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.
http://www.rpsupport.co.uk/downloads/rps_markforged_data_sheets/markforged_materials_datasheet.pdf
EDIT: Oh wow, I didn't realize this thing ran long ago and just got bumped on the facebook page. Woops.
David Chen Thu 22 Mar 2018 1:45PM
Thank you for the info. I knew someone had to have had the same idea at some point. Which models are widely used? For 'cosmetically satisfactory', do you mean color selection?
Skip Meetze Thu 22 Mar 2018 2:05PM
The Gripper https://plus.google.com/u/0/+SkipMeetze/posts/LmEnes8b5Vu is easy to fabricate, and even though it is still experimental it might be a good place for you to start. Nylon (printed with SLS or FDM) can be dyed post printing, but I think you are stuck with the uncolored or motley appearance with reinforced nylon.
Doc Davies Thu 22 Mar 2018 3:04PM
I read Skip Meetze's comments with a bit of concern.
Let me respond to the individual points for some clarity...
1) reinforced nylon has special design constraints that take special
knowledge to be successful,
Actually, we have not found constraints but rather opportunities. By that, I mean that with a little reasoning, one can make better use
of the integrated strength of the filament in the part. The printer itself functions almost identically to normal FDM printers. The only major difference is
choosing to either use (composite construction), or not use (just normal carbon reinforced nylon) Carbon Fiber, Fiberglass or Kevlar reinforcement. And then
just determining how the material should be added to the print. We've had success in both these areas.
We've had elementary and middle school students design parts for demanding situations like quadcopters, skateboards or school engineering projects
with little additional training. In fact, one elementary student successfully used TinkerCAD to make a viable design which proved functional in
a very rugged application.
The machine itself is more "industrialized" and rugged in student work environments (and trust me our kids tax our printers). Of course for the price....it better
be! But we chose it to supplement our Pre-Engineering courses at one of our high schools....and have had two engineering college representatives
commend us for teaching "potential" college students "state of the art" technology.
My goal, wish, dream, scheme.....is to get a metal 3D printer to further develop the students abilities, exposure and experience. We are currently working
with the College of William and Mary and Newport News Shipbuilding to obtain prototype devices for testing.
That folks, would open up an entirely new pathway for our projects.
(2) the increased strength compared to the
easier printing in unreinforced nylon using ordinary FDM printers is not
justified for our upper limb devices.
Yes, this may normally be true. But we have two kids, one who plays basketball, and one baseball who routinely break the current parts we make them with
standard FDM printing. We are currently making comparable reinforced parts for destructive testing before producing them in quantity for the kids. I'll keep
you informed as to how that experiment is progressing.
As for lower limb devices......after the testing we've done.....I don't know how you will produce functional parts without this approach.
(3) it is difficult to get a
cosmetically satisfactory hand with the reinforced nylon.
Well you've got me here in one sense......to paraphrase......"you can have a device in any color, as long as it's black"....
But that having been said, general consensus among our makers and users...is that the parts printed with reinforced nylon are of a smoother
surface texture and artifact free nature than normal FDM parts.
Now no one should have any illusions as to the increased COST of these types of parts.....the printer alone is ~$15K...and filament and reinforcing
material is expensive. But the parts are incredibly durable and strong. And we may find that the entire device does not need to be constructed using
these parts, but only critical sections. I believe that's an area we should examine closely.
In summary, I feel we should continue this line of experimentation and determine just how parts printed in this manner can supplement and extend
our current offerings and potential new designs.
Since I realize these comments may generate some, ah....discussion...please feel free to comment on this message or contact me personally
to discuss your opinions, observations or suggestions.
Doc
Bruce "Doc" Davies, Ph.D.
Co-Director
Chesterfield County Makerspace
David Chen Thu 22 Mar 2018 4:53PM
That's my thinking as well:
1) Not needed for everyone, but few better options are out there for select individuals
2) High quality black finish vs low quality colorful finish - I think older kids and adults would prefer the former.
3) Lower limbs - not sure how else you could possibly design for this without going to metal.
4) Price - Onyx Pro is about $7500 with tax/shipping, so definitely expensive, but I think a well designed corporate partnership program could fulfill the smaller volume of parts needed. Unless you absolutely need carbon fiber or kevlar for some reason, you don't need the $15000 Mark 2. And if even just a plain carbon nylon print is more durable, then thats a cheaper alternative that can be printed on a variety of printers.
5) Selective reinforcement - If key components are ID'ed so not every part needs to be reinforced, it would help cut costs. Parts could also be further modified to facilitate fiber routing to provide better strength, and print orientation could be adjusted as well.
If there are tangible benefits to be had, I think having the option would be appreciated. The main concern would be funding and cost, and if E-nable insists on making everything at no cost to the user, then you might have people requesting reinforced hands exclusively as it costs them nothing more to do so. But I think such supply/demand problems can be addressed should they appear, whereas allowing some users to participate in a wider range of activities is a benefit too good to keep buried. For someone in my profession (industrial design), I can think of no better material since I get exposed to solvents and high heat all the time in the shop.
David Chen Thu 22 Mar 2018 5:13PM
If your tests do show that this is something worth offering, I'd glady offer my printer up to make parts when its not in use.
David Chen Tue 27 Mar 2018 7:12PM
A standard Carbon Nylon hand does not need a markforge or its expensive Onyx material. One can print with CarbonX from 3DXTech on most printers that are not locked to a proprietary material. I'm currently retrofitting a Stratasys 768 for this purpose. Carbon X is not particularly cheap at $190/ 2kgs, but its significantly lower than Onyx at $220/kg It may even be possible to run it on the markforge with their new Gen2 formulation, and I'm getting a spool to experiment with it. If it works, then the fiberglass reinforced version will drop in price as well. Its not going to become $30 unless the filament makers bring the price down that low, which may happen over time but I don't imagine it will ever match dirt cheap ABS/PLA.
Given whats been discussed, I do think lower limbs should be explored, at least for kids. I don't think it would ever be $30 unless the printing is exclusively for the faring. But its plausible that a 3D printed "cup" can be done out of a elastomer like Ninjaflex, and have it act as the cushion material when bridged to a carbon nylon brace that is connected to a steel rod that connects to the foot or something to that effect. It would definitely be better to use carbon nylon in this application since its much easier to bang your leg accidentally on a table leg or something than your hand.
But regarding the cost, I think trying to keep everything near-free to make would significantly limit the potential reach of E-nable not to mention limb development. When there are no other options whatsoever, a $200 leg/foot is still leagues more accessible to a $2000-$20,000 one. Is it not better to provide the option to people than to not even have it due to some convention?
David Chen Tue 27 Mar 2018 7:14PM
Did anything ever come of this? https://3dprint.com/84190/3d-printed-foot-prosthetics/
David Chen Tue 27 Mar 2018 9:21PM
Something else that can be done to reduce the cost is to create a go-fund-me template that people can use, and a media press kit that they can then send to a local publication like a newspaper that can be ran on a weekly basis. Kind of like the missing people "have you seen me?" milk carton campaign. If all they need to do is raise $1-200, I think that would be pretty easy.
Doc Davies Mon 2 Apr 2018 3:28PM
David, why don't we continue this conversation. I have some funding from a foundation that I can use to purchase a couple of rolls of filament for you machine and mine. We can continue testing and work with some other folks who have shown interest in this approach. If you can provide a separate email address, I'll send you mine. The good news is, I've made contact with the local Markforged distributor and through him a gentleman AT Markforged that would be interested in discussing our ideas.
Skip Meetze · Thu 22 Mar 2018 12:54PM
We experimented with devices made with Markforged printers using fiberglass reinforced and carbon reinforced nylon. We abandoned the approach because (1) reinforced nylon has special design constraints that take special knowledge to be successful, (2) the increased strength compared to the easier printing in unreinforced nylon using ordinary FDM printers is not justified for our upper limb devices and (3) it is difficult to get a cosmetically satisfactory hand with the reinforced nylon. Also, the Ody Hand was a great exploration of Peter Binkley’s push-pull tendon technology, but it is not widely used in our community. I encourage you to get involved with fabricating proven e-NABLE devices to find where the properties of reinforced nylon might have value.