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with_joerg

Finishing a spruce top

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I get conflicting information on how to finish a spruce top. Some say that the last tool that the wood should have seen should be a scraper. OK, that works for my maple back. However, for my spruce top I always get these few patches where -- no matter what you do -- the grain seems to have been rubbed in the wrong direction. Then I saw on youtube that quite a few people sand the spruce tops w very fine grain sand paper. So I am now undecided what I should do.

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38 minutes ago, with_joerg said:

I get conflicting information on how to finish a spruce top. Some say that the last tool that the wood should have seen should be a scraper. OK, that works for my maple back. However, for my spruce top I always get these few patches where -- no matter what you do -- the grain seems to have been rubbed in the wrong direction. Then I saw on youtube that quite a few people sand the spruce tops w very fine grain sand paper. So I am now undecided what I should do.

My choice is horsetail...equisetium

 I use the cleaned up and applied to a backer version made by violin maker Dorian Barnes.

Joe

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If you're having trouble getting the finish you want with just scrapers you might want to give equisetum a try.  I like the results. Some folks use micromesh.  It's not illegal and you won't be shunned for using it.  For youtube violin advise, I restrict might viewing to Davide Sora's videos.  I also occasionally watch for a new way to use a sawsall, but that's for entertainment only.  The funniest part of those videos are the comments where people don't realize it's a joke.  Darnit, Joe just posted while I was writing.  I have and like the stuff Dorian makes.  Hopefully, I will be able to restock at the SVA.

-Jim

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Regardless of the final finishing, for an "easy" base make sure that you are not trying to add color to the base coats unless it is a colorant that is known for not "burning" 

somewhat hard to explain, but it gets into local absorption rates across the material and how your surfacing effects the absorption rates of the colorant. This is why to avoid "blotchy" looking varnish jobs it is bets to seal with a "clear" or colorless {baring the base color} material that will seal off and bring the absorption rates for the following coats back to even....

or simply put, by properly sealing with a clear coat, the clear coat will fill into and eliminate different absorption rates across the plate , soft woods are notorious for having blotchy uneven first coats based on their sensitivity to any kind of surfacing...

IF you have any colorant in your first coats, what will happen is in any areas where their is any difference in the evenness of the surfacing will show blotchy which is basically the rougher areas absorbing more material than the smoother areas right next door.

it is VERY difficult if not impossible to get a 100% evenly surfaces piece of softwood, particularly taking into account areas like the recurve and lip. The scraper is always suggested because it does not do what sandpaper does to the surface.

Scrapings final "texture" is very even...with sandpaper, even with the same grit, tiny fluctuations in hand pressure, grit wear etc, all translate to a surface that absorbed the fist varnish coat at different rates...different rates can translate to different level of saturation, which lead to a blotchy look 

an example, say we final sanded with 220...."this area" right "here" we reached the end of the paper life, because it was dull, we pushed a little harder right "there" then we changed paper, and now when we start again "here" we have sharper grit paper that requires less pushing, less pushing means less burnishing, less burnishing means more absorption right "here" but not "there" this becomes the problem with sandpaper, all those areas that look and feel the same, but from the coats perspective, it's all a little different, and sucks in the varnish differently spot to spot.

By scraping you never have this issues and the final surface is basically the same, the horse tail is abrasive enough to then go over the scraping and remove "stop marks" that may be left behind from not ramping off well.

The horse tail is abrasive enough to smooth the stop marks, but does not act like sandpaper and "bite" into the grain, therefore does not "mess" with absorption rates.You will not know how important this is until you apply a varnish coat on a not properly sealed work. Anywhere where a clear base has not "filled" up the grains will take mass amounts of color right into that spot, so get a good clear sealer on before using any color...

Using colors on raw woods is very dicey at best, only weak even colorants like tea can be used safely, I always suggest Joe Robsons varnish as it is great at getting color in without the blotch.


 

 

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I would add that you can get just fine looking work using sandpaper, it's just really the only way to play it safe with it is to make sure you get adequate "clear" coat on before you use any colorants....it's kinda the safe junior woodchuck way of getting a decent looking finish job...particularly using something like wax free shellac 

 

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I found a path in the woods which had tons of horse tail plants. I cut quite a lot and use is some. Split the plant and open the pieces and put them side by side on a surface with some tack or stickiness to it. Furniture round pads have such a surface. The violin makers of the 1700's did not have sand paper. It was not yet invented. They may have used horse tail rush. Kind of like very small bamboo with a rough surface. Once you see the plant this will make sense. Some times the grain direction changes on the top violin plate and the scraper has to move in another direction. This happens a lot in the cove areas of the upper and lower part of the plates. When you run into a problem change directions, sometimes 180 degrees. Sometimes come at it at an angle.

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Harvest some horse tail. Remove the radial "branches." Pull the central stem into sections of a length determined by its natural joints. Find a jar long enough to hold the stem sections between its base and its twist on, water tight lid. Line the bottom of the jar with water absorbent material--folded over cotton or paper towel. Damp the material with water followed by a dash of alcohol (to inhibit mold growth), place the separated stem sections into the jar and screw on the top. To use, pull out a section, cut one side of the cylinder lengthwise so that it will lay flat and "sand" paying attention to the top's grain direction, as has already been recommended.

If you've never used horsetail before, it's enlightening to try it on a thumbnail.

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I am able to get an almost flawless surface on spruce using scrapers alone - sharpening them like single bevel knives (with the exception of the last one) is part of this. The last scraper that touches the wood is a very thin, flexible kidney shaped scraper used for pottery work. This I have a 90° face on, which I polish periodically with a 5 micron belt. When I make the final passes, I can bend to fit any contours, and it removes little shavings that look like dust unless you look under a handlens. 

Another great technique is to prepare horsetail/equisetum as advised above and then alternate it's use with extremely sharp scrapers. If you hit a patch of wood with the scraper that doesn't respond well to seemingly any angle of attack, go at it with the horsetail a little bit, then the scraper, and back and forth every so lightly until you get where you want to go. 

Note - horsetail is a unidirectional cutting tool. Figure out which way your pieces cut before you get to work and you'll have more fun.

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7 hours ago, Michael_Molnar said:

I use single edge disposable razor blades. 

That's interesting: May I ask if you use them 'as-is' with a (presumably) straight edge, or cut / break them in some way? I ask as I have resorted to using snapped plate-glass, as I couldn't find a way to get a curved surface on disposable straight-edge blades without ruining the cutting edge.

thanks,

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3 hours ago, notsodeepblue said:

That's interesting: May I ask if you use them 'as-is' with a (presumably) straight edge, or cut / break them in some way? I ask as I have resorted to using snapped plate-glass, as I couldn't find a way to get a curved surface on disposable straight-edge blades without ruining the cutting edge.

thanks,

I use a tool post grinder to reduce the blade length and put a radius on the tips. Without the radius, I get marks from the sharp tips. Do not put a burr on the edge for scraping spruce.

Buy a 50 piece box of single edge blades at the local hardware store. They are used for scraping paint off windows. Make sure you have a sharps disposable container. I use a Mason jar with a slotted top. Do not throw used blades individually into the trash. 

I find that moderate light pressure works best on spruce. 

For strongly curved regions I use a "fingernail-shape" scraper. 

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4 hours ago, Michael_Molnar said:

I use a tool post grinder to reduce the blade length and put a radius on the tips.

...

That's extremely helpful - thanks very much indeed.

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6 hours ago, Michael_Molnar said:

I use a tool post grinder to reduce the blade length and put a radius on the tips. Without the radius, I get marks from the sharp tips. Do not put a burr on the edge for scraping spruce.

Buy a 50 piece box of single edge blades at the local hardware store. They are used for scraping paint off windows. Make sure you have a sharps disposable container. I use a Mason jar with a slotted top. Do not throw used blades individually into the trash. 

I find that moderate light pressure works best on spruce. 

For strongly curved regions I use a "fingernail-shape" scraper. 

Thanks for mentioning proper disposal. I really want to come up with some mini grinder machine that will eat up sharp things for disposal as safety for sanitation workers is something that concerns me.

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1 hour ago, Anthony Panke said:

It is also possible to wet the wood, let it dry, and scrape the raised grain down. This takes some repeats but gives nice results. 

I forgot to mention that this is part of my finishing regimen also

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1 hour ago, Anthony Panke said:

It is also possible to wet the wood, let it dry, and scrape the raised grain down. This takes some repeats but gives nice results. 

Ditto.

;)

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