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

[tominboise]

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?

 

[Nutfarmer]

Why not use a counter bore? Drill the hole then use a piloted counter bore of the correct diameter.

 

[tominboise]

Why not use a counter bore? Drill the hole then use a piloted counter bore of the correct diameter.

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?

 

[Flyinfool]

This a selection of 3/4 Dia C'bores.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Here is a pilot that will work. If you want a closer fit you can get the next size up for the pilot and then chuck the pilot into the drill press and file it down to size.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[Larry$]

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.

 

[Nutfarmer]

You would want a .750 counter bore with an interchangeable pilot. Then just purchase the pilot you need. If an odd size pilot is required most of us would make one on a lathe. Another way would be to center the drilled hole to the spindle of the drill press with the drill the hole was drilled with a clamp the part to the drill press table. Take 3/4 inch high speed steel end mill and plunge cut to the depth of the counter bore. Run the end mill slow. 100 rpm would be fine. Don’t try and hold the part on the drill press table.

 

[tominboise]

It's also around $100 for a counterbore set up, versus $25-35 for a router bit.

 

[o0norton0o]

I wouldn't do it with a router bit because wood cutting blades are all positive rake angles and usually aluminum is negative rake + some sort of lubricant to reduce chip welding.

Why does the counterbore have to be a flat bottom hole?? For a pan head or bolt? Why not just use a regular 3/4 drill bit outside the center bore and use a flat headed fastener?? No flat bottomed machining necessary...

 

[MrWhoopee]

Without a pilot, you won't stand much chance of getting the counterbores visibly concentric with the holes.

 

[tominboise]

I wouldn't do it with a router bit because wood cutting blades are all positive rake angles and usually aluminum is negative rake + some sort of lubricant to reduce chip welding.

Why does the counterbore have to be a flat bottom hole?? For a pan head or bolt? Why not just use a regular 3/4 drill bit outside the center bore and use a flat headed fastener?? No flat bottomed machining necessary...

On the extruded side, I need to clean off ridges to allow the washer to sit flat on the material and be sealed against the surface. On the opposite side, I may forgo the counter bore, but I may need the clearance to allow the fastener to clear structure.