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samualt
10-21-2004, 03:07 PM
Can I use Forstner bits on aluminum? I need a 1-3/4" diameter hole in 1/2" thick aluminum. Can I use a Forstner bit in a drill press to make the hole, drilling in aluminum? Has any here done that?

ger21
10-21-2004, 03:14 PM
It won't last long, probably not even long enough to get through the aluminum. How thick is the aluminum?

I'd drill the 2" hole in a piece of mdf. In the aluminum, use a 1-3/4 or 1-7/8 hole saw to cut the hole. clamp the wood to the aluminum with the hole where you want it, and use a flush trim router bit to finish the hole. A template made from Delrin or plexiglas might work better, as the mdf is a little soft. I made a 1-1/2" hole for a stepper mount this way and it fit perfect.

samualt
10-21-2004, 04:34 PM
That Hole Saw idea looks good. Here is a 1-3/8'' CARBIDE GRIT HOLE SAW from Harbor Freight, $7.99 (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=46151) that cuts " through hardened steel, cast iron, pipe, brick, ceramic and plaster up to 1-3/8'' thick". Or, at least that's what they say!

But I need a 1-3/4" hole. Maybe they'll have something that big in-store. I'm going to go see.

:cheers:

jeffs555
10-21-2004, 07:15 PM
I have an adjustable circle cutter similar to this, and have used it to cut holes in 1/8" and 1/4' aluminum. http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00925293000
It is a little slow, but cuts a nice hole, and can be adjusted to any size hole from about 1" up to 6".

I have seen a similar cheaper one at harbor freight, but couldn't find it on their web site.

PS With this type cutter, you have to make sure the aluminum is firmly clamped, and the drill press is run at a slow speed.

sol
10-21-2004, 07:36 PM
Yes you can cut al with Forstner bits and they will last reasonably well. I've cut holes up to 1.125" with them...used plumbing and locksmith hole saws for larger openings....
Yes of course the Al is rougher on them than wood but if you are patient and use plenty of coolant it will work fine.

These cheesy sets will get the job done;. Yeah, I've used ‘em for Al too. :rolleyes:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=38425

cbcnc
10-21-2004, 07:46 PM
Don't expect a holesaw to be very accurate.
All you need is your standard BiMetal holesaw in the size that you want. I'm not talking about a cheap Ace Hardware brand but a good industrial quality one. They are made by Starrett, Milwauke, Lennox and others. Most of the time they have a 1/2" hex shank and arbor. The holesaw threads onto the arbor. Then there are two pins that fit into the back of the holesaw.
I find that it is more accurate to not use the pins and thread the holesaw all of the way onto the arbor. Sometimes it is hard to get the holesaw off of the arbor though.
For a hole that size in aluminum use a drill press and clamp everything down tight. Use lubrication and feed slowly. I find that it is a good idea to predrill the 1/4" pilot hole first. Also as you drill you need to clear the chips out of the teeth as they tend to pack up in the gullets.


Chris

samualt
10-21-2004, 09:09 PM
jeffs555:
Regarding the circle cutter, how slow is slow? My drill press will only go down to 620 rpm. It is adustable with belt/pulley system from the top. But it's not a true variable speed. How slow did you run yours with the circle cutter?

sol:
Uhhhmmm...coolant? How do you mean? I have used oil on large holes I was using, but don't think I have ever run water or anything else on them. I guess I could put the drill press in the driveway and run a small hose to the clamped piece I was cutting...like that?

ger21
10-21-2004, 09:35 PM
The circle cutter I have (General, I think) recommends 250rpm, I think. I used it at 500rpm before, on a smaller drill press, but had problems with the chuck coming loose.

sol
10-21-2004, 09:56 PM
Hmm, when I wrote plumbing and locksmith hole-saws I meant exactly what Chris wrote about...

Coolant in my case reads: Any scrap fluid you want to pour on the Al...motor oil and transmission fluid are messy but work, just back off if it starts boiling or smoking; the idea is too keep the cutter from being damaged by too much heat.
I put an edged cookie sheet underneath the drill press to catch the drippings and use a squeeze bottle to apply the fluid...crude but it works.

samualt
10-22-2004, 12:41 AM
For anyone wanting to make 2" - 12" holes in aluminum you might try this Adjustable Hole Cutter (http://www.automotive-tools-parts.com/details/Adjustable_Hole_Cutter.html) rig for $57.99. It uses your drill. It is basically a jig with a cutter bit. Kind of interesting though. A little too large of a hole for me, but thought I'd mention it.

cbcnc
10-22-2004, 02:29 AM
For that matter (above) cut a hole in some 1/2" MDF and use a plunge router. Fit the router with a template collar and use a carbide straight bit to cut the hole. That would be definately more accurate than a hole saw.

Chris

ger21
10-22-2004, 07:43 AM
For that matter (above) cut a hole in some 1/2" MDF and use a plunge router. Fit the router with a template collar and use a carbide straight bit to cut the hole. That would be definately more accurate than a hole saw.

Chris

That's what I said in my first post. Just use a hole saw to remove most of the material first, and it would be a lot easier.

samualt
10-23-2004, 08:09 PM
Update:
I found a Lenox brand hole saw at Lowes Hardware, $10. It was bi-metal and said it was good for wood and metal applications. It came with the arbor so I didn't have to buy anything extra. It chucked right up in my drill press and worked perfectly! I cut through 1/2 aluminum and the hole saw still looks sharp. I ran it slow and fast and found that it did well at mid speeds (1100). I did have to stop a bunch of times because aluminum would gum up the teeth, always in the same place which was the two closest teeth (they arn't spaced evenly). If I didn't use much pressure it worked much better and faster. When I was doing it right a fine spray of aluminum powder and bits would be thrown up and shower the workspace. I never did get it hot enough to use water cooling or anything. In fact, both the hole saw and metal stayed luke warm only. It took about 15 minutes to cut a hole (1-3/4" diameter x 1/2" deep). I am very happy with the results!

:banana:

cbcnc
10-24-2004, 12:03 AM
samualt,

Good, I'm glad it worked out for you.
Variable pitched teeth are necessary because otherwise a harmonic vibration would start up from the teeth cutting in the same place each time.
Now that you have the arbor you can build up your set when you need different sized holes.

Chris

HuFlungDung
10-24-2004, 01:35 PM
Don't use a carbide grit holesaw for aluminum, or else you will end up with an "aluminum coated holesaw that won't cut holes in anything' ;) :D