Aluminium instead plastics and CNC milling

I overlook Zach Smith's aluminium extruder parts at flickr (can be found at [blog.reprap.org] - mind the "More pics on Flickr" link).

What if we'll make corner brackets (and some other stuff) from aluminium, too? Maybe we shall have a strong enoughth backbone for CNC miller?

And then we'll attach a dremel toolhead (this toolhead in plans list as far as I remember) and we'll achieve some other sort of self-replication: it (maybe) will be possible to mill all this staff, planned for extrusion.

I don't think so. I learned the hard way just how stiff you need to make even a small milling machine, with a Dremel type spindle, able to mill plastics. I naively thought that as long as you didn't feed too fast you would not need to apply much force so the worst you would get is a small deflection and loss of accuracy.

What actually happens when it is not stiff enough is that the tool "snatches" and chatters. It is a sort of positive feed back effect. The tool drifts a little off centre and bites into the plastic which drags it more off centre and it bites deeper until tool snaps or the motor stalls.

6mm * 150mm * 200mm AL sheet was not stiff enough to support the spindle, I had to reinforce it with 8mm x 20mm AL rails. Pictures here [hydraraptor.blogspot.com] of the one that did work, and here [hydraraptor.blogspot.com] for the version that didn't.

The corner brackets would be pretty stiff when made from AL but I think there would be too much flex in the steel rods at the mid points where that are unsupported. Also the drive belt system would have some compliance. You never see milling machines with this type of construction. Solid gantry geometries and heavy steel rails and drive screws are the norm.

Yes you can make a lot of the machine by milling. It does not have to be AL, I find plastic easier to work with. That is how I made my extruder but I am not going to make any of the other bits that way. If the extruder works it will make them. If it can't make them then there is no point making them. The whole point of the machine is that it is self replicating.

---

[www.hydraraptor.blogspot.com]

nophead,

I realize that the project has a lot of focus on being self-replicating but is saying that this is the whole point really factual. I don't have one yet myself (I'm working on it!) but it seems to me that a lot of the people here want a RepRap to build stuff. The fact that it can self-replicate just makes things easier for others and later for ourselves but it is ultimatly a machine that builds things. Or am I way off.

Cheers!

Well the design consists of relatively complicated plastic parts, which are hard to make, other than by FDM, and off the shelf items like rods and studding which are cheap and easy to get hold of. That means that if it can self replicate it is both easy and cheap to build.

If not, it is quite hard to make, you need to either be skilled at metalwork or have a CNC milling machine, etc., or you can pay somebody to make the parts in which case it will be relatively expensive.

Alternatively you can do what Forrest is attempting to do with Tommelise, and that is to make it both easy to make by hand and cheap by changing the design to rely less on FDM parts.

Another path, which I have taken, is to make or buy a milling machine, use that to make the extruder and then convert it into an FDM machine. More expensive but you do also end up with a milling machine as well as an FDM machine.

Yes the goal is to end up with a machine that can make things, but the self-replication aspect is what makes it cheap and easy to construct such a machine. Without it, it is either expensive and easy to make or cheap and hard to make.

---

[www.hydraraptor.blogspot.com]

If RepRap's backbone is not strong enought even with metal brackets, then I do not understand, why dremel toolhead included into plans list.

Assargadon Wrote:
-------------------------------------------------------
> If RepRap's backbone is not strong enought even
> with metal brackets, then I do not understand, why
> dremel toolhead included into plans list.

future plans. eg its not too far fetched to imagine a strenthened and more rigid reprap. he's saying the current version cannot support it. of course we would love to be able to do milling as well as FDM, but for the time being we're focusing on FDM.

I think the work Mike and Fernado are doing with resins and fillers is the most likely route to making a machine solid enough for milling. A lathe is another desirable product that requires, I would guess, even higher rigidity.

---

[www.hydraraptor.blogspot.com]

ZachHoeken Wrote:
> future plans. eg its not too far fetched to
> imagine a strenthened and more rigid reprap.

Do you mean that backbone concept will be changed? But it will require changing almost everything in reprap, except electronics and extruder.

You could reuse the motors,so "almost everything" is just a bunch of rods, studding, pulleys and belts plus a lot of FDM parts.

---

[www.hydraraptor.blogspot.com]

you're both right. a change that also allows milling is a big change, but its really only to the structure, and possibly also a motor upgrade. but its not really a change to the fundamental nature of the machine, which is a cartesian robot with a toolhead that does work. the software can be generalized to handle that, and the electronics can probably handle a larger motor. from there, you're really just looking at structure, which is something that alot of people are experimenting with.

also, if you're already starting from a machine that can do FDM deposition, then you're golden. you can simply test out a variety of designs, and you can also do lots of collaborative work on the internet, because other people can be testing the *exact* same design as you are... the amount of time it will take to refine the design will be much faster than what we have now, with people working in relative isolation.

once we have reliable and cheap 3D printing, the whole nature of this game will change DRASTICALLY. its going to be very exciting.

"the software can be generalized to handle that"

Automatically calculating tool paths from 3D CAD models is a lot more difficult for subtractive machining than it is for additive I think. That is one of the many things that makes an additive process attractive.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> You could reuse the motors,so "almost everything"
> is just a bunch of rods, studding, pulleys and
> belts plus a lot of FDM parts.

I speak about design, not about parts. I mean, you must re-engeenire all the machine to make new backvone.

Ok, I got the point.
Darwin will be used for next-step experiments, just like repstrap used for building Darwin itself. And we need selfreplication at this very first step to involve as much experimentatros as possible.

If enought people wiould be involved, it will be quite easy to redesign all the concept, becouse of large number of imroverers.

exactly =)