Clamping a large project — a cabinet case, a frame, a box — goes better with a few aids that hold parts while the clamps go on. These two are jigs to use with clamps you already own, not plans for making a clamp. Clamp types and how they bear on the work are in the clamps guide; flat-panel aids are in bar clamp projects.
| Jig | What it does | Stock | Clamps it needs |
|---|---|---|---|
| Clamping squares (make four) | Hold two parts at a corner while the clamps go on | 3/4 in plywood, about 10 × 10 in each | Two bar or F-style clamps per square, through its slots |
| Hooked pads (make six) | Hang on an edge so a clamp's small pad bears on a block, not the work | Hardwood, 3 × 1-1/2 × 1-1/2 in each | Any clamp whose pad is smaller than the block |
Both are BenchRoot designs, drawn and checked, not built. Neither is a clamp, and neither has a force or load rating.
Project 1: a clamping square
| Part | Qty | Size (in) | Material |
|---|---|---|---|
| Square | 4 | Right triangle, 10 legs; thickness as measured | 3/4 in plywood |
| Corner relief | 1 per square | 1 × 1, cut from the right-angled corner | — |
| Clamp slots | 2 per square | 1-1/4 × 3, starting 3 from the corner, 1 in from each leg's edge | — |
Measure the plywood rather than trusting the label: APA notes that panels are labelled by their actual thickness rather than a nominal size alone.
With 10 in legs the hypotenuse is 10√2, about 14-1/8 in. Each slot runs from 3 to 6 in along its leg and from 1 to 2-1/4 in in from it, so its far corner is 8-1/4 in from the corner along the two legs together — well inside the triangle, whose hypotenuse lies where that sum reaches 10 — and the two slots do not meet. The 1 in relief keeps the corner of the square out of any glue squeezed from the joint and lets the parts meet without touching the square there. A clamp's jaw goes through a slot, so the clamp must reach from its bar to the middle of the part it holds: Pony Jorgensen gives 2-1/2 to 3 in of reach for its steel bar clamps, and Bessey a 3-3/4 in throat for its K Body REVO. Measure your own clamps against the slots before you rely on them.
Making and using the squares
Lay out
From a corner of the sheet that you have checked square, mark 10 in along both edges and join the marks for the hypotenuse. Check the corner again with a square you trust; how to check one is in how to measure and mark accurately.
Cut the triangle
Cut the hypotenuse. If the corner is not square, true one leg until it is, and recheck.
Cut the relief and slots
Cut the 1 × 1 in relief from the corner. Mark each slot 1-1/4 × 3 in, starting 3 in from the corner and 1 in in from its leg, drill inside the waste and saw it out.
Use
Stand a square in the inside corner of a case or frame with its legs against both parts, and clamp each part to it through a slot with the clamp as its maker directs. Use two or more squares on a case, one at each corner being glued.
Check the assembly
A square holds one corner; it does not make the whole assembly square. Measure the diagonals as the corner clamp guide shows, and adjust before the glue sets.
Project 2: hooked clamp pads
| Part | Qty | Size (in) | Material |
|---|---|---|---|
| Pad blank | 6 | 3 × 1-1/2 × 1-1/2 | Hardwood offcut |
| Rabbet | 1 per pad | 1/2 wide × 1-1/4 deep, along the 3 in length | Leaves a 1/4 in lip and a 1 in body |
Pad sizes are this design's choice. They spread a small clamp pad's bearing over the block; they do not prevent denting on every wood.
The pad starts as a 1-1/2 in square blank 3 in long. A rabbet 1/2 in wide and 1-1/4 in deep along its length leaves a body 1 in thick and a lip 1/4 in thick that reaches 1/2 in beyond the body. Hung on the edge of a case side, the lip holds the pad in place while you set the clamp, and the clamp's small pad presses on the block's flat back instead of on the work. Small steel pads concentrate force and dent wood, as the clamps guide explains; a block spreads that force over a larger area.
Making and using the pads
Cut the blanks
Cut six blanks 3 × 1-1/2 × 1-1/2 in from straight-grained hardwood.
Cut the rabbet
Cut a rabbet 1/2 in wide and 1-1/4 in deep along each blank, leaving a 1/4 in lip. Ease the edges that will touch the work.
Use
Hook a pad's lip over the edge of the part, with the body against its face, and set the clamp's pad on the middle of the block's back. Tighten as the glue's maker directs.
Clamping pressure and glue
Neither jig changes how hard to clamp. Titebond asks for pressure enough to bring a joint tightly together, and gives open and assembly times for its own glue; the time it takes to set squares and pads is part of that assembly time, so rehearse the whole assembly dry first. Glues and gluing are covered in the wood glue guide and how to use wood glue.
Safety— Clamps under load
Use each clamp as its maker directs and within its capacity, keep fingers out from between a closing jaw and the work, and make sure a square or pad is seated before tightening so nothing can slip out. Support a large assembly so it cannot tip while clamped. See woodworking safety equipment and woodworking safety rules.
Before an assembly with squares and pads
- Each square checked with a square you trust
- Slots and clamps tried together; the clamps reach
- Pads hooked and seated before clamps tighten
- A dry run done within the glue's assembly time
- Diagonals measured after clamping
- The assembly supported so it cannot tip
Sources
Both jigs are BenchRoot designs; every dimension is on the drawing or in the tables and is a design choice, not a standard. They were drawn and checked but not built or tested for this page, and there is no download. Clamp reaches and throats are each maker's for its own clamp. The square's corner is only as square as it is cut and checked, and it does not make an assembly square; no clamping force, pressure or spacing rule is given.
- 1.
Product Catalog, Spring 2024. Pony Jorgensen.
Used for: Pony Jorgensen steel bar clamps with a 2-1/2 to 3 in reach, as one maker's figure for how far a bar clamp reaches from its bar.
- 2.
K Body REVOlution parallel bar clamps (KRE). BESSEY Tools North America.
Used for: Parallel clamps with clamping surfaces perpendicular to the rail and a 3-3/4 in throat.
- 3.
Titebond Original Wood Glue. Franklin International (Titebond).
Used for: Clamping pressure enough to bring a joint tightly together, and open and total assembly times stated for its own glue.
- 4.
Panel Thickness Tolerances and Labeling (Technical Topic TT-054). APA — The Engineered Wood Association, 2013.
Used for: Panels labelled by actual thickness rather than nominal alone, so plywood sold as 3/4 in may not be exactly 3/4 in.
About this guide
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.