Another chapter in the long saga of the Samantha frame fixture development.
I was looking for the solution to holding tubes along an axis by the outside of the tube, similar to what we’d want with a seat tube. This is strangely a difficult problem if we want tooling that allows an easy change in tube diameters.
I prototyped something. As it sat on the bench waiting for the Destaco clamps to show up from McMaster, I started seeing a different solution. This is always nice after a bunch of time has been spent doing tricky manual milling cuts.
Once I realized that a maximized vee block with shim pads for any tube diameter under that could do the job, it all fell into place. Now, any tube from 2.250″ and under can be held. Just shim the tube out or cut specific pads that can be screwed into the lug.
It occurred to me that making a longer pad for the rear of the vee block made a lot of sense. The tube will hit the rear wall first then slide down to the base of the vee. Simply make that larger.
As this is pinned to the Ø0.625/2.000″ ecosystem, it can be used in a huge variety of situations.
In fact, I had 4 extra plates cut so that I can make some modular tube holders for the top and down tubes. This should be pretty cool but I haven’t started designing this at all.
This development makes me re-think the choice to use 240mm as the centerline height of the fixture. 254mm (10.0″) would have been the absolute best choice given recent developments. This is future me talking to past me. Ugh. Development.
The Destaco 202-UB clamps come with screw pads that are just slightly shy of what I need in my system but they supply a 2-1/8″ spare part that makes up for that. Now I have all the adjustment range that I could need.
The slider transfer plates are another deep improvement that was made in this round.
The original opposing 8020 method was ingenious but it had issues. There are a lot of parts and cuts in the assembly. Facing the t-slot sides of 8020 against each other isn’t the most stable interface. I didn’t like it at the start but it did seems to work.
I decided to look into a redesign of this and found some improvements by moving to a new solid CNC design. The location pins and rail are machined into the structure so that changing the fixture settings is very quick and easy with little loss of precision and a minimum of stackup. The locking levers were brought in closer to the BuildPro plate, lowered for improved clearance, and the ends of the block tapered to get out of everything’s way.
The slide motion is significantly nicer now. The slide action is smooth and gentle. I even left the key under both the rails rather than using a single. This makes little sense but the system is so well aligned that it doesn’t get interfered with. Pretty cool.
So the fixture is reconfigured and set again for the next frame. It’s tightening up and presenting like an extremely well thought out tool with a lot of possibilities.
Who else sets their fixture with gauge blocks? 3.238″ per setup sheet magic calculations!!!
I mention in the accompanying video Ronen Sarig’s Silver Gosling bike built for his fiancée, Gaby. This bike is seriously on another level given the 5’2″ rider. Go check it out!
