Mark VII Lower Tube Reassembly

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The mark VII lower tubes(take the place of 'bench' tubes) are actually an assembly since the pair are connected to each other by two 'shafts' that serve as pivots when tilting(both ways). The 'shafts' also have cams and a lever that locks the upper assembly to the base when 'horizontal'.

Like the Mark 5/V casters, there are many identical parts that are assembled 'differently' depending upon where they are located.

I addition to the tubes, there are only 5 different parts including the screws.

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The 'shafts' are inserted through holes in the tubes.

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The 'cams' are attached to the shafts by a tension pin.

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To aid attaching the cams, the tension pins were 'started' into the cams.

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Now comes the 'moment of truth'. The cams will attach to the shaft either of two ways. Notice the 'ends' of the cams are different. The tapered 'end' allows the cam to slip into a 'socket/pivot' on the bottom assembly. The 'shafts are not straight, but bent. All that means they could be attached backwards.

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This thread is linked to from https://forum.shopsmith.com/viewtopic.php?t=11984

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A clue is found by looking at the front cams which are attached to the levers. The levers are identical, but have 4 holes for the mounting screws. This allows mounting the cams using either 'pair' of holes. The levers use alternate hole pairs. That still leaves the cams being able to mount to the levers either of two ways(remember the narrow ends).

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So we have to consider how the lever and cam are supposed to work. Two things determine the answer to this part of the Chinese puzzle. The lever is rotated towards vertical from its horizontal locking position to allow the cam to move in or out of the pivot bracket(this bracket will be shown later). When so rotated, the tapered end of the cam need be pointed 'down' towards the pivot bracket.

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The lever is rotated towards the near end of the tubes to lock the tubes down. Now for the 'final' 'kicker'. The shafts are bent in a 'U' shape so we still have to decide which of two ways to mount each cam. I went back and looked at breakdown pix, but nothing there was decisive. So pondering this I decided the shafts must be so shaped for a reason. Not having anything better to go on, I decided to assume they were 'bent' to increase clearance to the headstock. I am not completely satisfied with that conclusion, since the most clearance occurs at the release position, not the locked down position. Time will tell!

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So the back cam was attached so the tapered end matched the front cam.

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Similar(but mirror image) assembly for the right end clamp.

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This concludes this mental exercise. Only those of us who have struggled with reassembling a caster set will appreciate the mental part of this.

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