Success and Some Failure milling Aluminum

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jvabob
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Joined: Mon Dec 30, 2013 7:52 pm

Success and Some Failure milling Aluminum

Post by jvabob » Thu Mar 20, 2014 3:55 pm

I have a Shapeoko2 that I have upsized to 1 meter.... It is absolutely amazing!
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I have had a lot of success with it and have had quite a bit of success milling T6061 aluminum but I am running into a behavior I don't understand.
I have been trying to mill sort of a plaque out of aluminum with design in the middle and then cut it out with a profile.

I am using the 1/8" single flute upcut mill from Inventables at 30k rpm, 300mm min feed rate and .1mm depth of passes.
I have a spray cooling system using a mix of isopropyl alcohol and water.
I am using CamBam
I successfully milled the end plates I used in upsizing to 1m so I know that at some level I can mill aluminum successfully.

Here is the design
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As you can see in the upper left I started to have problems.

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I am "thinking" that possibly on that longer deeper cut the chips started to build up which caused it to wander back and forth on the x axis and then
ultimately the spiral upcut grooves on the bit caught on the built up chips and pulled the mill down deeper and deeper until it couldn't move forward.

That is my theory I would love to hear what the more experienced folks think my issue is.

If that is the case I am thinking turning up my coolant spray so that it puddles in the cut more could help flush those chips out.
I normally run the spray so it is evaporating quickly enough to keep the puddle the size of a quarter or less so I don't have to worry about warping my hold down board.

So who can tell me where I have gone wrong? :)

RobCee
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Location: Birmingham, UK

Re: Success and Some Failure milling Aluminum

Post by RobCee » Thu Mar 20, 2014 4:24 pm

It does look like your cutter is digging into the material. This is a typical rigidity problem with narrow deep cuts, especially if they get clogged with chips.

If you try making your profile cut 1.5x as wide as your cutter, it will make two passes around it for each depth slice - takes longer but easier on the cutter and the machine.
Also try the above with a finishing pass that removes 0.25mm from the profile afterwards (if you get that far successfully).
ShapeOko2 #3400 - Chinese 800W AC Spindle - Stiffened X-Axis - TR10 Z-Axis - Inverted Z Motor - Hall Effect Limits - Drag Chains & Custom Brackets

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

Re: Success and Some Failure milling Aluminum

Post by DanMc » Thu Mar 20, 2014 4:52 pm

Based on the first picture I think the problem could be the brackets holding up the Y rails. They are so long that they are probably swaying in the Y direction as you are cutting.

jvabob
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Joined: Mon Dec 30, 2013 7:52 pm

Re: Success and Some Failure milling Aluminum

Post by jvabob » Thu Mar 20, 2014 4:59 pm

The end plates are pretty rigid... there is a piece of 3/4 steel tube running 75mm up the back side of each so I will check but I cannot make them flex by pushing on them...

There may be some flex in the 2 pieces of slide that the gantry sits on.. I already have another piece I plan on adding to that.

Short term I will try the idea of widening my cut and check the rigidity of the end pieces... I could add more steel behind them to firm them up if need be.

Thanks for the input!

criznach
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Joined: Sat Dec 14, 2013 5:28 pm
Location: Great Falls, Montana, USA

Re: Success and Some Failure milling Aluminum

Post by criznach » Thu Mar 20, 2014 5:11 pm

I've been cutting 1/8" wide profile cuts to 1/2 inch depth with a 1/8" bit, and I haven't had any chip buildup problems. I've used both the standard inventables spiral bit and some Destiny Toolworks Viper bits. I don't use any coolant, but I do have a dust shoe and I vacuum the cut clean periodically. This has been giving me good cuts, but I think the tool is wearing a bit.

In this case, I'm suspect of the long unsupported Y rails. Does the behavior change if you cut in different quadrants of the work area? It may be flex closer to the middle of those long rails. I've doubled my 1000mm y rails. With the steppers engaged and the spindle in the middle of the work area, try pushing the spindle side to side and see if the bit moves at all. You'll get a little due to the delrin wheels, but anything more than a tiny amount will be a problem.

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

Re: Success and Some Failure milling Aluminum

Post by DanMc » Thu Mar 20, 2014 5:13 pm

You could check them with a dial indicator, they might still be moving.
One of my favorite exhibits at the science museum is like a W12x50 beam that's only a few feet long. Seems like it would be impossible to bend but their precision dial indicator says otherwise.

WillAdams
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Re: Success and Some Failure milling Aluminum

Post by WillAdams » Thu Mar 20, 2014 5:24 pm

DanMc wrote:One of my favorite exhibits at the science museum is like a W12x50 beam that's only a few feet long. Seems like it would be impossible to bend but their precision dial indicator says otherwise.
An excellent book to read on that sort of thing is _Foundations of Mechanical Accuracy_ by Wayne R. Moore:

http://mooretool.com/publications.html
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

akhlut
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Re: Success and Some Failure milling Aluminum

Post by akhlut » Thu Mar 20, 2014 5:31 pm

Consider moving to a lubricant instead of a coolant. The thermal conductivity of aluminum is second only to copper, so you don't have to worry about dissipating the heat from the cut - the AL will do that for you.

Some links:
http://bbs.homeshopmachinist.net/thread ... ting-fluid

http://blog.cnccookbook.com/2012/03/27/ ... g-success/

http://www.cnccookbook.com/img/CNCCookb ... okbook.pdf

Will Winder
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Re: Success and Some Failure milling Aluminum

Post by Will Winder » Thu Mar 20, 2014 7:39 pm

I've seen similar results when cutting aluminum, but usually not that bad unless I'm cutting too fast. Even still my machine didn't have dual-X rails at the time which is what I attributed most of the problem to. My Y rail is also unsupported and about 1 meter so I don't that should be the problem.

You might consider raising the aluminum up so that the Z axis can be more centered along the X axis.
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
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Location: Colorado

Re: Success and Some Failure milling Aluminum

Post by danimal » Mon Mar 24, 2014 3:22 pm

I was having the same problem and it was caused by the twisting of the x rails. This causes the bit to tip slightly taking a much larger chip size than it is supposed to. This drives it in the direction of rotation and into the side wall. I found some Plexiglas that was the exact same width as the t-slot in the extrusion and cut some strips of it to fit in there. This helped some, then I got some bolts out of an old IKEA desk and bolted the two rails together and that made all the difference.

The upcut spiral bits get more and more pull down leverage with each pass and cause the tip to get gradually worse as the job progresses. It was driving me crazy because I would get 90% done with a project, be on the final passes and the same thing would happen. Here are some pics of bolting my x rail together:

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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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