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PaulStrickland

Member
I'm either over-thinking this, or I'm about to save several thousand dollars.

I'm on the second practice kit and have zero metal experience outside of practice kit #1. One thing I'm noticing is that deburred holes on thin metal take on a starburst appearance - is this normal, or do I need to renew my deburring tool (that I bought used)?

hole.gif
 
Whoa- basically you have ended up machine countersinking the hole. The ridges are from the bit "chattering" in the hole. I think you are pressing way too hard with the deburring bit. I'm also guessing you are letting it turn too long as well. Just let the bit sit in the hole without much pressure and let it turn 2, 3 at the most full revolutions and then move on. I have a hex extension on mine that I chuck in a Black and Decker cordless screwdriver. A quick blip of the trigger gives me 2 turns which is enough.
 
Also, was the hole dimpled before you tried to debur? If so, debur first, then dimple. Dimpling a non-deburred hole can lead to cracks.
 
Good decision to ask. Those results are not acceptable. Looks like 1) you're removing way too much material, thereby forming a countersink and enlarging the hole to a razor edge, and 2) the "starburst" appearance you're talking about is due to bit chatter. Both problems can significantly weaken the hole and make it prone to cracking.

Your countersink bit may be part of the problem (unsuitable type of bit, or old and dull, etc.). But technique is definitely an issue. By looking at your results I'm guessing you're using some kind of power tool? and just going way, way too deep.

I generally use one of these countersink bits (http://www.averytools.com/pc-430-43-hss-three-flute-burring-cutter---100.aspx) on an 8" shank extension, and just turn it by hand. It generally doesn't take more than one or two revolutions of the tool, and very little pressure. The objective is only to remove the sharp burr that forms from drilling, NOT to countersink the hole.
 
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Paul, As you say, another thing that will help is a sharp deburring tool - I would get rid of that used item, and then follow the other posters' advice.

Regards, Merrill
 
Thanks for the help!

On the dimpled side - that's just what it looked like post-dimple.

I was pressing hard and I was rotating a lot more than twice - I wanted to "see" a result I suppose. I just tried a light touch with a couple of rotations and it seems smooth. Here's the new result, post-dimple:

newhole.gif
 
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