Why a leg vice is worth the effort

A leg vice is one of those tools that rewards you twice: once when you buy it for very little, and again every time you use it. Unlike a modern machinist's vice, the load in a leg vice passes straight down the moving leg into the floor, so you can hammer, bend and twist work in the jaws without the whole thing straining off the bench. That makes it the ideal gripping tool for forging, fabrication and anyone who works hot metal.

Most of the ones that turn up at farm sales, autojumbles and house clearances are filthy rather than broken. Give a tired vice an honest assessment, clean it properly, and it will outlast you.

Assessing a vice before you spend a penny

Look at the working parts first, because the screw is the one component that is genuinely difficult to replace.

• The screw. Open the jaws to their full travel and wind them shut again. A little slack is normal; a quarter-turn of lost motion at mid-travel is acceptable. If the jaws wander sideways or jam, the screw or the box nut is worn.
• Jaw faces. Chipped or chewed faces are common and usually harmless. Deep weld repairs are a warning sign — someone has been abusing it, and the hardening may be gone.
• The fixed leg and beam. Check the top of the leg and around the jaw for hairline cracks. A crack in the bow is repairable; a crack running through the mounting plate is more work.
• The spring. A leaf spring at the back keeps the jaws open. Missing or snapped springs are cheap to remake from a strip of spring steel and are not a reason to walk away.
• The mounting plate and wedge. Both are often missing. A plate can be forged or fabricated; the wedge that locks the leg into a floor socket is a five-minute job.

Solid cast or wrought iron vices of four to six inches are the sweet spot for a home workshop — heavy enough to be rigid, small enough to move.

Dismantling and cleaning without doing harm

Take the vice apart on a bench with a sheet of cardboard underneath — the screw, box and spring all come away once the retaining pin or collar is driven out. Do not hammer directly on the pin; use a brass drift or a length of soft steel.

For rust, electrolysis is the kindest method. A plastic tub, a tablespoon of washing soda per gallon of water, a scrap steel anode, and a battery charger on a low setting for six to twenty-four hours will lift rust cleanly out of the threads. Citric acid at around ten per cent, warmed and left for a day or two, works nearly as well if you have no charger. Molasses solution is slower but delightful on heavily scaled pieces.

Once out of the bath, rinse, dry immediately and wipe with oil to stop flash rust forming while you work. Use a hand wire brush or a cup brush in a drill at low speed for the stubborn scale. Never take an angle grinder to the screw or the jaw faces — you will round over the thread crests and destroy the bite that holds your work.

Putting right the usual faults

A slack box nut can often be shimmed or re-pinned. If the thread itself is badly worn, a replacement screw is a machinist's job, so unless the vice is something special, treat a wrecked screw as a source of spare parts.

For chewed jaws, draw-file the faces flat and true rather than building them up with weld. Forty-five minutes with a decent file will restore a surprising amount of grip. If a face is genuinely missing a chunk, a welding shop can rebuild it, but the piece must be preheated and cooled slowly or it will crack alongside the repair.

Worn pivot faces, a bent leg or a tired spring are all straightforward. Straighten a bent leg cold and slowly, with a hide mallet and a wooden block, checking against a straight edge as you go.

Lubrication, finish and the parts to leave bare

Finish the ironwork with boiled linseed oil thinned with white spirit, two or three coats, allowing each to dry. It gives a warm, dark surface that resists rust and never looks like a bad paint job.

Grease the screw with graphite grease or tallow. Thin oil runs off and collects grinding grit, which then acts as a lap and wears the thread. Keep paint well away from the screw, the jaw faces and the sliding contact between the legs — paint there will flake into your work and gum up the action.

Mounting it so it can take a hammering

The leg must land on something solid. A block bolted under the bench leg, a stump, or a socket set into the floor all work well. A vice hanging with its leg in mid-air will flex, and the bench will eventually split.

Set the top of the jaws around waist height, roughly 90cm from the floor, so you can swing a hammer downwards onto work held in the vice. Bolt it through the bench leg with three coach bolts or lag screws rather than two, and let the body sit slightly proud of the bench edge so long stock can hang past it. Wedge the foot tight, and the vice will feel as solid as a rock.