Hey guys, Ive been recently using Inventor in school to create 3D objects, and im getting the hang of it quite well. But I cant seem to find the best amount of room to give objects that need to be pressure fitted together. In the end I always end up having to sand them down quite a bit, and its always a little to tight. Ive been using about .4mm play between the objects and I havent tried more than that. What do you guys usually use in your modles?
Thanks
Matt
Hi Matthew,
I am mainly printing mechanical parts and I know whats bothers you. Unfortunately Simplify 3D what I am using to compile G-Code always do smaller internal holes than in the design software and external dimensions are comparable much more accurate. But at the end it is always a matter how tide you want both parts to fit. If you really demand good tide fit most of the printers could not catch with the accuracy required. Also most hobby CNC machine can’t do this also. With printing it is much harder than CNC machining as you have more parameters in the equation as under/over extrusion the accuracy of the filament diameter, thermal expansion retraction and also artifacts from retraction etc. My suggestion is to keep with your practice to finish by hand the assembly that need to fit tide or just experimentally to find for this part the exact dimensions. Unfortunately when you change the design the difference will vary and you will need to calibrate based on tries which is time and material consuming and only worth if you will make series of same part.
@George_Novtekov i guess its more of a trial and error thing then, well thanks for the help
I know simplify 3D has a feature specific to help with situations like this . Let me see if I can find it
If I want a running fit or clearance fit, I make the hole bigger by .4mm and If I need to, make whatever will be going in the hole smaller by .4mm as well. I’ve found that with parts that are small, I’ll run with a lower extrusion multiplier. Things tend to come out with better dimensional accuracy when I do that.
I mostly give my parts .1 or .2 mm room. Most of them fit at once after printing. But I always use the same filament supplier. So its a “best practice”.
Unfortunately the shrinking of the material isnt always that predictable.
@Matthew_Del_Rosso I know exactly what you are dealing with but it is not a trial and error thing. I print mostly high accuracy and tight tolerance assemblies on multiple printers with multiple filaments and always have the parts come out interchangeable. They fit together straight off the printer for me.
First, know what your printer is capable of. Mine can hold a tolerance of less than .1mm. Find out what your printer can do.
Second know the properties and behavior of the filament you are printing with. I calibrate each spool for dimensional and thermal properties.
With that in mind I put a .2mm clearance between any snug fit interfacing surfaces and a .3mm if I want movement.
I calibrate all my filament using these simple calibration clips http://www.thingiverse.com/thing:1037301. Check it out and if you want further tips or have additional questions let me know. I’d be happy to share with you what I have learned.
http://www.thingiverse.com/thing:1037301
What I do it’s print a calibration cube of know and different sizes on x, y and z so i can meassure how much size is growing on each axis, so, when I need to design something that needs to fit inside other something I use that meassures to increase/decrease the actual size of the part.
Most of the time I’m using .15mm
@Luis_Diaz Your 0.15mm clearance on a part matches the .3mm clearance between two parts that I use to allow for movement.
Here is the accuracy block I use. The differing dimensions allow me to see that I get the same growth rate in all the three axis. http://www.thingiverse.com/thing:1616694
The calibration clips also provide a way to know that you are not over or under extruding.
@Jeff_Parish I just see your previous reply… That model is great 
@Jeff_Parish Thanks, I will print a couple of the clips and see if I can get it calibrated properly.
This is what i was referring above https://www.simplify3d.com/get-your-calipers/
@Mindless yup, got one of those handy but its alway good to have room for some improvement