Thursday, July 21, 2016

Using A Radius Gauge

I recently managed to buy unused original 1950's stock of a handle that was used on my grandparents kitchen cupboard and I want to be able to reproduce it in the future.  The first step in this process is measure measure measure!

Replicating the exact mechanical operation of the handle isn't that important, what I'm mainly interested in is being able to reproduce it's aesthetics.  The first part I'm measuring is the radius of the beading on the outside of the handle.  One problem, I had no idea how I was going to do it.

Handle
Acetex 44L Handle
My go to tool for something like this would normally be a caliper.  Unfortunately in this case there isn't really anywhere to get the jaws of the calipers around the curve of the beading.  Not even 180 degrees of the beading is available to measure.  So to measure the curve you need to compare it to a set of reference curves.  It turn's out that the tool to use is a radius gauge.  After a longer than expected wait for $10 gauge from eBay, I was able to get started.

Gauge
Radius Gauge
The gauge comes with external and internal feelers with radii ranging from 0.3mm to 1.5mm in 0.1mm increments.  The concave gauges can measure radii where around 70 degrees or more of the total circle is available.

Gauge
Concave Gauges
The convex gauges can measure radii where 180 or less of the circle is available.

Gauge
Convex Gauges
Ideally when using these gauges you hold them against the surface you want to measure, hold everything up to the light and look for light leakage around the edges.  To take photos I've just put them on the table and placed the gauge against the handle.  You can see that the 1.2mm gauge is slightly too small.

Gauge
1.2mm Gauge
It's hard to tell from the below photo, but the 1.3mm gauge is almost perfect.  A little to big. but close.  This now gives a range for the radius of 1.2-1.3 mm.

Gauge
1.3mm Gauge
It should be said that I haven't verified these gauges against a standard, but I plan to take a few measurements in different ways and use them to build up confidence in the profile I measure.  From what I've been able to tell there are 4 beads that make up the central reeding.  They are evenly spaced and there is 7mm between the centres of the outer ones.  The radii of the beads is as seen before about 1.25mm.  The shoulders of the profile are made of two sections.  Coming from the beading is a flat section that I've eyeballed to be about 5 degrees less than horizontal.  I've tested the flatness of this section by placing a razor blade against it and checking for light leakage.  After this section is an unknown curve that is tangent to the other section but stops abruptly at the edge.

Schematic
Handle Profile
Still a lot of measuring to do. No idea how to do, but I'll figure it out.

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