how I measure across a large diameter

I can't recall where I saw this, but hopefully it helps someone in the future...

using a framing square, and a sliding square, I can measure the diameter of things accurate enough to do belt length calculations.
refer to the 2 example photos showing the method.....
use a sliding square and the inside edge of the framing square as legs of a caliper - keep the sliding square in proper contact with the other leg of the framing square.Attachment 33786
read off the value from the inner scale (or use another measuring tool to get the value)
Attachment 33787

and here the method is used for measuring the diameter of a lathe countershaft cone pulley...
Attachment 33788
you can see the use of a spring clamp to hold everything in place to get a better measurement

FWIW, I used a similar method to measure the headstock pulley diameters on the lathe, but instead of a framing square, I used another sliding square, set at 200mm, then simply subtracted the value on the ruler from 200mm to get the true pulley diameter. (no photos, sorry)

I've had 2 separate projects in just the last 10 days – each requiring a large diameter cutout, to match their equally large diameter inserts. But determining the diameter of these two different tapered objects – at the desired point of insertion – would've been a lot easier, if I'd have thought to use that neat little trick. Thanks for posting.
:beer:

I use this

Attachment 33866

Then this

Attachment 33867

And divide by this

Attachment 33868

Quote:

---

Originally Posted by high-side

I use this

---

Me too. Trouble is, the twine stretches – and wants to roll – on a tapered cylindrical surface. And the thought of pie gets you completely distracted – going for the ice cream. :beer:

Egad, you have invented calipers! Great idea to combine with the adjustable try square, easy and accurate!
Tell me, does your avatar ever request you to kiss his shiny metal #ss ? Could be he is related to Bender!

<!-- BEGIN /var/www/html/homemadetools/protected/modules/zeus/views/tool/postUpdate.php -->
Thanks desbromilow! We've added your Large Diameter Measuring Method to our Measuring and Marking category,
as well as to your builder page: desbromilow's Homemade Tools. Your receipt:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="https://www.homemadetools.net/homemade-large-diameter-measuring-method"> <img src="/uploads/230046/homemade-large-diameter-measuring-method.jpeg"/> </a> </div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="https://www.homemadetools.net/homemade-large-diameter-measuring-method">Large Diameter Measuring Method</a> <span> by <a href="https://www.homemadetools.net/builder/desbromilow">desbromilow</a></span> </div> <div class="tags">tags: <a href='https://www.homemadetools.net/tag/square'>square</a>, <a href='https://www.homemadetools.net/tag/measurement'>measurement</a> </div> </div> </div> </div>
<!-- END /var/www/html/homemadetools/protected/modules/zeus/views/tool/postUpdate.php -->

Quote:

---

Originally Posted by Howder1951

Egad, you have invented calipers! Great idea to combine with the adjustable try square, easy and accurate!
Tell me, does your avatar ever request you to kiss his shiny metal #ss ? Could be he is related to Bender!

---

When I built Bender, I deliberately made his posterior dull just to shut him up!! :)

<video controls autoplay loop>
<source src="https://diqn32j8nouaz.cloudfront.net/pizza_crust_pi_measurement.mp4" type="video/mp4">
Your browser does not support the video tag.
</video>

Pies to demonstrate PI