Thread: Corner being rounded over when trying to sand flat

I'm very interested in this, I have the same problem although I cut my boxes with a bench saw

I use a 400x500 sheet of sand paper that is fastened down on a flat bench top

I take a lot of care to sand evenly, rotating the peice in my grip often, and still end up with rounding off the corners

I've come to the conclusion that its happening at the end of the sanding stroke when the weight of my hand and the box gets concentrated to the edge/corner before changing direction

Hodgo

It sounds like technique to me...

Try doing it on a long strip of abrasive (from a roll) stuck down on a benchtop (you don't need an optically flat surface); only go in one direction and start & stop on the paper. Just push the parts in one long continuous stroke.

Personally I would use a small block plane. Rub the two joints together, plane off the burnished high spots and you'll get perfectly mating surfaces.

If the sandpaper is loose, even on flat surfaces, then this effect is being caused by the sandpaper very slightly being rucked up just before the wood hits that bit of paper *than the paper already under the wood, so gluing paper down improves things a bit. However, this may not eliminate the problem especially on small pieces or thin edges where obtaining even pressure is a problem.

I sometimes clamp workpieces in the middle and alongside a longer sacrificial piece of the same timber/metal, and sanded them together.
A curved edge will appear on the leading and training edge of the sacrificial piece but leaving the shorter (workpiece) flatter.
I do this often With Al.

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Maybe you should post this in the Boxmaking forum where the guys are dealing with this exact scenario all the time. Not trying to say that others here won't have the answer.

FG,

I used to have this problem with boxes.

Two suggestions:

1. Buy an A3 sized sheet of double sided adhesive (you can get this at art stores) to ensure your sanding sheet is flat right to the edge. I use a sheet of kitchen top melamine-faced chipboard so I don’t have to remove the paper after use. I also use wide sandpaper from The Sandpaper Man, and keep 120 grit on one side and 240 grit on the other.

2. Use light pressure and don’t hold the box at the corners. Hold mid-way along the sides.


I haven’t had the problem since I adopted this approach.

Happy sanding!

Regards,

Brian

Originally Posted by homey

FG,

I used to have this problem with boxes.

Two suggestions:

1. Buy an A3 sized sheet of double sided adhesive (you can get this at art stores) to ensure your sanding sheet is flat right to the edge. I use a sheet of kitchen top melamine-faced chipboard so I don’t have to remove the paper after use. I also use wide sandpaper from The Sandpaper Man, and keep 120 grit on one side and 240 grit on the other.

2. Use light pressure and don’t hold the box at the corners. Hold mid-way along the sides.


I haven’t had the problem since I adopted this approach.

Happy sanding!

Regards,

Brian

I bought some 450x300mm double sided sanding sheets mounted on very stiff cardboard from bunnings

they have them in stock for their floor sanding machines which they hire out

just a matter of clamping them down on a very flat surface, they seem to last a while too

There are some good replies above and there is also some related discussion in this thread from the boxmaking forum that may be helpful:

Sanding boards

Thanks all for the tips and links! Very helpful to know that it is a common occurrence.
Seems a larger flat surface and proper technique is what I need to work on. Don't have the depth available to keep trying to fix this box, but will try a bit differently on the next one!

I believe no matter how careful you are you will still get roll when trying to slide a box on a surface that wants to resist you, but in saying that i do get good results with small boxes 90 x 70 that i make for rings, rubbing in a circular motion and rotating the box every few strokes.

My technique on larger boxes is to cut the lid on the table saw, my 3TPI bandsaw blade is to messy for this, then tidy up and mate the surfaces precisely with a block or thumb plane and then sand with 400 - 600g paper paying attention not to roll the thumb over the edge at the corners. This normally gives a perfect result.

An easy way to hide that little roll on your corner would be to do a little 1mm chamfer on both edges.