Fiberglass Reinforced Composite Hand
My partners and I own a Onyx Pro from Markforged, and it does fiberglass reinforced parts that are incredibly strong. The carbon nylon base material also has very good material properties. I've always wondered what a full hand built with this printer with parts reinforced with fiberglass where ever possible would be like.
I know this company's printers have been used to design prosthetics before, but I don't know of any hands. I've attached the material data sheet on the carbon nylon and fiberglass at the end. The carbon nylon has an extremely high heat deflection (145C) and is very durable to abrasion and sheering. I printed a wheel hub for a friend who works in a skateboard wheel company to do destructive testing, and they were unable to break it entirely because it just bent with the force. Sounds like a great material for prosthetics since it cant snap and produce sharp jagged edges.
The material is much more expensive than off the shelf ABS at about $200/kg, and the fiberglass is also quite expensive though you don't really use a lot of it. I'd be very surprised if the material costs went $100, but I'd budget $150 for the 3D print material just in case.
I'm also interested in whether or not an easier-to-assemble hand can be made using this company's technology that doesn't require fasteners which can get lost.
EDIT: Oh wow, I didn't realize this thing ran long ago and just got bumped on the facebook page. Woops.
David Chen started a proposal Wed 21 Mar 2018
Printing Filament Comparison (PLA/ABS vs Carbon Nylon vs Reinforced Carbon Nylon). Closed Sat 7 Apr 2018
Most hands are made out of PLA and/or ABS, which though affordable and easy to source, have physical limitations such as low temperature tolerance, chemical sensitivity, and brittleness. It is still the ideal material for growing children as it is extremely low cost when buying generic, is widely available, and replacing it either due to outgrowing the hand or breaking it is financially insignificant. It also comes in a wide range of colors, allowing for more decorative options which kids in particular like to have.
For adults, late teens, or just extremely active kids, it may not be the best material for the aforementioned reasons. Carbon infused nylon may be more applicable since it has a much higher temperature tolerance, is chemically resistant, is very hard to break (usually just stretches and deforms), and with some printers, can be internally reinforced with fiberglass or carbon fiber filament. A composite reinforced hand may have significantly less flex and thus allow greater user strength and wider range of ADL’s such as cooking, cleaning, weight training, and sports. The drawback is mainly in the cost, with a 500g spool of 3DXTech CarbonX costing $46.00 from Matterhackers, which is about 4x the price of ABS and PLA. A reinforced hand would be even more expensive, as the only printers capable are from Markforged, which uses proprietary carbon nylon called Onyx that costs $200 a kg, and $230 for 150cm3 of fiberglass. For comparison, an Ody 2.0 hand scaled to 150% would cost about $5 in ABS, $20 in generic CarbonX, $60 in Onyx, and $125 if reinforced with fiberglass.
For most kids, this is both too expensive and probably unnecessary. But for individuals who are fully grown or participates in more rigorous activities, this may be a bargain since they will not be growing out of it, and can use it for the entirety of its longer life. $125 is still a bargain for a young professional if it means not having to replace it for years to come. However since much of these benefits are theoretical at this juncture, I would like to conduct tests comparing each printing method. I have a Markforge printer that can print the reinforced hand, and I have a spool of CarbonX that can be used for the carbon-nylon-only hand. I’m sure I can find someone local to do the ABS one, or perhaps someone here can print it and ship it to me. The tests I am interested in conducting are:
1) Strength – weight limit of how much a hand can hold when holding a weight with the palm up to simulate flexion. If the hand fails and breaks, the characteristics of the break will indicate any possible dangers during activity. PLA will likely be the weakest, but both PLA and ABS will likely break leaving sharp edges that could cause further injury if exposed during sports or physical exercise. Carbon nylon will likely deform and stretch but not snap entirely, so lacerations from sharp edges is unlikely.
2) Chemical Resistance – A variety of household cleaning chemicals and common solvents will be sprayed onto the hand using a spray bottle, then wiped off with a paper towel and/or rinsed under water. Signs of discoloration and physical corrosion will indicate chemical sensitivity and limitations in the types of activities one should avoid. PLA will likely be the most sensitive, with ABS being more resistant, and carbon nylon being the most resistant.
3) Thermal resistance & durability – Each hand will have the leather and straps removed, and washed in the dishwasher on normal cycle. Whether it deforms or breaks apart will indicate weakness to high heat and/or agitation. PLA will likely deform and fall apart entirely, though ABS may also weaken and parts may detach. Carbon nylon may or may not survive without any obvious damage.
Resources needed: Grant of $200 should cover the materials to make all 4 hands, especially if another volunteer can provide the ABS/PLA prints. Results will be documented via video, photographs, and written observations.
Time needed: Likely a month at most as it would take a week or two to procure and build all 4 hands.
Any hands that survive the testing and appears to be functional and safe may be sent to an appropriate candidate for personal use.
|Agree - 4|
|Abstain - 1|
|Disagree - 2|
|Block - 0|
Thu 22 Mar 2018
(1) reinforced nylon has special design constraints, (2) the increased strength is not justified for our upper limb devices and (3) it is difficult to get a cosmetically satisfactory hand with the reinforced nylon.
This work is not only important to produce the type of durable device needed for more demanding activities by our users such as sporting or strenuous activities and to start the development and research of lower limb devices.
Tue 27 Mar 2018
The material is certainly stronger, but most of our volunteers would probably not be able to make use of it. I expect you'll find good results, but will we be able to make them accessible to most of our volunteers to offer?