Official Luthiers Forum!

Well I am almost ready for the spray booth on build #1. It just needs a little clean up and then the neck glued on. Binding is done, recurve shaped and the top/back tuned to the best of my expierence has lead me too.


One area I have had some difficulties in is using the scraper to shape the recuve. The process goes smoothly for the right and left sides of the guitar top/back (with the grain), but as I approach the centers where the grain is short (Cross grain), I get a lot of tear-out or broken fibers in the wood. Trying to maintain the same curviture of the recurve all the way around the top, I feel I need to use the tool in the same motion/direction for the entire top/back..so I get consitant results. I think the scrapers I am using are "pretty darn" sharp. Not scarry sharp or anything as I really have not perfected a technique on the french curve scraper to get it super sharp. I do consider this maybe a small portion of the problem, but I also think it is my process of cutting accross the grain (which is usually a no-no) in the recurve area. Any suggestions?

The second area is I am now ready to do an initial final sanding to the top/back and sides while the neck is off. I want to be cautious not to change the shape of the top...especially in the recurve area. That area is starting to look pretty nice. Any tips on sanding the top/back especially the recurve? I have a RO Sander but it is flat and a little to large to get into the detailed areas of the carved top. Thoughts?

Thanks,

Joe

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Joe

Change technique and don't scrape cross grain after you get close to final thickness. Then remember why God made sandpaper. How did the Cremonese masters make it perfectly smooth without sandpaper, you may ask? The answer is they didn't. They left behind scraper marks that are now considered to be an essential part of the instruments' charm.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Another old school method of smoothing curved wood after scraping without the use of sand paper is using progressive grits of dry pumice and a small hardwood block (pre paper backed sanding)

My grandfather loved to sand using pumice. FF followed by FFF and FFFF

Joe--I sympathize with your attempts to scrape cross grain especially in spruce. Get too aggressive and it will tear out causing a great deal of sanding to repair. Try tilting your scraper to various angles when scraping to see which works best. Also try skewing it to give it a shearing action in combination with the tilt. There's many combinations of the tilt/skew so try various approaches. With all that said, I prefer using power sanding either DA disk or RO rectangular for doing the recurve. It's faster and the trick is to keep the sander moving even if it's in circles with the rectangular pad RO. I guess this applies to most any sanding application. Also, don't be afraid to hand sand or scrape across the grain especially in spruce--you'll find it works much faster and better at not bringing out the growth rings. The downside to power sanding vs scraping is, of course, the noise. And there's also the feeling of craftsmanship associated with scraping.
I've never had the patience and/or skill to roll what I would consider a reasonably aggressive edge on a scraper. I use the belt or disc sander to quickly generate a burr and then back to scraping. Beware of the sparks in a woodshop, however. I've found that sharpening by sanding parallel to the cutting edge(s) of the scraper also gives a smoother cut that sharpening across the edge. I suspect that the burr produced by sharpening parallel is somewhat similar to that produced by rolling and burnishing back the burr. I do, however, respect those craftspersons who've mastered the art of correct scraper sharpening.
Keep building!
Nelson

The right scraper can make a huge difference. I use a specially designed violin scraper that is 1/8" thick. This scraper is easier to sharpen and most importantly of all it doesn't chatter when going across the grain. My new scraper is almost 1/4" thick and is even smoother.

Where do you get this kind of scraper? At the moment you have to make them or have somebody else make them. I've heard rumors, however, that StewMac is considering carrying them. Let's all hope that they do. Once you used this type of scraper, you won't want to go back to a traditional card scraper.

I've never done this personally, but on another forum I saw Otis Tomas us a modified utility knife blade as
a scraper to do the recurve.

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Horton, MI

Mike--Is your violin scraper drawn back enough that you can burnish and roll the edge or is it full hard and you stone the edge to sharpen? I would think that a thick scraper made of 01 or A2, then hardened and drawn to about 60RC would really hold the edge.

To sharpen this kind of scraper, you use an Aluminum Oxide wheel on the grinder. Grind the shaper straight in to the wheel at 90 degrees. The slight curve of the wheel makes the "burr". Al Carruth says to hone the shaper flat on an diamond stone first. I like to hone it flat after grinding.

They are made is either A2 or O1 steel and have a 58/59 RC with a very slight tempering. You don't have to sharpen them often.

Mike--You peaked my interest enough to have one of our T&D guys make up a scraper like you described.
Amazing! It will cut spruce cleanly! I am impressed! Where have you been the last 10 years?
I sharpened it with the Tormek which has a wheel of about 10" diameter so the hollow grind is not all that hollow.
Would a smaller wheel making a deeper hollow be even better?
Nelson

Nelson,

can we see a picture of it?

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Joe

Joe--I'll try to get a shot of it this evening.
It's made out of 1/8"x1" 01 tool steel about 3" or 4" length.
It's shaped somewhat like the side view of a whale having drawn the shape using a french curve.
(Wonder what the difference is between a french curve and an english curve?)
Maybe Mike will get us a shot of his if he happens to "stop by".
Nelson

I learned about this type of scraper from Al Carruth. We made up some when I started on a mandolin project. Since then, he has found a machinist who will make him some more. Al doesn't want to be in the lutherie tool business so he doesn't make or sell these. See his web page for a description of what he had in 2000. http://www.alcarruthluthier.com/toolOfTheMonth/superScraper.htm

I'll go snap a picture of what I have and see if I can post it here.

OK, Here's a picture of my two scrapers. The small one is the one I made a few years ago. The large one is the one Al gave me a few months ago. Both work well. The large one is almost 1/4" thick and cuts very smoothly.

I measured it at 1/8"x1 1/4" O1 rather than 1/8"x1".
Somebody needs to come take this thing away from me before I scrape a hole in my gitfiddle!

Awesome! Thanks guys. What is the 01 designate? Is that a tool hardness?

I don't have access to any steel. Is there something around the shop that can be used? EX: I have been cutting up an hold handsaw for my scrapers. Will some other tool around the shop have the proper hardness/thickness for this?

Thanks again!!!

Joe

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Joe

Joe--The O1 (that's the letter O) designates oil hardening tool steel as opposed to, for example, A2 which is air hardening.
I would say that an old file would be a good candidate to make a thick scraper. Would take a lot of grinding to get rid of the teethc but
the hardness would be good.
http://www.onlinemetals.com/merchant.cfm?pid=11806&step=4&showunits=inches&id=246&top_cat=0
Online Metals is a good source for small quantities of metals. There is also a lot of good info online about hardening tool steels such as O1.
It can be done with a torch and a small bucket of oil to drop the piece into after it's heated cherry red. (Be careful, potential fire hazard)
Then there is the tempering process to draw some of the hardness back out of the brittle metal that results from the quenching.
Nelson