Reliable fit of small cylinders (3.8)

[[Re...]]

Currently we are validating geometric quality of 3D printed parts with narrow tolerances. 

On TPD drawing datum system ABC is applied on small planes/cylinders for long parts. I tried to gather as much mesh on or in these spots so that the fitted planes and cylinders are as reliable as possible. Before the ABC alignment a pre alignment is set where the whole part is best fit. I notice that whenever I rescan the same item, the results of position accuracy tolerancies vary and in some occasions lead to out of specs. 

My question is via which ways I can improve the fitting of small cylinders?

Sometimes the fit results in a slightly different direction and has big impact on all other measurements. 

I read on internet that a possible solution is to make sections where circles can be fit. With these circles I can construct a more reliable cylinder.

 

[[Ma...]]

You can play with angle selection of fitting element.

Also you can use bestfit on certain areas of a mesh to improve CAD<->mesh fitting

[[Re...]]

Hi Martin, 

Thanks for fast response. 

Angle selection of fitting element U mean to play with the Max Angle in fitting element; 

Your second remark: 

I already have a pre alignment with best fit of full part. You say it will help if I create another best fit alignment based on area's on datums or area around it?

This means I have to select MESH data manually with select through surface and make a new best fit alignment? 

This scanning program needs to run via kiosk without any manual steps, is this possible? 

 

 

 

 

 

 

 

[[Ma...]]

Increasing Max. angle can bring more selected mesh.

For bestfit - you can select areas on mesh, which can bring mesh into a correct position.
If it's rotary part, then it will help only with rotation.

Otherwise if you have problems with depth and or angle, then you can select only one mesh-cylinder for bestfit and measure only this one within bestfit alignment.
You can select measured cylinder and in properties you can select to calculate it only in certain alignment.

[[No...]]

Can you elaborate a bit more on what you mean by "small cylinders"? Is it a "short" cylinder (large diameter, short axis) or is it just a cylinder that is so small your scanner resolution doesn't give you enough points to work with?

Short axis cylinders are generally susceptible to a certain amount of tilting when their mesh surface is not perfectly even.

All that was said above CAN help, but depending on how much the surfcae deviates from a perfect cylinder, you may still end up with a tilted result. If all else fails your last resort is to add constraints in the measuring principle. For example, if the cylinder protrudes from a flat plane and you know it is perfectly rectangular, you might set the cylinder's axis orientation to that of the plane's normal.

 

Edited 44 minutes ago