2024-T3 Aluminum Cutting Question

(Charles Cade Lockwood) #1

I have someone that wants me to cut out a state for him in 2024-T3 aluminum for his Airstream camper (.03" thickness). This will be my first time cutting any kind of aluminum so I have a few of questions.

  1. What endmill should I get to cut this out?

  2. What should the feeds and speeds be set at?

  3. He also wants me to engrave some writing into the state. Is that even possible with a .03" sheet of 2024-T3? If so what endmill should I use for this?

Sorry for my ignorance. Kinda nervous about jumping into aluminum since I have only had my Shapeoko XXL since January of this year. Still learning more and more everyday!

Thanks in advance!

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(Vince) #2

That’s a pretty soft temper but ive read it chips well.

First thing is workholding. You’ll want to attach a sacrificial wasteboard then surface it so its machine level. Then use the superglue/tape technique to attach the sheet, use something heavy to press it down while glue is drying. Nyccnc has a good video on this technique.

Cutting - t3 to me = soft. That means a 0.125 single flute hss or carbide will be the best bet. Shoot for 0.001 chipload, use a cutting oil or wd40 to prevent chip welding. To play it safe, cut 0.010 doc but cut into the sacrificial board so you have a clean bottom edge. You might need to cut 15 or 20thou deeper

For engraving cut lines I reccomend a two flute 60 or 90 degree Kyocera V bit. For a larger, surface style engraving youll probably want to look into diamond drag bits. You’ll want to do any engraving first before the outer contour cut.

Due to you sheet thickness, setup needs to be on point but if you follow these tips you’ll be fine, that’s how I’d run it. Keep in mind that this part wont be able to be welded but rivets will be fine. It will also have poor corrosion resistance due compared to a 6061.

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(Dan Nelson) #3

Not to rock your boat, but T3 is a process, not a hardness:

https://www.engineersedge.com/aluminum_tempers.htm

That’s a very common caveat that folks fall into, you’re definitely not the first nor the last. Funny thing T351 is comparable to T4, and in some conditions T3 is superior to T4. I’ve been messing with material grades for years and I can’t say I’m any sort of expert, but I keep a few little webpage “helpers” bookmarked for this sort of thing. Another good one is:

http://www.matweb.com/

You can register a free account which will allow you to compare up to 3 materials at a time, pretty nice!

Dan

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(Vince) #4

Lol, Got me there but still doesn’t change machining recommendations

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(Griff ) #5

Ok, just curious here, I skimmed your link.

T3 is “solution heat treated then cold rolled “. That process then results in some sort of a hardness spec?
Digging back 40 years to some involvement in controlled atmosphere heat treating I recall that the guys in the shop would refer to different processes as resulting in different degrees of hardness. So maybe a T3 process results in a certain hardness spec?

Or is hardness more a function of alloy, less affected by process?

Again, just curious, sorry to sideline the thread. I’ll shut up now.

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(Dan Nelson) #6

Yes and no, a 6061 T6 isn’t nearly as hard as a 7075 T6. Different major alloying element, same process. The “T” temper is just a process, but two different pieces of 7075 that go through the same process should be the same hardness. That’s for heat treatable alloys, there’s also materials that gain strength through some work hardening processes like 5052 (different subject almost). Don’t know if that really answers your question, but to say “I want the hardnest aluminum so I’ll choose T9” completely misses the fact that T9 is just a process. As I mentioned ive been doing this stuff for years, but that doesn’t make me an expert…I’m like guy that read a lot about racing cars, but never sat behind the wheel on a track. It’s part of my job to have a good understanding of the product, but I don’t make it.

Dan

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(Vince) #7

Looks like the 2024-t3 is actually around 25% harder than 6061-t6.

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(mikep) #8

And 2024-t3 is much more “tough” - toughness, strength, strain…all related, but different.

To add to What @DanoInTx points out, the different processes result in different grain structure in the metal, which then has different properties. Crystal shape and stretch have a lot of impact on how the material behaves depending on what you’re going to do with it next - press forming, machining, welding, further heat treating post machining, etc.

In general, 2024-T3 is the most common 2024 you’ll find in the US. It’s not weldable because the welding operation messes up the grain structure. You must not weld 2024 if you’re using it for it’s specific properties. 2024 is great for riveted structures, highly corrosion resistant, and very strong. 2024 tends to be on the more expensive side. 2024-T3 is the go-to material for light aircraft. I’ve never found decent sized scraps of this anywhere, and never found it in anything but sheet and small dimensional shapes (angles, small tubes, etc).

6061-T6 and 6061-T651 is super common, and has totally different machining properties - much easier than 2024. You can anneal 6061, do beautiful shaping operations on it - it gets almost flimsy, then re-harden it. 6061-T651 has a lot of internal stresses that 6061-T6 does not - therefore if you heat treat 6061-T651 after machining, it’ll get all out of shape and twist. 606x alloys tend to be cheaper. A cut piece at the yard will look pretty “clean” without gummy chips welded to the cuts. If it’s a biggish block at the scrapyard, it’s very often 6061-T6, but if not marked, you can’t tell for sure.

5052 is generally easy to weld, but kind of gummy to machine. I don’t like machining it, and it’s generally cheaper than the others. If it’s not marked, with my luck, it’s probably 5052. If you’re looking at a cut piece at the yard, and the cut looks “gummy” - it’s 5052. I hate this stuff.

Cast aluminum (MIC6, there are a few brand names) has a very different internal structure (and that’s why it’s stays so flat) - and machines beautifully.

There are some brief, but clear descriptions of the various grades over here: https://www.onlinemetals.com/productguides/aluminumguide.cfm

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(Dan Nelson) #9

Don’t forget 7075! At “O” condition it can be formed like soft taffy, then heat treated and quenched to become amazingly stiff at T6. Its also really nice as T651 plate for machining (and expensive).

One thing worth mentioning in all of this is temper also determines form, meaning T6 is usually sheet goods under (from memory) 0.180” (and thinner) thickness, whereas T651 is thick plate and T6511 is extrusion. So depending on what form you need also decides the tempering process. And some series (2000, 6000, 7000, for example) are only available in certain tempers, and some can only be hardened from work/strain hardening (H rather than T).

Metallurgy is a fun topic, one I wish I understood better. But, ahem, we’ve totally hijacked this post now :no_mouth:

Dan

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(Charles Cade Lockwood) #10

Thanks everyone for the advice and the extra knowledge! It has been very helpful!

Plan on cutting this out this weekend so hopefully all goes well!

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