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I have an old Yairi classical that has a couple of cracks that are open, and have been for a couple of years, among other issues. No amount of humidity closes the cracks at all. It really needs a new top but I thought I would practice doing some crack repair on it first. I can't remember whether it was LMI or Stew Mac that used to sell a tool that would cut a v-groove along a crack, and then cut a spline to fit the v-groove. I don't see it on either of their websites. Does anyone know where I can find this tool? Thanks, Wendy

I don't recall seeing a tool like that but I have a Martin EMP-1 I bought that had a crack in the top that someone had tried fixing and the botched the job and ended up putting some kind of soft putty in to try and fix it. I fixed it in the same way you are talking about by measuring the size of filler piece I needed and then cutting it from a scrap of spruce that matched the color of the top I was fixing. I also found one that had very similar matching grain. Once I had the piece cut I then laid it out over the crack to make sure it would fit. Then I used an X-acto blade that I had mounted to a small scrap of wood that was cut at a 45 degree angle. I just used CA glue to glue the blade to the 45 degree angle of my "tool". I measured the thickness of the top to be sure I only cut the top and not braces. Using a straight edge I cut the 45 degree angle from the edge of both sides of the crack measuring the width to be sure both sides were parallel. Then I cut the angle on the new patch using a straight edge again to be sure my cuts were straight. Using a small light inside the guitar I started fitting the piece into the crack, that showed me where the piece needed to be trimmed to fit perfectly in the crack.
When I had it fitting correctly I used hot hide glue to glue it in place and then put cleats on the underside.

It was a tedious repair but it turned out really well. I then spot finished the lower bout and blended the finish in. The repair is just barely visible and it has been a couple of years and it is holding just fine.

I posted this picture in another thread a while ago but here it is again so you can see how it turned out. You can just make out the filler piece and the blend lines where I finished it. The filler is the 1/4" strip along the center seam and the blend lines are actually where I sanded the finish back and sprayed up to them.

So if you are careful and take your time you can do it with something as simple as an X-acto blade glued to a piece of wood.

Hope this helps and good luck.

Bob

Nice repair Bob! Really have to look to find it.

I think you're talking about something they called a "powerknife" that Stewmac sold (item #5359). One of those suppliers also had a "Sloane crack and splint former", and then there's the "Ibex Splint knife".

Hope this helps you find what you are after. I don't know who carries any of them now.

cheers

That is a nice repair Bob. Thanks for the info, if I don't find what I am looking for I'll probably try it similar to how you did it. Steve, I think it was the Sloan crack and splint former. I'll call Stew Mac Monday and see what they say.

Check this out:
http://www.mehr-als-werkzeug.de/product ... Former.htm

Scalpel and metal straight edge is all that's needed. Very lightly scored to begin. The splint can be planed to fit.

That is a nice looking repair Todd, I can see why you would have to refinish the top, something we don't really like to do unless it is necessary but that looked necessary.

Great job and on a great guitar.

Bob

How do you spot refinish stained or tinted finish? I have done similar repairs before, and as long as the finish is perfectly clear without staining it can come out nearly invisible. But as soon as you have to touch up stained or tinted finish it becomes extremely difficult to blend it. No matter what there are always visible line between new and old finish. Also it's really hard to replicate the color of aged sitka spruce because new wood is always much lighter than old wood, making an invisible repair really hard.

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@Tai Fu, Well in my case it comes from doing custom painting on cars vans and bikes for 20 years. It isn't an easy job if you don't understand color and using an airbrush. If you look at the picture I posted of my Martin you can see exactly where I sanded the old finish back which are the 2 grain looking stripes on either side of the center seam about 2 inches out. After the seam was repaired I used Vinyl sealer in a DeVilbiss touch up gun with a fine tip on it. The object was to keep the sealer off the rest of the top and only on the repair. In between double coats I wet sanded the edges with 800 grit wet or dry paper. The new finish clearly did not match the original so it needed to be tinted so after about 4 coats of sealer I started block sanding the area to level out the low spot created by removing the finish around the repair. BTW... I do not sand finish off but rather use lacquer thinner as a stripper because I did not want to thin the wood and I am not crazy about using chemical stripper. I did feather out the edges with sandpaper to get a smooth transition but most of the finish was removed using a small paint brush, lacquer thinner and a chisel point X-acto blade as a little scraper. I worked in about 1 inch wide strips at a time.

So after I had leveled the repair to the old finish I tinted the clear to match the base color of the old finish. When I sprayed the tinted clear I was very careful to not go over the old finish since I didn't want to shade the old finish. When I had the base color laid down and was happy the tint matched I had to blend in the old and new finish so I used a mask made up of Fine Line tape and a piece of cardboard. Fine Line tape is used for auto painting and specifically for stripes (it leaves a very clean line). What I did was use my airbrush and faked grain lines by moving the mask each coat where the blend line between new and old finish. I say faked grain lines but I didn't make them heavy enough to cover the wood but just dark enough to give a bit of a shaded line. I also tried to use the existing grain lines to cover my tracks to blend the edges in.

When I was happy with the blending I then used clear with no tint and applied about 3 or 4 coats and then started block sanding with 800 grit paper and a rubber block to level out the finish. It took probably 8 or 10 thin coats to get a perfectly level finish so you cold not see where it was repaired. All the while I tried not to get the new finish too far into the old and I ended up not going past the edges of the bridge. I took the final coat of clear out to the edges of the body from a line straight across the bottom of the bridge but those coats were thinned down quite a bit so when i buffed it out it was a smooth transition from old to new finish.

The whole finish process took about 6 weeks because I wanted to make sure each layer of clear was dry to avoid having it shrink back and show the blend line between old and new finish.

I would say that a repair like this is not for someone that doesn't know how to handle an airbrush or a small touch up gun. And a good understanding of color theory is a must. I can spot this repair every time I pick the guitar up to play it but anyone who has seen it can't tell its there even when I point it out.

I hope that helps.

Bob

Zoltan thanks, that is what I was looking for but after all the responses I have decided to just do it by hand. Nice repair Todd! I'm not too worried about matching the finish. Like I said this guitar should be getting a new top, but it won't. In addition to the cracks, a pickguard was poorly removed and then my pinky wore deeply into the top due to my poor technique. Improper use of a soundhole humidifier roughed up and wore the edges of the soundhole. This has been my "beater" guitar for years, long before I knew any better, hanging on the wall with no case, even when the humidity goes down to 8%. And yet it always sounds decent. The only reason I am finally wanting to repair the cracks is so the bridge can be reglued. I need to have 1 guitar that can just be sitting out ready to grab sometimes. Thanks for all the responses. Wendy