Pad Materials

[RWL]

9 hours ago, Daveylocker said:

Harbor Freight also sells an assorted set of these type of hole punches that should work well if they are large enough. I truly do admire your machining abilities thought, along with the photography. Fine craftsmanship!

That's what I have for the larger pads.  They are not very sharp and would benefit from a sharpening.  Also, there is a jump from 1/2" to 5/8" and the set would benefit from a 9/16" punch for concertina work.

 

In an old post, Mike Pierceall mentions making a punch from a piece of pipe.

 

As I thought about it this evening after having cut the 'sides' off of a 5/8" pad to fit one of the oval holes in my instrument, I don't see any reason why the pads have to be round.  They're probably round because it was a convenient way for the factory to produce lots of pads and round cutting dies probably being easier to make than square ones, but for a one-off, I don't see why the pads couldn't be square or rectangular and it would avoid having to buy punches altogether.  At this point I'm making mine round because I'm only making a few pads and I want them to be similar to what's in the instrument, but if I were doing all of the pads, I'd consider making them rectangular.  It would be a lot easier to cut them in bulk with a straight edge and a razor knife.

[RWL]

10 hours ago, alex_holden said:

Instagram caption: "I ground and sharpened a new 19mm arch punch for making pads. As supplied, they are way too chunky, have firescale inside the hole, and are not sharp enough to cut cleanly. This will be used initially for the air pad on No. 12."

Thanks Alex.

[alex_holden]

12 hours ago, Don Taylor said:

I would like some advice about card stock for pads. 

 

The heaviest weight that I can easily buy is Accent Opaque Digital Cover White Smooth, 120lb from Amazon.  There are 150 sheets in a ream pack so, by my reckoning, each sheet is about .4mm thick.

 

This is quite a bit thinner than the stock used on the old pads (which looks more like cardboard than paper stock) so I am concerned that it might not be thick enough or stiff enough.

 

Is there any reason that I should not glue several layers of the above stock together to make a thicker, stiffer base for the pads?

 

Added later:  I have since found this stuff which is 2mm thick: Cricut Heavy Chipboard - 11”x11” - 5 Sheets - Brown

 

 

The card I currently use for my pads is 600 gsm (I think that's about 400 lb?), 1.55mm thick, white, quite dense with a smooth surface. Unfortunately the supplier I bought it from has disappeared and I haven't yet found an exact equivalent elsewhere. It's easy to find greyboard that is thick enough, but it doesn't have a nice smooth white surface. 300 gsm white card is easily available here, so two layers of that would probably work well.

 

I don't see a problem with laminating it - I use two layers of my normal card on my 24mm diameter air pads for extra stiffness.

 

I suspect chipboard is a lower grade product and wouldn't be ideal.

[RWL]

Is chipboard the same as something like the thin cardboard that comes in new dress shirts or that's used in gift boxes?  I had thought about using those.  Both of those alternatives have at least one shiny white surface.  It's possible that they aren't that way in other parts of the world. 

 

The single layer of poster board is working OK for the pads that I did make although laminating two pieces of the .017" thick poster board would make these closer to the height of the original pads. 

[Don Taylor]

2 hours ago, RWL said:

Is chipboard the same as something like the thin cardboard that comes in new dress shirts or that's used in gift boxes?  I had thought about using those.  Both of those alternatives have at least one shiny white surface.  It's possible that they aren't that way in other parts of the world. 

 

The single layer of poster board is working OK for the pads that I did make although laminating two pieces of the .017" thick poster board would make these closer to the height of the original pads. 

I think that chipboard is cardboard without the corrugations, so it is solid cardboard.  I don't rhink that it always has a white surface.  The one I listed earlier (Cricut) seems to be a stiff, thick card meant for hobby modelling.  My old pads seem to have been made with something like this - thick, solid cardboard about .1" thick, but it has delaminated after 70 years.

 

After Alex's last message I have odered this stuff from Amazon: Extra Heavy Duty 130lb Cover Cardstock - Bright White - 350gsm 17pt Thick Paper.  This is the same thickness (.017") as the stuff that you used.  I will probably laminate two layers together, but will see when I get it.

[Don Taylor]

Any advice on glues to use for pads?

 

 

I have just made some test material using liquid PVA glue but I am concerned that the glue has soaked into the felt which is now hard and not very compressable. 

 

I may have been a bit liberal with the glue but the felt just seemed to suck it in.  Perhaps I should avoid smearing the glue on the felt and just put it on the cards and the leather?

[Theo]

1 hour ago, Don Taylor said:

 

 

I may have been a bit liberal with the glue but the felt just seemed to suck it in.  Perhaps I should avoid smearing the glue on the felt and just put it on the cards and the leather?

 

Yes, apply the glue to the card and leather, not to the felt.

 

After trying many adhesives I've now settled on using starch paste with the addition of about 20% of pva.  This is a common mix used by bookbinders for similar materials to those used in pads.  It's not a joint that is stressed, so use as little as possible consistent with getting a good enough bond.

[RWL]

I'm always interested in hearing what others are using.  I used spray on contact adhesive based on some other comments here at C.net

[alex_holden]

I've tried quite a few different glues and processes. My most recent method (suggested to me by another maker who I don't think posts on this forum) is:

1. Very lightly brush unthinned PVA (white glue) onto both sides of the felt and prop it up to dry. This 'sizes' the surface to make it less absorbent.
2. Brush a thin coat of PVA onto the card and place the felt on it.
3. Brush a thin coat of PVA onto the felt and place the leather onto it (suede side out).
4. Lightly press between two sheets of glass for at least an hour. Don't use too much weight or the felt will permanently compress.

The other maker applies the glue with a foam roller instead of a brush. I haven't tried that yet myself.

 

I have in the past tried applying glue to the back of the leather and it didn't go well for me - too much soaked in and made it go hard.

 

I make it in relatively small (A5) panels so there is less risk of the glue prematurely tacking up before you've got it into the press, and if it goes wrong you haven't wasted a lot of materials. I once tried to make a much larger (A3) panel and had to scrap it because the layers didn't stick consistently.

 

Something I can definitely say is a bad idea: double sided adhesive film. It seemed to work great at first, but over a period of years it can soften and creep sideways. It also leaves the sides of the pads permanently tacky so lint sticks to them.

[Don Taylor]

5 hours ago, alex_holden said:

Brush a thin coat of PVA onto the felt and place the leather onto it (suede side out).

Just to be clear then, the suede (rough) side of the leather finshes up on the outside, as the side that closes the pad hole in the action board?

 

All of my existing pads have the shiny side on the outside of the pad.

[alex_holden]

2 hours ago, Don Taylor said:

Just to be clear then, the suede (rough) side of the leather finshes up on the outside, as the side that closes the pad hole in the action board?

 

All of my existing pads have the shiny side on the outside of the pad.

 

Right. I've tried it both ways and I feel the suede (flesh) side seals slightly better. It isn't a big difference though.

[Geoffrey Crabb]

14 minutes ago, alex_holden said:

 

Right. I've tried it both ways and I feel the suede (flesh) side seals slightly better. It isn't a big difference though.

It can also reduce or eliminate any 'slapping' sounds during rapid playing. 

[Dana Johnson]

Flap valves for concertinas need to operate at very low pressures compared to their use in organs.  While the playing pressure may go up to perhaps 4 inches of water column,  the valves need to open at much lower pressure in order to play softly and not obstruct the air flow..  This means they should be as flexible as possible, yet still have enough spring to return to flat once the pressure ceases.  Dense leather needs to be quite thin to lift at low pressure, but it’s weight at those thicknesses make it vulnerable to sagging away from the reed pan.  If they are thick enough to resist this, they don’t lift easily enough and dull the sound.  Leather that is less dense can be thicker and gain spring by having the surfaces farther away from the center of bending.  Heavy hides like cow are very dense at the hair side, and if split thin enough lose most of the less dense flesh side.  The optimum comes when the leather comes from smaller animals whose skins are much thinner to start with and  include the least dense portion with the hair side being a smaller proportion of the thickness.  Low density valves require less spring force to close or keep from sagging even when they are thicker.  A lot of older instrument’s valves were alum tanned or tawed hair sheep , a naturally white leather with a tight outer grain from the alum which gives good spring without adding weight.  Unfortunately,  it also creates a slightly corrosive environment which can turn brass reed shoes dark where they have a valve next to them.  Alum tanned leather still has dome alum in it and will rot if the alum is completely washed out.  Finding leather that mimics alum tanned is a good goal, and the Columbia CPL at least works pretty well, while other leathers they have aren’t as good.  The aolian Morton CML maroon version of the CPL is treated with heat to help seal the grain side, and it can work well, but they don’t have it any thicker than their CPL which is my only complaint for either.  Welling and drying flat still may need to be done if it comes too soft.  
Dana