TOM's i3 Dolly Prusa - pre build question

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Uriel
Posts: 2
Joined: Tue Sep 26, 2017 3:16 pm

TOM's i3 Dolly Prusa - pre build question

Post by Uriel » Tue Sep 26, 2017 3:31 pm

Hello all,

i am totally new to the 3d printing world,but i am totally addict of building stuff on my own.
that is why the guide for the MK2 clone making my fingers go nuts :D

but i wanted to ask a few question before i am approving my huge shopping list in aliexpress.

1)rods- "8mm smooth rods, 320m, 330 or 350mm, 370mm"
what will be the difference between the sets?how it effect the build?

2)3d parts.
i saw few modification,is is possible to buy MK2 set so i can have a basic build and print the rest?
or that it wont work without the modified and i will have to search for 3d printing services?
and if so, what is the parts i will need to print?(there are 3 places where the 3d parts are mentioned and i got confused)

3) what will be downfall of this clone?
will it be able to print the same materiel as the real MK2 ?

Thanks in advance .

chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: TOM's i3 Dolly Prusa - pre build question

Post by chumm » Sat Sep 30, 2017 3:15 am

Hi Uriel, sorry for the late response.

1. The old i3 kits used 320mmx2, 350mmx2, and 370mmx2 rods, so this is easier to find as a single kit online. The MK2 replaces the 350mm with 330mm rods. Tom modified the Y rod holders to account for this, leaving an open end to let the extra rod length hang off. If you get 330mm it will fit perfectly with the unmodified parts.

2. The modified parts are the Y holders noted above and endstop holders for X and Y to use the common cheap physical endstops, as well as a Z nut holder to allow for using an M5 rod for the Z axis. The M5 rod is a terrible idea and he only did it to make the build as cheap as possible. If you buy standard T8 leadscrews and get 330mm rods for Y, you can use a set of standard MK2 parts. I'm not sure what the difference is on the MK2's endstops, but you can attach them anywhere you like with a dab of hot glue or tape, they are barely touched in operation so they don't need to be super sturdy.

3. The Dolly as-is is designed to be as cheap as possible. I don't have an MK2 to compare but I did build a Dolly as my first printer and the most obvious problem is that a 12v power supply just doesn't heat up a standard 200mmx200mm bed fast enough, nor to a high enough temperature to print ABS, etc. It is possible, just a huge hassle and takes forever. RAMPS only works on 12v without modifications, so you can't switch to 24v for quick heating without also changing the electronics (which would include swapping the fans and hotend/heat cartridge to 24v versions). I think the MK2 is 12v though so there's probably a way to do it, might be worth looking into how to improve that if you find it to be an issue.

It will print PLA very well and has a decent sized print area. Because it is a direct-drive extruder, flexible filament printing should be possible, although the idler springs are way too tight by default for this to work. Make sure to watch Tom's follow-up video where he identifies all the problems with the design. The idler springs are bad, the extruder pulley is poorly lined up with the hotend, the Y carriage screws crashes into the frame (you'll see Tom cut giant chunks out of his frame, good luck doing that if you had an aluminium one made like me). The Z probe in the original bill of materials is pretty bad and completely useless if you add any sort of print surface to your aluminium bed (it has to get super close to the bed to get a reading). The square frame and the Z motors are floating and held up only by a nut and washer, so the rigidity is really bad (I had to put mine on a non-slip mat so it wouldn't walk off the table). I guess people like their MK2s but I think the design is rickety garbage. One of the steps to level the frame is literally to pick it up and twist it back and forth until it seems like it's flat :roll:

Either way it's a good first printer to make. It's cheap, it works, and you've got hours of video of the assembly and a community of people who've also made one, so there's lots of help. Feel free to ask here if you run into any issues while building :D

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: TOM's i3 Dolly Prusa - pre build question

Post by slippyr4 » Sat Sep 30, 2017 9:50 am

The original uses common, cheap micro switches for end stops. I’m really not sure why Tom opted to use endstop boards; it meant the parts needed to be modified for little gain. I’d recommend you use micro switches just like prusa do.

Dolly was designed to be as cheap as can be. But if you can spare a bit more money you could make a better printer.

In particular, try and buy an aluminium frame instead of using wood. You can find them for about £/€ 50.

Then I strongly recommend that instead of RAMPS and an arduino, you instead buy an MKS Base or MKS Gen board. They are compatible with ramps, but all in one. And they have an extra mosfet so you can have the board control the extruder fan too. RAMPS has had its day, don’t bother with it. Toms marlin build will run just fine on either of those boards without mods. Or, if you get yourself a MK42 clone then you can run prusa firmware.
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

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PartTimeRonin
Posts: 85
Joined: Mon May 22, 2017 2:33 pm

Re: TOM's i3 Dolly Prusa - pre build question

Post by PartTimeRonin » Sun Oct 01, 2017 9:33 pm

How about wait for Prusa i3 MK3 STL file to be available?

chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: TOM's i3 Dolly Prusa - pre build question

Post by chumm » Mon Oct 02, 2017 2:03 am

PartTimeRonin wrote:
Sun Oct 01, 2017 9:33 pm
How about wait for Prusa i3 MK3 STL file to be available?
Seems all the changes made to the MK3 are way outside of the scope of a Dolly. The new Y axis and extruder idler are definitely worth working into a clone though once we have enough info on how they're set up.

Uriel
Posts: 2
Joined: Tue Sep 26, 2017 3:16 pm

Re: TOM's i3 Dolly Prusa - pre build question

Post by Uriel » Tue Oct 03, 2017 10:20 am

Thanks all for replaying.

changing the frame was on the top of my list.
i might have an access to a friend who works in CNC so he might do it free of charge.

electronics will also be replaced,but i think later on.

so i need to print the list in the tabel (where it says mdofifed) and thats all the parts i need?
or i missed somthing?


Thanks

chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: TOM's i3 Dolly Prusa - pre build question

Post by chumm » Tue Oct 03, 2017 9:09 pm

Uriel wrote:
Tue Oct 03, 2017 10:20 am
so i need to print the list in the tabel (where it says mdofifed) and thats all the parts i need?
or i missed somthing?
You need everything from the standard list, but some of those are replaced in the modified table. The "Qty needed" field will tell you when to use a modified part. The only one that is variable is the Y corners. You use 4 standard if you have 330mm Y rods, or 2 standard + 2 modified if you have 350mm Y rods. As noted above, if you purchase a pre-printed MK2 set you should be able to get away with not having to have extra parts printed as long as you have 330mm Y rods and use 8mm leadscrews instead of 5mm threaded rods for the Z axis.

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