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New 5×7, partly 2

October 8th

The woods parts are ready for finishing. Getting colder, so moved the wood stuff  indoors until I get time to lacquer. Onto the really fussy shit.

I’m always bemoaning my metalworking skills, but I’m really complaining more about my patience threshold. But I realized it’s a lot like working in the rain, once you make peace with getting suited up the day is much more pleasant and productive. Suiting up in this instance is setting up properly, taking some time with work-holding, clamping, and indicating parts so they have a fighting chance to spec out. I’m still not getting a very decent finish off an end mill, but at least I don’t have to file a long gradual taper out of a slot anymore.

Another recent revelation: keeping the shop clean. Working in a mess is annoying, time consuming, and distracting in a pinhole headache sort of way.

When installing the extensions and guides. I cut all parts to finial length, and double check the lens stage extension for squareness. The lens extension locates all the other rails so it needs to be absolutely parallel or the extensions will bind in the guides. After countersinking the bottom of the bed on the drill press, I clamp everything upside down, using blocks to make sure everything around the perimeter is flush and tight before screwing the guides in place. I make sandpaper blocks out of scrap MDO and double stick tape, they also work well as clamping blocks to keep everything in place without having to clamp down too much. The nice thing about Delrin is the tolerances can be much closer that aluminum or wood because the coefficient of friction is so low. I cut the Delrin guides to final length by scribing a line with a knife, then paring it down on the micro mill. A down-cut spiral router bit chucked in the mill worked really well, left a nice finish. If you cut Delrin with the wrong tool it can leave a gummy finish with a gray cast and texture that sort of looks like a well-used pencil eraser.

 

Part mapping

Here’s another revelation I can’t believe I didn’t think of sooner- punch identifying parts. Due to all the mirrored, flipped, reversed, or partially symmetrical parts, it’s really helpful to identify mating parts and surfaces with a punch so you don’t make two left-handed standards or countersink holes or mill gear slots on the wrong side of parts. There’s a lot of dis- and re-assembly making a camera, it’s pretty tedious, and punching also greatly reduces the fuckups. For instance, after installing the rail and guide components, its helpful to map out the mating faces of the parts so they go back together correctly. I’m not nearly good enough to make left- and right-hand parts completely interchangeable with each other- even if holes differ by a few thousandths of an inch, it can screw up alignment of the slide stages if the parts get flipped when reassembled.

 

Installing the ground glass frame guide rails was a little trickier. I inserted the holder with some feeler gauges to give the rails a little side to side clearance, then installed a screw through the top of the spring housing on each side. Then I taped it down so I could transfer everything to the drill press without loosing registration, or having it twist out of square to the back. I left the rails long and did not shape them beforehand, just to simplify this step a little (this also reduces the chance of the screws spilling the wood near the ends of the rails). Afterward I cut the guides to length and tapered them from the center spring housing down to about 3/8″ thick on each end with a block plane. After that I joined the ends with a piece of mahogany (shown in the photo at the top of the post). The piece is beveled on the inside face, to allow the GG frame to lift out of the guides without binding. Similarly, the GG frame is chamfered on the bottom around the perimeter so it nests into the guides easily.

To install the spring arms to the frame, I shimmed the bottom edge of the arm up a little so it wouldn’t bottom out the spring’s travel when installed. The tape and pencil lines keep the bracket and arm pivots along the same axis, don’t want it to twist in use.

 

Standards, fore and aft. Plenty of slotting for everyone. Dovetail slots, radial slots, stepped slots, through slots and stopped slots. Rear standard has rise, base tilt, swing and shift. Front standard (backwards in the photo above) has independent rise and center tilt on the stage pictured. The front will have base tilt as well,  but this stage will nest inside the front standard platform with the base tilt, and that will also have swing and perhaps shift as well, haven’t decided. I almost never use front shift, but it’s looking like there’ll be no weight penalty for adding it so why not. Haven’t made that part yet, but it will be similar to the rear platform.

To reduce weight, I re-made the tail ways on the rear rise movement out of Delrin, but oddly the parts were heavier than the aluminum, so decided to go ahead and use the original aluminum parts, and use the UHMW film on the bearing surfaces if needed. I might swap them out down the road if the rise doesn’t work smoothly.

 

Rear rise detail. The outer dovetail ways will attach to the shift/swing platform at the bottom. This involves edge tapping into 3/16″ stock of the platform, something I’ve never tried before.

 

After drilling holes in the standard, I clamped it in registration with the platform and used a punch to transfer the hole pattern for cutting the threads. I tilted the drill press table vertically, then set up a fence parallel to the bit then drilled and tapped each hole before moving to the next. Used 4-40 thread. Probably should have used 2-56, the head size of standard pan head screws is slightly over 3/16″, had to order some button head screws that have a slightly smaller diameter. The inner stage of the front standard was done the same way, but those screws heads need to be flush so they don’t interfere with the base pivot brackets, so used flat head screws to attach the standards to the torsion bar.

The torsion bar on the front standard is keyed into the stepped slots of the standards for strength. I cut the ends of the torsion bar a few thousandths out of square (top to bottom, not front to back). This also pre-loads a little outward spring tension so loosening the rise/fall knobs allow the standards to relax and open slightly so the lens stage will slide easily. On the mill I just set a .005″ brass shim under the far side of 6″ parallel bars and was careful to square both ends with the top facing down.

Front standard detail

Front standard is coming together. I had to relieve the front of the torsion bar to provide clearance for the swing/shift controls (yet to be machined) when using forward base tilt. Base tilt is 45° each way, way more than I’ll ever use, but the radial slot required for this much tilt was pretty minimal.

The bronze pivot bearings for the base tilt are a press fit and are difficult to remove, so won’t fully seat those until the final assembly. I’m using the same bearings for the base pivot on both standards. They are too long as well, will be cut to flush out with the inside surface of the standards when assembled. Since the pivot is so close to the radial slot locking knob, no other mechanical fastener will be used for the pivots, just the bearing. I left enough room between the standard stage and the pivot stage for some  UHMW film if needed to reduce friction between the nested parts, but with even the bearing only partially pressed in, the tilt is very sturdy and smooth to operate. In the photo above the base tilt brackets are still a little too long, need to shorten those by a quarter inch or so to provide clearance for the rise/fall knobs when using using full fall.

To lock down the base tilt on both standards, a 10-32 thread stud will be Loctite’d into the standard. This rides in the radial slot, and a disc spring and a thumb knob on the outside will keep a little pressure on the movement so it doesn’t flop around when loosened.

I decided to add axis tilt to the front standard. If I ever use forward tilt for a little extra bed extension, axis tilt will let me plumb the lens. I’m using the axis tilt design from my Arca Swiss. The lens board stage will be offset behind the standards, in line vertically with the base pivot bearing, and will be connected to the rise/fall plates on either side with thin aluminum plates, one of which will have a radial slot.

Arca Swiss axis tilt design, top knob controls tilt through a radial slot on the inside, pivot is on the lens stage and connects to the rise/fall plate. A nice solution, allows use of each movement independently, and having the tilt knob off axis from the pivot makes it much more secure when locked down.

Axis tilt and rise detail.  The title stage attaches to the rise stage, which slides in the dadoed slots cut into the standard.

I received the bellows from Rudy at Ecbuyonline. Very nice work, sized exactly to spec. The  material is thin and flexible, and all the folds are perfectly crisp and even. I routed out a recess in the rear frame to make installing them a little easier. Still need to paint the frames black. I’ll probably use double-stick tape to attach the bellows, since contact cement uses the same solvent as most spray paints and tends to turn the paint into a gummy mess.

Not much left to do, other than some final shaping and polishing of the metal parts, lacquering the wood parts, and final assembly. Still need to make some minor hardware like the lensboard clasps and ground glass retainers, and need to decided how the back will attach to the rear standard. I need to locate some knobs for this. Hate to use stainless steel, heavy and expensive, but not much else is available in the sizes I need. I should get a lathe at some point, but reluctant to buy another tool just to see it rust up in my unheated shop.

October 21

Almost forgot about the fussiest part of the whole build, the extension gears and shafts. One of the few parts of the camera that needs to be really accurate in all directions. If either the shaft or rack is too deep the teeth won’t mesh properly and will strip or skip, if either is out of parallel the spur gears will track badly and chew up the wood, if the spurs out of radial sync the extensions will skew and bind.

Using 20° pressure angle/ 48 pitch brass racks and spur gears. The pinion are factory-bored for 1/8″ shaft, but it’s a little too much torque for such a long skinny shaft so I use 3/16″ stainless steel tubing instead, which makes it a little easier fitting knobs on the ends, but requires boring out the hub to 3/16″.  (I could use a bigger spur sized for 3/16″ shaft, but then the bed would have to be thicker to accommodate it.) I cut the shafts flush with the bed, and tap the ends for 6-32 thread, then thread lock a stud in each end for mounting the knobs. The nice thing about 6-32 is it’s the stock thread size for 1/4-20 thread repair inserts, which works out well for stock size knobs. Just thread lock the insert in the knob, the thread a knob on to lock focus, and pin the knob on the other side for focusing. Having a metal lathe to make custom shafts and knobs would be preferable, but it’s a ok workaround.

 

Dadoes for the gear racks, 1/8″ wide by 1/8″ deep. After cutting the slot, I changed the 1/8″ bit out to 3/16″ without moving the fence, then reduced the depth of cut to 3/64″ to cut a gutter. This prevents the spur gear from marring the wood if there’s a little side-to-side play in the shaft.

With the rack in place, I laid out the spur gear placement on the shaft, and hold them in place with blue tape. They have to align both radially and laterally, to I lock them in place with a drop of red threadlocker so they don’t slip when drilling and tapping the gears and shaft for the set screws. Still, I wait to cut the rack to length until after this is done just in case.

I drill and tap the gear and shaft at once. I don’t have a bottoming tap, so drilled through the shaft and the hub on the other side and tapped through and through. The hold the shaft, I routed a V groove in mating pieces of wood sized to fit between the hubs, and shimmed under the outfeed side of the shaft to keep it from deflecting during milling.

The gear rack on the extensions are used to layout the shaft grooves and gear wells in the bed. I used the same bit for both operations, cutting the slots on the router table, and the wells on the mill with the bed clamped down to the table and using the X/Y feed. The shaft groove is slightly over-depth, so I can make some springs out of shim stock to keep the spurs tight to the rack with some tolerance for flex.
Once I put the shafts in place I realized that it would have been much better to extend the 3/16″ shaft on the side with the focusing knobs, and like the gears just pin the knobs to the shaft with a through set screw. As it is I tapped each end of the shafts for 6-32 studs and threadlocked those in place. The studs are strong enough for the lock-down knobs, but over time there might be too much torque from the focusing knobs on these small studs.

October 27

I had a decent weather window to spray the sanding sealer.  60°, not really warm enough in the shop for the lacquer to cure, but warm enough to spray outside if I keep the finish and parts warm in the house, take everything outside just long enough to coat, then immediately bring each back part inside. I have a 350 CFM hood vent in the kitchen, so the smell isn’t noticeable.  This morning it was pretty cold, so I totally bagged off a corner of the kitchen into makeshift a spray booth, but after coating only one part the smell was so overwhelming I had to open every window in the house to air it out.

I’m a little ambivalent about the chatoyance of mahogany. It’s a tad showy, I don’t much care for cameras that look like jewelry boxes. Even ‘straight’ grain reflects light differently depending on the angle. It’s really apparent on parts assembled from pieces with perpendicular grain. Anyway, even with just a sealer coat the transformation in the wood is pretty remarkable, from dull salmon pink to a rich honey color, and it will  get deeper on UV exposure. Some of the small parts are a little tricky to hold. The  pressure from the HVLP gun would blast them right off the turntable if not held down somehow. I use double stick tape,  binder clips, screws, and other jigs to hold the parts.

The rear standard is generally the most tedious part to spray, so I made a vertical lazy susan. By spraying light coats and rotating the part I can hit all sides at once. The thin interior margin that is covered by the panel is where the back nests and will be painted black.

Part 3 here