Newbie- Wood and Metal CNC

[Eric51]

HI,

I would like to build a CNC that can handle wood and some light metal work. My main question is with the router. I know I can buy a wood router, but I dont know if I can buy one for metal? or can you use the same one? I am afraid that the wood router would spin way to fast for cutting metal or aluminum? Is this true? Are there some powerfull lower speed routers for cutting metal out there and if so where?

Thanks for your help.

[ger21]

When you say metal, do you mean steel?

[Eric51]

Yes some steel and some aluminum.

[Cmailco]

Non-ferrous metals like aluminum, brass, copper, etc., should be fine. Ferrous metals are another issue all together, and you're going to have a tough time building a jack-of-all-trades machine that covers the gamut.

Wood routing rpm isn't an issue for carbide tooling in non-ferrous materials by the way. Shops routinely machine these materials at 30k+ on machines built to handle pretty much any ferrous material; Roeders, Matsuura LX-series, etc..

[Algirdas]

Wood routing rpm isn't an issue for carbide tooling in non-ferrous materials by the way
it's a part of true. Cutting speed must be calculated for any metal anyway. Faster = better is for wood and some plastics only.

[Cmailco]

Originally Posted by Algirdas Wood routing rpm isn't an issue for carbide tooling in non-ferrous materials by the way it's a part of true. Cutting speed must be calculated for any metal anyway. Faster = better is for wood and some plastics only.

Not to derail the thread but in response to Algirdas; I don't believe RPM is even an issue anymore, not when cutting aluminum alloys and graphite, which probably encapsulates some 80% of the high-speed machining market.

A client of mine recently went from 42k rpm machining centers, replacing one of them (the others will be phased out as funding allows) with a 60k rpm unit. Tooling has advanced some in the past 5 years, but not to the tune of 70% greater productivity. The limits are, and have been ,within the machine tool itself, not the tool. If I could build a 100k rpm spindle tomorrow, they'd use it. The only thing that changes are the techniques used to machine the workpiece but if you calculated SFM for many of these machining operations, say this one in particular for a 7075-T6 component, you'd see that it's running at ~2500 SFM, well beyond what most manufacturers recommend... well, other than those that say, "1xxx-Max".

[Algirdas]

it is again just a part of true. I see lots of bits burned out. One thing is theory, reality is quite different. High rpm is good for wood and some plastics. I'm not metal technology expert, just see in practice, what happens at high cutting speed.

[Eric51]

Thanks for all your responces!

[Cmailco]

Originally Posted by Algirdas it is again just a part of true. I see lots of bits burned out. One thing is theory, reality is quite different. High rpm is good for wood and some plastics. I'm not metal technology expert, just see in practice, what happens at high cutting speed.

Algirdas, here's a real-world example which is worth a million theories, so I'll just put it out there.

When we started collecting cutting data at one shop I use to work at, we had 20k rpm to work with. The components were typical monolithic aerospace, some titanium but we'll stick to our 7075-T6 materials for this discussion. Aero parts being what they are, we weren't always fortunate enough to use short gage length tooling which meant, finding a sweet spot for various L/D ratios and recording data for cutting conditions which produced the best material removal rates. There is software which does a very good job of this, with use of a mic, but we did it the 'old school' way at first.

Anyhow, the starting point was 20k, then work backwards to find the most stable cutting condition at various axial depths, then radial depths consistent with the various machining operations, ie, 100% radial for slotting or rough pocketing, 50%, 25%, etc..

That aside, a 3/4" 3 flute end mill at L/D ratios of 4-5 would often tend to work best somewhere around 18k rpm. Mind you, we cared nothing for the actual rpm or SFM, just a stable, productive cutting rate where maximum material removal rates could be achieved.

If you do the math, 18k for a 3/4" end mill is a tad better than 3500 SFM. Too fast??
Well it's a bit beyond what many tool manufacturers might 'recommend' but like I said, the limitation isn't the tool material. You won't 'burn up' a carbide tool on aluminum, though you may weld the material to the tool if you're careless.

[Algirdas]

Thanks a lot for Your nice explanation. It's again only the part of truth
You won't 'burn up' a carbide tool on aluminum
I will. Very easy. Sure, workpiece will be destroyed before.
though you may weld the material to the tool if you're careless
It's not so easy carbide with alluminum, suppose.

[thackman]

You will not find a hand held router for metal because the cutting forces involved make it totally impractical. With that said since you are building this yourself you do have several options. In the metalworking world it's called a spindle or head. In reality you are not looking for a router but rather considering using a router for your spindle. There are several places to buy replacement head's for mini mills that you should be able to make a mounting bracket for fairly easily. You can buy just the spindle box or an entire head complete with motor. One thing you have to consider is that cutting metal involves much higher forces than cutting wood. I have a big hand held 3Hp router that weighs 9lbs but a 1hp head for a mini mill weights over 30lbs.

Assuming that we are talking about cutters around 3/8" in diameter I'll have to disagree with the earlier posters that mentioned cutting metals at high RPM's (6,000rpm+) . It can be very effective and is common a common practice for industrial grade machines but it is also a very sensitive process and the slightest amount of vibration or change in chipload will snap the carbide cutter. If you are building the machine yourself it will be almost impossible to make it rigid enough for you to utilize more than 6,000 rpm in either steel or aluminum assuming that you are running cutters in the 1/2" to 1/4" range. Most mini mills top out around 3,000 rpm. If however you are doing fine detail work with 1/16" cutters you can very easily run them at 30,000 rpm for metal. To give you an idea of the ratios of weight to power needed, I have a 2,000lb CNC mill with a 5,000 rpm 2HP spindle. That 2HP requires 20amp at 240volts and is great for running 1/2" end mills to hog material off of blocks of aluminum. I have had several instances where I needed to run small cutters and 5,000 rpm just isn't enough for 1/8" and below but so I mounted a rotozip to the side of the head for a 30,000 rpm subspindle. After about 80 hours of use I've almost worn it out but got the job done. Once it dies I'll replace it with a small trim router like a bosch colt.

http://www.littlemachineshop.com/pro...1663&category=

http://www.littlemachineshop.com/pro...1663&category=

[Eric51]

Thanks, Thackman you post was most helpfull.