Forstner bits in aluminum??? (Now with finished pics)

[William Falberg]

If it really has to be precise I'd scribe the exact radius; drill it out as far as I could be accurate (with whatever drill is handy); then file it down exactly to the scribe line.

[Chuck Isaacson]

Well, the neighbor had the bit that got it close enough and then I worked it with a file a little bit. I think that it turned out pretty good though. I will give it a few days and see if it sags at all. The old one is now flat a s can be when there isn't a anchor hanging from it!! Word of advice for anyone putting a Freud FT3000VCE in a router table, GET AN ALUMINUM PLATE!!!! Then you will only have to do it once. Here are some pics. They kind of , I took them with the phone.

Chuck

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[Joel Gelman]

I came across this old thread when searching for info on using Forstner bits to drill into aluminum. For my application, I want to drill into aluminum only around 3/16 deep and 2 inches diameter. I can't use a hole saw because I do not want to drill through. I want a clean cut and to know the location of the center, which you would get with a forstner bit in wood. I was thinking the Amana 420908 carbine tipped boring bit with spurs, the aluminum plate clamped down, very slow speed, and the use of cutting oil. I am open to what would be better a Forstner bit other than a machine shop that has technology and equipment beyond a drill press.

[Mel Fulks]

Denatured alcohol works better than oil for drilling aluminum.

[Pete Staehling]

I don't know about using a forstner bit as I have never done it with aluminum, but I will say a few things that I'd consider.
+ Forstner bits are not all created equal. A carbide one might have less chance of being damaged. A very cheap one might be more expendable. Either might be an advantage.
+ Stopping and cleaning or resharpening frequently may help as may a low speed. I might choose a cheap bit and put up with frequent resharpening rather than ruin a nice bit.
+ Different alloys will drill more easily than others.
+ If you have some scrap you could experiment with a cheap expendable bit. I'd probably want to do this before i ruined a big plate.
+ Oil probably isn't the best lube/coolant, but is better than nothing. I am not sure what is best for drilling though. I know that for cutting threads we always used something called alumi-tap that was thin as water and white in color. It worked way better than oil for that purpose and I'd bet it would be great for drilling if available.
+ Having the work piece firmly clamped stationary is critical.

[Ole Anderson]

WD40 is a good lube for aluminum, Tapmatic for aluminum is best. I would try a forstner bit, but would drill an 1/8" pilot hole for the brad point first. HHS definitely harder than aluminum. Speaking from experience working with aluminum for 15 years, the shop that turned and knurled my big pieces turned me onto WD40.

[John K Jordan]

I came across this old thread when searching for info on using Forstner bits to drill into aluminum. For my application, I want to drill into aluminum only around 3/16 deep and 2 inches diameter. I can't use a hole saw because I do not want to drill through. I want a clean cut and to know the location of the center, which you would get with a forstner bit in wood. I was thinking the Amana 420908 carbine tipped boring bit with spurs, the aluminum plate clamped down, very slow speed, and the use of cutting oil. I am open to what would be better a Forstner bit other than a machine shop that has technology and equipment beyond a drill press.

Joel,

Is the part large or small enough to be portable? Any machine shop could mill a flat-bottomed 3/16" deep 2" diameter hole and mark the center. A rotary table could work but I think a CNC would be easier and quicker and could do a larger part that was difficult to hold or couldn't easily be rotated.

JKJ

[Robert Hazelwood]

The OP was drilling much smaller holes than you are considering. 2" is a very large hole to drill, you want a stout rigid machine that can operate at very low rpm. I'd estimate you want about 150 rpm to get the right sfm for aluminum and the cutting forces and torque will be very high. Most WW drill presses won't go that slow.

Maybe it will work at a faster speed, but it definitely seems like you are pushing the envelope. If you try it, clamp the workpiece down FIRMLY and use full PPE.

Short of taking it to machine shop, the other approach I can think of would be to use a variable speed plunge router with a circular template and a carbide bit. I think it would be challenging to nail the OD and get the center exactly where you want it, but with some creativity I bet you could get it quite close.

[Mel Fulks]

What denatured alcohol does is make the cutting crisp, negates the gummy quality. I learned that in a pattern shop,
we used to have to make changes to the aluminum match plates. And it's not messy.

[Jamie Buxton]

What denatured alcohol does is make the cutting crisp, negates the gummy quality. I learned that in a pattern shop,
we used to have to make changes to the aluminum match plates. And it's not messy.

When I drill or saw metal, it can get darn hot. Using a flammable cutting fluid on it would scare me.

[Mel Fulks]

Sure, it can get hot. Cooling is one of the functions of the alcohol. And there are a number of propriatary oil based
concoctions used in the drilling of metals that are flammable. But for those whose asbestos suit is at 'the cleaners' I'm
guessing a small bit of water renders the denatured alcohol non flammable. As I've said before nothing gets traction
here without a witness. Mine is at another trial today.

[Steve Jenkins]

For the 2” hole 3/16 deep I would use a forstner bit to drill a hole in a piece of mdf and use it as a pattern for a top bearing router bit. After milling the recess in the aluminum put the forstner bit in the recess and tap it with a hammer to mark the center.

[John K Jordan]

...I'm guessing a small bit of water renders the denatured alcohol non flammable. ...

I'm not sure that is a safe assumption. I remember mixing isopropyl rubbing alcohol with water as a kid to do a "magic" trick involving setting fire to it. Don't remember the concentration, it's been about 60 years!

So I took some 45% ethanol outside and poured it on a rock. It ignited easily with a flame and burned for a long time. Don't know what kind of heat by friction could cause ignition. This was 90 proof vodka I bought for making vanilla extract. (I'll bet the straight 45% would burn going down the throat - didn't try that!)

JKJ

[Bill Dufour]

My tablesaw came with a shallow grove routed into the cast iron top with 1/2 router bit. No idea if it was hss or carbide. Looked the same after 6" of cut. So no cutter wear to notice. A little JB weld fixed it right up.
Bill D

[Joel Gelman]

Thank you all for the feedback