minimal layer time, fan position

[kenjo 3]

So I was trying to print some nuts and bolts to see if they was actually useful for real use.

I'm printing this unmodified http://www.thingiverse.com/thing:193647 using ABS filament from ultimaker.

One thing that did not work was printing the bolts. what was happening was that the plastic was to soft and after a while just got stuck in the printer head and then the print was a failure.

I'm not sure if the problem is to much plastic or to little cooling. I was using 100% infill to get a strong result. since I don't know how to change the amount of plastic extruded I changed the minimum layer time from 3 to 10 to get more cooling.

Now what is happening is that at every layer ultimaker is doing a pause. as can be seen here.

https://goo.gl/photos/S4TqbWHuGJAGtw2j8

But it look to be very unoptimal as the fan is now blowing on the side of the object. Is this something that works on ultimaker 2 but not on ultimaker2+ ?

or is the move only done to get the printhead away from the object to avoid dripping?

[yellowshark 153]

Your problem is that with the bolts the layer time to print a layer will be very small, when ideally you want around 10 secs. As you set 3 secs. for your minimum layer time then the next layer will be printed before the previous layer has had time to cool and you will get, as you noted, a mess.

When you changed your minimum layer time to 10 secs. Cura then moved the printhead away from the bolt while it waited for the 10 secs. then moved back to the bolt and printed the next layer, and so on. It moves away so that if there is any dripping it will not drip on the bolt and also it takes the heat from the print head away so that the top layer can cool.

You have several solutions. For the bolt I would print multiple copies so that the total layer time is at least 10 secs. The problem with this solution is that Cura has a serious bug where the printing sequence of the multiple models is wrong. If you have four copies of the model, ABCD then the printing sequence is A,B,C,D then D,C,B,A then A,B,C,D etc. So B & C will be OK but A& D may not be.

Load you bolt into Cura and then select Tools/print all at one time. You want/need to spread the four bolts on the print bed to ensure you get a long enough layer print time.

[kenjo 3]

Yes 10 sec worked much better. unfortunately the bolt I printed had a design problem that made it really weak. the hole for the hex wrench is way to deep and makes the whole bolt easily snap of. But using the nut on the rod I was unable to break it without using tools.

I will test with PLA also later. and have some nylon and PETG ordered.

[yellowshark 153]

No reason why PLA should be better than ABS, probably the opposite. But I have used PLA for fasteners OK - like many things it depends on the stress that the part will be subjected to.

[kenjo 3]

the problem I have with ABS is layer separation I don't think it is happening on the bolts I printed as the break surface showed that the layers was more or less totally fused. But when I print larger prints in abs with an unmodified ultimaker 2+ the print almost self destructs there is visible cracks and its very easy to snap it apart.

Really wished I know it was this hard to print ABS before I bought it. Now it looks like I need to make some sort of door and top to keep the build area hot for ABS printing :(. Or find some other plastic that is car safe (can be very hot inside at sunny days).

[Labern 773]

PLA is a lot stronger then ABS and has better layer adhesion.

You can get high temp PLA's and colorfabb are soon to release a high temp filament. I currently use nGen which has a glass transition temp of 85deg.

For printing your nuts and bolts I would suggest printing a few at once as to prevent overheating. with ABS you don't want much fan or even no fan. lowering the minimum layer time can have a negative effect sometimes so for small parts its normally better to print more then one and bigger parts you can print a small tower next to the model.