Mendel Mono kit: Y smooth rod is not straight

FunKing

Mendel Mono kit: Y smooth rod is not straight
May 24, 2014 06:29PM

Registered: 9 years ago
Posts: 6

Hi there!

I'm building my first 3D printer, a Mendel Mono, from a kit I have just received.

I followed the instructions and reached the "Aligning the frame" section. At that moment I noticed that one Y smooth rod is not straight.

I rolled the rods on a flat surface. One rod is almost perfectly straight, while the other clearly isn't, showing a gap from the surface of at least 0.2mm in the middle of its length.

My guess is that 0.2mm difference is going to affect the quality of the prints. Could anyone confirm this?

Reply Quote

FunKing

Re: Mendel Mono kit: Y smooth rod is not straight
May 27, 2014 09:34AM

Registered: 9 years ago
Posts: 6

Update: I have measured the gap again with a digital caliper, and at the widest point (in the center of the rod) the gap is about 0.5mm! sad smiley

Reply Quote

Opus

Re: Mendel Mono kit: Y smooth rod is not straight
May 28, 2014 12:15AM

Registered: 10 years ago
Posts: 62

I'm not familiar with the Mendel Mono (looks a lot like a Prusa i2?), but you might get away with it. If the Y carriage runs on 3 bearings, then set the 2 bearing side on the straight rod, and the single bearing on the bent rod. It's only there to stop the carriage rotating around the other rod. The big question will be if the carriage can then move freely enough on those bearings to stop binding up, and what orientation the bend is at. If it's sideways then the carriage shouldn't move, it'll just put strain on the bearing. If it's up-down it'll tilt the carriage and that'll be bad.

Still, if it's a kit then the supplier should really replace the rod.

Edited 1 time(s). Last edit at 05/28/2014 12:15AM by Opus.

Reply Quote

FunKing

Re: Mendel Mono kit: Y smooth rod is not straight
May 28, 2014 12:49PM

Registered: 9 years ago
Posts: 6

Thanks for the reply!

Yes, it was a kit bought from RepRapPro.com. After deburring the edges and inspecting all smooth rods carefully, I noticed that almost the 6 of them were slightly bent, and just one seemed almost perfectly straight. Here are the measurements of the gaps of the rods when placed on a flat surface:

+----------+------+------+
|Rod length| Gap  | Gap  |
+----------+------+------+
|Z - 350 mm|0.30mm|0.35mm|
|Y - 400 mm|0.15mm|0.45mm|
|X - 428 mm|0.25mm| ~ 0mm|
+----------+------+------+

I sent a message to the RepRapPro support last week. Does anyone knows how long does it typically takes to get a reply from them?

Reply Quote

FunKing

Re: Mendel Mono kit: Y smooth rod is not straight
May 28, 2014 05:53PM

Registered: 9 years ago
Posts: 6

Just got a reply from support:

Quote
Ian
0.5mm will have an effect on the print bed. You can probably get around this by:

1. Bend the rod straighter. Put a straight rod on you desk, then put the bent rod on top of the first one, at 90 degrees, so the centre of the bent rod is on the rod below. The bent rod will roll so that the highest point is upwards. Pick up the rod, and, supporting the two ends, push down the rod in the middle. This may make it straight enough to use.

2. Install it on the machine, but align the rod so that the bend is horizontal, not vertical, so the bed does not move up and down as it goes along the rod. The linear bearings can cope with some lateral play, and the y-carriage height will not be affected. It will also be better to fit it on the side of the Y axis that has only one bearing on the y-carriage, not two.

However, we are happy to send you a new Y-rod if this doesn't help; just let me know if you still need it.

I managed to get the rods straighter - not perfectly, but much better. Still, the rods are not aligning properly. Then I moved the printer to keep just 3 of its legs on the table, and the remaining one hanging outside, and the rods seemed to be perfectly aligned! So, it seems that if I remove about 1.6 mm of the bottom of that leg, it would solve the problem - but I wonder what else I could do to solve it. For now, I think I might restart the assembly from scratch just to be sure...

Reply Quote