How would you machine this?...

[cnczoner]

I want to cut lots of holes (for venting and mounting fans) into a thin (1/32") aluminum cover (7" x 10") and looking for advice on the best/easiest way to do this. Most of the vent holes are 0.375" dia. (somewhat arbitrary), and there are also some smaller holes for mounting fans. There are also some milled arcs where the fan blades will be. The photo below shows the aluminum cover and the pattern of holes I will cut into it.

Should I drill the holes and mill the features (arcs, etc)? Or should I mill everything?

I do have a 1/8" stright-flute endmill, but I was thinking that I would sandwich the cover between two pieces of wood. Is this necessary with a straight-flue EM?

Alternatively, I could drill small (0.140" dia) holes in the 4 corners, and secure the aluminum cover to a piece of wood, then secure the wood to the mill table so I'd be able to see the top of the cover during the process.

Ideas, best practices, advice?

Cheers,
-Neil.



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[cnczoner]

Hmmm.... no opinions/advise after 83 views. I would've thought at least 1.2% of the people here would have done something similar.

[blackbeard52]

cnc

I have done a simular shield for sound proofing but the thickness was a bit more...What material are you using? 6061 or what? I have had great success using a step drill tin coated like this DeWalt DW1924B 3/8" Pilot Point Drill Bit..Available at HD.... the pilot cuts the initial hole at a smaller depth and the 3/8 od as it passes through making a clean hole. I would use this drill also to predrill the slots for the fans and tool change for the 1/8 bit. However I found that a deeper flute depth will give a greater finish such as 1/4" without loading as much.

Bob

[tauntdesigns]

I think I'd sandwich it in between 2 pieces of wood and then clamp it to table.

[ckirchen]

I noticed that you have the edges bent up already and from your drawing it looks like you have to cut pretty close to those edges.

I would cut a piece of wood (HDPE if you use coolant) to fit inside the bent edges and place it on the machine table with the bent edges pointing down. Hold it down with a couple of clamps (with wood/plastic under the clamps to avoid marring the aluminum) and machine several holes (some in the middle and one near each corner). Use those holes to bolt the aluminum and wood/plastic to the machine table (i.e to the t-slots). The piece might not need it, but the bolts near the middle will prevent it from chattering. Remove the clamps and machine the rest. And you will need to line up the holes with the t-slots before hand.

I second the idea of using a step drill. For the arcs, I would do .005" to .010" passes with a spiral flute 1/8 EM. You will need to use cooling with the EM to keep if from plugging up.

How's that for another way to skin a cat?

[cnczoner]

Thanks for the replies.

The edges came bent already (it's a cover for an aluminum enclosure). I agree with sandwiching and I'm thinking I'll bolt down the first sheet of wood, use the mill to cut an appropriate-sized groove for the edges of the cover, then sandwich the cover and another piece of wood.

I figure I can always stop the process a couple times to move a couple clamps.

Now, the puzzler -- why specifically a step drill. I don't use those often, so I don't have one handy but IIRC there is not spiral flute that would try to pull the aluminum upwards. Is this why?

Also, ckirchen, why a spiral flute EM? Wouldn't the straight flute EM be better or will there be a problem with clearing out the chips once the wood sheet is over it?

Cheers,
-Neil

[cnczoner]

Oh btw blackbeard52, I investigated and found out it's 3003 H-14 aluminum, .040 thick.
Cheers,
-Neil.

[Mcgyver]

how many? if you have a lot, get them punched, but for a one-of you can use a woodworkers brad point drill. this a a manual drill press op, you won't need to sandwich it, and imo would be the fastest way to go. the only drag is it acts like trepanning tool and produces slugs....if they are sticking to the point they have to be cleared after each hole. however, they produce a very need hole in thin aluminum. also, in the DP, this is a potentially dangerous job (much less so with the brad points imo) so keep your wits about you.

[tauntdesigns]

Just a couple of suggestions... I like your plan, btw

If you use an end mill (EM).. run your program one time on your wood base before loading the part to create a relief cut for the little circle cutout that will try to wad up under the EM.

Even center cutting EM's will cut deeper around the diameter and the little circle cutout will turn with EM and cause alot of pressure without the relief cut.

I hope that made sense,

Edit: I just re-read posts.. .040" thickness may not cause too much pressure, that's pretty thin alum.

[ckirchen]

I said a spiral EM because that's what I have and that what I've always used when cutting aluminum sheet.

I don't think a straight flute EM has a sharp enough edge on the end to plunge into the sheet. But, I've never used one, so I don't know if that's true. What brand of straight flute EM do you have?

[blksmith]

I would use a strippit or weideman cnc punch

[cnczoner]

I actually want to machine it on my mill as it's a learning exercise for me. And it's just one of these I need to do. (It's a cover for my file-server (which started life as a car-MP3 player project) here ).

The straight-flute EM I have is a Melin brand (McMaster). Good thought on the plunge -- I need to check if it's center-cutting or not. And I can drill first, then mill the circles, or just drill the round holes to size. Still curious about the step drill though.

Even center cutting EM's will cut deeper around the diameter and the little circle cutout will turn with EM and cause alot of pressure without the relief cut.

That's interesting, and I can totally believe this. Another thought is to use a 0.375" drill-mill, which I should have one of around here somewhere. But not sure if it will want to pull up as much as a regular drill, or less, or perhaps more?

I'm going to see if I can find my step drill and perhaps experiment with it.

Cheers,
-Neil.