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sanding concave areas


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We are currently preparing our deck for a refit. Sanding flat and convex areas has been a breeze so far with a sander and expensive sandpaper. However, the intersections of the coachroof with the sidedeck and the cockpitwalls with the cockpit floor are relatively large concave areas we cannot really use our sander for.

Can anyone recommend a good method or tool for this? Preferably not too expensive since we will likely only use it once. Or simple lots of elbow grease?

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We make custom sanding blocks from Divinycell (but any foam or even wood would do) and wrap with sticky-back sand paper. Radiuses can also be sanded with appropriate sized sanding drums on a drill.

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Old radiator hose or heater hose - just find some the proper diameter and wrap your paper around it.

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31 minutes ago, neuronz said:

We are currently preparing our deck for a refit. Sanding flat and convex areas has been a breeze so far with a sander and expensive sandpaper. However, the intersections of the coachroof with the sidedeck and the cockpitwalls with the cockpit floor are relatively large concave areas we cannot really use our sander for.

Can anyone recommend a good method or tool for this? Preferably not too expensive since we will likely only use it once. Or simple lots of elbow grease?

A good friend who used to run a Ferrari specialist panel beater / paint shop and now builds boats and teaches at a boat building school for home builders has a policy that unless you sand things for a living and therefor do it all day every day you should never use a power tool while sanding a curved surface (convex or concave). 

Any "former" you use will be close but not right.  Follow Will's advice and use a hard foam or soft wood block (so it can give a bit) and then some good old fashioned hard work.

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5 hours ago, Will1073 said:

We make custom sanding blocks from Divinycell (but any foam or even wood would do) and wrap with sticky-back sand paper. Radiuses can also be sanded with appropriate sized sanding drums on a drill.

+1

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One way to make shaped sanding blocks:
Put a sheet of coarse paper on the surface you want to sand, GRIT UP.
Use it to shape a styrofoam block.
Glue the paper to the foam.

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Much good advice above. I have found a dry sponge to be a useful, conforming sanding block in some situation. Usually works best for light sanding. If you need to form a shape surface etc.  some of the other suggestions above will work better.

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Might try a grill block. They work best on the hull but never tried on in your situation. they wear down real quick and it might conform to your radius.

 

https://www.amazon.com/Avant-Grub-Sanitizes-Restaurant-Griddles/dp/B071XK6XBB/ref=sr_1_9?crid=3TXB41WTSILDO&dchild=1&keywords=grill+block+cleaner&qid=1609651308&sprefix=grill+block%2Caps%2C245&sr=8-9

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14 hours ago, Diamond Jim said:

One way to make shaped sanding blocks:
Put a sheet of coarse paper on the surface you want to sand, GRIT UP.
Use it to shape a styrofoam block.
Glue the paper to the foam.

This method works very well.

I have also used that method to get pads to match the deck convex curve for mounting deck hardware.  Stick sandpaper to deck and sand underside of pad fore-aft to get close match of the pad to deck.  Then epoxy down or bed as desired.

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14 hours ago, Diamond Jim said:

One way to make shaped sanding blocks:
Put a sheet of coarse paper on the surface you want to sand, GRIT UP.
Use it to shape a styrofoam block.
Glue the paper to the foam.

This is the way. 

Make sure your adhesive is compatible with the foam, some glues will melt foam.  I prefer PSA backed sandpaper.  

Or just use your hand.

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Thx everyone. I will check if the curvature is constant enough for a custom sanding block. Otherwise we do have small sanding sponges already. Maybe there is something available one or two sizes bigger.

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3 hours ago, neuronz said:

Thx everyone. I will check if the curvature is constant enough for a custom sanding block. Otherwise we do have small sanding sponges already. Maybe there is something available one or two sizes bigger.

One thing I have found is if the radius is changing a sanding sponge can get you there. Just use your hands and eyes to make it look good. If it is a constant radius you need a form. At least I do.

JJ

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Sanding the easy direction, along the cove, can create long features that will show in a gloss finish. I suggest doing circles, or something random.

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6 hours ago, neuronz said:

Thx everyone. I will check if the curvature is constant enough for a custom sanding block. Otherwise we do have small sanding sponges already. Maybe there is something available one or two sizes bigger.

You’ll probably need a number of blocks, for different contours.  

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