Spacer Stack Calculator
You need a gear sitting exactly so far along a shaft. This works out which spacers and washers stack to that width, using the fewest pieces.
Inputs
This decides which pieces are even usable. High strength spacers have a bigger bore, and nuts only belong on a screw.
The space between whatever is on either side. Decimals are fine: 11/16 is 0.6875.
Results
Pieces needed
—
Stack thickness
—in
As a fraction
—
Off by
—in
How this is calculated
This is the change-making problem: given a set of thicknesses, hit a target using as few pieces as possible. It is solved exactly here rather than by grabbing the biggest spacer that fits and repeating. That greedy approach usually works with these sizes, but it is not guaranteed to find the shortest stack, and there was no reason to accept "usually".
Every available thickness is a whole number of 1/64", so the target is converted into sixty-fourths and solved in whole numbers. That avoids decimal rounding entirely: 3/8" is exactly 24 units, never 0.37499999.
With your numbers
Why the shaft rattles anyway
A stack that is mathematically exact still leaves a gear that can shift, because real parts are not their nominal size:
- Nylon compresses. Tighten a shaft collar hard onto a nylon stack and it will measure slightly less than the sum of its parts.
- Tolerances add up. Six pieces each a few thousandths under nominal is a gap you can feel.
- Fewer pieces is better. Beyond convenience, each joint between pieces is somewhere for slop to hide. A 1/2" spacer beats four 1/8" spacers for stiffness as well as for build time.
If a gear still has play after an exact stack, add a 1/64" washer and check whether it binds. That is the intended use of the extra-thin washers, and it is why they exist in that size.
Sources & assumptions
Thicknesses are taken from a VEX parts supplier's size listings rather than a VEX catalogue page, so treat this as "sizes you can buy" rather than "sizes in your kit". Check your parts bin. A stack you cannot build is not a solution.
Spacer inner and outer diameters are not considered. A stack of the right thickness still has to fit the shaft and clear whatever is around it.
- Robosource — VEX-compatible nylon spacers & washers (size listings) — checked 2026-08-17
- VEX Library — Using V5 Washers and Spacers — checked 2026-08-17
Save this run, and compare
Keeps what is on screen so you can change something and see both sides of the change. Saved in this browser only, never uploaded.
Save this as evidence
Collects what you entered, what came out, how it was worked out, and anything the tool flagged, with a timestamp and a version so someone else can reproduce it.
This is evidence, not a notebook entry. It deliberately does not write your problem statement, your reasoning, or your conclusion, because under RECF rules an Engineering Notebook has to be the students' own work and no tool may generate or organise its content. Take the numbers, decide what matters, and write it yourself.