Is there a way to accurately determine this radius?

Ultradog MN

Ultradog MN

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The bottom of this little cabinet is rusted/ rotted very badly.
I would like to cut off the bottom 4" and replace it with new metal.
The corners are radiused and I would like to duplicate them. I first would look for some pipe or tubing the right outside diameter and cut pieces to make the round corners.
If I can't find something off the shelf I will make a die and do it in the press.
The sides of the cabinet are made of 10 ga steel. Yes, heavy stuff.
I could match something after I cut the bottom off but would be glad to have the rounded corners made before I start the project.
I know, I know, it is a fool's errand to try to save this old shaper cabinet but I would like to give it a try.
So how how to measure the radius now?
Thoughts?
Cabinet is upside down in the photo.
 

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Cut it off where the clean metal starts under the door and make something simple to replace it.

Unless you're doing a restoration, then start with a better piece.
 
You're looking for accuracy that you can weld/grind/sand/paint over. You've got "some" wiggle room.

I'd get a compass and start cutting out paper circles until you can make one fit. Once you're dialed in real close, firm cardboard like the back of a notebook, or a cereal box... Then you can carry that off to the sheet metal/scrap yard/pipe store place to see how close you might come.
 
Assuming the radius is a true radius, you can measure the width and the length to find the square.
Then using the Pythagorean theorem you can calculate what the diagonal should be.
Then measure the diagonal and subtract the true diagonal from the answer from the Pythagorean theorem, the divide the difference by 2 to get the radius.

Where x=measured diagonal

EDIT: I think my calculation is wrong.

These directions should be right. Although I like the answer below a lot better.

  1. Measure the length and width of the rectangular object.
  2. Identify one of the rounded corners.
  3. Divide the radius by half, as each corner has the same radius.
  4. Apply the Pythagorean theorem to calculate the radius. The Pythagorean theorem in this context can be expressed as:
    radius^2 = (length/2)^2 + (width/2)^2
    where 'radius' represents the radius of the corner, 'length' is the length of the rectangle, and 'width' is the width of the rectangle.
  5. Solve the equation for 'radius.' Take the square root of both sides of the equation to find the value of the radius.
    radius = sqrt((length/2)^2 + (width/2)^2)
By following these steps, you can determine the radius of the rounded corners on the rectangular object using the Pythagorean theorem.
 
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So, if you have an oxy-acetylene torch you can use that to remove the rotted metal. It's an old trick I learned when restoring my Triumph TR4, put on a big tip and hit the rotted metal quickly. What's bad will go away, leaving decent metal to join to.

If I was doing this I would get a metal strip in whatever gauge you like and attach it around the bottom, bending it to fit as I went. Trying to start with tubing will probably end up with too much effort for what you're trying to accomplish. The torch, and a rosebud tip will make bending to match easy.

You'll have a lip around the bottom , but you could buck some rivets to hold the new piece on giving it a true "period correct" look.

John
 
matthewsx said:
So, if you have an oxy-acetylene torch you can use that to remove the rotted metal. It's an old trick I learned when restoring my Triumph TR4, put on a big tip and hit the rotted metal quickly. What's bad will go away, leaving decent metal to join to.

If I was doing this I would get a metal strip in whatever gauge you like and attach it around the bottom, bending it to fit as I went. Trying to start with tubing will probably end up with too much effort for what you're trying to accomplish. The torch, and a rosebud tip will make bending to match easy.

You'll have a lip around the bottom , but you could buck some rivets to hold the new piece on giving it a true "period correct" look.

John
Click to expand...
Exactly, celebrate the extra details!
 
You can easily and fairly accurately determine the radius with a simple setup. The tools required a an inside square and some pins of knoiwn diameter. I used the center finding attachment from my combination square and my pin gages. Place the square firmly against the radius and slide the pins between the square and the radius. Select a pin that provides a slip fit with no slop. I tried to measure a piece of aluminum round that miked at 1.4695. A .2518" pin slid in while a .2528" was a light interference fit. The radius will be 2.914 x the pin diameter.
Radius Measurement..JPG
Accuracy will be about 1/3rd the accuracy of the pin accuracy with careful measurement and a true square If a square isn't conveniently a hand, one can quickly be made on the mill. Likewise if gage pins aren't available, one can turn suitable test pins to suit.
 
Piece of paper & a dirty straight edge. Or clean straight edge that you've covered in graphite from a pencil. (Edit: hell, if you're "old-school" like my 41yo butt you have a 2mm pencil & the requisite soft 2mm leads laying around & you can just make a rubbing with the lead against both flat surfaces. Think I might be one of the last engineers to be taught manual drafting in college)

Tape the paper down & "roll" the straight edge down onto the each flat.

Remove the paper & place it in a flat surface, then measure the distance between the dirt. That will give you the length of the arc.

Then radius = arc length / (π/2)

(Radius = arc length / swept angle in radians, and 90° = π/2 radians. Assuming, of course, that it's a 90° angle. If it's any other angle just multiply by π/180 to convert to degrees.)



Sent from my SM-N975U using Tapatalk
 
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