ATI countersink Improvements

These are ATI brand aircraft countersink tools. They are used to assure square, consistent depth countersinks when a drillpress with depth stop can’t be used.

I’m a fan of these, and bought a small lot on eBay (Boeing surplus). Most have pretty small and narrow cages. Most of those cages were also modified to allow better clearance for aircraft fabricators technicians, but at the cost of stability. For my usage, i rarely have clearance issues, and would prefer a wider, more stable base.

While i was at it, i figured i’d give them a knurled surface, and debossed identifier, so that i could have a single adapter set up for all the common sizes i deal with. That way you can just grab a size, throw it on a hand drill, and get perfect depth countersinks each and every time, regardless of the location and orientation of the part.

These have some relatively tricky features to model and print.

3D printed threads

The bottom threads are an uncommon 5/8-36 thread. Since i wanted to have a model where the threads were printed in, and the threads are so small, i had to create a taper on the lead in to the threads, and have those threads mate seamlessly with the straight thread section. For extra security, should a tap be needed to chase damaged threads, i also added the lead-in on the bottom edge, to help start the tap. Inventor doesn’t offer modelled threads, so i needed to do the thread modelling manually.

Tapered Knurls

The external knurls are a fun touch. The are created with a tapered spiral coil cut extrusion, which is patterned, and then mirrored. This creates a parametric knurl that is a 3d feature on the model, and can be printed in.

Highly Parametric

As always, i strive to make my models about as re-usable and adaptable as possible. The thread pitch, nominal diameter, 3d printer clearance, knurl count, bottom flange OD and internal clearance ID are all adjustable. The top notches/crenelations are designed to mate with the stock parts, but could be changed to improve the accuracy of the crenelations. Stock parts have a 36TPI pitch and there are 30 crenelations, which means that each notch change is 1/(36*30) = 0.000926”. If i changed the notch count to 28, each notch would be 10 times closer to 1 thou per notch (1/(28*36) =0.000992” ). This would break comparability with the stock parts however, and that level of precision isn’t needed in my applications. It does surprise me that the manufacturer didn’t think that one through though.