How can I make a very small slit in a piece of wood? The slit needs to be .5mm high, 2.25mm wide, and 6mm deep.
This is for a jack in a harpsichord, I’m replacing all the tongues to take Derlin plectra instead of leather. The tongue itself I’m making from basswood, first roughly whittling it, then using sandpaper and a pair of calipers until it’s just right to fit. It’s tedious but doable. I’ve yet to figure out a way to cut the slit at the top of it to insert the plectrum in.
I tried an Xacto knife, but can only use the tip (the rest is too thick) and it’s nearly impossible to get a clean slit all the way though. I tried drilling a line of small holes, but my smallest drill bit is 1mm and the slit needs to be half that.
(Why don’t I just buy new jacks? The harpsichord is 80 years old and nothing in it is of standard sizes. Everything expected to work with what’s already there has to be custom made. Word of advice to anyone thinking about taking up the harpsichord: buy a brand new one out of the box and have a professional assemble it for you.)
It looks to me like you want a narrow slot on the end of a stick of wood, the sort of thing you’d get if you took a hacksaw to the end of a 2X4, but smaller.
One of these 0.3 mm abrasive disks, and a moto-tool might do the job for you.
I’m having trouble visualizing what you want. But if you are trying to put the slit at the end of a piece of wood, the very thinnest scrollsaw blade I can find is 0.02 inches which is darn close to .5 mm (1 mm == 0.03937 inches).
Your best bet would probably be to get some very fine surplus carbide bits (e.g. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=34640) and use them in Dremel tool. They start at #80 which I think is just over 1/4 mm. Drilling ounds kind of tedious though, so you might look for a mill or burr in a similar width.
Or perhaps purchase smaller drill bits? Here’s a hobby page where you can get a set of small metric bits, or just get a #76 bit (which is 1/2mm, near enough) with a pin vise.
You need to make what are essentiually tiny mortises. I don’t think there is a good way to do them directly without a lot of hand work. If you’re making the part from scratch I’d start by splitting the piece on a table saw. Make the slots on the cut face of one of the halves then glue it back together.
I wasn’t clear in my first post, the slit isn’t in the end of the piece of wood, but inside it (at the end). That’s why I first thought of drilling it out.
To illustrate what I’m talking about, here’s a drawing of what the tongue should look like (not to scale, but reasonably proportioned):
I will look at those small drill bits linked to. What is a pin vice? Is it like a little screwdriver you can put small drill bits on?
Making it in two pieces might work. I’m only worried about the joint, since the plectrum is what plucks the string. It isn’t much force, but it is repeated. Would there be any risk of the glue failing and the top snapping off?
Go to a hobby store that carries lots of model-airplane stuff. Buy a control surface hinge slotting kit. This will have a couple of special blades for an exacto knife handle that will allow you to make thin, deep, slots.
Roughly how large is the piece of wood in your drawing? A properly glued joint should be extremely strong however precise gluing of tiny bits of wood could be very difficult at best.
My first thought was to use something like a Dremel with an extremely fine carbide bit (like those Harbor Freight ones) and a router base. I assume that you don’t want to freehand the cut so build a little frame that the router base sits in which only allows the tool to move in a straight line exactly as long as the slot. Set the bit to the depth you want and have steady hands. Make sure that everything is clamped so it can’t move around, for a cut that small you don’t have any wiggle room.
If you don’t have a Dremel you can probably do the same thing on a good drill press, just chuck the bit in (check your runout first), fix the depth and build some stops onto the drill press table so that your piece of wood can only move enough to let the bit cut the slot that you want.
My Dremel has arouter attachment, and some very small cutty things (sorry, I fly by the seat of my pants, so I don’t know the names) The router bits are very spendy, but it sounds like your project is worth the price, maybe.
Unless I am mistaken that is a through mortise (as opposed to a blind mortise.)
Gorilla Glue is allegedly the best product on the market. It is a bit pricey at ~$5/oz. Cut the ‘gain’ in one portion and the other is flat. Apply Gorrila Glue per directions, to the part with the gain and clamp together. Should result in a perfect part if done carefully.