[feconkar]

Hi,

I have a Bridgeport j head clone milling machine about 5 years. When i bought that machine it's high speed gear was not working beacuse of a broken teeth. I have weld a teeth with tig weld and it worked and still working ( a little bit loud gear sound but okay).

I don't know how much time it will keep working but i have devoloped a plan to improve my j head clone. To simply the expression i will write down the plan step by step.

- i will switch the sytem on step pulley (low speed) system permanently.
- i will swtich 1500 rpm 2 hp motor with a 3000 rpm 3 hp motor
- i will add an sensorless vector drive

i want to keep pulleys because of their torque increasement. But my highest milling speed will be around 600 rpm with this setup. I don't want too much speed but at least 2000 rpm will be good for me for highest milling speed. At this point maybe i can remove or adjust the diameter of the timing belt. If i decrase the diameter of the big timing belt wheel, may be i can gain some rpm from here.

And now i want your opinions or advice about this setup. Is there a project that you can show me to get inspire or to follow. I know there are more experinced machinist and engineers in here and i want to hear advices from them.

[Jim Dawson]

In the Bridgeport J head, the gear is used in low speed, not high speed. High speed is direct drive from the spindle pulley. It would be possible to remove the low speed idler shaft and still run the machine just fine.

Stay with a 1500 RPM (4 pole) motor. It has twice the torque of the same power 3000 RPM (2 pole) motor.

Installing a 3 HP, 1500 RPM motor is OK, it will run at 3600 RPM (or more) just fine with a sensorless vector VFD.

The lowest speed in direct drive is 660 RPM with the motor running at 1800 RPM with the step pulley system. With a sensorless vector VFD it will run from about 10 RPM to 4500 RPM using the step pulleys. With a 3 HP motor there is enough torque to tap 12mm in steel at reasonable tapping speeds.

So:
Keep the step pulleys
Install a 1500 RPM, 3 HP motor
Install a sensorless vector VFD

It will run good.

[feconkar]

In the Bridgeport J head, the gear is used in low speed, not high speed. High speed is direct drive from the spindle pulley. It would be possible to remove the low speed idler shaft and still run the machine just fine.

Stay with a 1500 RPM (4 pole) motor. It has twice the torque of the same power 3000 RPM (2 pole) motor.

Installing a 3 HP, 1500 RPM motor is OK, it will run at 3600 RPM (or more) just fine with a sensorless vector VFD.

The lowest speed in direct drive is 660 RPM with the motor running at 1800 RPM with the step pulley system. With a sensorless vector VFD it will run from about 10 RPM to 4500 RPM using the step pulleys. With a 3 HP motor there is enough torque to tap 12mm in steel at reasonable tapping speeds.

So:
Keep the step pulleys
Install a 1500 RPM, 3 HP motor
Install a sensorless vector VFD

It will run good.

thanks a lot.