Milling Aluminium

[Stuart Munro 1Participant @stuartmunro1]

Hi, As an engineering novice (a retired accountant whose friends advised me to do something useful in retirement!) i'm a little confused about the type of slot drill most appropriate for cutting into and milling aluminium. I understand a slot drill is needed to both 'punch' down through the aly but not sure if I should use HSS or Carbon bits, coated or uncoated.

I had a couple of uncoated bits which chipped very quickly. This may well have been due to inadequate clamping of the work piece but before replacing the bits would welcome any advice on what best to buy.

Thanks

Stuart

[Stuart Munro 1Participant @stuartmunro1]

Best type of milling bit to use

[JasonBModerator @jasonb]

Uncoated is best for Aluminium as it helps stop a build up of metal on the cutting edges, the addition of a lubricant in the form of Paraffin or WD40 will also help reduce this problem.

HSS or Carbide will both work, HSS is a little less likely to chip until you get your setup sorted out.

You can get cutters specifically for aluminium which have a steeper helix angle to help remove the swarf which is handy if using high feed rates.

[John HaineParticipant @johnhaine32865]

Also depends on the aluminium. Some machine very nicely, but common aluminium sheet can be a pig, very sticky and sticks to the cutters.

[old martParticipant @oldmart]

You would get the best use by keeping the really sharp cutters exclusively for aluminium and never using them on steel. A lubricant used sparingly is essential to keep the aluminium from sticking to the edges. Always put something soft under the tool when changing cutters as a drop onto the bed, or floor can chip the ends. Chipped carbide cutters will still cut quite well and can be used for roughing.

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Haine on 27/03/2021 16:00:08:

Also depends on the aluminium. Some machine very nicely, but common aluminium sheet can be a pig, very sticky and sticks to the cutters.

+1!!!

Pure Aluminium is horrible to machine, gooey, sticky, yuk. Other alloys are made to bend or extrude, so DIY store metal, sheet and scrap window frames are best avoided too, as are those intended for electrical work (bus-bars), for welding, or their thermal and anti-corrosion properties. As more aluminium alloys don't machine well than do, it's best to buy the right thing than to muck about with an unknown alloy.

UK metal supermarkets publish this guide, note only one of the machinable candidates is unambiguously 'Excellent', and there are dozens of Aluminium Alloys that aren't rated at all:

• Alloy 1100 – Good Machinability (Best if Hard Temper)
• Alloy 2011 – Excellent Machinability
• Alloy 2024 – Fair Machinability (Best in Annealed Condition)
• Alloy 3003 – Good Machinability
• Alloy 5052 – Fair Machinability (Better if Hard Temper)
• Alloy 6061 – Good Machinability (T4 and T6 Tempers only)
• Alloy 6063 – Fair Machinability
• Alloy 7075 – Fair Machinability (Best in Annealed Condition)

Other alloys can be machined, it's just that they are more-or-less difficult, some much worse than others. Having suffered by trying to learn on a scrap box full of unfriendly metals myself, I recommend beginners start with metal designed to be machined, only moving on to the nasties once one knows what to expect of a decent metal.

Same problem applies to other alloys: steel, brass, and bronze also come in varieties that machine well, are truly horrible, or in between. It pays to buy metal that's meant to be machined so the material can be eliminated as the problem when a job doesn't go well. Look for 'free-cutting' or 'good machinability' in the specification.

Dave

[Stuart Munro 1Participant @stuartmunro1]

wow, stepped away for 10 and a wealth of info floods in. thanks everyone. will now read and digest

stuart

[Stuart Munro 1Participant @stuartmunro1]

Thanks again,

Dave, your comments on grades of Aly alloys is very helpful; I hadn't thought much about this before. I have noticed that when I buy the metal from someone like GLR Kennions (my preferred source) they do advise on machinability etc of each grade on sale but alas I'm using some cheapo 'B&Q' sourced stuff for a small supposedly quick job so I've no idea what it is.

And WD40 for a lubricant – i'll certainly try that.

Many thanks

Stuart

[JasonBModerator @jasonb]

You will find a lot of the ME supplierts list HE30 which is 6082 in new money and that would be your best bet for general work and is readily available.

Close to Dave's 2011 is 2014 which you may find being sold as HE15 by the ME suppliers which does machine nicely although it will wear a hole in your pocket as it is quite a bit more expensive so best kept for jobs where it's strength and bearing properties are needed such as IC engine con rods.

If you are going to be using a lot of WD40 then get the liquid in the 5lts cans and hand pump bottle as it's cheaper than spray cans but paraffin from petrol station or garden centre is far less costly.

[Stuart Munro 1Participant @stuartmunro1]

Again, thanks for the quick and helpful comments.

Stuart

[Ron LadenParticipant @ronladen17547]

I guess I use aluminium quite a bit and for most cuts I use the 2 flute uncoated HSS cutters from ARC,s premium range. Good pricing and good quality they work really well.

[HopperParticipant @hopper]

You need to have your spindle rpm appropriate to the diameter of slot drill you are using too.

[Stuart Munro 1Participant @stuartmunro1]

Thanks Hopper, got that one. Aly can be cut at quite a high speed I believe. I have a chart with my mill instructions showing SFM of 268 (Aly 2024) to 400 (aly 7075). Clearly the RMP to achieve this varies with mill diameter. But I'm naturally cautious:

I do confess that as a novice the whole concept of a faster feed to reduce chatter leaves me nervous. My inclination is to reduce rpm (correct I think) and reduce feed (wrong). So logically I should go at the right speed as above, but feed faster to reduce the chatter.

Practice and practice again!

Stuart

[Stuart Munro 1Participant @stuartmunro1]

p.s. Learning to mill in a covid crisis is interesting. It's all book (or today internet) learnt whereas it would be much better to be instructed by someone looking over my shoulder.

Stuart

[Dave HalfordParticipant @davehalford22513]

Posted by Stuart Munro 1 on 28/03/2021 10:34:36:

p.s. Learning to mill in a covid crisis is interesting. It's all book (or today internet) learnt whereas it would be much better to be instructed by someone looking over my shoulder.

Stuart

It should be Stuart, except if you take a college course on either machining or welding they teach on industrial grade machines, then you go home and find what you have is incapable of the same work.

[Stuart Munro 1Participant @stuartmunro1]

Dave, Just what I thought but I do believe that the a model engineering organisation runs day schools in London. Might be worth checking out once we can gather inside once more.

Stuart

[Stuart Munro 1Participant @stuartmunro1]

I do have a possible alternative training option – sit in with an experienced engineer if you know one. Luckily I do know one who runs his own shop. But again, I have to wait for the end of covid restrictions.

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