Quick answer: The splice is where a sanding belt is joined into a loop, and the joint you choose decides whether the belt can run in either direction and whether it will leave a mark on the work. The butt splice is the standard – bi-directional, works for almost everything. A lap (overlap) splice is directional and must be run with the arrow. Sine-lock (wave) splices run extra smooth on wide belts and glass. Top-skive and tape-on-top joints are for wide belt sanders where a standard joint is leaving a mark on the wood.
The five sanding belt joints
| Joint | Bi-directional? | Best for |
|---|---|---|
| Butt splice | Yes | Almost everything – the standard joint |
| Lap (overlap) splice | No – run with the arrow | Thin backings, some metal and older machines |
| Sine-lock (wave) splice | Yes | Wide belts, glass fabrication, Hetran-type machines |
| Top skive | Yes | X-weight cloth wide belts leaving a joint mark on wood |
| Tape on top | Yes | Wide belts in furniture and woodworking where a mark-free joint is needed |
1. Butt splice
By far the most common joint and, in most cases, the best. The two ends of the belt are cut at an angle – normally 67 degrees – and butted together, then joined with a strong tape on the back. Because nothing overlaps, the belt runs in either direction: it doesn't matter which way you slide it onto the machine. The only limitation is that a butt splice isn't a zero-tolerance joint, and on a small number of wide belt applications the joint can transfer a faint mark – which the top-skive and tape-on-top variations below solve.
2. Lap (overlap) splice
Here one end of the belt is skived thin and glued over the other end. Most abrasive materials are printed with an arrow on the back, and that arrow exists for the lap splice: the belt must run so the overlap trails, or the leading edge of the joint catches on the work and peels open. Lap splices are common on lighter backings and on some metal-working belts, but a butt splice is a better choice for almost everyone. Our lap vs. butt splice guide compares them side by side.
3. Sine-lock (wave) splice
A butt joint cut in a wave or zig-zag pattern instead of a straight diagonal. The wave spreads the joint across the width of the belt so it passes over the contact point gradually, and the belt runs smoothly without hinging in either direction. Very common on everything from narrow belts to wide belts, and on Hetran-type machines; it's the joint of choice in glass fabrication and many woodworking shops.
4. Top skive
On a top-skive belt, the abrasive grain along the joint is shaved off on our scuffing machine so the joint sits below the surface of the grain. It's used specifically on X-weight cloth belts where the joint is leaving a scuff on the workpiece – most often in wood and furniture manufacturing on wide belt sanders.
5. Tape on top
Exactly what it sounds like: the joint tape is applied on the abrasive side of the belt instead of the back, giving a scuff-free joint as the belt runs across the work. Another special-made joint for woodworking wide belts.
Why a joint can mark the work
On a wide belt sander the contact drum sandwiches the belt between itself and the wood. Where the belt passes through the contact point – roughly 1/8" on most machines – anything that's thicker than the rest of the belt is pressed harder into the surface, and the grain at the joint digs in a little deeper. If the splice is a different thickness from the rest of the belt, it leaves a mark once per revolution. The fix is a top-skive or tape-on-top belt. It's not a common problem – the standard butt splice is good enough for the large majority of operations.
Is the splice causing my chatter marks?
Here's the quickest test. Take a lumber crayon or pencil and draw a line across the abrasive at the splice. Lightly sand a piece of scrap and look at where the crayon rubbed off. If the distance between crayon marks matches the spacing of the chatter marks you're seeing, the splice is to blame. If it doesn't, the problem is elsewhere – see our chatter guide and wide belt sander troubleshooting.
Which joint should you order?
- Not sure? Butt splice. It's our standard and it's right for almost everything.
- Wide belts for wood or glass: sine-lock for the smoothest running.
- Wide belt leaving a mark on furniture parts: top skive or tape on top.
- Your machine manual specifies directional belts: lap splice, run with the arrow.
Every belt we make is spliced in-house in Anaheim, California, and we can put any of these joints on any size. Order custom sanding belts or shop wide belts and sanding belts.
