Rivets reproduction

[joel-mercier 0]

Hello forum,

I am Joël, living in France and using a Ultimaker2 that I bought a year ago. until now I didn't print much but now, I have more time to spend on it.

Right now, am trying to print an Iron bridge structure but I got a problem in between the rivets. A line of plastic appears. Is it possible to avoid it?

The diameter of the rivets is 0,4mm. I thought that is could be coming from the "Z hop when retracting" parameter that I've set to "3" and the "minimum travel" parameter at 1,5mm but it doesn't change anything... Is there any way to improve it?

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Thanks in advance for your answers

Joël

[Labern 774]

Is it actually retracting between each one? if not then you will need to reduce the minimum travel and the minimum extrusion before retracting.

As the rivets are rounded and small adjust the retraction minimum extrusion and travel amounts as small as possible. You can look in layer view to check to make sure its retracting between each one. If you make the amounts to small it may have excessive amount of retracting, so just lower them enough to make it so it retracts.

[joel-mercier 0]

Yes right, I was able to figure it out checking at the layers view in Cura. By playing with parameters I was able to see the retraction (blue lines going up) on the concerned layers. Now I'll have to try it out but it will take time as I have to redo the 3D model as I have a problem of scale with the original/real one. I'll keep you inform.

Thanks again...

[macgraj 0]

Hey Joel-mercier,

have you managed to print it again? Do you still have the same problem?

[joel-mercier 0]

Hi !

I am still in the modeling stage. I went back to the real bridge to take measurements and plenty of pictures. I am hoping to be able to start printing at the end of the week or early next week. For sure I'll keep you informed.

[joel-mercier 0]

Good evening,

I am done with modeling my part. I import my model on Cura then I switch on layer view. I focus on the layers concerning the topics (the rivets) then I need to have the settings as you can see on the picture to visualize a proper "Z hop". Would that setting work? does it influence the quality of the print or just the nozzle trajectory?

[gr5 2,173]

I advise against Z hop. It can greatly reduce the quality. It's most useful for delta printers, not X/Y printers.

I would print it as shown but I would also try printing the part up on the long edge (try both!). That way the rivets are a simple bump out and no retraction needed. I would also enable the brim feature if you print it on it's side to keep it from falling over during the print and possibly even add a few 45 degree supports to be removed later using cad software that meet the part half way up. But it should be fine without any supports.

[gr5 2,173]

I would also grab the last layer printed from the gcode file and run it through something to count the G11 (retract) commands and also look at the extruder position (which is in cubic mm which is confusing) and try to figure out how many retractions there are per mm. Then knowing it retracts about 4mm or 4.5mm figure out how many times each spot of filament goes back and forth through the feeder. If it's more than 100 you will probably get grinding. But maybe not. I've done > 100 and been fine on some printers/filaments and on others it fails around 30 to 40 times having the same spot go through the feeder.

[joel-mercier 0]

Do you mean that I might destroy the feeder for the printer? Actually the complete bridge counts 2 bays of 11 sections each x2 sides means 44 sections as the one seen on the last screenshot.

(Cf. "viaduc de la renvoise")

[gr5 2,173]

No - but you may grind the filament into dust. For example I printed the eiffel tower which has hundreds of girders per layer - each tiny girder is a separate "island" on a layer. I actually had a half kilometer of retractions! On average each piece of filament went through the feeder 20 times and it was no problem.

Then on a different printer I was printing big ben and there was a few layers where there were 40 retractions per piece of filament and the filament ground down to half it's normal size and eventually failed. I had to reslice it with fewer retractions - it came out great.

Some printers/filaments can do 40 retractions per spot of filament without grinding it down too much. Other filaments get ground down until it can't feed anymore and the feeder stops feeding and the print fails (nothing extrudes).

There is absolutely no damage to the printer.

[joel-mercier 0]

Ok. I'll try to print it as I've programed it first (maybe tomorrow evening) if there is no risks for the printer, only risk of wasting a bit of material... Then I'll try later this week to print it standing as you suggested but for that I'll design the inner parts first. To be followed and thanks for sharing your experiences ;-)

[joel-mercier 0]

Trick to count G11 command : Edit the geode as text file, copy and paste in a spreadsheet then apply a filter that is equal to "G11" then count the remaining lines ... Maybe everyone already know but am happy to have found it ...

Anyway, the point is that from my gcode I can find 10548 "G11" ... may be too much...

[gr5 2,173]

Sometimes if you do a find/replace all it tells you how many it replaced so you can change G11 to X11 and then undo. or use "find" dos command or "grep" unix command.

10548 is fine as long as it is a big enough print. 10548 X 4.5mm retraction (the default I think) is only 47 meters of retractions. I've had a half kilometer of retractions. But if you are only printing 1 meter of filament that's 47 retractions for each spot - marginal but might work. If you are printing 4 meters of filament that should be fine. More importantly just check ONE LAYER. the layer with the rivets.

Anyway you won't break anything - the worst thing that will happen is you will grind the filament at the feeder and have to remove the bowden at the feeder to get it out. Make sure you push down on the ring around the bowden while pulling up on the bowden. Perhaps use needle nose pliers for pushing down.