3D printed spacers and feet
A spacer is a block with a hole. A foot is the same block with a softer bottom. Both are easy, and both still fail when the thickness is guessed or the bore is drilled to the wrong number.
Spacers and feet are the easiest replacement parts to get right, and the easiest to get wrong for a boring reason: nobody measures the thickness they need. A spacer has three numbers that matter, the thickness between the two faces, the bore for the fastener, and how parallel and flat those faces are. A foot adds two more, how much it compresses and whether it stays where it is put. Get those and the part works first time. Guess the thickness and you will print it three times, then shim it with a washer, which is what you should have measured in the first place.
What the spacer is actually doing
Before measuring, say what the gap is for. Four jobs, four different parts.
- Standoff. Holds two surfaces a fixed distance apart around a screw and carries a compressive load. The thickness is a design number; the bore is a clearance hole.
- Shim. Takes up an existing gap, usually under a millimetre. Printed shims below 0.6 mm are unreliable: the first layer squashes and thickness becomes a range.
- Wear pad. Separates two moving surfaces. Thickness matters less than the surface: a printed pad slides on smooth metal and grabs on carpet.
- Foot. Lifts a machine or a piece of furniture off the floor, spreads the load, damps vibration and protects the floor. Compression and grip matter more than thickness.
The distinction matters because a standoff is measured with callipers and a foot is measured by how the thing sits. A foot that is dimensionally perfect can still walk across a tiled floor.
Measure the gap, not the old spacer
Old spacers crush, crack and go missing. Measure the parts that have to end up at the right distance: assemble the joint loosely and measure the gap.
| What | How | Datum |
|---|---|---|
| Gap to be filled | Assemble the joint, tighten the fastener, measure the remaining gap with a feeler gauge or depth rod | Between the two faces the spacer separates |
| Fastener diameter | Callipers on the screw shank, not on the hole it came out of | Across the shank, at the unthreaded part |
| Bore in the mating part | Inside the hole, two directions 90 degrees apart | Across the bore, at the top and the bottom |
| Washer or head diameter | Callipers across the bearing face | Under the head, where it presses |
| Available depth | Depth rod from the surface to the first obstruction behind | Along the fastener axis |
| Face area available | The land the spacer sits on, not the spacer itself | Between the surrounding features |
| Load, for a foot | Weigh the thing, or estimate it, and note whether it can be loaded unevenly | Per foot, as installed |
Measure the gap in more than one place. Four feet under a cabinet are rarely on one plane, and a rocking frame has a gap that changes as you push a corner. That variation decides whether you need a compliant foot or whether the frame is twisted and no spacer will fix it.
The three dimensions that matter
A spacer has a short list of dimensions that decide whether it works, and a longer list that does not.
Thickness
This is the functional number, and it comes from the gap, not the old part. Print slightly oversize and sand back, or print three at 0.1 mm steps and pick the one that fits. A printed face is never exactly the modelled thickness: a 3.00 mm part often measures 2.95 mm.
Bore
A clearance hole wants 0.3 to 0.4 mm over the shank, and printed holes come out undersized by 0.1 to 0.2 mm, so drill to size afterwards if the screw must slide. For a bolt that clamps the joint the clearance barely matters; for a shoulder that has to pivot it matters completely.
Face flatness
A spacer with dished faces rocks and takes the load on one edge, which is how printed standoffs crack. Print it with the load faces horizontal, on a brim, and check with a steel rule and a light behind it. If the middle of the rule shows light, the faces are not flat.
Do not stack three printed spacers to reach a thickness you did not measure. Three faces mean three chances of a rock, and the stack creeps under load far more than a single part.
Compression and creep under a foot
A foot carries a static load for years. That is a creep test, not a strength test, and it is the reason a rigid printed foot slowly flattens and a soft one takes a set.
For a hard foot in PLA, PETG or ABS, keep the load low and the bearing area generous. A rough bench figure: shape the foot so contact pressure stays under a few tenths of a newton per square millimetre, and check by standing the machine on it for a week rather than trusting a datasheet. A foot that has visibly flattened has already changed the height of the machine.
For a soft foot, TPU works if it is printed solid, in a shape that is mostly wall, and if the compression is limited. A TPU pad under a heavy machine creeps into a permanent set within weeks, and the machine sits lower on one corner. TPU is right for a light chair leg, not for a 60 kg machine.
Two more effects matter in a workshop. Vibration makes a rigid foot slide, so a printed foot on a smooth floor needs a rubber or cork pad underneath. Heat from a motor softens the foot, so a foot near a heat source should not be printed at all.
Make the foot stay where it is put
A foot that falls off when the machine is lifted is a foot that will be lost. Three ways to keep it, in order of how well they work on printed parts.
- A recess and a press fit. The leg or frame has a socket; the foot has a spigot that presses into it, with 0.2 mm of interference and a chamfer to start it. This survives lifting.
- A screw through the middle. A countersunk hole through the foot into the existing thread. Best of all, because the foot cannot walk, but only where there is a thread to use.
- Adhesive or a magnet. A magnet pocket needs a closed floor at least 0.8 mm thick, or the magnet pulls through. Adhesive on a printed face holds poorly unless the face is abraded first.
Whatever the retention, put a chamfer on the bottom edge and give the contact face a 1 mm recess for a rubber pad. A flat printed face on a hard floor is a slider; a recessed pad is a foot. Where the foot bolts to a bracket rather than a frame, the bracket page covers screw bosses and panel thickness.
The tolerances that do not matter
Half the dimensions on a spacer can be almost anything, and treating them like fits wastes prints.
- Outside diameter. Only has to clear its neighbours and look tidy. A millimetre either way changes nothing.
- Corner radii and edge chamfers. Cosmetic on a spacer, useful on a foot because a sharp edge on a floor chips.
- Surface finish on the sides. Irrelevant unless the part slides.
- Infill. A spacer in compression wants more perimeters and less infill: four walls and 20 percent infill carries more than two walls and 60 percent.
The dimensions that do matter are the thickness, the bore if something pivots or slides through it, and the flatness of the two load faces. Print the first one, measure it with callipers, and adjust the model by the difference. That removes most reprints from this part type, which is otherwise the easiest thing on the site to get right. For the wider set of parts, the hub at replacement parts by the thing that broke covers covers, brackets, knobs, clips and caps.
When a spacer is not the fix
Two situations look like a spacing problem and are not.
The first is a machine that rocks. If a frame is twisted, adding a foot to the low corner lifts the whole machine by that amount and leaves it rocking on the other diagonal. Check with a straight edge across the frame and a flat reference surface, then fix the frame or use adjustable feet rather than printing a shim to hide the twist.
The second is a joint that has come loose because something behind it failed. A spacer under a motor mount can hide a worn bearing for a while, and then the mount cracks. If the gap was not there when the machine was new, find out why it is there now.
And a plain warning about loads: a printed spacer carrying a structural load is a part that creeps. Under a shelf, a machine or anything that holds weight above head height, use a metal spacer or a bought foot. The safety lines are set out in whether to print a replacement part, and the caps and plugs page covers the parts that hold something in rather than something up.
Questions
How accurate is a 3D printed spacer?
The thickness is the only number that usually matters, and a printed face lands within about 0.05 to 0.1 mm of the model, often slightly thin because the first layer squashes. Print one, measure it with callipers, and adjust the model by the difference.
What infill should a printed spacer or foot use?
Perimeters do the work in compression, so use four walls and around 20 percent infill rather than two walls and a high infill. A foot that has to flex should be printed solid in TPU instead, with the compression limited.
Can a printed foot hold up a heavy machine?
Not for long. Printed feet creep under a static load, so a heavy machine flattens them over weeks and sits unevenly. Use a bought foot or a metal spacer under anything heavy, and reserve printed feet for furniture, light equipment and benches.
Written for the Refabrication preview. Sizing, material and safety notes here are general guidance, not engineering or compliance advice. Check any part against your own equipment, loads and local requirements before you print or install it.