random orbital sander techniques

[TheUnicorn]

I've just got my first ROS (bit late the game) and have a couple of questions about best practise, seem to have found a lot of contradictory advice online.

Firstly should I be sanding with the grain? I thought that the movement of the sander head meant this was not nessacery, but have seen contradictory advice.

Secondly should I let the head get up to speed before I put it on the wood, or switch on with it in contact. I thought that the slower movements before and after the machine was at full speed were likely to gauge the surface, the advice always seems to be to remove the sander from the wood before switching off, so why is the same not true before switching on. again, have seen advice both ways online.

Thanks in advance

 

[Droogs]

If it is running when you apply the sander there is a large chance that the edge will catch on the wood and you end up with a big divit or score to get rid of

 

[TheUnicorn]

If it is running when you apply the sander there is a large chance that the edge will catch on the wood and you end up with a big divit or score to get rid of

I definately follow that logic, however the manual says to run it up before contact, I'm wondering whether it might be worth getting it up to speed on a thin piece of cardboard then sliding it off to begin sanding?

 

[Sgian Dubh]

I find it's a bit like landing an aeroplane, for want of a better description. As you switch on 'land' the sander gently on the workpiece as if landing a plane. In other words, there's some forward movement of the tool as it picks up speed - it all takes less than a second between triggering and engagement of the sander with the surface being sanded. After that it's a case of making gentle sweeping back and forth movement with the tool. Generally I sweep with the grain first, then across it, and frequently add in some random circular movement. Slainte.

 

[Keith 66]

If you let the machine run up the disc will start to rotate completely & will rev up to motor speed, this will cause a dig in on landing.
Just plonk the thing down & pull the trigger. The trick with random orbital sanders is not to lean on them & press too hard, keep the disc flat to the surface & dont stop moving it. Swirl scratches can happen with grits of 80 & coarser but will sand out easily with 180 or 240 grit, For woodwork i never need to go beyond 240 or 320 grit. If cutting back fibreglass or plastic prior to polishing 400 & 800 discs are good but i dont use them often.

 

[Sideways]

The manuals for the Mirka electronic sanders say to put the tool on the surface first, then start the tool.
Lift off the wood at the end before stopping.

 

[TheUnicorn]

The manuals for the Mirka electronic sanders say to put the tool on the surface first, then start the tool.
Lift off the wood at the end before stopping.

odd that the different manufacturers say different things (mine is makita), I guess the potential pitting / marks from a bad landing would be worse than the scratches from the machine getting up to speed