Veneer for harp soundbox.

[tom42cook]

harmonic curve........absolutely interested to know more tom42cook!!!!

G'day Szczepan4069
I was hoping no one would ask – I’m such a slow typer I thought I’d offer and then not have to do it.
The curve of a harp neck is one of the weakest parts of the design. Cut from a solid board there is so much run out that it will crack under tension about a hand span or less from the shoulder. Two options exist to counter this:
1 re enforce the underside of the neck with carbon fibre, splines or brass, shown here: http://www.sligoharps.com/8book.pdf and here (under the construction link):http://www.cunninghamharps.com/ or
2 for the entire neck: use laminated piano pin block, or laminate your own using a really good glue with absolutely no creep- probably one of the epoxy type.
The shape of the curve varies from maker to maker and is there to give the optimum string length for each note. This is dependent on string material and desired tension – folk harps having a lower tension generally than classical pedal harps and lever harps designed as a stepping stone to pedal harps.
Again, if you have a harp to copy then the job is easy. If not, decide on tension and string material and determine your string length for each note (keeping in mind lever harpists prefer to tune to open E flat). I’ve never used one, but there a few string length calculators on the net that should help.
Then start drawing (I won’t lecture an architect on how to do that!). The string rib and the bridge pin define the vibrating length, the rib will be something like 66deg from horizontal (when harp is resting on all 4 feet, not playing position) and the string about 33deg from the rib. After that you just need 36 parallel lines evenly* spaced, at 33deg, measure off the length for each note to find the ideal or theoretical position for the bridge pin and join the dots with an attractive curve. To complicate matters the string spacings vary between harps and across the range of the instrument – bass end having a wider spacing than the treble. Some also start to fan out the highest strings, ie progressively less than 33deg to the rib. You’ll also find that when you draw your harmonic curve some bridge pin positions fall above or below the line – this is where the time honoured tradition of FUDGING is required. Now place the tuning pin positions, from the player’s p.o.v. each string touches the far side of the bridge pin and winds on to the near side of the tuning pin (this shot section of non sounding string is sometimes called the string reserve) to keep the string firmly against the bridge, build in a 10 -15 deg deflection towards the player. Type of lever used can influence how much space you need between bridge and tuning pin. You should now have two pretty curves that will have holes drilled all along them eventually. Draw in two more (sort of) parallel lines above and below to define the top and bottom of the neck. Tuning pins can go quite close to the top edge but leave a lot of wood under the bridges for strength and space for levers.
All of this is a great deal easier to see on a real live harp than it is to describe in words so again I’d advise you to cheat and copy a good existing harp.
If you’re not falling asleep at the end of all that check out this link for sound board design:http://www.sligoharps.com/5book.pdf. He talks a bit about solid spruce sound boards with veneer over the top, a technique used on many brands.
This bloke really seems to know his stuff, it’s worth spending some time to see the whole site.
I hope thats understandable, I think I will rest my typing finger now.
Tom

[ckngumbo]

What an interesting thread!
Thanks

[szczepan4069]

tom,
fabulous!...thanks for the desriptions of the neck and the "science" of the harmonic curve. i sort of thought there was some science... some of the information i found on the web also suggested a range (string length) within which one needs to stay ....depending also on which type of string one chooses to use. I have also downloaded all those "book" pdf files from the website you suggested ...sligoharps.
they are a good read....and a good resource to folloas a step-by step through the sequences of building a harp.
i think the next thing i will start doing is drawing up a design for a harp. as you quite rightly pointed out...hahahaha.....i do a little bit of drawing already...
i do have the added tools of perhaps doing a quick 3-d model in "sketchup". but for now i will perhaps put together a quick sketch and post it on here for your thoughs in the next couple of days......it will be rough ..but perhaps i'll use it as a design in progress!!??

again, regards and thanks for your input....

[tom42cook]

i think the next thing i will start doing is drawing up a design for a harp. as you quite rightly pointed out...hahahaha.....i do a little bit of drawing already...
i do have the added tools of perhaps doing a quick 3-d model in "sketchup". but for now i will perhaps put together a quick sketch and post it on here for your thoughs in the next couple of days
again, regards and thanks for your input....

I shall have to down load sketch up - I'd be very pleased to see some drawings.
If your daughter is thinking of the classical side of harping, might I suggest using concert tension and spacing? It supposedly makes transition to a pedal harp eaiser later on. My other half teaches on a pedal harp, if you're keen I could do some measurements for you before you put pen to paper.
I might take a while though. And I don't do imperial
Tom

[szczepan4069]

hi tom,
thats the way she was looking to head......so any advice on concert tension and spacing would be greatly appreciated....i'll start and draw something up............get this ball rolling......nothing like tinkering with ideas!!!
cheers
szczepan

I shall have to down load sketch up - I'd be very pleased to see some drawings.
If your daughter is thinking of the classical side of harping, might I suggest using concert tension and spacing? It supposedly makes transition to a pedal harp eaiser later on. My other half teaches on an Aoyama Vega (look it up) if you're keen I could do some measurements for you before you put pen to paper.
I might take a while though. And I don't do imperial
Tom

[tom42cook]

I've dug up a pic If you are still interested Szczepan4069.
After nearly 3 years it has developed a crack in the neck but then I didn't reinforce the underside during building - I thought the laminations would be enough but then I got some glue creep... so now all the strings are off for a tedious repair.
Tom

[szczepan4069]

Tom,
many thanks for the image. its a beautiful piece of work. there are a number of aspects about this particular harp i like. i like the overall simplicity of the design. i like the curved back of the soundbox - is that fully laminated at the back or is it segmented staves that have been formed and sanded down?
cheers
szcz

[tom42cook]

Its 6.5mm 4 plylaminated myself. I couldn't get bending ply in rocky so I tried 3mm luan. The first time it took the bend well but I scrapped it for some other now long forgotten reason. The second time using ply from the same board it snapped at the narrow end, so the third time I layed up single veneers on a construction foam male mold. Next time I will try harder to get bending ply sent up.
Tom

[szczepan4069]

i am going to head down to wood world in the next two weeks......inland on the gold coast...see what the will have in the way of veneer. what was the thickness of the soundboard you built?...and material??

[tom42cook]

The sound board is compund tapered, 3mm at the centre top (less at the edges) 9mm at the bass end (less at the edges). I used reclaimed spruce from an old piano so its had something like 50 years to season. Then hide glue and silver ash veneer (vertical) over the top.

[kamusur]

Great stuff Tom


Steve

[szczepan4069]

been inundated with project work...will get to the design of the harp in the next few days....hopefully

[tom42cook]

been inundated with project work...will get to the design of the harp in the next few days....hopefully

Another example of work interfering with life eh?
Tom

[szczepan4069]

Another example of work interfering with life eh?
Tom

its always like that....as soon as you get the enthusiasm levels up......the material, the workshop organised mind on the job.......work seems to interfere.....

[szczepan4069]

anyway.............continuing finally on my merry way......i bought a stick of sitka spruce down on the gold coast.....and also put together a drum sander that i know i will need shortly after starting the sound box for the harp. here are a couple pics of the drum sander. Probably not the best place to stick the pics - but considering its part of the process i'm following...a quick description of the handiwork shouldnt be too problematic for the admin team here....

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....its a start....designing the harp has started will get those images up once i get back from china end next week....