Solution to chicken-and-egg problem - I found a cheapish FDM service!

Hey guys. A friend just pointed out fdmonly.com, a service to FDM simple parts, and I mailed them the darwin extruder .STLs expecting them to come back with some ludicrous price - but they say they'll make all five of the extruder parts in ABS for $208 USD (about

I've wondered how much it would cost to have a dozen (or two) complete sets CNC'd from compatible plastic would cost... you know for a group buy.

I've just found that Eric M. Has had pretty much the same thing done with another company - its in the builders blog.

These parts aren't CNC millable, or I'd be able to get them done at Uni or in a nearby workshop.. they need FDM I'm afraid :/

How is it that they are not suitable for CNC milling?

The extruder head parts can be made using a cnc mill, although you may need an extra long 3mm ball end mill, although I think you can avoid this if you work at it.

Some of the other plastic parts of Darwin have oddly-shaped cavities with large voids and small holes which are impossible to fabricate with a cnc mill.

Are these voids important? Or are they just to avoid printing the material?

Could the parts be made to match the faces, and work?

i'd definitely be interested in exploring this. the problem is that we're looking at a huge cost for the parts. if we could get the extruder parts down to ~$25-$50 per kit and the darwin kit down to < $125 then it would be a viable option. otherwise its going to be a big expenditure and a huge bummer when we finally get them and a few weeks later darwin manages to replicate and we get ALL the parts for ~$25.

my feeling is that it might be worth it to get a quote on cheaper CNC manufactured parts and perhaps hack the files that arent suitable for CNC so that they can be made that way. if someone wants to give this a look, please do so. all the files are on sourceforge.

i cant make any guarantees (as these things are decided by a vote) but the RRRF would probably be very interested in getting a batch of these made. i'm busy with other parts of the project, but if someone wants to do the legwork (finding a low price, getting the files ready, getting a quote, etc.), i would be very appreciative.

I'm pretty sure I can machine the plastic parts of the extruder quite cheaply, say USD$20 for a set of plastic pieces. (Following the actual CNC conversion of my mill, a task that's been awaiting completion for _some_time_now_.)

Regarding hacking the files that aren't suitable for CNC, I was going to say that that's not possible, but it is, sort of: Joost has built a Darwin-clone using wood and metal pieces instead of the plastic ones.
[forums.reprap.org]
These can be fabricated using normal woodworking and metal tools. (That's how Joost did it.) Using jigs and fixtures, someone making multiple sets could do this more efficiently than Joost did so, but it still looks like a hell of a lot of work. (Joost: "You have not seen what I 've already invested in blood, sweat, tears & time to get to this point?") I don't have the experience to guess how much it would cost a person time-wise to make 10-20 sets of these. Not counting testing and measuring to make sure the person on the other end can assemble them into a working apparatus.

Joost estimated it would take 8 hours to make one machine without the efficeincies of jigs and fixtures. I would say this method of making kits would be possible, but very high labor:

Joost, question. How many hours would it take a person to make 10-20 copies of the metal/wood bits (the plastic replacing ones) of your RepStrap?
sebastienbailard: provided they have done all the prep work and only machine (manual ), I'd guess 5 minutes per corner bracket (40 min p copy),
hey can anyone help a newb finish his java 3d install?
There're many constraint brackets, but there's only 2 holes in there - so add another 60 minutes (alu)
The bed is 30
Carriage is about 1 hour
bed corner and idlers about 2 hours
(are you adding up??)
I'm going to cut and paste and make this a forum post.
Motor brackets were difficult to figure out - I still have an issue with it - but I'd see another hour or 2
i went to my Java directory ( cd /usr/lib/jvm/java-6-sun/ ) then I tried "mv tom/java3d-1_4_0_01-linux-i586.bin" and got " mv: missing destination file operand after `tom/java3d-1_4_0_01-linux-i586.bin' "
directions of wiki at [reprap.org]
So in total: 40 + 60 + 30 + 60 + 120 + 120 = 430 min - let's say 8 hours
Right. I figure this would be a 1 person workshop making multiples, using jigs and fixtures, and I don't have the experience to guess.
sebastienbailard, I think you are able to do it in a day. And having some better tools helps a lot. I did most of my sawing for example using jigsaw or manual for the alu parts
Joost, understood. I'm trying to guess how many an equipped workshop with an semiskilled workman (me) could fabricate in a day, using jigs and fixtures or a benchtop cnc mill to make it as efficeint as possible. Answer: I have no idea.
sebastienbailard, my guess is <1 day. There's 1 catch though, and those are the corner brackets.
I've used hardwood, and that gives problems. If you can machine those from plastic are alu (latter would nice) then you only need to drill and tap some holes
Wood is a bit to brittle and cracks
I've used hardwood, and that gives problems. If you can machine those from plastic are alu (latter would nice) then you only need to drill and tap some holes

Note: I'd be highly reluctant to attempt such a job, unless I was making complete machines, because of the potential quality assurance issues.

For comparison, there's a guy who sells hobby cnc routers (motor-less, spindle-less, electronic-less) on ebay for USD$200-300.
[myworld.ebay.com]
[cgi.ebay.com]
He's making the standard cnc-router design, and I think he's using a big CNC machine to do so, so he can make them with much less effort.

I think these machines might make very good RepStraps / RepStrap kits, btw, assuming the quality is acceptable.

Edited 2 time(s). Last edit at 05/30/2007 01:52AM by SebastienBailard.

Hi Folks - isn't the idea that once we have a single reprap built then we'll be able to print the various plastic bits for the next one. Zaphod has printed the extruder bits from memory.

Also - I like Joosts design but I've decided to use perspex for my bits and just use the blood sweat and tears approach. That's kinda fun and I'll learn a lot in the process.

I also want to try extruding perspex.


Nathan.

Nathan: Yes, as I see it, the use of CNC stuff is for impatient people wanting to build something (a Repstrap) *now*, rather than wait for a fully working RepRap Darwin v1.0 to print their parts, or pay $2300ish for a commercial RP service to do it.

I think it's great for those with the ability and experience with CNC to take that route (and fine for anyone with the money to spend to get a set of commercially RPed parts, for that matter!) ... but the longer term approach is definitely to have Repraps make the RP-able parts for the next 1,2, or more Repraps.

The ultimate solution to any Reprap "chicken and egg problem" is to have a single (mostly replicable) working "chicken" :-) Adrian has already constructed the full mechanics of just such a device (on video!) ... so we're getting closer and closer to that point.

[Hmmm, maybe we could name Adrian's Darwin v1.0 constructed on the video "Chicken", if it hasn't already been named??? :-) ]

Jonathan