Caliper Extension to Measure Internal Dimension

Caliper Extension for Internal Dimension Measurement

Caliper extension for measuring internal dimensions, e.g. for checking if extrusion frames are exactly square.

BOM:

- 1 x standard digital caliper
- (printed) 1 x base1 top, 1 x base1 bottom
- (printed) 1 x base2 top, 1 x base2 bottom
- (printed) 1 x long clamp
- (printed) 2 x short clamps
- (printed) 1 x small pin, 1 x large pin
- 1 x aluminum tube, 200mm x 10mm x 1mm (for internal dimensions from 500mm - 700mm)
- 1 x aluminum tube, 400mm x 8mm x 1mm (for internal dimensions from 500mm - 700mm)
- 6 M3 rivet nuts
- 6 x M3 x 15 screws
- 6 washers M3, 7mm
- 2  nails 25mm x 1.5mm

Parts can be printed in PLA or PETG

Check if the small aluminum tube nicely slides inside the large one before buying!  

Assembly:

Print the needed parts as listed in the BOM. Apply the rivet nuts to the base tops using a soldering iron. Apply the nails to the printed pins so that tip of nail extends the pin by 1-2mm with a soldering iron. Please watch your fingers!
Assemble base1 top, bottom and long clamp with screws and washers. Check for the orientation of the clamp before fastening. Assemble base2 top, bottom and 2 short clamps. Cut the aluminum tubes according to what you want to measure (I needed to check if the 560mm diagonals of a 400mm aluminum extrusion frame is exactly square, so I cut the tubes at 200mm and 400mm). Attach the tubes with the clamps. Tight the screws firmly to prevent the bases from moving but not too firm, because it will make it harder for the smaller tube to slide in the large one. If needed, pad the base with tape.
Start measuring!