Lighting the Sanding Table for Quality Control
Ideas for how to supply raking light on the workpiece to make sanding imperfections easily observable. June 28, 2007
Here's a tip for sanding face frames that needs a little more development. I've known about it for sometime but haven't yet been able to implement it. If you take a cone type lamp like a flashlight and aim it 90º straight at a cabinet door or face frame, you get illumination that is not unlike a regular incandescent or fluorescent light bulb.
If, however, you aim the light horizontally across the face of the door, etc, you get a completely different view of the product. Every scratch or imperfection just jumps out at you. (If you have never tried this, break out a flashlight and see for yourself.)
I would like to develop a down draft sanding table that has a bank of lights like this. I have experimented with a small LED light like electricians wear on their hardhat and I've tried automobile lights. Both of these lamps have diffusers built into the lens that also contribute shadow to the beam of light. I am looking for shadow free, directional light. Low profile would also be good.
Carter Products sells a product similar to this but they use a regular flood type bulb. This bulb produces a good light but generates so much heat that it would be uncomfortable to work with for very long. Has anybody done this, or could anybody suggest the right kind of lamp and fixture to use?
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From contributor S:
Try 12 volt lights like car headlights. I think that is what the Carters are.
From contributor J:
My shop is all fluorescent lighting and I am always holding work up at an angle as you described. Could you use a 4' fluorescent bulb at the rear of your table? It wouldn't generate much heat and seems like it would do what you need it to? Just a thought.
From contributor T:
Back when we did a lot of remodeling we would use a 2' florescent fixture with a pigtail and kick it around the baseboard when we finish sanded the drywall. With the light aimed up the wall, it would show up all sorts of spots that needed sanding. Then I got smart and stopped doing drywall altogether.
From contributor E:
I thought about using an 8ft 6 bulb T8 fixture just over and forward of the sanding. The trick is using 6500k bulbs. I recently switched over the fixtures in my booth to 6500k and the room is like a lab. Very bright. I can see every little bit of the spray pattern and surface. Of course it doesn't hurt that there are 12 bulbs overhead, 2 each left and right and 4 in the forward filter wall at 7.5ft. That's 20 4ft in the main working area. There are 10 more to the rear of the room.
One friend thought I'd lost my mind until he used it one day, and walked out with a smile on his face. Enough of the right kind of light is a challenge. My dingy woodworking area waits for a new set of lights. They're not free. Looks like I'm not the only one sick of holding up a flat to see if it's smooth and hope the angle of light is telling me the truth.
From contributor G:
I looked at Carter lights at IWF, laughed at the $300 price, bought a $30 double halogen lamp from a big box store and never looked back. The one I bought is to hang above your workbench. I made a mounting bracket to hold it horizontally and mounted it to the back of the sanding table so it projects very low angle light. It was a pain to clean the sanding table with the light fastened to it so I remounted it to the wall right behind the table. It works great! I put a shelf a couple inches above the light to set sanding supplies on and to keep the light out of our eyes. Again, it works great! Our two tables are 30" deep and 60" long. The lights might not be strong enough to illuminate across a 4' deep table. A third light per table would be nice for longer doors and such but two work. They do put out heat, but in the two years we used them it has not been a problem.
From contributor A:
I actually installed a T8 fixture 5 years ago. It's just above bench height. Works great for seeing 320 grit scratches in finish.
From contributor O:
What you're seeing when you hold a piece up to near-vertical, so the light rakes across the surface at a low angle, are the tiny shadows under every scratch and bump, contrasting sharply with highlights on the adjacent high spots. This effect will be even more pronounced if the light emanates from a small point in space. Fluorescents are very good at generating a lot of light cheaply, but since the light is generated at the inside surface of the glass tube, over a large area, they inherently tend to eliminate the very shadows you find so helpful. If you want to exaggerate the shadow effect, you'll want to use as small a light source as possible, which means incandescent rather than fluorescent, and low-voltage rather than line voltage (low-voltage filaments are smaller). I'd try a little MR16 flood bulb. They do get hot, though.
From contributor R:
Used the Carter lights many years ago on stroke sanders in the factories. As I recall it was a 12 volt headlight and transformer and it didn't generate much heat at all. There was a transformer to convert 120 v into 12 v.
From the original questioner:
Contributor J succinctly explained the phenomena I was observing:
"what you're seeing when you hold a piece up to near-vertical, so the light rakes across the surface at a low angle, are the tiny shadows under every scratch and bump, contrasting sharply with highlights on the adjacent high spots."
I first noticed this with a flashlight. I tried to replicate it with an automotive headlamp and my last effort was with a small LED lamp. All of these light sources have a lens to diffuse the light source. These particular lenses, however, are somewhat robust. They all have some structure designed to help keep everything intact and it is these extra elements that make the light source uneven.
We use MR16's in the showroom and these are available with a 15º to 40º cone of light. As contributor J said, though, they are really hot. I guess now I will follow this up with a bulb specialist to see if they can advise further. It's a nifty concept and if I can get it put together well I will report back.
From contributor U:
I have one of the regular desk lamps that attach with a clamp on the edge of the table. The arm of the lamp goes into a hole in the clamp, and it is adjustable in lots of ways, up and down, front to back. I think I would call it a double cantilever design. Wal-Mart for less than 10 bucks. Works very well.