How to make holes the right size?

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Paul De Bra 05 Jun 2011 19:10

Sorry if this has been asked and answered before.
It's known that when you design a 3mm hole and print the part the hole comes out smaller. This is unfortunately also true for larger holes.
I printed the AA 4 battery holder http://www.thingiverse.com/thing:8939 and the AAA 4 battery holder http://www.thingiverse.com/thing:8940 by Shack90. The holes come out too small: the batteries do not fit. I assume that the design is correct and that I have some setting that makes holes come out smaller than designed and that this can be corrected. I assume that when Shack90 printed these parts the batteries must have fit, so I must have some setting wrong.
Any ideas?

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Paul De Bra, 05 Jun 2011 19:10

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Re: How to make holes the right size?

Renosis 05 Jun 2011 19:40

You just need to calibrate properly. For example, when you print your 20mm cube, does it actually measure 20mm?

Once you know that is right. You need to move on to circular size calibration. Naturally circles are going to be tighter, that is just the nature of this type of 3d printing. Nophead has a well done blog post about the problem:

http://hydraraptor.blogspot.com/2011/02/polyholes.html

But, if you don't want to read alot of stuff…. just try scaling up a tiny amount.

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Renosis, 05 Jun 2011 19:40

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Re: How to make holes the right size?

Paul De Bra 05 Jun 2011 20:11

The outer sizes are fine. I tried printing a tube (19mm internal diameter, 29mm outer diameter) and the outer diameter is fine but the internal diameter is around 18.5mm, not 19mm. When I print a 20mm cube it's 20mm.
I was puzzled by the AAA and AA battery holders. My assumption is that Shack90 can print them and have the batteries fit (but he does not show it with batteries), whereas whey I print them the batteries do not fit. The height of the battery holders is fine. The holes are just not wide enough.
So I thought there might be something to configure to make holes come out slightly larger (without scaling the whole object).

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Paul De Bra, 05 Jun 2011 20:11

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Re: How to make holes the right size?

Renosis 06 Jun 2011 04:03

Wasn't referring necessarily to outer diameter… If you read that blog, it explains why this happens, and what you can do to avoid it. This blog talks about the inner diameter of holes (circles) created by FDM printers.

I suggested that you check to make sure that 20mm cubes come out to 20mm as a starting point. Because if that is wrong, nothing else is going to come out right.

If you read that blog, it explains what causes the problem (there are very many things which cause holes to be smaller than what they are designed to be). Who knows, it could very well be the battery holder designer's printer that is not calibrated properly. You may need to adjust the design files accordingly, because maybe he designed it to fit on his poorly calibrated printer.

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Renosis, 06 Jun 2011 04:03

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