Monthly Archives: January 2017

Sieg SC4 Lathe Power Feed

Disclaimer

Be advised this modification is not to be entered into lightly as it requires knowledge of electricity, wiring, machining and general mechanical assembly.

General Info

The purpose of this modification is to add a variable speed/reversible carriage/cross slide power feed to the Little Machine Shop 3595/3540 (Sieg SC4) lathe. This mod greatly increases the usability of the lathe by disconnecting the carriage and cross power-feed from the spindle and adding an independent motor to power the carriage and cross-slide power feeds. All-in-all this is a simple modification that requires only minor modification to the lathe, but adds a lot of flexibility.

  • Total disconnection from lathe spindle gearing.
  • Quickly reconfigurable back to factory gearing configuration for threading.
  • Variable speed using a PWM controller (Pulse Width Modulator) allowing from roughing cuts to very fine finishing cuts using any lathe spindle speed.
  • Reversible direction allowing turning in both directions.
  • Provision for a limit switch to stop feed motor. This is very nice for turning down a part in multiple passes.

Parts List

  • Drive motor available from Little Machine Shop (or find your own).
  • Drive motor to gear adapter (build-your-own).
  • PWM controller these are cheap and available on the net.
  • 28 vdc 1-2 amp power supply if you use the motor above. There are many places on the web to get one. Here is where I get some parts MPJA.
  • Two (2) motor mounting brackets (roll-your-own).
  • Options:
    • Enclosure to house components
    • Connectors and wiring to suit.
    • Limit switch and bed attachment fixing.
    • Special plug to use lathe 110 vac auxiliary power connector to the power supply.

Mechanical

  • The first thing required after the parts are gathered up is to make the motor mounts. The way I did it was to use two of them. See the motor mounting pix below.
    • The first is made from a small piece of aluminum L bracket which attaches to the forward L/H mounting hole of the lathe and to to one of the 10-32 screw holes in the motor and acts as a pivot point for motor adjustment.
    • The other is also aluminum L bracket that attaches to the motor via an adjusting slot and 10-32 cap screw and the other leg attaches to the backup gear cover structure. I drilled and tapped two 8-32 holes for this (see pictures).
  • The next thing to make is the Motor Drive Adapter. The shaft size of the LMS motor is 8mm and the gear mounting hole is 16mm (.630). The length needs to be adjusted to mesh with the gear on the lead screw and a set screw added to hold the adapter to the motor. You will also need to thread the end of the adapter (I used a 1/2-20 nut) to secure the gear. And, don’t forget to mill a slot for the key.
  • IMPORTANT: Swing the gear idler assembly out of the way to disconnect the lead screw gear from the spindle.
  • Select and install the gears you want to use. I used a 100 tooth on the lead screw and a 80 tooth on the drive motor, but many others can be used as long as the drive motor adjustment will work. There is some restriction to gear combinations due to the narrow space where the motor is located.
  • Next the gear cover will need to be modified to clear the drive motor gear. This is easily done with a hack saw after it has been removed from the lathe.

Control Box

  • You will need a control box to  house the components needed to supply power for the drive motor. This is mostly a personal preference and I’m not going to spend any time detailing with how I did it since it’s such a simple circuit. Here is the Schematic Diagram of how I did it.
  • Controls
    • Motor speed
    • DPDT center off switch to select motor direction from forward to reverse.
    • Momentary normally closed SPST switch to reset the limit switch relay.
    • Green Power-On LED.
    • Red LED to show when the limit switch has been tripped.
  • See the picture gallery for a pictures of my control box.
  • Of note may be that I used 3 strong ferrite magnets to attach the control box to the lathe’s gear door rather than permanent fixings.

Operation

  • Operation should be obvious so I’ll only detail how the limit switch works. The limit switch will stop the power feed when tripped allowing you to repetitively make passes stopping at the same place every time
    • When the carriage trips the limit switch it will latch the limit switch relay and remove power from the motor stopping operation.
    • To release the lockout condition (reset the relay):
      • Switch the direction switch to reverse and press the momentary spst (NC) switch until the red LED goes out. This switch is the one in series with power to the relay coil.
      • Or, manually move the carriage away from the limit switch until the red LED goes out.

Picture Gallery

Click on picture to enlarge