Set default to Inches?

Discuss Cura Type A, our fork of the Cura slicing software, here. Unstable releases may be made available in this section.

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Fast one
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Joined: Fri Feb 20, 2015 12:24 pm

Set default to Inches?

Postby Fast one » Tue Feb 16, 2016 8:15 am

Does the new Cura software allow setup selection to inches or mm like CAD software does or is mm the only choice?

Elijah
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Re: Set default to Inches?

Postby Elijah » Mon Feb 22, 2016 2:34 pm

Good question - Millimeters are how almost everything in CNC is measured. (Sometimes inches are used on mills and routers, but hardly ever in 3D Printing - in fact I've only seen it happen once for its own sake)

When exporting your files to STL, make sure to spec millimeters as your unit of measure of choice. If you want to design in inches, you may. It's only in the export process that the change needs to be made.

As a quick workaround, If you import a file into Cura, and it's way too small, you can try scaling it up on all axes by a factor of 25.4, as there are roughly 25.4 millimeters in 1 inch.

It wouldn't hurt to add a unit selection feature to Cura, but it would likely be a fairly low priority. I'll pass along the thought to our software team.
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Type A Machines

Fast one
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Re: Set default to Inches?

Postby Fast one » Mon Feb 22, 2016 11:08 pm

People who design in inches on CAD software should be able to transfer STL files in inches to Cura and proceed without the extra step of scale conversion which is an unneeded chance for error. After a year of using Cura I'm tired of reloading the file and changing the scale; how things are measured in 3D printing has nothing to do with this request. You might consider this a low priority but I see no reason to upgrade Cura software for changes I don't care about while this change hasn't been added. All CAD systems I know of allow inches or mm to be set as a default because customers demand both. Is anyone at Cura listening or do they only care about the european customers who use mm and expect everyone else to do the same?

Elijah
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Re: Set default to Inches?

Postby Elijah » Wed Feb 24, 2016 11:15 am

When I suggested that everyone in CNC uses millimeters, it is because millimeters are practically universal in the US as well as in Europe when it comes to 3D Printing. Sorry if I didn't make that clear.

That said, you can export CAD files that are designed in inches to an STL file whose units are in millimeters without having to do all of the design work in millimeters. Your workflow would not need to include any scaling in Cura, and the exported STL file would leave the CAD software in the correct dimensions.

I looked at an STL file that came off of OnShape (which is a free online CAD program) and pasted a facet below to examine its precision.

The file was selected at random with the only condition being that it was designed in inches, and you can see the entire project if you're logged into OnShape: https://cad.onshape.com/documents/77740 ... e786e5d9b5

I exported it at the lowest possible resolution, and in ASCII format (as opposed to binary which I usually recommend) so that we can read the facet as humans. The STL units are in millimeters, but as I said before, the part it came off of was designed with inches as the unit of measure.

Code: Select all

facet normal -0.258542 -0.000310713 0.966
    outer loop
      vertex 39.6316 76.2125 135.625
      vertex 38.9925 76.2109 135.454
      vertex 38.9398 63.5351 135.436
    endloop
  endfacet
 


What I'm noticing is that these values are being described with four significant figures to the right of the decimal point, meaning that the precision of an STL file in millimeters is 0.0001mm, which converted to imperial units is 3.94x10^-6 inches. The precision of the Series 1's motors are around 0.006mm, meaning that the STL is more dimensionally precise than the Series 1 itself can produce.

While there is certainly something to be said about using integer units or units that are as rational as possible, I'm not sure that a CAD file designed in inches will come out any worse if the machine isn't using inches at it's primary unit.
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Type A Machines

Fast one
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Joined: Fri Feb 20, 2015 12:24 pm

Re: Set default to Inches?

Postby Fast one » Fri Feb 26, 2016 1:58 pm

I don't see any thing on the Onshape site that will help in exporting STL files in inches from the Keycreator CAD software that I use to Cura. The easy customer solution is to have a selectable option on Cura for mm or inches. Is it difficult to add an automatic multiplier of 25.4 to the STL file import section of Cura as a default selection?

Elijah
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Re: Set default to Inches?

Postby Elijah » Mon Feb 29, 2016 3:30 pm

Fast one wrote:I don't see any thing on the Onshape site that will help in exporting STL files in inches from the Keycreator CAD software that I use to Cura. The easy customer solution is to have a selectable option on Cura for mm or inches. Is it difficult to add an automatic multiplier of 25.4 to the STL file import section of Cura as a default selection?


Not knowing KeyCreator, I would have to assume that, like many of the CAD programs that I use, when exporting an STL file, there are a number of options, in which "units" are a field. An automatic multiplier button is a good idea. In fact I believe KISSlicer had something like it. The workaround in the meantime is to, as you said, replace "1" with "25.4" on the scaling tool.
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Type A Machines

Fast one
Posts: 59
Joined: Fri Feb 20, 2015 12:24 pm

Re: Set default to Inches?

Postby Fast one » Mon Feb 29, 2016 11:18 pm

Note the last post on the Cura site for this request: https://ultimaker.com/en/community/1062 ... etc?page=4. It sounds like this fix is in the new software but you say it isn't.

ss4925802
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Joined: Wed Apr 06, 2016 11:36 pm

Re: Set default to Inches?

Postby ss4925802 » Wed Apr 06, 2016 11:38 pm

I agree with the first comment about that ....
Graduated from Soran University with First Class Degree with Honours in Computer Science.

Elijah
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Re: Set default to Inches?

Postby Elijah » Thu Apr 07, 2016 10:37 am

Ultimaker's version of Cura is not the same as Cura Type A, which is a fork.
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