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CNC Routing brass plate

12/18/18       
Richard

Hello all.

I have a job that involves routing out a decent quantity of small (Approx. 5/8" Square) Hebrew letters & tabs from a 6"x 25" brass plate. The brass is 0.05" thick and has been glued to a piece of solid wood which in turn is screwed down to my spoil board.

We are using a 2 flute 1/16" diameter end mill in 3 passes. Cutting at 6 IPM with an RPM of 15000. I had tried to run it faster last time we ran the job but was snapping bits.

These settings are what we found worked last time but this time the operator is snapping tools like crazy, 15 already! Mostly seems to be on the letters not the tabs.

What am I missing? I will attach pictures.

Thanks in advance for any insights.

Richard


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12/18/18       #2: CNC Routing brass plate ...
Dropout Member

I'd bet it's the hardwood that's breaking them.

6 IPM seems really slow. Even with a chipload of 0.0005 you'd be at 15 IPM.

Can you rough it out first with a 1/4 or 1/8 bit?

12/18/18       #3: CNC Routing brass plate ...
Richard

Thanks Dropout.

We started off at 10 IPM last time we ran this job. And bits kept breaking until we slowed it down to the 6 IPM we're at now. That being said it's easy enough change the speed and see what happens.

I had thought about running a rough pass first. My concern was that there are many areas that the 1/8 diameter tool can't reach. This would mean that the 1/16 tool would be running at full speed from minimal load to full load. I thought the sudden change in load may be asking for trouble. Again I could test this anyway.

What puzzles me most is what had changed from the last time we did this? Plus the discrepancy in tool life. The 1 st tool we ran this time cut 40% of the job. The other 14 all broke before completing the remaining 60%.

All this is further complicated by the fact that I am not in the shop to witness any thing & am relying on the operators eyes & ears.

Anyway I will test tomorrow. I the meantime any ideas are welcome.

12/19/18       #4: CNC Routing brass plate ...
Tom Gardiner

Have a look at how well the wood is held to the table. It is possible that there is a small amount of play allowing the material to vibrate. This would explain why the first bit went well and then all hell broke loose.

12/19/18       #5: CNC Routing brass plate ...
Richard

Thanks Tom.

I will look into that. I know that there was a bow in the wood making it hard to secure.

Also I have confirmed with my supplier that I am in range for the feeds and speeds. He gave me a chipload of 0.0002. He has recommended a slightly shorter tool. 1/8 cut length instead of 3/16.

We'll see how it goes.

12/19/18       #6: CNC Routing brass plate ...
Paul Miller

Website: http://MCCWOODWORKING.COM

That speed seems really slow. That thickness is less than a 1/16". Are the bits breaking because of excessive heat? I cannot remember ever routing brass, but we have cut aluminium much thicker than that. When cutting metal, we use a coolant in a spray bottle and continually mist the bit. If you are not familiar with coolants, you will be amazed how misting the bit carries the heat away.

12/19/18       #7: CNC Routing brass plate ...
Gary Balcom Member

Agreed. That chipload seems ridiculously low. Are you sure there isn't a metric/english conversion mistake there? Also, if I was breaking that many bits, I'd try replacing the collet.

12/19/18       #8: CNC Routing brass plate ...
Dropout Member

Also, I'd use an O flute if you can.

http://catalog.eoasaw.com/Asset/Amana%20Aluminum%20O%20Flute%20Feed%20Char
t.pdf

12/19/18       #9: CNC Routing brass plate ...
rich c.

Have you tried misting coolant on it? What alloy brass are you using? Same as last time?


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