.

PS to interested readers. All my projects work under same restrictions, need here - power there. And 'need here' are the projects getting my electricity in doors; 3ph 440v. I had caplock mistakenly down for that, which also related in #PH$$).
Lol again.

[tonyfoale]

Now, as to your software capable of heavy lifting; has it a winch attached?
Lol.

I think that I put a link to it in my original post or else it is in the PDF that is mentioned in the original post. If you cannot find it, tell me and I'll check where it is.
I am off to bed now, it's late as I have just finished watching the delayed qualifying at COTA in TX. The old fella did well.

[Paul Alciatore]

Marv, That is a great method. I just have to play with it.

One additional source of error that I see is the fact that most caliper jaws are very narrow as well as having a sharp point. So there is very little area that bears on the part being measured and they can easily make a dent of unknown depth in it. A gentle technique is definitely in order.

[tonyfoale]

Here is a link to my calculation software, it is an unrestricted download.
RadiusGauge software

It will work equally well with Marv's method.

Click image for full size version.

To use with Marv's method.
1. Chose "External" for type of measurement.
2. "Ball diameter' set to zero.
3. "Probe spacing" is the caliper reading.
4. "Gauge displacement" is the height (length) of the caliper jaws.

As a test I used Marv's figures, which were:
<<
For the bench block pictured, I made the following measurements...
c = 2.859 (no. 3 in my list)
s = 1.159 (no. 4 in my list)

and computed a diameter of 2.922.
>>

The software came up with a radius of 1.461 which is the same as Marv's result.

[Jon]

Congratulations mklotz - your Circular Object Radius Computation Method is the Homemade Tool of the Week!

This win is particularly notable because, as mklotz mentions, it advances the same principle seen in a previous award-winning tool by tonyfoale. It will be interesting to see if someone can iterate upon it further.

Some nice entries this week:

Bandsaw Floating Jaws by rgsparber
Lever Feed Mini Lathe Tailstock by threesixesinarow
Brake System Bleeder by The Aussie Shed
Sheetmetal Punch by janochek
Bandsaw Vise Screw Jack by rgsparber
Jigsaw Cutting Station by Junkyard
Threaded Rod Cutting Fixture by rgsparber
Scratch Stock Beading Tool by Mikhandmaker
Lathe Centering Tool by Vyacheslav.Nevolya
Axle Stand by PowerMk
Lathe Split Nut by bobneumann
Trailer Axle Ends by Menga
Solid State Engine Design by TilenThaler
Battery Spot Welder by mariost
Kant Twist Clamp by Kwandotechnic
Center Drilling Fixture by kess
Cultivator by GabrielR
Drill Press Lift System by tonyfoale
Slag Chipping Hammer by Raytonian


mklotz - we've added your tool entry to our All Homemade Tool of the Week winners post. And, you'll be receiving a $25 online gift card, in your choice of Amazon, PayPal, or bitcoin. Please PM me your current email address and gift card choice and I'll get it sent over right away.

This is your 13th Homemade Tool of the Week win. Nice work

Here are all of your winning homemade tools:

Bore Measurement Gauge by mklotz

tags: gauge, dial indicator, measurement

Miniature Indexing Faceplate by mklotz

tags: indexing unit, collet

Pocket Tools by mklotz

tags: magnet, measurement

Bench Block Clamping Setup by mklotz

tags: clamp, V-block

Model Cement Mixer by mklotz

tags: mixer, cement

Sphere Drilling Jig by mklotz

tags: jig, drilling

Countersink Gage by mklotz

tags: measurement

Bench Motor by mklotz

tags: chuck, motor

Lathe Height Gauge by mklotz

tags: lathe, height gauge

Sensitive Drilling Platform by mklotz

tags: drilling

Miniature Nut Driver by mklotz

tags: nut driver

Pantograph by mklotz

tags: pantograph

Circular Object Radius Computation by mklotz

tags: caliper, measurement

[old_toolmaker]

This method works well, but the accuracy is dependent upon the condition of the caliper jaw tips. If they are worn from use, accuracy, will be compromised accordingly.
Back in my early years before the electronic calculator, we solved these trigonometric issues via long hand with pencil and paper.