How to cut aluminium?

[casstony]

Is it ok to cut aluminium with an angle grinder or should I use a hack saw? I'm wondering if it will clog up the cutting disc.

I'm cutting up a Vixen-style dovetail into shorter segments and want to do a neat job, but I'm also curious about aluminium cutting in general.

[bojan]

Use a hacksaw, and use kerosene (or petroleum) for lubricating (and to prevent clogging the hacksaw teeth).
Never use an angle grinder for aluminium.

[merlin8r]

I use a Makita Compound Mitre Saw. The instructions say you can do this. Just do it slowly! An angle grinder may well melt the aluminium as it spins so fast. If you were in Sydney I'd be happy to cut it for you. See if you know anyone with a similar saw.Clear skies,Shane

[Glenhuon]

Like the man said, never use an angle grinder for soft materials like aluminium. It will jam in the cut and either shatter the blade or fly back at you. Either way the consequences could be nasty.
Cutting by hand with a hacksaw needs a coarse toothed blade 12-10 teeth per inch and kero for lubricant. Petroleum is not recomended as the heat generated by the saw could ignite it.

Retired Fitter

[gbeal]

If you are energetic take the hacksaw route. If not, sidle up to an alloy joinery sho[, the type that make windows etc, you may be able to convince someone to cut it for you.

[jjjnettie]

I used to do light weight aluminium fabrication for a number of years.
We used beeswax to lube the blades.
If you have a straight edge on the piece you are cutting, that you can butt up against the back of the saw bench, use the mitre saw, otherwise use a hacksaw. Mark your cut with masking tape because pencil can wipe off.

[casstony]

Thanks for the advice guys. One more question: roughly what speed should I run a countersinking bit at and should I lubricate this with kero?

[Glenhuon]

I'd keep it down to 400rpm at most, otherwise you get a bit of "chatter and the csink looks rough. Yep, lubricate with kero, gives a better finish and lengthens the life of the countersink bit.

[OneOfOne]

Also when countersinking, I have a "single flute" countersink. A normal "woodworking" one with 4 flutes will often leave a very rough finish, especially if the speed is too high. Generally with ali, slow is better than fast as it has a tendancy to "grab"...not as bad as brass though!

[GeoffW1]

Hi,

Other posters have covered the most of main recommendations. There are a few issues at work:

- Clogging a cylindrical grinding wheel with aluminium or other non-ferrous material can cause the surface layers of the wheel to disintegrate and fly around. The danger is not so acute with an angle grinder disk which usually has embedded fabric reinforcement, but it still isn't recommended.

- Using a compound mitre saw with a blade which is normally intended for wood will certainly work, but you must take it very very carefully and not press the progress of the cut at all. This is because the teeth of such a blade have positive rake angles and can 'hook' and catch the metal, jerking it forcibly away. Something usually shatters, like the carbide tooth inserts on the blade. You can buy aluminium saw cutting blades from Bunnings etc and these have different cutting tooth angles. At the very least try to arrange 2 point mechanical clamping of the job with a G-clamp or similar.

- Aluminium dust is injurious to the lungs, and can also form an explosive mixture with the ferric oxide dust produced by grinding steel. Explosions in home workshops from such a mixture of grinding residues are rare, but not unknown.

- All in all a hacksaw is recommended as our colleagues have suggested.

Cheers

[Lee]

I've always clamped the aluminium to a piece of timber when cutting with a drop-saw - especially with Al angle - place it over a block of timber, helps to brace it while it cuts too....

[Phil]

I use a jigsaw make life easy.
phil

[casstony]

Thanks again for all the info guys. I got the first cut I needed done at a local windows place, but I don't want to bug them again.

Phil the jigsaw sounds good (since I have one). What type of blade would you recommend? From the other posts I gather the jigsaw would be run at a slow speed?

[davidpretorius]

the aluminium oxide that forms the skin on aluminium will clog.

bees wax is what they put into aluminium cutting discs to stop the clogging

saint gobain partno 1610216 from a mitre 10 store 102 standing for 4" or 102mm.

[davidpretorius]

aluminium being soft needs high speeds

[GeoffW1]

Hi David,

'Fraid not, the aluminium oxide layer is very thin, about 0.05 mm max, and it is not this which clogs the teeth of a file or blade, but the parent metal. Aluminum oxide is also known as carborundum, and is not soft but very hard and brittle, and is widely used as an abrasive grit in grinding wheels and papers. Ever see a white cylindrical grinding wheel? Aluminium oxide.

All the same you have posted very good advice, a jigsaw is a great idea, very safe, and I would use a blade about 4mm pitch, or about 6 tpi. Generally you would use a coarse blade in softer metals, and don't force the cut.

Cheers

[GeoffW1]

Yes, higher speed settings I reckon also.

Here is an interesting comparative reference which is quite relevant.
http://www.bahco.com/files/Selection%20Guides%20for%20Bandsaw% 20Blades_cmjmkoklqluaoifancqqipjno. pdf

Bandsaws have to have the correct settings and blades as a machine tool class, because otherwise they will throw the blade.

I once had a terrible time with a bandsaw trying to saw up a radial car tyre, I could not get the right combination, and it threw the blade persistently until we sped it right up and took the cut very slow.

Cheers

[monoxide]

nothing will give a better cut than a drop saw with a proper aluminum cutting disc, i used to cut a lot of aluminum extrusion with one, very smooth almost polished cut but the blades are expensive. i always used lanolin spray as lubricant.

a rough cut will take a long time to clean up with a file or the like and it will never look professional (before we got the cut off disc i used an electric hacksaw but the cuts looked horrible)

[Orion]

lol...just get a plasma cutter!

[casstony]

The pst now has its own dovetail. With a cheap mount left out on the back veranda the dovetail minimizes set-up time. For countersinking a mulit-fluted bit at low speed seemed to work best.

[Starkler]

I need to trim 15mm off the ends of my truss poles so I can achieve focus with a paracorr.

Does all the same advice apply here for cutting aluminium tubing? Hacksaws and the like are out of the question as I need square and clean edges and absolute repeatability on the cuts.

[ausastronomer]

Hi Geoff,

To do this it's a good idea to "borrow" a proper pipe cutter. You can buy a reasonable quality one for under $50, but thats a lot of money to cut 8 pieces of pipe. If you know a plumber he will have one or alternatively you could go to a metal fabricator who might charge you $10 or so to do the 8 poles. No point doing a 1/2 pie job on a beautiful SDM scope.

CS-John B

[AstroJunk]

Or go and have a nice afternoon out in the contryside and get Peter to lop the ends off for you! (I'm pretty sure he uses a std pipe cutter)

[skeltz]

MY FRIEND RICHARD AT HERES THE LINK http://www.baytop-observatory.com/
he has cut aluminium several times quite succesfully with a circular saw with a mitre blade.. do not use a ripping blade thats all
cheers skelty

[rumples riot]

Just a little advice.

the use of a carbide tipped blades is a no no for cutting aliminum. The correct saw to use is an aliminum blade; they look similar but are very different. Using the former can and does throw teeth and could cause serious injury. The item can also be ejected from the cutting bench and cause further injury. An ali blade will set you back a bit , but will be worth the money.

BTW I know this because my employees use ali blades for cutting Ali T Bar for exposed grid systems in office and commercial buildings (tiled ceilings). I am a ceiling fixer by trade and have seen ali cut with standard blades in the past and the disasterous results that can occur even in the hands of experts. Something which most of you are not. (No offence intended I just don't want to see anyone get hurt).

Don't risk the blade exploding and causing your death.

[ausastronomer]

I personally don't agree with people recommending cutting aluminium with a circular saw in any way shape or form. As Paul points out the use of the wrong blade can be very dangerous. For trades people and skilled handymen who know what they are doing, it's fine. To tell someone who may not understand the different complexities of circular saw blades how to do it in an internet message is like sending a 10 yr old boy in to open against Brett Lee.

CS-John B

[rumples riot]

BTW Geoff a Hack saw is fine. To be a square line simply wrap a piece of paper all the way around the pole at the correct cut off point and then mark that with a fine tipped texter. Take the paper off and cut with the hacksaw. I typically use a 32 tooth blade for cutting ali by hand. Once cut then use a fine file to take the edges off. It will be clean and just what you want. Something like this you want to take you time with. Unless you are familiar with a drop saw I would not attempt it. You can cut it on the wrong side of the tooth and that will ruin that pole.

[CoombellKid]

Sorry for off topic, but since you guy's are talking about gutting things and
sound alot more knowledgeable than me. I brought a angle grinder the other
day and it came with a few different blades and a steel brush.

So my Q is what would you cut with a diamond tip blade?

regards,CS

[rumples riot]

Diamond blades will cut all masonary including concrete and brick. It will cut plastic also.

[Starkler]

Thanks John and Paul for the warnings re carbide tipped blades, which incidentally I have seen recommended on tool vendor websites for cutting aluminium :shrug:

I don't want to risk manual hand cutting with a hacksaw, as any variation in final lengths may throw out the alignment at the top end of the scope. 1mm error at the bottom would cause maybe 5mm displacement at the UTA. It looks like I'll have to track someone down with the correct machine tools.

[CoombellKid]

Why of course, you see the council cutting up the pathment with the o'l
diamond blade motor mower looking thing all the time. Doh! I guess I should
thought about that one a lil more. Although I dont think I'll attempt that with
my you beaut fathers day special $30 angle grinder from Mitre 10 :lol:

regards,CS

[erick]

A whole $30! I think I bought mine for $18.94 or similar. :D I suspect it's not designed for a full tradesperson's workload! But it's done a few small jobs for me successfully.

[GrahamL]

finished up nice tony :).

geoff most small engineering shops would cut your poles for a few dollars .

[OneOfOne]

If it was me, I would cut it off with a hacksaw and the put the end into my mill and run a cutter over the ends to make them "identical". Don't you have a mill in your garage? Do you want to "borrow" mine? I spent most of the weekend in the garage working on my mill and lathe...

[Starkler]

Trevor the ends of each pair of truss poles are screwed to a wooden device which clamps to the uta (see pics) and removing the fitting to work on the poles singly might screw things up (alignment).

The ideal arrangement would be some kind of drop saw with a depth stop so that each cut could be made identical and perfectly square. I need to take identical lengths off each pole and am nervy about the prospect of stuffing it up :whistle:

[OneOfOne]

Hmm....I see what you mean.

I don't know how you could easily do that...if you decide the fitting needs to be removed then I can run a cutter over the ends to square them up for you. This would allow each one to be trimmed to a fraction of a mm with a nice machined end.

You could run a pipe cutter around the ends but I don't know if it could be set to cut exactly the same lengths, cutting to right depth and not damage the fitting inside I don't think would be a major problem. How would you get the cut off bit off the end?

Let me know how you go.

[Glenhuon]

Looking at the pic I'd say you have no alternative to removing the fittings. Any good machinist should be able the then trim the poles to within thousandth of an inch and redrill the screw holes in a like manner using a mill. Having said that, it looks like given how the truss is constructed, any tiny misalignment will be compensated for by adjusting the secondary mirror during collimation. Just the observations of a retired fitter :)