I'm going to switch out the motor with a DC motor so I was wondering what HP range should I look for? 1hp, 2hp or 3hp, or is anything over 1hp not a good idea on this head? Thanks

It depends how hard you are going to work it, whether you need it or not. I put a 7.5hp motor on a small knee mill so that it would have low end torque for tapping. Speed control was via VFD in this case.

Why are you going to DC? A spindle motor makes a lot of turns, compared to a servo driving a table screw. Brush wear and maintenance is something to consider. A DC controller is likely at least as expensive as a VFD for a 3 phase motor. You can run one of these from a single phase supply, providing you oversize the VFD by 50% if you want full nameplate hp out of your motor.

I believe that the J head is stressed for 1 HP. Anything more and you are asking for trouble.
Example. I was just called in on a 2J head BOSS 5 machine which has 2 hp. He was cutting copper (slotting it on the side). To make a long story short he put a twist into the spindle splines. Makes it impossible for the spindle to go up and down. It takes the bull gear and splined gear hub with it.
If you need more HP get a series 2 machine, or some other mill that is made for whatever you are trying to do. Just my 2 cents.

George

I'm looking at getting a 1HP bridgeport Series I in about 3 months and after talking to a friend about DC motors over AC motors it sounded like DC was a batter way to go.

My options are Phase converter / new motor (AC or DC). 1HP is enough for the type of work I want to do, but I was intrested in knowing if I should spend some more and get a bigger motor or not.

FYI, my series 2 came from the factory with a 4HP 3 phase motor. I don't know if the splines are beefier then a 1hp J-head or not...

I don't think that you would ever be able to use more then 2hp to it's full potential. The Bridgeport just isn't rigid enough to push an endmill so hard that it would require that much power.

A series 2 has a LOT beefier spindle. While a series 1 accepts a QC30, the series 2 accepts a QC40.

George

I don't think that you would ever be able to use more then 2hp to it's full potential. The Bridgeport just isn't rigid enough to push an endmill so hard that it would require that much power.

3/4" rougher, 3000rpm, 1"DOC at max powerfeed speed will do it:D
Watched my boss do it once, was pretty funny, he was as amased as I