[sdantonio]

Hi,

My background is all in wood, so working with metals is a new thing to me.

My girlfriend designes motorcycle parts and accessories (heated electric vests and stuff like that) and is now branching out into small custom aluminum parts. She wants me to make her a small CNC to cut out the parts and says a table size of 9in X12in would be great. I figure this can be set up like the moving table plotter ChrisD made and posted pictures about the other week. http://www.cnczone.com/forums/showth...chris+plotterI could equip it with a laminate trim router and a TIN coated end mill. This would also put a small machine in the house in the event that I want to throw on a dremel and do a circuit board or something small like that.

I'm assuming my old 100in-oz motors would probably work ok for this with a xylotex board and one of my old 24V, 15A lambda power supplies.

Having never cut Al or any metal on such a setup, what router speeds (RPM, feed rate, etc.) would you suggest? Also, considering the above description, am I missing anything that would be obvious to a seasoned metal worker?

Steven

[lakeside]

Alum will cut at 200 sfm(surface feet/min) 4xsmf/dia of tool=rpm

[MarkT]

In general, aluminum will machine comparitively slower than you are used to in wood. I would say the surface feet per minute (SFM) would fall in a range of 200-3000. Often this depends on many variables - rigidity of machine, rigidity of tool holders, endmill / router bit design, cutter coating, type of coolant, method of coolant delivery, rigidity of part set up, (place repeating decimal here!).
I work on industrial CNC routers as a technician, but I am a machinist by trade. Routers will not machine aluminum in the same manner CNC mills will. I would recommend you contact a quality tooling representative and ask for assistance specifying your specific application. You are going to have to buy the tooling at some point regardless, might as well get free information support with it!
Best of Luck!
MarkT.

[sdantonio]

Thanks for the answers. Now here is a really stupid sounding question. Exactly how is surface feet per minute defined?

Lets say I have a 1 inch router bit and I move it through the substrate (aluminum or wood) af a rate of 1 foot per minute. Would that be considered 1/12 surface feet per minute or am I confusing that with 1/12 square feet per minute?

I would also assume there would have to be some variable in there for depth of cut?

I've done several searches on the web and found a number of sites that quote values in surface feet per minute, but none that define what it is.

Thanks
Steven

[MarkT]

Look at it this way and perhaps it will make more sense. If I have a 1" diameter cutter, and it is spinning at a given revolutions per minute, at THAT specific RPM at THAT specific diameter, the Pheriphery of the cutter is traveling at a rate of a fixed feet per minute.
Clear as mud??
MarkT

[sdantonio]

I think so, let me think about that for a while, but it is beginning to make sense.

Thanks

[sdantonio]

Ok, now I understand. I just had to go downstairs and talk to one of the machinists about a sample he submitted recently to my lab and I asked him too. It's much easier when you chatting back and forth than when you shooting off short messages.

I was stuck trying to figure how the linear speed of the tool and the depth of cut come into play and it turns out that they dont.

now, it there a way to figure those in or is that trial and error for an individual machine? I would think that would be trial and error and would be limited by things like how fast can I go without skipping steps, binding, etc.

Thanks again
Steven

[ger21]

Depth of cut depends on the diameter of the tool, more so with smaller tools that may break if you go too deep.

You might want to download the aluminum router bit catalog from www.onsrud.com

In the back it will give you chip loads for all their tools at a given RPM. The chip load is used to calculate the feedrate needed. Keep in mind that router bits for cutting aluminum are ususally designed for much faster cutting speeds than endmills.

And jmo, but I think a laminate trimmer spins way to fast, and will have too much runout for this application.