Hi there, all,
Well, this is going to be a bit embarrassing but I hope you'll all see the funny side!
This is connected with my Pete W's Tin Shed project. My immediate objective was to get all four corners to here:
Now those screws are 200 mm long and I wanted to drill the pilot holes nice and square so the business end of the screw was well within the end-on eco-sleeper. So I wanted to use this gizmo with this electric drill:
As you can see, the gizmo has a clamp that holds on to the snout of the electric drill. That presented a problem - the clamp is 43 mm diameter and the snout of the drill is only 38 mm. That's OK, says I to meself, it's about time I showed the guys on Mad Modders that some machining does sometimes get done at Pete W. Towers!
Question - what material to use? It didn't seem right to use metal, Tufnol would be my first choice but I happened on an eBay seller who was offering 50 mm diameter black nylon off-cuts so I bought one. Nice material for some jobs but a mistake for this one.
Step one was to turn a 43 mm diameter alloy disk with a 38 mm recess in one side and a centre drilling in the other side. (I apologise for the grotty photos, in some of them the camera seemed uncertain where to focus.)
Having done that, I cut a suitable length of the nylon rod and faced both ends. Here I should explain that, for reasons I won't go into, my tool-grinding equipment is temporarily inaccessible so I was using the best (only) tools that were available. If, Heaven forbid, I were to repeat this job, I'd grind a bit of HSS with lots of top and side relief, I think that would cut the nylon better than my brazed-tip TC tools.
Rather than drill and bore out the centre hole of the bush, removing all that material as swarf, I thought I'd use a hole-saw so as to end up with a usable nylon slug for the 'come-in-handy' box. The nylon rod quite liked the hole-saw - in fact it liked it so much it wouldn't let it go!
Oh, well, it'll be OK removing the job from the chuck - I haven't machined the OD yet. Having separated the hole-saw from the job, I re-chucked and bored out the centre to 38 mm.
I had been concerned that the bush wouldn't be stable enough to have its OD turned un-supported (in practice, it was a lot stiffer than I'd anticipated) so I made a mandrel by reducing the end of a length of alloy bar to 38 mm (a light push fit in the bore of the nylon).
In order to get traction, I fitted the recessed disk over the end of this mandrel and used a running centre to push it against the outer end of the bush to maximise the friction between the other end of the bush and the mandrel shoulder. This arrangement, I hoped, would allow me to turn the OD of the bush to 43 mm.
I don't have a photo of that part of the proceedings. The nylon didn't so much cut as semi-melt and move, a proper mess. However, I persisted and eventually ended up with a flanged bush.
I'm not proud of it. The jagged end you can see in the photo is where I tried to fettle it with a triangular shaper.
Now we come to the really embarrassing
I'd been concentrating on the diameters of the bush, 38 mm ID and 43 mm OD. Somehow, being fixated on those, I'd lost sight of the requirements for the length of the bush. As you can see in the photo, the width of the gizmo's clamp is greater than the distance between the front of the drill and the back of its chuck. So all the aggro and drama had been for nought.
I actually drilled the pilot holes for the screws with my bigger drill which has a 43 mm snout, seen here fitted to the gizmo (supported for the photo by my lovely but shy assistant).
Oh, well, at least I cleared all the stuff out of the lathe swarf tray and gave it a good oiling! I didn't neglect the running centre - it was like that when I bought it, part of a job-lot!
I ought to explain the 'devil's visiting card' under the eco-sleeper in the first photo. I went to quite a lot of trouble to bring the upper surfaces of the lower sleepers to the same level plane. However, while the eco-sleepers are nominally 200 by 100 mm cross-section, the two longer ones are actually only 196 mm so they've had to be packed-up so that all four upper surfaces are co-planar.
I mentioned earlier that my first choice for a bush like this would have been Tufnol. I didn't have any the right size for this job. I do have several pieces of Ferrobestos but I figure that's a no-no material these days. No-no for use and no-no for disposal, there's a pretty fix to be in!