Approaches to turning a spool-shaped object (capstan drum)?

M

MikeMT

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Hi All,

I'm thinking about a hobby project for which I want to turn a small capstan drum to fit on a shaft. I worked up a conceptual model (drawing attached) with function but not machinability in mind and have since been trying to think through how it could actually be turned. I think I see a couple challenges to actually making this design:

1. My first thought was this seems similar to a pulley, and the standard way I see for turning pulleys is to drill/bore out the center bore, then mount the part on a mandrel and turn the OD features. But seems a tapered or other mandrel wouldn't provide good support for a piece this long, especially considering the center bore is only about half of the part length.​
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I think mounting this in a chuck without tail support would probably work, though it would require 2 setups (drill/bore the shaft bore and OD in one setup, then flip and bore out the cavity). Securing it for the second setup could be a little tricky, but maybe this is still the best way?​

2. Tool/tool holder clearance when turning the external recess between the "spool ends." I imagine I would use several partial depth cuts with a parting tool to make a starting "kerf" at one end to avoid plunging the turning tool, but seems the angle of the tool/holder required for turning to the far shoulder could interfere with the part at the start of the cut.​

Totally open to changing the design to make it easier to machine, e.g. making the end "flange" a separate part that gets welded/screwed to the main body or...

Would appreciate if anyone has any thoughts on this--thanks for reading!

Mike
capstan concept.png
 
Leave an extra stub on the end for mounting in the chuck turn your spool and machine the bore and part the spool as a final lathe op. The keyway can be cut on the lathe, or the mill. Drill the cross hole after parting.
 
Supposing you didn't have enough material for a stub for mounting you could hold the piece in your 3-jaw and bore the 1" and 2" holes, then make a 1" mandrel with a securing bolt and washer on the end to fasten the part. Do the rest like RJ suggested above
That's my spill
 
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Hey thanks much for the thoughts guys.

Either way I guess I'd need something along the lines of a 1/2"+ carbide boring bar to bore the full (4 1/8") length of the part from one end huh? That would certainly make it a more straightforward set of operations than I had been imagining--and with a stub it could be done with a single setup.

Mike
 
I would make this part in one fixation on the CNC lathe. The difficult part to make (for me) is the key way because it is to long for my current broaches and those are also metric. I would drill (and tap) the 5/16 hole using the radial drill holder in the tool post. Tapping could also be a problem because my taps are metric.
If more than one part needs to be made, I would make a holder for a DCMT insert, so all turning (not facing) could be done with one tool .
 
Thanks Hubb--I should have mentioned I'm limited to a manual lathe, but it's interesting to hear how you would approach this part with CNC.
-Mike
 
My complements on your drawing, well drawn, nicely dimensioned and appropriately toleranced. I couldn't have done it better myself. I'm guessing this isn't your first.
 
Gee, awfully kind of you MrWhoopee... I'm an amateur through and through, albeit one who did pretty well in high school drafting class a few decades ago, and I have always appreciated (and tried my best to emulate) well done drawings made by the pros. Easier than making actual parts :).
 
You can always center drill your mandrel so the tailstock can be used for additional support.
 
rabler said:
You can always center drill your mandrel so the tailstock can be used for additional support.
Click to expand...
This makes me think about something that was originally on my mind--would a tapered, pressed-on mandrel actually firmly (and concentrically) hold this part? The typical taper on the mandrels I see is 0.0005/inch. So over this ~2" bore, you'd have 0.001" of taper on the mandrel--could you expect to press it in enough to make it a tight fit at both ends of the bore? Due to the length of this part it seems it might not be all that stable if you didn't have the full bore in contact with the mandrel.
 
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