Thread: I would kill for flexible electric sander...Argh!

Depending upon the radius of your curved areas, I believe soft backing pads are available
for random orbital sanders, angle grinders, and car polishing machines.

Assuming you are fairing a hull try this;

http://www.atlcomposites.com.au/file...ard_senior.pdf

there is a smaller version to use with a sander polisher

http://www.atlcomposites.com.au/file...ard_junior.pdf

You will still need to follow up with a torture board (good job for apprentices)

If you provide some more information like hull shape, materials and what you are trying to sand I can give more info.

AD

Most professionals use "inline" sanders and home made "surface knockers". An inline sander is usually air powered and much as the name suggests, a strip of paper on a long, rectangular pad, that vibrates along one axis (back and forth).



You can make one of these from an electric sander, if it has an orbital/inline switch. I have a 1/2 sheet sander that I've converted, which simply means I've attached an 18" (457 mm) flexible pad to the foot of the sander and the sand paper is attached to this. The flexible pad can be made of several things, I have a few different types, an 1/8" (3 mm) plywood pad and also a few that I've made from biax cloth, each of different thicknesses, which controls flexibility. The thinnest one is 4 layers of 12 ounce (400 gsm) biax, laid over a piece of plate glass (to keep it flat), then machined to shaped when cured. This one is very flexible and good for places with tight curves.

A surface knocker is also home made and is a polisher/sander tool, with a home made disk. Again I use thin plywood, plexiglass or layers of biax. Each is cut to 1/8" (3 m) shy of the size of a full sheet of sand paper, but the corners are heavily rounded over, to prevent it from digging in. On the back is glued (epoxy) a standard round backing disk, so it can be attached to the tool's arbor. This tool is a rough surface fairing thing. It will very quickly remove high spots, but does require some practice, as it'll remove material very quickly and you can make more work for yourself, in short order. The biax pad shown here is 6 layers of 12 ounce and moderately flexible.






A standard polish/sander with a 7" or 9" disk will do a fairly good job (7" shown), if in skilled hands. It's not as effective as swinging a full 9"x12" sheet of paper, but if used carefully can knock down the highs.

Last on the list and an unavoidable tool is the long board. This is just a flexible piece of material with a couple of handles. Final, fine tuning of the surface usually needs the long board, with a fairly fine grit (100 - 120). You can make a surface really fair, once you learn how to work this tool, but your elbows will get with it quickly.

Smoothing the surface after it's fair, can be done with a number of regular tools, like the DA, random orbit, palm and partial sheet sanders, etc. Fairing and smoothing are different operations. Once the surface is fair, you move onto smoothing it up. Smoothing usually continues through the painting process, as you fine tune the surface with primers and topcoats.

I have a sander that I bought from supercheap auto. They no longer stock them, but somebody else might. It has 3 circular pads that are articulated to sand curved surfaces. Mine is called a Boehler 3d sander

I've used those 3 pad sanders, which look like an electric shaver on steroids. The problem with them is they don't have a large enough surface area, on each disk, so they tend to follow the irregularities of the surface, rather then knock them down. This type of tool is a really fancy finishing piece for quick smoothing, but can't be trusted for fairing. The process of fairing is to identify the highs and lows, so they can be filled or knocked down flush with surrounding areas.

The fairing process is pretty straight forward: first identify the highs and low spots. The easy way to do this is a light pass, with a long board or inline sander, the full length of a panel or hull side, all in the same direction. This places a light, unidirectional scratch on the high spots and bridges the low spots, so both are easily identified. The lows are then filled and the highs knocked down. Another quick pass with the long board or inline sander, reveals what was missed or still needs attention. Again, the lows are filled and the highs brought down some more. Eventually, you'll make a pass with the long board or inline sander, that places a uniform scratch all over the surface. This is when you know it's fair. Then you move onto smoothing and finishing operations.

Hey PAR
your second & third images earlier, from the messing-about forum.
Have to be a member to see them.
Couldn't just attach them here could you?
cheers

Fein 8" random orbit sander using Velcro discs....for large areas to remove allot fast..Rupes 8" disc sander geared head machine also using velcro discs and a 38mm thick soft backing pad. Use the Rupes the get rid of the real highs..then use the inline sander to fair...Then use the 8" Fein random orbit to really smooth...I think when i had to sand hulls...i would take maybe maybe 6 different types of sanders..they all had there place.
Sanding the outside of a hull also has to put into perspective...A work boat it nothing like your show pony...And the time to sand and prepare was proportional to the amount of money there was to spent on the hull. If the boat was to be raced and the hull had to be as good as you possibly get it...then sanding boards were the final stage....long boards maybe 1m long 100mm wide..This was always done by hand....lots of sweat lots of time...finish you can achieve no machine can match.