Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

 I made the 4 off 5-40 brass nuts for this engine. Not exactly thrilling stuff, but I put my new mini chuck to use, and it worked a treat. Not very complex so I'm not going to waste your time with a blow by blow account, but here they are with the mini chuck in use







That little chuck is going to be exceptionally useful over time.

Two "whoops" moments today. The first was sweeping my precious nuts off the bench onto the floor. Happily found my nuts again though.

The second had me turning the air blue.



I was going to re make the connecting rod out of bar stock, and figured out an intricate sequence to machine it without marking out, using a rotary table to make various rounded features. I'm pretty sure that would have (or could have) worked, but on a whim I called PM Research and discovered the price of a new casting was six dollars. With brass bar being close to the value of gold, or so it seems, I bought the replacement part. I was pleased to discover that PM Research have been so busy they have had to add more staff just to deal with orders. The nice lady I spoke to was very new, and I was her first foray into supplying spare parts. In the background I heard one of the main people there assuring her that "lot's of people need to buy replacement part one offs". I suppose that reassured me a bit also.

Anyway, here is a sequence of pictures for the sake of it. Made much the same as the last one, although I hope to get the split line in the right place this time.

I have learned to spend a fair amount of time measuring castings and understanding the starting part, so as to think through where the stock is on the part, and understand whether the starting part is symmetrical, or how it relates to the finished part. After that I drew up a machining plan. So first step was getting the thickness of the bosses to size, which involved taking slightly more off one side over the other to try and keep the bolt bosses central.





I then set up a knee (angle plate - we call them knees at work, and I quite enjoy using that term) to hold the part for drilling and tapping the bolt bosses. I aligned it by touching off on the tops and sides of each bolt boss, and tweaking it until they were evened out.



I machined off some of the gate feature - but not all of it. This is a qualifying surface - i.e. one I can use to register in later operations, knowing it is perpendicular to the axis of the part. I also cleaned the tops of the bolt bosses.



Having done that, I established the center of the part by touching off on the sides in both X and Y directions. I spotted the qualified surface just in case that might be useful later on. Then drilled and tapped the bolt holes.



Then I set up an aluminum jig plate that I had used previously to hold the bed casting (sole plate?). I used this piece of aluminium because I had fly cut it previously on both sides, and I knew it was flat and parallel, and also preferred over drilling into the mill table. I suppose I could have used this in the first place and drilled the holes in the part in the same set up as milling the thicknesses. Oh well.





Here I am using the qualified surface to verify squareness to the X and Y axes.



I used a gauge pin to center the little end under the spindle - just done visually to get the zero point.



After that I lightly marked the center of the little and big ends, and performed a quick measurement of the big end to be sure I was central.



After drilling and reaming the two holes, I was pleased to find that a .250 gauge pin would slide in, but a .251 gauge pin would not.



Note: I checked the little end using the actual wrist pin as well, in case I needed to ream slightly over to fit that, but it fit perfectly. Also - the final hole size in the big end will be .375. I have a .25 hole in there right now to aid in set up for slitting the big end. After that is done, and the caps milled to size, then the end cap will be attached and the hole opened up to .375. I probably don't need the .25 hole in place, but I think it may help visually, plus I can touch off on a gauge pin inserted in it when setting up the slitting operation. This is the part I got wrong before (aside from breaking the thing being foolish later on). So - getting there. But that's all for today.