how to include an existing urdf file into anothe urdf file with xacro

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Hi, I have written a short urdf file to describe my tool and a launch file to open it in rviz. So far everything displays correctly and there are no errors.

Now, I want to include another urdf file and position it with respect to my part with a joint. The other urdf file is using xacro, which I find really confusing to use. When I try to launch it, I get an error that "no link elements found' and in rviz it says no tf data and there are no fixed frames available. I tried to put assembly_tool] but it can't find this frame. The first is my urdf file and the one below is the relevant excerpt of the existing urdf that I want to include and the third the launch file I use. Could anyone tell me where my problem lies? Thanks in advance!

<?xml version="1.0"?>

<robot name="grinding_tool" xmlns:xacro="http://www.ros.org/wiki/xacro">

<xacro:include filename="$(find compliant_tool_description)/urdf_src/compliant_tool2.urdf.xacro" />

<!-- Useful definitions -->


  <xacro:macro name="grinding_tool" params="ee_link_name">

  <xacro:property name="ee_link_name" value="ee_link"/>

  <link name="ee_link"/>

  <link name="assembly_tool">
    <visual>
      <geometry>
        <mesh filename="package://grinding_tool/meshes/assembly.stl" scale="0.001 0.001 0.001"/>
      </geometry>
      <material name="gray">
          <color rgba="0.8 0.8 0.8 1.0"/>
      </material>
    </visual>
    <collision>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <geometry>
          <box size="0.42 0.17 0.15"/>
        </geometry>
     </collision>
     <inertial>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <mass value="3.3"/>
        <inertia ixx="0.0019"
                 ixy="0" iyy="0.072"
                 ixz="0" iyz="0" izz="0.074"/>
     </inertial>
  </link>

   </xacro:macro>



<gazebo reference="tool">
      <mu1 value="200.0"/>
      <mu2 value="100.0"/>
      <kp value="10000000.0" />
      <kd value="1.0" />
      <material>Gazebo/Grey</material>
  </gazebo>

  <gazebo> 
        <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
          <robotNamespace>/</robotNamespace>
        </plugin>



  </gazebo>
</robot>

The only thing I adapted was including a joint: comp_grinding_joint to connect my urdf to the compliant tool urdf.

<robot xmlns:xacro="http://www.ros.org/wiki/xacro">

  <xacro:include filename="$(find compliant_tool_description)/urdf_src/include/compliant_tool_parameters.urdf.xacro"
                 ns="cmptool"/>

  <!-- Useful definitions -->
  <xacro:property name="meshes_path"
                  value="package://compliant_tool_description/meshes"/>
  <xacro:property name="meshes_scale"
                  value="0.001 0.001 0.001"/>

  <xacro:macro name="compliant_tool" params="ee_link_name">

    <joint name="comp_grinding_JOINT" type="fixed">
          <origin xyz="0 0 0.0019" rpy="0 0 0"/>
          <parent link="assembly_tool"/>
...

<link name="${ee_link_name}_sliderplate">
      <visual>
        <origin xyz="0 0 0.057" rpy="${cmptool.PI} 0 0"/>
        <geometry>
          <mesh filename="${meshes_path}/sliderplate_with_joint.stl" scale="${meshes_scale}"/>
        </geometry>
        <material name="gray">
          <color rgba="${105/255} ${105/255} ${105/255} 1.0"/>
        </material>
      </visual>
      <collision>
        <origin xyz="0 0 0 ...