Assembly of a Hohner 270 with the Blowyourbrassoff.com replacement comb by Chris Reynolds www.blowyourbrassoff.com 2008
This is meant to be an instruction sheet to aid in the assembly of a Hohner 270 chromatic harp using one of my replacement combs. I will try and show pictures of each of the steps in the process as well as explain how it is that I assemble one of these harps using the molded comb. Above is a picture of how the comb will arrive to you. The comb is pre-drilled and comes with the necessary screws to attach the reedplates and coverplates. The coverplates are held on by individual screws rather than just two screws that pass all the way through the comb. This will allow you to remove just one coverplate while working on the harp and providing extra protection to the reeds you aren't working on. The comb is also shipped slightly oversized, which is done to allow the builder to finish the comb down to a nice fit with the reedplates during assembly. The first step in the process is to make sure the comb is nice and flat. The best way to achieve this is to take a hard flat surface such as a piece of granite or a piece of glass and using some spray adhesive stick some 220 grit wet/dry emry cloth to the surface. This will let you sand the top or bottom surface of the comb against a nice flat surface. Use a straight edge to check the surface frequently as you sand to make sure that you are getting the surface flat. I use a piece of precision ground steel and lay the comb on it and hold it to the light so I can see if the surface is flat or has gaps where I can see light. After you're satisfied that you have the comb flat on both sides it's time to move onto the reedplates.
The first thing I do to each reedplate is enlarge the coverplate screw holes. I open them up with a 3/16 drill bit. I do this because I like to have adjustability in my parts. When I go to assemble the harp I don't want the screws holding it together to shift the parts around, so I find that making the holes larger than they need to be gives me the ability to move the parts around a bit.
Next the five nail holes along the back of the reedplate are opened up with a 3/32 drill bit. This will allow the plate to be positioned without the screws interfering with it's position. I do this to both plates.
After all the holes have been enlarged I take a countersink and debur the edges of the holes so that there won't be a burr on the edges to interfere with the mating of the comb and reedplates.
When you enlarge the holes on the top reedplate you may still have a couple of holes that aren't perfectly lined up. Don't panic. What you'll need to do is to elongate the hole slightly to allow the screw to enter the comb without binding on the reedplate.
A small jewlers file can be used to elongate the hole slightly and takes very little effort. In fact I would recommend being cautious when doing this as it's quite easy to file the hole out more than what is needed. Next we'll start assembling the comb with the reedplates so that the ends and back of the comb can be finished down to match the reedplates.
To start assembling the harp I put the comb front down on a precision ground piece of steel. It's actually a precision ground parallel that I use on the milling machine to make sure parts are aligned. I use this so that I can make sure the front of the comb and the front of the reedplate are lined up. I snug up each screw being careful not to move the reedplate. Then I'll check it by looking at the front to make sure that I did get the two aligned and then move on to the bottom reedplate. At this time you need to drill the spring retaining pin hole through the comb with a #30 drill bit. You need to make sure that this hole is drilled straight as the pin might bind in the hole if you don't. After I'm satisfied with the location of the reedplates it's time to sand the back and ends of the comb down to match the reedplates. I do this on a belt sander but if you don't have one another way of doing it is to use spray adhesive to stick your sandpaper down to a hard flat surface and then work the comb back and forth by hand. I'm sure you're wondering why I leave the combs oversize in the first place. Well I always try and put a lot of emphasis on fit and finish when I'm building a harp. So I usually leave a little extra material that I can finish down by hand ensuring that I get a really good fit. This is most likely the step that is going to turn people off from the project but it shouldn't, just think of it as the point where you really get to put in some time making it just right.
After the comb has been brought down on the belt sander, or by whatever means you choose, it's time to do a bit of hand sanding. I'm starting off here with 500 grit and after I'm satisfied with the way the surface is looking I'll move on to 1200 grit. After that it's on to the buffer to get the comb smoothed out even more and put a gloss to it.
Here you can see I'm using a loose buffing wheel and Scratch Out by Kit. I have found this to be a really good buffing compound on these combs as it's meant to be a scratch remover for plastics. If you are going to use a buffing wheel to polish the edge of your comb I would advise you to use a loose buffing wheel such as this as it won't be to aggressive when buffing. It doesn't take much and if you've taken your time with sanding you won't need to do much buffing at all.
Here are the parts to my old 270 ready to be assembled. I took the time while I had it apart to buff the mouthpiece and coverplates as well as the slide and channel surfaces to make sure they were free of gunk and nicely polished. I then sprayed a little simple green on them and scrubbed them with a toothbrush to make sure they were good and clean. I then washed them with dishsoap to make sure all the simple green was cleaned off. What is left is a nice clean shiny part ready for use. To assemble the harp I start with the reedplates. I assemble them using the flat surface as before to make sure they are positioned where I want and that they are even with the front of the comb. Then I move on to the mouthpiece and install it. I'm assuming that if you're taking on this project you really don't need to be told how to disassemble your harp and then reassemble it. The original wood screws for the mouthpiece work just fine on this comb and will thread themselves into the pilot holes easily enough. When you are ready to install the coverplates use a 1/16 dill bit and drill the four coverplate support post holes in the comb. You can then just push the support posts into these holes and when the coverplates are installed the pins will stay nice and secure. That's about it. For those who don't have the tools, workspace, or desire to assemble the harp themselves I will assemble it for them for $25.
The finished harp