How Do You Make Perfectly Round Corners?

[silverwingit]

I don't know how well I can describe this, but, I draw the corner, then use my round knife and rock it forward a little, move the leather into it rock forward again and keep going around until done, like you're just taking off a little chip at a time. It amazes me how a bunch of small straight cuts makes a smooth corner. Leather is soft, so when you stick the knife in and try to just cut around the corner you stretch it out of shape, even if it's 10 oz. firm leather. If you cut a little at a time, you're pushing down and not out. Like the difference between using a rolling blade and a drywall knife on chap leather. Maybe that's almost clear.

Kevin

IMHO, Kevin has it right. Unless you are cutting the exact same radii all the time (and how boring would that be?), use what a mathematician would call a piecewise linear approach like Kevin describes. It works with all curves, not just circular ones, and not just ones that cut a 90 degree corner.

Scribe your curve (a 90 degree circular arc in this instance) however you do it. Then start where the curve first breaks from the adjacent straight line and angle your knife (any good, sharp knife, not just a round knife, though that works best for me, too) to make a very fine cut at a very oblique (slight) angle from the straight line, shaving off just a sliver of leather. Then repeat, advancing the cut's position to be just slightly ahead of the previous one and at just a slightly less oblique angle so as to shave off a similar sliver as the last cut delivered. As you repeat this process a smooth curve will gradually appear just along the curve you've scribed, ideally removing the scribe mark itself. With experience you realize that you needn't completely remove each sliver and can use the rocking motion that Kevin described.

It's easy and takes only a moment or two and again, it works with ~all~ outside curves. Inside curves are another story.

Michelle

Edited August 31, 2013 by silverwingit

[Northmount]

Here is another option I just found http://www.allimageprinting.com/corner_cutter.html corner cutting press and pliers type with dies.

Tom

[silverwingit]

Sheesh, Tom, I just realized I have one of those somewhere. I'll have to give it a try sometime.

[Crimson Hides]

I recently order a set of corner cutter from Elfita

Very happy with their service.

http://beavertools.co.kr/xe/index.php?mid=knife&document_srl=527

[FlHobbyist]

My strap end cutters came in from China and they look like they are indeed around 90 degrees. In the next day or two, I'm going to cut out a couple of small pieces with one of them, and I'll post the results good or bad.

The one I bought (though the listing will disappear in 90 days or so. ): http://www.ebay.com/...984.m1497.l2649

The term most of the ebay sellers are using to describe them is "English Semi Point". Though it is very important to check the picture and make sure the cutters are 90 degrees and not 180 degrees. Many of the sellers are not particularly good at English since it is apparently a second language for them.

Edited September 12, 2013 by FlHobbyist

[FlHobbyist]

As promised here is a picture of some corners I cut with the Chinese punch. It was sharper than I thought it would be, albeit the leather is pretty thin. I rubbed the punch in paraffin just to make it go smoother.

[KandB]

FIHobbyist thanks for sharing - I'm buying a set now!

[strudell]

KandB did you get the punches and have an equally positive experience with them? What was the shipping time to CA?

I'm considering grabbing the set myself.

Shane

[Palermo]

Use geometry.. Straight lines make a perfect circle. This is my method

Straight cuts

Edited February 5, 2014 by Palermo

[FlHobbyist]

Use geometry.. Straight lines make a perfect circle. This is my method

Straight cuts

Wouldn't one need an infinite number of straight lines to form a perfect circle? I understand how to make a circle with a compass, though I don't know how to make one from geometry alone, other than making a polygon with an infinite number of sides. Edited February 5, 2014 by FlHobbyist