Abrasive / Vac General settings?

[hamsey]

I keep reading about turning down the suction when you start going up in grits. Is there a general rule of thumb about what suction setting to use with which grit?

If not, what are the signs to watch for when to turn suction up / down?

Also, What about which grit to finish with depending on what type of finish. Reason I ask is I am doing wainscot in the house (extremely slow but learning lots) my final grit before paint was 400/Prime/400 Net/Top coat/ sand if needed/final top coat. This explains the slow part. I finally did a search and read that I should only go to 180 before primer. I have a walnut board that is going to top a half wall that I was planning on going to finish with 2000 platin when I read in another thread about going up to 600 grit so it takes the finish better. I also have a bunch of charcuterie boards to make for family and was going to finish with the platin before oil and wax. Not sure if this is right though.

Thanks for any help. Never thought much about finishing but I much to learn.

 

[Michael Kellough]

You must enjoy sanding  [smile]

The suction should be low enough that you can easily move the sander when it’s off and the suction is on. Easily is too hard for me to define and when the grit is coarse you need to discount the friction the abrasive exerts but for the smoothest results you want the least suction, just end to keep dust from piling between the abrasive and the work. For your comfort you’ll want more suction so you can breath easier. It’s a compromise for you to make.

The smoothest results I’ve ever had are from a Porter Cable random orbit sander that didn’t have dust collection and used psa disks from 3M. I had to wear a mask and do a lot of cleaning and I won’t go back to that.

You should make some test pieces sanded to the range of grits you use and finished the various ways and see for yourself. For opaque coatings you’ll probably find 120 grit is fine enough for heavy coatings but you need to go to 220 for others. For clear coatings 220 might be enough for heavier viscosity products but most will need 320-400. For me only the thinnest coatings, oils and wax benefit from finer grits. I only sand beyond 600 when going for gloss and for wood that has such subtle color and grain that any finish would obscure.

 

[rst]

The finer the grit, the more the vac needs turned down to the point of lowest setting when you get above 400 grit.

 

[Alanbach]

For me the rule of thumb is simple. I want the lowest vac setting possible while still not being able to see any dust. I turn it all the way down, sand a bit, then use my finger to look for dust on the table around my workpiece. If I see dust I turn it up a bit, wipe away the dust and repeat the process until I see no dust. I usually end up in the 25% -35% suction range.

 

[Sparktrician]

I'm with [member=66185]Alanbach[/member] on this one.  For me the determinant is whether the sander is leaving almost microscopic swirls in the wood being sanded.  If the vacuum is too high, it causes the abrasive to drag on the material, causing swirls.  As the inimitable Sedge has said (repeatedly), "Let the tool do the work!"  In my world, that means ~1/4 power suction, and just barely guiding the sander with absolutely minimal downward pressure from my hand on the sander. 

 

[hamsey]

Thanks for all the good info. Along with over-sanding I also had the suction to high. Now what to do with all this high grit abrasives I have  8)

 

[wwb119]

[member=66185]Alanbach[/member],  [member=7493]Sparktrician[/member] -  that's a great rule of thumb, thanks for the guidance. I had the vac set way too high....

 

[CeeJay]

I always have the MIDI on 1/5 for sanding.

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