Custom Weld Fixtures and Welding Jigs, Machined to Print

Welding fixture or welding jig: does the name change anything?

The difference is the cutting tool. A jig guides the tool to a set spot on the part, the way a drill jig guides a drill, while a fixture supports and locates the part; in welding, fixtures hold and align the pieces being joined (source 1). Welding fixtures hold the subcomponents of a welded assembly in place until they are joined into one unit (source 2). Whichever name your print uses, it is quoted the same way. Tooling that guides a drill or a trim cut through the part is a jig in the strict sense, covered on drill and trim jigs.

The fixture locates from the weldment’s own datums, by the usual locating rules: take the reference features from the print, rest the primary surface on three locators, the secondary on two and the last on one, locate from a hole with a pin plus a second locator that stops the part turning, and avoid two locators controlling the same movement (source 3). If the weldment is dimensioned from a mounting face and two holes, the fixture locates from that face and those holes, so the fixture and your inspection read the same part.

How does a weld fixture handle distortion?

Welding heats the joint edges locally. The heated metal expands, and as the weld and the metal next to it cool, their contraction is resisted by the cold metal around them; where that stress passes the yield strength, the metal deforms for good. The results are longitudinal and transverse shrinkage, angular distortion, bowing and dishing, buckling and twisting (source 4).

A fixture answers that in one of two ways. It can restrain the parts, which holds dimensions but leaves more residual stress in the weldment and a greater risk of cracking in crack-sensitive materials (sources 4 and 5). Or the parts can be pre-set: held away from nominal and left free to move, so the distortion pulls the assembly into line. The amount is hard to predict, and it is found with trial welds on a representative piece (source 5).

Either way the allowance comes from your weld procedure, so it goes on the fixture print as a number at each locator it affects. If trial welds have not set it yet, put shimmed or adjustable rests on the fixture print at those points, and they are quoted as features of the fixture.

Where do the clamps go, and how does the weldment come out?

Clamps should push the parts into the locators or supports (source 3), and they have to stay clear of the torch while the joint is welded. The finished weldment is one piece and larger than anything that went in, so the lift-out direction and the open height of every clamp belong on the print. Toggle clamps are bought by part number; name each one on the fixture print and the mounting holes and risers are made to fit it.

A tack fixture only has to hold the parts until the tacks are in. Tack welds are small, temporary welds that hold the parts ready for final welding, and once an assembly is tacked it may not need a fixture for the finished weld (source 6). A weld-out fixture holds through the whole weld and the heat that goes with it. Say which of the two the print is for.

A robot cell asks more of the fixture. Each weld joint typically needs to sit within half the diameter of the welding wire, the robot has to reach every joint without striking the fixture, and the part has to load and unload easily (source 7). Where the print specifies pneumatic clamps, such as toggle clamps enclosed for dirty environments like spot and MIG welding (source 8), name the model on the print and the mounts are machined to fit it. If the fixture mounts to a positioner or table pattern, send the pattern with hole size, spacing and fit class, and the mounting is quoted with the fixture. Integrators building a cell around the fixture will find the rest of what they order on fixtures for automation integrators.

What are the base, locators and pads made of?

Base plate grades are covered as machined parts on the steel page, and steel fixture details covers how base plate, alloy steel and tool steel details go together in one fixture.

Locating pins and rest pads take the wear, because every part is dropped onto them and slid into place. Where the print calls for tool steel there, D2 has good resistance to wear from sliding contact with other metals (source 9). Hardness verification can be arranged and quoted.

Copper goes where the weld must not fuse to the tooling. Copper and ceramic are used as temporary backing: they support the molten root without fusing to it and come off when welding is finished (source 10). Other alloys and plastics quoted on request. Name the grade on the print.

Can custom details go on a modular weld table?

Yes. A modular weld fixture table carries a grid of bores that its bolts, clamps, stops and squares fit. Siegmund’s System 16 uses 16 mm bores on a 50 mm grid, System 22 and System 28 use 22 mm and 28 mm bores on a 100 mm or diagonal grid, and System 28 is the one recommended for multi-ton structures and significant distortion forces (source 11).

The table and its standard squares, stops and clamps come from the table maker. What gets quoted here is the piece the standard kit does not cover: a locator shaped to your part, a nest, a V-block, or an adapter plate with pins sized to the table’s bores. Name the table system and bore size on the print. For a large assembly the machined work is the same: locating details that bolt to a heavy table or to a fabricated frame.

Who orders weld fixtures?

Fabrication and welding shops order them in one of three ways. Some send the complete fixture print. Others build the frame, uprights and gussets from their own plate and send out only the details that need a mill or a grinder: tool steel locating pins and rest buttons, pads machined flat to seat the part, clamp risers, and dowel holes reamed to size so locating dowel pins can be force fitted without anything else holding them (source 12). A set of six pins is as normal an order as a full build.

The third is overflow: your prints are already drawn and your own mill is booked, so the details go out on a purchase order instead of waiting for a slot. Vendor setup in a day: W-9, NDA, net terms available. Machined parts for fabrication and welding shops covers the rest of what a fabricator sends out, from turned details for weldments to machining after welding.

What goes on a custom welding fixture print, and what does the quote cover?

Besides the allowance, clamp and mounting details above, a complete fixture print carries the weldment datums the fixture locates from, each locator’s position and tolerance, the base thickness and the flatness of any datum face, and the grade of every detail. What to send for a custom fixture has the full checklist.

The quote covers the machined base, risers, locators, pads and clamp mounts to the tolerances on the print, the hardware the print lists, and assembly where the print shows an assembled fixture, as one order with one contact. Ground locating pins and pads bring in precision grinding. Anything that cannot be made or inspected as drawn is named in the quote rather than substituted. A welded fixture frame, where the print shows one, is quoted in the same order. Duplicates for a second cell are quoted with the first. What paperwork ships with a fixture is covered on check and inspection fixtures.

Sources

All accessed 27 September 2026. Where a figure here differs from your print, the print governs.

1. Carr Lane Manufacturing, "The Differences Between Jigs and Fixtures": carrlane.com/engineering-resources/technical-information/design-standards-engineering-information/differences-between-jigs-fixtures (a jig guides the cutting tool, a fixture supports and locates the part; fixtures hold and align workpieces in welding).

2. Wikipedia, "Fixture (tool)": en.wikipedia.org/wiki/Fixture_(tool) (welding fixtures hold the subcomponents of a welded assembly in place until joined into one unit).

3. Carr Lane Manufacturing, "Locating & Clamping Principles": carrlane.com/engineering-resources/fixture-design-principles/locating-clamping-principles (reference features from the print, 3-2-1 locating, locating from a hole, no redundant locators, clamping force into the locators or supports).

4. Bill Lucas, with Geert Verhaeghe and Rick Leggatt, "Distortion: Types and Causes", TWI Job Knowledge: twi-global.com (localised heating and contraction, plastic deformation, the six forms of distortion, restraint raising residual stress and cracking risk).

5. TWI, "Distortion: Prevention by Pre-setting, Pre-bending or Use of Restraint", TWI Job Knowledge: twi-global.com (pre-set parts left free to move, the amount found by trial welds, jigs and fixtures holding dimensional accuracy, restraint and cracking).

6. TWI, "What is a Tack Weld? (Definition and Guide)": twi-global.com (tack welds hold parts ready for final welding; a tacked assembly may not need a fixture).

7. Rob Goldiez, "Robotic Welding Fixtures: Design Tips and Best Practices", Hirebotics, 6 April 2022: blog.hirebotics.com/robotic-welding-fixtures (each weld joint typically within half the wire diameter, robot reach to every joint, easy loading and unloading).

8. DESTACO, "Pneumatic Toggle Clamps for Spot & MIG Welding or Assembly, 8021 & 8071 Series": destaco.com/clamping/Pneumatic/Pneumatic-Toggle-Clamp/standard-pneumatic-clamps-8021-8071.html (enclosed design for dirty environments such as spot and MIG welding).

9. Hudson Tool Steel, "D2 Tool Steel": hudsontoolsteel.com/technical-data/steelD2 (good resistance to wear from sliding contact with other metals).

10. TWI, "'Backing' for approval of welding procedures/qualifications": twi-global.com (copper or ceramic temporary backing does not fuse to the root and comes off after welding).

11. Siegmund, "Systems in comparison": siegmund.com/en-us/Product-Information/Product-Information/Systems-in-comparison (16, 22 and 28 mm bores, 50 mm and 100 mm grids, bolts, clamps, stops and squares per system, System 28 for multi-ton structures).

12. Wikipedia, "Reamer": en.wikipedia.org/wiki/Reamer (reamed holes of precise size allow locating dowel pins to be force fitted with no other retention).

13. Wikipedia, "Young's modulus", table of approximate values: en.wikipedia.org/wiki/Young%27s_modulus (A36 steel 200 GPa, aluminium 68 GPa).