[How do I?] Radius gauge for 'large' values of radius

[THX-1138]

[First post, please be kind. ]

I have a 25 piece radius gauge set from the Little Machine Shop; ¹/64" to ¹⁷/64" by ¹/64", ⁹/32" to ½" by ¹/32".

Which has been great.. except now I want to verify the outside Z-axis curvature of an outer bearing race roughly 4¾" in (outside) diameter. It looks as though the curvature, if continued, would make a sphere. But I don't know what I'd use for a 2⅜" radius gauge to verify it with precision.

[New here, so I don't think I can post an image.]

Oddly, this wasn't for a press-in or inset bearing, so the outer surface isn't parallel to the axis. And I haven't seen the inner race for more than forty years; this was a scrap I picked up working at Fafnir-Textron's bearing factory.

I could try to verify the sphere premise by making a pseudo-gauge for the radius in the XY plane and see if it matches the curve on the Z axis, but it wouldn't be very precise.

Any suggestions? Thanks!

 

[mmcmdl]

Make a few more posts and then post a pic ! We might have a better idea as to what you're needing .

 

[jwmelvin]

Print with computer, glue to card stock, and trim carefully?

 

[woodchucker]

welcome to HM.
I have wanted a set of larger radius gauges a few times as well. My set goes up to 1" if I remember.

I have used compasses and drawn my radiuses. Now that I have a rotary table, I can make my own gauge next time.

 

[Aukai]

Welcome, nobody bites here, so don't be worried about that.

 

[RJSakowski]

I have made a radius gage similar to that used by lens makers. It consists of three points in a straight line which are made to contact the surface of the curve. The center point is midway between the to outer points and the distance of the outer points from the connecting bar is equally set . Once the gage is fit to the curve, the difference in height of the center point and the outer points is measured.

From there, the radius of the curve can be determined with a little math. An easier way is to draw it up in a CAD program and let the program do the math.

 

[RJSakowski]

For maximum accuracy, you want the distance to be as large as possible and still contact the curve but you should keep the contact points within a quarter circle.

 

[francist]

I made this inexpensive circle cutter for trimming paper clock dials. Length of key stock for the beam, blocks of wood to fit, and a few bits and bobs to fill in the rest. Once established the radius is fixed using two set screws, the white porcelain knob just provides a handy place to hold. Will easily cut card stock using a standard X-Acto blade.

 

[pontiac428]

[First post, please be kind. ]

But I don't know what I'd use for a 2⅜" radius gauge to verify it with precision.

Any suggestions? Thanks!

A compass does the job nicely. And they call it a primitive device!

 

[C-Bag]

It's probably not accurate enough, but sheet metal guys use this for finding out the radius of like a panel. Then you can select the proper english wheel anvil or planishing anvil. I bought one of the cheaper plastic ones and it has served me well.