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How sharp can you dress a wheel corner?

Cole2534

Diamond
Joined
Sep 10, 2010
Location
Oklahoma City, OK
Was doing a little grinding over the weekend where I was looking for a sharp inside corner. The best I got was about a .015r. The wheel is a white Norton 46j, iirc. This is close enough to stone in, so I quit there.

Was I not dressing properly or is there a physical limit based on wheel construction?
 
Practically speaking, that's about it. You can do a bit better with the ruby red wheels, about 100-120 and a hard bond. It's nearly always faster to undercut the corner, it removes the corner radius issue.
 
The corner radius relates to the grit size. Somewhere I have a formula. Sorry I don't know how to format this better from my Excel tab. From a Radiac grinding wheel catalog:

Radiac Catalog, Pacific Catalog
gritparticlemin radiusmax radiusmin finishmax finish
in
typical460.020.02none32none
540.017.017.022032
finer600.016.016.0201520
70
800.0105.010.0201218
90
1000.0085.008.0101015
1200.0056.005.008812
1500.0048.004.006610
180
2200.0026.003.00556
 
Conrod is spot on with those numbers in post #4.
The 46 wheel has a grit diameter of .014 so getting a .020r is in the right ballpark.
60gt =.010 dia grit
100gt =.005 "
120 gt = .004 "
It is darn near impossible to get a dead square inside corner so a good part design will have a mating part with an outside corner bevel.
I have grease penciled up the part face. Come in with a hand feel rub a 100 or 120 gt wheel back away. 003.. then rub me grease and down grind to just rub my grease on the down feed touch.
Likely to get a .007.008 radius in that corner.
Then I would dress a 45* in my wheel and touch the inside radius and take ,004 to .006 down feed There might be a slight undercut then but one could not see it by eye.
I have also used a tool bit as a corner scraper and after just the grind with a 100 or120gt , I would give a few scrapes with my hand scraper.

We used to have grease pencils that were real grease in black and red, the grease would smear and one could get .0001 or so match. The new ceramic pencils are not that good.
 
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Was trying to recreate the case in the center. My tool made the ones on both sides.

Certainly not perfect, but I think they'll cycle.

The radius on the extractor rim is what I was trying to avoid. But it's a blow-back action, the extractor is probably more about making sure the shell properly hits the ejector more than about pulling the case from chamber.
 

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With a.014dia grit in a 46 wheel one might think a .007 radius would be possible with a supper hard 46 wheel. I used to dress both the OD and the face of a wheel needing a small radius inside corner.

Dressing into/towards the corner needing the small radius helps. The orange wheels used to be the choice for a small radius and they could get closer to grit size so a 120gt might get down to .005r. Often a shop might have a 220 and a 600 orange wheel for a sharp inside corner. The 220 with a .0025 grit and the 600 with a.0007 grit.
But you can only grind the corner because trying to grind the wheel width, or on the part face likely will burn the part.
 
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Was trying to recreate the case in the center. My tool made the ones on both sides.

Certainly not perfect, but I think they'll cycle.

The radius on the extractor rim is what I was trying to avoid. But it's a blow-back action, the extractor is probably more about making sure the shell properly hits the ejector more than about pulling the case from chamber.

Ooo, now I'm intrigued. What caliber is it? Carbine or pistol?
 
.351wsl for a 1907.

One of my buddies loves off the wall cartridges. He found another more popular case that could be modified to fit the .351 role, so I ground the lathe tool mentioned in the OP for him to prep the cases.
 








 
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