Smooth wood

[Leo Voisine]

Well - somebuddy gots to be first here.

Me Me ME

So - when making wood smooth - WHY - would a scraper - be better than sandpaper?

When would sandpaper be better than a scraper?

[Joe Lyddon]

Hey Leo, what happened to arcticfox? ;D

[TDHofstetter]

A scraper (specifically a card scraper here) is tuned to have a tiny burr on its edge. That burr acts like a tiny plane, shaving wood fibers off the surface. Typically, one scraper with one burr can smooth a particular surface from start to finish.

By comparison, sandpaper abrades the wood - leaving behind ditches & corrugates. If much wood is to be removed, one needs to start with low-grit-count sandpaper, which leaves large scratches, then step up no more than 150% in grit count to repeat the process, obscuring the scratches left behind by the lower-grit paper with smaller scratches, then stepping up again & again to slowly dimish those scratches until they're smaller than the eye can detect.

Sandpaper does have its place, certainly. When a job MUST be done FAST (like for example sanding a hardwood floor, although that example is extreme), sandpaper wins - hands ALL the way down. Or production work - since a scraper's burr must be refreshed periodically and ya can't expect a grunt to learn to do that well, production "smoothers" use sanders. Or when the surface isn't completely flat - scrapers aren't as handy as sandpaper on concave or convex surfaces, even if the radius is large.

Sandpaper also wins the nod for turned objet d'art. I shudder to think about leaving a scraped finish on (or in) a bowl, particularly inside where the grain changes direction four times per revolution... a scraper CANNOT leave as fine a finsh working crossgrain as it can working with the grain, so a scraper always leaves an inconsistent surface inside a bowl.

[Leo Voisine]

Oct 31, 2009 12:00:25 GMT -6 Joe Lyddon said:

Hey Leo, what happened to arcticfox? ;D

I made a post in general stuff

[fredbelknap]

I used a scraper to true up a 10" bowl. I made the blank by gluing some 7/8" cherry boards together. The sides were wavy. I stopped the lathe and used a scraper to true it up by hand. It took a while then I used a 80 grit gouge on it. Did ok. I have some problems using a skew.
Fred

[Gecko]

So I was scraping a box the other day and this question popped into my head. Does a scraper leave to smooth a surface for finishing? I have read not to go over xxx grit or the finish doesn't have anything to adhere to. Thoughts?

[TDHofstetter]

I don't agree with those who say a super-smooth surface won't take finish. I routinely sand turned objects to 2000-grit, and it takes my finishes of choice (shellac, BLO, Danish oil, lacquer, carnauba, etc) just fine, every time. It ought to - wood's inherently porous even when it's sanded supersmooth, and most film finishes will bond just fine to glass long's it's dry.

BUT... there's a catch in there. The sandpaper (I'll get to the scraper in a moment) has to be kept CLEAN and SHARP. If it clogs so you're rubbing fibers against fibers, then that rubbing will BURNISH the wood instead of sanding it, and burnished wood DOESN'T take finish very well - especially stains. The surface fibers have all been rubbed over & squashed out of shape, and there's very little strength in that one-thousandth-thick surface.

BUT... scrapers - as long as they're kept sharp - aren't bad at all about burnishing. A good sharp scraper shears the fibers, leaving an excellent surface for finishing.

BUT... a finish scraper really does need to be kept sharp. Let it get dull - dull enough that it won't easily scrape your thumbnail - and it'll burnish like crazy & your finishes will suffer.

[sachbvn]

I like the last thing Tim just said.... if the paper gets clogged - you are basically just smashing the wood into an almost "glazed over" type state.... so.... it's kind of.....what - sealing itself off from taking finish? Ya know?

I have a scraper - I really need to tinker with it more. The thing heats up - I make more dust than curls... I need to practice. Also - that Veritas jigger that holds the scaper at a certain angle and gives a more substantial "base" to hold on to...that looks pretty good.


Zac

[Stretch]

Many people hold a hand scraped surface to be superior to a sanded surface. I think this holds true when the finish is only an oil finish with no film finish over it. We've done tests, and with the finishes we use, I couldn't tell the difference between a hand scraped surface and a surface sanded to 180 grit on an orbital. Even so, using a scraper can have advantages over sand paper. Burn marks left be a router can be removed with just a few strokes from a scraper, but take forever to sand off even starting with 80 grit. I'm known to make scrapers out of cheap HF chisels especially for this purpose. Take a worthless chisel, and burnish a burr on it and it's a real time saver. You can also grind it to match the profile and not feel bad about it because the whole set of six chisels only costs around $15.

[TDHofstetter]

It sounds like that scraper's burr is either too small or not sharp enough, Zac... although you may not want it MUCH more aggressive than that or it'll be a little prone to gouging.

I've got quite a few card scrapers with different burrs on 'em for different levels of aggressiveness, depending on what I'm doing. You can have two very different burrs on opposite edges of the same scraper, too - that's handy.

Here's a neat li'l shopbuilt scraper holder that does the job for very little outlay of shop time or material:

www.woodworkingtips.com/etips/etip050500sn.html

[sachbvn]

Book marked - thanks Tim!

I don't know what the problem is - it just seems like I have a hard time getting that burnished hook on the scraper.... I'm using a screwdriver to burnish it...and I am pushing hard as hell - first at 90 degrees - then a little less, then a little less.... and at best I can just get the tiniest of hook....

When I get more shop time - the kinda shop time where you can fool around - I will look into making something like that scraper holder.

Zac

[TDHofstetter]

By any chance... is that screwdriver shank showing wear marks from the burnishing? If it is, then it's not hard enough & it may be rolling the burr too far around into a teeny roll, or just wiping steel off the screwdriver shank instead of pushing the scraper's steel around.

A smooth (NOT TOOTHED) kitchen sharpening steel works really well, or a wrist pin (from an automotive piston) with a wooden-dowel holder, or an automotive valve stem. They're all crazy hard steel. If yer not careful, I'll make ya up a purpose-built steel card-scraper burnisher with two turned handles...

[sachbvn]

lol - Tim, your knowledge and ability to Dx problems over the internet forums with laymen's terms - amazes me.

That is EXACTLY what is happening.... it's marking the screwdriver to blue blazes....it's the newer "Craftsman" kind.... I mean - they got that matte coating on them.

I'll try finding something super hard or just buy a dang burnishing tool - see how that works.

FYI - I am wearing gloves when burnishing, I don't want to turn my hand into a scraper holder!


Zac

[admin]

Nov 1, 2009 22:43:15 GMT -6 sachbvn said:

lol - Tim, your knowledge and ability to Dx problems over the internet forums with laymen's terms - amazes me.

I've long suspected that Tim is secretly the earthly preincarnation of Yoda.

"Turn some bowls, you will"

Hey, it could happen.

[fredbelknap]

Zac I like you am having a problem finding something that is hard enough to burnish a scraper. Last week I was digging around in a drawer and found a center punch about 4" long, the kind to punch metal to start drilling, and it seems to do pretty good. I have thought about ordering one but they want a lot for them and I'm always thinking I can find something that will work.
Fred

[sachbvn]

Stupid thing is - going by what Tim said - I'm sure we could find all sorts of "hard enough" things from an auto parts place, or a garage (mechanics place, not OUR garage lol) - I'll keep my eye peeled for something that looks hard enough.


Zac

[TDHofstetter]

A quick interim burnisher... is a 1/2" drill bit's shank. That's hard carbon steel or HSS. The shank isn't usually as hard as the flutes, but it's pretty good. Don't do it with your favorite 1/2" drill bit, 'cause the shank may wear, but if you've got a broken one by all means use it.

If there's a machine shop in the neighborhood, ask 'em if they've got a double-ended 1/2" four-flute end mill that's not worth sharpening any more. THAT will be clear hard, all the way through, and the center (between the two sets of flutes) is nice & smooth. It won't be really long, unfortunately - only about 4" or so unless it's a long-reach end mill... but two turned handles that barely house the flutes will still leave a good 1-1/2" of clear hard round steel in the middle.

[fredbelknap]

Tim I have a set of cabide drill bits and the shank on them is to soft.

[TDHofstetter]

Carbide... or titanium nitride? Plated? Or maybe cobalt? Masonry bits? If they're masonry bits with the little carbide tipe, the body will be pretty soft - that body only needs to be tough, not hard.

[sawduster]

I fiddled around with all sorts of stuff I tried as a burnisher. Then a fella elsewhere came out with a burnisher kit, basically a hardened polished steel rod and a ferrule. A make your own handle sort of deal. It was like $15 and it is some of the best $15 I ever spent.