How can i invert my E axis?

Hi, so i just edited this post rather than making yet another. Anyway, the old post is below, but i have one new question: How might i set my firmware to have a negative E_STEPS_PER_MM value? I have a new extruder and it has different gearing such that the shaft needs to turn in the other direction to extrude. It extrudes quite nicely if i just check the reverse box on repsnapper, but that won't work for skeinforge G-code or anything else. I tried simply added a - before the values in my configuration.h file, but that first of all didn't have the intended effect, and also caused it to run until i unplugged it when i told it to extrude even a very short length.


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EDIT:I found out how it's supposed to mount. There were 2 holes underneath the motor i had been ignoring because the motor is flush with the plate they're drilled in, so you'd never be able to put a cap screw in them. I was looking at some more comprehensive drawings of the extruder i found here: [www.mendel-parts.com] when i noticed that in those, those 2 holes are countersunk. Mine weren't for some reason, but i solved countersunk them and now as soon as i can get to the store to get some metric screws with the correct head that are threaded all the way up, it should be possible to mount.

The plate also hits 2 screws i had sticking up which were just too long, but i replaced them with shorter ones. Lastly, it rubs against 2 of my bearings which stick up slightly above the mount, but they were rubbing unimportant blank areas of the plate, so i've simply ground the plate down until they don't touch.


So i bought this kit:
[www.mendel-parts.com]

and it's a really great extruder, but my is it poorly documented.

The only instructions relevant to this that i can find are here:

[www.mendel-parts.com]

Pages 24 through 26 appear to be related to this extruder. However, at least on my computer viewing through Chrome, the drawings are the wrong size and i only see the corners of them sticking onto the page from the right. Page 25 has no visible drawings.

Now, i found some forum threads with pictures of what appeared to be an identical extruder, and i've managed to assemble it nicely from that. This gives me this extruder:

[imgur.com]

I suspect it's built correctly because it extrudes excellently, so now i have only one problem left with it.

My X carriage attaches to my old extruder with 2 m4 bolts something like 49.5 mm apart. Up until this point i've been working on the assumption that the two m4 bolts attaching the motor mount to the big bottom plate on the extruder matched up with these holes. They don't though, they're 55 mm apart.

So, do i have an abnormal X carriage (I bought the RP parts from nophead about a year ago, because mendel-parts.com was very out of stock on RP parts at the time but still had hardware sets/electronics) or is the page for this kit wrong in saying it fits with the standard carriage?

Edited 3 time(s). Last edit at 10/29/2011 04:52PM by Parker .

The Prusa and Mendel carriages have holes 50mm apart, which is the standard spacing for both Wade's and Adrian's NEMA17 extruder.

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[www.hydraraptor.blogspot.com]

Thanks Nophead.

I have another question though before this extruder is genuinely working: How might i set my firmware to have a negative E_STEPS_PER_MM value? I have a new extruder and it has different gearing such that the shaft needs to turn in the other direction to extrude. It extrudes quite nicely if i just check the reverse box on repsnapper, but that won't work for skeinforge G-code or anything else. I tried simply added a - before the values in my configuration.h file, but that first of all didn't have the intended effect, and also caused it to run until i unplugged it when i told it to extrude even a very short length.

You can also reverse the wires going to your motors to reverse the direction. There's usually a #define statement in the firmware code to reverse any of the axis.