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Lutier needs help please

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James Morse14/12/2018 15:23:43
3 forum posts
2 photos

Hello everyone, and thanks for letting me join.

I build clavichords and I have a question about cutting brass.

To make what are called tangents, I use .025" (.6mm) brass sheet from K&S. It is their #16405. That is half-hard alloy 260 ASTM B36.

The tangents are triangle-shaped pieces about 30-40mm long by between 3mm and 7mm wide at the top and 1-2mm wide at the bottom.

I want to consider cutting the pieces on a saw versus cutting them with shears because even a decent bench shear causes the metal to curl.

A friend of mine in the UK says he uses a Proxxon saw (the better one) to cut the brass, using an HSS slitter saw. He commented that even on the slowest speed, he felt the saw was still a bit too fast. He mentioned that he lubricates with oil but it is not the easiest process. It does require some type of jig or hold-down to hold the work piece, that part I can figure out, if the saw is the appropriate tool.

Here are my questions: Is this the best way to do the cuts?

What type (number of teeth, etc) blade should I use?

What speed should the saw be going (rpm)?

Will I have to lubricate?

Do you think the cheaper of the Proxxon saws would work? I have a good table saw and cutoff saw and so on, so I really don't need another woodworking saw so if the cheaper one would work, I'd prefer that.

I realize I will probably have to do some clean up of the cuts and that's ok - mainly I just want to be able to get a nice straight cut and be able to do it fairly accurately and not have the brass all mangled like shears tend to do. As part of the installation of the tangents, it is expected that some fine adjustments are done by hand, so it is not necessary at all that the tangents come off the saw "finished" but they should be at least flat and close to what they should be when done.

If there are other ways to accomplish the cuts, I would definitely want to know. Basically I just need a way to make accurate cuts on the brass sheet without distorting it.

If this post needs to go into a different part of the forum, I trust that the moderators will help me with that. I much appreciate any help.

Jim

Barrie Lever14/12/2018 19:00:20
323 forum posts
1 photos

Hello Jim

Welcome to the forum.

Have you considered getting the parts laser cut? Then you can spend a little time getting a really nice edge finish on the parts.

Regards

Barrie

Tomfilery15/12/2018 09:51:24
113 forum posts
4 photos

James,

I don't think the Proxxon saw would work well with brass that thin and, if it were me, I'd be worried about the blade grabbing the brass and throwing it back at me, or pulling my fingers into it! I don't have one of those saws, but a friend does and I've used it a number of times for cutting wooden strip. Additionally, you'd have to find a slitting saw the correct diameter and with the appropriate sized hole for mounting it (10mm IIRC).

You might be better off looking at the Proxxon Scroll saw (or similar - effectively a motorised fret saw) and using a piercing saw blade (also called a Jewellers saw).

If you need to make quite a few of the tangents (so that hand cutting is out of the question) you might be better off looking at getting a guillotine - which would be less likely to distort the material than shears.

Regards Tom

Ian P15/12/2018 10:37:37
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2179 forum posts
90 photos

Whatever method you use to make these parts (saw, guillotine, shears etc) the main difficulty will be holding the material. Cutting brass sheet into a truncated triangle shape only 1mm wide at one end does not sound like something one can do by hand and get consistent results.

If there is one tangent per key (I know nothing of stringed instruments) are they all identical in one keyboard or are they a range of sizes? Either way though having them laser cut would be ideal. You could have a whole sets made with a so that the part that gets delivered to you is like a hair comb with a tiny break off tab retaining each one.

I use a laser cutting company in the UK (but you don't say where you are) that have an automated online quoting system and its easy to see the effect on price that material type, thickness, and quantity have on the quote. Delivery is a few days later.

The laser cutting does not distort the material and the edges would probably not need any further finishing.

Ian P

Neil Wyatt15/12/2018 10:55:29
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16578 forum posts
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My inclination would be to use a cut-off blade in a rotary tool (dremel etc.) and make a jig/table for it.

A toothless blade will be less likely to snatch or distort the brass.

You can then adjust the speed for best results. I suspect in this case the best speed is determined by trial and error.

Neil

Barrie Lever15/12/2018 11:25:12
323 forum posts
1 photos

James

In the back of the ME magazine there are a few companies advertising Laser cutting.

https://laserframes.co.uk/ looks like they know what they are doing.

I am a big advocate of using the right process and technology for the current application, I am not a wild fan of laser and water jet cutting for every 2d cutting application unlike some people who are just driven by the cost per part advantages. This is despite me owning a laser cutter, although it is a Co2 type which does not cut metal.

Laser cutters dont always cut an edge that is perpendicular to the surface of the sheet material that is being cut, this usually occurs when the laser is getting towards it's max thickness cutting ability, the focused laser beam looks like an old egg timer and the most effective part of the beam is the narrowist, if the material thickness is creeping into the wider part of the beam then the perpenidcularity of the edge suffers.

Also lasers can char the edges of some materials leading to ongoing processing problems.

Water jet cutters have horrible diffusion of the jet but are good for cutting materials like armoured steel.

Having said the above, laser cutting will be great for your small parts.

Best Regards

Barrie

Michael Gilligan15/12/2018 12:36:33
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14020 forum posts
608 photos

James,

If you do decide to make your own Saw Table; it would be worth looking at this thread about Myford's device:

**LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=129700

.

MichaelG.

.

Also recently mentioned here:

https://www.model-engineer.co.uk/forums/postings.asp?th=137597&p=1

Edited By Michael Gilligan on 15/12/2018 12:42:51

James Morse15/12/2018 19:01:38
3 forum posts
2 photos

Thank you everyone for all the help.

I'm in Virginia in the US.

The instruments have 61 tangents (one per key).

My friend did indeed say the table saw method was fraught with difficulty and danger.

The lathe saw setup is very nice! That would be nice equipment to have.

Fret saw would probably work, perhaps an electric one. Hand fret saws probably were how they did it when clavichords were popular several hundred years ago.

Laser cutting is pretty expensive, but I wouldn't rule it out.

I can snip up to 8mm with my flush cutters (actually they were made for cutting model railroad rails). So the top and bottom I can snip off, as long as cut strips the right angle to create pieces of a known length that will be known widths at the top and bottom. The bottoms should end up about 1mm and the tops do vary between 3mm and 7mm give or take. I know how wide they have to be because I know the string spacing, so I can know the angle to cut for given lengths needed.

They tangents are angled in the key and are also angled on their sides as described above, so that as they lift up the strings (2 or 3) that they are playing, as they travel up past/through the adjacent strings they don't touch those adjacent strings. One can know the angle the tangents (their axis) have to be relative to the key, and where the base of the tangent has to enter the key, because geometrically it's possible to find a point outside a circle where a line from that point will be tangent to the circle (the tangent's head's arc of travel). Thus their name. The tangents lean more in the bass where the arc is smaller and less in the treble. I think most people do it by guess and gosh and experience, however all the relationships can be known by various methods whether geometric or mathematical. It is better to set the tangent as close to where it should end up as possible so it doesn't get loosened up in the wood of the key.

The guillotine cutter seems like a nice option and I would only need a very small one - no tangents are longer than 2". A little wider like 6" would be nice then I could work with the sheets as they come. One 6" x 12" sheet should be enough for several instruments.

Even the guillotine cutters for very small cuts say to expect some curling.

The Dremel-type tool with a toothless blade - mounted to make a miniature table saw - this could work.  It might be the best and cheapest solution for something I will want to do on an ongoing basis.

I have put a picture of a key side-on showing the tangent. It should be viewable in my Album 1. If you can't see it let me know and I can insert it in the posts.

Thank you so much for all the assistance. I hope I answered any questions. I look forward to any further comments and suggestions.

Edited By James Morse on 15/12/2018 19:26:08

Michael Gilligan15/12/2018 20:12:47
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14020 forum posts
608 photos

Posted by James Morse on 14/12/2018 15:23:43:

... To make what are called tangents, I use .025" (.6mm) brass sheet from K&S. It is their #16405. That is half-hard alloy 260 ASTM B36.

The tangents are triangle-shaped pieces about 30-40mm long by between 3mm and 7mm wide at the top and 1-2mm wide at the bottom.

.

Three more thoughts:

  1. It is perfectly possible [albeit rather tedious] to do this by hand, with a piercing saw
  2. Photo-etching may be a cheaper alternative to laser cutting
  3. It may be practical to deeply score the brass [an engraver's pantograph machine should do this nicely] and then snap-off individual 'tangents'

MichaelG.

daveb15/12/2018 21:00:42
609 forum posts
10 photos

I would go with photo etching, if they are a standard size you could do the artwork once and print them as needed.

Bill Phinn15/12/2018 22:14:37
208 forum posts
41 photos

Posted by Michael Gilligan on 15/12/2018 20:12:47:

It is perfectly possible [albeit rather tedious] to do this by hand, with a piercing saw

+1 for using a piercing saw. For 0.6mm sheet you would ideally use a 6/0 blade or finer.

Ady116/12/2018 08:24:30
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3463 forum posts
513 photos

A decent angle grinder setup with a jig vice ?

They do good stainless cutting 1mm discs nowadays, take your time and don't force the job

I originally got one for big choppy uppy jobs but the fixed angle grinder at the end of the thread gives me enough control to make teeny weeny jobs like small tool hss grinding and cutting a simple pleasure

Michael Gilligan16/12/2018 08:43:46
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14020 forum posts
608 photos
Posted by Ady1 on 16/12/2018 08:24:30:

A decent angle grinder setup with a jig vice ?

.

dont know ... for 0.6mm Brass sheet !?!

MichaelG.

Ady116/12/2018 09:19:34
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3463 forum posts
513 photos

He can scale his setup to the job, doesn't have to use a rage or a lidl unit lol

It's the controlability you get when you cut

ebay has plenty of discs at 0.9mm 0.8mm etc

edit- If he can develop a cutting disc system the amount of time and effort saved will be huge

Edited By Ady1 on 16/12/2018 09:37:12

Michael Gilligan16/12/2018 09:46:22
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14020 forum posts
608 photos

James,

Having never studied the insides of a Clavichord, I was fascinated by what you are doing.

Your style of Tangent seems very different to that mentioned here: **LINK**

http://www.traditional-brassware.co.uk/about-my-work/tangents/

If you don't mind a little topic-drift ... could you explain

Are we looking at 'Ancient vs Modern' ?

MichaelG.

 

Edited By Michael Gilligan on 16/12/2018 09:47:13

Ady116/12/2018 09:46:58
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3463 forum posts
513 photos

Another approach is a fly press die punch

ega16/12/2018 10:51:43
1265 forum posts
108 photos

I have been very impressed by the performance of the Evolution circular saw. Used in a radial arm saw small workpieces can be clamped in position before cutting. If necessary a sacrificial sandwich approach is possible (I can't say I have used it for thin brass but it seems doable).

Edited By ega on 16/12/2018 10:53:55

Russell Eberhardt16/12/2018 16:06:11
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2482 forum posts
85 photos

Clockmakers and jewelers have been cutting such thin brass parts by hand for centuries. The tool to use is a piercing saw. Explanation here.

http://dave-cushman.net/bee/piercingsaw.html

Russell

David Kenyon 216/12/2018 17:15:09
200 forum posts
147 photos

I made a Congreve clock which needed a number of long triangle pieces of brass cutting for the rolling ball table. I experimented using a cheap electric tile cutter which is basically a mini saw table. I swapped the diamond tile cutter for a Hss blade but because of the high speed of the motor the blade wore out quickly. I then filled the water cooling bath up with a cutting oil mix and tried again , this time successfully cutting out all my pieces out. I am sure with a bit more experimenting the tile cutter could be modified into a decent saw table for thin metal.

James Morse19/12/2018 15:13:08
3 forum posts
2 photos

Thank you all for the new set of postings. I am considering all suggestions including the previous ones plus the angle grinder, the Evolution saw, and the electric tile cutter. Also the piercing saw, which, rather anticlimactically, I'm tending towards. I think this is how they would have done it at the time.

As to Law's tangents, for my purposes they aren't appropriate. I'm building to a certain design so in order to imitate as closely as possible I would want to use the same type of materials. Law's hinges are to die for and very well known and respected (and used) in the keyboard world.

Tangents can be cast brass, and they can be different thicknesses. I can't speak to the tonal effects, if any, of these various designs. If one is drilling a hole (for Law threaded tangents) it would be more difficult to adjust the angle of the tangent and Law mentions the perils of bending them too much. Also weight could possibly be a small consideration depending on if the keys are back heavy or front heavy but that would be not a primary consideration because there are ways to balance the keys. Whether thinner more springy tangents is a good thing might be a consideration. If the instrument is fretted (more than one note per pair of strings) the tangents do often have to be bent sideways to get the right pitch, whereas in the case we have here of unfretted, that is not an issue. The main reason I would use the .6mm sheet brass is because that's what Hass used, and they had been doing this a long time. There is always the issue of "if they had x available they would have used it" if one wants to go that route and it's actually an improvement, however I don't see it applying here.

Also I prefer to make the parts myself and so far everything I need I can make from stock material except the strings and probably the hinges (not so easy to make well, like Law does them).

Once all the woodworking is done, the finish work is mostly all metal - balance pins (they would be in already), hitch pins, bridge pins, tuning pins, tangents - it's all small and jewelry-type work. For instance to clean up the tops of some brass pins I use the flush cutters, burr tools, and so on. So a piercing saw would probably be what was used, although I can't say that for sure.

If you want to see more detail on the instrument it is after the Hass 1767. Most - not all, but most - details are covered in "The Clavichords of Hieronymus and Johann Hass", a doctoral thesis published in 1994 for his degree at the University of Edinburgh. I have that resource (it is publicly available), as well, a plan by Ken Bakeman which is that instrument - some internals modified, however the scaling and so on is for that instrument.

Clavichords are deceptively simple. One tries as much as possible to imitate good builders, however, to assume that because the construction and appearance of an instrument are similar doesn't mean it necessarily sounds exactly the same (no two will) any more than making a violin copied after a Stradivarius means it will sound exactly the same as a Stradivarius. It is a starting point to try to see and understand what the master builders were attempting then imitate that, then gain experience. Because all the parts work together, usually if one tries to "improve" a design, they find that it compromises some other aspect. By 1767 clavichords had been made for several hundred years so they probably had it down pretty well.

It is just one design of many possible.

Many times there are various ways to do things. For instance for the key guides, which keep the keys in line in the back, I use small boxwood slips 1mm thick by 4mm high, which are inserted into the backs of the keys and ride in slots in the key rack. I use a double bass FF gut string (largest string) for the pivot on which the keys rotate. There are other ways to do these things. I follow Hass as well on things like that. If I were making a historic design that did differently, then likely I would follow that different design. For an experienced builder, they may well make changes to a design, however generally for someone with not a lot of clavichord building experience, it's better to follow a known and proven design.

And of course it is possible to make one's own design, although chances are it will look like a design already out there. Soundboard construction is an area not fully understood because it is complex. Small changes can make big differences in sound. Here again it's best to start by imitation and try to understand the reasons builders did things a certain way before thinking one might make improvements.

I much appreciate all the help, and I hope I answered all questions, if not, let me know. When I do the actual work I'll update with the method and results.

For those so inclined, there is a lot of literature - Boalch has a compendium of all known historic instruments. The British Clavichord Society has their newsletters available. I have received generous and continuing help from Peter Bavington in London who is highly respected throughout the clavichord world.

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