Juntunen Guitars Posted January 28, 2013 Author Report Share Posted January 28, 2013 I was using a CNC to cut out the back and had a bit of a scare. When you carve wood into an archtop back or top it naturally wants to cup up, well I didn't think of that and was using a vaccum press to hold down the top which works great as long as your work doesn't cup and pull off the vaccum. Luckily I saw it when it happened so I was able to finish off the last 20 minutes holding the edges down so it didn't cut too much off and I left the file oversized so I will just scope out some wood from the back by hand and then once it flattens out I will run it through the CNC again closer to its final thickness. Here's the nice gouge it left, if I hadn't have caught that it could have been a ruined back. Quote Link to comment Share on other sites More sharing options...
Prostheta Posted January 28, 2013 Report Share Posted January 28, 2013 Ouch. Point taken about the cupping. The question has to be asked though - if the deformation strength is enough to pull the top off a vacuum, how much will it deform a body? I am sure that once it has been reduced down in thickness, stresses will be over much shorter distances so cupping will not be problematic. Has the inside been carved or is that straight from a cut outline? My question is down to whether it would be worthwhile carving the negative inner prior to carving the outside in order to reduce the weight of stock and hence the ability to cup. Quote Link to comment Share on other sites More sharing options...
Geoff St. Germaine Posted January 28, 2013 Report Share Posted January 28, 2013 My experience with my first archtop top and back, which both exhibited this cupping, is that the the top/back are so flexible once completely carved that very little pressure is required to clamp down any cupping of the plates to the sides. The sides are so stiff that I can't see the top/back deforming them. If both sides cup in the same direction, then the net force in either direction is going to be very small. I also found that any initial cupping due to carving the outside of the plate greatly reduced once the inside was carved as well. On my top I went from about 3/8-1/2" of cupping at the lower bout (in the same spot as Juntunen's back plate) before carving the inside to about 1/16-1/8" after. I think that makes some intuitive sense when considering internal wood stresses and what would be released by carving out the inside. Juntunen, that back plate looks phenomenal. It would have been a shame to have lost it. I'm looking forward to getting my two "master grade" flamed maple backs started, because the figure is so intense. Great work! I have a question about your neck jig. Does the jig have your neck angle built into it? I'm currently planning out the jig I'm going to build for doing the neck side of the joint and while the Benedetto jig seems nice, it's rather large. While I'm sure it would be great if I was doing a ton of necks, for only doing 3 and maybe a few more after, something simpler that came at the expense of more setup time would be fine for my use. Quote Link to comment Share on other sites More sharing options...
Prostheta Posted January 28, 2013 Report Share Posted January 28, 2013 Thanks for confirming Geoff. Pretty much what I figured by vocalising the problem, writing it down. Without having tried it - or even though about it before - it would seem that carving the inside first (even just roughing) to reduce the distances/areas over which stresses can accumulate would prevent the cupping during this stage. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted January 29, 2013 Author Report Share Posted January 29, 2013 Juntunen, that back plate looks phenomenal. It would have been a shame to have lost it. I'm looking forward to getting my two "master grade" flamed maple backs started, because the figure is so intense. Great work! I have a question about your neck jig. Does the jig have your neck angle built into it? I'm currently planning out the jig I'm going to build for doing the neck side of the joint and while the Benedetto jig seems nice, it's rather large. While I'm sure it would be great if I was doing a ton of necks, for only doing 3 and maybe a few more after, something simpler that came at the expense of more setup time would be fine for my use. I'd have been pretty mad if I lost that back as well and no the jig doesn't have the angle built in. The jig is actually made for flat top acoustics instead of archtops but the way it works is by screwing the neck in so you have to have the angle already cut which isn't difficult if you have the plans laid out and then any changes that need to be made are taken care of when setting the neck. I don't actually know what the Benedetto jig looks like, I haven't read any of his books or really looked into his guitars much other than buying the plans for one but from what I've heard his books are filled with a lot of good info. As for the cupping I think it has something to do with the fact that a large majority of the carved top is open end grain and since end grain sucks up and loses moisture faster than the rest of the wood it will warp mostly but this is countered when you open up all the end grain on the inside when you carve it. My top cupped too, it wasn't a big deal but since I was doing it by hand I just used some cam clamps and clamped it down until I finished the outside and then it flattened out again as I carved the inside of it. I haven't really thought about it though I just know it will happen. Prostheta, as far as I know it will cup regardless of what side you carve first, I just did the outside first since that's how I did the top and because I have a concave cradle made that I can set the back upside down in to carve the inside of it. I will have to look into what happens when you carve the inside first. I know a violin maker who also does cellos and mandolins who carves the outside of a top or back first always, I'm not sure why but it's just what he does, his name is Steve Rossow, I'm not sure if you have heard of the CNC made copy of the "Betts" stradivarious violin that was made from an MRI or CAT scan of the violin but that's who I'm talking about. Look it up, there's a few articles online about it. I was actually just looking at the scan of the strad violin today, it's pretty cool seeing literally EVERYTHING done to that violin, you could even count the grains per inch in the top but this is a whole other topic and I'm rambling now. 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted January 30, 2013 Report Share Posted January 30, 2013 I'll have to do some reading on this one. Do you have any specific links saved to spare me the Google trawling? Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted February 3, 2013 Author Report Share Posted February 3, 2013 I'll have to do some reading on this one. Do you have any specific links saved to spare me the Google trawling? Links for the violin stuff? http://waddleviolins.com/index.php?contentID=86 I was wrong on the scan, it was a CT scan, not MRI. I was talking with Steve Rossow on tuesday about carving the outside first and he said for structural purposes the reason he carves the outside first is because when you put a top that's had the inside carved first into a vacuum press it will pull the top down more since the top flexes more so it will warp the top. So if you carve the outside first you can flip it over into a perfectly formed cradle and it won't deform. Quote Link to comment Share on other sites More sharing options...
Geoff St. Germaine Posted February 3, 2013 Report Share Posted February 3, 2013 Yeah, that makes sense with the vacuum press. I imagine as you carved the top with the inside already carved the top would pull down more and more as material was carved away and you'd just end up with a mess. Quote Link to comment Share on other sites More sharing options...
Prostheta Posted February 3, 2013 Report Share Posted February 3, 2013 Stands to reason. Ah, the vagaries of this type of work eh? Quote Link to comment Share on other sites More sharing options...
Geoff St. Germaine Posted February 3, 2013 Report Share Posted February 3, 2013 Yeah, every way of doing something has it's downside to account for. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted February 11, 2013 Author Report Share Posted February 11, 2013 Yeah, every way of doing something has it's downside to account for. Definatelly and this build has been a big learning curve so far. Back to the build. The back on this thing was just causing issues left and right but I finally got it figured out. So at first I had to carve out the back a bit by hand. It wasn't holding down still so I took some thicker self adhesive foam to the vaccum press hoping it would be just soft enough that it would pull everything down, it was a little to sketchy so I decided to just carve the inside a little thicker and try my luck It ended up working just fine. During this whole back problem I've been getting more and more mad at this so when I was cleaning up at the end of the day I found this fortune cookie paper from earlier in the week when some friends and I went out to the chinese buffet. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted February 11, 2013 Author Report Share Posted February 11, 2013 After lots of sanding and scraping. Working out the recurve which is the same as the tops, 3mm at the shallowest point. and 4 on the outer rim. Then carving the last bit by hand. And then finally I got the side dots in. I found a good deal from a company called rescue pearl. They sell a lot of inlay material and you can buy a package of 100 abalone side dots, or a choice from several other sizes for fret markers for only $18 and they do deals like that for pearl, reconstituted stone, even mamoth tusk aparently. 1 Quote Link to comment Share on other sites More sharing options...
Geoff St. Germaine Posted February 11, 2013 Report Share Posted February 11, 2013 Your back plate carve looks great! Quote Link to comment Share on other sites More sharing options...
Pestvic Posted February 13, 2013 Report Share Posted February 13, 2013 That carve looks top notch man, damn! Quote Link to comment Share on other sites More sharing options...
John Abbett Posted February 18, 2013 Report Share Posted February 18, 2013 This thread is amazing work. It makes me want to build another Archtop. Very nice attention to detail and quality work. I can't wait to see the finished project. John Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted February 21, 2013 Author Report Share Posted February 21, 2013 This thread is amazing work. It makes me want to build another Archtop. Very nice attention to detail and quality work. I can't wait to see the finished project. John Thanks, I'm getting excited to see it too, it's getting close to being ready to put on the finish. Here's a quick update. I got the back glued on and I got the backs binding installed, I forgot to get a picture of routing the dovetail though. Quote Link to comment Share on other sites More sharing options...
Geoff St. Germaine Posted February 21, 2013 Report Share Posted February 21, 2013 Looking great, as always. Your work looks very clean! Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted February 21, 2013 Author Report Share Posted February 21, 2013 Looking great, as always. Your work looks very clean! Thanks, that's my OCD showing, even if I know no one will ever see whatever mark is bothering me I do my best to hide it. That's what killed me when I glued the top on because I had a couple holes from drilling the depth marks that I wasn't able to get rid of... Reminds me of a joke a friend of mine said where he was trying to decide if it was bad when you started calling OCD "CDO" because it's in alphabetical order Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted March 27, 2013 Author Report Share Posted March 27, 2013 Here's the long overdue update on this build. I forgot to take many pictures because I was working on this around my baritone build and an 8 string electric... I'm getting to busy and they all three have to be done by May. Couple things I had to finish before the neck set. Like glue on the heel cap and glue down some loose fret ends. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted March 27, 2013 Author Report Share Posted March 27, 2013 Setting dovetail joints I think is kind of fun, setting them on an archtop has an extra step where you have to fit a portion of the neck to the recurve and this has to be constantly adjusted as you fit the dovetail so you don't take off too much or too little and if the recurve section isn't at the right height it hangs the neck basically on a shelf so you don't know how tight the dovetail actually is. I much prefer setting dovetails on flat top acoustics over archtops but it's not that much worse. It took me about 5 or 6 hours to do this one so hopefully the next archtop I do doesn't take me that long. It was also nice that you only need to set about an inch and a half into the recurve and the rest is just free floating. I start with an undercut. For those who don't know, when you glue a dovetail you don't need a huge glueing surface, all you need is glue on the joint and on the edge of the heel. Most old acoustics like Martins and Gibsons do this as well. I just take a chisel and cut away wood. This also makes fitting the neck to the body easier. Normally I would do this before glueing the heel cap on but I wanted to try it differently this time. I tried a bunch of different ways to fit the neck extension to the recurve. I found that pulling sandpaper like you would when setting a neck to the body worked good for roughing but I gave up on that idea and just switched to some curved scrapers which worked better for me. You could use chalk to see the high points but I don't like this because it doesn't always transfer to the wood and the chalk is a pain to get off spruce. Another way would be to use carbon paper but it's the same thing as chalk minus the clean up. I think it's easier to just set the neck in the pocket and see where the high points are. It's faster this way too and if you put a light on the other side you can see where it shines through. I believe it's up to a thousandth of an inch that the human eye can see a gap in things and when you add light it's plain as day where high and low points are. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted March 27, 2013 Author Report Share Posted March 27, 2013 So I learned a good lesson this week. I got pretty sick last week and was working on final sanding out this guitar. I thought it was good after I was getting impatient from my headache and whatever I was sick with and figured if there was any scratches left it would be on the edges and get covered with the burst so I went and sprayed sealer well when I went and checked on it I noticed a bunch of scratches that were not going to be covered by the burst, if anything they would have sucked in the color so I spent the day basically sanding off the sealer in a bunch of places and re-sanding it... awesome... Lesson learned, don't work on guitars when sick. Either way here's some pictures of the body with sealer. I'm really happy that the back didn't get scrapped after that mishap with the CNC because it looks great with a finish on it. 1 Quote Link to comment Share on other sites More sharing options...
ScottR Posted March 27, 2013 Report Share Posted March 27, 2013 The maple back and sides looks killer! SR Quote Link to comment Share on other sites More sharing options...
Geoff St. Germaine Posted March 28, 2013 Report Share Posted March 28, 2013 That's coming along fantastically! Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted April 16, 2013 Author Report Share Posted April 16, 2013 Ok so this guitar had a nice run in with something in the spray booth. Not sure what happened but it got bumped so I had to sand off the sealer and spray the top again. I'm starting to think this guitar just wants me to smash it Either way I got the top sprayed again today and then got the amber sprayed as well. Tomorrow I'll get the burst sprayed hopefully and then I'll be well on the way of finally finishing this guitar. I didn't have enough pictures to put up to make it worth while so I'll try and put some up tomorrow once the burst is done. Quote Link to comment Share on other sites More sharing options...
Prostheta Posted April 16, 2013 Report Share Posted April 16, 2013 Agh. Shared space eh? Whenever I cause an accident, I will at the very least admit it if I cannot help put it right. Scumbag scratch fairies. Quote Link to comment Share on other sites More sharing options...
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