What makes a bar clamp
A bar clamp has a fixed jaw at one end of a bar and a sliding jaw that locks anywhere along it; a screw or lever then applies the force. The bar decides the opening, from a few inches to several feet, and the jaws decide the reach and how the force meets the wood (see the plate above). The clamps guide covers the whole family and how much pressure a glue joint needs.
Four kinds
F-style clamps
The classic steel bar clamp: a cast head at the end of a flat bar, and a sliding arm that grips the bar and carries a screw with a small swivel pad. Pony Jorgensen’s lock with a multiple-disc clutch and are rated at 600 lb, or 1,000 lb in the heavy-duty version with a 3 in reach; its deep-reach models reach 5, 7 or 9 in at 1,200 lb. Its aluminium-bar versions are lighter, at 1,000 lb, with a rectangular bar that gives a stable surface for edge-gluing. The small pad concentrates force, so it needs a block or caul under it, and nothing holds the jaws parallel: under heavy load the arm can flex.
Parallel-jaw clamps
A heavy bar with two large, flat jaw faces built to stay square to it. Bessey rates its K Body REVO at a nominal 1,700 lb with a 3-3/4 in throat, in lengths from 12 to 98 in; Jorgensen’s Cabinet Master is 1,500 lb with a 3-7/8 in throat, from 12 to 72 in, and Jorgensen says its jaws stay parallel to keep corners square and panels from bowing or lifting. The large faces spread the force and the parallel jaws push squarely, which is why they are the cabinetmaker’s clamp for cases and panels. They are also the heaviest and most expensive of the four.
Pipe clamps
Two fixtures — a head with a screw and a sliding foot — fitted to ordinary threaded pipe. Pony’s #50 fixture takes 3/4 in black pipe of any length at least 7 in longer than the work, grips it with a multiple-disc clutch, and presses with a face about 1-3/4 in square; a 1/2 in version is lighter. Because the pipe is bought separately and can be any length, pipe clamps are the cheapest way to get long reach. The round pipe can roll, the faces are small, and Pony states no force for them.
One-handed clamps
Closed by squeezing a trigger or grip lever, so one hand can hold the work while the other sets the clamp. IRWIN rates its SL300 at 300 lb with a 3-1/4 in throat; Pony Jorgensen’s E-Z Hold range runs from 50 to 600 lb by model, and pairs of them join end to end for twice the opening. Most convert to spreaders. They are ideal for holding and dry fits, and for light glue-ups; for a hardwood panel they give less force than a screw clamp.
Compared
| Clamp | Jaw | Stated force | Keeps parallel? | Best for |
|---|---|---|---|---|
| F-style steel bar | Small swivel pad on a screw | 600 lb; 1,000 lb heavy duty (Jorgensen) | No — the arm can flex under load | Edge-gluing, frames, general glue-ups |
| Parallel jaw | Large flat faces square to the bar | 1,700 lb nominal (Bessey); 1,500 lb (Jorgensen) | Yes, by design | Cases, cabinets, panels, square assemblies |
| Pipe clamp | Small faces on fixtures | Not stated (Pony #50) | No | Long glue-ups; many clamps on a budget |
| One-handed bar | Plastic pads on a trigger jaw | 300 lb (IRWIN SL300); 50–600 lb (Jorgensen E-Z Hold) | No | Holding, dry fits, light glue-ups |
Ratings are the makers’ own, in their own terms; what a clamp applies when tightened by hand is usually less.
Gluing up a flat panel
Edge-gluing boards into a panel is the job bar clamps are most often bought for, and the one where their faults show. A bar under the panel pulls on the panel off-centre, and a row of them on one side can bow it toward one face.
Clamping a panel glue-up
Dry-fit first
Arrange the boards, mark their order, and clamp them without glue: every joint should close with light pressure.
Set the clamps out
Open each clamp to size. Lay the first ones on the bench, bars down, spaced evenly along the joint — closer for thin boards — with one near each end.
Glue and lay the boards
Spread glue on one edge of each joint and lay the boards across the clamps in order.
Clamp lightly, then alternate
Snug the bottom clamps, then add clamps over the top between them, so the bars alternate above and below.
Level the joints
Clamp cauls across the ends, or tap boards level, until the faces are flush. Check across the panel with a straightedge.
Tighten evenly
Tighten each clamp a little at a time until every joint shows a thin, even bead of squeeze-out. Stop there.
| Symptom | Likely cause | Fix |
|---|---|---|
| Panel bowed across its width | Every bar on one side | Alternate clamps above and below; use cauls |
| Gaps near the ends | No clamp near the end of the joint | Place a clamp close to each end |
| Boards stepped at the joints | Boards slid as clamps tightened | Clamp cauls across first; tighten gradually |
| Dents at the edges | Small pads on bare wood | Put blocks or cauls under the pads |
| Dry, starved joint | Too much pressure, or glue set before clamping | Tighten only to an even bead; work within the glue’s open time |
| Joint opens after unclamping | Edges did not fit; clamps forced them | Re-joint the edges so they close by hand |
Cases, frames and spreading
- Cases and cabinets. Parallel-jaw clamps push squarely on a carcass and help keep it square; still check the diagonals.
- Frames. Any bar clamp closes a frame’s joints; check it for square before the glue sets. Mitred frames are easier with a band clamp — see the corner clamp guide.
- Spreading. Bessey, Jorgensen and IRWIN clamps reverse to push outward, to ease a dry fit apart or brace a case from inside.
- Limits. A bar clamp’s pressure is at its pads; wide work needs cauls, and very long work may need two clamps joined, as Jorgensen’s E-Z Hold allows.
How many to buy, and which first, is in how to choose woodworking clamps.
Sources
Forces, reaches and constructions are each maker’s own figures for its own clamps; they are stated in different terms and are not directly comparable. The panel glue-up sequence and its faults are established bench practice explained in BenchRoot’s own words.
- 1.
Product Catalog, Spring 2024. Pony Jorgensen.
Used for: Steel bar clamps: cast-iron heads, a multiple-disc clutch holding the sliding head anywhere on the bar, 600 lb (2-1/2 in reach) or 1,000 lb heavy duty (3 in reach); deep-reach versions with 5, 7 and 9 in reach at 1,200 lb; aluminium bar clamps at 1,000 lb with a rectangular bar for a stable edge-gluing surface; E-Z Hold one-handed clamps from 50 to 600 lb that convert to spreaders and join end to end; the #50 pipe clamp fixture for 3/4 in black pipe, with a clamping face about 1-3/4 in square and a pipe at least 7 in longer than the work, and 1/2 in and professional versions; the Cabinet Master parallel clamp.
- 2.
Jorgensen Cabinet Master Medium-Duty 90° Parallel Jaw Bar Clamp. Pony Jorgensen.
Used for: 1,500 lb; a 3-7/8 in throat; 12 to 72 in; large jaws that stay parallel to keep corners square and panels from bowing or lifting; a built-in stand; a reversible head for spreading.
- 3.
K Body REVOlution parallel bar clamps (KRE). BESSEY Tools North America.
Used for: A nominal 1,700 lb; a 3-3/4 in throat; 12 to 98 in; clamping surfaces perpendicular to the rail; spreading without tools; workpiece supports that keep the work off the rail.
- 4.
SL300 One Handed Bar Clamps / Spreaders. IRWIN.
Used for: 300 lb of sustained force; a 3-1/4 in throat; removable pads; conversion to a spreader; an I-beam bar that reduces flexing and bowing.
- 5.
Classic Pony Pipe Clamp Fixture for 3/4-inch Black Pipe (#50). Pony Jorgensen.
Used for: 3/4-14 NPT pipe; a multiple-disc clutch that holds anywhere on the pipe without slipping or crushing it; a 1-3/4 in clamping face; the pipe 7 in longer than the work.
About this guide
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