Prototyping 2 - Day 4

Ahh Day 4. Daaaaaaaaaaaaay 4. The main thing I remember about that day was that it was f**king s**t. Everything that wanted to go wrong, went wrong. Machines, tools, parts, everything just gave up on me today. I started off in the morning by drawing out the DXF profiles for the internal split barrel. This was the only component which I hadn't prepared files for. As the component had been made in CAD, it was simply a case of jumping on Solidworks and converting the correct entities. I turned off a length of the aluminium on the manual lathe and got it into the CNC to cut.

So I go to run the program and a few seconds into it BAM! I always watch the machine working to make sure nothings going to collide, so i was quick to hit the feed hold and then the emergency stop. What a pain. The tool had been going to face off when the material just went, ah f**k this and decided to try and tear itself from the chuck. Brialiant. In the process, the tool head carried on blissfully unaware that the tool had snagged and the material was no spinning around off centre, and so it just ploughed on and started to rip the tool from the turret. GREAT. Just what i want first thing in the morning.

The material had been in the chuck very tight, and because it was thick walled the incident didn't distort the tube, just left surface damage. That meant that I could just twist it half a turn and secure it in the chuck again if I needed too. In reality, the biller was too long for the machine to hold properly. It needed to be halved again before I could continue, which I didn't do in the first place because it's very wasteful (you need material for the chuck to grip) and also I honestly didn't expect the machine to be so weak at holding the part.

The more annoying thing than the material being ripped out was the tool being moved. It needed to be released and put back in it's place. But of course when you put it back, how can you be sure it's in exactly the correct place?

You can't. I ran the profile again and took the part out, put it in the nylon support material which was cut manually to fit, and well would you look at that. It's a sodding mile out. Is that a 1mm gap?? 1mm isn't a lot to normal people, but to me, running on a machine which goes down to a 0.001mm tollerance? 1mm might as well be a mile. So I had to spend half an hour flicking through a manual and the CNC control software finding out how to re-calibrate the machine so it would cut accurately with the tool in it's effectively new position. Time wasted, material wasted, what a bad morning.

After calibrating the machine I ran the programs I needed to run and the results came out fine. Cutting aluminium is pretty horrible. The boring bar isn't very sharp, and it makes the worst god aweful whining sound when it runs. Machines talk to you when they run, you built up a relationship with them where understand what they're feeling and you can help them out. The machine was telling me today that it really wasn't enjoying it's self. There wasn't much i could do apart from spray lubricant on the tool, so it angrily spat out a load of swarf and tangled it's self in it. That swarf is metal. Metal. It's basically a long thin coiled knife, so i ended up needing pliers to get it off without shredding my hands.

The parts came out alright and fitted together well after all the fuss with the machine. There were little problems like shown below, where the machine wouldn't cut the alli off cleanly and leave huge burrs, but they could be taken off my hand easily, so it didn't really matter.

With those done and most of the day gone thanks to things going so unsmoothly, I quickly progressed onto cutting some of the basic plano convex optics for the 90.2 lens. With acrylic already cut, I just needed to turn down a length for the chuck to grip and start running the program.

Mounted in the machine everything looked good. The billet was a little long but with the large step at the back pressing against the face of the chuck teeth, I had confidence the machine would hold it in place well enough. So off I went and cut the surface, nothing tricky, just a gentle large radii cut out of acrylic.

What is wrong with everything today?!! 49.44? Are you joking! I've just calibrated the tool, why is it over cutting!? It should be 50.00 dead! ARGH. Recalibrated AGAIN, and recut again! I was half tempted to give up before I ended up wasting yet more sodding material.

Okay so it's cut to the right size now. Why is there so much crap on the surface?? Damn swarf is remelting even after adjusting the feed speeds. No! I will not be treated like this by a machine! I hit re-run on exactly the same datum so the machine would cut it's own melted swarf off. That did the trick! Double pass to ensure surface quality! Look at the difference! That'll polish up perfectly! Finally things going my way, now all I have to do is part off and I have a lens element finished right before the end of the day! What could possibly go wrong now??

...............................................................

BAM!

Life hates me. How could the simplest thing go wrong. I was parting off the lens with a straight tool, using endless lubricant, when the swarf resolidified around the tool so thickly that the strength of the new bond was enough to rip the entire part from the chuck of the lathe and fling is a couple of meters behind the machine, snapping the lens in half in the process. ARGHHHHHHHHHHHHHHHHH. You can see where it all went wrong in the photo below, after I cut the remaining half of the optic off. The area where the swarf became solid again can be seen right at the top. What a crap end to a weeks work! Atleast i could catch up on sleep and start a fresh on the Monday.