The Craftmans Shop > Model Engineering
Rockerblock engine--something a little different--
Brian Rupnow:
After a nice break and a drive with good wife, I had to come down and check on the state of my crankshaft, which has been basking in its own private bathtub. The water didn't have as much effect on the cardboard "washer" as I had hoped for. The next trick was to put one end of the crankshaft in my shop vice with aluminum soft jaws and carefully apply some heat to the center of the con-rod, while applying fairly gentle pressure on the con-rod. Once the heat migrated down the con-rod and softened up the Loctite which was preventing it from moving, it began to move freely, and I immediately squirted everything with lubricating oil to keep the heat from affecting the crankshaft itself. The rod now moves freely. I set the crankshaft up in my lathe and put an indicator on it to see if the runout had changed after I cut the center out between the web plates. I discovered that this crankshaft is quite a "flexible flyer". Initially it had about .015" total indicated runout. I grabbed the free end and gave it a tug in the direction it had to move and after doing that a couple of times I had it down to .004" total indicated runout. I had read before about how flexible these single throw crankshafts are, and as I understand it some snowmobile crankshafts with integrated connecting rod are adjusted for runout in the same manner. At any rate, I'm happy, and I think the crankshaft will work fine. I'm not going to pin the pressed connections. Both the rod journal and the crankshaft itself are small enough that I don't want to weaken it by drilling for pins.----Brian
Brian Rupnow:
Those curved spoke flywheels are really, really nice.--But---Oh my God--What horrible little piggies to machine. The worst part is figuring out where to start. I opted to plunge at the major diameter of the recess in the side of the flywheel. Just because of the geometries involved, you can only plunge about 0.050" before the heel of the parting off tool starts to drag. Then you move in towards center the width of the parting off tool you are using to plunge with and plunge again. Moving back and forth between the two positions you keep plunging until you reach the depth you were aiming for. Then grind an HSS tool with the cutting face reversed to what you would normally see, and cut in towards the center in auto-feed mode, taking 0.010" depth of cut. This requires nerves of steel and eagle eyes on the digital readout. When you get about .050" from the minor diameter of the recess in the face, kick out the automatic feed and take the last .050" by hand feed. I have one side of one flywheel finished. I'm going upstairs now and have a strong drink now to calm my shattered nerves.
AdeV:
You need one of these Brian:
http://www.ebay.com/itm/391730204091
See attached (large) pic for details. It takes a V-bottomed insert, so you can plunge AND cut sideways with it. SO with that particular tool, you'd plunge at between 60-75mm diameter, then cut inwards/outwards as required. That particular one is a bit of a fat one - requires a 6mm wide insert - they come in anything from 3mm upward (insert width).
I have several of these tools, but never actually found a use for them... maybe I need to set up a flywheel relieving service :D
awemawson:
Brian, could you not have machined it on the vertical milling machine on a rotary table with less strain on your nerves?
Brian Rupnow:
--- Quote from: awemawson on April 25, 2017, 02:27:54 AM ---Brian, could you not have machined it on the vertical milling machine on a rotary table with less strain on your nerves?
--- End quote ---
Awemawson--The thought did cross my mind. I opted for the lathe because it is marginally quicker. I have a 3 jaw chuck mounted on my rotary table, and I think that with the reverse jaws it could hold the part. Even so, considering a .010" depth of cut and a 3/4" endmill, that's a lot of cranking to put in a recess 1/4" deep.
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