Belt-sander Linisher

Now don't laugh. I know this looks rather Heath-Robinson, but it does what it was meant to do, it does it well and was easy and quick to make and didn't involve spending very much money. All pluses in my book.

I am making a set of dining chairs. This project has been dragging on for a year now. I originally intended to get them finished for last Christmas and now I'm beginning to wonder if they will be finished by the next one. The back legs are curved, and I made them by bandsawing to a template and then flush-trimming them on the router table. But my router table is very slightly hollow. It wasn't when I made it, but it has since sagged. Not by very much, but enough to have real-world negative consequences – the finished surface is not as clean as I had hoped, due to a very slight instability.

I have various sanders in my workshop, but none are really suitable for sanding the long, slow, concave faces of the back legs, so I decided to make a linisher. It's more of a rig than a jig; a regular belt sander is mounted on its side and an over-long belt runs over a curved block. It's crude, but it works.

My belt sander is a Bosch PBS 75A and it has 2 M6 holes tapped in the side. I assume they are for some sort of accessory, but I can use them to mount the machine.

Bosch PBS75 sander - note the two M6 tapped holes

I started with a nice big baseboard which is held down on the bench with a couple of holdfasts. On it is mounted a spacer to lift the snader up a bit, the curved platen and a work surface.

But lets start with the rear upright support. It has a slot routed in it and is then let into the back edge, making sure that it is square to the base.

Chopping a notch in the back edge of the baseboard

The rear support is glued into the notch, nice and squarely

I cut a piece of plywood to fit around the dust port and air vent of the machine. I drilled for a cylindrical nut, then bolted it to the belt-sander. A Bristol lever through the back slot secured the sander in place.

An L-shaped bracket is bolted to the sander…

I discovered, the hard way, that the edge of the belt very quickly scours a wear groove in the baseboard, so I lifted it up 6mm by putting a piece of MDF between the sander and the baseboard.

At this point the belt sander can be used as a linisher for flat and convex faces, simply by sticking a working platform in front of the belt, held in place with double-sided tape, which then lifts the workpiece up into the path of the belt itself. But the point of this exercise it to enable it to sand internal, concave faces.

It can now be used for flat and convex faces

But the point of this exercise it to enable it to sand internal, concave faces.

So I fabricated a block, three layers, with the centre layer having a gap in it. The gap is about 9mm, good clearance for an M8 stud.

It is then bandsawn to create a variably curved face. Part of it is nearly flat, part more generously curved.

Two embedded nuts are installed in the baseboard so that the curved block can be bolted down. That short slot is going to give us the adjustment we need to tension the belt.

The curved block is mounted on two M8 studs, with embedded nuts underneath

The belt itself is a bit tricky. I used mesh abrasive, but had to have a couple of attempts at gluing it before I got it right. I discovered that the abrasive itself is in two layers, the mesh, and the velcro-type backing. This backing can be removed with cellulose thinners and an old chisel, to leave just the mesh. So I measured the length I needed to go round both the sander and my block, then made a suitable scarf joint, using contact adhesive. The first couple of attempts failed because I was too impatient to let it all cure properly, but after gluing again and clamping overnight, I had a strong bond that was flexible enough to go round the rollers.

It's important to install the belt so that it runs such that the exposed edge of the join trails rather than leads in the direction of travel.

I found that I had to tension the belt just about as tightly as I could to stop it from slipping. There is not as much traction here as with a normal belt. Usually the belt would be in contact with the drive roller for 180 degrees of it rotation, but because this belt comes away from the sander, that traction is reduced to more like 120 degrees – 33% less contact. So it is quite easy to make this stall, I have to treat it gently.

But I have to say that I am delighted with the end result, my concave faces are now lovely and smooth. It was well worth the couple of hours I spent making it.

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