Thread: How to measure the angle on a short bevel

Shine a laser on it and measure the angle of the light reflected from the bevel you're interested in. If you can measure it with a caliper you can use trigonometry.

I doubt the angle is that critical for a fabric cutter so a caliper and a bit of trig should do it.

Yes, trig. Don't want to insult your intelligence Ern, but if trig isn't a strong point for you then:

Sounds like the two bevels form an isosceles triangle, and your saying the bevel is 2mm long - I take it that is the ground edge that is 2mm long. So measure the thickness of the cutter, with a vernier or micrometer.

Let's call the angle "A" (and note that the included angle would be 2A). The Sine of A = ½ the thickness of the cutter divided by 2 (because the bevel is 2mm).
So if the cutter is 0.75mm thick then Sin(A) = 0.75*½ then divided by 2,
so Sin(A) = 0.1875.

Trail and error in Excel tells me that the angle would be close enough to 10.5° in that case, so the included angle would be 21° (so I'm thinking that the cutter may be a little thinner than 0.75mm because 21° sounds a bit high? - maybe not)

Paint the bevel with a black felt marker as often as is necessary to reveal the work.
Leonard Lee was fond of saying that the bevel angle needed to be supported by the mass of steel behind it.

This thing is a fabric cutter?
I cannot imagine a total included bevel angle of more than 10-12 degrees. That's five or six per side.

I do some analog photography and need a Nikon rotary wheel paper cutter in the darkroom.
I think I got it right, 10 degrees total included bevel angle.
Basically flat on the strop.

Yes, 10-12 sounds more like it (20 is a meat cleaver )

Another way to find the angle.

Flat magnet, digital camera and a photo editing program.

Thanks gents.
I remember falling at the T hurdle back in school, so your worked eg is welcome FF.

At under $8 a piece for new ones, is it even worth the effort?
https://www.amazon.com.au/Fiskars-Ro...R4JV99JKEXYDE6

$1.60 each if you want to go generic
https://www.amazon.com.au/Hakkin-Rotary-Compatible-Fiskars-Truecut/dp/B01LS0INM2/ref=sr_1_1?ie=UTF8&qid=1522756402&sr=8-1&keywords=fiskars+rotary+blade

My partner likes the ones that cost $10 each.

I like the challenge.

If I can meet it I'll have saved her $30 and given myself some satisfaction.

Is that alright by you elanjacobs?

do you have a fine enough stone?

a coarse stone (and I'm sorry but don't know what in this context would be considered coarse) will result in an edge that is grabby in some fabrics.

Originally Posted by FenceFurniture

Yes, trig. Don't want to insult your intelligence Ern, but if trig isn't a strong point for you then:

Sounds like the two bevels form an isosceles triangle, and your saying the bevel is 2mm long - I take it that is the ground edge that is 2mm long. So measure the thickness of the cutter, with a vernier or micrometer.

Let's call the angle "A" (and note that the included angle would be 2A). The Sine of A = ½ the thickness of the cutter divided by 2 (because the bevel is 2mm).
So if the cutter is 0.75mm thick then Sin(A) = 0.75*½ then divided by 2,
so Sin(A) = 0.1875.

Trail and error in Excel tells me that the angle would be close enough to 10.5° in that case, so the included angle would be 21° (so I'm thinking that the cutter may be a little thinner than 0.75mm because 21° sounds a bit high? - maybe not)

So, the cutter is 0.3mm thick, the bevel c. 1.5mm long. Sin(A) is then 0.1.

Now what are you doing in Excel?

6°, or 12° included.

So in one cell I put =0.15/1.5 which shows 0.1

In cell A1 I put my estimate of the angle, say starting at 10.

in cell A2 put =sin(radians(A1)) (degrees have to be converted to radians for excel to be able to work them)

Then just play with the value in A1 until it gives a close match to the 0.1 cell.

Originally Posted by rsser

Is that alright by you elanjacobs?

"I like the challenge" would have sufficed. No need to get snarky about it.

Originally Posted by FenceFurniture

6°, or 12° included.

So in one cell I put =0.15/1.5 which shows 0.1

In cell A1 I put my estimate of the angle, say starting at 10.

in cell A2 put =sin(radians(A1)) (degrees have to be converted to radians for excel to be able to work them)

Then just play with the value in A1 until it gives a close match to the 0.1 cell.

scratching my head

In cell A1 type "=.15/1.5"
In cell A2 enter "=asin(A1)*180/pi()"
the result 5.7 is half the included angle