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From Blender to Prusa i3 MK3S with exact dimensions?  

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MD_Reptile
(@md_reptile)
Active Member
From Blender to Prusa i3 MK3S with exact dimensions?

Ok so I have purchased a i3 MK3S recently, after deciding I didn't wanna wait til april for a mini. I won't be getting it for another couple weeks, but tonight I walked out to my truck and discovered some lowlife busted one of the rear windows out.

How do these things have anything to do with one another you ask? Well simple! I am gonna be fairly broke having just sunk a lot of money into my printer, and rather than pay a few hundred dollars to have somebody come out and fix my window on my old beat up truck, I'd much rather 3D print a replacement out of plastic and then hot glue that sucker in, because yeah! And I don't much care about appearances or even if its legal to replace a rear window with plastic.

So that brings me to our questions - how exactly can I take a 3D model from Blender 2.79 and get an exact size and scale for the dimensions of my window, then import that model into prusa slicer and print it with the right size to match up to my window?

I can take measurements of the window (the matching window is still in the vehicle and I can measure that) and get a very accurate real life measurement of how big the panel needs to be and I am familiar with blender and making a 3d model and all of that... but the issue is that blender doesn't really match up nicely to real world units. For instance, I know that my window is 18 inches in height - and I have a reference blueprint of the vehicle so I can make the 3d model very closely match the shape of the existing window no problem.

Armed with that information, how exactly do I go about making the 3d object then splitting it up into 4 (or maybe 6) chunks that I can print on the i3, then hot glue into place in my vehicle?

What I've tried so far is to make the model closely match the shape of the window as a whole, and I planned to later chop that model into separate chunks to be able to fit into the print area of the i3, with some kind of notches or slots to allow them to connect together as a whole.

When I brought the test model into prusa slicer I noticed it was super tiny, so I greatly increased the scale to get it nearly where I imagine it would be in real life size - but of course that is nowhere near accurate I soon realized!

So I tried making a simple cube in blender, and setting the scale to 18 in every dimension, and then importing the STL, and that is still only a small cube on a big plate, though much larger than the super tiny scale of my window model. So I'm wondering what is the Blender units > prusa slicer units > real world units conversion?

Please help me figure this all out and save some money some junkie decided I could live without.

Some other maybe helpful info:

- the window is flat, its a rear window and has no curve, and does not move or roll down. I hope this makes it a more simple repair.

- so far I'm only aware of the height of the model, though if I can get that to be accurate then I can simply make that match perfectly and the rest should "just fit" since I'm using a reference model of my vehicle and trying to match the shape to that.

-  I have no idea how I'm going to print several parts and link them together with strength (it does have to be a window after all), any suggestions there? The entire window will be too large to print as one part.

- this is my first 3d printer, so I will be probably screwing this up repeatedly.

- perhaps I should print a little extra size to the model, so it has a lip that overhangs the actual visible area of the window, as real glass does in a vehicle, so it will be better sealed into the slot it belongs.

- google is not being very enlightening on this subject, some people say scale things up in blender, some say enter cm units in blender, some say blender has no real units for its stl files... nothing is clearly answering this question for me.

Posted : 28/01/2020 6:49 am
Lichtjaeger
(@lichtjaeger)
Noble Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?

I use Blender 1.81 and there, the units are metric. But as far as I remember 1bu should be 1mm after stl export.

Posted : 28/01/2020 7:02 am
MD_Reptile
(@md_reptile)
Active Member
Topic starter answered:
RE: From Blender to Prusa i3 MK3S with exact dimensions?

I do see now that the slicer has a size in millimeters in the same area where I scaled up the model - if I set those sizes very accurately then the 3d print should come out that size? I feel like that may be a stupid question but I'm hoping to get the model as close as possible to done before the printer arrives so I can make that one of the first few things I print. Can anybody confirm the accuracy of the millimeter setting in the slicer?

Posted : 28/01/2020 7:02 am
RH_Dreambox
(@rh_dreambox)
Prominent Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?

The gcode that comes out of the slicer program is very accurate. If I draw a cube of 40x40x40 mm and print it, its dimensions will be 40.0x39.9x39.9 mm. The 0.1 mm taken in X and Y coordinates can be fine-tuned (extrusion) if necessary, but for my purposes the dimensions are sufficient.
When it comes to the metric system, there are a few countries in the world that have not yet succeeded in eradicating the old inch system. After all, it's been over 50 years since the world countries decided to introduce the metric system :-).

Bear MK3 with Bondtech extruder...
Posted : 28/01/2020 8:29 am
Neophyl
(@neophyl)
Famed Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?

Blender 2.8 has revamped the units system to make it much easier.

For 2.79 I usually set my global scene units

Length=Metric
Angle=degrees
Unit Scale = 0.001

I then set my Display to have

lines =300
Scale = 0.001 (matches the unit scale from scene)
Subdivisions=10

This gives me a 300x300mm grid with each line on the grid 1mm apart which equates to the bed on my CR10 in size and gives me a nice visualisation of if a part will fit .  So if I create a 20mm cube and export the stl it will be exactly 20mm when imported into Slicer.  No scaling required. 

There are various methods to split up your model into parts that will fit on your printer bed and loads of tutorials online about how to do that but I just split them in blender itself and then add 2-3mm pin holes to all the parts so that I can add locating pins during assembly to make aligning when gluing together easy.

Posted : 28/01/2020 9:02 am
rmm200
(@rmm200)
Noble Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?

Printing 3D parts is neat - but I will mention that you can get a piece of plexiglass the right size from a home supply house for under $20.

https://www.homedepot.com/p/OPTIX-18-in-x-24-in-x-0-093-in-Clear-Acrylic-Sheet-Glass-Replacement-MC-05/202038047

Posted : 28/01/2020 4:36 pm
MD_Reptile
(@md_reptile)
Active Member
Topic starter answered:
RE: From Blender to Prusa i3 MK3S with exact dimensions?
Posted by: @robert-rmm200

Printing 3D parts is neat - but I will mention that you can get a piece of plexiglass the right size from a home supply house for under $20.

https://www.homedepot.com/p/OPTIX-18-in-x-24-in-x-0-093-in-Clear-Acrylic-Sheet-Glass-Replacement-MC-05/202038047

This is a pretty good point - I suppose that'd be a much quicker band aid fix!

Posted : 28/01/2020 5:58 pm
hawai
(@hawai)
Estimable Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?

Once you got yourself a hammer, everything looks like a nail...

Although the idea of "quickly" printing a replacement part sounds awfully cool, for the window I would like to add the question of transparency into the mix. Achieving transparency with FDM printing is a tall order (I've been fighting for weeks now and have settled for moderate translucency). Every line you print will generate an optical interface that reflects light going through, the more lines the milkier the effect. So, unless you don't want to see through your window or want to spend more money on a large bore nozzle and spend a lot of time experimenting with print settings to achieve at least an acceptable level of translucency I'd grudgingly go for the acrylic sheet.

In regards to your blender problem for less artsy and more constructed parts you might want to look at Autodesk Fusion360. They give you a non commercial license for 1 year for free.

Posted : 29/01/2020 7:34 pm
rmm200
(@rmm200)
Noble Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?

Another note on Fusion 360. Well couple of notes. Hobbyist license is just plain free at the moment. Mine has no one year expiration although that could change at any time. Second note: there are some really great Fusion 360 tutorials. Watch the "die trying" series even if you don't have Fusion 360. You know you always wanted to print hypoid gears.

Posted : 29/01/2020 9:37 pm
MD_Reptile
(@md_reptile)
Active Member
Topic starter answered:
RE: From Blender to Prusa i3 MK3S with exact dimensions?

I took some time to start working on a potential replacement off the i3 - which shows up on monday!!! Hurray!

 

Anyway I measured the nearly exact size of my window, and found I can print the whole thing in 6 parts, but I still haven't settled on a way to link those parts together (hot glue will hold the exterior perimeter in the window slot) but I think a good idea might be to put some holes to fit nuts and bolts through each part, and run a strip of metal with matching holes across all the parts, hopefully reinforcing them. I also found that transparent filament is a thing, and I want to try that out.

If this all turns out to be a terrible idea and doesn't stay in - I'll just go with the plexiglass/acrylic replacement idea instead, but I am gonna take a shot at it! Below is an early prototype (I thought I was going to need to split into 9 parts, but after measuring it I see I can do it in 6 instead) but this is sort of the idea I'm going for:

Posted : 31/01/2020 11:14 pm
hawai
(@hawai)
Estimable Member
RE: From Blender to Prusa i3 MK3S with exact dimensions?
Posted by: @md_reptile

I also found that transparent filament is a thing, and I want to try that out.

Right this moment there are some pieces printing in Taulmann T-Glase, according to their marketing the most translucent filament currently available. With 0.3mm layer height and 2 perimeters, 0%infill on a round upright printing piece I achieve just translucency. Nothing anywhere near what would work for a car window.

Assuming that you want to have at least 3mm thick panes that would result in 10 layers, giving you 20 optical interfaces across the thickness of your pane. From my limited experience with transparent printing I would assume you could at best hope for a frosted glass effect if anything. Using the largest available nozzle could reduce the number of interfaces (I have settled for translucent over transparent for the current project) and thus increase the translucency a bit. At least that is the theory.

An in regards to connecting the pieces, depending on the planned thickness a nut and grove type connection might give yoy some initial stability.

Posted : 01/02/2020 1:10 am
MD_Reptile
(@md_reptile)
Active Member
Topic starter answered:
RE: From Blender to Prusa i3 MK3S with exact dimensions?

I do understand that the transparent filaments are not completely transparent, especially with thicker parts - but really all I want to achieve is "nearly" transparent... where the police probably won't pick on me in the event that violates any laws (which I don't think it does, locally I think its ok to have no visibility through the rear window as long as there are both rear view mirrors on the left and right side of the vehicle), and to make it look a little less out of place, although even with it somewhat transparent it'll look odd because the rest of the rear window is tinted dark... but meh... I don't much care as the vehicle is getting old and already has many blemishes and rust spots.

At the end of the day I just want to take the garbage bag off the back of my truck and put something else in its place 😛

 

The more final shape I've got together:

The thickness I'm going for is 5MM which is pretty standard for auto glass in the front and rear, and will hopefully fit snugly where the original glass did.

This post was modified 2 years ago 3 times by MD_Reptile
Posted : 01/02/2020 9:52 am
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