I wanted to share my process of building a wire strung Irish harp because I love this instrument and I am hoping if there is more information out there for people It might make building and playing them more accessible, one big disclaimer I am not a professional harp builder this is just a slice of how I do things as a hobbyist that will hopefully at least inspire someone to learn more on their own. I will preface this entire entry with an acknowledgement that I learned a tremendous amount from the Sligo Harp website (http://www.sligoharps.com/btlh.html) I can’t speak highly enough of the resources there. That being said, the content on that website is geared towards building a modern, gut/nylong strung lever harp, which is almost a completely different instrument from a wire strung traditional Irish harp, so this guide will focus mostly on the unique aspects of the wire harp and design/construction techniques. Again, Definitely check out the Sligo harp website if you are considering building any type of harp. Enough with the preamble, on to the content:
Design
The first part of building a harp is doing the design. Fortunately you don’t have to start from scratch if you don’t want to. The first option is to appropriate a historical design, Rick from Sligo harps mentions this in his guide but in context of a historical Irish harp there are some advantages and disadvantages
Disadvantage: there are only 17 surviving examples of Ancient Irish harps and they are all behind museum glass so good luck measuring one
Advantage: they are museum pieces so for the most part people have been studying them in great detail leading to some great information such as Laser scans and MRI tomograms.
If you want to borrow a design, check out the following resources. The historical harp society of Ireland has been collecting resources for builders for the past few years, Karen Loomis wrote an ENTIRE PhD thesis on two Irish and Scottish harps that includes aforementioned MRI scans of two very famous harps, and “the Irish and Highland Harp” by Robert Bruce Armstrong is the seminal survey of existing ancient Irish and Scottish harps at the time. the Wire strung harp website also has good information, and there are many others.
HHSI: https://www.irishharp.org/
Loomis: https://www.karenloomis.com/research
Armstrong: https://archive.org/details/musicalinstrumen0000arms
https://www.wirestrungharp.com/harps/
If you want to design your own, Then the first step is to pull out your preferred spreadsheet program and sharpen your pencils, because before you think about the structure of the instrument you have to know how long the strings are going to be
Again, I can’t recommend the Sligo harp guide enough. In fact, I follow the principles laid out in the “String Theory” article (http://www.sligoharps.com/string.html) pretty closely when designing new string regimes and new harps, just with a few tweaks unique to the Cláirseach. For the rest of this part I will procede as if you have read the above linked article and just highlight a few considerations for the Cláirseach.
...Now that you have read the string theory article, I can show you a snip of the spreadsheet I use to calculate the string lengths for my most recent harp 
there are a couple things to note
1) You will notice the strings are metal, brass, silver, and even gold have historical precedent and are one of the major differences between a modern harp and a historical Irish harp. These strings are also monofilament (i.e. just wires, not wound strings like on a cello)
- for brass I recommend using spring hard wire, often called music wire. This is often sold for instruments like dulcimers and harpsichords and is available from multiple online sources
- gold and silver are a little more tricky and I am just now experimenting with silver bass strings, stay tuned.
2) I try to stay within the bounds of plausible string lengths for historical Irish harps
3) The metallurgy of the strings becomes denser (red brass) and softer (silver) towards the bass end to compensate for the shorter length of the strings. Because the strings of the Cláirseach are metal they are already shorter than the equivalent range of gut or nylon strings.
– for a “low headed” cláirseach, there is some evidence to suggest that they would use precious metal bass strings such as silver and gold to get the same tone quality that you would from a longer bass string
- later in the history of the cláiresach “high headed” models were developed where the harmonic curve of the harp swooped upwards so that the bass strings could be made from brass rather than gold or silver
Now that you have determined the number, range, and length of the strings you can start designing the rest of the harp around that.
It pays to futz over the design for a while here. As a starting point I assume a string spacing on the sound board of between 0.75” and 1”, and a string angle between the soundboard and the strings of about 30-35 degrees and adjust from there. The angle of the strings and even the spacing between them changes from bass to treble and can be adjusted based on the aesthetics of the harp. I have learned two hard lessons but your millage may vary.
1) assume the strings will be slightly closer together than they look drawn on the page
2) you don’t have to be dogmatic about the calculated string lengths, A small change in the lenght of a string in order to reposition it better on the neck is less noticeable than a wonky tuning pin sticking way out of line because you decided it HAD to be EXACTLY 29.329” long
The actual shape of the harp is up to you, I would keep a couple design considerations in mind.
- the harp is 3 dimensional, Consider the shape and size of the soundbox as well
- the one I have built here is between 4.75” and 5” thick and tapers from 4” at the top to 14” at the bottom 
Wood selection is another dimension. This particular harp is under approximately 650lb of pressure from the strings alone, so the structural elements have to be thick enough and strong enough to withstand the pressure. However, the wood has to be thin and flexible enough to produce a strident sound quality.
- Many historical examples are made out of a willow soundbox and use other hardwoods for the neck and fore pillar.
- I have never been able to obtain Willow, I have had success with maple, walnut, and Cherry for all components of the instrument, so far I think I like maple the best.
- I use 8/4 material for the neck and pillar but The pieces don’t always stay 8/4. Between carving, decoration, the fore pillar of the most recent harp is only about 1.25” at its thinnest part but the cross section is a fat “T” and is the full 8/4” at one end. there is historical evidence that the components of the harp could be thinner I have just not done it myself.
- The sound box is traditionally one big hollowed out log of Willow. This is not practical for many builders and I piece my soundbox together with separate boards 
The soundboard itself starts as 1/2” thick, I have made soundboards that are much thinner (0.25” thick) this one is so thick just because I ended up doing some carving on the inside (more on that later)
The sides are approximately 3/8” thick and were resawn from a 5/4” board
The top and bottom blocks in the picture above need to be thick because they will take the main loads and be accepting the large mortise and tenon joints that secure the pieces of the harp together. I glue the bottom block up from several pieces. I will go into more detail on this later but for now just make sure you consider the size of the parts when laying out the strings and designing the shape.
There are many more design considerations but I think they will become evident as I outline more of the build process. for now, if you only take away one thing here it is:
Design the harp around the strings, whether you use a historical example as a guide or use the Sligo Harp article accommodate all your other design choices around the strings