Brush Sanders, Cross-Grain Scratching, and Finish Quality

      Brush sanding equipment is highly useful for some purposes, but it will not do away with hand sanding. February 24, 2008

I was flipping though the latest periodical yesterday, and ran across an article about Supermax brush sanders. Does anyone own one of these? I understand the concept of how these machines work, but for the life of me do not understand how they would not leave small minor cross-grain scratches in the top and bottom rail of a 5-piece raised or flat panel door, or any other products with the grain running side to side. I see how these would be dynamite for the door parts before assembly or crown moulding, chair rail moulding, that have the grain running with the direction of the spinning brush. But I'm sure I would be seeing small scratches across the grain, even with a 180 grit or finer brush. Or are the cross-grain scratches that small that when a stain is applied they don't show up? Or am I overthinking this?

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
I read the same article and am anxious to see some other opinions as well. The article made it sound like no hand sanding at all on doors? Usually things that sound too good to be true...

From contributor G:
Selling point, as all production claims like this are... Almost true. It kind of depends on your QC level. Some hand work is 99% of the time needed before finish. These machines are great for a distressed look.

From contributor Y:
I read the same article. I couldn't help but wonder how much the magazine got paid for the advertisement. My experience with brush head sanders is this. If run aggressively enough to remove even most of the crossgrain scratches, edges and details will suffer too much. I do not believe the claims for a second and can only guess that the shop owner in the article is not nearly as fussy as me on the definition of crossgrain scratches. I have a $50,000 Quickwood rotating brush head sander and can't achieve his claimed results. Or maybe I spent $47,500 too much!

From contributor B:
How good of a job does your Quickwood sander do? I am going to the Vegas show to look at sanding machines and the Quickwood was on the top of my list. Any info from an owner versus a salesman?

From contributor Y:
I actually bought my sander used for much less than new price. For what I paid I am happy. It is best used for denibbing and light whitewood sanding. I personally would not buy it again if I had to pay anywhere near new price.

From the original questioner:
Thanks so much for your responses. It pretty much sums up the gut feeling I had about this product when I first read the article. $47,000 too much... What does "whitewood sanding" refer to? Anyway, thanks again for the info, guess I will continue to look for a better way to polish sand.

From contributor Y:
Whitewood sanding is when you sand any wood, white in color or not, prior to finishing. Sealer sanding is of course sanding the first coat of finish, which is usually a sanding sealer. Contributor B, did you see anything interesting at the show? I was there and noticed there are now several different types of finish sanders.

From contributor B:
The Quickwood Pro 1100 is what I plan on buying. The salespeople were very helpful.

From contributor M:
I've been working with brush sanding for a while with Quickwood and wanted to say that not making cross gain scratches with a linier sander like the Supermax machine is 100% not possible, as you sand cross grain. If you can see it in clear coat, it is something else. For sure you can see it in stain coats.

Also, I have had people claim that brush sanding could remove cross grain scratches and I have not seen that in my 15 years doing demonstrations with the Quickwood machine.

Anyway, the Supermax machine is a good machine for the money, but it might be better at flat stuff than raised panel doors, as a 2 dimensional machine like a sander with 2 spindles across a belt sands only in 2 directions. Your cabinet door is 3 dimensional and 2 directions are not sanded the same as the other 2 directions. That is why most people think that sanding in a circle gets all dimensions of the door.

But its also a question of money and what a machine costs, so to make a 2 dimensional sander sand in 3 dimensions here is what you should try. Send the door through the machine at a 45 degree angle to the spindles one time and turn the door 180 degrees around and send it through again in the other 45 degree angle. If you do this with a 2 dimensional sander it should work.

From contributor A:
"...Send the door through the machine at a 45 degree angle to the spindles one time and turn the door 180 degrees around and send it through again in the other 45 degree angle. If you do this with a 2 dimensional sander it should work..."

You state that "it's not possible" to remove the cross grain scratches with a tool like this, then you say to run the doors through twice at opposite 45 angles and this should take care of it. I guess what I'm hearing is that then you'll have "X" scratches throughout the door or whatever 2 or 3 dimensional project you run. I agree that it would work well with flat or with a single direction of grain like crown moulding. I disagree that it's a question about cost! It's a question about quality.

From contributor M:
I think that I did not explain myself clearly. The machine will never remove cross grain scratches. Sending the door though the machine in a 45 degree angle will only help in sanding the door evenly as the Supermax sander or any other sander with just spindles across a belt will not sand a 3 dimensional door. The rest of the problems with a sander of this type will still be there - I am only trying to make the uniformity better. If you are looking for quality, do not get a sander with a single or double spindle across a belt. It will never give you quality on cabinet doors.

From contributor I:
If you understand the concept behind brush sanders, they are absolutely valuable pieces of equipment. The best machines have a rotating head unit such as the Quickwood or Fladder type machine. It is true that many small scratches will be induced by this type of sanding, but when done properly, these scratches absolutely disappear in the finished product. These machines are invaluable for breaking the edges, de-nibbing the fuzz, and uniform pore opening in the raw wood. This will lead to a more consistent quality piece after piece. They also do a fantastic job of sealer sanding. And of course the secret to sealer sanding without burning through the stain is to sand properly in the raw wood sand process. You have to round the edges enough to get enough mass area for stains and sealers to adhere. Straight line brush sanders with only spinning heads and no rotation are only good for flat panel type products and no good for doors with profiles of any kind.

These machines as a general rule will not take out cross grain scratches due to the fact that they remove very little stock. Cross grain scratches must be addressed in another way such as a random orbital or using hand sand methods only on the rails where the cross grain is located. If you want a superior color balance and top quality consistency door after door, then you should absolutely investigate these sanders. Some of the companies will come on site and do a demonstration for you.

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