How do you know when your finished POWER-SANDING?

[should_have]

How do you know when your finished POWER-SANDING?

I hope I don’t get in trouble for paraphrasing from this article.

“How do know when your finished power-sanding? Wipe some mineral spirits on the surface and sight across the wood toward a strong light. Pay no attention to the beautiful color that appears; instead, look at the surface for telltale scratches, especially the ugly orbital kind. You would like to see a uniform appearance with no rough areas or single outstanding scratches. Sometimes it’s easiest to see this right at the moment of evaporation, when the ruts of the scratches will be shinny with fluid while the top surface is dull with dryness. If you take this step, you’ll avoid the agony that many experience when they apply a stain only to see the scratches jump out.”

Two Questions

1. Don’t have any mineral spirits, but to have: Denatured Alcohol, Lacquer Thinner and Turpentine. Plan on using an oil base stain on top of Red Oak Flooring (Bat Top), followed with a water base Polycrylic. Can I substitute any of these for the Denatured Alcohol?

2. First sanding step/phase used 5” 100 Grit Abranet Sanding Disc. Everything I read says do not skip grids while sanding. Abranet comes in 100, 120, 150, 180, 220 etc. One guy at Woodcraft says he goes from 100 strait to 220.

Ok folks, what sequence/step of sanding grids should I migrate up to 220. Can I skip 120 and 180, i.e. 100 – 150 – 220? (Using Bosch 3107DVS 5” Random Orbit Sander)

Thanks in advance for all replies.

Mike

[crokett]

I go from 150 to 220 all the time. May not be the correct way but I've never had a problem. I also don't do the wipe with mineral spirits test per se. I wipe the dust off with mineral spirits. I've found my fingers to be pretty reliable as far as telling me when I am done sanding. I suggest getting mineral spirits - you can wipe dust off with it, it doesn't raise the grain like water does and it evaporates more quickly than turpentine, etc.

[Knottscott]

The only sure fire way I've found to illuminate the smallest sanding marks is to apply stain and finish it! Honestly, it's tough to know for sure when you're, but it seems I always find a few places once the piece is finished and sitting in it's permanent location. One tip is to get some task lighting in your shop and look from various low angles after wiping on some mineral spirits (relatively inexpensive stuff....get some).

I typically go from 50/80 to 100/120 to 150/220, then apply a finish and followup with 300/400 grit by hand, but it depends somewhat on the wood, the finish, and the application.

[SARGE..g-47]

I use distilled water to raise grain in the early stage. It can be purchased cheap at a drug store. The minerals have been evaporated away so that doesn't become a problem after the finish is applied.

And I always use mineral spirits (odorless.. which still has odor but not to the degree of regular) as it will telegraph any swirls or machine marks allowing you to take care of them before the fact. Pay me now or possibly regret it latter.

I hand scrape all hardwood allowing me to start with 180 and then 220. I will start with 120 on softwood as a hand scraper is not as effective on softwood. But... depending on the soft-wood, I might stop at 180 girt as the 220 if overdone can overheat the surface and burnish it. That leads to closed pores and not accepting stain as well or blotching.

If I have any end grain that will show, I cut the stock slightly "proud" and take it off with a pass on a block plane or a pass with an overhead bearing template bit to smooth it. If I use stain I will then seal the end grain with a light coat of shellac. If no stain is used (which is the case with most hard-woods) I use with the exception of oaks as in my mine there is no reason to chose a hard-wood for it's natural beauty and then disquise it. There are other ways to tone it for a deeper, richer finish and not hide the natural beauty .

[Jeffrey Schronce]

Can I skip 120 and 180, i.e. 100 – 150 – 220? (Using Bosch 3107DVS 5” Random Orbit Sander)

Absolutely. 100 - 150 - 220 is fine. Generally you don't want to jump more than 50g at a time. Doing so will result in extra effort to remove the machining marks from the prior grit. Example, going from 100 to 220 will require much more effort to remove any swirl marks using the fine 220 grit. Recent articles indicate going past 180 is generally not needed. Thus 120 to 180 may be the way to go. What grit you start with will of course be dictacted by the material you are working with and how it was surfaced. I have stuff that comes off the planer that only needs a light hit with 220 and I am done. As Sarge notes, there is no need for lower grits if you have hand planed or scraped the surface.

[JimD]

I never check at this point. If you don't have a lot of experience, however, it makes sense to check at least one surface closely so you know about how much sanding it takes to remove the marks from the last grit. With experience, you should be able to tell by feel. Getting the light just right is as important as what you put on the wood - you may be able to see the scratches without wetting if you get a strong light at a low angle.

I cannot think of a reason to not skip from 100 to 150 to 220 other than wasting time and buying more abrasive.

I've also read FWW's test on how much to sand and whether scraped or planned or sanded is best. I pretty much agree but on highly figured wood I think I can tell a difference by going above 220. Maybe I am fooling myself but on the rare events when I work with a piece with a lot of figure, I like to use 320 or even 400 as the final sanding.

A little hand sanding with the grain with the same grit as the last power sanding grit is also not a bad idea. I do not see swirls as long as I sand correctly but I think the wood looks a little more clear without the invisible circular scratches from finish sanders.

Jim