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Scale Merlin Crankshaft
- Thread starter dynamotive
- Start date
- Replies 47
- Views 23,256
Peter S
Diamond
- Joined
- May 6, 2002
- Location
- Auckland, New Zealand
I was recently admiring a small crankshaft at a friends place - it turned out to be a Merlin crank, about 100mm long (4"), made from lead and "forged" (in a closed die I think) in a scale model forging press many years ago at Vickers in Sheffield. He showed me a photo of the model press that produced the little crankshafts - cool!
Well, I just purchased one of Dynamotive's Merlin casting sets off an estate sale. I've been doing my due diligence in searching all the information about building the Merlin that I can find, when I came across this thread. It's a shame no consensus was found about the crankshaft. For posterity, I have an old Boss Bridgeport and a manual mill. Between the 2 I will fab the crankshaft out of billet, which by far seems to me to be the way to go for a one off crank.
I am sure this is the start of years of late night milling...
John
I am sure this is the start of years of late night milling...
John
kustomizer
Diamond
- Joined
- Aug 17, 2007
- Location
- North Fork Idaho
If you don't mind, post some pics and keep us up to date with more pics I imagine several of us would like to see it progress.
Will do. The plan is to use the CNC Bridgeport sporting a 4th axis to rough the crank, and then switch to a tool post grinder on an ancient Monarch lathe to finish the journals. It will likely be a few months before I get started so I can finish off a couple other projects already started.
triumph406
Titanium
- Joined
- Sep 14, 2008
- Location
- ca
There was an investment caster in Fullerton (so cal) who was investment casting small replica V-8's for somebody back East. The crank was investment cast along with heads cases covers etc.
With a 3D printer it would be easy to make a 3D pattern using filament specifically for wax investment casting. Finding somebody to cast the crank economically would be your greatest challenge
Mike Henry
Titanium
- Joined
- Aug 18, 2001
- Location
- Batavia, IL USA
I'm not sure if it is the same casting kit, but Terry Mayhugh on the Home Model Engine Machinist web site did an extensive build page with detailed descriptions and photos so you may want to check that out if you haven't already found it.
Quarter Scale Merlin V-12 | Home Model Engine Machinist
Quarter Scale Merlin V-12 | Home Model Engine Machinist
Yes, that is the same casting set. Dynamotive, the OP for this thread has pretty much abandoned the project after getting a prototype to the running phase.
As for my Merlin Project, I recently bought a full size 1940 Stearman which I will be restoring for at least a handful of years. She stalled after having engine problems on takeoff. The fact she nosed into a thicket of trees near vertically...and both pilots walked away, is a testament to the design ethics of the war era!
I am still slowly programming the merlin into the virtual world during times I am away from home and cannot work on the Stearman. I have all but the cylinder block castings converted to Inventor code. I can then start programming the CNC machining. If all goes as planned, I should be able to automate the 2,000 or so 2-48 bolt threading the engine requires. Then, when I am finally ready to start, it will just be a matter of setting up and letting the old Boss do it's thing.
As for the crankshaft, I purchased a section of 4340 Alloy steel to machine the crank as a billet. I know the 4340 is overkill for this project, but I cannot accept using less than the best materials. I still remember my materials instructor at college telling us how 4340 is the "perfect" material for crankshafts, as it is the best combination of strength and fatigue resistance...you know, in case I need to run this engine reliably for missions over Europe LOL. The crank is programmed into Inventor and will be cut to shape using 4 axis on the Boss. I also found an ancient Dumar grinding head for a lathe. I will play around with it and possibly final grind the journals.
Anyway, that's the update. It won't happen fast, but it will happen!
As for my Merlin Project, I recently bought a full size 1940 Stearman which I will be restoring for at least a handful of years. She stalled after having engine problems on takeoff. The fact she nosed into a thicket of trees near vertically...and both pilots walked away, is a testament to the design ethics of the war era!
I am still slowly programming the merlin into the virtual world during times I am away from home and cannot work on the Stearman. I have all but the cylinder block castings converted to Inventor code. I can then start programming the CNC machining. If all goes as planned, I should be able to automate the 2,000 or so 2-48 bolt threading the engine requires. Then, when I am finally ready to start, it will just be a matter of setting up and letting the old Boss do it's thing.
As for the crankshaft, I purchased a section of 4340 Alloy steel to machine the crank as a billet. I know the 4340 is overkill for this project, but I cannot accept using less than the best materials. I still remember my materials instructor at college telling us how 4340 is the "perfect" material for crankshafts, as it is the best combination of strength and fatigue resistance...you know, in case I need to run this engine reliably for missions over Europe LOL. The crank is programmed into Inventor and will be cut to shape using 4 axis on the Boss. I also found an ancient Dumar grinding head for a lathe. I will play around with it and possibly final grind the journals.
Anyway, that's the update. It won't happen fast, but it will happen!
