Sand or Scale down in S3D

[CCRN]

Good Evening To All,

I am working on a project for a city wide competition for work. It involves making a toiletry set for the homeless, so I figured it would be a great excuse to extrude some plastic!

I found this design http://www.thingiverse.com/thing:1444094 and printed both parts. The problem is they fit together so tightly, you cannot get them apart easily.

I hand sanded the sides of the base and it now fits well, but the finish looks matte. I figure there are going to be variances in sizes when printing other's designs, so I was considering using the scaling feature and shrink the bottom part by a small amount.

Any thoughts? I am only off a fraction of a mm I suspect based on measurements after sanding compared to S3D.

Thanks,
Jerold

[jsc]

S3D can inset outlines in the XY plane, which sounds like what you want. It is better than scaling because scaling will change the position of features based on their location. You can find it as Horizontal size compensation under the Other tab.

[CCRN]

What would be a good way to decide the value. Measuring isn't going to work because there is a 0.3mm difference between S3D and a printed model. Guess I will use a negative tenth of a mm and see how the fit is.

[jsc]

If you have a .3mm discrepancy between the model and your printed part, I suggest you run an extrusion calibration to make sure you're not over or under extruding. But you can measure the OD of the bottom part, subtract off the ID of the top part, and add .1-.2mm for clearance. You can also print up a series of bottom parts using different processes with increasing compensation numbers.

[CCRN]

Well, I may have misspoken. I designed a box in OpenSCAD tonight for the soap bar. My printed measurements match the S3D x y and z and they match my OpenSCAD length width and height variables. The z axis is off 0.03 mm, x and y are off about 0.02. I think those variances are fantastic and I am so surprised at how accurate the M2 prints. Will run an extrusion calibration to verify. Do you have a design to recommend for calibration checking?

The problem with measuring the bottom piece is it has a variable width. It looks like the X value shown by S3D is the point with the largest width. S3D shows 30.60 mm for X on the bottom, and I am measuring about 30.50 OD sanded for the bottom piece I printed. The ID of the top is 31.04 mm. That would make the adjustment about 0.6mm, correct? Seems like a lot, considering the amount of sanding I did, which wasn't much.

Going to try some samples series with -0.1, -0.2 and see how these work out.

Appreciate your help,

Jerold

[CCRN]

Looks like -0.15 was sufficient. The bottom fits but can be removed. The designer says there is a 0.2mm gap for 0.4mm of play, suggesting I may have a calibration issue to work through.

Thanks,
Jerold