BIZOMAT MAKEOS · Fabrication
Intermittent Fillet Weld Plan (Continuous Leg, Segment Count and Pitch, Cost Saving)
For a lightly loaded joint, can I use intermittent fillet welds instead of a continuous weld, how many segments at what pitch, and how much does it save?
Plan of a fillet-welded joint along a given length: the throat and leg needed with a continuous weld and its cost (as the fillet weld joint design tool), then intermittent segments of a chosen length at the minimum leg for the plate thickness — the total length needed, the number of segments so that the clear gap between them stays within your limit, the pitch, and the cost of the intermittent weld (as the same tool for the shorter total length), with the saving against the continuous weld.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load on the joint | kN | Load the welds carry along the joint. |
| Joint length available to weld | mm | Length of the joint that can be welded. |
| Allowable throat shear stress | MPa | Allowable shear stress on the weld throat. |
| Minimum leg for the plate thickness | mm | Smallest fillet leg for the plate thickness from your welding code. |
| Thinner plate thickness | mm | Thickness of the thinner plate (the leg should not exceed it). |
| Segment length | mm | Length of each intermittent segment. |
| Largest clear gap between segments | mm | Largest clear gap allowed between segments (from your code; often a multiple of the plate thickness). |
| Cost | ||
| Convexity and overfill allowance | % | Allowance for convexity and overfill. |
| Weld metal density | kg/m³ | Density of the weld metal. |
| Deposition rate | kg/h | Weld metal deposited per hour of arc time. |
| Operating factor (arc-on share) | % | Share of paid time the arc is on. |
| Filler deposition efficiency | % | Share of filler bought that ends up in the weld. |
| Labour and overhead rate | $/h | Labour and overhead per paid hour. |
| Filler price | $/kg | Price of filler. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Load on the joint
- What it is
- The total force the fillet weld must carry along the joint, taken as shear on the weld throat and spread evenly along the welded length.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The throat and leg needed, and the intermittent length needed, rise in proportion to it.
- Get it right
- Enter it in kN, not N: divide a value in newtons by 1000. Use the total joint load, not the load per segment.
What this means: Joint length available to weld
- What it is
- The length of the joint along which weld can be laid, from one end of the joint to the other. A continuous weld uses all of it; intermittent segments start and finish at its ends.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 600 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer joint lowers the throat a continuous weld needs and leaves more room for gaps between segments.
- Get it right
- Deduct any length you cannot reach or must leave unwelded, such as at a cope or notch.
What this means: Allowable throat shear stress
- What it is
- The highest shear stress you allow on the weld throat, from your welding code or design standard for the filler and parent metal.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher allowable lowers the leg and weld length needed.
- Get it right
- Take it from the code that governs the structure; it already includes that code’s safety margin.
What this means: Minimum leg for the plate thickness
- What it is
- The smallest fillet leg your welding code allows for the plate thickness, so the weld puts in enough heat to fuse properly. Intermittent segments are laid at this leg.
- Units and format
- Enter a number in mm: millimetres. The form accepts 1 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger minimum leg shortens the intermittent length needed but raises the weld metal per millimetre.
- Get it right
- Read it from the welding code table for the thicker plate if your code says so; the tool does not look it up.
What this means: Thinner plate thickness
- What it is
- The thickness of the thinner of the two plates joined. The tool checks that the continuous weld leg does not exceed it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the thinner plate, not the thicker one; a leg larger than it cannot be laid properly on the edge.
What this means: Segment length
- What it is
- The length of each intermittent weld segment, measured along the joint. All segments are the same length.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Longer segments mean fewer of them for the same total length needed.
- Get it right
- It must not exceed the joint length; check your code’s minimum segment length too.
What this means: Largest clear gap between segments
- What it is
- The largest clear distance allowed between the end of one segment and the start of the next. The tool adds segments until the gap is within it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller limit can force more segments than strength alone would need.
- Get it right
- Take it from your welding or structural code; it is a clear gap, not the centre-to-centre pitch.
Cost
What this means: Convexity and overfill allowance
- What it is
- The extra weld metal above the ideal triangular fillet, from the convex face and overfill, added to the weld metal mass for costing.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Weld metal mass, arc time and cost rise with it.
- Get it right
- Type the percentage itself, not a fraction; base it on your own measured welds if possible.
What this means: Weld metal density
- What it is
- The density of the deposited weld metal, used to turn the weld volume into mass for the costing.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 20000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Weld mass and cost rise in proportion to it.
- Get it right
- Use the density of the filler alloy, from the filler supplier’s data.
What this means: Deposition rate
- What it is
- The mass of weld metal deposited for each hour the arc is burning, for your process, filler size and settings.
- Units and format
- Enter a number in kg/h: kg/h. The form accepts 0.000001 kg/h to 50 kg/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 kg/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher rate lowers the arc time and labour cost.
- Get it right
- Take it from the filler supplier’s data for your wire size and current, or time your own welds.
What this means: Operating factor (arc-on share)
- What it is
- The share of the welder’s paid time that the arc is actually on, the rest being set-up, cleaning, repositioning and breaks.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 5% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Labour cost is arc time divided by this share, so a lower factor raises it.
- Get it right
- Type the percentage itself; measure it on your own jobs rather than using the arc-on time alone.
What this means: Filler deposition efficiency
- What it is
- The share of filler bought that ends up as weld metal, after spatter, stub ends and slag losses.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 20% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Filler bought is weld mass divided by this share, so a lower efficiency raises filler cost.
- Get it right
- Type the percentage itself; it depends strongly on the process, so use the filler supplier’s figure.
What this means: Labour and overhead rate
- What it is
- The cost of one paid hour of welding, including the welder’s wage, on-costs and the workshop overhead charged per hour.
- Units and format
- Enter a number in $/h: money per hour. The form accepts $0/h to $10000/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $80/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Labour cost rises in proportion to it.
- Get it right
- Ask your finance team for the loaded hourly rate, not just the wage.
What this means: Filler price
- What it is
- The purchase price of the filler wire or electrodes per kilogram.
- Units and format
- Enter a number in $/kg: money per kilogram. The form accepts $0/kg to $1000/kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $4/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Filler cost rises in proportion to it.
- Get it right
- Use your current supplier price, including freight if it is significant.
Method and formulas
- Throat = F ÷ (L τ); leg = throat ÷ 0.707, rounded up to a whole millimetre and not below the minimum; cost from weld metal, arc time, labour and filler (as the fillet weld joint design tool).
- Intermittent length needed at the minimum leg = F ÷ (0.707 a τ); segments = the larger of that length ÷ segment length and the number that keeps the gap within the limit.
- Pitch = (joint length − segment) ÷ (segments − 1); cost as the same tool for the total segment length.
- Example: continuous needs a 5 mm leg; 4 segments of 50 mm at 183.33 mm pitch save 66.667%.
Limitations
- Static load spread evenly along the joint; fatigue loading and sealed joints need continuous welds.
- Segments of equal length; end segments at the joint ends.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Replace a continuous weld on a lightly loaded stiffener
- Set out stitch welds on a frame
- Cut weld cost and distortion on long joints
Who it is for
- Fabrication engineers
- Welding supervisors
- Design engineers
What you get
- Continuous weld leg and cost
- Intermittent segments, pitch and gap
- Cost saving
Interpreting the result
- Intermittent welds pay off when the minimum leg already gives far more strength than the load needs.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1433–1486. Topic reference; no source tables or recommended settings are reproduced.
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