Hi

I have recently been trying to make a set of radius sanding blocks (for woodwork), in fact the subject of a recent post I did on casting. I’m stuck in a hotel for the weekend, so I’m busy drawing up the 3-D printing designs for all 16 sanding blocks I need.

I have a question that I think probably only a moron would ask, but I’ve been thinking about it too long and I’m going around in circles (no pun intended).

For example, a particular sanding block needs to precisely sand a 60 degree radius of a 2 inch circle – which happens to make the block exactly an inch wide. But I need to take account of the sandpaper, which is 0.015” thick.

The question is, does the addition of the sandpaper to the block:

1) simply “translate” the 2” radius on the sanding block by 0.015” or

2) create the next 0.015” ring of a concentric circle, meaning that to create a sanding surface of exactly 2” od , I need the sanding block to have radius 2”+0.015”.

it seemed obvious to me that the answer was (2) but the more I think about it I’m not sure!

Pic below hopefully explains. Feel free to tell me I’m a moron.

Steve

Edited By Steve355 on 10/07/2022 01:53:11

Edited By Steve355 on 10/07/2022 02:06:02

True, but the reason is (apart from being late when I wrote it) that these blocks are called radius blocks (used a lot in luthiery), and radius gauges are called radius gauges, not diameter gauges. It only takes a minor slip of the brain to confuse them in a post because of that. That’s my excuse anyway.

It’s 32 planes…

I have already made 11 of them but stopped at the point of profiling the soles for 10 of them, as 3d printing a sanding block massively helped getting the first one to work properly.

You are right that it would be useful to make them oversize. But I want to use them to make other planes, and certainly for the concave blocks, I wouldn’t be able to get into gaps – see pic.

On the casting, it didn’t go well, but I learnt a lot. You are right about the surface finish and shrinkage. If anyone has any practical ways of milling or turning these shapes, I’m all ears. I think in the end I might just use 3d printed blocks. They are accurate and stable enough. I’d love to have them in brass, but unless I stop somewhere with “making the tools to make the tools to make the tools” my wife will never get her greenhouse and my son will never get his sash window, which in the end is what all this is for, in the end.

That’s a very useful way to visualise it, thanks.

That’s really useful Jason, thanks.

I can see that the difficulty with that method is that on a lathe there is no Z axis movement. So a concave surface would either need to be cut in one pass, or the cutter would have to be carefully extended after each pass.

Or (2) the workpiece could be mounted on an angle plate on the cross slide.

Or (3) I could do it on my horizontal mill, although I can’t drill a hole through the 1” arbor, but I might find a way to make it work for some of the larger blocks.

Steve