how I measure across a large diameter

[desbromilow]

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.
read off the value from the inner scale (or use another measuring tool to get the value)


and here the method is used for measuring the diameter of a lathe countershaft cone pulley...

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)

[Scotsman Hosie]

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.

[high-side]

I use this



Then this



And divide by this

[Scotsman Hosie]

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.

[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!

[DIYer]

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:

Large Diameter Measuring Method by desbromilow

tags: square, measurement

[desbromilow]

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!!

[Jon]

[jdurand]

Pies to demonstrate PI