Saturday, 28 July 2007

Making my own T-beam

As mentioned earlier, I've had an unexpected hard time finding a suitable T-beam. There are lots of them available, but none wide enough for me to make holes for the pickups without intersecting the top flange completely.

For now, I have given up on finding a T-beam, and I will be making my own. It will consist of a 120 mm (4.7") wide and 10 mm (0.4") thick flat bar of AlMgSi0,5, also known as 6063 Aluminium, which will act as the top flange of the t-beam. The vertical part of the T will be a 30 x 10 mm (1.2" x 0.4") AlZnMgCu 1,5 (aka 7075 aluminium).

6063 is a fairly soft aluminium which should make it fairly easy to shape the neck, make holes for the pickups and make a recess where the bridge will be (otherwise the bridge will be too high). I've heard that it is so soft that it can be difficult and "gummy" to shape, but I could't get a piece of 6061 Aluminium, which was my preferred alloy. We shall see how much of a problem it'll pose.

7075, on the other hand, is very hard and strong, which is nice because the vertical flange will have to withstand the pull of the strings. It will be more difficult to drill, saw and file, but fortunately, the shaping needed on this bar is much simpler than on the top one.



I plan to join the two bars with screws and two component epoxy adhesive.

I ordered the bars yesterday, so now it should only be a matter of days before I can get going. All in all, I'm quite satisfied with the solution. I'd have preferred a "real" T-beam, but this solution allows me to have a stronger alloy where it really matters: The bottom flange.

10 comments:

drew said...

Hows it going with the Tbeam?

Alexander Gorm Øst said...

Thanks for asking. There hasn't been much progress lately. I've had many other things to do apart from building the guitar.

The process slowed to a halt when I was about to make a full scale drawing of the guitar and had to decide the curves of the "shoulders" of the top flange... the area where the neck becomes the body. Not because that particular area was anything special, but that's about how far I went until other, more pressing tasks arrived.

I've been on paternal leave for the last nine months, and am about to start working again. Which leaves less time for the guitar. On the other hand: My brother, who's a skilled carpenter has returned to Denmark (which is where I live) and has promised to lend a hand. I expect that to speed things up quite a bit.

Still, I don't expect anything playable to be ready until next spring. I don't mind. Metalworking is new to me, and I like the process to be slow, so I have time to consider alternative approaches to the details.

I think I'll turn this comment into a status report one of the coming days... just to let people know, that nothing much has happened.

metalcarver said...

One thought about the neck, if you use wood or polymer for the back, make sure there is a little play or give in the joining/adhesive. The coefficient of thermal expansion for aluminum is much higher than wood or polymer. That is it could curve when exposed to cold or bend backwards in stage lights. Les Paul made one in the fifties (I think) and it went wacko in the stage lights.

Also thank you for the link (Metalcarver) but I made my guitars entirely on manual machines, alas no CNC although my new job is as a CNC machinist. I hope to get active again soon. You get a big attaboy for your work.

Dave

Alexander Gorm Øst said...

Hi Dave.

Thanks for the advice, and sorry for the delayed response.

I was planning on epoxy gluing the wood pieces to the back of the neck, but your advice makes me reconsider. I guess I will try screwing the wood pieces not too tightly to the back of the neck and perhaps even putting a layer of grease between. That, I imagine, will let the pieces slide relatively freely when they expand and contract. I'll have to figure out a way to allow sufficient play - and make it look and feel nice.

Alternatively, there might be some glue that'd allow the pieces to slide. ...lots of options to consider.

Learning that you use no CNC for your guitars makes me even more impressed! I've corrected the link.

/Alex

metalcarver said...

I can't remember the exact numbers but as I recall the coeff. thermal expansion for steel (strings) is about 5 times that of wood. i.e. a wood guitar strings will tighten up when cold, slack off in hot lights. The coeff. for aluminum (aluminium?) is 5 times that of steel. It wasn't planned that way but on my guitars with wood neck/alu body the effect was somewhat self cancelling. The effect of steel strings and aluminum guitar all the way to the bridge will be to make the strings slack off in cold and tighten up in hot. It will be about the same degree of change as with a wood guitar but in the opposite direction. The actual dimension change is really pretty small in either case but a solid bond (alu + wood) lengthwise is the worst case scenario. It's (alu neck/back) worth pursuing because 1) I think the tonal results will be very good and 2) I've used metal handles all my life and they suck. Wood feels so much better to the hand. The speed of sound through aluminum is faster than through steel and both are much faster than through wood. Also in wood the speed of sound is 3 times faster with the grain than across the grain.

I'm anxious to see your results. Also I'm experienced with diapers and would like to reassure you that they won't affect the final tone too much.... :)

Dave

Alexander Gorm Øst said...

Thanks again. That's a lot of relevant information. It makes me a bit concerned about my rosewood fingerboard, which i intended epoxy gluing on the top aluminium flange. Won't that flex the neck as well? Mounting it loosely as with the back of the neck isn't really an option, partly because there'd be bad transmission of vibrations to the alu part of the neck, partly because the guitar would go out of tune if the distance from bridge to nut changed without the distance between the frets changing accordingly.

I'm not that concerned with the negative effect of diapers ;-) Actually, I've bought and modified an ukulele for my daughter, so until now, she's made me work more with guitars than I'd otherwise have.

metalcarver said...

How about using the top of the T beam as the fretboard. Your fingers mostly touch the strings anyway and alu can be anodized a really nice black or any other color ( search on PK guitars) I think you could use standard frets and wood slitting tools on the aluminum.

Davde

Alexander Gorm Øst said...

Sounds like a good idea, but with my current guitar building skills, I think it is out of my league cutting fret slots. But for a future, improved version, it is really worth considering.

I did a search for PK guitars, but found nothing resembling your suggestion. Can you point me directly to the site?

/Alex

metalcarver said...

Yeah,

This is guaranteed to make your eyeballs leak out of your head...
http://www.pkselective.com/pkguitars.html

Alexander Gorm Øst said...

That really looks good. Imagine what fascinating fret markers you could make that way.