Does the material affect tab and slot dimensions?

Not in our model. Every figure is a function of material thickness, not alloy, so 0.063 inch aluminum and 0.063 inch stainless get the same tab and slot geometry. Choosing a material on this page just narrows the thickness list to the gauges we actually stock in it.

Should tabs sit flush or proud for welding?

Proud, by 0.005 to 0.010 inches. That leaves positive material to fuse into the joint. A tab drawn flush with zero clearance risks a visible gap at the joint line and gives the weld nothing to consume.

Slot & Tab Size Chart — Recommended Dimensions

Q: How wide should a tab be?

At least twice the material thickness. So 0.126 inches in 16 gauge steel, and 0.250 inches in eighth inch plate. Narrower tabs deform as they are pushed into the slot, and they have very little shear area if the joint is welded. Wider is fine, and often better on a long joint.

Q: How long should a tab be?

At least three times the material thickness, measured as how far it protrudes. That gives enough shear surface for a welded joint and enough engagement for the tab to actually locate the mating part rather than just touch it.

Q: How much clearance does a slot need?

It depends on the fit you want. A press fit uses 0.005 to 0.010 inches of total clearance and holds the parts together on its own. A slide fit uses 0.010 to 0.020 inches and assembles by hand every time. Our default for a self-fixturing weldment is the laser kerf plus 0.004 inches, which works out at 0.012 inches on thin gauges, 0.014 in the middle, and 0.019 on plate.

Q: Is the slot the same size as the tab?

No. The slot is larger than the tab by the clearance, and the clearance is added to both dimensions. A slot for a tab that is 0.126 inches wide in 0.063 inch material is 0.140 by 0.077 inches at our default clearance. Drawing the slot at nominal tab size gives a joint that will not go together.

Q: What is the narrowest slot you can cut?

One and a half times the material thickness, with a floor of 0.020 inches. Narrower than that and the two cut walls trap heat between them, so the web distorts. This limit applies to plain channels rather than tab slots, because a slot for a minimum-width tab is always comfortably above it.

Q: Do I need corner relief in a slot?

Add a radius of at least half the material thickness at internal slot corners. Sharp internal corners concentrate heat during cutting and stress in service, and the laser leaves a small radius there anyway, so modelling one means the part matches the drawing.

// The One Rule

Clearance goes on both dimensions.

A tab is a rectangle of sheet. The slot it goes into is the same rectangle, grown by the clearance in both directions — across the width and across the thickness. Miss the second one and the joint binds on the material itself.

slot width = tab width + clearance · slot height = thickness + clearance

The thickness term is the one people forget. A tab cut from 0.063″ sheet is 0.063″ thick, so its slot has to be 0.077″ tall at our default clearance — not 0.063″. Draw it at nominal and the parts will not assemble no matter how wide the slot is.

The clearance is not the kerf. Kerf compensation already happens automatically — the toolpath is offset by half the beam so your CAD dimensions are what you get. Clearance is what you add on top of that so two correctly-cut parts still fit together. Our default is kerf + 0.004″. See the kerf guide if that distinction is doing work for you.

// Choosing a Clearance

Three fits, and what each one costs you.

Tighter is not better. A press fit that binds is worse than a slide fit that needs one tack weld, because you find out about it during assembly rather than in CAD.

// Per Gauge

Every gauge we stock.

Tab and slot geometry is a function of thickness, not alloy — 0.063″ aluminum and 0.063″ stainless get identical numbers. So the table is one row per gauge, with the alloys that carry it. Slot sizes shown are for a minimum-width (2× t) tab at our default clearance.

// Getting It Right

Five things beyond the two dimensions.

The slot size is the arithmetic. These are the decisions that make the difference between a joint that self-fixtures and one that fights you.

Radius the internal slot corners.

At least half the material thickness. Sharp internal corners concentrate heat while cutting and stress in service, and the beam leaves a small radius there whether you model one or not — so modelling it means the part matches the drawing. The table above gives the figure per gauge.

Draw tabs proud for welding, not flush.

Stand the tab 0.005″–0.010″ past the far face so there is positive material to fuse into the joint. A tab drawn dead flush leaves the weld nothing to consume and risks a visible gap at the joint line. Grind it back after if the face has to be flat.

Keep 2× thickness of wall around the slot.

Between the slot and any other feature or the part edge. Thin webs lose rigidity while they are still hot and pull out of flat, which shows up as a bowed part rather than a bad slot. The table gives the minimum wall per gauge.

Tab length is engagement, not decoration.

3× thickness minimum. Shorter and the tab touches the mating part without locating it, which defeats the point of a self-fixturing joint. On a long seam, use several short tabs rather than one long one — easier to assemble and it distributes the weld.

Watch the slot against deburring.

Slots narrower than 0.125″ can catch the brushes on our Weber 1350, so on thin gauges a minimum-width slot and machine deburring pull against each other. Flag it on the order and brush pressure gets adjusted, or those features bypassed. The table marks which gauges are clear.

// Common Questions

Slots and tabs, answered.

What comes up most on self-fixturing joints.

How wide should a tab be?

At least 2× the material thickness — 0.126″ in 16 gauge, 0.250″ in 1/8″ plate. Narrower tabs deform as they are pushed in, and they have very little shear area if the joint gets welded. Wider is fine and often better on a long joint.

How long should a tab be?

At least 3× the material thickness, measured as how far it protrudes past the mating face. That gives enough shear surface for a weld and enough engagement for the tab to actually locate the part rather than just touch it.

How much clearance does a slot need?

Depends on the fit. Press fit is 0.005″–0.010″ total and holds the parts on its own. Slide fit is 0.010″–0.020″ and assembles by hand every time. Our default for a self-fixturing weldment is kerf + 0.004″ — 0.012″ on thin gauges, 0.014″ through the middle, 0.019″ on plate. That deliberately lands in the slide-fit band: a slot that assembles beats a slot that binds.

Is the slot the same size as the tab?

No, and this is the mistake that costs a re-cut. The slot is bigger by the clearance in both dimensions. A 0.126″-wide tab in 0.063″ material needs a slot 0.140″ × 0.077″ at our default. The height term — thickness plus clearance — is the one people leave at nominal.

Does the material affect the dimensions?

Not in our model — every figure is driven by thickness, not alloy. 0.063″ aluminum and 0.063″ stainless get the same tab and slot geometry. Picking a material on this page only narrows the thickness list to the gauges we actually stock in it.

What is the narrowest slot you can cut?

1.5× thickness, floored at 0.020″. Narrower and the two cut walls trap heat between them, so the web distorts. In practice this limits plain channels rather than tab slots — a slot for a minimum-width tab is always comfortably above the floor, because 2× t plus clearance beats 1.5× t at every gauge we stock.

Do I need corner relief in a slot?

Add a radius of at least half the material thickness at internal slot corners. The beam leaves a small radius there anyway, so modelling one makes the part match the print — and it takes the stress riser out of a corner that will be loaded in service.

Flush or proud tabs for welding?

Proud, by 0.005″–0.010″. That leaves positive material to fuse. Flush tabs with zero clearance risk a visible gap at the joint line and give the weld nothing to consume. See the laser design guide and welding joint types.

Where do these numbers come from?

The kerf bands and the kerf + 0.004″ clearance are the same figures the per-gauge DFM preflight reports on every material page. The 2× tab width, 3× tab length, and the press/slide clearance bands are from the laser cutting design guide. Minimum slot, minimum wall, and corner radius are the preflight's laser design limits. The deburring caveat is from the Weber 1350 guide. Nothing here is estimated.

Slot & TabSize Chart