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a nine cylinder radial engine, plans by "ageless engines"
madjackghengis:
Well all, that nice steel blank which looks so good on the rag balled up a lump inside the hole when I went to press a shaft in it, so hot rolled steel is not an option, no matter how pretty it looks before the work. I've been cogitating on this problem, once the holes for the main shafts and for the crank pin as well as the alignment pin are drilled, bored and reamed, trying to use a carbide face mill to reduce the thickness of the web of the crank means interupted cuts, which have no relationship with flat. After long thinking, I decided to get back to the already hardened steel and try again, another way.
these are the two new blanks I will be machining to try to get a crank that is straight.
using the shaper to clean one face of the one blank
and working on the other blank. After cutting both sides of both blanks, I found two to three thousandths from parallel between the two sides of both blanks. After checking everything else, I checked my parallels I was using, and it turns out I was using a set which are not parallels at all, but just mostly the same size. Going through my blank tool bit drawer, I found two half inch tool bits which miked out to exactly five hundred, and put both blanks back in the shaper and did a three thousandths finish cut on both sides of both blanks, ending up with the sides parallel within about a thousandth, I think I can work with this, and work out the difference as I shape them to their final dimensions.
This is one of the blanks on a tool maker's flat, with four cigarette papers to test flatness, one paper is a bit loose, but still sticks, the other three feel pretty much equal. The second blank finished up pretty much the same. I'm caught between machining the cheeks down to their proper thickness at the crank pin, and then drilling, reaming, and boring as appropriate, or doing the cheek thinning first, and then reaming and boring the respective holes. Since both the main shaft holes, bored, and the crank pin holes, reamed, are in the thinned section, and their presence contributed to the interuption of the cut, leading to not flat surfaces, I think I will try thinning first, and then putting in the respective holes. Having made three sets of cheeks, I have decided its the long haul, and if they don't work out I've got plenty more old steel, for the next set of blanks to be cut from. I will produce a straight well mannered crank shaft that fits the bearings, and rotates moving all the rods, no matter how many blanks it takes. I have taken great liberties with the design of the crankshaft, as I don't like the original design, and none of my experiences does anything but further solidify my belief the original design is lacking in both strength and stability. I am ready to have a straight working crank today, if it is at all possible, however I've got a couple more ideas if these don't produce it. Thanks for all the comments and support, makes me feel like I'm in a modelling club, something I've always wished for but was never around. Lots of inspiration for good quality work. :mmr: :beer: mad jack
Bernd:
Pretty presistent you are there Mad Jack. :clap:
Before long you'll be able to say' "I now know how not to produce bad crank cheecks." (Think fo Thomas Edsion when asked about his light buld. He said he knew 101 ways how not to make them)
Hang in there I'm sure you'll get a pair soon. :thumbup:
Bernd
kvom:
I think milling before drilling will be superior, as milling can relieve some stress in the metal and cause the holes to move.
madjackghengis:
Hi all, Kvom, that is essentially what I concluded, and yesterday, machined the blanks so that all that is left is the reaming of two sets of holes, and the boring of the mainshaft holes, since I don't have that odd sized reamer. I don't know what kind of steel this is, though I suspect it is something like 1045 or the like, but it must be around C40 or better rockwell by the way it machines. The hot rolled I tried was easy to get to dimension and form, but didn't even take a light press fit without damage to the bore, and the crank has to be assembled serveral times to put this engine together. I have a few more ideas if today doesn't make things happy, I only know plenty of people have built this engine before me, and been successful, and therefore I will be. I will take scrap and weld it together to make a crank if that's what it takes. I took some pictures yesterday, getting the cheek blanks ready, and will take more today, as I make holes and cut out the profiles and see how things go together. Till then, :mmr: :bang: mad jack
madjackghengis:
having machined the step in the crank cheek blanks in the shaper, and matched them as close as possible, I put them in the mill vise and drilled and reamed the crank pin hole and the alignment hole, and bore the main shaft holes, as they are not a standard size.
with all the holes done, I profiled the blanks by scribing the outline of one of the old ones on both blanks, and cut them out with the bandsaw, then used a belt sander to get them close, and a file to finish them as matching, and to the line.
here's my tangential radius profiling attachment for my work bench, set up to finish off the radius around the crank pin end
another view of the profiling attachment
with the cheeks on a mandrel, machining the radius on the counter weight end on the lathe
the new cheeks, ready for deburring, with an old cheek showing the un-even surface of the interior which caused the problems with getting the crankshaft straight. An example of cutting hardened steel with a multi-insert face mill and interupted cuts causing mountains and chasms.
another shot of the cheeks on a mandrel, machining the radius.
I turned the ends of the existing crank pin down to match the reamed holes, assembled the crank, fitted it in the case, found it was too wide, took fifteen thousandths off each end of the crank pin shoulder in a four jaw chuck, pressed the crank back together and found it now fit, with about ten thousandths end play, probably should have measured before machining.
I think a new crank pin is in order, this time with real, actual numbers to work with. I've got a piece of stock missing in the shop, and its what the crank pin and shafts were supposed to be made of, but I can't find it. When I do, I will make a new crank pin, and a new front prop shaft, as the one I just made seems to have a slight bend in it. I think the unknown steel I used because it was heat treated is still soft in the core explaining two bent prop shafts which have appeared when they were straight the night before. Have to find that heat treated 4140 stock and finish the crank, so I can move on to more interesting things, such as the master rod and the oil pumps.
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