For Part 2 we're going to focus on the Scotch Yoke. Like many cast parts, this has no reference surface to start with. We have to figure that out for ourselves.
Let's make the top our first cut and go from there.
Getting started in the mill. I have a small piece of cardboard on the back side and a rod on the front. The cardboard takes up some of the irregularities of the cast part. The rod is there to make sure the back jaw is allowed to locate the part and reduce the influence of the front jaw. Does that make sense?
Using a parallel to line up the yoke as close to straight as possible. The idea here is to get close...there is no "exact" yet.
Top surface cut. This will be the first reference surface.
I'm using an edge finder to locate both sides of the yoke. Now, mind you, these are both rough. I'm not after and exact reading, just an approximation. I'll find the rough center based on this so that I can cut the slot.
About to cut out the slot. I'm using a 3/8" diameter 3 flute carbide endmill. Shameless plug...I'm in love with CGC end mills. These things are awesome. Not only are they awesome, they're made in Wisconsin. Because everything made in Wisconsin rules. At this point, I also need to trim the ends a bit to square them up.
The slot needs to be 1/2" wide and 3/8" deep. In order to do that, I cut down to near full depth, and then moved over to finish each side with a small move down to get the final depth.
Using a 1/2" gauge to verify the measurement on the slot.
Setting up to drill the hole for the file shaft. With the ends and bottom machined, I can reference them to locate the hole.
Drilly drilly.
Ream.
Now we get to the tricky part. I need to set this part up to cut a 1/16" slot and center said slot on the part. I'm using some thin cardboard as packing to protect both the part and the vise jaws (rough castings, remember). The height is based on the overall length of the yoke.
With the part squared and ready, in comes the slitting saw!
Finished slit.
This hole falls in a funny spot. I elected to spot face it with an end mill before drilling. Had I just gone in with a drill it would have walked off the line and gone all crooked. We can't have any of that crooked stuff 'round here.
All the way through with the tap drill. A no. 7 in this case, since it's a 1/4-20 thread.
Followed with a 9/32" drill half way through.
Counter boring.
Tapping the hole.
I don't know why I lived my life so long without having one of these tap guides. They are brilliant!! Chuck up the guide, locate the hole, tap away!
The rest are pics of the finished part. If you look real close on this one, you'll see my mistake. It won't affect the function, but I'm still peaved with myself.
I'm not sure what we'll cover in Part 3. I think it will be the slider that fits into this yoke. I just knocked that out this evening and the game of catch up continues.
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