How do you get sander marks out of wood before staining?
From contributor M:
Don't know if you're referring to hand sanding or large production sanders, but the method is pretty much the same. I usually start with 100/120 grit and work my way through each successive grit (100, 120, 150, 180, 220) up to about 180 grit. Usually when you go above 180 you begin to compromise the ability of the stain to penetrate the wood. Good way to check for sanding marks before staining is to wipe the wood with lacquer thinner or mineral spirits and view with a high angle light source.
So yes, as long as you don't think there is any danger of sanding through, you should be able to start over again with no problems.
Is this on a wide belt Timesaver type machine? What type of material are you sanding? What type of finish are you using? Could probably give you a little better direction with answers to these questions.
When using a 1/3 sheet (or 1/4) vs. an orbital sander, there is an easy way to know that you have removed all the previous grits scratches. It does go against logic and the usual teaching and you have to pay attention to being thorough. You will be alternately sanding with the grain and against the grain of the wood.
Decide what is the final grit you are going to sand to and that grit will be sanded with the grain of the wood. If you want to sand to 220 and you are starting with 120, 150, 180 then your sanding schedule would begin by sanding against the grain with the 120. With the grain with 150, against the grain with 180, and with the grain for your final 220.
This makes it very clear and easy to know when you have removed all of the previous scratches. It is important to change your paper frequently especially on the finer grits, and make sure you do not allow junk to build up on the paper, which can leave deeper scratches.
It should take just about half the amount the sanding time on successive grits (to remove the previous) as it took for the previous coarser grit, but again, keep your paper fresh. One of the toughest points I ever have had to get across in training others is that their labor involved in overuse of a piece of sandpaper far outweighs the cost of the sandpaper, not to mention it simply stops being effective when overused. Try it on a sample first and see if it works for you.