MGN12H rails questions

Okay so I've got some 800mm mgn12h chinese rails. Sure the one item of feedback is bad but mine are nowhere near as bad as this guy makes out.

One is a bit notchy though it improved with a good clean and lots of lithium grease. The other two are very smooth.

Couple of questions:
How many ball bearings should the carriages have? The notchy one appears to have a gap of one ball's width on one side and two ball's width the other side. Should I be looking to add one more ball to one side or two to one side and one to the other to fill them completely?
What material should I buy? I presume for wear to be even, I ought to be using the same material the rails are made from which is I presume stainless steel?

Thanks in advance.

The plan is to use them on a 2040 based large kossel.

Edited 1 time(s). Last edit at 08/04/2016 05:50PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I removed all of the bearing balls in mine, then cleaned and lubed them. When you remove the rail, put it carriage side down on a towel, then remove the rail from the carriage. If you do it the other way around, the balls will find new places to hide.

Use a micrometer to measure the size. If there is any play in the carriage, then you can use oversize ball bearings. If there is a discrepancy in the number of ball bearings per side, I'd order enough ball bearings to do replace all of the existing ones.

Edited 1 time(s). Last edit at 08/04/2016 08:03PM by etfrench.

A missing ball or two isn't going to affect the performance in a 3D printer. The load ratings of the assemblies are based on that load being divided among a certain number of balls. If a ball is missing, the others have to take on its load. Since 3D printing puts only minimal loads on these things, I wouldn't worry about it. That said, if you bought new parts they should come with a full set of balls...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

So, the question is... Are MGN12H rails worth it? I'd be interested in hearing about your experiences so far with them. I'm considering rail instead of delrin wheels, but it seems in the UK that the only choice is the chinese vendors on aliexpress

Very happy to post as I find out more about how well they work but I'm waiting on a big bag of t nuts as I object to £5 for 10 of them. But once I've got the t nuts I'll do the mechanical build, I'm also in batch 3 for a duet wifi so it'll be a while before I know how well it works.

If I can get the one sticky rail to run smoothly I'll consider it $136 well spent. Otherwise I'll buy some delrin wheels and move on.

I only measured one ball bearing which was 2.75mm which is a size I can't find, perhaps they are meant to 2.78mm which I can find.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

If you want a Chinese set the guy I bought them from promised me a big discount, as one was a bit sticky so let me know and I'll order them see how much he reduces them by.

Given I got 2 good one dubious maybe order a few spares and sell the least good ones on.

Edited 1 time(s). Last edit at 08/05/2016 01:03PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I recently replaced mine and they were 3/32" or 2.38mm diameter. I wonder if there is a difference between robotdiggs MGN12 rails and yours?

I need to take them all out and measure them. Maybe I measured an outlier.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I see a pattern forming here!!! I have two sets , and similar tale as DJ one flawless second some resistance in motion and a third one nasty had a deformed block



never measured the ball bearing but did find a flat one amongst them all, where I found I had resistance I removed a ball bearing and greased it up, glides silent and smoothly.
I reckon out the two sets I got grade A complete matching set to use and a second set that in need of replacing one block and at £5 I live with it. think for the price these rails are the future for beam build delta's,

So I've been messing with these rails and the sticky one is now not sticky. A really good clean out with some brake cleaner, then lots of grease and plenty of sliding the carriage up and down and its runs nicely. I have to say its most likely the waxy coating they put on them for transit which causes the stickiness and some rails seem to be more heavily coated than others. Can't wait for the build to begin.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

That sounds promising, maybe I'll have to take you up on that discount you mentioned.

I'm trying to make a CoreXY machine at the moment, and the minimal size of rail compared to Delrin wheels on extrusion is hard to beat when you want to maximise build area.

I emailed the guy will PM you if I hear back from him.

Worthy of note: I started building my large kossel, frame built to 0.1mm precision, pleased with that. However looked at mounting the rails and they'll need m3 t-nuts which seem to be not available in the UK, so another agonising 3 week wait to get some from China. But once I'm done I'll have a bunch spare, to stick on eBay.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Full length tnuts are fairly easy to make if you have a drill press, a mill, or lots of patience for hand layout. I used .125"x.5" aluminum bar. I think the full length tnut may be more precise as the holes don't deviate from the centerline. They are much cheaper as well.

For the rails I printed some T-nuts with my Prusa. There are several designs on thingiverse. They don't have to stand huge forces.

Both reasonable ideas but I'm not using any printed parts for anything load bearing. Also I've built the frame now so I'm only using drop in (half) t nuts.

I could use m4 if I drill some of the holes in the rails out to 4mm, but this is the first printer I've built where I'm refusing to bodge anything. That might change if I get bored waiting.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
However looked at mounting the rails and they'll need m3 t-nuts which seem to be not available in the UK, so another agonising 3 week wait to get some from China. But once I'm done I'll have a bunch spare, to stick on eBay.

You can get m3 (or 4 or 5) drop in tee nuts from Ooznest in the UK. Here you go [ooznest.co.uk]. Just select the thread size from the drop down list. Delivery has always been really quick (like next day) for all the stuff I've bought from them.

Good tip thanks.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I got my t-nuts(a few sizes) from this seller, was quite happy [www.ebay.co.uk]