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Home Machine Shop Tool Making – Machining A Pinion Head Depthing Tool – Part 3


In the previous video’s of this series I made the tool bed, the carriers and the adjustment screw. In this final video, I finish off the depthing tool, by making the steel runners and the brass wheel bushings. By making a range of runners and bushings for different combinations of wheels and pinions, the tool can be made quite versatile, and I’ve chosen 1/8″ as the base diameter for the runners. so some will need to be trimmed to a thinner diameter to fit various pinions, and some will need to be bushed to accommodate the larger bores of the wheels. One will end up as a cone runner to enable depthing from existing pivot holes. So I’ve cut 8 blanks from silver steel to
cover a range of options. each of these were then loaded onto the small lathe to clean up the saw cut, and give them a light chamfer. Most of the runners will need a point for scribing on one end, so I took care of that operation first, setting up for a 30 degree included angle cut. I’ve set one runner aside to be made into a cone runner which I’ll explain later. The rest were given that 30 degree point. Then I used a fine cut file to make the very tip more like a 60 degree point, just to give it a bit more strength. I’m not going to harden any of the runners, but since they’ll only ever be scratching brass, they should wear quite well with just this 2 stage point. Next I turned 2 of the shorter runners down to match the pinions on the clock that I’m working on right now; I’ll have to do this again for other pinion sizes in the future, but these sizes at least I know I need now. This little off cut of silver steel is going to become the tip of the cone runner. As the name suggests, a cone runner is a different type of runner with a cone shape on the end. It’s used for depthing from an existing hole. First up it was faced, and then turned to diameter. It was then drilled and reamed to accept that runner shaft that I set aside earlier. The reaming ensures that the runner shaft is a nice snug fit. It was then parted off, reversed and set to run true in a 4 jaw chuck, A 60 degree point was then formed on the end. A touch of loctite bonds the cone tip to the runner. And that gives me the cone runner, 2 long runners for wheel bushings, 2 cut down to fit pinions, and a few spares for the future. Now the bushings are designed to be a close fit into the various wheels, and then they slip onto the runners. This particular one will fit the 1/2″ bore of the main wheel from the Large Wheel skeleton clock, but they are all essentially made in the same way The wheel needs to fit on quite firmly, with a snug seating. So the diameter needs to be dead on, with a good undercut. Once that’s sorted, the central hole is drilled and then reamed 1/8″ to match the runners. I’m parting these runners off a little differently to normal. I made the parting cut almost all the way
through, then backed out the tool, and took another fine cut to leave a reasonable finish to the cut-off side. This way all surfaces are true to the central bore, and I can avoid having to resurface that cut-off side. I then repeated the operation for 3 additional bushings to match some common clock wheel bores. So that gives me a set of 4 that’ll certainly cover me for the time being. And that’s all parts complete, so time to put it all together and give it a run. OK now that the tool is ready for use, let’s talk a little bit about depthing. Depthing a gear train is the process of finding by trial and error the correct distance apart that two gears will perfectly mesh. Once we have that distance, the tool is used to transfer it directly to the plates so that we know where to drill our pivot holes. The pinion is fitted on one runner, the wheel is fitted on the other using a bushing, and then the carriers are positioned to bring the wheel and pinion into a loose contact. The adjustment screw is then brought to bear on the closest carrier, and used to slowly nudge the pinion closer to the wheel. And this is the process of depthing. With every shift closer, the parts are checked both visually, and by feel, until the perfect meshing of wheel and pinion is achieved. And it’s amazing what a difference even the tiniest adjustment can make. The runners now record the optimum center distance for this wheel and pinion combination. They’re now pulled up within their carriers,
so that the tool will sit horizontally when its held onto the clock plate. And just like the classic depthing tool, this distance is then scribed onto the clock plate, to give the drilling location for the pivot hole. And as I mentioned earlier, when required the cone runner can be installed, to set off a distance from an existing pivot hole. And that’s the Depthing Tool complete. It really is an essential tool for anyone
making clocks, or small geared mechanisms. Thanks for watching, I’ll see you later. And if this is you’re first Clickspring video, thanks for checking it out. Make sure you subscribe for regular toolmaking video’s like this one, as well as video’s on a longer term clock making project. You might also want to have a look at the
blog site, for some more tool making projects. But before you go be sure to give the video a thumbs up, share it with a friend and leave me a comment. Thanks again for watching, I’ll catch you on the next video.

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