Slow build log - not much defined on this one yet

[Eric Baack]

Did a bit more machining today






https://youtu.be/VbIo1BHR5LQ


https://youtu.be/fkp3XovDezs

[Gordon Bellerose]

Eric. I did not follow your CNC build thread too closely, and now I regret that.
It looks as though your machine is very close to being able to do what you want. Other than some speed settings, and some software issues you mention, it looks good.
Of course I know that a lot of effort went into this, just like everything else we do.

1. Did you build from a kit, or did you fab everything from scratch?
2. If from scratch, where did you get your plan?
3. Where did you get all the gear (bearings, rails, motors, screws)?
4. If a kit, where did you purchase it, and how much was it?
5. How big a machine is it? Cutting table size?
6. What do you think the final cost was?

Oh, by the way the Fly is looking good so far.

[Eric Baack]

I built it from scratch. I do have access to a mill and lathe at work and can use that from time to time so that helped. A lot of the materials came out of the scrap bin at work other then a few of the bigger pieces. I drew up the plan myself in solidworks. I'm a mechanical engineer and am fairly savvy in that sort of thing. The linear bearings in the X/Y are the skate bearings on aluminum rail. The Z axis use to be the same but was converted to IKO bearings that were pulled from old automated sewing equipment at work. The Z is driven by a 5 start 1/2-10 screw with a 34/15 belt drive step down. The Y axis is a pair of .2" pitch belts in tandem to up their load capacity and the X is a pair of HTD belts with a cog and motor that rides on the gantry. It runs pretty smooth now after I replaced the single start 1/2-10 screws on all of the axis. The Z axis was binding until I did a bit of precision adjustment work with a hammer on one of the brackets that was a bit out of square.

It cuts 18" x 38" x 5" and is about 2' x 4' x 18" tall. I probably have $500 into it in all. The motors and drivers came from work except for the z axis motor that I got on ebay. The break out board is a chinese import that I got for around $60. The computer is my wife's old XP machine.

[David King]

Driver volts and amps?

[Eric Baack]

I'll have to go look that up. The drivers match the motors and plug into 110 AC. X and y are about 2.4 amps per phase and the z is 1.4 amps per phase. 5 phase motors all around.

[Eric Baack]

It's the vexta UPK series, Nema 34 for X and Y, Nema 23 for Z

And the back of the guitar.... I need to do some work on the neck pocket though. It did round off a couple of edges that it wasn't suppose to.











And a little video, nothing too exciting.

https://youtu.be/pYdZyS7bIT8

[Eric Baack]

And with the body cut out of the blank. A good bit of fitting left to do on the neck.

[David King]

Eric,
That's an interesting approach to the neck joint. I never liked the butt joint area on any glue-in neck as it seems like a very weak link at the most critical part where the stresses happen to be the highest. I'd be tempted to add splines where your neck laminations are that would key into the body. Of course the judicious use of CF under the fingerboard could help achieve the same result. As I'm sure you know, an end grain to end grain glued butt joint has almost no tensile strength with most glues.

[Eric Baack]

It is similar to what I found of parker fly neck joints online.. but I do believe those tend to get some carbon fiber skin as well. I'll look into some splines in the neck join area.

I'm not expecting much strength from the end grain portion of the joint. That part of the design is just to have a smooth transition into the body.

[Eric Baack]

I might have to sit down and run the calculations for stress in a cantilever beam too see what I'm feeling with

[Barry Daniels]

I wouldn't go that far. You would likely find that there is not much stress on the joint because the string pressure is basically in line with the neck and only offset from the neck by 0.1" or so. Where you should concentrate your efforts is on the quality of the joint. Does it mate up precisely? Have the surfaces been smoothed after coming off the CNC? If you can get near perfect wood to wood contact throughout the joint then any type of glue would be up to the task and the stresses involved. Splines or screws are probably not necessary unless your joint is less than perfect.

[Peter Wilcox]

You would likely find that there is not much stress on the joint because the string pressure is basically in line with the neck and only offset from the neck by 0.1" or so.

Until it falls off its stand.

[Barry Daniels]

Well yeah, there is that. Most guitars are not designed to survive that which is what keeps us repairmen employed.

[Eric Baack]

I made some templates by printing a cutaway view of the neck joint so that I can shape both pieces to fit precisely. I put some heavy tape on the back of those and cut them out. I have it very close now but the neck protrudes a tad above the top of the body still and isn't flush where the heel meets the body yet. I spent some time using the dremel to get it close and now I'll move to sandpaper to dial it in.

being a mechanical engineer, stress calculations aren't that difficult on something like this. It is mostly a matter of finding the correct centerline.

[David King]

Just seeing how Fender's bolt-on necks respond to years of stress tells me that the neck may develop a kink at that spot after a few years.
I wouldn't worry too much about it either but definitely something I'd watch for.

[Eric Baack]

that neck joint was a bit of a pain to get it fitted up. I ended up marking one part with pencil and test fitting then sanding away the transfer marks a bit at a time. That was about a 2 hour process...

[David King]

Chalk works well too. Two hours is nothing.

[Jason Rodgers]

I've seen at least one or two other folks on the interwebs do this cylindrical neck joint, but I'm not sure how they cut and fit it. The example that I thought looked really cool and elegant had the neck profile continuing uninterrupted from the shaft right into a curved pocket. The pocket didn't hold the neck all the way around to the fingerboard edge, so I suppose you could call it an elevated fingerboard. If I remember correctly, it was bolted on.

To fit a joint like that, could you actually wrap sandpaper around the tenon (or the pocket) and use it as a caul itself to get close, then finish up with chalk fitting?

[Eric Baack]

would it be a bad idea to use epoxy on the neck joint? We have some very nice epoxy at work and I can add some flock (chopped cotton) to provide structure in a couple of small gaps.

[David King]

Epoxies work well for this and most of them are easily reversible with heat.