Why are my dimensions rounding up?

graham_brown146

I have sketched and extruded my design. However, in both areas the dimensions always appear rounded up. eg: 23.5mm will be added in the dimensions box but will always appear as 24mm on the sketch or 3d model. It's still 23.5mm if you click on the box. Is that just how it appears and will it print as intended? 
Cheers 

NeilCooke

Check your decimal place settings in preferences and in the current doc (hamburger menu top left)

michael3424

graham_brown146 said:

Thanks Michael. Yes, I'm 3D printing. They are simple shapes but I didn't know about 'scale factor'. Wouldn't they print at the designed dimensions?

Depending on the filament type and profile, I often have to scale an STL-iimported part in the slicer by a small amount to get the nearly-exact-dimension that I want.  In PrusaSlicer, the scale factor is often slightly smaller than 100%, say 99.7%.  It gets more complicated if you want exact hole diameters.

S1mon

Scaling the whole model seems strange.

I have often added extra clearance on faces that will be touching mating parts. 3D printing will have certain types of dimensional errors depending on the technology, tessellation, calibration, maintenance, environmental conditions, and axis. FDM will often be off in Z (build axis) by something on the order of the layer thickness (either the layer is there or it's not). X+Y is more a matter the tolerances on the other variables.

For hole diameters, I recommend building a test part with a series of hole sizes. If you're also using bosses, build those too, as the material may cool and shrink differently in the middle of a large plate than it will in a thin walled boss. Keep in mind that a particular 3D printer may have different tolerances on different areas of the build platform, and at different build heights. If you really need to control this kind of thing, you might have to do a lot of careful testing.

This is a really good use for move face to add clearances where necessary. It makes it easier to have configurations for production vs prototyping.

The reality is that even with the best machines and processes, 3D printing will never get the precision and control of machining or injection molding - unless you start talking about some of the metal powder sintering/micro-machining stuff. I've worked on a project where the mold inserts were built this way, and those were almost as good as a tradition machined + EDM insert.

NeilCooke

Check your decimal place settings in preferences and in the current doc (hamburger menu top left)

michael_kline

Displayed precision is different than model precision. The model is the dimension you made it. Turn up the displayed precision if you need those numbers displayed in the model.

Since you mention printing, I assume 3d printing, which if you are new I will caution you about layer squish and expansion. Most parts do not print at designed size. You will need to incorporate a scale factor in most designs if you need dimensionally accurate parts.

graham_brown146

Thanks Neil. That helped so much. 

graham_brown146

Thanks Michael. Yes, I'm 3D printing. They are simple shapes but I didn't know about 'scale factor'. Wouldn't they print at the designed dimensions?

michael3424

graham_brown146 said:

Thanks Michael. Yes, I'm 3D printing. They are simple shapes but I didn't know about 'scale factor'. Wouldn't they print at the designed dimensions?

Depending on the filament type and profile, I often have to scale an STL-iimported part in the slicer by a small amount to get the nearly-exact-dimension that I want.  In PrusaSlicer, the scale factor is often slightly smaller than 100%, say 99.7%.  It gets more complicated if you want exact hole diameters.

S1mon

Scaling the whole model seems strange.

I have often added extra clearance on faces that will be touching mating parts. 3D printing will have certain types of dimensional errors depending on the technology, tessellation, calibration, maintenance, environmental conditions, and axis. FDM will often be off in Z (build axis) by something on the order of the layer thickness (either the layer is there or it's not). X+Y is more a matter the tolerances on the other variables.

For hole diameters, I recommend building a test part with a series of hole sizes. If you're also using bosses, build those too, as the material may cool and shrink differently in the middle of a large plate than it will in a thin walled boss. Keep in mind that a particular 3D printer may have different tolerances on different areas of the build platform, and at different build heights. If you really need to control this kind of thing, you might have to do a lot of careful testing.

This is a really good use for move face to add clearances where necessary. It makes it easier to have configurations for production vs prototyping.

The reality is that even with the best machines and processes, 3D printing will never get the precision and control of machining or injection molding - unless you start talking about some of the metal powder sintering/micro-machining stuff. I've worked on a project where the mold inserts were built this way, and those were almost as good as a tradition machined + EDM insert.

graham_brown146

Thank you Simon and Michael. I didn't realise it was inaccurate like that. My design is best described as a puzzle which has to fit neatly together. Sounds like it's just trial and error on the first one.