I'm looking for suggestions on how to machine a slot into an aluminum round rod

Hi All,
I need to create a slot as shown in the attached graphic. It needs to be precise and repeatable - ideally in one pass.

I have these tools that might help...


I don't have a mill which is what I think I need.

Any suggestions?

P.S. The squared corners at the top of the slot are not required. They can be round (such as would be created by a drill bit or other rotating tool).

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makermarc (author) 1 year ago

Thanks everyone who has responded. I really appreciate all of the great suggestions.

I think all are viable in one form or another.


To answer a couple of the questions below.

- The stock I'm using is 6061-T511 round rod. 9.5 mm diameter. It's hard stuff as far as aluminum goes and the diameter creates some challenge with the tool selection to achieve precision too (I think).

- For precision, I need +/- 1 mm

- I'm using a 7x12 mini-lathe by HiTorque. I purchased it at LittleMachine Shop and is a pretty solid lathe. It can cut hard steel, but with my limited experience I'm not very good at working with steel yet. In any case, I work with aluminum for now so it is no big deal. BTW, if anyone is interested, I've 3D printed a few lathe tools and placed the designs on Thingiverse.com... http://www.thingiverse.com/MakerMarc/designs


Steve, the toolpost idea is a good one, but I hadn't figured out the best way to cut the inlet. I suppose a milling mount for the tool post would take care of that problem. I'd thought of getting one, maybe now is the time.

Hey, Downunder. You win the prize for having the best guess on what I'm making. You guessed wrong, but you still win because no one else tried. :-) It isn't a trigger, but that sounds like a fun project. Of course after I read your comment I went to youtube to figure out how to do that.

The coping saw and bandsaw are good ideas too, but I don't think it will work for my purpose. With a bit more explanation you'll see what I mean.

I'm doing low volume manufacturing on this part which integrates with a larger assembly. Right now I'm able to produce about 50 units per day (if I need to), but that is without this new part. So, I think using hand tools may cause my production rates to go down too far. Plus, I suck at cutting straight lines with a saw!

Kidding aside, my take on all the responses is this...

1. Mill - Most ideal option but high $$$.

2. Tool Post Milling Attachment: Meets requirements and reasonable $.

3. Band saw: High $$$.

4. Coping saw: Great for prototype, but may be too slow for production.

Did I get that right?

BTW, your responses will weigh heavily on my wife's reaction when I tell her I'm going to buy a new tool :-)

Thanks again! This has been a great help! I hope I can return the favor from time-to-time.


This is an example of classic lathe accessory to mill on a lathe


It replaces the top slide.

makermarc (author)  steveastrouk1 year ago
Thanks for the link. For some reason I thought they were more expensive. Here is the link from where I bought my lathe... http://littlemachineshop.com/products/product_view.php?ProductID=1956.

Not a bad price.

So assuming I go that route, here is a follow-on question. Can I mount the part without putting a bunch of scratches in it? It seems like round rod would be a challenge to mount on a vertical plate and hold steady without really clamping down to the point of indenting it.

My concern is I have +/- 0.2 mm tolerance on the OD for the final part. The 9.5 mm round that I purchase is precisely the size I require so I don't need to machine the diameter. I simply polish it with fine grit sandpaper and anodize it.

The diameter of the stock doesn't really leave any room for machining out deep nicks. I could go with the next larger size round rod and do the milling first and then machine it down to 9.5 mm, but that not very efficient for making 10's a day.

Of course none of that matters if I can mount without dinging it.

Yes, handling aluminium can be tricky. If I have a nice surface finish already, then I wrap the part in masking tape before clamping, and I put clamp blocks made from phenolic plastic between any screws and the part.

makermarc (author)  steveastrouk1 year ago

That will probably work for what I need.

Another idea I had while I slept... Make a collet holder out of an aluminum or steal block. Then I just need to mount the block, which would be be a lot easier. And of course the collet would be gentle on the surface of the part.

I did a quick look on google and didn't see anything like that, but I'm sure it must exist.

If you're making a bunch of these things, then yes, a collet would be a good idea - though they are not immune from marring surfaces. One of the best ways would be to get a 5C collet chuck for your toolpost or milling table



You COULD do it with the work held in the lathe toolpost, and a cutter in the chuck. You could cut the long part of the cut with the cutter, then finish the curve off by hand.

+1 my first thought.

As long as it is a steel Lathe +1

Ah yes, my experience is always with a metal turning lathe. Should have specified.

I have a drill press and a mill vice so now with the one tool I have a mill, a vertical lathe, and a drill press. I have made armor piercing ammunition, firing pins for my rifle, and a whole host of other things under 1/2 inch in diameter.

makermarc (author)  Josehf Murchison1 year ago

Josehf, that sounds really cool. I'm not sure what I'd do with that type of ammo; deer don't usually where armor :-), but sounds like fun. I'm gonna have to google that!

So, given the option between buying a mill or a setup like yours, which do you think is preferred?

I was a Big Game hunter before I lost my eyesight, there are beasts out there with bones as hard as steel.

A milling machine can run you quit a bit with tooling.

My drill press and milling vice cost me just under $100 when I bought it, they would probably cost twice that today. But since I use it as three tools for shaping metals I would probably spend the $200.

I have two Instructables where I used it to make parts.



If your lathe is a steel lathe, steveastrouk has a good one. If not what grade of aluminum is your bar stalk?

Some grades of aluminum are as soft as hardwood, if your aluminum stalk is that soft you could put the parts in a jig to hold it in place and the jig guides your router.

To find out if your aluminum stalk is the right softness try cutting it with your wood tools.

If I would not know better I would say it is for the trigger or a gun...
Normal steel could be done in a bandsaw if the round piece is clamped or welded onto something flat to prevent spinning - should only take a few minutes.
Hardened steel requires special tools so you are best off to machine first then harden.
Drilling won't work with a normal workshop setup as the drill will wander off on the round surface.
But with a drill press you might be able to drive a small milling cutter through the material and use a machine vice to move it around for the cut.

Tomahawk921 year ago

A mill would be best i believe. But the drill could do some of the work then follow up with a coping saw or something similar. This route is less accurate than a mill and gets less and less accurate if you don't have a good eye or steady hand. If that drill was a drill press it could be done pretty well.

How accurate does it need to be?

And do you have access to a coping saw or jigsaw with a blade that can be used on metal? Really any type of thin saw that could make curves.