Newbie- accuracy in aluminum?

[theophilus]

I'm looking to build a CNC mainly to cut aluminum. I like some of the kits (solsylva, or fine line automation) but I haven't found many posts about aluminum.

Is it reasonable to cut 6061 aluminum with a gantry style CNC?

Is it pretty easy to get the accuracy consistently < 0.005" on one of these machines, or is that really stretching the capabilities of the machine?

Solylva doesn't recommend cutting metal: http://solsylva.com/cnc/faq.shtml#metal

Sample size of 1, but ilya gets 0.004" in Al:
http://www.cnczone.com/forums/showpo...65&postcount=7

Otherwise, I'm really just guessing that it's vaguely possible..?

[louieatienza]

theophilus I've built a Solsylve router, and have had some luck cutting aluminum. Mind you I'm only doing passes at .032"-.040" at 35-40ipm, using a single O flute bit. I've been happy with the results, though with my setup I probably get close to .005" and that's all I need. Hope to improve on that with the next build...

[CarveOne]

Originally Posted by theophilus I'm looking to build a CNC mainly to cut aluminum. I like some of the kits (solsylva, or fine line automation) but I haven't found many posts about aluminum. Is it reasonable to cut 6061 aluminum with a gantry style CNC? Is it pretty easy to get the accuracy consistently < 0.005" on one of these machines, or is that really stretching the capabilities of the machine? Solylva doesn't recommend cutting metal: http://solsylva.com/cnc/faq.shtml#metal Sample size of 1, but ilya gets 0.004" in Al: http://www.cnczone.com/forums/showpo...65&postcount=7 Otherwise, I'm really just guessing that it's vaguely possible..?

The Solsylva designs tend to be made of wood and plastic materials. They would not be as stiff as an aluminum extrusion or steel construction machine. I built a Solsylva 25x37 out of red oak with 1/2" lead screws and it still isn't what I would want to cut aluminum to any kind of precision with. It has cut one sample to within 0.002" of the part size though. Tweaking the motor/leadscrew settings and taking shallow cuts at acceptable speeds will get it there. My weakest link is the Z axis and Y axis flexing in the aluminum angle carriage design. Just replacing those with steel angle carriages would be a big improvement.

My recommendation for cutting aluminum would be a metal machine of some sort, whether homebuilt or purchased. Better yet, get a CNC milling machine for aluminum and use a CNC router for wood and plastic.

CarveOne

[CNCMAN172]

You can cut aluminum on a gantry mill with high accuracy provided the mill is accurate already in other materials. I routinely cut aluminum on a home made mill using a Bosch 1617EVS 2-1/4 HP router with variable speed. My mill is constructed of wood and aluminum. The table top is actually high density MDF.

The keys to cutting aluminum: The correct feedrate, spindle motor RPM, depth of cut, and the size and type of the endmills being used, and the HP of your spindle motor.

Aluminum comes in various grades with 6061 being one of the most available and reasonable pricewise.

I can maintain an accuracy of .001 to .002 on my mill depending on the aluminum I am attempting to cut. Some aluminum is more gummy that other alumium which is a challenge as it can quickly cog your bit which greatly impacts the quality of the cut and often will cause your machine to snap a bit.

It is a good idea to consult a CNC calculator like ME consultant as it will point you in the right direction and there are free versions you can download.

http://www.hobbycncsoftware.com/cnc-...ing-calculator

What you will quickly discover is each machine is different. The stiffness of your machine also impacts your ability to cut aluminum without chatter.

So where do you start?

I have found the following parameters seems to work well on a hobby type machine using a wood router with variable speed.

12,000 RPM
6-15 IPM feedrate
1/8" 2 Flute carbide cutters
.015 to .030" depth of cut

I have discovered that two flute cutters normally do a better job cutting aluminum because they do not clog as easiliy. There are a few other things to keep in mind that can help you on this journey.

Alumunim is known as a soft metal but it is much harder than wood and it will dull your cutters over time. If you notice the cut is not as clean it is time to change the cutter. You can use a lubricate to help you extend the life of the cutter and often it will allow you to cut faster and slightly deeper. I have used many cans of WD40, especially when using smaller cutters like 3/32 and when cutting deeper.

It is a good idea to keep the swarf out of the cut as best as possible as this stuff can actually pack up and makes your cutters work harder. Some people use an air nozzle to keep the swarf away from the cut. Aluminum shavings can fly everywhere so always use eye protection. Using a lubricate actually keeps most of the stuff on the table using a mister but you need to still keep the swarf out of the cuts and that can require a vacuum. I use a shopvac with a dust deputy to suck up aluminum shavings. It does a good job.

I have cut aluminum as thick as 1.5" thick on my machine. Trust me cutting stuff that thick on a hobby mill takes a long long time. I was completely amazed at the final product which was a spindle holder for my new 3KW water cooled spindle motor.

The attached photos show you some aluminum. You will learn as you go and get better and better as you learn more about aluminum and your machine. I cut the thick 1.5" aluminum with no lubricate and the 1/8" endmill with two flutes had to be the longer type as standard bits are only 1.5" long. I was happy with the results and it was all done with just a roughing cut. I need to start programming a finish cut as you often get small chatter marks when cutting aluminum so you if rough cut the item and then do a finish clean up pass taking off .003" you can have very smooth parts. I keep learning as I go so hope some of my experience you will find useful.

Russ
CNCMAN172

[theophilus]

CarveOne-- Thanks for the carriage info. Can you adjust for it with backlash compensation settings in Mach3 or equivalent SW, or is it more complicated than that?

CNCMAN172-- Thanks for the photos. It sounds like 0.005" is in range if I'm willing to go slow. That's fine, it would still be faster than cutting by hand on a borrowed mill.

[CNCMAN172]

Absolutely, if you can cut items in wood or plastic with that precision you can do it in aluminum as well.

The key is to start very light in the depth of cut and slow your feedrate down. I can tell you getting the right spindle speed is absolutely critical. Watch the flakes of aluminum, if they appear to be shaved you are doing it right. If the cut looks like the alumium is rolling out or back into the cut you are doing things wrong. You need to reduce your depth of cut and reduce your feedrate and possibly adjust your spindle speed.

Use the ME consultant calculator as a guide. Do something less than what it recommends and slowly work your way up to a more aggressive setting.

For example as a start you might try a depth of cut of .010" which is very thin and listen to your machine. If it starts sounding loud something is wrong, so make some adjustments, first to feed rate. Shoot some WD40 and see if it gets quieter. Watch the cut closely and make sure you see little flakes that appear to be shavings. ALWAYS WEAR SAFETY GLASSES your eyes are worth a fortune.

I think you will be surprise if you play a little at what you can accomplish. I don't care that it is slower than a large commerical machine myself because I am not a production shop and only need various pieces for my own use. It is kind of fun to see something materialize out of aluminum as the edges are so sharp and defined unlike wood. Engraving is just amazing.

Good Luck

CNCMAN172

[CarveOne]

Originally Posted by theophilus CarveOne-- Thanks for the carriage info. Can you adjust for it with backlash compensation settings in Mach3 or equivalent SW, or is it more complicated than that? CNCMAN172-- Thanks for the photos. It sounds like 0.005" is in range if I'm willing to go slow. That's fine, it would still be faster than cutting by hand on a borrowed mill.

Yeah, it's more complicated than that. Software based backlash compensation has a limited range of effectiveness. You need to reduce the mechanical backlash as much as you can by mechanical adjustment means first, then use software compensation as a last resort. It is not intended to cure a loosely built machine.

CarveOne