Profiling

[Terry McGee]

A question that occurred to me as I was plotting the widths of David's reeds is how did they manage to cut reeds to fit these slots so accurately? I've done a lot of sheet metal work over the years, predominantly in association with custom research electronics equipment. My experience with cutting metals on guillotines and shears is that it's pretty hit and miss because of creep, and you end up with distorted strips - usually with a twist, and often with a compressed and sloping edge. Not my ideal starting point for a precision end product! And we mostly worked in aluminium, brass, copper and mild steel, while the steel for reeds is much harder.

 

Now, I imagine there's a fair amount of filing in the final fitting, but obviously one would like to get pretty close from the start. So, what's the trick?

 

Terry

[Terry McGee]

Just bumping the question above back into view. Perhaps I'm getting into trade secret department here? Or is it so well known (to everyone other than moi) that it's embarrassing!?

 

Alternate form of question - do we know how the period makers used to do it?

 

Terry

[Chris Ghent]

There are only three reedmakers who post here consistently and none of us is too reticent. I think there are as many methods of achieving a good clearance as there are makers.

 

Historically frames were punched out, usually in two steps, the frame blank in one and then the window in the frame in the next. Diesets are remarkably consistent. However it is very expensive to setup diesets to get two components (in this case frame and tongue) to fit together with around 1thou (.025mm) clearance. One way around this is to use, as many classic period makers did, a tapered reed. If the window in the frame and the reed blank have the same tapering angle then the blank only needs to be advanced until the side clearance is right and then the narrow end can be cut off to fit.

 

The advent of surface grinders changed things somewhat. You can see one being used in the Pathe newsreel. There are two ways to use one, to create the profile and to create the window/tongue clearance. For the later you can stack a bunch of reeds on their side and adjust their width to within a few tenths of a thou (a few .0025mm). This would typically be used to create a parallel sided reed. If your punched frames are consistent then creating a bunch of close fitted reeds is within grasp.

 

More modern technology is expensive. Wire EDM is probably the weapon of choice, and could cut both frame and tongue to fit very closely.

 

Reading back I see I have given the impression it is easy with the right process. While I have no experience of EDM I suspect it is the same as the others in one respect; none of these methods is totally easy. They come down to a concentration of intent and a lot of operator skill.

 

It can be done with no machinery at all, I can think of two modern era makers who made/make their frames with a jewellers saw and tongues with a guillotine and files.

[Terry McGee]

Thanks Chris.

 

I guess I'm still trying to get a handle on how hard the steel in these reeds is. For example, I use a lot of 1mm thick stainless steel strip, cut up into very short lengths, in my flutes. These pieces live in the slots where the keys pivot, and provide a smooth and hard surface for the tip of the spring to bear on. The period makers used blued spring steel, but it ultimately rusts, so I went with stainless. I cut the strips with a large bench shear. Now stainless is pretty tough stuff, and I reckon the cutting edges on the shear are showing the worse for wear. But I'd guess that reed steel is harder again, and I wondered how long a bench shear would last cutting that sort of stuff. Or is the reed steel not as hard as I imagine? IF I took to it with tinsnips, how would I fare?

 

Terry

[David Hornett]

Thank you Chris. My problem was cutting spring steel without a shear, but here is a rather fast technique that shears leaving very minimal filing that came to one evening while watching a rather boring weather report:

 

 

1 Go to the Micromark site and purchase yourself a 'Metal Forming plier' that shapes squares (ie right angle bends), they form part of a set of four pliers, I don't know if you can buy them independently.

 

2. Get a carbide scribe, fine tip.

 

3. Get the .40, .50 .82 mm blue tempered steel (I am using clock springs)

 

4. Cut into 5 - 6 inch lengths, I use hand shears.

 

5. Scribe a line slot width in the direction of the rolled steel, (ie the length of the clock spring) Make 3 heavy passes with the scribe.

 

6. Place pliers so the single centre tooth is precisely over the scribed line.

 

7. Softly squeeze, the steel will shear for three inches perfectly straight without damage.

 

8. Turn around and do the same from the other end and you will have a 6 inch length

 

9. File strip to desired width (I use a filing jig that takes strips) Cut to reed shoe requirements with hand shears or bend and snap if too thick along another scribed line, and profile the reed (I have made an adjustable profiling jig for this based on Terry's research charts)

 

10. (widths when sheared + or - .05mm.)

 

There we have it. In 10 minutes I can cut 10/20, 5 - 6 inch long flat (entirely uncurled, except for the natural clock spring curve) lengths

 

Below are the sheared lengths, shear and the clock spring (.45mm) from which they came, alongside the Micromark catalogue page. I hope this may help someone out there

 

David

 

 

[Chris Ghent]

Wish I had known of this when I was using a shear. Does it work if you scribe on a diagonal, that is, not parallel to the rolled grain of the steel..?

[David Hornett]

Chris,

 

Yes and no. The shearing processed described won't shear below .45cm, the steel distorts and rips. (The steel in the picture is .45cm, I made a mistake when I said .40cm, sorry). Unfortunately I have no more clock spring to try, I got so carried away the other day that I cut about 60 lengths and used it all: but I did slip and scribe one piece at a slight diagonal, pictured, the end fractured as you can see, so I suspect it will, but is more difficult. The trick to the pliers is that as the steel shears it slips between the centre toot and the two side teeth, the acute angle coupled with the steel being forced apart causes the shear, on the thinner steel the pliers punch a hole through it and rip it. Sorry i can be of no more help: but on 45mm steel with the grain it was miraculous.

 

I now wonder if the .48cm steel used in the reeds Terry and I measured, no thinner, was because it was too hard to shear straight at smaller thicknesses??

 

PS: the concertinas I am making have 'square reeds' like the Jones, ie parallel sides.

 

David

[Geoffrey Crabb]

Just bumping the question above back into view. Perhaps I'm getting into trade secret department here? Or is it so well known (to everyone other than moi) that it's embarrassing!?

 

Alternate form of question - do we know how the period makers used to do it?

 

Terry

 

Well Terry, I could say, That's for me and others to know and you to find out.

 

But seriously, I can only offer the Crabb method which was successfully used throughout the existence of the firm and which I have continued to use on the odd occasion..

The attached may be of interest:

 

 

 

Geoffrey

[Terry McGee]

Heh heh, Geoffrey, and now that I know, I suppose you're going have to kill me? Ah, well, such is life.

 

Thanks heaps for your notes - there's plenty there for me to think through.

 

Turning the stock over to avoid having the rounded edges on the diagonal corners is clever!

 

And thanks Chris and David for your explanations of other approaches.

 

I will fall quite for a while while I digest all this!

 

Terry

[David Hornett]

Thank you Geoffrey, certainly seems a much more sensible method than scribe fracture shearing AND I have a nice little Norton No1 too..

 

David

[alex_holden]

I have just finished building a reed tongue shear tool based on Geoffrey's description, except that it's fitted to a toggle press rather than a fly press:

https://www.holdenconcertinas.com/?p=704

Edited September 29, 2016 by alex_holden

[Henrik Müller]

I have just finished building a reed tongue shear tool based on Geoffrey's description, except that it's fitted to a toggle press rather than a fly press:https://www.holdenconcertinas.com/?p=704

Very impressive, Alex, very neat! Has certainly kicked off some thinking here...

/Henrik

[alex_holden]

Thanks Henrik!

[David Hornett]

Remarkable! I use an old paper cutter with high speed steel blades and rare earth magnets to set the reed width by holding the steel sheet: very cumbersome, I can't use the whole sheet width ('cause of the magnets holding down the edge) and it's followed with a bit of filing to size. I so wish I had seen your invention first.

 

David

[alex_holden]

I must admit I haven't managed to dial the fence in precisely enough to avoid filing altogether, but it's much more predictable than doing it by eye with a bench shear.

 

What sort of paper cutter do you have that can shear spring steel? I could do with one strong enough to cut the bellows card stock: mine chokes on more than about four sheets of paper.

[David Hornett]

It is an old toggle levered cutter, made from cast alloy, used for heavy card and sheetmetal. It cuts .8mm tempered steel into 6 inch strips, and .45mm (and thinner) into foot long strips. I could send a photo if you wish but I have never seen another. I still have to file a goodly amount too -- the thicker metal (.8mm) also gets stress fractures on the edge from the pressure of the blade passing, so I leave enough to file these out.

 

I cut my bellows card with a 12 TPI bi-metal blade band saw into long strips, clamp all the strips together (18 all up) and run the electric planer over them, remove the outer cards on both sides, and there we have the cards all the same width.

 

David

[Chris Ghent]

My recollection is the stress fractures come from the blades being too sharp, a less pointed shape on the blade shears the steel in a way that fractures rather than being cut. If you see a good shear cut it will be something like 1/3rd cut and 2/3rds fractured. The bench shear I used at first, designed for working on bandsaw blades I think, created tiny crescent shaped fractures all the time. I would think I had removed them by filing but they would have long invisible tails in the steel and the reeds would fracture in use.

[David Hornett]

Thank you Chris,

 

I think I am being a little overcareful with the thicker reeds, they peel off the cutter with a more abrasive side to the cut than the thinner steel, so although I cannot see the dimpling you mention I leave enough material to remove just in case.

 

Are you going to Nariel this year? We shall be there, hopefully in the usual spot near the river.

 

David.