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OK to use a spade bit to drill aluminum?

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#1 bykhed

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Posted 17 October 2010 - 12:49 AM

I'm building a version of Pierre's alt-az mount, using pillow bearings and a stainless shaft for the altitude part. I need to fit an aluminum round on the end of the shaft to mount the saddle. The shaft is 3/4" and all I have is a drill press. Is it OK to use a spade bit to drill aluminum? Diameter is 3/4" and depth about 1.5". Any feedback or alternative suggestions greatly appreciated!

-Matt

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#2 Olivier Biot

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Posted 17 October 2010 - 03:48 AM

Funny that you mention this as we had a discussion during our Friday night ATM gathering, where we ended up talking about things not to do when milling/routing/drilling aluminum.

One of them was using a spade bit for drilling aluminum. One of our fellow ATMers did this for drilling holes on an aluminum panel, hence it was sheet metal. Even then I'd never do this since I have yet to see a spade bit that does NOT wander away (the center point usually draws a small circle instead of being centered).

If I were you I'd get a metal cutting bit (and patience & lots of lubrication with paraffin/bees wax) for the job. If you need a tight fit, then you may want to drill the hole a tad smaller and use a reamer to get to the desired diameter.

#3 Mark Harry

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Posted 17 October 2010 - 07:36 AM

I'd think that would be somewhat dangerous. Save the spade bits for coarse holes in wood.
M.

#4 Gary Fuchs

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Posted 17 October 2010 - 08:52 AM

The spade bit doesn't sound like a good idea.

What Olivier said: a metal cutting bit (Home Depot should have it) and take your time. Probably will be easier if you drill it in steps. (Obviously make sure the piece is very securely held.)

Gary

#5 roscoe

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Posted 17 October 2010 - 09:06 AM

Well, I've done it......because I was desperate......and lived...... but if you really have to, be sure your workpiece is SECURELY clamped to the drill press table, run it at its lowest speed, and if possible clamp a piece of wood on top for the drill to make a hole in first to guide it. Use only a new bit, so it is as sharp as possible, and consider shortening the shank, so it has less room to wobble. Use some oil - wd40 will do - to lubricate it, feed it s l o w l y , and wear safety glasses.

Or, as others have suggested, buy a reduced-shank 3/4" twist bit, and drill it that way. A small (3/16 or so) guide hole will keep you on track. Still, follow my guidelines above. I think you'd be happier with the results this way........
Russ

#6 Achernar

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Posted 17 October 2010 - 09:12 AM

NO. no. no, don't use a spade bit, aluminum has a way of grabbing a drill bit and that can lead to an accident. If you have a drill pess that stands on the floor instead of one of the very small ones, you can purchase a 3/4-inch twist drill bit. There are reduced shank bits available so you can use them in a standard 1 hp free standing drill press. Clamp the work securely when drilling at all times, and make sure to use safety glasses or goggles because flying metal shards will be generated by drilling metal. Run the press at a very low speed and use tallow or some other lubricant that works for aluminum when you drill the hole. If the part is too big for a drill press to handle, you can use a large power drill and a drill guide to drill the hole, or better yet take the part to a machine shop who can then machine a hole to the exact requirement for your project.

Taras

#7 df_2112

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Posted 17 October 2010 - 09:24 AM

This is a timely discussion. I have a project that requires similar milling with the same equipment.

Does anyone have a good idea of a good step interval for twist drills? I was going to start at 3/16 and go up by approximately 1/8ths using cobalt twist drills. For a nice clean finish would larger or smaller steps be needed?

#8 Gary Fuchs

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Posted 17 October 2010 - 10:49 AM

I was going to start at 3/16 and go up by approximately 1/8ths using cobalt twist drills.


I've done that with good results.

Gary

#9 Ed D

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Posted 17 October 2010 - 10:54 AM

Use drill bits made for metals. Start with a 1/8" hole (3/16" is fine) and step up in increments of 1/8" or 3/16". For the final size, approach by using one or two drill sizes in 1/64" or 1/32". Use plenty of lube to keep the work piece cool and flush out the hole - WD-40, wax, milk, etc. It should go without saying that you need to clamp the piece down, and use common sense and patience.

Good luck with your project.

Ed D

#10 bykhed

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Posted 17 October 2010 - 11:24 AM

Thanks for the input everyone. I tried the big box stores and they didn't have large reduced shank bits. I'm going to try a specialty hardware store today. My drill press is large and substantial and I use it all the time to drill aluminum using up to 1/2" bits with no problems. So I think with the right bit I'll be OK if I take it slow and use lube. I plan to drill a small guide hole first to ease the process and may even drill the hole in step intervals. I'll post my results when it's finished. Thanks again!

-Matt

#11 Intergallactic

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Posted 17 October 2010 - 11:42 AM

The thought if this makes me shutter. :crazy:

#12 Mary B

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Posted 17 October 2010 - 01:08 PM

If it is a thru hole get yourself a step bit. I have several and made 12 3/4 inch holes in 1/2 inch thick aluminum plate in 2 hours. Started small and stepped up to 1/2 inch then switched to the step bit for the final diameter.

#13 roscoe

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Posted 17 October 2010 - 01:23 PM

Oh Yeah--------don't EVER EVER use a spade bit in metal with a hand-held drill, even with some sort of jig. And for that matter, above half inch in metal with any sort of bit -even hole saws -- is a job for sturdy folk with big forearms.
And, be sure your drill press, especially if it's a benchtop, is bolted down.

Or..... take it to a machine shop, and for a small price, you'll get a hole that's straight, square, even, and in the right place, and if you want a shaft, they'll even press it in for you. Might not cost you a whole lot more than a drill bit, either.......
Russ

#14 bob71741

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Posted 17 October 2010 - 01:23 PM

I always used punches for holes in Al, but when the form factor or size prevented using punches, I borrowed home made sheet metal bits from the machinists; they would take a twist drill and grind away at the bit leaving a center point and cutters at the flutes on the periphery only leaving something akin to a spade bit.

I thought that I had seen some commercially bits like that in the early 80s but cannot find now. The closest that I found is a two piece design; drawing on patent available here: http://www.freepaten...com/4992009.pdf

Bob

#15 Sean Cunneen

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Posted 17 October 2010 - 05:07 PM

I've done a lot of drilling in aluminum with spade bits I modified myself. I prefer them to spiral bits in hole sizes larger than 3/8". I have a small drill press, 1/3hp. Your experience may differ but I had the most luck with one of the higher speeds for a smooth cut.

First: buy the very cheapest spade bit, the expensive ones are too hard(material-wise) to work with. I file off the outside spikes, all you want is the center spike and uniform bevels on either side. I found for me older filed bevels worked better than new ones, the new bevels were too aggressive.

Drill a pilot hole, you'll need to drill from front and back to get a clean hole. The hole should be the same diameter as the shoulder of the spike on the spade bit. The pilot hole helps to keep the bit speed up other wise the aluminum in the hole will get too hot and bind.

Do not use cutting oil, you need the chips and ribbons to exit quickly, the oil tended to mush things up(for me)

Make sure your drill press is perfectly square, you want to cut evenly.

Clamp down your workpiece, otherwise the bit will chatter, grab the piece and make ouchies.

Go slow, feel for the cutting action. When you find the sweet spot, the cut aluminum will start to ribbon, you will feel the constant pressure and it will cut nice and smooth, the bit will cut down nice and straight.

Once I figured out the filing and drill speed, I was very impressed with how fast it went and the quality of the holes.

Good luck!
Sean

#16 bykhed

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Posted 18 October 2010 - 12:05 AM

I found a reduced-shank 3/4" twist bit at the hardware mecca in my area, McGuckin's Hardware in Boulder, CO. It was pricy but I'm sure I'll find other uses for it in the future. Managed to get all the addition hardware I needed for this project in the nuts & bolts department as well. I'll be mounting this on a home-built column atop a Houston Fearless RCA TV camera tripod (it is such a beautiful thing!). Bought the tripod from a fellow astronomer and all it needs is a good cleaning and some paint.

-Matt

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