Options For High Speed Milling

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TomS

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Now that I have a few weeks of run time on my CNC conversion (PM-932) it's become apparent that the 1970 RPM top speed is limiting me on feed rate and not nearly fast enough for small end mills. I've been looking around the internet to see what my options would be for a high speed spindle and have a short list of three ways to go. Subject to change of course based on the feedback I'll get from the experts on this forum.

The three options I've come up with so far are:

1. Replace the mill motor with a 2 - 3 HP three phase motor and wire in a VFD.

2. Buy a high speed air cooled spindle (about 1.5 to 2.2 kw) and VFD.

3. Buy a router motor and variable speed controller.

All three of these options have pro's and con's. Option 1 is relatively inexpensive. My guess is about $500 to $600 for the motor and VFD. But I think the upper RPM limit is about 6000 RPM. A little slow for 1/4" and smaller end mills in mild steel and aluminum, particularly if they are carbide. Option 2 can either be inexpensive or the most expensive option depending on where I buy the spindle and VFD. Ebay sells an Asian spindle and VFD for about $350. Not sure of the quality I would be getting for this price but I'm not optimistic it's top quality equipment. On the other hand one U.S. vendor has the 1.5 to 2.2 kw spindles listed at just shy of $900. Add in a VFD and the package price is around $1,200. Then there's option 3 which I'm not sure is viable but certainly is the least expensive. I would think the bearings for a name brand router motor would be good quality but will they hold up to the rigors of machining metal? What about motor torque at lower RPM's, e.g. 8,000 to 12,000? I would think flood coolant is out of the question as well as mist and cutting oil.

I'm anxious to here everyone's comments and opinions on how best to approach this high speed milling question I have.

Thanks in advance.

Tom S
 
#1 Fist question I would have before adding any speed to the original spindle is find out how much more rpm the bearings will handle.

#2 If I ever move up to a high speed spindle, this is the one I'm going to get. By most accounts I've seen, the guy that owns Light Object is real easy to get along with and goes out of his way to make most happy (some you cannot make happy no mater what).

http://www.lightobject.com/15KW-24000rpm-CNC-Spindle-220V-Germany-shaftball-bearing-P638.aspx

#3 I've seen some of the router guys use the Dewalt 611 trim router with success on aluminum. The variable speed is PWM so it shouldn't loose torque at lower rpm. BTW that is what I have on my CNC router that isn't finished yet.

Rodney
 
I just put a Porter-Cable 7518, 3 1/4 HP motor on my router. About $300 from many sources, I bought mine from Grizzly. Adjustable speed 10 to 22 K. Speed control seems to work well, but a little slow ( a half second or so) to recover after a heavy momentary load. In general it seemed to work fine. I ran it for about 24 hours in two 12 hour runs at 13K, didn't even get warm. I was cutting 1.25 thick UHMW in this case, but a lot of guys use them on aluminum from what I understand. I would expect to get 400-500 hours out of it. You can get collets for them from 1/8 to 1/2 inch, by 16ths. I would not be afraid to use mist coolant with it, the fan in it blows down and is like a leaf blower, it must take about 1 hp just to run that.

For really high speed work in the mill, I use a Harbor Freight pencil, air die grinder (about $20) mounted in the spindle. The specs say 50K, but I normally don't run it flat out. Seems to be holding up well, and I have a lot of hours on it. I have run endmills down to 0.020 with it. I use an in-line oiler with it.
 
Hi Tom
this is like what I have... (I got the 1.5 but with the er20 collet I wish I would have gotten the 2.2. It will take tools up to 1/2" )
coolant is not a problem because the air blows down towards the tool and it will not enter the motor.
Ebay item number 251263506939 $355 and free shipping
Steve
 
Thanks for your input. I did some more searching and reading last night trying to determine which option will cover an RPM range from 7,000 to about 15,000. If I use carbide end mills exclusively this would get me into the desired RPM range. From what I learned router motors don't work well below 10,000 RPM. How slow can you effectively run a high speed spindle without losing too much torque? I'm mostly looking to machine aluminum and mild steel so I need something that has enough power in the lower end of the RPM range. A 3/8" end mill would be the largest end mill I would use in such a set up.

Tom S
 
jumps4 said:
Hi Tom
this is like what I have... (I got the 1.5 but with the er20 collet I wish I would have gotten the 2.2. It will take tools up to 1/2" )
coolant is not a problem because the air blows down towards the tool and it will not enter the motor.
Ebay item number 251263506939 $355 and free shipping
Steve
Click to expand...

Steve - I got the high speed spindle idea from your build thread. Are you happy with the quality of the spindle and VFD?

Tom S
 
RJSakowski said:
Tormach has some solutions for high speed spindle requirements. http://www.tormach.com/product_pcnc_acc_spindle.html

Possibly some ideas on how to solve your problem?

Bob
Click to expand...

Thanks Bob. I looked at the Tormach offerings and the Spindle Speeder is interesting but the price (~$1,400) is out of my price range. The Companion Spindle is similar to a router motor and the price is attractive. Looks like anything electric driven is limited on the lower end to 10,000 RPM.

Tom S
 
I have the Dewalt 611 trim router and think it is grand! I also have the same air powered pencil spindle noted above as Jim and the guys here helped me get my high speed engraving spindle basics nailed down. The only item I have a comment on is related to Carbide small end mills on high speeds. I tried that. Broke most everyone of them (with CNC being used for engraving). So brittle and delicate. Of course, I am also very new and learning but did fare much better with HSS in those really small sizes. I now also love Cobalt. I'm just curious what type of material you would use these Carbides and higher speeds upon? When I used my setup for engraving on Brass- the carbide would just not last long when cnc driven. I also ran them on Steel and Stainless. In the end I needed a mount w/ a spring spindle and HSS. Thought I would toss in my newb feedback on really really small carbide EMs
 
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