What tool do I need?

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Sep 26, 2010
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I want to create a 7/8" diameter flat bottomed recess in a thick piece of aluminum. The intent is to use it on top of a floating nut as gun slide support.

Thanks in advance for your help!
 
If you have a friend with a mill or lathe get them to help otherwise make sure you have a spare piece of aluminium. If you have a piece of 6061 T4 you should be able to slowly cut a hole with a good forstner bit and a lot of oil or water. You will need a drill press set to its slowest speed. You could buy a flat bottomed end mill but for what a 3/4" end mill will cost you could get it cut at a machine shop. If you have that cheap soft stuff from a home store, well lets just say you probably wont get the results you want. Unhardened or unhardenable aluminium is sticky and will stick to the cutting edge of your bit and you will get tearing and lots of heat. Have a small stainless toothbrush like you get at Harbor Freight and pull the bit or mill out every 10 sec and brush the cutting edge off.
 
How flat and how deep? It sounds like you could use a 7/8 wood bit. the cheap two flute kind. There will be a smaller center hole for the point. Drill a pilot hole and if your needs aren't too deep for the recess I think it would work, maybe have to dull two of the drills.
 
You could probably get away with an end mill bit in a variable speed router. The guys cutting 80% AR lowers are using those.
 
Another way to do it is drill a hole all the way through, then fix a plug in to the depth you need. Or take a piece of aluminum the depth of the hole, drill a 7/8 hole in it and fix that to the main plate.
 
Thanks guys. It is T6061 so I will try a forstner bit with oil. I only need to cut about 1/8" deep to give enough depth to hold the nut in place.
 
Originally Posted by 2015_PSD
Thanks guys. It is T6061 so I will try a forstner bit with oil. I only need to cut about 1/8" deep to give enough depth to hold the nut in place.



Even better that its a shallow hole. the deeper , the more the shavings stick to the sides of the forstner bit and mess up the sides of the hole.
 
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