Feeds and Speeds

Just another little tidbit, this time from the CNC project. Because I lost some sleep over this.

So I'm milling a lot of aluminum and making a horrible mess. Kept adjusting the feed rates, spindle RPMs, and all that trying to get this silly thing to make some cuts and feeling like I was getting slower and slower and the results just weren't looking right. So finally I remembered that I don't really know much about machining and punted from the internet to see what kinds of settings other people were using.

Long story short it seems hard to find just a simple table that would get a person, you know, like in the vague area of what they should be doing. But eventually I did find some equations.

The results? I was off by about two orders of magnitude on my last attempt. And killing my bits prematurely. Here's the basic idea:

RPMs = feed rate / (number of flutes * chip size)

that's pretty rough and there are lots of variables to take in to consideration  (coolant, how much block am I actually cutting, is it a pocket, bla bla bla) but this seems like a good starting place. Re-arrange that for whatever variable you have easy control over.

The idea is simple actually: your chip size has to be bigger than the roundness of your bit (which really does always have a little bit of roundness and usually a chamfer leading to the cutting surface). Otherwise you are just scrubbing the outside of the bit against the aluminum until it wears down or melts/wears away. This is called burnishing. You might as well have loaded the machine up with a slightly roughened carbide rod instead of a proper endmill. A good size for this is 0.004 inches and up on a 1/4" bit. So I tossed together this little chart with the idea that I would be taking out 0.005 inch chips. ipm = inches per minute and all the numbers in white are RPMs for the spindle:

		flutes
ipm	2	3	4
0.25	25	17	12.5
0.5	50	33	25
1	100	67	50
2	200	133	100
3	300	200	150
4	400	266	200
5	500	333	250
10	1000	666	500
15	1500	1000	750
20	2000	1333	1000
50	5000	3333	2500
100	10000	6666	5000
150	15000	10000	7500
200	20000	13333	10000

Now is this some kind of be-all-end-all chart? No, but it's a good place to start and a good place to see if you've really screwed up or not. You can also see some of the trouble of using bits with lots of flutes on aluminum. Aside from troubles clearing chips before the next cutting surface comes around: if your machine isn't very fast it's difficult to move forward fast enough to do more than burnish the aluminum away. 

So there's a really simple "this is the sort of feeds and speeds that make sense for milling aluminum" chart I wish I'd found really early on. I might not have been grinding away with a 4 flute 1/4" bit at 0.5ipm and 1500rpm trying to get the darn machine to settle. Oops.

Lots of really good in depth stuff is on here as well

Information that will be useful in the future...

Typical velocities of some insects:
Dragonfly: 15.6 mph
Hornet: 12.8 mph
Horsefly: 8.8 mph
Honeybee: 5.7 mph
Housefly: 4.4 mph
Damselfly: 3.3 mph
Scorpion Fly: 1.1 mph

So that range is ~700 centimeters per second down to ~50 centimeters per second. So somehow I need a response and trigger time somewhere around 1/700th of a second for the fast guys and 1/50th of a second for the slow guys if I'm going to be predicting just where they will be at... uhm... I've said too much already...

What to do with an extra day?

Since both parties had an extra day and never got to meet up, what better way to end a rock climbing trip than with more rock climbing?

Stone Summit Climbing Gym, on the north side of Atlanta

This place was excellent. Sixty foot ceilings, excellent equipment, and some great climbers. In fact we even ran in to a few people from Aiguille back home!

We climbed till we couldn't.

and about that fail part...

"More people drop out of distance races due to stomach issues than do from injury"

 Asleep, then awake, sick as a dog. The one thing I didn't test out beforehand was the prepackaged freeze dried food, and it did not agree with me at all.  This marks the coffin for productive work on the trip itself for me. At most I had a couple short climbs on boulders on the way down the mountain, but it was quite over with. We would spend the next night in a hotel.

The long way down. Mike found a super-banana.

This turned out to be a lucky break in a way; it ended up raining on the mountain the night after we left (Marcus, no tent, freezing rain might not have been so hot), and the second group we were going to meet up with had to cut short and head out early too.

Back to Neel's gap:

Neel's Gap: this place felt eerily similar to a Buddhist Sanga. Shoes hang like prayer flags from the tree outside.

We had just a couple more stops to make before the final drive home.

What remained of Mike's hands when we got to the bottom.

Night Three: Triumph and failure...

Thanksgiving is always a time of mixed thoughts for me anyway, and I should assume the same no matter where I am or how removed I may be from 'real life.' On normal years it's a time when family and friends converge. My brothers, nieces, parents, cousins, etc, as well as often those who are part of my family that I am not related to. It's also a reminder of a friend lost, who died trying to rescue a stranger from a car accident. These things happen, and it's not to us to judge them.

We gathered in our makeshift camp with our makeshift family for Freeze-Dried Thanksgiving Dinner. It was...not good. But the company was great. As the sky found its stars* I packed the astro-gear up and took another climb to the peak. This time it was clear: still below freezing, but bone dry.

So I'm sitting up there looking at the stars, trying to get my bearings. Great at knowing which way is north, and normally instantly identify all the reference stars...but I'm used to being at sea level. Even on the clearest of clear nights it's nothing like this. After trying to trace from constellation to decide which one was the north star and actually failing (well there goes my astro-cred!) I went for the simplest idea I could think of: take a long exposure sans-tracking:

Well there she is. And with that we were up and running!

Milky Way, the off season part. But wow that's a lot of stars.

And of course, part of the reason I was up there in the first place:

Orion Nebula as seen from 4500ft

Once I had decided i was frozen enough I packed it up and stumbled back down to camp.

Day 2

I really need to come up with some more interesting titles for posts. I'll try and make up for it with pretty pictures.

 

Climbing was excellent. The natural rock in this area (the infamous Blood Mountain Boulder Garden) was sharp, but not terrible. Enough to want to tape up our hands. I'm still waiting on my comrads to 

get their video stuff together from the day, because I think there was plenty of nice shots taken. I see a couple of shots have been slipped in to Marcus's Documentary Reel, but I think there's something a little more focused to come