Sharp Corners

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daves1459
Posts: 93
Joined: Mon Jun 07, 2010 7:58 pm

Sharp Corners

Post by daves1459 » Sun Sep 16, 2018 8:59 pm

Here's a technique that some of you may find useful: For my NYC & HR 999 project I had to make corner braces for the cab walls. Luckily about 85% of the original 1893 drawings exist so, in this case, details of the braces are available. The original braces were an iron casting 1/2" thick that tightly nested into the cab corners. The front braces were fitted to a compound angle corner. My challenge was to emulate those braces in 1.6" to the foot scale rigid enough to clamp for silver soldering. That meant one vertical bend per brace. I decided to use 1/16" 1/2 hard 360 brass. First I tried to simply anneal the brass an bend in a brake with a 1/16" form radius. Three problems here: 1. The outside radius as 1/8" and didn't nest well in the corner. 2. It was difficult to get the bend square with the base. 3. For the compound bend it was difficult to control the distance between bends. For the second try I sawed out and sanded the brace shape for both sides in one piece then milled a 90 degree groove .050" deep at the bend location, formed the bend(by hand). and fixtured to a second piece base then silver soldered the joints. The photos show the finished results. Milling the groove on the bend line then forming solved all three of the first try problems. The .010" thickness after milling gave .010" outer radius to the bend. For the compound bend the bend spacing was .410". Reducing the spacing by .010" to .400" provided a good fit to the corner.

Dave
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BigDumbDinosaur
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Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Sharp Corners

Post by BigDumbDinosaur » Sun Sep 16, 2018 11:32 pm

Pretty cool. I wonder if it would be worth the trouble in the future to make a mold and cast those braces. It seems you had to go through quite a bit of work to get to the finished product.
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daves1459
Posts: 93
Joined: Mon Jun 07, 2010 7:58 pm

Re: Sharp Corners

Post by daves1459 » Mon Sep 17, 2018 8:10 pm

BigDumbDinosaur wrote:
Sun Sep 16, 2018 11:32 pm
Pretty cool. I wonder if it would be worth the trouble in the future to make a mold and cast those braces. It seems you had to go through quite a bit of work to get to the finished product.
Once I figured out the milling of the "V" slot to form the bend it took about two hours to make each corner brace. Having never made any patterns or castings I have no idea about having castings made. Although I would think the 1/16" thickness through out the entire part would cause mold filling problems with out special processing.

I'm concerned that my original purpose for the post has been lost. My purpose was not how to build corner brackets. Rather it was a method to accurately make sharp corner bends in materials more than .010" thick. In rereading my narrative I should have explained the method differently as it would also apply to other metals.

Dave

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