Where does your consistency come from?

I’m writing this article to start a conversion in the minds of the readers and the industry in general. I’ve been blessed in my career to have seen literally thousands of sanding processes and nearly the same number of variations on why things are done certain ways. This has taught me humility when I first approach a new customer because you never really know what inspired them to do things that, on the outset, seem rather silly and counterproductive. Often times you really have to ask the right questions so you can understand why they have come to such radical and strange ideas on how best to sand products for consistency. This article will not cover simply hand orbital sanding a raw piece off the planer. If you have not hand sanded something properly sanded through a wide belt or drum sander you really might not understand what I am getting at with this article. Where does your consistency start, at your wide belt or hand sanding table? Answering this question accurately is the beginning of understanding why your sanding doesn’t give you the consistent results you are looking for. Let me start by relaying an experience from a recent customer. This was an extreme situation but it is proof of concept and a vivid illustration of my concept I need to get across. This customer has a DMC two head sander. Drum, combination head. (Combination heads have a drum and a platen in one head) The parts coming to this machine were sanded to 80 grit and they ran 180-220 to finish sand out the scratch and make the parts ready for hand sanding. Already an astute individual can spot a problem. Those two grits cannot remove the 80 grit scratch without abusing the belts dramatically. Very short belt life, heat, and polishing would all be huge issues. They fixed this by sanding everything with 120 grit on an orbital sander. This broke the surface back open for sure. It gave them most of what they wanted in the finishing area. The surface took stain well after this onslaught….but at a price. I set the machine up with 120-150. For most readers this would seem a good choice for getting rid of the 80 grit scratch, but seem a poor one in terms of removing the final scratch with the orbital machine. Most wood workers with wide belts think that the finer the grit on the last belt going to the hand sanding table, the easier the hand sanding. This is where they lose consistency and perspective. The scratch must be three things for success at the hand sanding table. The scratch must be long, shallow, and soft. Shallow does not just come from smaller grains, but also from the type and structure of the head producing it. Longer contact area means longer, more shallow scratches. Soft comes from low sanding pressure and low heat. A soft, long, and shallow 150 grit beats a hard polished 220 grit any day of the week.

The results.

This part is not as simple as it may seem. Properly explaining it is the hardest part. We put some cherry and soft maple panels through the machine and hand sanded them to remove the scratch pattern from the wide belt. We sanded half of each part with 150, as I suggested they finish with, and 120, because that was what they used all along. We sanded just enough off to get rid of the scratch and avoid swirls. I knew what was going to happen before we stained them, but it’s nice to show the customer instead of telling them. Both sides of each panel matched color almost perfectly, within the normal variations for wood color and grain structure. The only difference was that the 120 grit side had way more swirls than the 150 grit. I should have taken the time to sand a panel with 180 grit just to show how close the color would have been, but we didn’t have time. There would have been almost no difference.

How is this possible?

The first head of a wide belt machine has as much to do with the final color as everything that happens after. My parts were broken open by the first head in the wide belt sanding process. That openness survived the properly set second head and the hand orbital sanding process as well. This is part of the reason I only sand enough to remove scratch pattern and not to polish the product. Enough over-sanding to close the product back up is actually hard work. The wide belt set up becomes more critical with the addition of more sanding stations. The more heads the more chances to start heating up the wood and polishing it closed. Often smaller machines fall prey to operators who want to sand much more than a belt can handle to avoid a belt change. They had inconsistency because they hard polished the surface closed and tried to break it back open with their hand orbital sanding. The doors already in the stain room showed the classic signs of the results of too much polish being opened back up by an orbital machine. Light and dark streaks are easy to recognize as inconsistency in the hand sanding process. The dark streaks really are just the mass of scratch pattern that opened the wood up, while the polish from the 180-220 remained on large parts of the product. Consistently open grain is the key to color consistency. This must be established on the first wide belt drum and maintained throughout the rest of the process. If the product is polished from the wide belt, producing consistency and openness with the hand sanding process is a pipe dream.