Building first Prusa - confused on rod lenghts

Hello,

I am in the process of building my first Prusa (iteration 2) and I see conflicting info on the rod lenghts. I am following the Prusa Mendel Assembly (iteration 2) instructions. At the beginning of the instructions is says...

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In this manual it is assumed that the smooth rods are 405mm each. The resulting threaded rod lengths are:

1x 500mm - low center rod
2x 450mm - top rods
6x 400mm - frame vertex
4x 320mm - lower rods for front and back side
2x 250-300mm - Z smooth rods

I have the following lenghts...

2 - M8 x 210mm zinc steel threaded rod
4 - M8 x 294mm zinc steel threaded rod
6 - M8 x 370mm zinc steel threaded rod
3 - M8 x 440mm zinc steel threaded rod
2 - 8mm x 350mm Stainless Steel Alloy 303, Precision Ground Bar
2 - 8mm x 406mm Stainless Steel Alloy 303, Precision Ground Bar
2 - 8mm x 420mm Stainless Steel Alloy 303, Precision Ground Bar

I purchased the rods from Ultimachine, which states they are compatible with both the original Prusa & Prusa I2 designs.

I have been following the instructions and have the frame all set using my above rod lengths.

Now...for the jigging. it says to use the following lenghts...

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(Optional but recommended) A piece of threaded rod or wood or any other material with precisely 320mm length. This is your frame jig J1.
(Optional but recommended) A piece of threaded rod or wood or any other material with precisely 234mm length. This is your frame jig J2.

My triangles are made up of 370mm rods as opposed to 400mm the instructions call for. Am I going to be ok using those jig lengths? Any info would be greatly appreciated.

Thanks,
Dave

The two 420mm ones need to be 400 for the V2 prusa. Here is my cutting list fro Prusa V2 kits I sell here in NZ

Threaded rod
6 x 370 Triangle end frames
4 x 294 Front and rear lower bars
3 x 440 Top and underneath bars
2 x 210 Z axis bars
1 x 50 X idler
1 x 16 Extruder idler

Smooth rod
2 x 400 X carriage (extruder)
2 x 406 Y axis (bed)
2 x 350 Z axis (up & down)

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Experimenting in 3D in New Zealand

Well now I am extra confused since I thought my smooth rods are ok. In the V2 X-axis instructions it says...

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2 495mm smooth rods (420mm in recent instructions)

I have 420mm's so I should be good in that respect. It's the threaded rods and the jigging that have me confused. The whole first paragraph in the instructions has me confused. Why does it say this??...

Quote

In this manual it is assumed that the smooth rods are 405mm each. The resulting threaded rod lengths are:

1x 500mm - low center rod
2x 450mm - top rods
6x 400mm - frame vertex
4x 320mm - lower rods for front and back side
2x 250-300mm - Z smooth rods

The extra 20mm of smooth rod for the X won't harm anything. Your Z motor mounts will have to each be an extra cm further away from the top frame vertex, and you can use 4 x M8 nuts to lock them in place.

Quote
NelsonRap
The two 420mm ones need to be 400 for the V2 prusa

Thank you so much! I have just been trying to assemble my x-carriage and couldn't get it to fit within my z-rods (even with extra spacing) and it's been driving me crazy.

NelsonRap Wrote:
-------------------------------------------------------
> The two 420mm ones need to be 400 for the V2
> prusa. Here is my cutting list fro Prusa V2 kits I
> sell here in NZ

NelsonRap, so do you jig your triangles to 290mm and the horizontal pieces to 234mm? I jigged the horizontal pieces to 234mm but the triangles to 305mm. Will this make a difference? People on IRC were saying that as long as the triangles are equilateral it doesn't matter.

I can see that the horizontal distance would matter since the z rods would off, but the triangles I am not sure about. The only thing that will happen is it will make my triangle a little taller.

Edited 1 time(s). Last edit at 07/11/2012 09:29AM by iLikeWaffles.

I don't think it makes much difference, so long as everything is equal, true and parallel. I got really anal when I built mine to make sure it was perfect

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__________________________________________________________________________
Experimenting in 3D in New Zealand

It's better to pick cut a jig or something vaguely to what you want, then use it very carefully, if everything is the same that's good enough. My prusa2 started life as a v1, so all the lengths are randomly off, but it's fine.

The Prusa version 1 specified 406mm for the x-carrriage rails, but these are too long to fit into the new design x-ends and 395mm is specified. In fact 400mm works fine both for the x rails and the y rails (specified as 406mm). I presume this odd metric length is a conversion from 16 inches?

We are including them in our kits at 406 and 395, but we'll be standardising on 400mm for both when our current stocks need replenishing.