New "Thinline" style body...D-Fir over Basswood

Discussion in 'Tele Home Depot' started by Jim_in_PA, Oct 22, 2019.

  1. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Guitarbuilder's "Press a Button and out pops a guitar build" thread inspired me to document my steps at creating a new "Thinline" style body this week with a d-fir top and a basswood core. More and more builders are getting interested in CNC and even a very modest machine can be used to help with guitar building. I happened to have the CNC first and started the guitar thing a year later...it seemed like a good idea. I think that's held up as I'm really enjoying this.

    "Build Number Two" was also a D-fir top, but it was over some very heavy heart pine. I learned a lot from that work including a really nice burst finish that I remain proud of. Unfortunately, that finish has been marred by something heaving accidentally falling on the body, leaving a massive dent that really isn't repairable without completely destroying the finish. I may yet do that, but I already had the intention of doing more bodies of this style and had the material. So while I was working on other things, I set up to do the deed.

    The basswood blank was glued up the week before. The material was wide enough for a two-board blank and I used T-88 for the joint. Since it would be topped by the d-fir, it was setup with a 38mm thickness. I have my design and machine instructions setup to cut the body as a two-sided job which keeps everything in perfect alignment. My reference point for x-y zero is in the center of the blank which makes two-sides a whole lot easier to design and cut. So after fastening the basswood blank to the machine's spoilboard, I told the CNC software where the center point was using my machine's laser positioning feature.

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    The next operation was to cut two .25" holes on the y-axis centerline to serve as exact registration points when the blank needed to be flipped over to cut the other side. Note that I'm going to cut the back of the guitar body first and then flip it for the top side operations. Before I do that, I'll take a drill and extend the holes into the machines spoilboard a little more because the protective limits on my CNC don't permit going more than about a quarter inch into the table for safety reasons.

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    The back side only gets a few operations...ferrule recesses, control cavity accommodations and a slight round over at the edges to reduce manual sanding later. First the ferrules...and I left the dust collection hood off for these photos so that the operations can be seen and photographed. Normally, I wouldn't do that.

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    Next the control cavity cover recess and the deeper control cavity get cut. The former is 2.2mm deep and the latter only needs to go in about 7mm because after I flip the blank, the rest of the control cavity can be hollowed out from above and everything stays clean at the edges. These cuts on the bottom use a down-cut end-mill (spiral router bit) which also results in a very clean edge.

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    Lastly for the bottom, the body edge is treated with a round-over cutter to reduce work later with sandpaper. For a double-bound body, this step would be replaced by cutting the necessary recess for the binding just as it will be done with the d-fir top here.

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    So now it's time to flip things over...and this is the reason for the holes I mentioned previously. .25" location pins can be spotted in the holes so that when the blank is flipped over, it's oriented exactly in the reverse from the backside and everything will line up "perfectly"

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    At this point, the "core" of the body needs to be pocketed out for the hollows under the f-hole as well as for the control cavity and wiring channels. All of the cuts shown here in this screen scrape will be "hidden" by the d-fir top when it's glued on. You would do this exactly the same way if you were using a hand-held router with a template. The difference here is that it's all completely done in about 15 minutes, including "human time".

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    This part is way too messy to do without the dust boot, so I waited a bit before taking the photo...you can see that the pockets are nearly done here and are identical to what was shown in the previous image. Only the control cavity remains to be cut and it will be perfectly lined up with the work already done on the bottom side.

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    After completing this cutting...it's time to get the d-fir on top.
     
  2. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Because I chose to assemble the d-fir pieces on top of the basswood before previously gluing them up to help with grain matching, etc., I used a template I cut awhile back for layout purposes to draw in the outline of the finished body, using the index holes to place it in the correct spot.

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    I could then take the three pieces of vertical grain d-fir (6mm thick) and shift them around, recut some edges, etc., until I got them exactly the way I wanted them to be. Careful attention to grain and color can all but eliminate the signs of joinery when you have to use multiple boards for a panel...it's actually the very first step in finishing any woodworking project and can be the difference between great and "Wow". I spent probably about 30 minutes doing this until I got to where I felt I had the best result with the material I was using.

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    To get the top down and joined, I first put the template back on and again drew the outline so I had the body boundaries as well as the pickup pocket boundaries. Why? I'm going to clamp this down with 1" pocket screws and they need to be anywhere BUT where the actual visible body top will live. :) Here's a shot partway though the "clamping" process. The real clamps were used to draw the panel to panel joints in tight as they were slightly sprung after jointing them. Titebond Original (type 1) was used for this lamination.

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    "Holy-Moly, that's a lot of screws!"

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    In case you were wondering, this is what the end of the vertical grain d-fir looks like...

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    I let that go for about 4 hours and then it was time to sand away any unevenness...80 through 220...which I decided to do prior to cutting the rest simply because everything was captive on the table and is darn easy to sand when it's flat like that.

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    Along the same lines, I decided to hit the d-fir with a couple applications of Z-Poxy since the d-fir is soft and again, it was really easy to get it on and sand it back at this point. Let's just say it's an experiment for now.

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    The CNC work for the top is pretty much identical to what one would do with a hand-held router and templates as I mentioned previously. The exception is that the final "cut out" is last instead of prior to all the pocketing, etc. For this top, the neck pocket, pickup pockets, f-hole, string-through holes and "control holes" all got done first. That was followed by preparing for the binding and then final cutout. I use "tabs" (leave small pieces of wood) at the bottoms of the cutout toolpath to keep the body safe during that final operation and then use a small, pointy hand saw to release the body from the scrap portion of the blank once it's removed from the machine.

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    Here you can see the control cavity from the bottom and the wiring channels that intersect it

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    At this point, I feel a need to point out one mental mistake I made that I'm going to have to make up for after-the-fact. I make a habit of checking the depth of things before I take them off the machine. Human nature being what it is and wood being what it is, verifying things is sometimes important. I did that for the neck pocket and the pickup pockets but I forgot to do the same for the binding relief. And, of course, Murphy's Law being what it is, I didn't discover that I inadvertently cut the binding relief 1mm too shallow. My bad. I forgot to adjust it for "this" particular body as compared to the previous which was a slightly different thickness.

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    There are worse things, of course, and I can either choose to just shave down the binding or do the work to get the recess deeper. "Stuff happens".

    Beyond this, the body has had the contour sanded at the OSS and is ready for all that finish sanding that has to go into every project as well as dealing with the binding. Oh, and then working to duplicate that burst finish from "number 2". :)

    Total actual cutting time on my CNC was a cumulative of about 40-45 minutes. Most of rest of the time was stock preparation, gluing, making changes and adjustments to the design and CAM output and sanding.

    One last thought tonight: This body is REALLY light in weight compare to previous efforts. That basswood was a good decision on my part and I will likely be using a lot of it going forward for that reason where solid color comes into play. I haven't weighed it yet, but...it's "down there".
     
    Last edited: Oct 22, 2019
  3. photondev

    photondev Tele-Holic

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    Thanks for documenting your CNC build. It is looking awesome.

    I am fascinated by many aspects of CNC, unfortunately I cannot justify the investment of time and money at this time.
     
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  4. ejphotos

    ejphotos Tele-Meister

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    Ooh, I like that control layout! Looks like it'll be nicer than your other thinline body too
     
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  5. cleanheadsteve

    cleanheadsteve Tele-Meister

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    great info and photos. enjoying very much

    Sent from my SM-S767VL using Tapatalk
     
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  6. Gipper

    Gipper Tele-Meister

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    I am curious as to what bit size and feed rates you are using to do the hollowing procedures.

    Thanks - Brian
     
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  7. oldrebel

    oldrebel Friend of Leo's Gold Supporter

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    Great job!!
     
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  8. erix

    erix Tele-Meister Silver Supporter

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    Thanks for the nice build sequence. Love that top!
     
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  9. maple

    maple TDPRI Member

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    Festool
     
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  10. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Yes, I agree. Since I had already done this control arrangement for the "more customized" build in sapele in another thread, it was almost a no-brainer to "let the wood shine" and do back side access. Keep your crossables crossed that I can nail the burst again. ;)

    My machine can theoretically hit 400-500 ipm, but the realities of acceleration don't support that on small work. The top-side hollowing was done with a .375" (3/8") up-cut end mill running at 12K RPM with a maximum feed rate of 300 ipm and 41% step over. I only took a .35" bite per pass, although I can easily hog a half inch per pass with that cutter in something like basswood. I used a raster on the y axis with a finishing pass which results in the most efficient cutting for these larger pockets because of the longer distance for each pass of the cutter that allow more acceleration than they would parallel to the x axis.
     
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  11. Gipper

    Gipper Tele-Meister

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    Nice! The advantages of running a spindle as opposed to a mounted hand router like my machine. I run 2.5 hp porter cable router and with a 3/8 end mill typically cut at 70ipm at a depth of 1/4" . Takes me about 35 minutes to do this.
    20191005_121320.jpg
     
    Last edited: Oct 23, 2019
  12. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Wow...that's going to be a stunning body, Brian! Can't wait to see what you do with that for sure!!

    I suspect I can push my machine a little harder if I want to, but since I'm not doing production work most of the time, I see no reason to "seek the limits". You are correct that the spindle helps a lot and I can fine tune the RPM and feed speed based on my ears on the fly because it's all software controlled. But machine stiffness maters big time, too. IMHO, that's the biggest limiting factor relative to speed with many popular CNC machines. They can cut beautifully...but one has to be patient to avoid any deflection that will make the cut "less pretty" as well as increase risk of breaking a bit. It's not a "negative" relative to the machines because while affordable, again, they work very nicely and precisely as long as you keep their performance factors in mind. My "little" 4x4 Camaster Stinger II SR-44 weighs 900+ lbs naked, has a very heavy welded steel base structure and the gantry is made of 1/2" thick aluminum, yet I CAN push it hard enough to actually see an effect on the cut quality. So for the actual pocketing shown above, I'll guess that the cut time was about 15-18 minutes with the .375 end mill (including the pickup pockets and control recess) but I can't break it out because all the operations are in one file when they go to my machine, including tool changes. (manual change, but automatic measurement)

    Sometimes I get surprised by what can be done with the smoothness of the spindle, too. That happened yesterday during an inlay pocket job for a client...'got a tiny 1mm two-flute moving at 75 ipm at a 1mm depth of cut (only three passes to get to 3mm) in air dried black walnut and I think I could have pushed it faster. I had a conversation with Ron from Precise Bits (Tinker and Tinker) awhile ago when I bought some of his fret slot cutters (.023") and found I was being WAY too conservative, even with that tiny bit. We did the math together over the phone and even with that little thang, I can set it for 24-30 ips at 18K rpm with .4mm depth of cut. Each 2mm deep slot takes a quick 5 passes. I was moving at a quarter of that previously for fear of breaking the expensive little cutter off. What a difference in the time to do that task at the more appropriate speed!
     
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  13. Macrogats

    Macrogats Friend of Leo's

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    All the techno jargon goes over my head, but that is some great documentation of your building process Jim. Many thanks for sharing.
     
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  14. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Yea, like anything, there's a "language" associated with certain kinds of tools and techniques. Suffice to say, it's all about making the "spining cutter" work efficiently and cut cleanly...no different than using a hand-held, honestly. ;) I do enjoy documenting projects and have done that for many years in the large woodworking forum I help moderate (Sawmillcreek) and plan on continuing that here. I learn a lot from all the other build threads that folks are posting and hopefully someone will get some little thing from mine, too.
     
  15. dreamingtele

    dreamingtele Friend of Leo's

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    I love thinlines!! and thanks for documenting!!
     
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  16. roffe

    roffe Tele-Meister

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    That fir top is NICE.
     
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  17. Gipper

    Gipper Tele-Meister

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    I am totally self taught in using my cnc and I have always based feed and speed in how the cut sounds and accuracy as well as what it is doing to my tooling. Having the tip of my end mill covered in gunk or burnt looking tells me the balance is off somewhere and I adjust accordingly. I actually started a piece of light african mahogany on fire once cutting a small deep pocket...things j7st got hot enough to start it smoldering!

    http://romaxxcncrouters.com/store#ecwid:category=2549172&mode=product&product=10142276

    This the machine I have. Had it about 10 years now and it has never let me down.

    This is what the body looked like finished.
    20191006_114703.jpg 20191006_114718.jpg
     
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  18. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Wow...beautiful end result, Brian! Pretty much all of us who use CNC are "self-taught". (The same applies to any tool for the most part) Yes, some of us might have taken some basic training, etc., but there's no substitute for ruining some wood and breaking some bits. :) :D You dive in and you learn. I'm about a year and a half in now and while I feel really comfortable with things at this point, I still make mistakes. But I'm also willing to commit to "scary things" now, such as boring all the 20mm and .75" dog holes in this new guitar-focused workbench top yesterday afternoon...sometimes you just have to "push the button" and trust in your calculations. :)

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  19. Gipper

    Gipper Tele-Meister

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    Yep I know what you mean about diving in. Also learn that there often more than 1 way to do something. Figuring out the best way is the key.
     
  20. Jim_in_PA

    Jim_in_PA Tele-Meister Ad Free Member

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    Did some work on this build today...it was time to sand and do the binding. As I noted, I failed to check the vertical depth of the binding recess (width of the binding) before taking it off the CNC, so to correct, I used the nice StewMac cutter with the appropriate bushing in a fixed base router to clean things up. It worked beautifully. Honestly, I made do them this way all the time because the recess can be cut post-profile sanding which makes for a much better fit for the binding when gluing it up.

    I did this work on my main bench because the low angle of the sun was coming right in the slot-window above my new guitar bench (go figure) and it was blinding. Holdfasts secure the body to the bench and I made partial perimeter cuts and then moved the body around to finish the other end.

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    Then it was time to stop and smell the super glue...err...attach the binding. :)

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    I wasn't happy with two little spots in the tight curves and fixed that with more glue and a couple of tiny quick clamps

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    Not shown...a whole bunch more sanding...
     
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