General advice sought on machining brass with a high speed CNC router

I'm about to buy a 3-axis router whose main function will be 3D milling of small brass parts with a lot of surfacing. The cutting area is 24" x 31" x
5", and the machine is extremely solidly built compared to many I have look ed at. I'm opting for this unit because I also want to use it for a variety of woodworking operations. The seller is a moldmaker with a collection of CNC machines, both knee mill and router based. He says that I shouldn't buy the machine because it is simply not fit for working in brass. His argumen t is not based on the stability of the machine, but the spindle, which is 1 .5kw, and runs at 8000 to 24000 rpm. He cuts aluminum and plastic with this spindle, but uses heavier machines with slow spindle speeds for brass.
Now I must admit that my CNC experience is only with knee mills and slow sp indle speeds, but my research leads me to believe that high speed routers c an cut brass just fine, as long as you do it properly. He also said that fo r brass I shouldn't implement a spray lubricant, but instead a good vacuum system. He uses spray for aluminum, but says it's not necessary or appropri ate for brass. This makes sense to me. The guy is obviously very conscienti ous and doesn't want to sell me something that isn't going to work, but I t hink he might be less that up to date on how HSM is now being implemented f or nonferrous. I've talked to some other manufacturers of similar machines who claim I can even use their systems to cut stainless, as long as I have proper cooling spray.
So, any tips or links on high speed machining of metal?
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On Sun, 2 Nov 2014 05:10:19 -0800 (PST), robobass

I don't know how good your spindle is for side loads which is maybe why the seller is cautioning against the buy. But if the thing will machine aluminum easily then I think it would work on free machining brass alloys. You should use some type of cutting lube though because not only will it lower the cutting forces it will help prevent the brass from sticking to the cutter. You won't see a thick layer of brass sticking to the cutter after just a little bit of cutting but you will see that a very thin layer is present because the cutter will have changed to a brass looking cutter where the chips flow across the cutter surface. After cutting a while with no lube eventually this layer will be substantial enough to significantly increase cutting forces. This may lead to broken cutters or failed spindle bearings. If you are using modern carbide cutters optimized for brass of small enough diameter you should have no problems (I think!). Eric
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robobass wrote:

You should take the advice of an expert, even if he doesn't articulate it well. I use a 1500 Lb bridgeport mill, with everything in the machine built out of slabs of cast iron with cross sections of several tens of square inches. It is JUST BARELY stiff enough to do moderate milling tasks! I can easily flex the machine by a few thousandths of an inch by leaning on it.
Do not buy the wrong machine just because you want to do some routing, ALSO. If most of your work will be milling small brass parts, trying to do it on a 24 x 31" machine with questionable rigidity is VERY likely to not work well.
You don't state the accuracy required in the small parts, or even DEFINE what small means! Are we talking 1.5 x 3"? How are you going to fixture such parts on the router? If 3D surfacing, would a 1/8" ball-end mill be the tool of choice? If you need to change tools, how will you touch off the tool length?
Jon
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My ~1960 Clausing mill weighs half as much. With all the axes locked 15 pounds deflects the spindle 0.001", measured with a B&S Bestest graduated to 0.00005" (1.25 Micron). The head deflects 0.0005" relative to the table at 50 lbs. I pulled on the vise with the spring scale and braced the other hand on the head
With care the machine can cut brass within 0.0005", as I learned when copying the Variac brush holders.
jsw
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On Sunday, November 2, 2014 8:10:23 AM UTC-5, robobass wrote:

Many HSM advantages come with advanced CAM systems. Tool paths generated for HSM.
I would not think a CNC router is up to the task of 3D surfacing brass. Try before you buy?
A Haas Toolroom Mill could probably do OK.
G'luck PaulS
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