Spindle selection

[sergizmo]

Hey guys,

I'm going to be building a small CNC mill. Shooting for 175 pounds total. I currently have Sherline CNC and manual mills. While they are nice machines, I want something that can remove material quickly.

The parts made are putters. Material is 6061 T6 aluminum and free cutting brass. The aluminum putter is 3.98 by 3.5 by .9 while the brass is 4.25 (variation on this depending on weight) by .99 by .9. I want to be able to put a slightly oversize blank in (say 1.125 by 1.125 brass) up on parallels in a vise and do most of the machining. Not feasible on a Sherline. Currently this requires a to-size blank with a bunch of operations. Right now I run a 3/8" two flute end mill 2,800 RPM, .02" DOC at 8IPM with about a .15 stepover in aluminum. In brass .025" DOC at 8-10 IPM. I want to at least triple the material removal rate.

Originally I had planned on using an X-2 spindle with belt drive kit. After doing some digging, it became apparant that this was a real crapshoot. Living in Canada, I really don't want to have to ship back defective parts. And frankly, I don't trust Chinese stuff.

I then took a look at the Finleys. In particular the 50-13 belt driven ones. Nice, but over $1,200 just for a spindle. And they seem to have some kind of proprietary collet (RD20) that you can buy from them at the low price of $45 each. So, looking at $1,500 here. I'm sure these are nice, but I just can't justify that for a home build.
http://www.finleyspindles.com/

Then I started reading about folks here doing shallow DOC high feed and speed machining. Since the materials are brass and aluminum, this could be a perfect solution. Keep the DOC the same but up the RPM and feedrates bigtime. I checked this out on a horsepower calculator.
http://reference.kennametal.com/Calc...gHPTorque.aspx
3/8" two flute end mill, 8000 RPM, .02" DOC, 32 IPM feed with .15" stepover in 6061T6 (95 HB) only requires .02 HP! Less than a pound of force at the cutter. This would be quadrupling my current material removal rate for aluminum.

So I'm thinking buying this: http://www.sherlinedirect.com/index....Product_ID=753
with the timing cog and 3/4-16 nose. The steel case should be a bit better than my current ones with aluminum ones.
Coupled with this motor and speed control:
http://www.pennstateind.com/store/TCLVSKIT.html
(buy appropriate timing cog to get in the 8000 RPM range).
I could even use all my old end mill holders.

I'm worried about
1) Balance/vibration. The Sherline end mill holders are quality units, machined in one setup. I just don't know if they are balanced enough for higher RPM's.
2) Drilling. Using a 3/8 drill if I gear the spindle to run fast - will there still be enough torque? Using shallow pecks I certainly think so, just throwing this out there.
3) If the Sherline spindle is up to this? It has two 20mm ID bearings. I'm retty sure the rest of the machine is the limiting factor (low weight, 1/4-20 and 3/8 screws, pretty thin column, etc...) and not the spindle. But I'm not 100% sure.

Outside of those concerns is there anything else I should be worried about in this course of action? What does the Zone think of all this?

Thanks,
Serge

[sansbury]

What about a Taig spindle? Still (reasonably) inexpensive but just a bit beefier than a Sherline.

[sergizmo]

Really? The Sherline has slightly larger bearings: 20mm ID, 42mm OD vs 17mm ID, 40mm OD. Both have one up top and one down below. Due to this I would think the Sherline spindle would be slightly stronger. Am I wrong?

There is no doubt that overall the Taig is much stronger machine. I don't think the Sherline spindle is it's limiting factor though. Actually I think the spindle/speed control unit is considerably more capable than the rest of the machine.

Does anyone have any other spindle possiblities besides: Sherline, Taig, Finley and X-2?