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.


https://www.youtube.com/watch?v=_VrFV5r8cs0

[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.

[pat warner]

I know you don't need this (statement) with your fixturing but..........
I've through slotted 3/4" 6061.
Two sliding lock fences (http://patwarner.com/images/router-X-cut-jig.jpg) with slots shown, are also router cut.
With solid fixturing and the right cutter, not like butter, but you can get through the stuff without much chatter.
If the work moves or if you have only marginal control with your router I'd do the same as you (look for another method).

[Keith Weber]

4 or 5 hours to cut 14 1/2" long slots with a 3/8" mill??? I'd be embarrassed to call myself a machinist if I was that guy. Like you said... An hour or two (tops) while eating a sandwich and joking with the guys.

If you did decide to give it a shot on your CNC machine, I really don't see that it would be an issue unless your router is only a one-speed with an extremely high rotation. And even then, the problem would not be it catching, but rather the aluminum chips melting and gumming up the bit. I'm assuming that a CNC big enough to have a 3 hp motor would have ball-screws and not ACME screws, so backlash is practically non-existent. Without backlash, your feed would be smooth and controllable. With a smooth feed, it will not catch (like you mentioned concern for). My Bridgeport cuts through aluminum like butter. Your CNC machine would be the same as long as you could clamp it down in a vice. WD-40 is an excellent lube for cutting aluminum to prevent gumming. I usually crank with one hand and spray the WD-40 with the other. I really need to get an auto sprayer!

If you were local, I'd just say bring them by and I'd let you test-drive a Bridgeport and a couple of guitars! :-)

[John Coloccia]

I know you don't need this (statement) with your fixturing but..........
I've through slotted 3/4" 6061.
Two sliding lock fences (http://patwarner.com/images/router-X-cut-jig.jpg) with slots shown, are also router cut.
With solid fixturing and the right cutter, not like butter, but you can get through the stuff without much chatter.
If the work moves or if you have only marginal control with your router I'd do the same as you (look for another method).


What do you use for a bit? My friend recommended an O flute bit. I associate those more with plastics, but I guess it makes sense on the CNC. The biggest issue with aluminum is clogging, and these O flutes are hard to clog. Combine that with a fast feed rate, and you can get the big chunks to carry off an awful low of heat. I don't think that would work for hand feeding, though.

My whole shop is basically setup around making and repairing guitars so I don't have a lot of the basic jigs that most others have laying around. I have a lot of...uhm...let's say "exotic" jigs, tough :)

Keith:
Part of why I'm installing TSlot on my CNC is so that I can more easily handle attaching vices and things like that. With an MDF top, every widget becomes an exercise in either making a tooling plate, or finding a place in the main MDF surface that hasn't already been drilled for something else. It was getting to be a real pain. I've taken the time to do a little maintenance on the CNC while it's in transition, so it's just not running at the moment. On the list, though, is to get some appropriate vises and start fooling around getting my feed rates dialed in for aluminum work. The machine is indeed outfitted with some beefy ball screws and linear rails. The machine itself is pretty stiff and was actually designed as an aluminum cutting machine. I just happen to have a high speed, 3 phase spindle on it. I can slow it down to about 10,000 RPM or so, with the VFD, but the torque is not great at that point. I can move the axis pretty quickly though, so high feed rates really aren't a problem.

[Dennis Ford]

I would probably use a router but it could be done without much trouble with a drill and a scroll-saw (and a file for touch-up). Use some lube on the scroll-saw and the file.

[jack forsberg]

problem with a router is the lowest speed are to fast(9000 rpm) so you need a rheostat for speed control. you need about 3000 rpm for a 1/2 bit to get the SFMP cut. aluminum is easy to mill with a standard wood cutting 2 flute carbide bit at these speeds with good control. Hell cast iron is easy to mill with a hand held router if you get the SFPM on target.

here is me milling a cast iron opening for an Oliver sander with a router. But i thought you did not want to use a router?


https://www.youtube.com/watch?v=xxQO6hILZLY&feature=c4-overview&list=UUI6jpIs2zjN9DmVvK2ZAWXA

[Edward Oleen]

I've done something similar in aluminum angle. I drilled the end holes and several holes in between.

The steps were:
Sand the aluminum with fine grit sandpaper to get the oxidation off. Sand it ACROSS the width, not along the length.

Locate the slot: mark the center line, the sides, and the ends with a really sharp scribe.

Center punch the center line with a sharpish center punch. The first punch at each end should be 1/2 the width of the slot from the end, successive punches should be the big drill diameter apart.

Drill the pilot holes with a very small bit - these are starter holes for the big bit, which will be the same diameter as the slot is wide.

go back and drill the "big" holes

Deburr as necessary - I used my a fine file, which I had to card often.

Now get out the magic tool: a Dremel tool. Chuck up a "cut-off" wheel and slice out the remaining metal between the screw holes.

It will probably take a few of the abrasive disks, but they cut aluminum like butter. You will NOT be exerting lots of muscle power - you will simply be guiding the tool which does the work. It WILL turn out beautiful, as long as your hands don't shake while using the Dremel.

I first tried filing, and messed it up. I found that I could be powerful - running the file - or exceedingly accurate - running the Dreme.l

Yes, it took me some time, but it worked superbly. Not only nice looking, but accurate. I was making a part for a home-built (it was a friend's project) guidance system for an astronomical telescope.

[pat warner]

"What do you use for a bit? My friend recommended an O flute bit. .................."
*********************************
Since you have it all mapped out, I doubt my input will amount to anything.
Noetheless, the tool is a short single flute solid carbide spiral from Onsrud, 63-620.
Never collects chips, cuts clean shallow or through slots up to ~ 3/8" deep.
I have others for deeper cuts, but without rock solid workpiece confinement
& first class router control you will booger the cut.

[John Coloccia]

So what I ended up doing is very carefully measuring the hole height, drilled two holes on the edges, and then used a burr to slightly widen them until I was happy. Then I clamped it in my cross vice, put the bit in the hole, and moved the vice until the bit was right at the edge of one of my "good" holes. And then I went and drilled the holes. I have about 1/2mm of adjustment but that's enough and it saved me from slotting 14 holes..I just slotted 2. Hybrid approach, I guess.

[CPeter James]

Next time, drive up to NH and I'll do it just to use my milling machine.

CPeter

[Larry Edgerton]

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


Oooohh........... KTM. A man with good taste!

Larry

[Keith Weber]

LOL! Nothing but the best, Larry! 2012 KTM 300XC

[Steve Rozmiarek]

problem with a router is the lowest speed are to fast(9000 rpm) so you need a rheostat for speed control. you need about 3000 rpm for a 1/2 bit to get the SFMP cut. aluminum is easy to mill with a standard wood cutting 2 flute carbide bit at these speeds with good control. Hell cast iron is easy to mill with a hand held router if you get the SFPM on target.

here is me milling a cast iron opening for an Oliver sander with a router. But i thought you did not want to use a router?



Once again Jack, I learned something from you, thanks!

[Charles Coolidge]

Meh center cutting end mill chucked in my drill press, Harbor Freight compound vise, a few pecks and its done.

[Larry Edgerton]

Borrow someones domino.......

Larry

[John Coloccia]

Meh center cutting end mill chucked in my drill press, Harbor Freight compound vise, a few pecks and its done.

That's a good way to drop the chuck mid cut and make a big mess.

Just FYI. There's a reason mills have draw bars.

[Phil Thien]

That's a good way to drop the chuck mid cut and make a big mess.

Just FYI. There's a reason mills have draw bars.

And depending on where the bit is at the time, it can get real exciting real fast!

[Charles Coolidge]

That's a good way to drop the chuck mid cut and make a big mess.

Just FYI. There's a reason mills have draw bars.

LOL no its not because I didn't suggest you could mill horizontally with a drill press, peck drill it, end mill WAY stouter than a drill bit.

[jack forsberg]

Once again as wood workers if you looking for ways to work metal with wood working machines its not had to mill aluminum with them. I put a small dab of lock tite on the stub Jacob taper for side load on my press to do slots. wood working drill press in general never swap out a chuck over its life anyway. The VFD gets the speeds down.


https://www.youtube.com/watch?v=eIEwVt3kswU

[John Coloccia]

I see what you mean. That probably would have worked to. Fortunately, I was able to nail the height I needed, and once the setup was ready I blasted through them. Even doing it by hand, in a drill press, only took me about 2 hours, and that included layout, deburring, cutting, test fitting, etc. I'm sure I could have knocked it out in an hour or so with a mill. I really don't understand why my guy made such a big deal about it.

Pretty much, it's the last time I'll ever have to do something like that. Now that the TSlot table is on, and I have ways to index tooling plates, vises and things like that, a lot of this stuff will just be done on the CNC...even the aluminum work.