To really make wide belt machines shine, try these seven best wide belt sanding practices and processes. Then let me know how they work for you.
For this article lets assume your single head sanding machine has a combi-head - a drum/platen combination in the same head, which is the most common machine in this category. For a single drum the rules all still apply.
1. Know what you want to achieve.
For most cabinet and furniture shops, you need to sand parts flat, but you also need them to accept stain. This means you need to fracture and tear open the wood with your rougher belts and sand to a very fine scratch pattern with your finer belts, leaving the parts open to accept stain. If you are doing cross grain you want the sharpest, softest scratch possible, so it will melt away in seconds with your hand sander, instead of taking minutes per door to grind the surface scratches away. You want the least amount of heat and compression of the wood fibers possible.
2. Know your sander is working right.
To check the level of your machine, use two boards a few feet long with a bit of warp. Set them on a table with the warp in the middle of the part, turned up. Using a coarser belt, take a light sanding pass on the boards run through the machine together. Flip them over and take another .010” off , but run them on their respective sides, about 2” off the edge of the conveyor.
Measure only in the center of the boards. If it matches, your machine is accurate. If not, almost every machine has a way to level the head to get the machine absolutely dead on side to side.
3. Multiple passes
It will most likely take more than one pass to level out a part and give you the scratch you desire. But running multiple passes on the same grit is a very bad idea. There is a maximum for each grit when it comes to stock removal. This is well known. What is not well known is that there is a minimum to remove a scratch and that is the really important number. This is not the actual depth of scratch, but the amount that must be removed from the top of the mountain to touch the bottom of the valleys without going further into solid material.
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. To set it up, sand a part with just the drum head. Then stop the machine and run the part back under the head without moving anything. 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.
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.
6. Understanding your scratch pattern
After all these steps, 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. It is the softest scratch pattern you will ever try to sand. It melts away under your random orbital sander.
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.
Read more about Steps 4-7 in wide belt sanding here>
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