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Implied Measurements for Darwin

Posted by reece.arnott 
Implied Measurements for Darwin
August 06, 2008 04:11AM
There are few measurements that are not spelt out in the instructions that I had a couple of problems with last week so I thought I'd share what I'd worked out.

Firstly the horizontal measurements between the corner pieces are around about 360mm (362mm if you do it exactly).

The vertical spacing between the corner pieces is not specified and depends in some respects on how long you want the legs at the bottom to be. I've set the legs to 50mm and the vertical spacing to 350mm. You could probably set them to 40mm and 360mm if you haven't cut your diagonal rods short.

The spacing between the top of the corner piece and the bottom of the Y bearing bracket is 20mm.

I think it might be helpful if this was in the instructions. If I get some time in the next couple of weeks I'll mock up a little diagram and post it.
Re: Implied Measurements for Darwin
August 06, 2008 08:17AM
Hi Reece,
IIRC the spacing of the horizontal rods (which is the thing that is important) is 400mm (500 - 20 - 28 - 44 - 8). That would make the gap between the corner blocks (which are 44mm wide) 356mm, how did you arrive at 362?. It is better to set the rod spacing than the block spacing as it eliminates the tolerance in the corner blocks.


According to the wiki the Y bearing brackets should be 16mm above the corner blocks. That is what I did and it seems to be about right although thinking about it, the idler pulleys are bigger than the drive pulleys so the idler end should be higher. I will take another look at it this evening.

Edited 1 time(s). Last edit at 08/06/2008 08:34AM by nophead.

Re: Implied Measurements for Darwin
August 06, 2008 01:49PM
Hmm, y-axis alignment seems to be a big can of worms.

The belt clamps on top of the x-motor bracket are not at the same height as the x-idler bracket.

The y-idler pulleys are bigger than the toothed pulleys.

The y-drive shaft needs to be lower but you can't adjust the motor end.

Having the belts on a slant will introduce some error, I haven't quantified how much yet.

Re: Implied Measurements for Darwin
August 14, 2008 01:43PM
Nophead, how much of a slant do you have there? I'm using Ian's cast parts, and everything more or less worked out, to within a mm or so. My Y belt is 25 mm from the rod at the drive pulley, and 26 mm at the belt clamp. Maybe your corner block is a bit thicker? Or, if your y idler pulleys are larger, then your drive pulleys must be a bit on the small side. Odd that they're too low; maybe add a spacer to the belt clamps?

Agree about the spacing - it's the rod measurement that's most important. I ended up setting all mine to 406 mm.

Re: Implied Measurements for Darwin
August 15, 2008 05:06AM
I got 362mm by using 45mm instead of 44mm for the width of the corner blocks and remembering that there are 2 of them smiling smiley

Re: Implied Measurements for Darwin
August 15, 2008 01:45PM
Yes I forgot to add the rod diameter back so I get 364mm as my corner blocks are 44mm not 45. A good reason for setting the distance between the rods rather than the brackets if there are two sizes of bracket.

Not sure why you used 406mm instead of 400mm. Did the bed brackets line up with the holes in the bed OK?

I need to raise the belt about 4mm where it meets the X motor bracket. I think putting y-belt clamps under the belt will fix that. I also need to raise the idler shaft by about 3.5mm because the idler pulleys are about 7mm bigger in diameter than my drive pulleys, YMMV.

The misalignment does not cause much error. For example if it is 4mm out and the carriage moves to within 50mm of the end then the error is only about 0.12mm over half the length of the bed.

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