Replies

1. 
   mvflaim | Dec 06, 2007 06:33am | #1

   You start with a coarse grit like 80 and try to remove any machine marks and rough edges you encountered while building the piece. Then after those marks are removed, you switch to 150 grit to remove the marks left 80 grit sandpaper. Once the 80 grit marks are removed, you switch to 220 grit to remove the marks left by the 150 grit sandpaper. After you sand with 220 grit you're ready for finishing. Remember to always sand with the grain. If you sand against the grain just for the fun of it, you will see the marks left by the sandpaper I speak of. Have fun!

    

   
   

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   Edited 12/5/2007 10:34 pm ET by mvflaim

2. 
   KelsoChris | Dec 06, 2007 06:35am | #2

   Generally I dont sand any higher than 220 if I am not staining and and 150-180 if I am.  As I remember reading somewhere you have to remove all the cross grain scratches with the same grit they were made with, they cannot be removed by a higher grit.  When power sanding I will go one notch higher than I plan on stopping at with the RO then drop back one grit and hand sand.  So my schedule would be this 120-150-180 with the random orbit then hand sand with a block @150.  I would start lower if the need presented itself.

3. 
   saschafer | Dec 06, 2007 07:22am | #3

   Do you drive a car with a manual transmission? Skipping grits is like shifting from 1st to 4th. It works, sorta kinda, but not really well.

   After you've sanded a surface with a given grit, its roughness is approximately the same size as the size of the grit. Imagine a landscape covered with 80-grit boulders. Your goal is to smooth all of that out. You've got several buckets of rocks, gravel and sand. How do you go about your task? If you use just the 320-grit fine sand, you'll eventually get the job done, but you'll end up using a whole lot of it. If you first use some of the larger rocks to fill in the bigger nooks and crannies, then some smaller ones, then some gravel, and finally the sand, then you'll have accomplished the goal much more efficiently.

   Getting back to sandpaper: Each grit only cuts as fast as the size of the grains allows; the finer the grit, the slower the cutting. So, while you can use 320 grit paper to remove the scratches created by 80 grit paper, it will take you forever (and use up a lot of sandpaper).

   -Steve

    

1. 
   Woodman880 | Dec 06, 2007 07:29am | #4

   The responses have been informative, thank you.

4. 
   hammer1 | Dec 06, 2007 07:11pm | #5

   You only need to go through a succession of grits if the milling process has left deep marks. If your machines are sharp, set up well and you have worked with the grain, I would start with the finest grit needed. For me, that's often 220 and where I stop. I'm a fan of Norton's 3X paper, fast cutting and long lasting. I avoid power sanders these days but there was a time when I used them a lot. They just make a lot of extra work, same with using 80 grit when something finer will do. Fine edges and molding details can have their crispness removed by coarse grits. An overworked piece looks it. There's no sense in overworking a piece if it isn't necessary or putting deep scratches in where they don't exist. If you are sculpting in something like a Maloof chair joint, you may want to use files, rasps, power sanders or coarse grits. A flat table top or veneered plywood can easily be ruined with 80 grit. Choose your sanding grit to match the need for the job at hand.

   Beat it to fit / Paint it to match

5. 
   K1500 | Dec 07, 2007 06:39am | #6

   My progression (on work that needs it) is Belt 80, Belt 120, RO 80, RO 120, RO 220.  Others do it differently, and many times the belt sander is not needed.  I would still start at 80 unless the surface or materials do not warrant it.

   One other tip, use sand paper as if someone else is paying for it.  Worn out paper doesn't cut well and can scratch your work.  Worn out 80 is not equivalent to 120, it is just worn out 80.

1. 
   nboucher | Dec 07, 2007 09:16pm | #7

   "use sand paper as if someone else is paying for it."Well said!

2. 
   SteveSchoene | Dec 08, 2007 01:42am | #8

   I would add a step to the progression.  After RO 220, hand sanding 220, with the grain. 

   The need for belt sanding is extremely rare for furniture building.  Much better to do a cleaner job of machining the wood.  For flattening large heavy glue ups where not everything can be aligned perfectly, then the Belt sander has a important place.  Since I often hand plane surfaces, I usually start and end at 220 hand sanding. 

    

6. 
   HowardAcheson | Dec 08, 2007 10:51pm | #9

   Here's some info that may be of interest. Sanding wood--hard or soft--beyond 220 does little more than burnish the wood making staining difficult. This is particularly true if you are using a pigment stain which sits on the surface and relies on "nooks and crannies" to impart color. Softer more porous woods can be sanded to to 220 but harder less absorbent woods may stain best if only sanded to 150.

   A number of years ago a large cabinet/custom furniture shop I was involved with did series of adhesion tests with various finishes and sealers. As part of this test we explored adhesion based on sanding grit. We found about the same adhesion up to 180 - 220. Beyond 220 adhesion dropped off due to burnishing of the underlying wood particularly when non-linear machine sanders were used. This was tested on birch panels. We also found that the resulting smoothness of the first coat of finish was not materially affected by the smoothnes of the underlying wood for sandpaper grits between 150 - 220.. The smoothest surface substrate for final finishes was obtained by sanding lightly after the first coat of finish was applied and dry. Which makes the case for a thinned first coat of finish.

   So our conclusion was that sanding beyond 180-220 was not necessary and could be actually detrimental.

   But, most important was that there was a big appearance affect if the surface was not HAND sanded in the direction of the grain using the highest grit used on the sanding machine. A flat pad sander produced a much flatter surface than a ROS. However, both required final hand sanding with the grain for optimum appearence. If not hand sanded, swirl scratches could show. Final hand sanding using a sanding pad in the direction of the grain is a must.

   To carry it one step further, sanding at 320-400 grit after the first coat and subsequent coats was the optimum. No improved appearence was noticed by between coat sanding beyond 400 for varnish. 400 was the sweet spot for thinner finishes. Between coat sanding was always done by hand whether for flattening or for adhesion.

   I think you will find similar thoughts in the popular finishing books but YMMV.

   Finally, the first coat of ANY finish will raise little shards of wood and cause them to raise whether the surface was sanded, planed or scraped. When the first coat of finish dries these hardened shards are what causes the surface to feel rough. Sanding with 320 paper will remove these hardened shards and subsequent coats will go on smoother. So, smoothness counts after the first coat of finish, but not much before that.

   Howie.........
1. 
   danmart | Dec 08, 2007 11:03pm | #10

   Howard

   I was wondering if the cabinet shop that conducted the tests used hardwood or plywood? Maybe you could add to the information a bit?? I think I have been doing things similar to your summary/findings when I seal with shellac and rub out the first coat. I tend to raise the grain with a damp cloth and sand 220 before the first coat to cut down on the little nubs.

   dan