Seeking suggestions for something akin to a bowl

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ChrisNM
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Joined: Fri May 11, 2012 10:25 pm

Seeking suggestions for something akin to a bowl

Post by ChrisNM » Fri May 11, 2012 11:14 pm

Greetings everyone,

I have a peculiar project in mind that requires a convex (circular) "dish" shape to be cut into a 2" x 2" square piece of mild steel, about an inch thick. The convex part needs to be roughly 1-1/2" in diameter, about 1/2" deep at the center.

I've never tackled something like this before, so this ought a be quite an adventure. :lol:

I have a lathe with a 4-jaw chuck at my disposal, along with a non-CNC mill/drill. Don't have much to invest in tooling right now, kinda hoping there's a "simple" method available.

Ideas, anyone?

Thanks ahead of time for your thoughts.
Chris

kd4gij
Posts: 40
Joined: Sat Apr 09, 2011 1:55 pm

Re: Seeking suggestions for something akin to a bowl

Post by kd4gij » Fri May 11, 2012 11:51 pm

A radius turning tool would be the best way to cut that. There is serveral plans out there to build one if you don't have one.
G0704 mill
Craftsman/atlas 12x36 lathe
4x6 vert-horz.band saw, Craftsman 113 table saw,and radial arm saw.

Harold_V
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Re: Seeking suggestions for something akin to a bowl

Post by Harold_V » Sat May 12, 2012 3:32 am

ChrisNM wrote:I have a peculiar project in mind that requires a convex (circular) "dish" shape to be cut into a 2" x 2" square piece of mild steel, about an inch thick. The convex part needs to be roughly 1-1/2" in diameter, about 1/2" deep at the center.
I'm getting mixed signals from your comment. You suggest that the center would be ½" deep, which implies a concave surface, not a convex surface. Which one of us is confused? It makes a little difference in how you might approach the problem.

Welcome to the forum!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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wsippola
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Location: Trenton, On

Re: Seeking suggestions for something akin to a bowl

Post by wsippola » Sat May 12, 2012 8:24 am

Assuming you mean concave, a google search for finding the radius for a given chord and height gave the formula r= (4hxh + CxC) / 8h, where h is the .5", and C is the 1.5". Assuming I did the math right, I get a radius of .8125" required to give the dimensions you are looking for.

I doubt you have a 1.625 ballmill or other specialty tooling. What you could try, depending on your lathe, is to set the tool tip to be .812" from the pivot point on your compound slide. Slacken off the compound clamping nuts enough that you can swing it, and use the topslide as a radius turner.

You'll have to figure out if there will be clearance between the compound and the chuck to make this feasible, and how to set your tool. Good luck, and welcome to the board,

Wayne

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refinery mike
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Re: Seeking suggestions for something akin to a bowl

Post by refinery mike » Sat May 12, 2012 8:44 am

Wayne, i have been calculating that radius and when i got ready to post it you had beet me to it. SPEEDY!

ChrisNM
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Joined: Fri May 11, 2012 10:25 pm

Re: Seeking suggestions for something akin to a bowl

Post by ChrisNM » Sat May 12, 2012 11:17 am

Hi everyone,

Thanks for the welcome, it's appreciated.

Oops! Jeez! Yes, I did mean conCAVE, not conVEX! Silly me... okay, so my excuse was that it was late when I posted that message last night (yeah, yeah... excuses, excuses... :( )

Wayne, your calculations seem to be just about right -- 1-1/2 to 1/58" would do the trick for the diameter. You're right, I don't have a ball mill that big (and I bet one that size would be pricey, but I haven't checked yet). The technique you mentioned sounds kinda scary! But as I said, I've never even thought about turning a concave surface before, so this will definitely be a new experience for me.

kd4gij -- 73's to ya -- I'm off to google 'radius turning tool'!

Thanks for the suggestions thus far....
Chris

Edit: I just googled radius turning tool -- that seems to be for convex (ball end) shaping. Also checked McMaster, they have a 1-1/2" ball end mill for about $100 -- hmmm -- that's why I was wondering if there was a way to do it on the lathe...

Torch
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Location: Muskoka

Re: Seeking suggestions for something akin to a bowl

Post by Torch » Sat May 12, 2012 3:06 pm

One of my very first projects was the construction of a ballturning toolpost. I shamelessly stole the design from Steve Bedair's website, with some modifications to suit. It was easy to fab a reversed tool holder to cut coves and concaves.
ballturning_reversed-800.jpg
(Please ignore the finish -- like I said, it was one of my first projects. But it works, and would do your "bowl".

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Lew Hartswick
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Location: Albuquerque NM

Re: Seeking suggestions for something akin to a bowl

Post by Lew Hartswick » Sat May 12, 2012 4:54 pm

To the OP. If youre anywhere near Albuquerque stop in and I'll do it for you. I have access to several
radius turners, a commercial one and one I designed and built.
That is why everyone should put a "where you are" in their data.
...Lew...

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