I have been lurking here for about 2 weeks following links to various DIY

I have been lurking here for about 2 weeks following links to various DIY 3d printer vendors. I am amazed at the ever increasing models and variants of them. Found a local one offering Mendel kits and their own model Mix G1. Has anyone here seen, used or have an opinion of this ?

I can tell just from the thumbnail that the machine in that picture is going to have terrible Z-wobble.

And apparently they’re using steppers with a bit more than 202.35 steps/revolution - take a look at the steps/mm value they’re giving for the pulleys: http://www.mixshop.com/index.php?main_page=product_info&cPath=44_53&products_id=172

Sounds like somebody forgot how to do basic math and just used a ruler. The numbers are also different for X and Y, which are presumably using the same pulleys.

Doesn’t exactly inspire confidence about their engineering.

Thanks to both of you for the enlightenment ! Being new to this I’m just learning all the details of what to look for.

Where can i download the pieces of X ?

… and yet the prints (the results) off the machine look pretty good. That doesn’t matter though because we’re on an internet forum. Right?

@Billy i don’t know 'bout you, but i see bad z-wobble. http://www.mixshop.com/index.php?main_page=popup_image_additional&pID=145&pic=1&products_image_large_additional=images/large/products/ms-g1_11_LRG.jpg

That’s not “bad” Z-wobble. You’re crazy. Those are thick layer heights. Let’s see some of your prints?

@Billy I see, this is how an internet form works. Instead of focusing on the subject, you’re now calling me crazy and are trying to divert to what i can achieve. I’d like to believe that my prints do look nicer than those of the G1.
I’m pretty convinced that it is z-wobble that we’re seeing. The ATX PSU in the back stands 150mm tall, so the layer height would have to be pretty close to 1.25mm

You’re crazy in the context I used is hardly an insult at least not in the US. If you took it as one then I apologize and that was not the intent.

I’m not trying to divert what you can achieve. I called you out. Go ahead and show your prints. If you’re going to criticize someone else’s work then I think it’s fair game for you to show how your work is so much better.

Did you look at the other pics in the gallery? They look fine too.

The builder community has a huge problem with automatically dismissing the work of others. If someone’s work does not fit whatever the latest common wisdom fad it is automatically dismissed. Unless the guy is showing the work of another printer then his results speak a million times more than forum back seat engineering. “You’re doing it wrong” does not fly when the results are decent.

As for his STEPS values there is nothing wrong with getting out the calipers and tweaking. I’m sure you both have flow tweaks of exactly 1.0 right?

It’s called extrusion multiplier in Slic3r, and yes, it is set to 1.0 in all of my profiles.

If the steps/mm on the machine doesn’t match the math, that indicates a mechanical problem that needs to be fixed.

“Needs” to be fixed? If the output quality is good then that is all that matters. Stuff happens in the real world. If you can’t depend on ideal inputs then the can’t expect ideal outputs using ideal math. Steppers error is 5%. Filament tolerance is large. Belts can’t be infinitely tight. Tweaks are fine. They bridge the gap between the ideal and the real world.

btw. My STEPS are set to 140.0 on XY and I end up with nice dimensions, but I could end up with even better numbers if I tweaked my numbers a bit. I just don’t care they are good enough.

In these situations, empirical measurement is more likely to introduce error than it can properly compensate for.

@Billy have fun tearing that octopus apart :stuck_out_tongue:
I must admit, i have the multiplier set to a value other than 1. Which is not a problem, since the amount extruded is right in the end.
With belts, motors and pulleys, it’s a different story, because there is only one exact value that will make your printer move the exact distances you feed it. Any other value is simply wrong, and, like @Whosa_whatsis said, is an improper “workaround” for other issues. An incorrect steps/mm value for any of the moving axes will create a whole array of other issues.

As for the somewhat negative attitude towards certain concepts, may i say this: Most of the printer users, and sadly, many of those that design such printer like the G1, come from a non-engineering background and use their accumulated judgment to build those machines.
There’s a reason why one can study engineering, and that’s because mechanics and electronics use many concepts that are not instantly obvious to the untrained eye. A hacker with an electronics background might mess up mechanical parts. A designer will most likely mess up both mechanics and electronics and even a Bachelor of Engineering will not get everything right on the first try - but he’ll have the capacity
to analyze issues and learn from prior mistakes. A capacity that a chunk of the printer sellers seem to lack.

Forgot to respond to the bit about dismissing the work of others, which is totally untrue. New concepts are great, and we’re all excited to see them. What draws our ire is when people don’t do their research and make the same mistakes that have been made (and pointed out) a thousand times already, like constraining the ends of the Z screws.

I think I am just being more realistic about potential sources of errors in our machines. I see it everywhere in the toy machines we are building. Anyway, how accurately can you possibly lay down something as complex as quickly cooling molten plastic? It’s all a huge hack and I don’t pretend there is anything even close to science being practiced.

While many components are based on experiences gathered over the last years - mostly how things dont work - , there are certain parts where a bit of math or applied mechanics doesn’t hurt.

“I can tell just from the thumbnail that the machine in that picture is going to have terrible Z-wobble.”

That is your first post in this thread. Did you even look at the gallery before posting? No need because you already knew it had “terrible Z-wobble” That is the definition of dismissive.