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Craftsman advice needed... how to make a mould (somewhat OT)

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CONGER

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Greetings Woodworkers.

Somewhat off topic... but I need to make a mould for the case of the ukulele that finished recently.

Please let me explain...

I want to make a case for the uke. The uke should embed snugly into a moulded 'slot' in the case; the case will also contain other components, each in a purpose shaped 'slot'.

The (simplified) idea is to make a simple mould case (read box)... half-fill the box with moulding mass... press the (well wrapped!) uke, and other parts, into the moulding mass... cover the surface with cling-foil... fill the box with moulding mass... and wait for the mass to harden.

Remove the components... then saw the the mould halves into a number of strips... from end to end. Each strip would represent a cross section of the uke & components.

Then... using the strips, make a similar number of 'strips' of wood... each strip would have an outline of the uke & components.

Finally... join the wood strips together to make the lining for the case.

Sorry... complicated, but the simplified(!) result of long deliberation!

Now... the problem (#1!)... I need to find a suitable mass.

I tried using papiermache (paper with wallpaper glue)... the idea was fine until I realised that the mass (papiermache) would not dry. Of course, papiermache needs to dry... it does not cure or set!

I tried a similar mixture using sawdust... same problem.

The next option would be gypsum... that would cure... but I do not have a saw (bandsaw) that will cut the gypsum... and the 'sliced' gypsum sections would probably be rather brittle.

I would appreciate some inspired suggestions.

Thanks, gerard.
 

Jacob

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Instead of attempting to cast it (messy etc) I'd be inclined to cut/carve it from something easy like rigid plastic foam. Don't know what sort but I'm certain there is something out there which would do - some variety of insulation material?
Could be single block or built up in layers e.g. profiles cut through on one sheet which is then laid on another for the base.
 

Scouse

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If I understood correctly, and you are making a sort of form fitted case, I would be inclined to simplify the process. Pressing an instrument into a fairly firm substance risks damaging the instrument.

I'd wrap the uke tightly in clingfilm/ shrink wrap plastic sheet, and cover the instrument in fibreglass sheet strips pressed gently onto it and it's components. When the resin cures, remove the instrument, leaving a complete negative mold.
 

bugbear

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CONGER":21p45m46 said:
Remove the components... then saw the the mould halves into a number of strips... from end to end. Each strip would represent a cross section of the uke & components.

Then... using the strips, make a similar number of 'strips' of wood... each strip would have an outline of the uke & components.

Finally... join the wood strips together to make the lining for the case.
Do you mean "strips" as in a coopered form (e.g. the back of a lute), or strips as in "bread and butter" (sometimes used for model ships' hulls) ?

BugBear
 

mack9110000

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I've probably totally misundertood this but, would expanding foam not work ?
mack
 

CONGER

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Ahh BugBear... my description is probably insufficient. Apologies.

Somewhat simplified...

Place the uke in a bread baking form.

Fill the baking form with bread dough (moulding mass),

Bake (cure) the lot.

Remove the 'loaf' from the baking form.

Remove the uke from the (now) top of the loaf... place the bread on the cutting board with the impression of the (now removed) uke on top.

Cut the loaf into slices... each slice will have a profile on top, which represents a 'section' of the uke.

Place a slice on a piece of wood, and trace out the uke profile.

Repeat for all slices.

Cut the wood suitably.

Join all the wooden 'profiles' to get a wooden 'loaf' with a form into which (after finishing), the uke can be laid.

Clearly there are optimisation steps for the above process... and clearly the 'case' will have to be made in 2 parts, each of which will have a profile representing the uke (upper / lower side)... but the process whould be similar for both 'clamshell' halves.

Missing in my equation, is a suitable moulding mass... I have tried papiermache... but it does not 'cure'... and (using the above bread form example) it does not dry (unless I heat it... and that would endanger the uke). Gypsum would be an alternative... but sawn into slices it may well be too brittle to work with.

Thanks for your patience... gerard.
 

mack9110000

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It can be cut quite easily with a handsaw, so a "bandsaw" should be a cakewalk.It sets quite rigidly, rather like cutting polystyrene.
mack
 

monkeybiter

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If you do attempt this with expanding foam make sure you give it plenty of room to 'escape' as it expands, I once made a hollow walled cupboard [breeding insects as live food for lizards] and filled the wall cavities for insulation. I pre-drilled plenty of holes but it still bowed the chipboard all round as it expanded. You wouldn't want that pressure on a musical instrument.
 

bugbear

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CONGER":1uhlz7ym said:
Ahh BugBear... my description is probably insufficient. Apologies.
Aah - bread and butter, with vertical slices. Got it.

Even if you find a process that works, it sounds liable to be heavy.

I know that modern cases are fibre glass (which we can consider to be modern, super tough, papier maché).

Older cases are either wooden (and not as closely fitted as modern cases)



Or made from (steam bent, moulded) cardboard/strawboard, with the joints (and surface, sometimes) done in cloth or tape. Still not as "fitted" as a modern cases though.

BugBear
 

dunbarhamlin

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Caution: stuff what cures in a short time is commonly exothermic - don't want cuked uke :shock: May not do the finish much good , and don't remember if you used hide or yellow glue - if the latter, might not be good for that either. Similar concerns with what might be outgassed during cure.
That's going to be an awfully nice but monstrously heavy case. If you do find something to use as this, why just use the result as the case innards? Probably be lighter than wood.
Perhaps use a sheet of thin card as a separator - really don't want to saw through the uke :cry: .
Alternatively, create a case for the body and then make tranverse slices with your neck profile - spot glue all together and snug up to the instrument for custom fit.
 

CONGER

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Good stuff.. and thanks... but somehow I feel that my description is still inadequate... mea culpa.

BB & DBH... The filler material serves only for me to be able to get to the outline (section by section) of the uke (and components) as they will sit in the final case. After the outline has be transferred to the wood (from which the case will be built)... the filler 'slices' will be discarded.

The outer wall-thickness of the final case is yet to be determined... I suspect that it will be something like 20mm... and that will indeed not be light... but filius is a large fellow (195CMish)... he can take that!

The uke is largely finished... 2 years in the making. It is a solid body thingy... according to filius' own design.

Here is a pic of the raw cut... it looks a lot different now(!!)... and it can be played (not by me!). I will post another pic later.



-gerard-... who is still missing suggestions for the filler!
 

MIGNAL

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Even cases that are specifically made for a particular instrument have some 'breathing space', usually they line it with a fur fabric.
 

monkeybiter

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You could experiment with a setting/curing compound like silicone sealant/mastic bulked up with granulated [by hand/wire brush] expanded polystyrene to reduce weight. It should be firm enough and I don't think it exotherms. I presume you intend to cover or coat it.

Weight could be reduced further by including some sacrificial wooden blocks to be removed later creating spaces on the hidden side.

Might be worth a try.
 

dunbarhamlin

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Hehehe - I like it.
Perhaps you should change your sig to Deus Carpa :D
I'd be inclined to french fit, and use gouges to get a a close-enough fit for the back and line with 1/4" foam.
Or - if you are going to line the case, then wrapping the instrument in the lining "stuff" (and then the polythene or whatever) might provide enough insulation to use something like the cans of gap filling foam. I'd want to experiment with scrap first, to see how hot it got.
 

Jacob

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dunbarhamlin":1j4caevx said:
Hehehe - I like it.
Perhaps you should change your sig to Deus Carpa :D
I'd be inclined to french fit, and use gouges to get a a close-enough fit for the back and line with 1/4" foam.
Or - if you are going to line the case, then wrapping the instrument in the lining "stuff" (and then the polythene or whatever) might provide enough insulation to use something like the cans of gap filling foam. I'd want to experiment with scrap first, to see how hot it got.
Scuse my ignorance, but what's "french fit" ?
 

dunbarhamlin

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Mmmm, perhaps I'm not using the proper term.
I mean building to thickness with a base and stacked plies with cutouts done with a scroll saw.
 

bugbear

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Jacob":1vli5oth said:
dunbarhamlin":1vli5oth said:
Hehehe - I like it.
Perhaps you should change your sig to Deus Carpa :D
I'd be inclined to french fit, and use gouges to get a a close-enough fit for the back and line with 1/4" foam.
Or - if you are going to line the case, then wrapping the instrument in the lining "stuff" (and then the polythene or whatever) might provide enough insulation to use something like the cans of gap filling foam. I'd want to experiment with scrap first, to see how hot it got.
Scuse my ignorance, but what's "french fit" ?
A nice (commonly felt of flock lined) hidey hole for each item.

Here's a nice example;



BugBear
 

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