UM2 Precision: Printing Threads and Gear Wheels possible?

[donidu 0]

Hi,

for my robotic projects I’d like to print small gear wheels and some parts with tapped-holes. However, my first attempts with simple items which I printed just for a test were not very promising:

 

• Nut and bolt (8 mm, a little more than 1/4 inch): thread looks creepy, but nevertheless I was able to screw the bolt with some force into the nut
  
• Gear-wheel 10 mm diameter (about 3/8”): teeth look quite coarse , not useable
  

The material was PLA and I used the default setting of the UM2, print mode ‘high quality’.

I know there are a lot of other parameters that can be changed but maybe someone here can give me an advice which parameters to change first or let me know if it is realistic to print gear-wheels or threads of this dimension at all.

Tom

 

[Daid 306]

I've done quite a bit of tinkering and tweaking on this area with my UM-Original. The UM2 gets about the same precision.

https://www.youmagine.com/designs/cat-gears-key-chain

These are the smallest gears that I think are possible. Printed with 0.4mm shell thickness. The problem lays with the 0.4mm nozzle that needs to put down 0.4mm lines.

http://www.thingiverse.com/thing:24253

These are the smallest threads I managed to make. Printed in this direction. Printing them sidewards is impossible at anything but "huge" scale.

On settings:

For gears you most likely want to lower the shell thickness to 0.4, you might need to tweak the infill-overlap and lower it (in expert) so prevent over-extrusion. And temperature, for small things you want to slow down the printing speed and lower the temperature. You could go as low as 190C. Also, turning off the heated bed and printing on tape is what I would recommend for anything small and not flat (but there will be people who disagree with me on this)

 

[IRobertI 521]

A look at the models you're trying to print would help. However, threads on an 8mm rod would be pretty damn tiny (depending on pitch of course) and not very structurally solid. You could probably print them fairly well by setting the layer height very small but it's really pushing it.

A gear wheel at 10mm diameter would mean the gear teeth are sub mm in size. The nozzle on the UM2 is 0.4mm so that is the absolute minimum size a single line of plastic can be (you may get it down to like 0.3mm but that's more for cosmetic things IMHO). So if my assumptions are correct those details are simply too small to be printed well. And they certainly wouldn't hold up to any kind of abuse.

 

[gr5 2,265]

You could go as low as 190C

 

If you are printing this cold (which is fine!) keep the speed around 20mm/sec.

 

[donidu 0]

Wow, have a look at the photo! I had to work long yesterday, so I couldn’t do much testing and further optimization, but I printed the white gear wheel with parameters based on Daids recommendation. The diameter is 9mm only and it looks very good. The black gear wheel and the black nut and bolt are the objects that I have tried before with the setup mentioned in my earlier posting.

For my project I can scale up the gear wheels, so I believe it will work. The tapped holes are not so important as I can drill them manually, but even this could be possible with this parameters.

I think in my first test mainly the printing temperature was too high for the small surfaces and the heated bed was counterproductive, as the little black gear wheel looks a bit melted already.

 

Here are the parameters I used for printing the white gear wheel, if anyone needs it too:

Material: ColorFabb PLA white, layer height 0,06 mm, Shell Thickness 0,4 mm, infill overlap 10, heated bed 0°, temperature 200° Celsius.

 

 

[gr5 2,265]

Drilling PLA is more like melting PLA. The friction causes it to heat so fast you never really get to the cutting state so much as pushing around soft pla with the drill bit. Unless you dip the drill bit in ice water every 3 seconds.

If you want to use metal M3 (3mm) threads (the small bolts that come with the UM and UM2) you can set the hole diameter to 3mm and it will print a bit small and the 3mm screw will self tap screw threads nicely. Not as strong as using a metal bolt but pretty decent.

 

[donidu 0]

Good idea! I've already found out that heat can be problem when working with PLA when I tried to smoothen the surface of a printed object with small drillng machine (Dremel). Although I did not put much pressure on the grinder, the surface meltet and became quite bumpy, so that I rather took a piece of sand paper to do it by hand.

For the drill holes I'try use a sharp drill with little pressure, low rpm and I'll lift it every second. We'll see what happens.

 

[IRobertI 521]

I've used a power sander on PLA before. I used wet sandpaper and periodically dripped some more water on the surface, worked fine. So as long as you cool it you can be quite aggressive.

 

[SandervG 1,521]

power sander

 

Yes .. ?

:cool:

 

[daveholbrook 0]

I've successfully printed M10, M8 and even M4. However the M4 holes did require an M4 plug tap run down them but after that they were fine, and the tap located perfect.These were all done on an ultimaker 2 using just the high quality settings on Cura.