Success and Some Failure milling Aluminum

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Will Winder
Posts: 435
Joined: Fri Apr 20, 2012 2:40 pm
Location: Hudson, MA
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Re: Success and Some Failure milling Aluminum

Post by Will Winder » Tue Mar 25, 2014 2:04 pm

I mention telling the CAM software the wrong sized bit because I do it regularly for other applications. Like when cutting a hole thats too small for the current bit, if I don't mind the hole being oversized I just tell CamBam the bit is smaller than it is (which gives a warning but generates the gcode anyway).
ShapeOko #367: Dual-Y drive, Belt on outside, 1000mm Y-Axis, DW660 Spindle, Nema-23 X/Y motors.

Primary developer on Universal Gcode Sender.

danimal
Posts: 332
Joined: Wed Mar 13, 2013 5:53 pm
Location: Colorado

Re: Success and Some Failure milling Aluminum

Post by danimal » Fri Mar 28, 2014 9:45 pm

I do not have too many problems with profile cuts, but it seems like the best solution is to just keep normal tool paths and apply a finishing pass. If you have these binding issues on a single channel, you will likely have them on an offset one as well because the end result is that the mill is being deflected off track in the direction of its rotation, and the first pass for a pocket is pretty much the same as a profile pass. Out of curiosity which direction does your mill travel (CW or CCW) on a outside profile (Anyone)? I ask because I have the option to switch directions, but I have never tried anything other than "conventional" which is the default direction.

I have problems sometimes when making press fit parts and I have to make 3 or 4 test parts to verify the diameter of circles and I am not sure where the error was coming from. I have since switched over to GT2 belts and pulleys and G540 with 10x micro stepping, so I will know if it was either the controller or backlash as soon as I have time to mill some more parts. I have thought about making some of the mill-able wax blocks for test fitting more intricate parts but have not had the time.
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

DanMc
Posts: 257
Joined: Fri Apr 13, 2012 3:34 am

Re: Success and Some Failure milling Aluminum

Post by DanMc » Sat Mar 29, 2014 12:20 am

danimal wrote: Out of curiosity which direction does your mill travel (CW or CCW) on a outside profile (Anyone)? I ask because I have the option to switch directions, but I have never tried anything other than "conventional" which is the default direction.
I find I get more accurate cuts running in "climb"

RobCee
Posts: 587
Joined: Wed Jan 08, 2014 11:33 am
Location: Birmingham, UK

Re: Success and Some Failure milling Aluminum

Post by RobCee » Sat Mar 29, 2014 9:46 am

Climb milling will only work well with a very rigid setup, due to the forces on the cutter - particularly in aluminium
ShapeOko2 #3400 - Chinese 800W AC Spindle - Stiffened X-Axis - TR10 Z-Axis - Inverted Z Motor - Hall Effect Limits - Drag Chains & Custom Brackets

danimal
Posts: 332
Joined: Wed Mar 13, 2013 5:53 pm
Location: Colorado

Re: Success and Some Failure milling Aluminum

Post by danimal » Sat Mar 29, 2014 2:02 pm

I found this great write-up about the differences between climb vs conventional.

http://www.cnccookbook.com/CCCNCMillFee ... tional.htm

After reading and analyzing this I think that climb is the better choice even for profile cuts even for a stock shapeoko if you have your feed speeds properly adjusted. In climb you will have to add your machine's effective backlash to your desired end mill chip size and adjust your feed speeds to achieve a compromise between the two.

Here is my plan:
1) Measure static run-out
2) Verify run-out using a drilling operation and measuring the diameter of the hole.
3) Run a circle square diamond test subtracting the run-out value from the dimensional error.
4) The resulting dimensional error should be close to the backlash value and I should be able to get it for both the x and y axis.
5) Subtract the backlash value from the total desired chip-size and run feed calculation.

I think that this would have multiple benefits for the shapeoko. First it is very difficult to run the machine at optimal feed speeds due to the 30,000 rpm spindle / router options. Anything that increases your effective chip size would be beneficial because it would bring your machines optimal feed speeds down. Second, according to all the sources that I could find climb should give you the best surface finish on your part.

As RobCee pointed out, it would be an added stress on your machine if your machine is chewing into a larger chunk of material, and would require more machine rigidity. But if you can accurately measure your backlash and account for that in the chip load for your mill, then it should produce better more accurate cuts with a better finish quality. Thoughts?
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

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