Vinyl Mounting Block
Vinyl siding is a wall made of overlapping curves. There is no flat on it and no plumb on it, which you find out the first time you try to hang something: a floodlight screwed straight to a panel rocks on two high points, its gasket seals against air, and the screws pin a panel that is supposed to slide as the sun moves across it. A mounting block is the fix. It takes the siding profile on its back and gives you one flat vertical face on the front, and everything after that is ordinary.
They are sold, in three sizes, in white. Printing one gets you the size and the screw pattern you actually want, in about 450 cm³ of plastic — but only if your siding is the profile this one is drawn for, and that is the first thing to check rather than the last.
What is in the file
siding_block_v3.stl is a Fusion assembly exported whole, not a print plate.
There are three separate solids in it and one of them is the part.
| Solid | What it is | Print it? |
|---|---|---|
| The block | 200 × 190 mm pad, stepped back, Ø55 mm bore, six screw holes | Yes |
| A 4 in round weatherproof box | Ø101.6 mm barrel, five 3/4 in NPT hubs, two mounting lugs — a manufacturer’s model dropped into the design to check the screw pattern against | No |
| Two Ø4.83 × 12.5 mm cylinders | thread bodies belonging to two of that box’s tapped holes, shaken loose in the tessellation | No |
Splitting the STL to objects will not get the box off, and that is worth knowing before you spend ten minutes trying. The block’s six clearance holes and the box’s six tapped holes are drawn on the same six circles on the same plane, so the two meshes are stitched together there — to a slicer it is one connected body. The two loose thread cylinders sit inside two of the six holes and plug them.
Open siding_block_v3.step or siding_block_v3.f3d, delete the box, export
the block on its own. It takes a minute and it is the only clean route.
The numbers that matter
Measured off the STEP file, not off a drawing.
| Feature | Dimension |
|---|---|
| Overall | 200 mm tall × 190 mm wide |
| Front face | 190 × 180 mm, inside a 5 mm 45° bevel |
| Corners | 30 × 30 mm off at 45°, so the outline is an octagon |
| Thickness | 20 mm just below a course line, 7.3 mm just above it |
| Back | three flat ramps, 1 in 10 |
| Course pitch | 127.0 mm (5 in) |
| Step at each course line | 12.7 mm (1/2 in) |
| Centre bore | Ø55.0 mm, straight through |
| Fixture holes | six, Ø5.2 mm, through |
| Solid volume | about 450 cm³ |
The back is the whole design
The front is a flat plate and takes ten seconds to describe. The back is three flat ramps separated by two 12.7 mm steps, and the steps are 127 mm apart.
That is one course of vinyl siding. Within a course the panel face leans out as it comes down to its butt, so the block has to lose thickness on the way down to stay in contact — 12.7 mm of it over 127 mm, a slope of 1 in 10. At the butt line the next panel below starts tight to the wall again, and the block steps back to meet it. Two of those steps land on the part, 127 mm apart, and they face upward: each one tucks under the rolled butt edge of a panel. Push the block up the wall and it stops itself in exactly one place. That is the only alignment feature it has and it is enough.
5 in exposure with a 1/2 in lap is D5 — “double 5” — and it is not the only kind of vinyl on the market. D4, D4.5, D6 and D7 all exist, and none of them fit this. Hold a tape on your own wall before you slice anything: butt line to butt line is the exposure, and how far a butt stands proud of the panel above it is the lap. If they are not 5 in and 1/2 in, the STEP file is the one to open — those two numbers are the entire back of this part.
The hole pattern is a 4 in round box
Six Ø5.2 mm holes, all centred on the middle of the pad: a pair 88.9 mm (3-1/2 in) apart vertically, a second pair 88.9 mm apart horizontally, and a third pair 69.85 mm (2-3/4 in) apart horizontally. Those are the fixture and cover screw spacings of a 4 in round or octagon box. Six holes for a fixture that uses two, so whichever pair your strap or cover lands on is already there.
The Ø55 mm bore through the middle is the wire pass-through, and it is worth being clear about what it is not: it is smaller than the Ø96.5 mm mouth of the box behind it, so you cannot push a device through the block into the box. This pad suits anything that screws to the box’s ears with its leads passing through — a lamp holder, a flood bracket, a camera plate, a receptacle already made up on a 4 in round cover. It does not suit a device you were planning to set into the box afterwards.
Parts
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- ASA filament, 1.75 mm — search. Nothing in the workshop is ASA, so this is the one line on the page with no part number behind it. It is still the right answer: ASA is the only common filament that holds its colour and its impact strength in years of direct sun, which is the exact duty this part signed up for
- ABS, 1.75 mm — the nearest thing actually on the shelf, and a substitute rather than a match. Same heat resistance, same need for an enclosure, but ABS chalks and yellows under UV where ASA does not. On a north wall it will be fine for years; on a south wall it is a two-season part
- PETG, 1.75 mm — solid white, which is the colour most siding wants anyway, and the honest choice if your printer is open-framed. It will embrittle and go dull outdoors; plan on reprinting rather than pretending otherwise
- PLA+, 1.75 mm — for the test fit only. A PLA block on a sunlit wall will sag out of shape before it fades, and it is holding a light fitting up
- Printed on a Bambu Lab A1. The 256 mm bed swallows the 200 × 190 mm footprint with room to spare; the open frame is what makes ASA a fight
- 4 in round weatherproof box — Hubbell-Bell 5361-7 is the one to buy. The part the block is drawn around, and the part that does the containing. Note the hubs: the 5361-7 has 1/2 in, and the box modelled in the STL has 3/4 in. Every 4 in round box readily available is 1/2 in hub, and 1/2 in is what most fixtures and the liquid-tight kit below actually want — so the mismatch is in the model, not the shopping list. The six-hole pattern is identical either way, which is the part that matters to the block
- Stainless machine screws, 10-24 × 2 in — search. The block adds up to 20 mm between fixture and box, so whatever screws came in the fixture’s bag are now too short
- Arlington 8141DBL siding mounting kit — the bought version, box built in, sold for “1/2 inch lap double siding”, which is the profile this model is cut to. Buy one if you want to hold the geometry in your hand before you commit a 450 cm³ print to it
- Siding removal tool — the zip tool. Six dollars, and without it you unlock a course by breaking it
- Folding utility knife and blades — vinyl scores and snaps far more neatly than it cuts
- Jigsaw blades, T-shank — for the box opening through siding and sheathing. A fine metal-cutting blade and a slow speed; a coarse wood blade tears vinyl and melts it back together behind itself
- Twist drill set and a countersink and step-drill set — for opening the six screw holes back up after printing
- Butyl sealing rope, 5/16 in × 20 ft — sold for septic tank risers, and it is the same butyl that comes on a roll as flashing tape. A bead of it behind the top edge of the block is a better seal than any caulk, because it never skins over and never cracks
- Exterior polyurethane sealant — search, plus a caulk gun and a finishing tool. Read the caution below before you point that gun at anything
- Non-contact voltage tester — the breaker labelled “outside lights” is not always the breaker feeding the outside lights
- 12/2 UF direct-burial cable if you are running a new circuit out to the wall, and lever-nut connectors or solder-seal butt splices inside the box
- Liquid-tight conduit and fittings — a substitute worth naming: this kit is 1/2 in and the box’s hubs are 3/4 in, so it wants a reducing bushing at each end
- Electrical tape, a digital caliper, a deburring tool, a needle file set and wet/dry sandpaper
Things that mount straight to the pad, all of them already on the shelf here: a twin-par flood light holder, which screws to a 4 in round box on the 3-1/2 in pair; a 10 in wet-rated LED wall sconce; or a duplex receptacle already made up on a 4 in round cover, which is what the 2-3/4 in pair of holes is for. Put a weather-resistant GFCI in it rather than a plain receptacle. The in-use cover in the workshop is a 1-gang rectangular one and will not land on this pattern — a round box wants a round in-use cover.
If all you want to hang is a battery camera, skip the whole exercise. A set of no-drill vinyl siding hooks clips into the butt seam and puts no hole in anything.
Print settings
| Setting | Value |
|---|---|
| Layer height | 0.2 mm |
| Walls / perimeters | 4 |
| Infill | 15% gyroid |
| Supports | None |
| Material | ASA, or PETG on an open printer |
| Orientation | Front face flat on the plate |
| Bed needed | 200 × 190 mm |
| Roughly | 175 g, and an overnight print |
Front face down, and there is no second option worth arguing about. The flat plumb pad is the only surface anybody ever looks at, and printed against the plate it comes out as good as the plate is. Everything else follows: the back ramps become a 5.7° upward slope, the two course steps become plain vertical walls, the Ø55 bore and the six screw holes run straight up, and the 5 mm perimeter bevel flares off the first layer at 45°. There is not a single overhang in the part and not one support anywhere.
That first layer is 33,700 mm² of it, which is the catch. In PETG it is a non-event. In ASA or ABS it is a 200 mm flat slab on a heated bed with corners that would very much like to lift, so run a brim, run a draft shield, and if your printer is open-framed put a box over it. This is the part that punishes choosing the right material and printing it the wrong way.
The six holes come out of a printer undersize, as printed holes always do. They are Ø5.2 mm nominal — clearance for a 10-24 screw and not a millimetre more — so run a drill through each by hand before you are up a ladder holding a light fitting in one hand.
Seal the top and the two sides. Never seal the bottom.
Vinyl siding is not a seal and was never meant to be one. It is a rain screen: water gets behind it on every wall in every storm, runs down the housewrap, and leaves at the bottom of each course. Run a bead of caulk along the bottom edge of this block and you have built a cup in the middle of that drainage path, with a 55 mm hole through your sheathing at the back of it.
Butyl behind the top edge and the two sides, nothing along the bottom, and the hole for the box flashed properly behind the siding rather than caulked in front of it. If that hole is not lapped over by the housewrap and the course above, no amount of sealant on the outside will fix it — it will just take longer to find out.
Installation
-
Measure the wall first. Butt line to butt line, and how far a butt stands off the panel above it. You want 5 in and 1/2 in. If you get 4 in, or 4-1/2, stop and edit the STEP — the print is four hours and the disappointment is permanent.
-
Kill the breaker and prove it dead at the wires you are about to touch, not at the panel.
-
Pick the height so the block straddles a course. Its two ledges are 127 mm apart and each wants a butt line. Mark the centre of the pad; that is where the box goes.
-
Unzip the course above with the siding removal tool, and lift it clear so you can reach the back of the panel you are cutting.
-
Cut the opening and mount the box. Fine blade, slow speed, and cut vinyl cold — a fast blade welds the kerf back together behind itself. Fish the cable, flash the hole behind the siding, and fix the box to the sheathing or a stud through its two lugs. Plug the hubs you are not using.
-
Bed the block. Butyl rope behind the top edge and down both sides, and nothing at all along the bottom.
-
Push it up until both ledges bite. They land under the two butt edges and the block stops. That is the position; there is nothing to measure and nothing to level, because the siding is already level and the ledges are parallel to it.
-
Screw the fixture through the block into the box. Longer machine screws than the ones in the fixture’s bag — the pad is up to 20 mm of extra stack. Snug, then stop. You are clamping a fixture to a steel box through a plastic pad that is resting on a panel which has to be free to move all summer, and the one thing you must not do is pin that panel.
-
Relock the course above, dress the sealant on the top and sides, leave the bottom edge open, and put the power back on.
What will bite you
Your siding is probably not the profile this is cut for. D5 is common and it is not universal, and a block drawn for 5 in exposure sitting on 4 in siding touches in two places and rocks in between. This is the failure that costs a whole print, and the tape measure that prevents it takes thirty seconds.
It is trim, not an enclosure. The printed pad carries no connections, holds no splices and is not listed for anything. The box does that job, and the box is a bought part for the same reason a breaker is. Nothing on this page is an argument for printing an electrical enclosure.
The screws hold the block on, and there are no others. There is no separate mounting hole in this part — the six holes are the fixture’s, and the fixture clamps the pad to the box behind it. Fit the fixture and the block as one assembly. Take the light off later and the block is loose in your hand.
PLA will not survive a summer on that wall. Dark vinyl in direct sun runs past 60 °C, which is PLA’s glass transition, and the block is a load-bearing plate under a fixture the whole time. It sags, the fixture tilts, and the seal opens. PETG is the floor for anything on an outside wall and ASA is the answer.
The bottom edge is supposed to look unfinished. Every instinct says finish the job with a bead of caulk all the way round, and every instinct is wrong. The gap along the bottom is the drain, and a wall that cannot drain rots from the inside where nobody sees it for six years.
Files & downloads
Printable parts
CAD source
The design itself, if you want to change it rather than print it. A STEP file is exact geometry and opens in almost anything; a Fusion 360 archive keeps the modelling history, so you can go back and edit the sketch that made the part.
- siding_block_v3.f3d Fusion 360 archive — the editable design, with its history
- siding_block_v3.step STEP — opens in Fusion 360, FreeCAD, Onshape, SolidWorks