Thread: ROS finish problem

You should be using the belt sander with the grain up to 180 or 240 and then switching to the ros at 240 and going up through the grits. As others have said coarse sanding with an ros is really for removing paint and carving. At the coarse grits 40 60 80 you will see isolated large protruding pieces of grit and if you press hard they will bite deep into the wood and leave a mark which is up to a millimetre below the working surface. That means you have to take off more than a millimetre to eliminate the scratch. And I must add that going past 360 is good for jewellery boxes and turning but for furniture its unnecessary. If the furniture is to be used it will get the odd bump and scratch over the years and a superfine finish can be very unforgiving.

Sheddie, I reckon that today I worked out a good way to trap these annoying little buggers much earlier in the sanding process. But first a little preamble so it gets perspective.

1. In the course of my sanding marathon of 14 kms on the 1 metre timber length (not 900 km as was suggested earlier - that's from here to Brisbane, and it was only to Mt Victoria ) I learnt that Festool Granat 320 grit and above drops a fine white powder on the job when the discs are new. This happens for about the first ten or so strokes. The same thing happened with Klingspor 800 and 1500 PS 33. 320 is the coarsest Granat I have used, so don't know if it happens with coarser grits - this might be relevant later).

2. I have been making panels from Red Cedar which is of course extremely soft (using those Mountain Ash bar clamps you sold me - I like 'em). Because the cedar is so flexible at the 14mm thickness I used that the panels still had some curves to be sanded out, and so I started at 120 grit. This left plenty of swirls in the soft cedar because at that point I was only after getting the panels flattish and smooth without any ledges.

When it came to proper sanding of them I knew I was going to eventually find plenty of swirls but that they would not be seen until the timber started to get glossy at around 800 grit (they will show up a couple of grits earlier with hardwoods).

So, I decided to run over the previous 120 grit finish with 800 grit Klingspor so it would drop the white dust and reveal the swirls - worked a treat, and I was able to spend the required time with 150 grit to get rid of the swirls (if it was harder wood then I'd probably stay at 120 or whatever was required for a while). They were really easy to see and get out with the 150 grit because the swirls had all filled up with a white powder.

O'course the Granat discs will probably not have DE hole patterns to suit your sander, but in this case that's irrelevant because we want the dust left on the job for visibility. Perhaps even turning the extraction off might help when using the fine grit after the coarse.

A caveat - I have only done this with red cedar, starting at 120 grit which is a different ball game to hardwoods starting at 40 grit, so your mileage may vary.

This is certainly a technique that I will employ for suitable situations in future.



And I just had another thought - you could rub talcum powder over the surface to show them up after the coarse grits. Probably easier, quicker and cheaper than changing to a fine paper.