The Ultimate Primer on Single-head Wide Belt Sanding - Steps 4-7
October 13, 2014 | 3:25 pm CDT
Does Your Sanding Make Sense? Inside Wide-Belt Machines

More solid best wide belt sanding practices and processes for the best quality wood sanding results possible.

4. Drums are for cutting and platens are for the finishing pass only.

A properly set up platen will be just barely lower than the drum it follows. I like to set it up by sanding a part with just the drum head. Then I will stop the machine and run the part back under the head without moving anything. I then drop the platen as I either roll the belt on the head or push the belt side to side with the tension roller released. Once you feel drag on the belt you have your platen set.

This relationship means the platen will never be the primary cutting tool, but will only leave the final scratch pattern. Because this relationship takes effort to master, I don’t like to change the adjustment for the platen when I am not using it. I just remove the platen altogether while I am running just the drum. Some machines have the ability to turn the platen off, but it is only on bladder platen machines or machines set up for veneer. In most machines you can just pull it out quickly and easily.

5. Know your stock removal.

If you use an 80 grit to knock down the surface of a cabinet door (my personal favorite starting grit), make sure all the doors go through the same height setting so they are all the same thickness. This is important to the next step. If you refer to the chart above, you need to remove .008” off the tops of the mountain peaks to touch the valley floor below without removing more solid material. If you put in a 100 or 120 grit belt, all you need to remove is .008” and no more. I would choose 120 grit.

Run your first part on the 120 grit and measure the stock removal. Once you took off .008”, run the whole load on the back side. Then drop the machine .008” more and run the whole load on the face. This is very light work for the machine so you can run the feed speed pretty fast. 25 to 30 fpm is usually no problem.

Once your whole load is at 120 grit and the same size, put your platen back in and put the 150 or 180 grit belt in. Don’t move the height of the machine. Run your first part and see how much comes off. If you look at our chart above, you need to remove about .004” to get rid of the 120 grit. Adjust if necessary, and run the load on the back, then drop the machine .004” and run the faces.

Faster feed speed is your friend for keeping the parts and belts cool. This is easy work for a sanding machine. 25 to 30 fpm is no problem.

6. Understanding your scratch pattern

Your parts may look rougher than you are used to, but this where the magic happens with your hand sander. That scratch will be all long scratch, very shallow scratch. The fact that it looks sharp is because the wood has no polish on it at all. That is the softest scratch pattern you will ever try to sand. It melts away under your random orbital sander. I usually follow with either a 150 or 180 grit disk.

Only sand until the scratches are gone. The point at which the scratches are gone and the surface is level is the point at which the sander will start to dig into the now flat surface and try to peel up new wood. This is where orbital marks come from. If you stop sanding at the moment the scratches are gone you will see almost no orbital marks at all.

7. Two pass process

If you only have a small amount of stock removal you might be able to get away with a two pass process, but this is where most operators lie to themselves. If you measure the stile or rail of your product and only sand off .010”, a 120 grit will handle that okay. The problem lies in the joints that may be .010” to .030” thicker than the rest of the door. You can pretend you are only taking off .010”, but you aren’t fooling the sanding belts or the hand sanders who have to fix your damaged, compressed wood.

On planed solid wood it is easy to just remove .005” or .010” of material. This is when it is acceptable to just do a single pass or double pass. You can keep the sander moving quickly so you don’t need to take much time doing it. Use the platen for your final pass for anything where hand sanding is required or going right into stain. Most of the time, when good finish is required, multiple passes are better than one.

I hope this article helps you better understand the capabilities of your single head machine. Using these techniques will yield results that can match any machine out there for quality of result. Patience is required, but this is not meant to be a slow process. You can run stacks of material very quickly using this process. You just need to understand the steps to get through it quickly without fighting the final product. You will soon forget what a burned up belt looks like and your abrasive life will skyrocket.

Have something to say? Share your thoughts with us in the comments below.