Last time, I'd drilled and bored out the brackets for the bearing and ballnut. To complete these parts and approach the point of assembling this machine, I need to machine the pivots that locate them on the tube bender arms.
To recap, here's what the guts of the tube bender will look like, once I've replaced the original ratchet lever mechanism with a ballscrew actuator. The brackets sit at each end of the ballscrew:
The ballscrew is machined up and is ready to go. The pivots for the brackets will look like this:
Luckily, I have the appropriate tapping drills (7mm for M8 and 8.5mm for M10), a 3/4" end mill for counterboring the bush and a clearance drill for the bushes through holes (10.3mm for 10mm machine screw).
I need to bore out the holes in the arm to suit the 3/4" bushes. Renishaw probe to find the centre, 3/4" end mill to bore through:
I have some 3/4" brass stock which fits nicely, as indeed it should:
Bore it out 10.3mm to clear the 10mm machine screws:
But oof, what is this??? The X axis keeps faulting with "loss of position". With the cross slide stationary, I can feel the servo motor rotating slowly, despite there being no linear movement of the axis. Clearly there's some loss of connection between the motor and the ballscrew.
Ah, the locknut has come loose. The pulley is keyed to the ballscrew but the nut has worked loose, resulting in lost axial movement (hysteresis). No wonder the closed loop controller was struggling. I guess I never got round to final fitting of the nut ie locking the thread.
Tightened it up, this time with some mild nut lock.
Back in business. Pretty close to the required 14mm:
All 4 bushes completed:
And the M10 threads cut:
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