# Corner rounding bit-quality of cut



## Walt (Nov 20, 2012)

I recently purchased an Interstate brand 3/16" radius corner rounding bit from Enco for use in making my bike lights out of aluminum square bar stock. I need to round the corners off. My first bike light built this way
	

		
			
		

		
	



	

		
			
		

		
	
 would be painful to land on! 

After playing with it for a while, I'm satisfied that I'll never get a really good looking cut out of this tool.

What brand should I invest in for a high-quality cut: a smooth radius and the smallest visible line at the tangents?

Walt


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## Hawkeye (Nov 20, 2012)

Some of us have had good results using ordinary router corner rounding bits, in both HSS and carbide. The key is to run them at the speeds and feed rates required for the metal being machined, not wood-cutting speeds.

I've used them as fixed tooling in the metal lathe as well.


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## kd4gij (Nov 21, 2012)

You need to take light cuts with a corner rounding bit don't try to take all at once. I usley take .005 passes. take .005 down then .005 in on the next pass.


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## xalky (Nov 21, 2012)

Hawkeye said:


> Some of us have had good results using ordinary router corner rounding bits, in both HSS and carbide. The key is to run them at the speeds and feed rates required for the metal being machined, not wood-cutting speeds.
> 
> I've used them as fixed tooling in the metal lathe as well.


 That was gonna be my reccomendation too. They work well on aluminum.


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## Tony Wells (Nov 21, 2012)

Unless your machine just can't handle it, there's no reason to take it all at 0.005/pass. Leave 0.010/0.015 for finishing and make it in two passes; one rough and one finish. That small a radius should run at a pretty high speed. Climb cut the finish, with just a little drag on the stops if it tries to grab. You should be able to get an acceptable finish. Perhaps you could run a vibratory finishing operation. 

Oh, and BTW, don't try to take it to a absolute tangent position. Leave a little on both axes. Only 0.002 or so, and it won't leave an undercut line, and the step will not be visible. If you don't want or can't do the vibratory, a little Scotchbrite will work wonders. Or even an quick acid etch will give a uniform mat finish. Just be sure to neutralize it if you do the acid treatment.


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## OakRidgeGuy (Nov 21, 2012)

I love Scotchbrite pads! Thanks for asking this question, fore now I don't have to ask about it!


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## Walt (Nov 25, 2012)

Tony Wells said:


> Unless your machine just can't handle it, there's no reason to take it all at 0.005/pass. Leave 0.010/0.015 for finishing and make it in two passes; one rough and one finish. That small a radius should run at a pretty high speed. Climb cut the finish, with just a little drag on the stops if it tries to grab. You should be able to get an acceptable finish. Perhaps you could run a vibratory finishing operation.
> 
> Oh, and BTW, don't try to take it to a absolute tangent position. Leave a little on both axes. Only 0.002 or so, and it won't leave an undercut line, and the step will not be visible. If you don't want or can't do the vibratory, a little Scotchbrite will work wonders. Or even an quick acid etch will give a uniform mat finish. Just be sure to neutralize it if you do the acid treatment.



Thanks to all.

I had to look up what climb cutting is, then found this thread:

http://www.hobby-machinist.com/showthread.php/9691-Climb-Milling-I-Knew-Better

Walt


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