Technique for making slots in aluminum angle

[John Coloccia]

I have 14 slots (elongated holes) to make in a 3/16" thick aluminum angle. I've already tried local machine shops. They don't want the job. Anyhow, I also won't do it with a router. The chance of a catch that I can't control is too high in my opinion. The hole needs to fit an 8mm bolt....so lets say about 9mm or 10mm, and the slot is about a 1/2" long.

Short of drilling 10mm holes and then brute forcing the rest with a die grinder, does anyone have a good technique for making these slots?

[jack forsberg]

drill a 13mm hole and use a larger washer

[Ole Anderson]

I would use my mini-mill, but that isn't an option for most folks. You could try using a cross vice with a drill press, but my experience is that most drill presses don't have the stability to pull it off. With a spiral carbide bit at slow speed in a router table setup with stop blocks on three sides to limit movement of the work piece, I would be comfortable doing the work if the work piece is big enough to have some mass. But drill a starter hole first. I would use a bit smaller than the slot width so you can work your way around the slot and not try to cut the full width in one pass. Edit: Let me add that I have not tried that trick with a router table, but I have worked extensively with 3/16" aluminum angle and plate over the years, so I am not just winging it with my suggestion. Working with heavy aluminum is not that much different from working with a very hard wood.

[John Coloccia]

drill a 13mm hole and use a larger washer

That's not a bad idea. I was considering that, but the head of the bolt is only 13mm. It will just end up deforming the washer. One solution is to possibly drill a 10mm hole, and locate it very precisely so that one edge of the hole is almost snugged up against the maximum adjustment one way, and then I'd have 2mm of wiggle room. That's a possibility. I'd really prefer it if I can make the hole a little tighter and just get an honest to goodness slot, though.

re: router table.

There's no way I'm going near a router table with a light, 46" length of 1 1/2" angle. One dumb move and that thing can whip around and hit me who knows where. There's no way I would have the strength and reflexes to control a router bit trapped in a slot.

[Charles Wiggins]

I have 14 slots (elongated holes) to make in a 3/16" thick aluminum angle. I've already tried local machine shops. They don't want the job. Anyhow, I also won't do it with a router. The chance of a catch that I can't control is too high in my opinion. The hole needs to fit an 8mm bolt....so lets say about 9mm or 10mm, and the slot is about a 1/2" long.

Short of drilling 10mm holes and then brute forcing the rest with a die grinder, does anyone have a good technique for making these slots?

If I were going to do it in my shop:
Layout the slots.
Center punch the two ends of the slot, and maybe a third punch centered between the two if the slot were long enough.
Put the stock in a drill press vise or clamp it to the table.
Drill a pilot hole through each punch.
Use the pilot hole to drill the full sized holes.
Use a small flat file to take down the points left between to true up the sidewall of the slot. You'll need a good file card. Aluminum is soft and clogs a file quickly.

[John Coloccia]

Ja ja....that's about my current plan. I'll probably use a die grinder with a burr instead of a file, just to speed it up. If the slot were longer, I could fit my vixen file in there and be done almost as quickly. 2 9mm hole drilled edge to edge is longer than I actually need, but it's probably the quickest way to knock this out.

Man, I really miss having access to a mill and metal lathe. One of these days I'll make some room to bring in a Smithy, or something, that can knock out these stupid little tasks.

[Charles Wiggins]

Ja ja....that's about my current plan. I'll probably use a die grinder with a burr instead of a file, just to speed it up. If the slot were longer, I could fit my vixen file in there and be done almost as quickly. 2 9mm hole drilled edge to edge is longer than I actually need, but it's probably the quickest way to knock this out.

Man, I really miss having access to a mill and metal lathe. One of these days I'll make some room to bring in a Smithy, or something, that can knock out these stupid little tasks.

There's not too much problem drilling overlapping holes in aluminum as long as you have the stock anchored and there's a decent amount of "meat" between the next pilot hole and the preceding full sized hole.

[Keith Weber]

John, there's no point in denying it. It's inevitable -- you NEED a Bridgeport! Come to the dark side! Come! Only the first part will be expensive. After that, each part gets cheaper. Eventually, you'll wonder how you functioned without one!

Keith

[Peter Quinn]

I wouldn't do it with a router table either.......I'd make an MDF template on the router table to accept a bushing guide, clamp that to the angle stock, then knock out the slots with a plunge router and light passes, maybe a slow speed so the aluminum doesn't melt and stick to the cutter. Solid carbide spiral, no problem. Sort of like a mortising template for slot mortises. I've done small slots on the DP using a mini xy vise, not sure id want to do 10mm that way on a consumer grade model like I own. Maybe if you punch the left and right first you could clean up the remaining points with a 1/4" end mill on a DP? Quicker than a file perhaps.

[Ronald Blue]

If you want the slot to end up at about 1/2" in length and you drill a 9 mm hole on one side I would try a rat tail file and see how fast it cuts. Look for a mill bastard(I think) because the teeth are less aggressive and cut smoother. I think you will be pleasantly surprised at how quickly it files and you will have better control over the cut and cut quality. Your holes will overlap enough i think it will be difficult to drill the second hole. Just my observation but 9 mm is about .354 so you have less than 5/32" (.01562) to remove to get to the 1/2" dimension. Good luck.

[John Coloccia]

John, there's no point in denying it. It's inevitable -- you NEED a Bridgeport! Come to the dark side! Come! Only the first part will be expensive. After that, each part gets cheaper. Eventually, you'll wonder how you functioned without one!

Keith

I'd love one. It's a matter of space. My shop is a converted 2 car garage. 1/4 of it is taken up by my spray booth and finish "stuff". Another corner is taken up by a CNC machine and dust collector. Another corner is unusable because of an oil tank (it was even worse before I had it moved). Another corner is taken up by the entrance way, and there are two posts right in the middle. It's a really difficult space to work with.

My parents just moved to the area and have a humongous basement that I have pretty much full access to...they don't go down there for ANYTHING. I was thinking of bringing in a Bridgeport and a lathe there. It's a 10 minute drive any time I need something done, but that's not bad. Older Bridgeports for pennies. No one wants them anymore. Pretty soon they'll be like pianos...if you take it away, you can have it for free. They're hardly even worth retrofitting with DROs if you're a real machine shop. You just clamp something in the "small" CNC in the corner and have at it with the rotary encoder.
Half the machine shops I know don't have a knee mill anywhere in sight.

[johnny means]

I've worked aluminum before by using a template from 3/4" MDF. After making the template and drilling a few entrance holes into the aluminum, I adhere the aluminum to the template. I then route the aluminum like I would any laminate or veneer. This has given me clean results on up to 1/4" aluminum.

[Michael Wildt]

Drill the holes in either end of the elongated slot, then use a jeweler saw or similar and cut the sides. A touch up with file and done.

[Keith Weber]

Another corner is taken up by a CNC machine and dust collector.

How about using the CNC machine? I'm not sure if your spindle is closer to being a router, or a dremel tool, but I would think that if you were able to clamp down your aluminum and program light passes, you should be able to produce slots quite easily with that.

[John Coloccia]

How about using the CNC machine? I'm not sure if your spindle is closer to being a router, or a dremel tool, but I would think that if you were able to clamp down your aluminum and program light passes, you should be able to produce slots quite easily with that.

It's a 3hp, high speed spindle. I know people that have had good luck cutting aluminum with this thing, but I'm not really into experimenting right now. Maybe later, but right now I just need to get it done. I have a couple of days until the aluminum shows up, so I thought I'd consider my options. I should say that the aluminum is for angle brackets to hold down my CNC t-slot top. I'm replacing the old MDF top. There's no top on it right now, and by the time I'm done futzing around with it, figuring a clamping and registering setup, etc, I could just drill holes and file it by hand if I had to. It's sort of an interesting science experiment, but I'm not really in that mode right now. I just need it done.

I'm in a bit of a pickle because I had a shop ready to do it, and then he turns around and wants about $500 for the job. He basically explained that it will take him 4 or 5 hours, and he's sick of loosing money on jobs, and he basically doesn't want to do it. I was polite about it, but I know my way around a machine shop and there's NO WAY this job, with the loosey goosey tolerances I gave him, should take more than an hour or two, and that's if he's goofing off eating a sandwich at the same time. I can see not wanting to take the job, because it's boring and not a huge money maker, but give me a break...this ain't my first rodeo.