What hp spindle

[Art]

I am seriously considering getting a spindle because of the noise of my PC router. Some where I heard that a 2 hp spindle would match a 3.5 hp PC router. Presently I don't see that I will not cut deeper than .5" at 300 IPM. Will a 2 hp be OK or should I spend the extra money for a 3 hp?

[Richards]

I have a 3hp Colombo spindle on my PRT-Alpha. One of its features is an amp meter that shows how hard it is working during a cut. The forumula to compute horsepower, when the amps used is known is:

(I X E X Eff X pf) / 746 = hp

Current drawn when I'm cutting particle board, melamine, or MDF is always less than 6 amps, so (6A X 240V X 100% efficiency) / 746 = 1.93 hp, and (6A X 240V X 75% efficiency) / 746 = 1.45 hp. (I have no idea how efficient a spindle is or what the power factor (pf) is, so I Googled several Amp to HP conversion charts and used typical hp ratings for a known current to arrive at the figures.)

When my Colombo needs major surgery, I'll most likely replace it with the 2.2hp spindle that Shopbot sells. If, by chance, I install a heavy duty vacuum pump that allows me to make 1-pass cuts, then, I'll go for the 4hp unit. However, my 3-hp spindle has never limited the depth or feed speed of the cuts I make except on very hot days when the shop temperature is over 110 F. On those hot days, I make lighter passes to keep the bearing temperature below 140 F. On days when the shop temperature is 80 F or lower, I can run the spindle all day long without worrying about overheating the bearings. As I understand it, keeping the bearings at a temperature of 140 F or less is essential to get 2,000 hours per set of bearings. Also, it is very important to warm up the spindle properly by running it at moderate speeds for ten minutes before cutting and then letting it cool down by running it at moderate speeds for ten minutes after the work is done.