Disclaimer

English is not my first language, so I asked an AI to help write this description.
If something sounds weird, please blame the AI, not my caliper. 😄

Large Diameter Caliper Adapter (x10 Multiplier)

3D printed adapter that turns a regular Mitutoyo caliper into a large-diameter gauge.
Clamp it on the end of the caliper, calibrate once, then just measure and multiply the reading by 10.

Perfect for pipes, tubes, drums, domes, tree trunks and other round-ish objects that are too big for normal caliper jaws, or where you cannot get all the way around and a reasonably accurate diameter is all you need.

Key features

• Extends the usable diameter range by a factor of 10

• Simple one-time calibration with any cylinder of known diameter

• Uses the caliper's depth rod as the measuring element

• Second version supports very large diameters (up to ~1100 mm) using 10 mm OD carbon fiber or aluminum tubes

• Only printed parts plus tubes for the long version, no fancy hardware needed

How it works

The adapter is basically a lever with a 10:1 ratio:

1. The caliper depth rod moves a small distance inside the adapter.

2. The outer arms of the adapter touch the big cylinder.

3. The caliper shows a small value T.

4. Real diameter = T x 10.

Because printers and plastics are not perfect, we use a small correction called the calibration constant C.

Quick calibration (do this once per printed adapter)

1. Zero the caliper
   Close the jaws and press zero so the display reads 0.

2. Pick a reference cylinder
   Measure its diameter normally with the jaws. Call this value D.
   Compute: Dref = D / 10.
   Example: cylinder is 100 mm -> Dref = 10 mm.

3. Measure with the adapter
   Mount the adapter on the caliper and measure the same cylinder using the depth rod.
   Let this reading be Tref. Example: Tref = 14.8 mm.

4. Calculate the calibration constant
   C = Tref - Dref
   In the example: C = 14.8 - 10 = 4.8 mm.

5. Zero the caliper with the offset
   Open the caliper jaws until the display shows C (4.8 mm in the example).
   Press zero again. Now the display reads 0, but the jaws are actually separated by C.
   This compensates for the adapter geometry.

6. Record C
   Write the value of C inside the adapter with a marker or a small label so you don't forget it.

You only need to do this once for each printed adapter (unless you reprint or change parts).

Using the adapter to measure large cylinders

1. Make sure the adapter is firmly mounted on the caliper.

2. Check that the caliper is zeroed with the correct offset C.

3. Place both inner contact surfaces of the adapter against the cylinder.

4. Read the value T on the caliper.

5. Actual diameter = T x 10.

Accuracy notes

• This is a convenience tool for general large-diameter measurements.

• Accuracy depends on:

  • how well you calibrated (good reference cylinder),

  • how carefully you seat the adapter on the cylinder.

• It is not a replacement for specialized high-precision metrology gear.

Long-range version (up to ~1100 mm)

The second design uses 500 mm long, 10 mm OD carbon fiber tubes (or aluminum tubes) pressed into the adapter body.

• Geometry is the same, still a 10:1 ratio.

• Calibration is identical: compute C once, then measure and multiply by 10.

The tubes in the photos are generic 10 mm OD CF tubes from AliExpress / Amazon (any similar tubes should work).

By following these procedures, you can conveniently measure large diameters using your caliper and this 3D-printed adapter. Enjoy your printing and happy measuring!