CNC cutting aluminium failure, tips needed!

CNC cutting aluminium failure, tips needed!

Postby Kayak23 » Fri Aug 04, 2017 9:25 am

Hi. I'm fairly new to all this cnc stuff so be gentle.

I'm usually to be found working with wood, but recently I've been starting to customise my motorcycle and one of the things I'm trying to do is to cnc machine an aluminium speedometer mount/bracket.

I've drawn it all up in Vcarve and done a million prototypes in acrylic, tweaking the design as I go.

ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr
ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr
ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr

I'm using a 4mm downcut carbide cutter.

So as you might expect, the cutter handles the acrylic beautifully but I bought this specific cutter as I thought it would do ok on aluminium(4mm thick T6).
It didn't.

In the below video, you can see that it snaps on the second hole! I turned the feed speed down to 30% and (as advised by the cutter supplier) coated the ally in wax to try to give some lubrication and also blasted with air, and yet it breaks so quickly.

Can anyone suggest the fundamentally wrong thing that I must be doing and perhaps suggest how I might resolve it?
Any help much appreciated thanks.

Youtube clip below.

https://youtu.be/WBEhoWDnd_g
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Re: CNC cutting aluminium failure, tips needed!

Postby IslaWW » Fri Aug 04, 2017 12:29 pm

Kayak...
Get a single "O" flute UPCUT bit, cut your feedrate in half, maybe more. Use an inside profile, spiral ramped option at about .030 pass depth on the tool

https://youtu.be/FdyZLi6phVI
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Re: CNC cutting aluminium failure, tips needed!

Postby Kayak23 » Fri Aug 04, 2017 3:05 pm

Wow thanks Gary.
That's a crazy video. So you're cutting the aluminium dry there?
I can see a mist on the cast iron but seemingly not on the ally?

I've managed to get it done now. I pretty much did what you suggested(before I saw your advice) but I used a 6mm HSS 4-flute upcut cutter that I found.

I don't think it was the ideal tool but it worked ok when I slowed the speed way down and kept misting it with oil.

ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr

ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr

ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr

ImageUntitled by https://www.flickr.com/photos/79912681@N06/, on Flickr

:D
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Re: CNC cutting aluminium failure, tips needed!

Postby Leo » Fri Aug 04, 2017 3:27 pm

You got it done which is all that really matters.

Just a couple of comments on cutting Aluminum and from your comments.

When you used the down cut cutter you were pushing the aluminum chips down into the bottom of the cut with nowhere to go. The chips got hot and welded to the cutter made an awful mess, the cutter was no longer cutting and broke. Seems all normal to me. If you find the broken pieces you will likely see the aluminum packed and welded into the gullets.

What Gary suggested with an up cut bit was to help to EVACUATE the chips. The downcut pushes the chips and compacts then - opposite of evacuation. That is what is really important with Aluminum - Get those chips out of there. Then you went to a 4 flute upcut - well that is better, but not best. The gullet (grooves) in the flutes are small and narrow on a 4 flute cutter that is designed for steel. Not really enough room to evacuate chips from aluminum. Best would be a 2 flute, or even a single flute cutter. Bigger gullet to evacuate chips. A squirt of WD40 works, some cutting fluid works, a mister works, dry is OK if you have the right feeds and speeds and gullet clearance. Aluminum is gouey sticky soft stuff and welds to the cutter easily. The fluids mostly help to get the chips to "slide" on the cutter and help to let the chips slip ans slide out the the gullets. Coatings on the cutters also help in much the same way.

Brass (alloy360) is FAR easier to cut than aluminum.
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Re: CNC cutting aluminium failure, tips needed!

Postby ger21 » Fri Aug 04, 2017 3:54 pm

Nice sander.
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