Sanding "Heat" Cracks

[Don Stephan]

Occasionally I've seen caution to avoid sanding so much the wood is heated and cracks. Has anyone experienced this, and if so what do these crackis look like? With the grain? Across the grain? Very small hard to find cracks or noticeable ones? Thanks.

 

[Kevin Jenness]

I had some obvious checks open up between the fibers when sanding the base of a partially dry endgrain hollow form aggressively with 80# to remove a tailstock nub. Now I use a carbide burr in a rotary tool and clean up carefully with a sander. I think it's unlikely to happen when sanding at a moderate rate on dry wood with sharp abrasives.

 

[Kent Reisdorph]

I have not seen this, at least not that I can recall. I suspect that most folks use too much pressure when using a drill to sand or a RO sander. More pressure = more heat.

 

[Dave Landers]

They're usually small cracks and often there's a bunch of them together. They're like any other crack you get from drying wood too quickly (cause that's what is happening).
The cracks are not really about sanding too much (that has other issues) but it's about friction and heat - pressing too hard, sanding with old paper (no grit left), lathe (or sander) running too fast, etc.
Friction heats, and thus drys out, the surface of the wood quickly, and the wood reacts. (Even "dry' wood is not truly dry).

 

[robo hippy]

Like Dave said, a bunch of very small and usually very short cracks, and on the end grain. I have seen the same thing from torching the wood to get the color, and especially if the wood is still kind of wet. It is not easy to do on dry wood, you have to spin pretty fast and apply a lot of pressure. I am not sure it can be done with any of the power sanders, you have to do it with hand sanding, and more often the finer grits. If you are hand sanding and have your hand on the wood, you can feel the heat, unless you are using a sanding pad. Never do the sanding pad thing, it lets you know when the wood is getting too hot...

robo hippy

 

[Richard Coers]

The most common issue is with very hard exotic woods. Especially if they were bought with a wax coating. It's really a moisture issue with the wood that causes it.

 

[Scott Hoefs]

A couple months ago I had a small scrap piece of maple (firewood) laying on the ground outside and a friend challenged me to turn it. So... I did. I made a vase. The wood was not green but also not dry. I turned a 3x10" vase. Given it was a challenge I turned it fast, hollowed it fast and sanded it fast. As I was sanding the inside, it got hot and sure enough cracks developed. It happened because the wood had a high moisture content and I sanded it aggressively, causing heat buildup. Nice pencil holder though.

 

[hughie]

It will happen on many of the Aussie hardwoods if you get carried away. Luckily, many of these hardwoods are often very dark CA will take care of it

 

[Jaramiah Severns]

I’ve had this happen with cedar, poplar, and walnut. In every case, the wood was a little on the wet side (~18%MC) and I was power sanding with the lathe going way too fast. Once I slowed the lathe (and the sander) down, this stopped happening.

 

[Don Stephan]

Thanks everyone for the explanations!