A bit of progress today. The build is now on the fiddly parts stage - making up all the linkages and so on. On plans these look easy, but they take a lot of time to make - for a good runner they need a good bit of accuracy.
The plans mostly call for 1/16" (1.6mm) brass plate for many of the linkages, but I only have 2mm and 1.2mm available - so I'll be using the 1.2mm plate and compensating for the thickness difference where needed. For a start, two ruler-wide strips sawn off the big bit of stock I have:
I felt like a bit of exercise, so filed one edge of one piece nice and straight:
Then I marked the strip for the eccentric rod, sawed to just over size and filed it down, and then filed a curve on the end to match the ring I turned up for the eccentric last Saturday. It's nice to file a fitting curve that's also shaped well enough that the ring can just sit on top of it:
Then I drilled the hole for the connection to the valve rod - I decided to make the pin size a bit bigger - 2mm instead of the 1.6mm:
The valve rod's hole will have to be enlarged as well, but that's not a problem.
On to a bit of silver soldering - things located with some flux and a sliver of silver solder plate on top:
A bit more flux added to protect the silver solder sliver:
And a quick showing-of-the-torch and cooling down. The job looks horrible here:
Into the citric acid pickle. The level in my pickle container was running a bit low, so I popped into the kitchen for some boiling water from the kettle (that also made a nice cup of coffee). The addition of hot water makes the pickling job go faster, and I just plonked it down on top of the firebrick with a piece of aluminium to distribute and use of the latent heat left in the fire brick:
The pickle has been used a bit, that's why it's starting to turn green - from the copper dissolved in it.
By the time my coffee was finished, the pickle had also done its job - and things were looking a bit better:
After a bit of clean-up, the eccentric rod looks OK:
As you can see, the bronze ring looks - and is - very copper coloured. I've noticed this in the past as well after silver soldering and pickling, and I have a hunch its because the zinc in the bronze starts to evaporate at silver soldering temperatures, while the pickle might also leach it out of the copper. I didn't want to fuss around too much and remove a lot of material from the workpiece though, as it was pretty close to final size already. This is something I'll have to keep in mind for future builds.
A quick trial fit, and a problem :
:
The eccentric rod is a whole 1mm too long... I traced that back to a calculation error, but fortunately I won't have to re-make any parts to fix the problem; the valve rod has enough length and available play to it to shorten it by 1.5mm to ensure adequate clearance. As stated earlier, the smaller holes in the valve rod is not a problem; those will be opened up to 2mm to match the eccentric rod.
On to the connecting rod, and a start on the fork from a bit of 4.6x8x11.2mm sized brass - here drilled through 3mm:
Next I milled a 7.1mm deep x 4.6mm wide slot through it:
A 4mm cutter works well here; mill down to depth on the center line in 2mm steps, and then clean up the sides to width - makes the slot come out very nice.
I might get lynched or laughed at for what I'm going to say next, but I'm going to do it anyway.
Often times I notice posts where machinists are chasing extremely close tolerances on chucks and collets, and then are disgusted that the "cheap" items they buy are out by quite a bit. I know there are very close tolerance kit out there - at a premium - and if I'd bought one of the premium kits I'd be disgusted as well. My budget simply does not extend to the premium tools, so I have to make do with the less accurate and affordable stuff.
When I make my own kit, I try and do it as accurately as possible - as I have done with several collet chucks - but once I add the budget collets I can afford to it, a lot of that accuracy goes down the drain. Well, rather than fight an impossible battle, one can use a bit of run-out in one bit to minimise run-out in another bit. Nowhere perfect, but it helps. The one 16mm ER25 collet I have has an eccentric run-out of about 0.05mm close to the chuck, and the 3.5mm ER11 collet I have has an eccentric run-out of about 0.04mm. If the two are combined, and the run-outs set 180o apart, that leaves just a 0.01mm (0.0005") run-out on the workpiece close to the chuck, and I can easily and fairly accurately skim a bit of 3.2mm brazing rod down to 3mm while maintaining a fair modicum of accuracy:
Sometimes even the weak points of tools can be used to advantage
The same bit of 3.2mm rod flipped, turned down to 3mm, and threaded M3:
Another bit of silver soldering - please excuse the out-of-focus photo :-[:
I could have soft-soldered the last joint, but there was some turning left to do on it, and I wanted the strength of a silver soldered joint. Very carefully and slowly, I used the sharply honed parting tool to skim the workpiece down:
With the rod in place and used to set up nice and square, it was easy to drill the 2mm cross-hole:
After a bit of rounding over with a file, and some elbow grease, the bit looked like this:
Next up, the big end connector. Not really hard to do, but when I started to drill 2.5mm for the M3 threaded hole, I noticed that the workpiece wanted to move downward; I'd forgotten to add some paper to prevent that, so I just used some bits from the mill clamping kit to make an impromptu screw-jack:
Dark photo - if you click on it, the detail should be better.
Rather than sawing off the workpiece from the parent stock on the band saw or with a hack saw, I just slit it off - not all the way through, but just till the workpiece started lifting:
Using the slitting saw meant I could get very close to final size with little surface finish needed, and by leaving the last bit attached, it was easy to just break it off. If I slit it all the way through, I would have had to hunt through the shop for the workpiece wherever the saw tossed it.
On the plans, this bit remains fairly rectangular, but I thought it might look better rounded over, so I did a couple of quick facets on it:
A bit more file & emery work, some tapping, and a bit of reaming, and the connecting rod was done:
:
Well,not quite - it still needs a lock-nut.
Regards, Arnold