This is a story of a sanding machine and two different ways of getting the job done. Both methods sound very similar at the outset, but the effect on the wood is not.
Long ago, I visited a customer in Rochester, NY. I was working for a former employer on brushes for a Quick wood brush sanding machine and was addressing some of the customers concerns about sanding.
The first thing I noticed about the product was the very hard polish on the doors. The hand sanders were having a hard time with random orbital sanders to remove it all. I am way too nosey to leave it alone, so I asked to see the sander.
They have a newer Timesaver 3 head, with a drum, drum, and combi-head. The grit sequence is 120-180-220. The required stock removal is .015” total, but this did not include imperfections in the joints on the doors and frames.
I talked to the owner about the polished condition of the doors and he knew it was causing some issues, but his main concern was reducing the amount of time it takes to remove the scratches from the doors with the orbital sanders.
The idea was to make the scratches as fine as possible to reduce labor. The reality of the situation was that the sequence was making it much harder to remove the scratches.
Let me explain.
When a sanding belt is cutting correctly, the abrasive grains are tearing through the surface under low pressure. They are fracturing the wood and leaving it soft and very open.
The goal of the subsequent belts is to remove that scratch pattern completely, without going further into the solid wood underneath the valleys created by the original belt.
If we take too much material for a belt to handle, the belt will not keep up with the stock removal. The excess material that is not removed fast enough will start to create serious pressure against the resin coat that holds the grains into the belt. This will result in several adverse consequences.
It will compress the wood structure, effectively work hardening the surface with the heat and pressure.
The rubber drums will start to give more under the pressure so the hard and soft parts of the wood will generate surface unevenness and hard and soft areas (and varying openness).
We'll go into detail in the next installment.
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