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  #1  
Old 06-11-2017, 03:34 PM
jjwdawg jjwdawg is offline
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Default Aluminum Advice

I have a large aluminum-cutting job coming this week, and I'm trying to get my process dialed in ahead of time. The material will be 1/8" thick 5005 with a black anodized finish. My only aluminum-cutting experience has been polymetal and really thin (.040", I think) sheet.

I don't have the material on hand to test with, so I'm using the only thick aluminum I had - an old road sign, about 0.100 thick. I've no idea what type of aluminum it is, whether it would be classified as hard or soft, etc.; and I suspect that's the main cause of my frustration :-)

I'm using a Southeast Tools SOU302 1/8" O-flute bit with a .055" pass depth. I'm misting enough to keep things cool, I think.

I was advised to try 60IPM & 12k RPM, but, having already broken a few bits on my own earlier, I decided to start slower, 15IPM & 8k RPM. I did a test job of various shapes totaling about 30-40 inches of cut. This seemed to work well and leave a good finish, but it's painfully slow.

Next, I jumped to 60IPM/12K - it got about 5 inches into the job before snapping the bit.

So, my question is: should I keep testing to see how much chipload/feed I can get out of this type bit? Or, should I assume that my material is just wonky, and I should wait until I get the real stuff in hand?

Anyone with production experience with this type of material who could share some feed/speed/bit suggestions? This job has the potential to turn into steady, long-term business, so I want to get it right!
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  #2  
Old 06-11-2017, 06:26 PM
CosmosK CosmosK is offline
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I get good results at 7k RPM and about 10 IPM with a similar cut depth using a 2 flute.

You might want to calculate your SFM and compare that to numbers out there for carbide on AL. Onsrud may have published numbers. However, I doubt their carbide is much different than other end mills, so I'd check around and compare. This SFM number is a "don't go above" number so you don't overheat the bit, but there are other reasons to slow down.
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  #3  
Old 06-14-2017, 05:00 AM
UglySign UglySign is offline
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How about going in w/ a larger (1/4"~3/8") bit first to hog out
then follow up w/ a 1/8" bit? Less passes for both.

Less chips in the channel-cut to break the bit w/ mister going.
Clearance Clarence!

I use Onsrud's 63-626 (3/8") & 63-606/10 (1/8's) in situ's like that.
The 626 makes the perfect chip size to get right under your heel.

I get them from http://www.cncrouterbitsxp.com/
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Old 06-14-2017, 09:33 PM
jjwdawg jjwdawg is offline
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I got my real material in today, and I decided to divide the job into phases and only use the 1/8 bit on the small holes that required it. My thought was that I could live with the slow speed on just these few toolpaths.

The job starts with a series of small round holes. The first 3 are 0.250 in diameter, then a 0.141 diameter hole, then another 0.250. I'm milling these in two passes of 0.065" each, with a spiral ramp, climb cut, 8000 RPM, 15 IPM.

The first couple of holes seemed to work more-or-less perfectly (first pic).

The third and fourth seemed OK, but it left some chips in the bottom (only seems significant since the first two were perfectly clear?). (second pic)

On the fifth hole, it made one loop around and lost it (third pic).

I'm starting to wonder if this might be a machine issue? Could this be due to runout in the spindle or some vibration along the x or y? I have other anecdotal evidence that has me thinking in this direction:

About 6 weeks ago, I had a job cutting .040 aluminum sheet. I cut it with an SOU502 (1/8 o-flute for soft plastics - all I had at the time) at 16,000 rpm and 60 ipm. It worked perfectly - I cut several large square parts and some more intricate detailed pieces without any problems.

Today, I had another request to cut that same material. This time, I used an SOU302 (for hard plastics & aluminum). The job was a bunch of 15x15" squares. I got about 1-1/2 squares cut before the bit snapped. Thankfully, I was able to finish the job using a larger-diameter bit.

Since the only thing I did differently today was to use a (I assume) better/more appropriate bit, it seems that the machine itself may be a contributing factor.

Any thoughts? Are there any simple tests I can do to eliminate machine error as a possibility?
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Last edited by jjwdawg; 06-14-2017 at 10:18 PM. Reason: fixed photos
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  #5  
Old 06-14-2017, 09:42 PM
CosmosK CosmosK is offline
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I assume you're running pretty aggressive feeds still. Also, anodize can leave a very hard surface, so this will take a toll. So, given these, I wouldn't jump to calling it a machine issue. These machines aren't really meant to be metal working machines. Taking lighter cuts can help compensate.

What feed and RPM are you cutting with?

If you're just making holes, why not use drill bits?
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  #6  
Old 06-14-2017, 10:13 PM
jjwdawg jjwdawg is offline
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Quote:
Originally Posted by CosmosK View Post

What feed and RPM are you cutting with?

If you're just making holes, why not use drill bits?
Thanks for the reply. Today, I was running 8k RPM, 15 IPM, .065 pass depth. These first few features were round holes, but the part has a lot of D-shaped holes and other odd shapes that can't be drilled and can't be routed with a larger bit.

The main reason I'm considering the machine is because of the comparison of the two similar jobs I've done in .040 aluminum (this is separate from the .125" job that led me to start this thread) - A few weeks ago it ran like a champ and today it's breaking bits.
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  #7  
Old 06-16-2017, 11:41 AM
CosmosK CosmosK is offline
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I suppose. Maybe check belt tensions, not sure. I suspect the material and the anodize. Easy test is grab some material from the old job and see if it still runs fine. Lots of different types of Al out there. 7075 is as strong as steel.
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  #8  
Old 06-16-2017, 05:18 PM
jjwdawg jjwdawg is offline
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I was able to do enough testing to convince myself it was not a runout issue, etc. In order to get the prototype done without breaking my last bit, I backed my cut depth down to .01 for the 1/8" bit, and ran it at 7000RPM/15IPM. This worked OK, but was very slow, of course. I used a 1/4" bit for the larger features and was able to be much more aggressive. For now, I'm assuming that .06 was just too much bite for the small bit. I'm waiting for more bits to come in before I do any more testing :-)

Thanks!
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