The ability of 3d printing to form any shape is quite remarkable. To be able to imagine a part, design it and then simply place an order online and have it arrive in the mailbox is amazing. Especially when the part in question could not realistically be made any other way.
Take for example these lock levers from my 1962 Valiant. The originals are a diecast aluminium and feature a very fine spline. I doubt they would be able to be manufactured any other way. Even with CNC machining I imagine the part would have to be made in two pieces if it was possible at all.
The replacements were needed due to an oversight on my part. I had made some lovely new door trims for my the Valiant. The fronts turned out so well i went ahead and made the rears to match. However in my enthusiasm I did not take into account the lock levers which only feature on the rears. Show here is the locking lever spline protruding through the trim baseboard before trim, and after I had finished the trim with the padding. No spline protrudes and therefore the original lock levers do not fit. So how to fix this without remaking the whole door trims?
3D printing to the rescue!
Step 1: Measure
Carefully measuring the spline dimensions gave me the basics. A 20 spline shaft with an outer diameter of 8.29mm and an inner diameter of 8.08mm, a length of 12mm and a spline depth of only .2mm. This would surely be stretching the the limits of 3d printing accuracy, but I had been very happy with shapeways SLS fine detail on some previous models, so I thought it would be worth a shot.
Step 2: Modelling the Critical Details
To the modelling. I am using modo because it is what I am competent in - a dedicated CAD program would be much better no doubt, but the principles should apply to all 3D packages.
Starting with the critical details first, in this case the splined section, I made a cylinder of the inner spline dimension. A key point here is that the cylinder had 80 sides. This allowed my to select every 4th side and scale from the centre point to the outside spline dimension. This forms the basic spline shape.
Step 3: Finish Modelling
From there I fine-tuned the inner and outer ends of the spline as needed, and then made the rest of the lever model around it. Taking into account the fact it needed to me about 10mm longer to clear the new door trim. I also made the base quite wide to cover the hole through the trim and was able to form the countersunk screw hole on one end of the splined section. The basic shape of the lever was supposed to be based off the main door latch handle so the style kinds of matches.
Step 4: Upload and Order the Design
After a few hours of tweaking the design I uploaded the model to Shapeways. I had to save it out a few times to make sure it uploaded in the correct dimensions, but once I was sure it was correct I ordered 2 in black strong and flexible and waited for the postman.
Step 5: Install Parts
A few weeks later my nicely bubble wrapped levers arrived and I went straight out to test them. To my slight amazement and immense relief, the splines came out perfectly, and they slid straight onto the shafts in the doors. My diligence in measuring everything paid off and I now have some custom door lock levers, and didn't have to modify my nice new door trims. Initially I was intending to order them in stainless steel, however the plastic ones seem to be perfectly strong enough, so unless they break I will stick with them.
Now, what to build next...