The other day I was looking at the quick-fit clamp in AOI. I wanted to see how I could modify it to grip the PTFE barrel better. I wanted to make sure whatever I came up with didn't violate the >45 overhang rule. That's when I realized it already has overhangs. There are 3 horizontal holes without the 45-degree peaks, a beveled edge that creates a 60-degree overhang and dome-shaped indentations on the sides and bottom. I'm pretty sure this part can't be printed on a single-head RepRap / RepStrap without modification.

This morning, I went through the STL files for Darwin 1.0.2 and thermoplast extruder 1.0 to see how many overhangs I could find. I found 24 parts that probably can't be printed as-is without support material. Now, I just eyeballed these, looking for anything that didn't seem quite right. I could be completely wrong.

Here's the list:

reprap-thermoplast-extruder-1.0
----------------------------
clamp.stl - 3 horizontal holes
offset-motor-holder.stl - 6 horizontal holes plus logo
poly-holder.stl - 4 horizontal holes plus logo
quickfit-clamp.stl - 3 horizontal holes, >45 overhang on bevel, overhang on indentations
screw-holder.stl - 4 horizontal holes plus logo


reprap-cartesian-bot-1.0.2
-----------------------
Bed-corner.stl - 2 horizontal holes plus horizontal overhang
Circlip-M8.stl - >45 overhang on bevel
Corner-bracket.stl - >45 overhang on rounded corner
Diagonal-tie-bracket.stl - 1 horizontal hole plus >45 overhang on rounded corner
Extruder-quickfit-dock.STL - horizontal overhangs in all orientations
Extruder-quickfit-latch.STL - horizontal overhangs in all orientations
Fan-leg.stl - 1 horizontal hole
Optoswitch-bracket.stl - 1 horizontal hole
X-carriage.STL - 1 horizontal overhang
X-idler-bracket.stl - 1 horizontal hole plus >45 overhang on rounded corner
X-motor-bracket.stl - horizontal overhang
X-opto-flag.stl - >45 overhang on rounded corner
X-square-jig.stl - >45 overhang on rounded corner
XY-pulley-idler.stl - >45 overhang on bevel
Y-motor-bracket.stl - horizontal overhangs in all orientations
Y-motor-coupling.stl - 2 horizontal holes plus horizontal overhang
Z-motor-bracket.stl - 2 horizontal overhangs
Z-motor-coupling.stl - 3 horizontal overhangs
Z-opto-flag-base.stl - 1 horizontal hole

Yes but Darwin has a support extruder so I assume that is required to replicate.

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[www.hydraraptor.blogspot.com]

I think this is great information, if for anything it puts the support extruder into the spotlight... the importance of it. As a lot of the RepStrap designs don't seem to be concerned about support material....

Just observing photos on blogs and the forum... does anyone outside of Bath have a RepRap with support material extruder assembly?

Vic has one in NZ [blog.reprap.org]

I don't know of anybody else who has one. Personally I am waiting to see if the support works before attempting to build one. I can't imagine it working for HDPE either, so not much use until CAPA becomes available.

Perhaps a lot of parts could be modified with tear shaped holes, etc, to make it self replicate without support but then that would be self replication for the sake of it. I don't think an FDM machine without support is very useful. Most practical objects you would want to make need support.

It may be possible to use the same material for support and build. Some commercial machines use ABS for both. The support is grey so you can see which bits to remove but I don't know if it has any other difference. I guess they control the shape and temperature to make a temporary weld that you can snap it off easily. It was on my huge list of things to try with HDPE before my extruder expired.

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[www.hydraraptor.blogspot.com]

I agree that a proper FDM machine needs a way to produce support material. I think there's a practical advantage to having a minimal, one-head system that can produce its own replacement parts, though.

Or, at the very least, it'd be handy if a minimal, one-head system can produce its own paste extruder. That would give new owners a practical first project.

Yes I suppose the paste extruder is the only thing that needs to be able to be made without support. The machine can just bootstrap itself before it replicates.

---

[www.hydraraptor.blogspot.com]

An alternative is to have it be able to produce both the thermoplastic extruder *and* the paste extruder so that it can be used to print the thermoplastic extruder *first* so that it has replacement parts of critical systems on hand during the build of other systems. It would suck to have to buy/make a new thermoplastic extruder the hard way after having a functional machine.

Demented

I'm gradually going through the parts, modifying them so that they can print without support material. As things stand there are a few (fixable) bugs in the Java geometry code that stops some of the parts printing anyway, so I've not been worrying about it too much.

I'm fairly confident that the parts can be re-engineered to print without support materials. I've fixed the opto bracket, X motor bracket and XY idler already.

Vik :v)

There's a new page with parts modded for single-head printing here:
[www.reprap.org]

For horizontal cylinders, because of the 45 degree overhang limit, teardrop cylinders are being made. However, Vik noticed that PLA can make loops and therefore bridge gaps, as written in the Support Material Miracle post at:
[www.blogger.com]

Also forrest said HDPE and HPP both do that as well.

So could a truncated teardrop cylinder be made? The top of the cylinder would be made by spanning the top gap, getting around the 45 degree overhang limit for the small space. The truncated cylinder would give more support than a teardrop cylinder, although still less than a completely round cylinder.

Does anyone with a fabricator want to try making a test truncated teardrop?

hi i am interested in making a rep rap .
i would like to know how many parts are available in new Zealand .
regards john Morgan

I'll send you a spreadsheet I've made over the last couple of years. Its a bit of a mess but the short answer is "everything but the electronics and the reprap plastic parts" (the most expensive bits ) and you could probably source most of the electronics (except for the boards themselves) as well if you really wanted, although it is easier just to buy one of the kits.

Edited 1 time(s). Last edit at 04/24/2009 05:11AM by Reece Arnott.