Carbon fibre, anyone?

[Longhorn6120]

I'm looking into the possibility of making a carbon fibre orthopaedic shoe insert for a family member. Looks like I can get a piece of CF for about 1/4 of what a pre-made insert would cost and as it's just a flat foot-shape I thought it might be achievable. Thing is, I've never worked with carbon fibre before so if there's anyone out there with experience I'd be grateful for any advice.

CF sheet will be 1-1.5mm thick and just needs cutting into the shape of a shoe insert. Is it easy stuff to work or does one need special tools?

Thanks in advance.

 

[angellonewolf]

when ive seen the car programs they seam to have the carbon fiber lay it down and put resin over it that it

there will be some oone along soon to help more ive never worked with it

 

[Al Strachan]

not sure if you are looking at cutting a pre made flat sheet, or forming something with CF material and resin?

 

[Longhorn6120]

I was thinking about cutting a pre-made sheet - something like this.

 

[a111r]

If they have a need for an orthosis, then why not get a NHS referral to your local service?
They're medical devices, custom made by those who've trained for the job.

 

[hotponyshoes]

Generally the orthopedic inserts have some sort of shape to them, I can't see what a flat bit would do to help apart from stiffen the shoe/boot up?

It's fairly easy to work with, just cover it both sides with blue masking tape and trim it out with a router bit. Watch the dust as it's nasty. There is a proper tape to cover it with before trimming but the blue masking tape does the job.

 

[Nick DV]

Cheap stuff is carbon mat and glass fibre resin, expensive stuff is made using pre preg c/f matt, vacuum bagged and autoclaved

 

[Longhorn6120]

She had a tele-appt with the GP, was told to go to a private podiatrist. They diagnosed Hallux Limitus, which is an early form of Hallux Rigidus. Surgery is recommended, but the pandemic has lengthened waiting lists to around 2 years. We're just trying to find a cost effective way of limiting the toe movement until she can get an op. CF inserts are about £45 each on Amazon so I thought I could trim one out of a sheet of CF.

 

[Longhorn6120]

Generally the orthopedic inserts have some sort of shape to them, I can't see what a flat bit would do to help apart from stiffen the shoe/boot up?

It's fairly easy to work with, just cover it both sides with blue masking tape and trim it out with a router bit. Watch the dust as it's nasty. There is a proper tape to cover it with before trimming but the blue masking tape does the job.

Stiffen up the shoe is exactly what we're trying to achieve. It'll go under the regular insole in the shoe so should be non-intrusive.

Thanks for the advice re cutting. I don't have a router set up, could I use anything else to cut it?

 

[Newlands]

You can buy carbon fibre woven cloth from East Coast Fibreglass Supples (and many other places as well, but that’s who I use). Maybe a metre of biaxial tape Like this for around a fiver.You’ll need a small pack of epoxy resin as well. Plus you’ll need to make a mould because feet aren’t exactly flat. Plus the other normal layup stuff like a set of accurate scales, rubber gloves, mixing pots, maybe cling film and release agent. It’s easy enough to work with - you can shape the finished layup with a sanding disc but wear a mask fer gawds sake.
But with a National Health Service, why would you want to? Seems to me that the mould is the tricky bit - it’s not a carbon fibre expert you need but an orthopedic surgeon.

Edit - I ought to add that epoxy can be horrible stuff - you can be ok with it one day, and the next find that you’re sensitised, and your life is a misery every time you get near it, including after it’s cured - I always wear nitrile gloves and a mask, and more than that if I’m sanding it.

 

[Longhorn6120]

So it's basically made like fibreglass then, flexible base with a resin to solidify it - is that right? Like I said before, I'm a total know-nowt when it comes to CF; never had any, never worked any, so even this is helpful, thanks.

Regarding the forming, again, it's to go UNDER a regular insole so will need to be flat. The regular shaped insole will be on top of it and will cushion and support the foot in the normal way, we're just trying to stiffen the shoe so the toes don't bend. I did consider plywood, but I'm not sure it would be both thin enough and strong enough. 1mm mild steel would be an option though...

 

[Longhorn6120]

This is what I'm trying to replicate, using some of this.

 

[carbon]

Carbon fibre sheet can be bought in various sizes and thicknesses from Carbon fibre sheet. It can be cut with basic tools ie hacksaw but do need to be careful with the dust produced, so basic extraction like a vacuum cleaner and a mask. It can also be filed to shape

 

[Longhorn6120]

Great, thanks. I will likely be doing it outdoors and will definitely be wearing a mask.

 

[carbon]

You would need to be careful that it doesn’t crack as carbon fibre splinters can be painful if you get them in your feet.

 

[Bladevane]

I'm no foot expert but if the item you require is flat and about 1.2 - 1.5 mm thick why not draw round the foot (or feet) then get someone to 3D print a couple? This at least would prove the principle and whether they assist to resolve the problem before you get into cutting CF along with the attendant H&S considerations highlighted above.

 

[Barking Mat]

Seems to me to be the same process as fibreglassing, same principle, different material.

 

[hotponyshoes]

So it's basically made like fibreglass then, flexible base with a resin to solidify it - is that right? Like I said before, I'm a total know-nowt when it comes to CF; never had any, never worked any, so even this is helpful, thanks.

Regarding the forming, again, it's to go UNDER a regular insole so will need to be flat. The regular shaped insole will be on top of it and will cushion and support the foot in the normal way, we're just trying to stiffen the shoe so the toes don't bend. I did consider plywood, but I'm not sure it would be both thin enough and strong enough. 1mm mild steel would be an option though...

You can basically play with it the same as you would fibreglass.
Main problems are cutting it, scalpel blade or pair of the proper shears will work, anything less and the weave will tend to fall apart on you.
It's stiffer so a lot trickier to lay up into a mold than fibreglass but that should not be a problem for a flat shape.

Apart from that you can just do it as if you were making something out of fibreglass.
Fancy resins, pre-preg, vacuum bagging and autoclaves are used to get the most out of the carbon cloth, ie, if you just make something out of it as you would with fibreglass then you may as well just use fibreglass as you won't really seen many advantages from using carbon.

For something flat and foot size a bit of 0.8mm or so titanium sheet would be cheap enough, last forever and (i'm guessing) be about as springy as a couple of mm of well laid carbon.

 

[slim_boy_fat]

You would need to be careful that it doesn’t crack as carbon fibre splinters can be painful if you get them in your feet.

A good point, but since it's to go under an existing insole that'd reduce the chance of any 'in use' damage?

 

[carbon]

Main problems are cutting it, scalpel blade or pair of the proper shears will work, anything less and the weave will tend to fall apart on you.
It's stiffer so a lot trickier to lay up into a mold than fibreglass but that should not be a problem for a flat shape.

The way I usually cut carbon fibre cloth is to use masking tape both sides then cut through the tape and the cloth together with a standard pair of scissors.

In my experience carbon fibre twill cloth is a lot more flexible than fibreglass chopped strand mat but I haven’t used much over 300gsm carbon fibre cloth. You have to be more careful when placing it a mould if you need a cosmetic finish