Slight inaccuracies with the printer

[Franny500 9]

Hello All, Happy New Year etc,

I printed off a sample bearing, similar to this but taller

http://www.componentforce.co.uk/userfiles/image/categories/nylonwashers9.0mmidto40mmid_4f7ae26403160_lg.jpg

I printed it in PLA and then checked it. And although two of the dimensions were out, one was particularly inaccurate. So I sent it to a friend to check it. Here's what he came back with -

Intrigued by that inaccurate centre bore on the bearing print I ran a quick check by recreating the design to the 10mm outer diameter and 6 mm inner diameter dimensions of the original. What I wanted to do was eliminate any possible error from the conversion to the .stl file on the original.

 

I then ran the design as a print and got the same results, the outside diameter was within 0.04mm of the nominal 10mm dimension which is a credit to the printer. But once again the inner diameter came out as only 5.5 – 5.6 mm, an error of 0.4 – 0.5mm which is huge compared to the actual dimension of 6mm, and 10x the error on the outer diameter.

Am interested to know why this is happening and if anyone could help explain and offer up a solution?

[Labern 775]

It's normal for inner holes to be smaller then outer dimensions when it prints.

Have a read of THIS as it explains it quite well

Edited January 4, 2016 by Guest

[Franny500 9]

Thanks Labern that is an interesting read.

I asked my more technical (than me, who isn't ?) friend and he was a bit surprised at the difference in the tolerance between outer and inner diameters. But thanks again for the reply, some interesting stuff to read there.

[Labern 775]

Yeah its something that I always add to my drawingsbut can be hard to judge. Nozzle temp vs speed can have an effect also

[yellowshark 153]

I have not read the link "this" but any circle will always give you greater inaccuracies than a straight line; it is inherent in the way a 3D printer prints a circular geometry. And yes as mentioned other print settings will affect the percentage error. The only thing you can do is to increase the design diameter until the desired diameter is achieved. Irritating yes but once you have done it a few times you should find you will get it right within three or four attempts - and reduce the height in Cura until you have got the design dims to where they need to be

[Franny500 9]

Thanks to both, we increased the inner diameter by the desired amount and it produced good results. Thanks for all your replies.

At a guess, do you think the UM2+ will have a same problem or is it impossible to tell?

[Labern 775]

It's the nature of extruding plastic. It's kinda acts like chewing gum an pulls in on circles.

Better cooling, more accurate temp sensors and feeders will always help to some degree.

[Franny500 9]

Excellent, thanks Labern. Very much appreciated.