This instructable should show you how to convert a melodica with a standard piano keyboard (in this case a Hohner Student 32, but it should be adaptable,) into a melodica with a uniform keyboard. If, as is probable, you don't know what that is, this link, http://squeezehead.com/uniform-keyboard/, should give you a pretty clear overview, and show you why I did it in the first place.
It would be unfair to make this instructable without referencing this,
watching the video if you intend to make a uniform keyboard melodica.
Finally, the price of making this was about £60, with £35 going on the melodica itself, and £20 on spray paint. You could probably make it for £45 or so, minus some of the aesthetic. The tools used are minimal, a hacksaw, a screwdriver set, a couple of files, super glue, and sellotape. You will need, one melodica, some square dowel, in this case 6mm by 6mm (which I got from here, https://www.amazon.co.uk/pack-30cm-Wooden-Craft-Sticks/dp/B00HNOIF4E,) and 12mm by 9mm (which I got from Homebase, you'll need a metre for 32 keys,) bluetack, 48 pennies, or coins of a similar diameter, both copper and black decent quality spray paint, (again, I suggest Homebase,) and some superglue, I used 3 grams.
Step 1: Marking, Sawing and Filing
The first thing you need to do is mark out the level of the white keys. Take a sharpie, spiky thing, or soft pencil, and mark a line around the black keys at the level of the white keys, being careful not to press on the white keys at all. Now, saw and file down to that line on the black keys, and on the white keys, remove all the material in front of the black key, so you are left with a straight white key, without any protruding edges. To do this, you will need to remove each key individually, by removing the exterior of the melodica, (once unscrewed, it should come away with ease, no need to force or saw at anything,) and carefully taking the spring off with a small pokey thing. It is incredibly important not to muddle the white keys, as they are all different, and getting them mixed up will mean they won't go back on, not without a lot of sorting out. This stage will take a while, but it is important you get all the black keys level. Also, it is the longest and hardest stage, so don't worry, it'll get easier.
Step 2: Making the Keys Equidistant
Now all the keys are all the same height, we need to make them all the same distance from each other. Thankfully, ,on the melodica, the springs are all the equidistant, however if you look carefully the springs aren't always in the centre of the key. what you need to do then is cut your 6mm by 6mm dowel into 7cm lengths, you'll need as many of them as you have keys on your melodica, so 32 for me. keep any waste material though, that'll come in useful later.
Next, we want to glue these pieces of doweling so they line up with the springs on the back of the melodica. I would recommend drawing centre lines on both the key and dowel, to make them easier to accurately line up. Also, do a quick measurement to see how much dowel you need past the end of the black keys: Remember, all the dowel should end level to the tip of the white keys, a small gap at the back of the melodica between the end of the dowel and the end of the key is irrelevant. To glue them, remove all the keys, being careful not to get them muddled up, and sellotape the dowel in position on all the black keys. Then, using the superglue, squeeze a small amount of glue where the dowel and key touch on the black keys from underneath. On the white keys, use three or so dots of superglue on the dowel, press it in position, and sellotape it together. In both cases, the sellotape acts as a clap, and you can remove it after a few minutes, once the glue is dry.
Assuming all the doweling is lined up to the screws, you should now have a row of equidistant keys.
Step 3: (Optional) a Spot of Testing
As I had 100 6mm by 6mm dice, I decided to do a spot of testing, just to see how it felt to play. I stuck down the dice with blue tack, and experimented with optimal distances. I learned that you should try to keep the keys pretty close together, as anything too close to the pivot point becomes unplayable.
Step 4: Adding These Whatever You Call Them Things
Now it is time to add the layered sorta thing. I don't know what to call them. The bits underneath the keys. I'm gonna call them squirgles for ease of reference.
To make sure you are positioning the squirgles correctly, you need to mark out where you are going to glue them. Lay out a set of pennies where the keys are going to be, so they form a tessellation, and draw around them. Then, assemble the squirgles. Firstly, each spot gets 12mm long slice of 12mm by 9mm dowel glued so that it is 12mm high and 9mm wide. All the furthest back squirgles get another 12mm by 9mm slice glued on top, and the ones in the middle are raised by 6mm using that 6mm by 6mm dowel left over from later.
Once all the squirgles are glued on correctly, use blue tack to fix the pennies on, and test each key. It is likely you will have to reposition some keys and file away some edges with a needle file, just to stop two notes sounding when you press one button.
Step 5: (Optional) Aesthetic
Get a can or two of spray paint in a cool colour. I recommend asking an assistant for a can of tartan spray paint, as that would look really cool. Failing that, glow in the dark paint or something cool like that.
Cover everything in a two mile radius in protective newspaper, a few pages think, and open every door and window in the house. Then, take all the keys off, being careful not to muddle them, and lay them out, along with the cover, and the pipe thing. Spray them with your awesome looking paint, and let them dry, for about 24 hours. Then, turn the keys over, and spray anything you have missed. Leave for another year or so. You could also spray paint your pennies, if you wanted to, but I didn't, as I went for a copper and black colour scheme. Be very careful all the while not to spray paint the reeds, that would be a bad idea.
Now put it all back together again.
Step 6: Final Touches, Sticking on the Pennies
First stick them all back on with blue tack, and make sure there are no complications. Now I have just left it there, but if you wanted you could stick them on with super glue. One reason just to blue tack them on is that they are easier to replace with new shiny ones, but they will come off more often.
Ta-da! Please don't hesitate to ask if you have any questions, and remember, this is only a rough guide.