Prints with holes

Hello everybody,

With this topic i would like to ask you guys if you would know how i could resolve some problem i've got with my makerfarm,

When ever i make a print with a hole inside its always to small,
The outside is always correct on 0.1mm tolerance, But the inside is most of time not a circle, It has a tolerance of 0.8mm most of the time,

One side is sometimes when measuring perfect on the measurement i wanted, But then when you go further in that circle it goes down.


Thanks if you would know the solution since i don't know what to do anymore with em :P

Just did a new print with some more traingles for a more precise STL file,

Still 0.4-0.5mm to small tho.

Hi,

A few things about circles. Many times the number of polygons used to make the circle is low which results in a "circle" made up of obvious straight line segments. In OpenScad you can add a line in at the beginning of the design that will increase the polygons so that it is obviously a circular hole. That said, I've always had trouble getting my holes to measure correctly. I've actually given up and just make them big enough so that I can run a drill through them to make them the right size. I know, shouldn't have to do this, but it does make for a quick solution and it is so easy that I haven't bee tempted to tackle the problem again.

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Originally Posted by KDog

Hi,

A few things about circles. Many times the number of polygons used to make the circle is low which results in a "circle" made up of obvious straight line segments. In OpenScad you can add a line in at the beginning of the design that will increase the polygons so that it is obviously a circular hole. That said, I've always had trouble getting my holes to measure correctly. I've actually given up and just make them big enough so that I can run a drill through them to make them the right size. I know, shouldn't have to do this, but it does make for a quick solution and it is so easy that I haven't bee tempted to tackle the problem again.

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I do this too! I make it so the hole is a little too tight and then just use that as a pilot hole to drill it to the correct size. I've given up on trying to get holes the 'correct' size. They always are too tight.

Same here: For things with holes I usually increase the diameter of the outer shell so that I´m able to drill the holes without having any issues with stability there.

Well i am making this: http://puu.sh/9lKzJ/6c39b12f5e.png
As you can see the circle is quiet good as pollys go,
I did change my save in Solidworks so it is more precise,
But when i do 12 in solidworks, also other prints from thingiverse, Its always aprox 0.2-0.6mm smaller,

As you probably would see is that its quiet hard to get this in a vice to get enough grip to not get it damaged and get it drilled,

I had a few trys so far ^^
Thats why i would like to get it more to the 12 so i wouldnt need alot of grip on the product as it wouldnt take much from it.

Dr. Luigi: It is very typical in the Open_SCAD source I play with to see where people have put fudge factors into the source code. For things like precision meshing gears, there are almost always some fudge factor numbers that get added to one thing (like how big the spaces are) and subtracted from other things (like how thick and deep the teeth are). The thing that made me just give up and drill to get precise holes is the fact a lot of these pieces of source code I was looking at were super well written and very clean. If the author needed a fudge factor to make the code work, what makes me think I'm going to get away without one?

So its normal that holes are always smaller for aprox 0.2-0.8mm (in this case with a diameter hole of 12) and there is nothing to do about it?

Kinda hoped it was a setting in my printer that made it not as precise,

Well i guess i will try to drill it, If it doesnt work well i will probably buy some gears in metal if thats the case.

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Originally Posted by DrLuigi

So its normal that holes are always smaller for aprox 0.2-0.8mm (in this case with a diameter hole of 12) and there is nothing to do about it?

Kinda hoped it was a setting in my printer that made it not as precise,

Well i guess i will try to drill it, If it doesnt work well i will probably buy some gears in metal if thats the case.

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Slic3r has some settings for how much to extrude on inner and outer perimeters. I suspect you could play with those to get it right. But I bet other parts of the print are not as good. I'm not as opposed to using a drill to clean things up as you I guess. The way I look at it, the drill is a precision instrument. I can just send it down the pilot hole once and I know exactly what I have.

We typically undersize holes and define at least four vertical shells. This leaves enough meat to drill out and tap into.

I haven't tried to generate a hole with a precise dimension, I'll see if I can find time for that this week. We slice with Slic3r.

I had to print something with a hole that had a "flat part" to it (like a D-shape), of 12.5mm diameter. I just printed a test piece, measured it out, and then as mentioned, just "fudged" the radius. Came out just about perfect.

For 3D printing just about any precision part, there is often some trial and error to get the diameters right (often depending on your printer as well as slicer settings), and you usually get the best fit if you can drill or file things a bit.

I have had reasonable success adding the nozzle diameter to any internal hole radii. So, for a 10mm diameter internal hole printed with a 0.4mm nozzle I would create a hole 10.8mm wide, thats a radius of 5mm plus 0.4mm for the nozzle.
Not an exact art but often very close.

I think Slic3r and CURA both have the same issue where they seem to calculate the inside diameter of a hole as being the outer edge of the inner-most shell.
Much like drawing a small circle with a fat marker.

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Originally Posted by 3D OZ

I have had reasonable success adding the nozzle diameter to any internal hole radii. So, for a 10mm diameter internal hole printed with a 0.4mm nozzle I would create a hole 10.8mm wide, thats a radius of 5mm plus 0.4mm for the nozzle.
Not an exact art but often very close.

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If this rule of thumb works on a lot of printers... It will be worth high lighting it! Next time I'm doing holes, I'm going to check this out.

Quote:

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Originally Posted by 3D OZ

I have had reasonable success adding the nozzle diameter to any internal hole radii. So, for a 10mm diameter internal hole printed with a 0.4mm nozzle I would create a hole 10.8mm wide, thats a radius of 5mm plus 0.4mm for the nozzle.
Not an exact art but often very close.

I think Slic3r and CURA both have the same issue where they seem to calculate the inside diameter of a hole as being the outer edge of the inner-most shell.
Much like drawing a small circle with a fat marker.

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This could be it indeed!

Thanks ;)
I was already wondering if it was due something like this, But i thought, well they should have fixed some error like that by now..