CASTING REED FRAMES

[Dave Leggett]

CASTING REED FRAMES

In constructing a few instruments of my own, I had always used reclaimed Lachenal reed-frames, suitably cleaned and refined. I had been given a large quantity of these by a friend years ago and acquired more since. Many that contained damaged, missing or brass tongues could be bought very cheaply. Modern wood-saw blades have been a source for my reed-steel.

I intended to make a Baritone Anglo. As this was to be pitched a whole octave below a standard C/G and reed frames of a suitable size for the lower notes are not easily obtainable, I had to reconcile myself to making them. I reckoned on having to make 1x reed frame for 50mm tongue-length, 2 for 45mm and 6 for 40mm. I was quite happy to fret-out the 3x larger sized ones from 2mm brass sheet but the 6 at 40mm were enough in number to justify making a casting-pattern in brass and using this to 'sand-cast' them. I would be casting in a bronze alloy using Delft Clay as the casting medium. As a working jeweller, I was already set-up to produce small castings in sterling silver using this technique. I experimented with alloys and found that 75% Cu: 15% Ag: 10% Sn gives a brassy-looking alloy that melts in an achievable range, (about the same as sterling silver: ca. 850-900C) and works amenably. The castings would have to be fettled, of course but if done thoughtfully, both the dovetail bevel and the slight flaring of the slot from front to back,  included in the pattern, may be achieved as integral with the casting process.

The idea of casting reed frames may seem a bit 'academic or old-fashioned', particularly in a role where CNC machines have taken over the territory traditionally occupied by precision press-tools.

I hope that the appended images will give any explanation you might want, that I haven't included in the above text.

KEY TO IMAGES

1) Lower half of casting flask (the drag)

2) Upper half                              (the cope).

Both contain the compacted and levelled 'Delft Clay' and show the impression left by pressing the pattern - flat, top down, (with a board) into the drag. Clay has been removed to a depth of 1.5mm from the drag reed-slot using the 'hag's tooth' tool (7, below) before the cope is applied and re-compacted. Release material is talc.

3) Low 'C' reed': 50mm in length, in frame fretted from brass sheet.

4) Low 'E' reed: 45mm in length , in frame fretted from brass sheet.

5) Casting pattern for 40mm reed frame and clamp plate.

6) Low 'G' reed in bronze frame: cast using (5) as pattern.

7) The 'Hag's Tooth' tool, with tooth 2mm x 1.5mm: simply made from sheet brass.

The final images show the finished 'Baritone' with normal sized Anglo for comparison.

 

Edited June 18, 2019 by Dave Leggett
Title omitted originally!

[alex_holden]

That's very interesting Dave. I've seen a Wheatstone Bass English where at least the bottom few (very large) reed frames appeared to have been sand cast in brass.

[Chris Ghent]

I have a few cast frames here, they were done in phosphor bronze in silicone moulds for a fellow from Queensland. They are relatively easy to reed, needing little file work, and it seems a valid method to me. 

[ttonon]

8 hours ago, Dave Leggett said:

Clay has been removed to a depth of 1.5mm from the drag reed-slot using the 'hag's tooth' tool (7, below) before the cope is applied and re-compacted. 

Hi Dave, thanks for the interesting pictures and info.  What's the reason to take that sand out of the slot, is it so that metal flows more easily to fill all portions?  I assume you then have to remove the metal hymen.  I'd opt to see pics of the freshly molded piece.  Do you have an idea of the surface roughness, particularly on the sides of the slot?

 

Best regards,

Tom

[Dave Leggett]

re. CASTING REED FRAMES

Thanks for your interest, particularly Alex, Chris and Tom!

I'm not familiar with the innards of Base English instruments, Alex.

I have heard it said that some of them used Harmonium reeds, but this was probably 'mis-information'.

 

Chris - Thanks for your experience of reeding frames cast in phosphor-bronze. I suspect that the silicone moulds that you speak of were used to cast wax models of the frame pattern which were then invested with a refractory medium for casting by the lost wax process. Silicone moulds would not withstand the searing temperatures needed to cast phosphor-bronze direct. Nice application for the technique but definitely 'industrial' and not suited to the amateur!

 

Tom - I have drawn some crude diagrams,explanatory diagrams, which are appended.

Its very necessary to rake-out the compacted clay that's penetrated the 'flared' area of the slot from the front of the pattern in the drag. Without doing this, the pattern will tear the moulded clay in the drag when its shaken out, because that portion of it would be under-cut. The gap left in the united mould is made-good from the cope when the parts of the casting-flask are united and the cope re-compacted.

In answer to your query, the casting process using Delft Clay produces very smooth surfaces, but like all castings, will need some fettling or file-work refinement, particularly within the slot.

(By the way, Tom, I guarantee that no virgins were hurt during the making of these reed-frames!!)

Cheers,  Dave

 

[Jake Middleton-Metcalfe]

as a side note I like how your end plates look, presumably your own design? Nice and original take on the idea.

[Wolf Molkentin]

On 6/20/2019 at 12:33 PM, Dave Leggett said:

I have heard it said that some of them used Harmonium reeds, but this was probably 'mis-information'.

 

I‘ve heard that said re the lower sides of my Lachenal NM baritone as well - which may be true insofar they‘re quite large and of a rectangular shape. OTOH harmonium reeds are not that different from concertina reeds AFAIK, apart from size and (outer) shape...

[ttonon]

Thanks Dave, interesting process, looks like fun.  In your first photos, it looks like you don't use runners, or passages to direct the molten metal to more than one area, and to let out air.  Interesting that you don't have a problem with getting air out of the way with the gravity feed.

Regards,

Tom

[Dave Leggett]

Thanks for your comments, folks.

TOM. I've never found it necessary to incorporate anything more complicated than a single sprue to admit the molten metal at the top of the mould. If you look at the hand-written notes at the end of my 'crude diagrams' it does say that an air vent is incorporated: it was omitted from the original photograph of the mould in order not to complicate the image. As for the rest -  well, I am allowed to retain a little mystique, surely?

Cheers,  Dave