There are many dial indicator support designs available; those which rest angled plastic on the rails are unlikely to tram accurately while those that clip to the extruders are not going to be highly repeatable in absolute measurement from use to use.

This dial indicator uses roller bearings in conjunction with hold-down magnets to provide excellent support stability and smooth and accurate and repeatable absolute tramming. A simple tramming coupler links the carriage with the extruder using magnets. The coupler has spacings for the correct lateral offsets for both modified and unmodified Replicator extruders. (The modification introduces a lever which collides with the dial indicator, requiring an additional offset.) Full design files are provided in Rhino3D and STEP formats. Carriage updated Aug 13, 2013.

A Dial Indicator is a very effective tool for managing build platform levels and checking the condition of the build plate. There are many available and this project uses a pretty common Mitutoyo 543-683.

With a stock of nice small bearings I decided a bearing based carriage might provide the smoothest tramming and a very stable geometry. The springs on the dial indicator require some modest down force - and the indicator itself and carriage do not collectively provide enough mass to do this. So small magnets are built into the design to ensure consistent contact of the bearings and the extruder rails.

So that the carriage can also be tracked with the extruder head, there is also a connecting arm which is magnetically coupled both to the dial indicator carriage and the extruder. It has insets for magnet spacings that suit use with both modified and unmodified Makerbot Replicators. (If you have improved your Replicator extruder with the spring-lever modification, the carriage needs to stand further off the extruder. You can find a version of this modification in my designs).

This design uses

• 4 x bearings 12mm OD, 8mm ID, 3.5mm depth
• 1 x bearing 12mm OD, 6mm ID, 4mm depth
• 8 x rare eath magnets 6mm x 2mm
• 1 x Mitutoyo 543-683 dial indicator.

Included in the downloadable materials are Rhino3D and STEP CAD files so you can use different bearings, magnets and dial indicators. Enjoy; this works superbly, delivering repeatable absolute readings from use to use.