These are jigs to use with clamps you already own, not plans for making a clamp. Clamp types, reach and capacity are explained in the clamps guide and the bar clamp guide, which also walks through a whole panel glue-up; this page builds two aids for that job. Case and frame aids are in clamp projects.
| Jig | What it does | Stock | Clamps it needs |
|---|---|---|---|
| Pipe-clamp rails (a pair) | Hold four pipe clamps upright at fixed stations, so boards lie across the pipes at one height | 3/4 in plywood, two pieces 36 × 3 in | Four pipe clamps, such as Pony #50 fixtures on 3/4 in black pipe |
| Cambered cauls (two pairs) | Help hold a panel's ends level while it is clamped | Straight-grained hardwood, four pieces 30 × 1-3/4 × 1 in | Two clamps for each pair, one at each end |
Both are BenchRoot designs, drawn and checked, not built. Neither is a clamp, and neither has a force or load rating.
Project 1: pipe-clamp rails
| Part | Qty | Size (in) | Material |
|---|---|---|---|
| Rail | 2 | 36 × 3, thickness as measured | 3/4 in plywood |
| Notch | 4 per rail | Centres 6, 14, 22, 30 from one end; width = pipe diameter + 1/16; depth = half the pipe diameter | Cut into the rail's top edge |
Measure your pipe, not its nominal size, and measure the plywood: APA notes that panels are labelled by their actual thickness rather than a nominal size alone, so a sheet sold as 3/4 in may not be exactly that. The 8 in spacing is this jig's layout, not a rule for clamp spacing.
The notches sit 6 in from each end and 8 in apart, so the four stations span 24 in of a 36 in rail and the rail is symmetrical end for end. Each notch is half the pipe's diameter deep, so the pipe stands half its diameter above the rail and the boards rest on the pipes rather than on the rails. How wide a panel the jig takes is set by the clamps, not the rails: Pony Jorgensen says its #50 fixture needs a pipe 7 in longer than the work, so 36 in pipes take a panel up to 29 in wide and 48 in pipes one up to 41 in.
Making and using the rails
Rip and cut
Rip two strips of plywood 3 in wide and cut them to 36 in.
Lay out the notches
Clamp the rails together, edges flush, and mark notch centres 6, 14, 22 and 30 in from one end across both, so the notches line up.
Size the notches
Measure the outside diameter of your pipe. Mark each notch that diameter plus 1/16 in wide and half the diameter deep, centred on its mark.
Cut the notches
Saw the sides of each notch and clear the waste; round the bottom to suit the pipe if you like. Ease the rails' edges.
Set up
Lay the rails on a flat bench, parallel and inside the reach of the fixtures, and drop a clamp's pipe into each matching pair of notches. Check that the fixtures clear the bench; if they do not, make taller rails.
Glue up
Lay the boards across the pipes and follow the panel glue-up in the bar clamp guide, with any clamps over the top set between the pipes in the rails.
Project 2: cambered cauls
| Part | Qty | Size (in) | Material |
|---|---|---|---|
| Caul | 4 (two pairs) | 30 × 1-3/4 × 1, crown on one 1 in edge | Straight-grained, dry hardwood |
The crown is a BenchRoot design choice, not a standard: 1/16 in at the centre, 3/64 in at the quarter points (7-1/2 in from each end), 0 at the ends.
A caul is a stiff bar clamped across a panel to help keep its boards level. A straight caul pressed only at its ends can bow and leave the middle of the panel loose; a slight crown means the middle meets the panel first, and the clamps at the ends bring the rest down. The crown here is a circular arc through the ends and a centre 1/16 in high; on a 30 in caul that arc rises 3/64 in at the quarter points, so marking those five points and fairing a curve through them traces it. Each pair goes across the panel near one end, a caul on each face with crowns towards the panel, and a clamp at each end of the pair. With 2 in left for a clamp beyond each edge, a 30 in pair suits panels up to 26 in wide. Cauls help; they do not guarantee a flat panel, which still depends on the joints and the boards.
Making and using the cauls
Cut the blanks
Cut four pieces of straight-grained hardwood to 30 × 1-3/4 × 1 in, with the 1-3/4 in depth standing upright.
Mark the crown
On one 1 in edge, mark the ends at zero, the quarter points 7-1/2 in in from each end at 3/64 in, and the centre at 1/16 in. Bend a thin, straight batten through the marks and draw the curve.
Shape and check
Plane or sand the edge down to the line on each end, leaving the centre highest. Check the pair against each other: their crowns should match.
Protect from glue
Cover each crowned edge with a strip of tape so squeeze-out does not bond the cauls to the panel.
Use
Put a pair across the panel near each end, crowns towards the panel, and close a clamp at each end of each pair until the faces meet. Then tighten the panel clamps as the glue's maker directs.
Clamping pressure and glue
Neither jig changes how hard a joint should be clamped. Titebond asks for pressure enough to bring the joint tightly together and gives assembly times for its own glue, and the Wood Handbook explains that pressure brings the surfaces into close contact, and that uneven pressure on poorly mated surfaces gives thick glue lines. Read your glue maker's instructions; glues and gluing are covered in the wood glue guide and how to use wood glue. Parallel clamps such as Bessey's K Body REVO have their own workpiece supports to keep the work off the rail, and may not need the rails at all.
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 do not stand a loaded panel on the rails in a way that can tip. Release clamps steadily. See woodworking safety equipment and woodworking safety rules.
Before a glue-up on the rails
- Pipe diameter and plywood thickness measured, not taken as nominal
- Pipes at least as much longer than the panel as the fixture maker requires
- Fixtures clear the bench with the pipes in the rails
- Cauls marked, shaped and taped, in matched pairs
- Glue, open time and clamping from the glue maker's instructions
- A dry run done with every clamp and caul in place
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 capacities, reaches and pipe requirements are each maker's for its own clamp. No clamping force, pressure or spacing rule is given; how hard to clamp a glue joint is the adhesive maker's guidance for its own glue.
- 1.
Classic Pony Pipe Clamp Fixture for 3/4-inch Black Pipe (#50). Pony Jorgensen.
Used for: The #50 fixture for 3/4 in black pipe threaded 3/4-14 NPT; a multiple-disc clutch that holds anywhere on the pipe; a 1-3/4 in clamping face; the pipe 7 in longer than the work.
- 2.
Product Catalog, Spring 2024. Pony Jorgensen.
Used for: Pony Jorgensen steel bar clamps with a 2-1/2 to 3 in reach; the #50 pipe clamp fixture for 3/4 in black pipe, with a pipe at least 7 in longer than the work.
- 3.
K Body REVOlution parallel bar clamps (KRE). BESSEY Tools North America.
Used for: Parallel clamps whose own workpiece supports keep the work off the rail.
- 4.
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.
- 5.
Charles R. Frihart and Christopher G. Hunt. Chapter 10: Wood Adhesives: Bond Formation and Performance. USDA Forest Service, Forest Products Laboratory — Wood Handbook, FPL-GTR-282, 2021.
Used for: Pressure applied to bring surfaces into close contact; uneven pressure on poorly mated surfaces giving thick glue lines.
- 6.
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.