Question about counterboring aluminum using a drill press and a router bit?

tominboise said:
They've all been drilled at 17/64". I would need a counter bore with an OD of 0.750 and a 17/64 pilot. Where would I find such a tool?
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I would drill the holes out as deep as I could with a 3/4" drill to provide a pocket for a 3/4" end mill or router bit. Position the work under the end mill mounted in the drill press, using the drilled hole as a centering guide and clamp the work securely to the table. Run the drill press as slow as possible to minimize chatter and slowly lower the end mill until you reach your required depth.

Run a practice piece on some scrap first to get the process down pat. You should be able to get reasonably clean counterbores. I have had good luck with Yonico router bits. https://www.amazon.com/Yonico-14955...nico&s=power-hand-tools&sr=1-20&ts_id=3116511
 
Maybe drill the concentric bores with drills then use a dremel guide to flatten the outter bore.

-drill most of the way down with the larger diameter drill
-drill the center hole using the first drill's tip bevel to get the center drilling aligned concentrically
-Use the dremel with collar guide to flatten out the bottom of the first drilling

dremel guide.jpg
 
Larry$ said:
A router bit will drill your counter bore just fine. Clamp the work so it doesn't grab. Run the bit as fast as you can. Use some WD40 so you don't get chip welding.
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Maybe it will, maybe it won't. The problem with router bits in a drill press is that the axial forces get large; the
shank can slide in that three jaw chuck.

Aluminum can be grabby; It's only a counterbore if it stops before becoming a through hole...
 
tominboise said:
I am working on a home project making some brackets to hold some car ramps on my car trailer. I do not yet own a milling machine, and I would like to counterbore /spotface some aluminum. The OD of the counter bore would be 0.750" and the depth -.0625-0.125". Half the counterbores would be in bar stock, and the other half would be to clean up the extrusion ribs shown in the pics.

I am wondering if this is a bad idea, or could it be done in my drill press using a carbide router bit? If so, should I run the bit at the highest speed I can? Any other tips?
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Yes, the router bit will cut aluminum and it will survive just fine. The trouble is, it's not gonna work like a drill. Drill presses don't do spot faces or counter bores without a solid pilot.

Are the fasteners written in stone yet? Instead of a counterbore, can you do a countersink for flat head screw? Those can be had in about any fastener grade, any thread pitch, etc to match your current bolt size. And drill presses are "kinda" good at large countersinking, as the hole gives the tool enough support that the drill press can usually handle the rest. I'm not giving an overall best recommendation here, but for what you're doing right now, I'd probably opt for a single flute type like this one. (It's really just the first one that came up, more for a type recommendation than that exact product, it's WAY too big.) Quarter inch flat head hardware is gonna be within a few thousandths of half an inch, so depending what you got, you might want half inch or a whisker over. I think this could solve a couple of problems at once?

 
Any unpiloted flat bottomed cutter is going to bounce around like crazy in a drill press, even if the work is clamped down. Either use a piloted counterbore or countersink the holes instead, as Jake suggested
 
I am to the point where I may just go ahead and order a mill from PM or Grizzly. I've been waiting around for quite awhile for one to show up locally.
 
It’s hard to do quality work with makeshift tools. Saying that I have been amazed at some of the work shown by some of the members here.
 
I agree that a drill press is not a good tool for this job unless you have a piloted bit. Lacking a mill, I believe you could create the counter bore with a template and a router with a bearing guided bit. A quality router with variable speed (slow it down) would be preferred. Getting the counter bore concentric would require accuracy when clamping down the template. Getting a precise depth would require a few test cuts and depth adjustments.
 
The OP would also need a slow gradual feed . Those fins can bend and break if not careful . You could fill it with wax to make things better also . We made a heck of a lot of heat sinks in the past .
 
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