Printing large models; accuracy, fit, alignment and bonding

Hello all!

I am making a motorcycle and engine and I wanted to check out the components to see if they work together as intended, before cutting in metal. This is the gearbox and all the parts you see in the pics will be printed in 1:1 scale. I want to check that the indexing, or shifting, works properly. I have printed the lower crankcase housing, it consists of 7 segments made in 6 prints. I have suppressed most fillets, as I need to make some small changes later on.

The segments were printed in Z-Ultrat with light infill, ABS/acetone mix on the perf. plate. The Zortrax machine is kept inside a closed cardboardbox with some vents. I keep the machine in the basement and it's about 10-12°C, but using a carboardbox keeps it nice and warm. Models warps very little and total print time for all segments was about 175 hours and were trouble free. The segments are printed in the direction of the arbor axis in vertical position. I use locating pegs to align the segments and bond them together with a rather thick mix of ABS/acetone to seal the gaps due to distortion.

I have made some pics that I hope you find interesting. I measured the crankcase across and it is very close. The measurement in CAD is 335.5 mm and the caliper shows the same. I lined the segments up using an arbor Ø61.9mm (CAD Ø62mm) and it fits tight in the bearing holes. The accuracy is very good for holes in the print direction, but not so much for holes 90° to the print direction. These holes tend to be slightly oval and a bit smaller than they should. The holes for the locating pegs are a bit on the small side, but its no big deal, I just open them up a bit. The position of the pegs are spot on, the segments align beautifully.

When measuring between the two arbors I get center-center (mind you, not 100% accurate measurement) 174.9mm (CAD 175,5mm) which is an error of about 0.35% which is totally acceptable!

There are some gaps due to warping, but its minimal. You can see the warp in the pics, and it is about 1-2mm which I think is acceptable. Warping is due to shrinkage and internal stresses, hence it is very difficult to eliminate the warping completely.


John Tangerås