Radius Stick for Guitar Back

[zendo]

I am contemplating buying a 25 ft. radius stick from LMI but I prefer to make one. I am making a mould to make my classical guitar which requires a radius stick to calculate the dome of the back. Does anyone have the measurements for a 25" and 15" sticks? Surely they are easy to make if one has the measurements. The maths is a bit beyond me. Thanks.

[dshaker]

Google the phrase "shipwright compass" and then look for a set of instructions that make sense to you.
A shipwright's compass is a relatively easy way of drawing curves with a large radius.

[routout]

I believe there is a PDF on here some where ,printable version of dish radii.

[kiwigeo]

Markus has done all the hard work for you....see here: viewtopic.php?t=6168

[blackalex1952]

I made a shipwrights compass a while back, which I threw together in a hurry out of scrap. I soon realised that I had to make a better one with a better pin set up for the ends of the compass to run on and improved centre scribe. This takes time. I have made radius dishes and curves using a non stretching rope on a brick with the scribe at the other end, and with the same rope tied to a ceiling beam in a high shed, with a router tied to the other end. Then I found the attached .pdf files. I put them on a memory stick and took them to officeworks where they printed them out for less than a dollar. You just need to get them to print actual size.They can also be used to program a cnc machine to cut them for you, I think but not sure.

[Steve.Toscano]

I have an excel spreadsheet that calculates exactly this, for an inputted radius. The beauty of having a mate doing a phd in maths .
Send me a pm with your email if you want a copy.
If theres enough demand i will put it online.

[zendo]

I have an excel spreadsheet that calculates exactly this, for an inputted radius. The beauty of having a mate doing a phd in maths .
Send me a pm with your email if you want a copy.
If theres enough demand i will put it online.

[zendo]

I have an excel spreadsheet that calculates exactly this, for an inputted radius. The beauty of having a mate doing a phd in maths .
Send me a pm with your email if you want a copy.
If theres enough demand i will put it online.

Thanks,

I would really appreciate an email copy... [email protected]
Sorry couldn't find the PM to send this
Zendo (Robert)

[demonx]

If someone really wants a product like this, I can make them accurately on my CNC (once it's operational again), however to pay Aussie material cost and labor it would most likely work out cheaper to buy the product from LMI or Stewmac, although could be handy for variations that are not off the shelf, like for example I CNC'd myself a cutaway form to suit the LMI side bender.

Not that long ago I made a Mahogany Radius block with the persons name inlaid across the top, obviously this sort of work it'd be WAY cheaper to buy the pine version from the US!

[kiwigeo]

Not that long ago I made a Mahogany Radius block with the persons name inlaid across the top......

This guy has an issue with working out who owns the tools in his workshop??

[demonx]

Not that long ago I made a Mahogany Radius block with the persons name inlaid across the top......

This guy has an issue with working out who owns the tools in his workshop??

It was a gift for a friend. The inlay was just a personal touch, obviously not something that's needed for it to work better!

It turned out really well, best timber radius block I've ever seen! I'd post a pic but I didn't take any.

[blackalex1952]

Just to expand on this topic a little: I use an iPhone and have a free app on it called "radius calc". There are also online calculators which can be used. An interesting method for profiling the liners using a router and jig is as shown in a photograph on Michael Collin's website (Michael wrote the book Building A Selmer Maccaferri Guitar). Selmer guitars due to the pliage, have a compound edge profile where the top joins the sides.http://collinsguitar.com/first-week-of- ... ng-course/
Incidentally, Michael has built his own CNC machines (2 so far as I know) and has made double top nomex Selmeroids as well.

[auscab]

I had Radius templates made by Steve ( SIMSO ) from this forum . CNC cut in perspex . He did a great job and posted them .
From one of those I taped it to a piece of MDF and cut it over size then trimmed it perfect with a flush cutting bit with a bearing running on the perspex . You have to be careful because the spinning bearing melts the Perspex when it comes in contact until it stops spinning .
I made plenty of different sizes off the original's in MDF . I then took a off a little extra for sandpaper thickness and double sided taped sandpaper to them for the sanding of radius dishes . with 80 grit, MDF disappears pretty fast .

Rob

[Steve.Toscano]

An interesting method for profiling the liners using a router and jig is as shown in a photograph on Michael Collin's website

Considering the linings and sides can be profiled with a block plane then finished with a sanding stick in under 5 minutes, what's the point of setting up a jig and router?

[auscab]

I use this one .
http://www.1728.org/circsect.htm

Over a 500mm chord, 7620mm which is 25' converted to mm gives a segment height of 4.10mm

Over a 500mm chord, 4572 mm which is 15' converted to mm gives a segment height of 6.84mm

[blackalex1952]

felix:Considering the linings and sides can be profiled with a block plane then finished with a sanding stick in under 5 minutes, what's the point of setting up a jig and router?

I am guessing that the reason for using the jig in the photos I posted on the Selmeroid designs is due to the pliage and neck angle requirements of those particular guitars. The sides are straight, although the back and top are not parallel at the sides. The pliage and the neck angle along with the arching (because the brace curvature varies) requires this, I assume. Otherwise yes, why go to all that trouble. That is one of the reasons I posted this. To invite comments from experienced builders. Getting a perfect glueing surface on the side to plate joins also would mean that the liners can be finer, perhaps, and that there are no voids that would difficult to see with an inspection mirror, resulting with joint failure down the track. If I am correct, it may be a good method for instruments built on a solera with compound radii on the plates and high arching.I have wondered about this jig and peered at the photos....I just realised that this might have to become a separate discussion to the original question...sorry if I have taken the thread off topic.