Breaking bits trying to mill aluminium

Talk about all things CNC
akhlut
Posts: 304
Joined: Wed Mar 27, 2013 1:16 am

Re: Breaking bits trying to mill aluminium

Post by akhlut » Tue Nov 04, 2014 3:12 pm

Arhau,

I've been busy lately - family, housework, homework. That being said, I've been playing around with OBS and I think I've got the hang of it.

What are you making? I'll make something along those lines in the video.

And don't feel bad. It took me a long time to get to this point with CAD and I am by no means a master at this, but I'll share my workflow and hopefully it'll help with your projects.

Matt

Auarhau
Posts: 243
Joined: Tue Feb 25, 2014 8:46 pm

Re: Breaking bits trying to mill aluminium

Post by Auarhau » Wed Nov 05, 2014 9:30 am

I'm trying to do something similar to what you did here. Only I already have the mount, I need a new Z mount plate to mount it to. I could make this part easier with a table saw and drill press, so this is more of a CAD exercise for me. I want to learn how to work out problems like this in CAD. I need the plate to be long enough to enable the end mill to reach all the way down to the waste board. And thick enough to avoid too much flex and also thick enough for the spindle to clear the Z motor mount. Because of how this spindle mounts, It wont reach far enough down when I mount it on a standard Z plate. I also plan to use Fusions integrated CAM to cut the part. So it should be a nice Fusion project:) I'm comfortable with 2D cad by now, but adding the third dimension complicated things (and also opens up a lot of new possibilities). A huge benefit I see is being able to pull dimensions from existing models, and use that to make new parts in stead of having to painstakingly measure the real life objects (which is hard to do accurately for some objects).

Image
Got the kress from here: https://grabcad.com/library/kress-1050- ... ng-spindle
Mount: https://grabcad.com/library/spindle-mount
(I haven't measured if these models are dimensional correct, but they sure look like the real thing. And still good for educational purposes).

This is where I'm currently at. My next step is to make a new plate that has the same bolt patterns for the v-wheels and delrin nut as the original, but new holes that fit the spindle mount and bolts. This is where I'm stuck:)
The next logic step for me is to then take this assembly in to the complete SO2 model, and mount it there to investigate clearance of the Z motor, and figure out how long and thick this needs to be.

This is perhaps a more involved job then the one you did here. But I think what you did in your model could easily be carried over to my problem.You imported the spindle and plate, and then made new clamps to fit both parts? I'd be very interested in how you went about doing that! :) And I'd be more then happy if you just ran through the same process, but if you want to try my problem that's almost the same problem only a different part.
ShapeOko 2. Nema 17 74 oz·in. GAUPS shield on Arduino Uno. DRV8825 Drivers x4 . Kress 1050 FME-1. Z Acme Screw. Threaded inserts table.

akhlut
Posts: 304
Joined: Wed Mar 27, 2013 1:16 am

Re: Breaking bits trying to mill aluminium

Post by akhlut » Wed Nov 05, 2014 4:11 pm

OK.

I'll make a video showing you how you can accomplish this. :D

aarvidsson
Posts: 150
Joined: Sat Aug 03, 2013 4:46 pm
Location: Frosty Sweden

Re: Breaking bits trying to mill aluminium

Post by aarvidsson » Mon Dec 08, 2014 6:25 pm

mmmmyeah, it's me again.

Is 2024 a good alloy to CNC?
ShapeOko 2 #4143

LouisV
Posts: 316
Joined: Fri Dec 13, 2013 3:41 am

Re: Breaking bits trying to mill aluminium

Post by LouisV » Mon Dec 08, 2014 6:43 pm

2024 is very strong and is used a lot in some aerospace applications. Its ok to work with, I'd say its in the middle. Its not gummy like some other alloys but it doesn't produce the best finishes and will take a little longer to mill over say 6061-T6

aarvidsson
Posts: 150
Joined: Sat Aug 03, 2013 4:46 pm
Location: Frosty Sweden

Re: Breaking bits trying to mill aluminium

Post by aarvidsson » Mon Dec 08, 2014 8:01 pm

oookay. The guy I got it from is actually working with military airplanes (scrap pieces of sheets, apparently) so that might explain the choice of alloy. It might also partly explain my problems with cutting it.

Here's where I stand:

* Quiet cut spindle at a reasonable speed (usually somewhere around half speed, as full speed means a bit breakage before I can even turn the dial back down)
* Great custom aluminium attachments for the quiet cut spindle (thanks, Akhlut!)
* 2-flute 1.5mm end mill specifically designed for aluminium (according to the seller, whatever that means)
* 0.2mm per pass, 250mm/min feed rate, 50mm/min plunge rate
* coolant/lubrication is either WD40 or methylated spirits

The sheet (30x30cm) is held down with long inventables-style clamps on the long edges, as well as double sided tape underneath.

Result: calamity ensues within a minute. Depending on the spindle speed it sounds like the sheet starts to vibrate and chatter, and if I can quickly shut the whole thing down I might get to keep the end mill. Most often not, though.

I've tried different end mills (2mm down cut, 1.6mm upcut as earlier mentioned), always with the same result.

The funny thing is that a 1.5mm diamond burr at 0.1mm passes works just fine. The sheet does not seem to vibrate very much at all, the whole affair is fairly quiet (as opposed to the previously mentioned audio nightmare) and the result it excellent. Trouble is, I've been told time and time again that this is Not The Correct Way To Mill Aluminium.

So - for a final recap: why can't I mill aluminium the way other people seem to be able to? Will the ordered-and-soon-to-be-delivered ACME Z axis help going forward? Would another spindle help? Stronger motors? Yelling at the sheets? Changing alloys?
I'm happy to keep milling with the burr (despite it taking a long time), but I'd love to come to grips with WHY the gods of CNC take every chance they find to dump on my feeble attempts...
ShapeOko 2 #4143

LouisV
Posts: 316
Joined: Fri Dec 13, 2013 3:41 am

Re: Breaking bits trying to mill aluminium

Post by LouisV » Tue Dec 09, 2014 12:16 am

Changing alloys would probably be your best bet, though I'd try to cut at 0.1mm per pass to see if that helps before abandoning 2024. The Shapeoko 2 is a good little machine, especially if it's upgraded over the stock design, but you really don't want to be machining exotic or aerospace grades of aluminum on it. They require a careful touch and in many cases a more capable machine than the Shapeoko 2.

7075-T6 (another grade of aerospace aluminum) gave my old upgraded Shapeoko 2 a really really hard time, and it was a beast of machine as far as Shapeokos go. :shock:

I highly recommend 6061-T6, it's a very nice alloy to machine and is pretty forgiving to new comers. You can technically mill it without coolant or lubricant of any kind if the feed rate, depth of cut, and spindle RPM are set correctly (though I still prefer using coolant).

Caesar S
Posts: 197
Joined: Mon Sep 29, 2014 7:19 pm
Location: Seattle, WA

Re: Breaking bits trying to mill aluminium

Post by Caesar S » Tue Dec 16, 2014 3:02 am

Another perspective might be the aluminum sheet resonates with the RPM of combination spindle + bit (# of flutes, length, etc.) + feed rate + direction of travel hence making the loud sound.

To test this hypothesis, place some rubber sheets under the aluminum to dampen the frequency resonance :D

aarvidsson
Posts: 150
Joined: Sat Aug 03, 2013 4:46 pm
Location: Frosty Sweden

Re: Breaking bits trying to mill aluminium

Post by aarvidsson » Mon Apr 27, 2015 6:49 am

Eureka! I've *finally* nailed milling thin sheets. The solution? Superglue. I use a thick (>4mm) piece of aluminium larger than what I need to cut, clamp that to the wasteboard and then dab a few drops of standard cyanoacrylate superglue on the thin sheet and slap it to the larger, thicker piece. Then I break out my 1.2mm 1-flute endmill (http://www.ebay.com/itm/1-20mm-0472-sin ... 58a7df7885) and run it at a feed rate of400mm/min, plunge 100mm/min and a pass depth of 0.2mm. The spindle (quiet cut chinese version) runs at full tilt. I'm fairly sure I could increase the numbers, but considering the number of end mills I've broken in the past, I'm just happy to have something that works.

When I'm done all I have to do is give the thin sheet a good whack sideways and it pops right off the larger sheet. No vibrations during machining, quiet enough that my downstairs neighbours have no idea what I'm doing, and even the wife acceptance factor is quite high.
Last edited by aarvidsson on Mon Apr 27, 2015 9:55 am, edited 1 time in total.
ShapeOko 2 #4143

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Breaking bits trying to mill aluminium

Post by cvoinescu » Mon Apr 27, 2015 9:00 am

And if it gets stuck and does not release, you can heat it to destroy the glue (but I would not do that indoors).
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Post Reply