It's time to get back to documenting my work. I accomplished a few things over the weekend.
The Cross HeadFor the beginning of the cross head assembly, I made the cross head itself and a cross head pin that will mate with the connecting rod. There are also slide bars and washers that will slide within slide bars and pillars that hold the slide bars. I decided I should make those together so they fit well together. So today it's the cross head and pin. Here's the plan from Stew:
As usual I'll do the cross head and then turn the pin to match it.
I started with some 1/2" CRS bar stock which matches the 12.7mm dimension exactly. I could have used 3/8"x1/2" as that matches the plan exactly, but this is what I had in my supply. I faced it, turned the shoulder, and drilled and tapped for 8-32 which is how I threaded my piston rod. I'm learning that when I make a choice like 8-32 as my substitute for M4 threads, I need to look forward in the print and write it down where it impacts other parts. In this case I had written 8-32 for this part.
I chopped the part off the bar stock with my bandsaw and left a little extra. Since the bar stock wasn't 3/8" thick, I had to mill off top and bottom as shown here. I'm using my DI to measure the amount, which isn't a critical dimension. Even if it was critical, I know I'm going to do some filing so I could simply use care to leave it oversize.
Next I rounded over the front edges with a file. No filing buttons here. I filed by eye and made a bevel first, which is easy to see if it is even width or not, and when I was satisfied, I did the final bit of rounding over. This was quick work.
Next I located and drilled the hole for the crank pin. I went with a D bit size, which is 0.246"
I rotated the part 90 degrees in the vise (you can barely see the D-size hole I previously drilled) and then I started drilling out waste between the arms of this little part. This didn't go so well at first because I hit the previously drill passage. So much for drills! But at least I didn't ruin the part.
I switched to a 2-flute 1/4" end mill which worked much better. Now I can hog out the inside of this thing. I had centered the mill on the part so this was quick work moving in X. Recall the part is over length so I could leave the bit on the right closed up. I assume that's better for the vise.
Here it's almost done and looking better. I wasn't too worried about the ends (certainly not the right end) and made light passes on the inside edges until they were at the proper thickness.
Next, I drilled for pins. I had to study this a bit, but I realized this makes sense. The cross head doesn't pivot, and the slide bars will thread onto the cross head pin. These little pins will keep the cross head pin from rotating and unscrewing the slide bars. I suppose loctite might do the job, too. I pulled out some 3/4" brass brads from my wood shop supplies, measured them, and found they would need a #63 bit. The smallest bit I have is #60, so I looked again for larger brads, which turned out to be 1" and needing a tiny little #57. It drilled way faster than I would have guessed. For sure I needed a starter drill (not shown) for these holes.
I centered these locking pins within the thickness of the material by eye. As you can see, my eye isn't too accurate with the pin hole closest to me in this photo. Oh well.
Next I machined off the excess length with an end mill on the edge of the vise. I suppose I could have clamped it vertically in the middle of the vise and skimmed off the top in that position. I took a few light passes so that nothing would snag and bend.
I found there was still some material remaining in the thickness of the arms of the part. I clamped it in the middle of the vise, removed the parallels, and lightly took some passes. I got a little too aggressive and popped it back like this. Thankfully I didn't ruin the part (or me!).
I guess I was feeling lucky and went back at it despite my near miss. I continued very light passes (< 5 thou) and it finished up fine.
The corners still need rounding over and I decided I'll make buttons to help guide that. But it occurred to me that I could locate those buttons with the cross head pin, so I decided to make the crank pin next. Rounding will happen later.
The Cross Head PinRecall I made the cross head hole with a D bit which is 0.246. Here I have some 1/4" rod and I skimmed those few thousandths until I got a nice snug fit. It presses in with heavy finger pressure. No press needed of course.
I decided to thread the ends for 10-32 so I turned the 7mm length down to the necessary size (0.190") and threaded it. I turned it around, parted it off, and did the same. Not much to it.
You might notice I did better on the left than the right. I did the right side threading first and found I couldn't get the thread all the way to the shoulder, so I used the parting tool clean it up. On the left side I showed I learned something and used the parting tool up front to turn the minor diameter. When I threaded it, the threads came out perfect right up to the shoulder. Well, maybe the threads aren't exactly perfect, but I can run a nut right up to the shoulder. I've never read how to do this before, but it sure turned out nice. Or maybe I just got lucky.
Next I turned a 3/8" button and attached it with a nut on the 10-32 threads. I could see this might work, but the nut is too big and would interfere with filing. I didn't think to measure the nut.
So plan B was simple enough. Make a couple filing buttons that are tapped for 10-32 instead. Note that I needed to drill a recess to clear the wider part of the cross head pin. The buttons fit nice. It was looking like easy filing ahead.
And filing was fast and easy! The nice thing was that this part was big enough to clamp. Filing it down maybe took 2 minutes. Maybe.
Spiffy. And it looks right at home on the engine!
And that's it for today. Next up, I will switch to the connecting rod assembly, and then later I'll get back to finishing the remaining parts for the cross head assembly.
Todd