Reed Shoe Thickness

[David Hornett]

Hi,

 

Has anyone out there in concertina land experimented with shoe thickness. My shoes are currently 2mm, but if I made them say 1.5mm would the tone change, possibly negating the need to undercut the reed, at least to the same degree? I could do some tests, but hopefully someone has beaten me to it.

 

All the best

 

David

[Dana Johnson]

I've done the experiments. .062" ( about 1.5mm) works down to about C3, but needs to be a hard or hard rolled alloy to keep from bending or stripping threads. I use C35300 hard engraver's brass, C36000 would also be a good one if a hard temper. Some brasses are designed for ductility or malleability and those need to be thicker for structural reasons. ( as would Aluminum alloys. ). Below C3 however, the reeds don't spend proportionally enough time in thin reed shoes to gain their full power. I go to .093" below that. High reeds could use thinner stock, but then the tiny clamp screws can bend it much more than you'd think, so .062" is about the lower limit.

Low notes get longer fast, so you may need even more thickness to maintain power below C2. Bass accordion reeds have window depths upwards of .375". Wheatstone and other old reeds were partially swaged or forged in the punching process and used relatively soft brass. The reeds from my old Duet were .080" for the whole range. They would have been too bendable any thinner than that.

Dana

[David Hornett]

Thank you Dana. Why I ask is because I have had my lever posts cut from titanium, with pivot holes and a small hole in the base for the spring foot, rather than nesting the springs in the wood (The last 4 instruments I stamped them out of nickle silver rod, but decided a weight reduction would be nice, so titanium) With the left over 1.62mm metal I had 5 shoes cut in each of my eleven shoe sizes, just enough for a 3 row with a few big 2mm brass reeds.

 

I have made a little milling jig to cut the rebate taper on the sides to slip into the shoe plate (I made it for the brass shoes and it works just fine on the titanium too) but I very much doubt any file can touch the work hardened reed slots, I have tried and it is hard work, hence my question, which can be read, "Should I bother?. So, thank you for your answer.

 

PS: The titanium is fractionally under half the weight of the same note in half hard brass, and I notice that working the brass with the milling jig to grind the side tapers, noticeably tempers it to a rather hard substance.

 

 

David

[Dana Johnson]

Titanium is an interesting metal to work with, but should be fine for reed shoes. While it's strength is fairly high, it is much more flexible than steel, more like brass, but it's elastic limit is much higher so there is little risk of permanent deformation. OTH while it usually machines well, as you say, it work hardens fast. Light cuts need really sharp tools ( and files ). I don't know how you cut your windows, but the work hardening doesn't extend that deep. If you want a good working set of reeds. ( and given the effort required to make them in the first place, you should) you will have to put in the extra effort the titanium requires. The back draft or relief angle in the window is very important. In a concertina, it essentially equalizes the playing pressure required to reach a given volume. Without it the reeds will get progressively more difficult to play as you go up the scale and won't have much dynamic range.. High reeds require more draft angle than lower ones. I don't know if this is an acoustic phenomenon, or simply compensation for the shoe thickness not scaling with Reed length. Whatever the case, it will make the difference between a poor instrument and a good one.( so will a lot of other things, but at least get this one right ). The other biggies are close fitting reeds, ( no more than .0015" gap on either side ) and good choice of woods for Reed and action pans. ( these have a large influence on both tone and responsiveness ). You mention a jig to cut the dovetail bevel on the shoe. It is important that the shoe sides have a "waist" and are not dead straight. This is only a thousandth of an inch or so, but helps reduce the pinching of the reed when the dovetail slot expands with humidity. The Reed shoe makes firm contact at the non window area at the tip and heel of the reed primarily. ( it blends, not an abrupt thing ).

On older concertinas, the windows were punched out then broached to size. In the punching process, the sides of the Reed shoe bow out slightly to get away from the punch as it forces its way through the metal. It meets with the wall of the die where the dovetail is formed When the punch is withdrawn, the sides of the shoe return, leaving the sides of the shoe slightly bowed in. With milled or wire EDM cut windows, the waist is not automatically created and you have to find a different way to create it. If your concertina won't see much humidity change this is less of an issue, but dry winters and humid summers will give you a lot of grief without it.

[David Hornett]

Thank you Dana,

 

The reed shoes are lazer cut, and so the cut edges are work hardened, but following your advice I'll undercut these windows, as I have already with the brass reeds for the other instruments.

 

I have managed to get the tongue clearance on my others down to between .03 and .04mm, although the profile has caused some headaches, seems that G5 have objections to it, the only reeds that have broken after 10 hours or so are the G5s (3 of them), so I have taken to reducing the shoe lengths for these, so far seems to have worked.

 

Yes the crimping in the pans may cause some problems over time, however I am hoping that my slightly wider frames and the pans being made from the very oily huon pine will negate this.

 

The milling jig is a dremel 3000 with a tungsten carbide mill bit laid on its side. The vice and carriage are fitted to lineal bearings. The reed is crimped in a 7degree angled vice and adjusted against a gate to get the cutter parallel and after a couple of passes the sides have been cut, can whip through 78 reeds in about an hour. Took me longer to make the mill than the concertina. I could mill the windows on the larger shoes with the same jig, but it all becomes so fiddly that it has been much quicker to file them.

 

Again, thank you so much for your help.

 

David

[Dana Johnson]

My G5 reeds are 18.67mm. I use that length through A#5. I could see problems with anything longer than that. Oddly, out of sixty plus instruments all using the same profile, I had one that I had to replace 2 out of 3 of the G5's and one of the A5's. None of the other instruments have given any difficulty. I asked for the bad reeds back so I could see where they failed, but they were never returned.. It hadn't happened before or since and some of the instruments are nearly 20 years old and played every day.

The steel I used at the time tended to crenelate when sheared and it is possible that micro cracks formed at the base of one of the battlements. This happens when the metal switches fracture sides from the bottom to the top during the cut. Since the clearance for a clean cut is both material hardness and thickness dependent I wouldn't be surprised if one of the stock thicknesses fell just at the wrong place. High shear angles at the cut can cause cracking perpendicular ( well little curved fractures ) to the cut. Any of which would be death to a reed.

Your side bevel jig sounds cool. Could you post a picture? Wider frames in titanium would help but it is amazing the force expanding wood can generate. The Huon Pine probably has a fair bit less expansion compared to English Sycamore. Not familiar with it, but soft woods are mostly better than hardwoods in this regard once they have lost their initial moisture. How is it for tone in the instrument?

I saw a set of water jet cut reed shoes once that came out very nice. Definite advantage in lack of melting in the cut over both laser and wire EDM . I think laser can do a finer kerf, but if the result is difficult filing, the small amount extra in the corners would be worth it in saved effort and files.

Dana

[David Hornett]

Thankyou Dana. My G5s are 17mm. I think it is just poor profiling and I am reforming my wicked ways. I tried to upload three JPGs, but too big so just one at reduced quality. I shall attempt to find your email address and send them that way.

 

All the best

 

DAvid