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What are those two green things on the shelf above your lathe ?
Might one or both of them be a "steady" ? (if so, it'll have three, threaded thingies pointing inwards.)
This can be fitted to the lathe bed and used to centralise the wayward end of the barstock while you centre-drill it.
No idea – came with the lathe but your suggestion looks probable but they are too small for 3.25” bar
I would be very wary of parting off anything that big in diameter.
Parting off is a dodgy process at the best of times, and worse if there is much backlash in the cross-slide screw.
The forces are huge, friction is high and, for a large diameter, the tool has to be long so its rigidity is compromised.
Even for smaller diameters, the tool needs to be set dead on centre height (or even slightly above, a heresy in normal circumstances) otherwise the tool will want to drag itself under the workpiece (made worse by cross-slide screw backlash).
Its useful for batch production but for one-offs I would just get the hacksaw out and take a deep breath.
But I would get as clever as I could in the turning operations so as to leave a smaller dia to saw if possible.
And/or I might part off to a shallow depth with a short, rigid tool, just to take some meat out of the work and also to guide the hacksaw.
For this dia, I would hacksaw in 4 or 5 different positions, to meet in the central bore.
Its almost impossible to leave a good face after parting off anyway, so you'll probably have to skim the back face afterwards.
The width of the hub needs to be 20mm, the ODs I need are 73mm for 10mm and I will be down to 50mm at the other end for 10mm length, the bar size is 82.5mm (3.25”) so I will machine the 73mm dia first for 26mm. Then about 11mm from the end (allowing for a facing cut) I will machine down to 50mm for about 15mm allowing for facing and tool width for parting off and I will insert parting off tool for maybe 10mm cross cut leaving me about 30mm to hacksaw and a reasonable guide for my not very accurate hacksawing abilities. Does that sound OK to you?
And I would seek to arrange things so that I bored ALL of the bearing diameters/faces without disturbing the workpiece in the chuck, for concentricity.
This is a very good point and I will need to change the design I was contemplating. The original fixed brake hanger is 20mm thick at the axle and is clamped by the spindle being done up. I need therefore to end up with the outer edges of the bearings in the hanger hub at 20mm with the inner race also being clamped when the spindle is tightened.
On the bearings I bought the outer race is flush with the inner race, they are 7mm wide, so I originally intended to machine from both sides leaving a 6mm wide step for the bearings once inserted to butt up against. There is no danger of a clash between the wheel bearing outer track and the inner hub bearing. I may have to have a shim on the swinging arm hub bearing (same OD as the inner track) to prevent contact between the outer race and the swinging arm.
Machining from one side only will not permit this step so I shall make a steel spacer the same bore as the spindle and the same thickness as the inner race of the bearings. The outer track of the bearing will now have to be an interference fit in the hub to prevent the caliper mount walking sideways under load into either the wheel or the swinging arm. If I do not end up with a good interference fit i.e. a bit too sloppy, there is always bearing lock or I could grind a small notch on the outer track of the bearings and drill and tap a 3mm grub screw radially (or both)
The dodge with using the tailstock to help centralise is a nice little sign of intuitive skills btw.
Desperation makes you innovate
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