An Elementary Q About Sanding and the Different Grits

[onocoffee]

This is something I've pondered over time and maybe have been reticent to ask since it seems to be a rather elementary question.

I mainly work with rough sawn lumber, surface them with a jointer and thickness planer and then make "fine" furniture (or so I'd like to envision myself). But I've been wondering: what grit roughness are you "supposed" to start? And when should you really use them?

Festool offers in Granat, Granat Net and Rubin 2 grits in P36 and P40 - what situations are these best suited? And if I have the choice between Granat and Rubin/Rubin 2, which is the "better" choice?

Or, if I start with P60 or P80 - what situations are those best suited?

I mostly use hardwoods like walnut, cherry and maple. For jointer, I use a benchtop Cutech 6" with helical cutters that produces a nice smooth finish. The planer is a DeWalt 735 with stock blades and it also produces a nice, smooth finish. With lumber that I've surfaced, I typically start with P80 Granat and move up from there to P120, (sometimes) P150, 180 and if I'm finishing with Sutherland Welles Botanical - I'll go up to P220.

For sanders, I have a choice of ETS 125, DTS 400, ETS EC 150/3, ETS 150/5, RO90 and RO150. My understanding is that the typical approach might be to work the rough material with the RO in Rotex and then move to the 150/3 and then the 2mm sanders for the highest grits.

However, I did see Larry Smith's video "Swirl Free Sanding" where he solely used the RO150 in Rotex mode to work walnut from rough to fine finish. I even tried it myself and was surprised with how nice the results were. I don't know what you may think of it, but I thought it was compelling.

Thanks for your thoughts.

 

[tjbnwi]

The abrasives;

Granat paper can be used on raw wood and finishes, it is excellent on finishes. The Granat Net is for finishes only, you need an interface pad to protect the sanders pad. The Rubin is best for raw wood, it is not good on finishes. My favorite paper was the discontinued Brilliant.

From your description of how the wood is coming off the machines I’d try 150, see how it goes, adjust from there. You don’t want to go to fine, it closes the pores and affects the stain/finish.

I’ve taught everyone in the shop how to sand swirl free with any sander (except one guy who had 20 years experience, he no longer works for me). It’s a master of pace and direction, also watching the paper to see if something buggered it up, you’ll notice oddities on the surface. Also, make sure you wipe the surface to remove any grit before moving to a finer grit.

Tom

 

[rvieceli]

I have switched over to Granat. paper. Great sandpaper and does a good job. I use one sander, an ETS EC 125 with a 150 pad on it.

Setting up a sanding station helps a lot. I use my main assembly table. Throw a moving blanket from Harbor Freight over the top. I set up two led work lights on the back of the table to shine on the workpiece at a low angle to help see imperfections, that really helps.

Personally, I have found that the lowest grits leave rather deep scratches that make for more work as you progress. If you need to remove a lot of material then a carving wheel in an angle grinder works better for me.

Ron

 

[luvmytoolz]

I love Granat Net, I find it lasts far better than normal Granat and have now stopped using the other types of Festool discs, although it does tear somewhat easily doing edges, not as bad as 3M Cubitron does however.

Mirka Abranet Ace in the low grits I find to be the best out of them all, with Granat Net fantastic for the 120g-240g range. 240g and up it's a toss-up between 3M Cubitron, Abranet and Granat Net.

 

[bobtskutter]

I've been recycling some garden timber recently (2x4's with lots of surface lichen).
I use 80grit granat in the Rotex on Rotex mode to remove the surface dirt, then feed it through my thicknesser.
I use 40grit granat if I need to remove a significant amount of material, e.g. if I'm scribing a board to fit around something.
I also have some Saphire 24grit, which has insane ability to remove wood, but doesn't last that long. I used it to reshape the mantle piece above my wood burning stove, and finished the job with 40/80/120/180 granat.

If I'm working with OSB (I like working with OSB), I use 80grit granat to smooth the surface, then flood it with a hard varnish finish. Then resand with 120grit, more varnish, then final finish with 180grit.

Regards
Bob

 

[jeffinsgf]

I agree with Tom and Ron. I think it is a common error to start with too coarse of grits. My planing equipment usually lets me start at 120. I only work backward to coarser grits if I still have milling or joinery artifacts after a thorough sanding with 120. If you need something coarser than 80, it's time to upgrade your planing equipment...unless of course, you're project is sculptural. That's different. I use Cubitron net (II? III? I forget) for 80 and 120, then Granat in 150, 180, 220 and 320. I rarely use 320 on bare wood, but with some species it is beneficial.

 

[onocoffee]

The abrasives;

Granat paper can be used on raw wood and finishes, it is excellent on finishes. The Granat Net is for finishes only, you need an interface pad to protect the sanders pad. The Rubin is best for raw wood, it is not good on finishes. My favorite paper was the discontinued Brilliant.

Thanks Tom - interested to know what makes Brilliant your favorite?

 

[onocoffee]

I agree with Tom and Ron. I think it is a common error to start with too coarse of grits. My planing equipment usually lets me start at 120. I only work backward to coarser grits if I still have milling or joinery artifacts after a thorough sanding with 120. If you need something coarser than 80, it's time to upgrade your planing equipment...unless of course, you're project is sculptural. That's different. I use Cubitron net (II? III? I forget) for 80 and 120, then Granat in 150, 180, 220 and 320. I rarely use 320 on bare wood, but with some species it is beneficial.

Thanks Jeff. With lumber that I've surfaced, I've typically started at 80 - but that's more because I was never taught, I just went with what I thought might be right. Starting at 120 would be a welcome change to the routine.

 

[tjbnwi]

Thanks Tom - interested to know what makes Brilliant your favorite?

Brilliant had a really good cut but was not as sharp as the current available sanding disks.

Tom

 

[smorgasbord]

Also, make sure that, for flat surfaces, you're using the "hard" version of the sanding pad. Wood is not a uniform density/hardness, with some species having noticeably softer earlywood versus its harder latewood, and the medium pad can let the sander sand deeper on the softer parts, leading to undulations.

Mostly, you're starting by sanding out the scallops left by your thickness planer. I sure wish I was re-outfitting my shop with one of those helical cutterheads that leave a better surface than the pounding of rotating straight knives. I've even thought about dedicating my wide jointer/planer combo to jointer duties and getting a lunchbox DeWalt or Oliver with a helical cutterhead. I do have a wide dual-drum sander, and run either 100/150 or 120/180 in it, and that takes care of the scallops, albeit with more time/effort. Then it's on the random orbit or even hand scraping for some projects.

On, and btw, the optimal grit progression is to go 50% higher with each pass. Two examples:

100, 150, 220, 320 (depending on species)
80, 120, 180, 220 (there isn't a 270), 320

On some woods like ebony or cocobolo, I march way up in grits. But then I pretty much always use oil finishes. Surface finishes don't need as fine a sanding.

 

[Cheese]

I agree with Tom and Ron. I think it is a common error to start with too coarse of grits.

I'll 4th that remark.

For wood that's been surfaced on a Dewalt 735 with a Byrd Shelix head, I'll start with 120 or 150 grit. Just try a small area and after sanding, use a raking light to pick out any deeper machining marks. If there are still machining marks then drop down 1 larger grit range and try it again.

I'm a fan of Granat and 3M Cubitron™ II (775L film backing) for bare wood & finishes while I use Granat Net and 3M Cubitron™ II Net (Xtract) for drywall and mud.

 

[Vondawg]

Smorgasbord’s point on the pad is an important one ! I remember having to go back and break out the big belt sander on a 30” deep 40ft Sapele Bar top for being to lazy to change to the hard pad you don’t forget those pucker factor moments lol

 

[Crazyraceguy]

There is a whole lot of nuance needed here. Much of it has to do with the actual material being sanded. The type of abrasive matters quite a bit, but so does grit range.
With decently milled wood, meaning that it is already smooth enough that you are not really removing anything, you just need to refine the surface. With the more common hardwoods, 120 should be a good starting point. This should be enough to take away the slightest mill marks, without making scratches that you need to remove later. The subsequent grits are just about removing the last grit's marks. Hopefully you aren't seeing individual scratches anymore. As the grits get finer, the surface should just get less cloudy looking.
The nuance comes from the goal at this point. It is very possible to sand too fine. This is dependent upon the finish desired, stain, film finish, wax-oil, paint, etc.
This brings up the next variable... sanding the finish. Of course, some don't need that. Sanding between coats and sanding to a full gloss are very different too. Between coats, you need physical scratches, for the next coat to stick.
Once you get to refining beyond that, it's just enough to remove the texture, so it can shine.

Not everything we sand is wood or finish though. Plastics and metal might need some attention. They kind of start the same way, using the finest grit possible, that still removes whatever is on the surface, but usually goes way higher.
The most important detail, in all of this, comes when removing runs, from paint or film-finishes. This is the exact opposite, of all the rest. Never start with a super fine grit and always backup the paper with a block of some kind. Fine grits will just polish to top of the run and inevitably result in sanding through, right next to the high spot. The goal is to knock the top off quickly, with either a coarser grit (or a card scraper) then blend it down, with steps of finer grits.

 

[smorgasbord]

Between coats, you need physical scratches, for the next coat to stick.

Depends on the finish being used. Penetrating oils don’t need this, and lacquer especially actually chemically bonds to previous layers.

 

[Crazyraceguy]

Depends on the finish being used. Penetrating oils don’t need this, and lacquer especially actually chemically bonds to previous layers.

You are correct sir. "Technically" lacquer really only ever has one layer/coat. It all "melts" into one, but it will lay out better, if you at least knock the nibs or texture off first.
Oils? I'm not so sure about that? I'm pretty sure that it is recommended by some manufacturers. Rubio says yes, Osmo say no. I can't see it hurting anything

 

[smorgasbord]

Oils? I'm not so sure about that? I'm pretty sure that it is recommended by some manufacturers. Rubio says yes, Osmo say no. I can't see it hurting anything

Well, Rubio calls their stuff "monocoat," as in one coat. Rubio does say:

The trick to the renovation process is a light abrasion that opens the initially applied Oil Plus 2C finish.

What does "opens" mean? It's all very obtuse. And Rubio is very scary with their claim that Oil Plus 2C is food safe - because that's only if their accelerator is not used.

I think sanding hurts what small build-up protection you get with penetrating oils. I use mostly pure tung oil (takes forever to dry) and Odies. I might use a white or gray woven pad between coats (and indeed, apply Odie's with such a pad), but not sand, and especially not with pure tung oil.

 

[Crazyraceguy]

Well, Rubio calls their stuff "monocoat," as in one coat. Rubio does say:

What does "opens" mean? It's all very obtuse. And Rubio is very scary with their claim that Oil Plus 2C is food safe - because that's only if their accelerator is not used.

I think sanding hurts what small build-up protection you get with penetrating oils. I use mostly pure tung oil (takes forever to dry) and Odies. I might use a white or gray woven pad between coats (and indeed, apply Odie's with such a pad), but not sand, and especially not with pure tung oil.

I'm pretty sure they mean "to break the surface" (open)
Yes, the name does imply a single coat is sufficient, but almost everyone does a second. Besides that, they even make a shine enhancer and a renewal product, for worn areas.
Heck, that's for furniture projects, I can't even image using it on a floor that way. (1 coat)

It may be a language conversion thing? I used to work with a guy whose 1st language is Spanish. When we would separate the sections, of a large reception desk, he would refer to that as "opening" it.

 

[smorgasbord]

Besides that, they even make a shine enhancer and a renewal product, for worn areas.

Do the instructions say to sand before putting those on? Just curious - I don't use Rubio.

 

[Crazyraceguy]

Do the instructions say to sand before putting those on? Just curious - I don't use Rubio.

I don't often either, especially on a floor. For me, it's more of a small table/furniture finish. I used it initially for things that are difficult to spray. They do recommend abrading with a nylon pad, before the renewal stuff. I would doubt it with the shine enhancer, but don't know for sure. I didn't even know it existed, until just recently.
I'm not really a big fan of the stuff. It works fine, but is way too expensive, for what it is. I started making my own wax/oil finish and never looked back. That's how I got into making cutting board butter, it's just a different oil.