Walls of printed layer fan too thick?

[dtgriscom]

I've finished building my Rostock MAX v2, and am following Gene's manual through printing the PEEK fan housing and the layer fan housing. I've calibrated the Z height and done the hot end temp auto-tune, but have changed no other factory settings.

Problem: both printed fan housings seem to be too small for the included fans. I trimmed the PEEK fan housing down a bit and was able to squeeze the fan in place, but the layer fan (see http://repables.com/r/212 )seems to be even tighter (ignoring the flare where it sat on the bed, the fan hole is about 29.5mm long, while the fan is 30mm).

My first thought was to boost the scale to 102% before printing, but clearly that's just kicking the problem down the road. So, I used OpenSCAD to make up a calibration shape consisting of 20mm square holes separated by 5mm lines, thickness 0.5mm (see http://repables.com/r/259 ), printed it in ABS, and made some measurements.

I found that the large-scale size is right on the money (measured dimensions +0.15% larger than expected), but the supposedly 5mm lines ended up between 5.5mm and 6.25mm. Part of this was my Z axis being a hair too low, and being right on the bed, thus squeezing the ABS out the sides. But, this also is similar to the dimension problems I'm seeing with the layer fan.

How should I handle this? Make some Slic3r configuration change? Scale up the shape before printing (somehow)? Break out the Dremel tool? Blame Putin?


TIA,
Dan

[Tinyhead]

Well... my answer probably won't be of too much help, but when I printed the layer fan shroud in ABS, it was just like you said; a bit too small. When I printed in PLA it was bang on. ABS shrinks somewhere around 1% and I'm not too sure yet what guys do to get around that. I would have done the same thing you did and scaled the part to compensate, but someone with real ABS experience should be able to weigh in on this.

[Howler]

I also just printed the fan shrouds and found them to be a little snug. I could get the fans in there, but it was VERY snug, and the PEEK fan wouldn't turn with the extra pressure. I just took a square file and filed the hole a little bit bigger for the fan.

[dtgriscom]

I'll look at the STL over the weekend and see if I can make the fan compartment larger, perhaps by importing into OpenSCAD and subtracting the appropriate fan shape.


... any other ideas?


Thanks,
Dan

[Eaglezsoar]

Well... my answer probably won't be of too much help, but when I printed the layer fan shroud in ABS, it was just like you said; a bit too small. When I printed in PLA it was bang on. ABS shrinks somewhere around 1% and I'm not too sure yet what guys do to get around that. I would have done the same thing you did and scaled the part to compensate, but someone with real ABS experience should be able to weigh in on this.

Normally when a part is created in Cad, they allow for the known shrinkage. If you design the part and don't allow for the shrinkage you end up with parts not fitting correctly as you have discovered.

[0rionN00b]

Ha! Funny you mention that..

you're right, I think... I needed that fan (today!), and printed it, only to figure out the same...

I was going to just re-print it 2% larger (scale in Slic3r) but I got impatient and enlarged it a bit with a Dremel...

works well!

I've finished building my Rostock MAX v2, and am following Gene's manual through printing the PEEK fan housing and the layer fan housing. I've calibrated the Z height and done the hot end temp auto-tune, but have changed no other factory settings.

Problem: both printed fan housings seem to be too small for the included fans. I trimmed the PEEK fan housing down a bit and was able to squeeze the fan in place, but the layer fan (see http://repables.com/r/212 )seems to be even tighter (ignoring the flare where it sat on the bed, the fan hole is about 29.5mm long, while the fan is 30mm).

My first thought was to boost the scale to 102% before printing, but clearly that's just kicking the problem down the road. So, I used OpenSCAD to make up a calibration shape consisting of 20mm square holes separated by 5mm lines, thickness 0.5mm (see http://repables.com/r/259 ), printed it in ABS, and made some measurements.

I found that the large-scale size is right on the money (measured dimensions +0.15% larger than expected), but the supposedly 5mm lines ended up between 5.5mm and 6.25mm. Part of this was my Z axis being a hair too low, and being right on the bed, thus squeezing the ABS out the sides. But, this also is similar to the dimension problems I'm seeing with the layer fan.

How should I handle this? Make some Slic3r configuration change? Scale up the shape before printing (somehow)? Break out the Dremel tool? Blame Putin?


TIA,
Dan

[dtgriscom]

Well, I finally solved it by reworking John Olaphson's housing using OpenSCAD. I wrote a script that imports his STL file and does the following:

1. Makes the fan slot 1mm wider and taller
2. Adds some clearance above the mounting screw so that a screwdriver can more easily get to the mounting screw

   

3. Added a bit of wall to better guide the air exhaust towards the part.

   

Here's the OpenSCAD code. It takes Oly's design, subtracts a cube to make the fan slot larger, subtracts a cylinder to add the screwdriver access, and then adds a plate to better guide the exhaust:

Code: Select all

extraHole = 1.0;
fanX = 30.3 + extraHole/2;
fanY = 10.3 + extraHole/2;

difference() {
	// Import original fan shroud
	import("./NEW2-Guanu-Blower-Fan-Holder-Shroud.STL");
	// Cut a slightly larger slot for the fan
	translate([16.7 - fanX/2, 11.6-fanY/2, -21.5])
		cube([fanX, fanY, 30]);
	// Cut out clearance for screwdriver access to the mounting screw
	translate([0, 11.6, 13.5])
		rotate(a=60, v=[0, 1, 0])
		cylinder(h = 10, r=5, center=true, $fn=60);
}

// Add a bit more guidance for the fan's exhaust
translate([32, 6.5, 8.4])
	cube([1.3, 10.3, 7]);

Here's the complete OpenSCAD file:

MakeFanHoleBigger.scad

The OpenSCAD code to rework Oly's design

(559 Bytes) Downloaded 304 times

And here's the resulting STL file:

MakeFanHoleBigger.stl

The resulting STL file

(551.8 KiB) Downloaded 324 times

(I've been trying to upload this to Repables.com, but to no avail. A subject for a separate post.)


Enjoy,
Dan

[joecnc2006]

If you were to enclose the bottom 1/2 the way to the end It will work better, I added tape to mine and it forced the air better towards the nozzle.

[Brian]

Well... my answer probably won't be of too much help, but when I printed the layer fan shroud in ABS, it was just like you said; a bit too small. When I printed in PLA it was bang on. ABS shrinks somewhere around 1% and I'm not too sure yet what guys do to get around that. I would have done the same thing you did and scaled the part to compensate, but someone with real ABS experience should be able to weigh in on this.

Normally when a part is created in Cad, they allow for the known shrinkage. If you design the part and don't allow for the shrinkage you end up with parts not fitting correctly as you have discovered.

Wouldn't the shrinking plastic cause the fan slot to get wider as the plastic moved away from the opening? Remember, the entire part will not shrink in all directions because it is not formed in a uniform process. It is built up from lines and walls which sit in top of previously laid lines and walls.