How to make a watertight part

[bbinnard]

By watertight I mean capable of holding water without leaking.



Here is a Factory FIle of the above part I just made: http://1drv.ms/1LvUQG2

I wanted it to be watertight so I made the part double-walled with each surface made of 4 layers. The bottom is double walled too, and I specified each surface to be made with criss-cross parallel lines.

The part looks solid enough, and the loops look like they are all connected to each other, but when I put water in it some of it leaks through the bottom and gets into the underlying infill spaces. I'm sure that, given enough time, that will leak through the bottom surface.

Apparently I need some different settings for extrusion width, or overlap, or something. I'd certainly appreciate any help from anyone who has made truly watertight parts.

[JoeJ]

I usually tend to add more outline perimeters and more top and bottom solid layers if I need something to be water-tight. I also like to over-extrude a bit for those prints to make sure everything gets very solidly sealed (usually no more than 5-10%)

[bbinnard]

I usually tend to add more outline perimeters and more top and bottom solid layers if I need something to be water-tight.

Well ok, i have specified 4 for top/bottom layers and 6 for perimeter loops. So how about 6 & 8? 8 loops seems like a lot actually, but i can try that.

I I also like to over-extrude a bit for those prints to make sure everything gets very solidly sealed (usually no more than 5-10%)

Very interesting. I've read in several places that over-extruding causes strings and blobs because of excess pressure in the hot end. So my current setting for Extrusion Multiplier is 0.90. I was pleased that my print of this part had no strings or hairs at all, and these have been a problem for me up to now. My printer is a delta-style machine with a bowden tube, and these are apparently more prone to strings than direct-feed extruders.

Perhaps I should change Extruder Width to 0.420 mm; it currently matches my printer's extruder diameter = 0.400 mm.

[KC_703]

Stringing and hairs can often be rectified by retraction settings.

If using a 3mm filament, they are often 2.85mm. Spot check the diameter of the filament with digital calipers. Set the filament diameter to the average taken.

Interestingly, a .95 of 3mm is 2.85mm... so a multiplier of 1.0 is usually over extruding a bit. I find a bit of overextrusion is good if the default speed of the machine is increased.

[bbinnard]

I understand how retraction affects strings and hairs; I was able to achieve a stringless print by specifying a retract length of 9.000 mm. I am wary of increasing Extrusion factor as doing that could result in strings reappearing.

[SvenZHB]

You probably print too hot. Reducing the temperature also reduces the danger of strings. 9.00 mm retraction is very much. With my 1.75 mm filaments it is recommended to use 3.5 - 4.5 mm not more.
Try to reduce the temperature and you should be able to change the extrusion multiplier and the retraction distance without problems and string building.

[bbinnard]

Thanks Sven, I have heard that recommendation before. For this part I reduced the temp from 200 to 190 and myt sense is that this is close to the lower limit for PLA - which is the only type of filament I use.

As for the 9mm retraction length - this is because my printer has a Bowden tube feed; apparently printers like this require a retraction value of 7 - 10 mm.

I am still thinking the key issue related to watertightness is how much the individual loops overlap each other. I doubt water leaks through the plastic of individual loop traces, but rather finds its way through tiny open spaces between the loops.

[SvenZHB]

That has nothing to do with bowden type as I also use a bowden type printer (400mm bowden length). There is PLA outside which starts printing at 150°C. Other PLA can be printed even with 230°C. However for testing purposes I would run one test. Lower the temperature as much as you can. if you reach the area where your extruder starts skipping or cannot extrude: Note this temperature add 10°C on top and try again.
So I was not answering because of your watertightness but helping you with your string problem.
So what PLA do you use?

[Tetraodon]

I believe PLA starts to dissolve over time in water - especially hard, alkaline water.