So, in preparation for the build for my big 3d printer, where I will have to mill quite a lot of aluminum, I’ve wanted to cut some metal, and see how it handles, and where the weakpoints of my specific machine are. Especially the spindle.
So, here it is, made out of two layer of 1mm brass
The cutout is made with a 2mm single flute endmill, I’ve used adaptive clearing, with a DOC of 1mm, using a machining boundary of around 3mm, at 10k rpm, 500mm/min, 0.3mm optimal load.
There was no significant chatter on the first piece, which was nice.
However, it got itselft dislodged, because of the cooling: I used rubbing alcohol to keep the bit cool and remove chips, but I guess it also softened the tape (using the masking tape and superglue technique). I couldn’t get it aligned again, so it’s going to look like this, forever:[attachment file=121042]
Second cut, again, worked without an issue.
And then I started redoing the first piece. And that’s where the issue started. Halfway through the cut, I stopped squirting alcohol on it for 30 seconds or so. The chips were coming out dry, but the sound didn’t change, so I didn’t think much of it. A few seconds later, the bit snapped. No sound of struggle or anything, just normal cutting, and then a small “tick”, and no more cutting.
Ok, I thought. Maybe it got too hot or some chips clogged the flutes. I tried again, with my last bit. And from the point of the break onward (I managed to salvage the cut, and brass is expensive, so…) the spindle just started to flex. It still fed, but the channel it cut was around 1mm smaller, and the bit had almost no movement. I slowed down the feedrate, paused often to let it cut it’s way back into place (the spindle shaft was flexing, so just letting it run would break the chip, but pausing ever so often let it settle back perpendicular). not a good look, but it managed. It was a bit out of tolerance, and the second wing didn’t much the first piece, but I would have to grind the many place where the bit couldn’t fully enter, so whatever.
I then run a small chamfering pass, and a couple of pencil passes (300mm/min, 0.1mm DOC) with a 10° 0.1mm bit, just to engrave the lines.
And then soldered it together, and promptly ruined by blobbing solder everywhere. Hint, grinding/sanding solder away, and reinscribing lines with a dremel.
An hour of grinding with various bits later, and it was finished.
I definitely need smaller bits for this jobs, but I also realized that the 500W spindle is definitely shit. So, I’m looking to get a new one, but I’m really not sure what my upgrade should be. My machine is quite big, and while I’m going to upgrade to stainless tubes soon, I’m not sure it could handle a real spindle, with a vfd and decent collets. But at the same time I really want to keep the ER system, it makes it so much easier compared to the limited shaft diameters you can grip with a router. So I’m thinking about maybe using a er16 collet extender with a 10mm shaft in a katsu router, but I’m worried the stickout is going to increase too much and give me similar issues again.