Welding Bimetal Coil Stock into Loops: Why Welds Break and How to Avoid It
Updated: October 20, 2026 · LIZEN Sawing Knowledge
Short answer: Most weld breaks come from one of four steps: welding (not enough flash or a weak upset), annealing (joint left hard, or overheated and re-hardened), grinding (joint ground thinner than the blade or overheated), or alignment (ends not square or stepped). Where and how the loop breaks tells you which step to check. Also check blade tension on the saw.
Loops breaking at the weld? Send photos and your coil spec. LIZEN will review them and reply.
Send weld-break details · WhatsApp +86 131 7575 3620 · sales@lizensaw.com
Where did it break? Quick diagnosis table
This table is based on common guidance from welder manufacturers and blade service shops. Use it as a starting point, not a final verdict.
| Where / how it breaks | Likely step | What to check |
|---|---|---|
| Clean break straight through the weld line, grey grainy face | Welding (not enough flash, weak or early upset) | Trial-weld an offcut; clean ends and jaws; firm upset |
| Break just beside the weld, glassy face, cracks when flexed | Annealing (not annealed, or overheated and re-hardened) | Re-check annealing per your welder’s manual; cool in air |
| Break beside the weld after running on the saw | Annealing or blade over-tension (heat-affected zone) | Check the tension gauge and the hydraulic tension valve |
| Joint thinner than the blade, breaks after some running time | Grinding (too thin or blued) | Grind only to blade thickness; measure the joint |
| Stepped joint, teeth out of pitch, blade runs off the wheels | Alignment | Square ends, back against the stop, replace worn jaws |
| Holes or burnt ends | Welding setting too high or upset too slow | Lower the setting, faster upset (per your manual) |
| Burn marks at the jaws | Dirty jaws or loose clamps | Clean the jaws, clamp firmly |
The four steps of a band saw blade weld
Welder manufacturers describe flash butt welding of band saw blades in four steps:
- Flash and upset: the ends are heated by current and pushed together to fuse.
- Anneal: the hard joint is reheated gently so it can flex on the wheels.
- Grind: the weld bead is removed flush with the blade.
- Inspect: thickness, alignment, tooth pitch and a gentle bend test.
A mistake in any one step can make a good blade strip fail at the joint.
Welding: flash and upset
- Cut both ends square to the blade back.
- Clean the ends. Remove oil, paint and rust.
- Clamp the ends aligned in the jaws, with the back against the stop.
- Use a firm, quick upset.
Standard practice is to use a flash butt welder rated for bimetal at your blade width × thickness. Some older resistance welders may not fuse M42 reliably. The correct setting depends on blade width, thickness and material, so take it from your welder’s manual. Before welding a new coil or size, trial-weld an offcut of the same coil.
Annealing bimetal welds (why it matters more than for carbon blades)
The back of a bimetal blade is alloy steel. After welding, the joint is hard and brittle. If it is not annealed, it will usually crack when it flexes around the wheels. If it is overheated during annealing, it can re-harden and break just beside the weld.
Shared principles from welder manuals:
- Pulse the anneal button; do not hold it down.
- Never heat the joint to bright or cherry red.
- Let the joint cool in air. Never quench it.
- Follow your welder’s manual for the colour cue and the number of anneal passes. Manuals differ.
- Test on scrap first.
Grinding the weld bead
- Grind the joint flush to blade thickness only, on both faces and the back.
- Use light pressure and avoid bluing the steel.
- Never grind the teeth.
Inspection before use:
- Measure the joint against the blade body with a micrometer. It should not be thinner.
- Bend the joint gently in an arc, like the saw wheel. It should bend smoothly, without a kink or angle. If it kinks, cut it out and re-weld.
- Check alignment, tooth match and an even anneal.
- Check that flash is removed on both sides and in the gullet, and that no tooth is damaged.
Alignment and tooth pitch across the joint
Standard practice is a square 90° cut to the back. Keep tooth pitch continuous across the joint. On variable-pitch blades, the joint should follow the pitch sequence. Keep the back against the stop when clamping. Worn jaws cause stepped joints, and a stepped joint can make the blade track badly and stress the weld.
It’s not always the weld: saw-side causes
- Over-tension: a break in the heat-affected zone next to the weld can be caused by too much blade tension.
- Hydraulic tension: a leaking tension valve can raise tension over time. Check it.
- Wheels and guides: small or worn wheels and badly set guides increase bending stress on the joint.
- Break-in: run new loops in gently, as your saw builder advises.
LIZEN also supplies metal band saw machines, circular sawing machines and circular saw blades. If you are unsure whether the saw or the loop is the cause, include the saw model in your report.
Coil stock factors to check (supplier side)
- Degrease the ends. Coil is oiled against rust. Clean the ends before welding.
- Store and handle carefully. Keep coil dry and coiled. Do not force or kink it. See the coil stock receiving checklist.
- Keep specs consistent. Use the same width × thickness × TPI × grade per order. See the coil stock order checklist.
- Record the coil label. Keep the label or batch details for traceability.
- M42 vs M51. The process is the same. Set the welder by width × thickness per its manual, and trial-weld each grade and size, because different grades can behave differently. See M42 bimetal band saw blades and M42 vs M51.
Weld it yourself or buy welded loops?
Welding your own loops from M42/M51 bimetal coil stock gives you flexible lengths and fast turnaround, but you need a suitable welder and a trained operator. If you prefer ready-to-use blades, ask for welded loops. LIZEN MOQ: coil stock 1,000 m; welded loops 300 (mixed sizes) for the first trial order.
Send LIZEN a weld-break report
If loops welded from LIZEN coil break, send:
- Photos of the break face (both sides).
- Where it broke: on the weld, next to the weld, or elsewhere.
- Running time or number of cuts before the break, if known.
- Welder model and saw model.
- Blade spec: width × thickness × TPI × M42/M51 × length.
- Coil label.
- The broken weld section (the piece with the joint), if requested.
LIZEN reviews the details and replies.
Send weld-break details · WhatsApp +86 131 7575 3620
FAQ
Why does my band saw blade keep breaking at the weld?
Usually one of four steps is off: welding (not enough flash or a weak upset), annealing (joint left hard or overheated), grinding (joint ground too thin or blued) or alignment (ends not square). Look at where and how it broke and use the diagnosis table. Also check blade tension on the saw, because over-tension stresses the joint.
Why does a bimetal blade break next to the weld, not on it?
A break just beside the weld is in the heat-affected zone. The usual causes are annealing problems, where the zone was left hard or overheated and re-hardened, or too much blade tension on the saw. Re-check your annealing against the welder’s manual, and check the tension gauge and hydraulic tension valve.
Do I need to anneal a bimetal band saw blade weld?
Yes. A bimetal joint is hard and brittle after welding and needs annealing. Standard practice is to pulse the anneal button, never heat the joint to bright or cherry red, and let it cool in air. Follow your welder’s manual for the colour cue and passes, and test on scrap first.
Can I quench the weld to cool it faster?
No. Welder manufacturers advise letting the joint cool in air. Quenching with water or oil can make the joint hard and brittle again, so it is likely to crack on the saw. Be patient, let it cool naturally, and then grind and inspect it.
How flush should I grind the weld?
Grind the weld bead flush to blade thickness on both faces and the back, and no thinner. Use light pressure and avoid bluing the steel. Never grind the teeth. Measure the joint against the blade body and do a gentle bend test before putting the loop on the saw.
Do M42 and M51 coil weld the same way?
The process is the same: flash and upset, anneal, grind, inspect. Settings follow blade width × thickness per your welder’s manual. Because different grades and sizes can behave differently, trial-weld an offcut of each grade and size before running production loops.
What should I send LIZEN if loops from your coil break?
Send photos of both sides of the break face, where it broke, running time if known, your welder and saw models, the blade spec and the coil label. Keep the broken weld section in case it is requested. LIZEN reviews the details and replies. Contact WhatsApp +86 131 7575 3620 or sales@lizensaw.com.
What is LIZEN’s MOQ for coil stock and welded loops?
For bimetal coil stock, the MOQ is 1,000 m. For welded loops, the MOQ is 300 welded loops (mixed sizes) for the first trial order. Send your width, thickness, TPI, grade and (for loops) length through the RFQ form, WhatsApp +86 131 7575 3620 or sales@lizensaw.com.
Prefer ready-to-use? Ask for welded loops (MOQ 300 loops, mixed sizes) or M42/M51 bimetal coil stock (MOQ 1,000 m).
Request a quote · WhatsApp +86 131 7575 3620 · sales@lizensaw.com