Thread: Cutting aluminium sheet

are you cutting all the way through ?
i used plasticine to build dams ( like a good dutchman) and flood the area with synthetic 2 stroke oil , only coz i had some handy (2mm deep ) it helped with my attempt at 3mm plate with a 2mm bit , running at 18000rpm , water might be better than something flammable ?

i was cutting out cogs for a clock , cutting all the way through ( cut2d with tabs ) , so used the machine to mark out the outline with a cut down sharpie and made heeps of small dams , i had problems in the centre of the sheet when vibration caused oil/aluminium sludge to get under the sheet and raised the height

yes i broke 3 bits before i got the feed speed right ( packs of 10 carbides off ebay , 2mm 2 flute bull nose's ) 1/2ing the feed speed each time i broke the bit , i ramped my z down , and 0.1 deep per pass , it was real slow

found i needed degreaser and windex to clean up the aluminium so the plasticine would stick to it if oil had been on the surface ( plastic protective covered aluminium)

also set the bits as deep as possible into the collet , my bits had 12mm cutting depth , when i order another batch i might look for 5 mm high flutes so the collet is closer to the job

i only ever use my spindle to a max of 18000rpm , just my choice ,

Hi Bob,
If you want to cut the sheet without breaking bits you are best to stay with an upcut bit 5mm or larger diameter. You are going to need compressed air and your kero and a Whisky as a lubricant.

What is happening is your feed rate is way too slow for 24000 RPM which is causing it to gall up. This in turn fills the flute of your bit with molten ally making it like a solid rod - you can't cut once it does this and the bit breaks. A lot of ally sheet material is gummy and it can vary across a sheet. What you need to do is cut fast enough to make chips and the air will expell those chips from the cut making it a clean cut each pass. Spray your kero around the cut as needed and when using air be careful of blowing chips into your eyes - yeah had it happen on a rebound.

With a 5 or 6mm upcut bit I would recommend 0.5mm DOC and 1200mm/min to start off with. I usually start at this and ramp up the feed rate to around 2m/min. Watch your chips and when you get a "C" shaped chip that is as fast as you need to go. Keep the air and kero going and watch for the sheet lifting during cutting.
The Whisky is for your lubrication as I reckon you will need it by the time you are finished.

Thanks Ken and Rod

I am cutting all the way through Ken, so although I could use your idea of mini dams all around the cuts, the last few cuts would be problematic. I will also have problems cutting in the centre of the sheet, because the nearest clamps are then 300 mm away, but I am having problems even when they are right next to a clamp, so central cuts would exacerbate the problem no end.

Rod
I could try putting everything back onto a 10 amp circuit so that I can use the 15 amp circuit for the air compressor. The trouble with using upcut bits is when I get towards the middle of the sheet it WILL lift. Maybe I can make up a temporary cross caul to hold the centre down. I did try going a bit faster, but the cutter started making a godawful noise and I chickened out.

So OK; swap over power circuits, fire up compressor, refill kero squirt bottle, use a 6mm up cut bit, 0.5 DOC with 1200 to 2000 mm a minute feed rate with a spindle speed of 20000 and shot glasses lined up along the edge of the table.

That all sounds pretty scary considering what happens at the slower speeds of feed and DOC but I will give it a go tomorrow. (I was looking for a smiley for apprehensiveness to put here)

I was originally intending to make these panels from 6mm aluminium plate. That should'nt take much longer that a couple of days to cut out that eh?

Can you use double sided tape to hold the aluminium down?

I've seen this work for perspex but I guess it also depends on what your table top is made of, if MDF I don't think it'll stick properly.

Hi Bob

I use 2 flute upcut bits for ally sheet at 0.5mm passes and about 20000rpm. Like Rod, I start out at 1200mm/min feedrate and ramp it up or down depending on the chip size coming off the cutter, and this varies with different types of aluminium. I think using downcut bits would exacerbate your problem by making it difficult for the cutter to clear the chips, so they re-melt and adhere to the cutter. I just use a bit of CRC or WD40 as a lubricant and it works well along with a shot of compressed air every now and then to clear away the swarf. I have used 1/8" cutters as well at 0.3mm and they handle it well too.

Cheers

Is there any reason you can't cut the sheets using a jig saw and an approprate blade

Bob,
Throw a weight on the ally while it cuts. Lead is good if you have some or a bag of sand will both help to reduce vibration and the sand will spread a long way if you nick it with the cutter.

Originally Posted by Ashore

Is there any reason you can't cut the sheets using a jig saw and an approprate blade

Yeah right. I make a machine that costs heaps of money, takes a year to make and is accurate to 0.0005 mm and it should do the job as easy as - so that I can use a jig saw for complicated jobs.

When I first envisaged the project, I actually tried a few samples using a jig saw. It takes ages to cut, is VERY noisy and jig saws are not that accurate. They are also very tiring to use when cutting through 20 or 30 metres of intricate outline.

Originally Posted by Ch4iS

Can you use double sided tape to hold the aluminium down?

I've seen this work for perspex but I guess it also depends on what your table top is made of, if MDF I don't think it'll stick properly.

Maybe Chris. I hadn't thought of that. It is however an MDF table

Originally Posted by Geoff Sims

Hi Bob

I use 2 flute upcut bits for ally sheet at 0.5mm passes and about 20000rpm. Like Rod, I start out at 1200mm/min feedrate and ramp it up or down depending on the chip size coming off the cutter, and this varies with different types of aluminium. I think using downcut bits would exacerbate your problem by making it difficult for the cutter to clear the chips, so they re-melt and adhere to the cutter. I just use a bit of CRC or WD40 as a lubricant and it works well along with a shot of compressed air every now and then to clear away the swarf. I have used 1/8" cutters as well at 0.3mm and they handle it well too.

Cheers

Thanks Geoff; noted. I do have some up cut bits so I will try them tomorrow.

Originally Posted by rodm

Bob,
Throw a weight on the ally while it cuts. Lead is good if you have some or a bag of sand will both help to reduce vibration and the sand will spread a long way if you nick it with the cutter.

Maybe I should get the wife to sit on it. That should hold it down. A good thought though and I will try it out with something, though the only thing I have at present is a bag of rice. Not heavy enough. Thinking, thinking, thinking.

Originally Posted by rodm

and the sand will spread a long way if you nick it with the cutter.

Ah, the voice of experience.

The only way to learn is to make mistakes. I am fast forgetter so sometimes I make them twice.

Originally Posted by Ashore

Is there any reason you can't cut the sheets using a jig saw and an approprate blade

1 reason , you cant put your Whisky on the same bench as the jig saw , but atleast it wont get sand in it again

Hi Bob,

Definitely not an expert but I've had good luck cutting 20mm and 12mm aluminium plate. A proper aluminium endmill for a start (got mine off Drillman on ebay) and its probably counter intuitive but double your speed to 1250mm a minute and drop your router or spindle to 10,000rpm and plenty of kero as lubricant. I put some concreter's plastic down on the bed to protect it from the kero. Hope this helps.
Cheers
Kim
ps. Should have mentioned .5mm per pass with 6mm endmill

Thanks Kim

That confirms what others are saying as well.