Power Draw Bar (PDB), Tool Won't Load or Release

Owned by Adam Brunner
Last updated: Oct 04, 2023 by Sam Bollen
4 min read

Background

Any machine that uses a dedicated tool holder also relies on a drawbar or power drawbar (PDB) to release it from the spindle. The release of the tool holder is caused when a pneumatic piston fills with air, pushes on the drawbar, and compresses a set of springs. When the piston doesn’t have air, the springs pull the drawbar up in order to hold the tool in the spindle.

Tools

  • Adjustable wrench

  • Pin spanner

  • Multimeter

Table of Contents

Adjust your central air and/or filter regulator lubricator (FRL)

Reason: Incorrect shop air pressure.

  1. Examine the shop air pressure, and verify that it recharges at a minimum of 90 psi (this is the pressure that the compressor turns on at). Based off what you find, do the following:

    1. Adjust your compressor based on the manufacture's guidelines.

    2. Find a compressor that can be set to recharge at a minimum of 90 psi.

  2. Examine the machine’s FRL, and set it 1-2 psi lower then your compressor’s recharge pressure up to 100 psi.
    Example 1: My compressor starts to recharge at 90 psi and goes all the way up to 105 psi. I need to set my FRL to 88 or 89 psi to get the most consistent results.
    Example 2: My compressor starts to recharge at 115 psi and goes all the way up to 100 psi. I need to set my FRL to 100 psi to reduce the pressure to the machine’s pneumatic systems.

Adjust the power drawbar bolt

Reason: Power drawbar cylinder piston is out of adjustment range.

  1. Loosen the power drawbar piston bolt and adjust it so that it sits within 0.5 mm (0.020 in.) of the spindle's spring stack when there's no tool loaded in the spindle.

  2. Determine the number of washers necessary to fill the gap between the bolt head and power drawbar. Then remove the bolt completely in order to install the washer.

  3. Retightening the bolt and inspect to ensure there is still clearance between the power drawbar bolt and drawbar.

Three-stack power drawbar

Two-stack power drawbar.

Note: hoses might be plumed differently than shown here.

 

Adjust the drawbar preload

Reason: Insufficient or excessive preload of drawbar springs.

  1. Put an empty Tormach Tooling System (TTS) tool holder into the collet.

  2. While using one hand to support the tool holder, use the other to push the Release Tool button.

  3. Depending on whether the tool holder releases or not, do one of the following:

    1. If the Tool Holder Releases. Tighten the Power Drawbar in quarter-turn increments with two adjustable wrenches. After each turn, push the Release Tool button. Stop when the tool holder does not release. Then, loosen the Power Drawbar one quarter-turn with two adjustable wrenches.

    2. If the Tool Holder Doesn't Release. Loosen the Power Drawbar in quarter-turn increments with two adjustable wrenches while pushing the Release Tool button. Stop when the tool holder releases.

  1. Put an empty BT30 tool holder into the spindle.

  2. While using one hand to support the tool holder, use the other to push the Release Tool button.

  3. Depending on whether the tool holder releases or not, do one of the following:

    1. If the Tool Holder Releases. Loosen the jam nut on the top of the spring stack then tighten the drawbar in quarter-turn increments with two adjustable wrenches. After each turn, push the Release Tool button. Stop when the tool holder does not release. Then, loosen the Power Drawbar one quarter-turn with two adjustable wrenches.

    2. If the Tool Holder Doesn't Release. Loosen the jam nut on the top of the spring stack then loosen the drawbar in quarter-turn increments with two adjustable wrenches while pushing the Release Tool button. Stop when the tool holder releases cleanly.

Check the voltage on the power drawbar board/solenoid (PCNC 770 & PCNC 1100 Only)

Reason: There may not be 12 Vdc going to the power drawbar board and/or solenoid.

  1. Using a multimeter, check for 12 Vdc on wires 501 and 502 at the power drawbar board.

  2. Depending on the result, do one of the following:

    1. If there isn’t 12V at the location: There may be an issue with the daughter board (31980) or wall wart power supply if you do not have an ATC. Contact Tormach Tech Support for guidance on how to proceed.

    2. If there is 12V at the location: Go to Step 3.

  3. Check for 12 Vdc on the wires that go to the solenoid at the time the power drawbar is pressed. These wires don’t have labels, but they're connected to the white connector on the back side of the PDB controller. Put the leads on each terminal once disconnected, and then press the PDB pendent.

  4. Depending on the result, do one of the following:

    1. No power at the solenoid connector at the time the pendent is pressed: The power drawbar board (31979) is likely bad and will need to be replaced. Contact Tormach Tech Support to verify this before placing an order.

    2. Power at the solenoid connector at the time the pendent is pressed: The drawbar solenoid (31498) is likely bad and will need to be replaced. Contact Tormach Tech Support to verify this before placing an order.