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Hemispherical concave shapes -or- rivet dies
February 28, 2011
7:53 pm
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Steve H
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I had a good friend blow me away yesterday with a poor-man's solution to making a damn-near perfect hemi-shaped concave hole.

I'm making some new rivet dies and while I do have a radius cutter, I found that it can take more time to use it than to just rough out a blank and then grind with an abrasive ball on a die grinder.

Denny Jensen came over, took one look at it and made in 5 minutes a great tool from an old bearing; Grind the face of the bearing on a belt sander to sharpen the edges of the race, press fit (or weld) a handle on the inner race and then force it into the cavity with plenty of oil.

Remarkably the inaccuracies of my prior cut were quickly realized by seeing the where the race was indeed cutting down the ridges. It took maybe only 10 minutes to remove enough material to satisfy even the most cue-ball concious.

The race was slightly undersized but as you rotate it, you could definately hit all the spots needed. All in all an amazing back-yard solution~:p

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February 28, 2011
10:26 pm
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david hyde
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Neat trick cybo.

Till now I've always just roughed out on the lathe then forced an emery flap wheel into it(on a 1/4" shaft) whilst constantly turning it around and around in all ways. Eventually the "wheel" become become convex spherical and it sorta grinds smooth to a kinda hemisphere.

I did seem to recall reading that the makers of concave mirrors for telesecsopes used to do something with grinding one thing into another. Apparantly if done correctly this will (and apparrantly can only end with) a perfect hemisphere ..... I think!

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March 1, 2011
2:19 am
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Steve H
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Very sweet, Dave. Color coded to boot! One of my favorite dishing shapes is the concave half of a ball joint from a model-T ford. Nice to have many different radii to choose from.

They only remember you when you SCREW UP~!!!

March 1, 2011
2:43 am
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Larry L
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So I dont quite follow Steve, are you holding your tool just by hand? is the bearing itself still spinning on the shaft? ( it looks like you just stuck a rod in an old bearing... Could you snap a close up of the sharpend side of the bearing/tool to show us how it looks?

Whatever you are, be a good one.
Abraham Lincoln

March 1, 2011
2:51 am
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Steve H
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That's exactly all it is, Larry. A rod on an old bearing. I didn't get it either but the belt sanded side of the race becomes ALOT of cutting edge. Yes, the bearing does still rotate, although by the time the chips got all caught up in there, it was starting to turn with more difficulty. Still, if you rotate it just a little, you have a new cutting edge.

You could mount it in a holder but it really worked best if you kinda wallowed it around in there. I'll try to get a close-up here tonite.

Speaking of- what rockwell are bearing races?? mid 60's?? Hard enough to cut normalized O-1 it was~

They only remember you when you SCREW UP~!!!

March 1, 2011
3:02 am
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Lewis
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I was afraid that was what you were doing. One of those things where it comes out round no matter what you do. I do like lathes.

I've always spelled it "wallered" but maybe that's because I learned it in Tennessee.

March 1, 2011
3:06 am
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Larry L
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Ive wallered plenty of things... Most of which would have been better off un-wallered..

Whatever you are, be a good one.
Abraham Lincoln

March 2, 2011
1:51 am
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Lewis
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Larry L;8038 wrote: Ive wallered plenty of things... Most of which would have been better off un-wallered..

Yup, it's usually the diagnosis, not the cure. 😉

March 7, 2011
6:05 pm
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Steve H
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They only remember you when you SCREW UP~!!!

March 7, 2011
6:26 pm
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David Browne
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Great stuff Steve. I had the same questions Larry mentioned. On wallering: I've wallered stuff too, but never on purpose. I'm just not that confident with my wallering skills at present.

I want to see more of that little brick-up forge you've got there...
-DB

March 7, 2011
6:42 pm
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Steve H
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Dave- I get laughs when people see that little forge. The fire-chamber is 4"X 10"L.
Honestly, it does probably 80% of what I need and if I need more, I have two others- one from a BBQ bottle, the third from a oxy cyl which I've used less and less it seems.

Someone mentioned alot of what we do is on the end of a bar; finials and such. As long as that's the case, I'm fine. While I've always admired big clamshell forges and such, I'm such a stinge on fuel that I'll stick with it for now.

Despite my liner being partially melted out, it still was capable of these forge welds last night:

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March 7, 2011
11:08 pm
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David Browne
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Steve, really...I'm not laughing...let's see it. :stomp:

I've got what I consider a small forge and a medium forge. I use the small one a lot more than the medium one. I still need a micro... and a large forge to complete the set. I'm thinking about a brick-up that can be configured quickly. shit...or skip the micro and get an induction heater...:banghead:
-DB

March 9, 2011
2:49 am
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Lewis
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Oooh, we can still forge weld with induction, right?

That does sound good.

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