Page 1 of 3

TOM's i3 Dolly Prusa MK2 scad

Posted: Thu Jun 29, 2017 1:56 pm
by Jim JKla
I am in the process of building a Dolly after following Tom’s excellent You Tube series I am building it a step at a time due to fiscal constraints. (Low disposable income).

I am using some 19mm MDF for the main frame and some 10mm MDF for the bed. (It was in my shed).

I also have plenty of 8mm & 10mm screwed rod these are offcuts from a warehouse ventilation job 10mm nuts and washers from the same source.

8mm nuts have come from Wilco, in the UK their shops have a “Pick and Mix” selection that includes 8mm Nuts and washers. Fill a bag from the selection for £2.99 (GBP).

I had my printed parts built by a local member of a 3DHub not cheap £51.85 (GBP) but at least reasonable and I was happy with the finished parts. This included a £4 (GBP) setup fee.

I have found an online suppier BOLTBASE for my other Nuts/Bolts etc. This is an ebay shop based in Alloa Scotland. Not that far from home in Newcastle, they do free shipping but I plan on visiting so I can fine tune what I get.

I have some silicone sheet I plan to use as a thermal barrier to replace the cardboard Tom used.

As I await funds I decided to try and build a virtual version and I am using OpenSCAD I have been able to retrieve the original SCAD files from the Prusa Github. This involves opening the Github file highlighting the code and pasting it into OpenSCAD then saving it as a local file being careful to have the original name.

Getting the exact shape for the main frame and the bed has set me on a learning curve as the files in the Github for these parts are .DXF (I am getting there). When I tried to extrude in OpenSCAD from the linked dxf file I got a lot of stange shapes I have yet to figure out why. So I have resorted to a scratch build process for these shapes.

For the first of Tom’s modified parts the y-corners I was able to modify the Prusa original SCAD as it is clear that Tom just opened out the end slot for the 8mm rods. However for my current virtual build I have just used the origonal y corners and made the screwed rods a couple of mm longer to compensate.

Now I am up to the point where I am ready for the x-end-motor piece I have the original but does anyone know it there are any OpenSCAD versions of these and the other parts Tom modified?

I have the actual parts printed from the .STL files and if push comes to shove I can probably try and reverse engineer using the SCAD of the original Prusa parts.

I am however reluctant to re-invent the wheel.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Thu Jun 29, 2017 4:29 pm
by slippyr4
Tom didn't use openscad to modify them so you won't find scad files for what you're look king for.

I can't recommend trying to use the DXF in openscad, it's not really what's intended. TOm published a PDF on his site which can be used as a template for the frame print.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Thu Jun 29, 2017 5:13 pm
by Jim JKla
I know about the pdf that's what I have used to make my chassis and bed but and that's not a lot of use when it comes to creating an OpenSCAD model.

I have managed fairly well considering a month ago I was at a level where I could read engineering drawings and make parts the old way (files, hacksaws etc.) I am an old school mechanic and started as an apprentice engineer circa 1972. (Yes I am that old)

I also figure if I can create an OpenSCAD model I am going to be in a position to build/modify parts from scratch.

I am a fan of all things open source and have done a lot of stuff in Blender.

I dare say by the time I get my Dolly running I will be well familiar with OpenSCAD. I have only posed the question here in the hope that there may have been someone down the road before me.

Also even if Tom did not use OpenSCAD he must have used something and theoretically the files should exist somewhere. I have a vague hope he may read this and post the files (you never know).

As I say if all else fails I will get out my old school Imperial Vernier Callipers and 0-1 Imperial Vernier Micrometer, and resort to reverse engineering. When I started digital Callipers were around but were considered lazy my tutors were of the opinion that you were not a proper engineer if you could not read a vernier scale. ;)

The plan is to post the results for comment criticism abuse whatever. :D

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Thu Jun 29, 2017 6:16 pm
by CDog
Haven't done it myself but there is at least one thread (google) that talks about using inkscape to modify the dfx files to dfx files that openscad can read. The inkscape plugins for this are on thingiverse.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Thu Jun 29, 2017 8:09 pm
by slippyr4
What changes do you want to make anyway? My build wasn't a dolly but as close to stock as I could.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Thu Jun 29, 2017 10:37 pm
by Jim JKla
I am probably looking at safety for the PSU but until I have the PSU and know the dimensions I will not know what is needed. I am probably looking at some sort of MOSFET mod for the heat bed.

I am probably looking at stiffening the chassis and at some point I plan on replacing the 5mm Z axis screw with 4 lead screws I am also thinking about using a similar mechanism for the Y axis.

Vacuum bed and magnetic mounting build plates.

Once I have a printer I am looking at using a variation to build a Dolly that will take my router I am also looking at making this have horizontally arranged X axis rails like the Anet A6 capable of cutting a Dolly chassis. In order to mount my router I am probably going to have to do a considerable increase in strength to take the heavier kit.

In due course I am looking at a new design with an increased build area probably with totally different methods for mounting the Y axis

I also want to look at a multi material option but that is some way down the road.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Fri Jun 30, 2017 12:40 am
by chumm
I think you'll find that the Dolly is decent at doing what it does, FDM printing on a medium sized bed, and that's about it. Just about any modifications you do will feel extremely limiting, in my experience (though I definitely recommend leadscrews right away, the 5mm threaded rod is awful). Basically every design decision in the I3 Mk2 is to use cheap mass produced parts and 3d printed parts to do everything, and this leads to a pretty rickety design. It of course is sufficient for FDM and holds together pretty well, but I'd definitely recommend building it stock then using your new printer and CAD enthusiasm to build something better.

That was the approach I took, at least. A friend wanted a printer after I made my Dolly so I took the opportunity to design and build a bigger, more powerful, more stable machine based on 2020 aluminium extrusion (the bed is a bit small bc I'm waiting for a decent MK42 to be widely available). It was a good opportunity to learn more about how 3d printers work and how to model a full project from scratch, so it seems in line with your interests.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Fri Jun 30, 2017 8:49 am
by slippyr4
I agree with chumm. The mods incorporated into dolly are really just to make it work with cheaper off the shelf parts. If you want a better printer then moving it closer to the stock prusa i3 would be the way to go- get yourself a MK42 bed, use TR8 leadscrews (ideally integrated into the motor, otherwise with couplers).

If you want to build a decent printer that can be adapted to do. NC and other tasks there are much better free and open source designs out there. Look at the various hypercube designs and possibly even the e3d big box.

Regarding the PSU cover - a chap from the reprap forums and I modified the SCAD file to make it parametric and thus suitable for virtually any power supply on the market. It's too complex for customiser on thingiverse but I am happy to share the scad file.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Fri Jun 30, 2017 4:11 pm
by Jim JKla
I had to start somewhere with resources I have to hand, that and a very limited budget.

I comited to the Dolly and paid for my printed parts only to find the next day an Anet A8 flash sale that would have been in budget If I had not bought the parts for the Dolly. Go figure.

Disapointed but not discouraged I will follow through on the Dolly and use my engineering skills and my limited funds to make it the best I can.

Once I have a printer no matter how basic I will have a start point.

I am an old school engineer/mechanic the one resource I lack is cash.

Since I started the thread I have re-built my virtual squashed frog in OpenSCAD and that virtual build is comming on a storm. Its just a shame it will not actually print.

Re: TOM's i3 Dolly Prusa MK2 scad

Posted: Fri Jun 30, 2017 11:45 pm
by CDog
You will never regret building a printer from scratch. You learn so much more that way than with any kit. I applaud you.