4.5" hole saw in 6062 aluminum, help needed!

kb0thn · Sep 25, 2009

So here is my story of the evening:

I have a piece of 0.1" thick 6062 aluminum sheet that I need to put four 4.5" holes in. I purchased a brand new Morse Cobalt Bi-Metal hole saw (http://www.mkmorse.com/mc1.html) for the job. Saw specifies 105 RPM for aluminum.

First attempt was with hand drill. Lots of catching and trying to break my arm. A few times with the drill running off on its own and wrapping the power cord around it. Okay, I learn ... decide to try cordless drill with clutch. Whenever the hole saw touches the aluminum the clutch engages. All this is a bit of a surprise, because I have put dozens of 3.5" holes in sheet metal with a cordless drill before. Usually a 10 second job and no fear of death involved.

After some more fiddling with hand drills I decide to put it on my CNC knee mill. But not mill it, just use this damn hole saw I bought. Clamp sheet to mill with strap clamps and a nice virgin piece of plywood for backing. Slowly feed. Hole saw grabs and pops the Rohma Supra keyless chuck off the arbor (JT33 taper). This is a big surprise, because that chuck has seen some serious use running things like 1" silver and demming bits through steel. So I cleaned out the taper and set the thing a little harder than I originally had. While fiddling around I notice that where the weld seam is on the hole saw there is a tooth that appears to have come from the factory sticking outside of what should be the OD. I carefully ground that down and figured that was the problem.

Take final attempt with newly reset drill chuck and dressed hole saw. Grabs again immediately, stalls the 2HP mill, pops the sheet metal free of the clamps, bends the arbor, and gives me a couple of nicks on my arms before I can hit the e-stop.

Throughout the different scenarios, I tried using Anchor Lube (thick water based cutting lube) and running dry.

What am I doing wrong?

Thanks,

-Jim

PS - only third time having to hit the e-stop since I started machining 7 years ago. First time was brand new machine, commissioning it. Home switch on z (knee) installed in the wrong spot from factory. During home cycle machine attempts to run ball screw through the floor and flip the machine over. Second time spindle faults, but machine doesn't shut down the axis drives. And now this. I guess I'm not doing too bad.

Hdpg · Sep 25, 2009

kb0thn said:
....What am I doing wrong?.....

Nothing I haven't done.

A big hole saw like that needs a lot of torque to drive it and in aluminum it will be very prone to grabbing because it is not rigid.

Try clamping it between two pieces of plywod not just on top of a piece of plywood. The piece of plywood on top acts as a guide so the saw contacts the aluminum evenly and even if it tends to grab it cannot throw off sideways.

Also use a lubricant, tapping fluid, kerosene, ATF (automatic transmission fluid) all work quite well. And go really easy on the pressure; just let it 'float' through the metal. If you have one use a compressed air dril and adjust the pressure so you don't get such a violent kick when it grabs.

dkmc · Sep 25, 2009

Grabs again immediately, stalls the 2HP mill, pops the sheet metal free of the clamps, bends the arbor, and gives me a couple of nicks on my arms before I can hit the e-stop.

Memorable evening....you KNOW you're havin fun at this point.

Home switch on z (knee) installed in the wrong spot from factory. During home cycle machine attempts to run ball screw through the floor and flip the machine over.

WHY must YOU have all this fun.....and some other poor soul is having a normal boring evening making widgits....??

1. Manual mill
2. Clamp it tighter to the table
3. loosen the drive belt a bit
4. Get the 'feel' of the tool and ease into the cut....only enough pressure to make it cut but not grab.
5. Booze
6. Balls
7. Boss....Talk to the metal....let it know who's the...

starbolin · Sep 25, 2009

Saw has too much top rake for your setup. The teeth dig down into the soft metal instead of peeling off a chip. If you are going to keep that saw I would stone off the leading edge of the teeth to make a zero rake cutter.

You already learned the other lessons: Don't use a four inch cutter on a hand drill and don't use a mill cutter in a drill chuck.

kb0thn · Sep 25, 2009

starbolin said:
Saw has too much top rake for your setup. The teeth dig down into the soft metal instead of peeling off a chip. If you are going to keep that saw I would stone off the leading edge of the teeth to make a zero rake cutter.

On my drive home, I was thinking about doing just that. I also realized that previous 3.5" holes were in steel rather than aluminum.

starbolin said:
You already learned the other lessons: Don't use a four inch cutter on a hand drill and don't use a mill cutter in a drill chuck.

Wasn't a mill cutter. It was the hex arbor that Morse supplies for use with their hole saws. I don't have anything other than the drill chuck that work with in my R8 taper machine.

Thanks for the less rake advice! I'll give that a shot tomorrow if I am feeling adventerous. If not, I'll just jig saw and drum sand the remaining two holes!

-Jim

John Welden · Sep 25, 2009

Mount the hole saw in a tool holder, not a drill chuck

Use the knee to feed into the saw, not the quill handle.

Spin it slow, lots of lube. put in in low gear.

Clamp it well.

Should go fine.

dfw5914 · Sep 25, 2009

As you have already found out, big hole saw + soft aluminum = no joy.

You may have better results with one of these:
http://www.generaltools.com/Products/Heavy-Duty-Circle-Cutter__55.aspx

LOW rpm, use WD-40 for cutting fluid.

Mark Leigh · Sep 26, 2009

hole saw

Hi , I have hole sawed 6 inch holes in .125 aluminum sheet for large Holley Carbs on Drag Boats. It can be done, the WD 40 or the trans fluid works.
The main deal is to use a straight bodied 1/2 drill with the 6 inch handle on it. Then use the trigger on it in a on and off again mode. This will keep the saw moving SLOW, use the fluid liberally keeping the saw covered around the perimeter, along the way through this stop and use a small wire brush to clean the teeth off. Clamp down very well, on top of some plywood for good even support.
I have also used a old Cinncinati drill press at work, flat belt deal, it will slow down to abou 25 rpm, it works also. Good Luck

stannp368 · Sep 26, 2009

4.5" hole saw in aluminum

The best way to do this is to clamp workpiece on a flat pc of wood onto the vert mill table. Drill a pilot hole then use a sheet metal fly cutter w/ an extended toolbit. Then finish w/ a bridgeport no. 2 boring head. Shortcuts like you were trying are not suitable to a good job

Sea Farmer · Sep 26, 2009

I vote with the previous posters' suggestions to use a circle, or fly-type, cutter, and plenty of lube. I've had good luck with this on both aluminum and copper sheet. I clamp on some flat scrap wood (the soft wood used in wine cases works well, and I always seem to have an empty wine case

). I don't like to use plywood in case I go too deep, as the density of the plywood changes and seems to mess things up when the cutter catches. Of course, a more careful operator would control depth-of-cut so this couldn't happen

jim rozen · Sep 26, 2009

Holes saws put large sideways forces on the spindle which is why the
taper came loose.

1) run it as slowly as the machine allows.

2) use WD-40 as the cutting fluid.

3) easy on the downforce.

Jim

Mike C. · Sep 26, 2009

Forget a hole saw on something this big. Lay out your circle with dividers. Go back in and lay out a circle 7/32 smaller than your hole, using the same center. Punch as many 3/8" holes as you can get using the inner circle (this puts the outer edge of your 3/8" holes 1/32 from the edge of the desired hole diam, so use some care). Knock out webs between holes with a jigsaw. Use a boring head or fly cutter to finish the hole to dimension. Yeah, it sounds a lot slower than just using the holesaw, but considering the results so far... I have done several big holes in steel and alminum this way using both a mill and radial drill.

I have to ask, though.... if you hav a CNC knee mill, why didn't you just circ interpolate the hole to begin with? You could set up as described with a center cutting endmill and just watch it eat.

kb0thn · Sep 26, 2009

why not CNC

Mike C. said:
I have to ask, though.... if you hav a CNC knee mill, why didn't you just circ interpolate the hole to begin with? You could set up as described with a center cutting endmill and just watch it eat.

Fair enough question. The part is a 32x24" and has some big lips formed in it. Fixturing it well enough to mill it would take some thinking and would involve tearing down a setup on the machine right now. There isn't enough clearance for the circle cutter I have, and I didn't feel like cutting it shorter.

Based on previous experience, I figured a $25 hole saw would do the job just fine and I would be done in 5 minutes ... VS an hour of resetting up the 4th axis job on the mill before Monday.

Being pig-headed about this, I've decided to try another approach. Bought a roto-zip and circle cutting jig this morning. Cut like a champ, besides the pivot screw slipping a few times and the arc radius changing. Due to all of the beating this piece has taken, I'm probably going to make doubler plates to hide all the gouges and screw-ups. Will definitely circular interpolate those on the CNC.

Thanks,

-Jim

Peter from Holland · Sep 26, 2009

kb0thn said:
So here is my story of the evening:

I have a piece of 0.1" thick 6062 aluminum sheet that I need to put four 4.5" holes in. I purchased a brand new Morse Cobalt Bi-Metal hole saw (http://www.mkmorse.com/mc1.html) for the job. Saw specifies 105 RPM for aluminum.

There it is
You purchased a new one
And those bite you After some use that saw isn`t that sharp anymore So use it on some steel first But even that may bite you
You can also stone it down a bit Not teeth by teeth like mentioned before but the bottemside Make those teeth a bit blund

Also if you use it in a hand held drill rotate the top of the drill a bit so that not all of the teeth are cutting the same time

If you want to destroy a self centering chuck use it with a hole saw The bigger the saw the better you destroy your drill chuck The trust bearing will overload
Use one with a key

Peter from Holland

Robert Campbell Jr. · Sep 26, 2009

Your troubles aside, a very entertaining read! Brought back fond memories....

Reduce rake*, slow, kerosene** and no stinking hand drills fer criminy sakes!
*Kiss flat on an abrasive grinding belt. Tiny flats, you've got to get the teeth in.
**No, I've never started a fire. Don't hold a lit match to the billowing vapors though.... :eek:

Bob

A_Pmech · Sep 26, 2009

Jim,

This is how I make large holes in aluminum every day. I use a Bosch plunge router with a center-cutting 1/4" endmill optimized with a high helix for aluminum. Combined with a good circle cutting jig it's like a hot knife though butter!

For best results, drill the correct guide pin hole in a block of scrap and secure it to the table under the work. This way, when the circle is nearly cut through you won't lose your center.

kb0thn said:
Being pig-headed about this, I've decided to try another approach. Bought a roto-zip and circle cutting jig this morning. Cut like a champ, besides the pivot screw slipping a few times and the arc radius changing. Due to all of the beating this piece has taken, I'm probably going to make doubler plates to hide all the gouges and screw-ups. Will definitely circular interpolate those on the CNC.

Thanks,

-Jim

wippin' boy · Sep 26, 2009

The teeth dig down into the soft metal instead of peeling off a chip.

i use the manual quill feed wheel (on my 50 year old gorton) any time i have such issues
this stops the tooling from sucking into material

Close Work · Sep 27, 2009

Made a lot of 5" holes in 1/4" thick 6061 aluminum using a drill press and also a BP with a chuck to hold the saw. Had some trouble also. The problem is that the hole saw teeth clog with aluminum chips which stick very tight to the very hot steel hole saw. The saw stops cutting. This is when using WD-40 as a lube with a piece of wood as a back up. The saw will grab initially because the hole saw cuts the soft material very aggressively. Forcing it doesn't work. Using a pecking stroke running at a fairly slow rpm, 100's rpm not thousands and raking the edge of the saw with a piece of hard wood or very stiff wire brush to knock off the built up edge and chips plugging the gullets of the saw between pecks worked. Basic problem is that the chips don't clear by themselves because they stick to the steel saw so you have to peck and clear and make progress slowly. Push it a little too hard and the aluminum gets essentially friction welded to the saw teeth and you have to spend a lot of time clearing the teeth with a steel pick or punch. The fly cutter has the advantage of clearing the chips. We tried a variety of lubes and found nothing better than WD-40. Some kind of Teflon or silicone based lube that inhibits the aluminum from sticking to the steel might help. We didn't have something like that handy.

Greg White · Sep 27, 2009

I have been reading here for a couple of hours and just got my first laugh of the morning,thanks guys.
I bought a whole set of those 1 lip adj. cutters on the bay cause they were cheap,still waiting to use em,hopefully i will get a chance.
Some of you guys are funny as hell,thanks.
Gw

willbird · Sep 27, 2009

Another off the wall idea is to hold the work at an angle of a few degrees, to prevent the saw from hitting all the way around (same idea as wobbling the hand drill around as another poster said) the hole will be slightly oval but the machine may stay together :-).

Bill

4.5" hole saw in 6062 aluminum, help needed!

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