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This is part of a larger series of projects I’m playing with at work and although you may not see the ultimate finished product there were a couple of set-ups and work-arounds that I thought were kind of fun.
Firstly, this is a facsimile of an 1890’s bronze doorknob. The original was made by the P & F Corbin Company and is their “Rope” pattern. I cast this one in urethane off of an original using a two-part silicone mould.
The casting came out great, the only trouble is I needed a means of attaching it to the square spindle so that it can actually function. At first I was just going to make new square spindles and then thread the end and tap the knob. Yeah, and then I started thinking about the knob unscrewing and it was no longer such a good idea. The original knobs are broached — I wondered if I could manage to broach these new ones as well without breaking the bank….
I thought I’d do a test, that’s always a good idea. I already had three new spindles I’d made on the shaper using some 5/16” key stock. The originals come in at 0.281” and I wanted the new knobs and spindles to be interchangeable with originals so I made my spindles the same size. I also have various odd slugs cast from leftover resin used in the past so I dug out one of those to use as a guinea pig.
My key stock spindles are of course not hardened nor are they of decent carbon steel to be sharpenable but the test was still very promising. Nice clean hole, perfectly sized. On to the real deal…
My first challenge was how to hold the doorknob. They’re not exactly conveniently shaped for rigid clamping. Without going too crazy with secondary moulds and castings about the only way I could think of was if I could clamp something around the cylindrical shank and grip it solidly enough to drill. The first experiment with a small block of wood promptly split so I was literally on my way to scout for a chunk of nylon when I thought of hard rubber. Hmmm, hockey pucks are hard rubber….
Fast forward to the lathe and drilling the first pilot hole. I didn’t want to risk a regular twist drill grabbing in the rubber so I went with a spade bit and it worked great. Didn’t seem fussy for speed at all and the hole was nice and clean.
Boring to size was next and equally satisfying. Nothing fancy, just one of my hand-ground HSS boring bars, and again not fussy for speed. I sized the fit on the shank to be snug but not tight, more on that later.
For the broaching part I knew I would want something solid on which to support the knob but not so hard it would mar the urethane. Hmmm, something like….hard rubber!
I was cooking with gas now and it didn’t take much to set up the ole lantern tool post to use as a makeshift radius cutter. Set the cross slide to centre, adjust radius with the compound screw, control depth with the carriage position. Easy-peasy.
The cast knob as it comes from my mould can typically have a bit of uneven sprue left at the end of the shank. It’s easy enough to take care of by hand on the sander or with a file but surely a milling cutter would do a nicer job…
In retrospect I could have oriented the puck horizontally supported on the two blocks instead of vertically like I have it, that way might have been easier to clamp. But I didn’t, and this way worked fine too. Note to self: if you have a choice of hole patterns on your mini pallets, consider using one that corresponds to spacing on 1-2-3 blocks. Very handy to just use studs through the holes instead of having to rely on clamps only.
With the ends cleaned up I drilled the pilot holes for the broach. By this time I had slit the puck so that I could use a hose clamp for extra oomph on the shank.
And the final test — broaching the square spindle hole….
The first one worked not bad. It was super-tight trying to retrieve the broach though so for the second knob I upped my pre-drill size to an “L” which gave another ten-thousandths or so to the hole. I think it helped, and I also pressed in three stages instead of all one shot. I still need to drive the knob off the broach but it’s manageable. I may put a bit of relief in but I don’t know, I’m leery about wrecking what’s working. I also need to drill and tap the spindles for the retaining screw but that’s for another day.
Thanks for looking!
Firstly, this is a facsimile of an 1890’s bronze doorknob. The original was made by the P & F Corbin Company and is their “Rope” pattern. I cast this one in urethane off of an original using a two-part silicone mould.
The casting came out great, the only trouble is I needed a means of attaching it to the square spindle so that it can actually function. At first I was just going to make new square spindles and then thread the end and tap the knob. Yeah, and then I started thinking about the knob unscrewing and it was no longer such a good idea. The original knobs are broached — I wondered if I could manage to broach these new ones as well without breaking the bank….
I thought I’d do a test, that’s always a good idea. I already had three new spindles I’d made on the shaper using some 5/16” key stock. The originals come in at 0.281” and I wanted the new knobs and spindles to be interchangeable with originals so I made my spindles the same size. I also have various odd slugs cast from leftover resin used in the past so I dug out one of those to use as a guinea pig.
My key stock spindles are of course not hardened nor are they of decent carbon steel to be sharpenable but the test was still very promising. Nice clean hole, perfectly sized. On to the real deal…
My first challenge was how to hold the doorknob. They’re not exactly conveniently shaped for rigid clamping. Without going too crazy with secondary moulds and castings about the only way I could think of was if I could clamp something around the cylindrical shank and grip it solidly enough to drill. The first experiment with a small block of wood promptly split so I was literally on my way to scout for a chunk of nylon when I thought of hard rubber. Hmmm, hockey pucks are hard rubber….
Fast forward to the lathe and drilling the first pilot hole. I didn’t want to risk a regular twist drill grabbing in the rubber so I went with a spade bit and it worked great. Didn’t seem fussy for speed at all and the hole was nice and clean.
Boring to size was next and equally satisfying. Nothing fancy, just one of my hand-ground HSS boring bars, and again not fussy for speed. I sized the fit on the shank to be snug but not tight, more on that later.
For the broaching part I knew I would want something solid on which to support the knob but not so hard it would mar the urethane. Hmmm, something like….hard rubber!
I was cooking with gas now and it didn’t take much to set up the ole lantern tool post to use as a makeshift radius cutter. Set the cross slide to centre, adjust radius with the compound screw, control depth with the carriage position. Easy-peasy.
The cast knob as it comes from my mould can typically have a bit of uneven sprue left at the end of the shank. It’s easy enough to take care of by hand on the sander or with a file but surely a milling cutter would do a nicer job…
In retrospect I could have oriented the puck horizontally supported on the two blocks instead of vertically like I have it, that way might have been easier to clamp. But I didn’t, and this way worked fine too. Note to self: if you have a choice of hole patterns on your mini pallets, consider using one that corresponds to spacing on 1-2-3 blocks. Very handy to just use studs through the holes instead of having to rely on clamps only.
With the ends cleaned up I drilled the pilot holes for the broach. By this time I had slit the puck so that I could use a hose clamp for extra oomph on the shank.
And the final test — broaching the square spindle hole….
The first one worked not bad. It was super-tight trying to retrieve the broach though so for the second knob I upped my pre-drill size to an “L” which gave another ten-thousandths or so to the hole. I think it helped, and I also pressed in three stages instead of all one shot. I still need to drive the knob off the broach but it’s manageable. I may put a bit of relief in but I don’t know, I’m leery about wrecking what’s working. I also need to drill and tap the spindles for the retaining screw but that’s for another day.
Thanks for looking!
