Bridging

[jdacal]

Still waiting on my M2 but playing around with S3D and CAD and coming up with the usual first time user questions.

I read somewhere that for large flat objects its a good idea to include slots in the base to make it easier to remove. First, is that true? Second, assuming it is... in the image I placed 2mm X 2mm slots on the base of this model which would require some bridging. Are there any special settings I would need in S3D to account for the bridge or would it automatically take care of that? Or do I need supports for a 2mm X 2mm bridge? Not sure how wide a gap has to be before supports would be needed.

EDIT: I might be a little confused about bridging and supports. I know you need supports if the angle exceeds 45 degrees. But how long would a bridge have to be before you have to support it? Hope I'm making sense here.

jimc, thanks for referring me to the forum!

Thanks!

2014-07-06_22-50-40.jpg (22.66 KiB) Viewed 10053 times

[Tim]

Generally speaking, as long as you wait for the print and glass plate to cool down to room temperature, the most you should need to pop the part off is a razor blade. The slots should not be necessary.

I generally don't worry about support material unless there is an overhang that is not supported at all on one or more sides. A hole printed like you have in your picture should not need support unless it's larger than, maybe, 10 to 20 mm. When bridging occurs over a place that is completely supported on all sides, like the hole, there will be very little sagging at the top.

There are settings for bridging parameters in S3D, but you should leave them alone until you've done some prints that require bridging and can see for yourself whether the result is good or not. Some plastics like PET+ are very poor at bridging, and may need a lot of parameter tweaking to get right. PLA is very easy to work with and bridges well. The main thing is to have the fan blowing on it full blast so that the plastic solidifies in mid-air. The S3D default bridging parameters should ensure that all that happens correctly.

[jsc]

I've done prints that have bridged 50, maybe 60mm, and it turned out alright. There was some sagging. I've spent some time trying to improve bridging, and the most I've been able to determine is that you should bridge fairly slow while underextruding (although some people say bridge fast, YMMV), and that as Tim says, you want the fan blowing; but! I've found that with my fan, blowing at 100% will actually move the bridged strands around and cause defects, so I bridge with fan at less than full on.

You can insert slots to ease removal, but I wouldn't. You will more likely encounter the problem of parts not sticking well enough. I have had some difficult to remove prints (large contact surface in PLA over glue stick), but some persistent prying, rinsing, and time in the freezer got them off eventually. It is pretty rare.

[jimc]

i dont really think the grooves are necessary. i have no problem removing prints. as tim said a razor blade and occasionally i will use a nice heavy duty 3" scraper i got from home depot. i have never not been able to get a part off. with pla using certain adhesives i have heard some guys putting their glass plate in the freezer when parts are difficult to remove. then they just pop off. i have never had to do it though. there isnt anything you have there, grooves or holes, that are so big that you cant easily bridge that with no support. like tim said its usually 10mm or bigger

[jdacal]

Thank you all. I will remove the grooves. Will play around with the bridging when I have to cross that bridge. No pun intended.