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Introduction #
Not every job has a pre-milled plinth block available to match the casing profile on the plans. When that happens, or when the plans call for a custom width or thickness that a supplier does not stock, you build the block yourself from raw stock. This guide covers milling a plinth block on the miter saw and table saw before it goes in. For the install itself, see How to Install a Plinth Block.
A plinth block is a simple shape, a flat rectangular block, but getting the proportions right matters more than the cut itself. The block needs to read as a deliberate, wider element under the casing, not like an oversized scrap. Confirm the width, thickness, and any edge detail against the plans or the customer's direction before you rip a single piece. The This Old House guide to trim covers how a block like this fits into the wider casing and moulding picture.
Before You Begin #
Prerequisites #
- You know the casing width and profile this block needs to sit under, and the finish grade (paint or stain)
- You know the projection the plans or customer want past the casing face on both sides, so you can set your rip width correctly
- Stock has had time to acclimate to the house before you cut it, the same as any other trim material
What You Need To Know #
- Mill in batches. If a job needs plinth blocks at several openings, set your table saw fence once and rip all the blank stock for every block before you move to length cuts. This is the same batching principle you would use cutting baseboard or casing for a whole house
- Rip to width on the table saw, then crosscut to length on the miter saw. Trying to do both operations on one saw wastes setup time and risks an inconsistent width across a batch of blocks
- Keep every crosscut square. A block that is even slightly out of square will telegraph as a visible gap once it is against the jamb
- If the design calls for an eased or chamfered top edge, confirm that detail before you cut. Do not add a profile detail the plans or customer did not ask for
Tools Required #
Power Tools #
Hand Tools #
- Tape measure: for setting width and length
- Combination square: to check every crosscut is square
- Sanding block: to knock down saw marks on the show face and the top edge before install
Supplies #
- 120-grit sandpaper, for a light knock-down on cut edges only, not a full pre-finish sand
Materials #
- Poplar or MDF, for paint-grade blocks
- Oak, maple, or alder, matched to the casing species, for stain-grade blocks
How to Make a Plinth Block Step by Step #
Step 1: Confirm the Dimensions #
Work out the block's finished width from the casing width plus the projection you confirmed with the customer or the plans, and set the thickness to match or slightly exceed the casing's thickness so the block reads as its own element, not a flush continuation of the casing.
Step 2: Rip the Stock to Width #
Set your table saw fence to the confirmed width and rip all the blanks you need for this job in one pass through the material. Ripping every block at once from a single fence setting is what keeps every block on the job the same width.
Step 3: Crosscut to Length #
Set a stop block on the miter saw at the confirmed block height and cut each blank to length. Check the first cut for square with your combination square before you cut the rest of the batch.
Step 4: Ease the Edges, If Called For #
If the design calls for a chamfer or eased edge on the top of the block, cut or rout it now, before the block goes in the wall. If the plans call for a crisp square edge, leave it as cut.
Step 5: Knock Down Saw Marks #
Give the show face and the top edge a light pass with 120-grit sandpaper to knock down any saw marks. This is not a pre-finish sand; leave the surface ready for the finish trade, not finished yourself.
Step 6: Stage the Blocks #
Set the finished blocks aside with the rest of the casing material for the opening they belong to, so they are ready to go when you get to the install step.
Close-Out #
Sweep up sawdust from the saw area; do not shop vac it. Break down any cutoffs and take them to the trash, unless a piece is long enough to save for another small part on the job.
Quality Check #
- Every block in the batch is the same width and thickness
- Every crosscut is square, checked with a combination square
- Edge detail (or lack of one) matches the plans
- Show face and top edge are free of visible saw marks
- Blocks are staged with the matching casing material
Troubleshooting #
Blocks come out slightly different widths #
This means the fence moved between cuts. Stop, re-check the fence setting against a scrap, and re-rip any block that is out of tolerance rather than trying to make up the difference at install.
Stock is bowed or twisted after ripping #
Wide rips can release tension in the board and reveal a bow that was not visible in the original stock. Let the ripped blanks sit for a few minutes before final crosscuts, and set aside any piece that will not lie flat for a straighter one.
Saw leaves burn marks on the cut face #
A dull blade or too slow a feed rate causes burn marks, especially in denser stain-grade species like maple. Slow down evenly through the cut rather than pausing partway, and swap to a fresh blade if burning continues across several pieces.
