Quarter Scale Merlin V-12

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Bentwings

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Don,
Thanks alot for the tips. Sounds like good advice.
Terry
I was just directed to this thread and build today. I do remember the casting kit from years ago. I wanted to get the set and do this engine. I could see much better then but I really did not have reliably shop to build and work in at the time. I’ll try and backtrack this group to satisfy my ire to see one of these completed. Msleave for now.

byron
 

Bentwings

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Terry,
I've got quite a bit of experience in cranking out dubiously large amounts of power from small motors - for slotcar racing (a hobby) and for robotic applications (my usual line of work) where power to weight is an issue.

You can only get so much torque out of a saturated armature so the only way to get more is to spin the beans out of it and gear it down as I am sure you are well aware.

I posted on the site an article on getting more out of your A.C. motor (a lot more) which is germane.

www.homemodelenginemachinist.com/showthread.php?t=25236

Also from my automotive experience - starter motors are not 100% duty rated - they burn out if you run them too long but normally longer than it takes to crank the battery flat. So you can overload a motor for brief periods given the relatively light time-duty cycle of a starter.
With a motor that runs close to saturation this won't help but a motor that runs at 20% saturation can be loaded to 500% for brief intervals.
The "brushless" servo motors we use in our robots are built like this they will handle 200% load for 20 minutes and 500% for 5 seconds.

Anhoo - the reason for my response is that you will need to gear it down and those ganged planetary gear drive sets used in cordless drills and pneumatic tools can be cannibalised to form the basis for your reduction gearbox.

A lot of starter motors now do just that as opposed to the direct drive types on older cars.

And as Naiveambition pointed out you can go scrounging for an actual starter built for the purpose from something or the other - none spring to mind but perhaps some other members might make suggestions.

Another thought for a compact gearbox would be a harmonic drive - I could give you a perfectly serviceable 50:1 450W unit out of a robot (too much lash for precision but still a perfectly serviceable unit.) I have a few lying around.

Just a suggestion.

Regards,
Ken
I’m just starting to learn about stepper motors. These can be pretty strong in small sizes with some careful thought I’d think a planetary gear trace could be mad roughly cylindrical.encasing the often more or less square shape of steppers. There ar some complicated drivers available but I have not progressed that far yet. Just something to think about. These little motors can produce amazing torque fo their size.

byron
 

pascal

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I'm going to try to justify some of the craziness that I'm about to apply to these very expensive parts with some background theory. Precipitation hardening is a common way of strengthening 356 aluminum which is a popular casting alloy. To promote this process, certain impurities such as magnesium and silicon must also be present in the aluminum melt. As the castings cool these impurities form simple compounds which gradually, over time, come out of solution (precipitate) and they end up distributed throughout the casting. These precipitates harden the casting by preventing its plastic deformation (bending or stretching) when it is put under stress. These precipitates strengthen the casting, but they also make it brittle. This hardening process is kicked off just after the castings solidify, and it continues for hours to days or even weeks later depending upon the casting's storage temperature. Because of this process's dependency upon time, it is also commonly referred to as age hardening.
A casting that has been age-hardened has little tolerance to bending, twisting, or stretching. If a 356 casting warped during its solidification, and if it requires straightening before it can be finish machined, then it must be annealed. This can be done by heating the casting to about 700F and then allowing it to air-cool. The common shop technique of using an acetylene torch to create a soot coating for use as an annealing temperature indicator also works for 356. If, after straightening, the part is left in its annealed state, significant strength will be lost. For 356 the tensile strength loss can be as great as 10,000 psi. Unfortunately, a 700F annealing is not high enough to kick off another age hardening cycle.
The casting can be re-hardened, though, back to its maximum strength by heating it to 1000F for a dozen or so hours and then quickly quenching it. What makes this difficult to do in a home shop is the fact that aluminum melts at 1035F, and so careful temperature control is required. There is also a chance that the casting will deform under its own weight if it isn't properly supported. In addition, air-cooling needs to be minimized which means the quench tank needs be located within seconds of the furnace.
Unlike the more familiar hardening process associated with steel, precipitation hardening does not occur immediately after the quench. The metal may remain soft enough to be straightened for up to a full day after the quench.
Production castings should normally be straightened by the foundry before age hardening has progressed to any significant extent. An even better solution, of course, is to design the part so warpage is a minor concern, and the casting can be corrected by finish machining. The Merlin castings were not straightened by the foundry, and their thin-wall and complex cross sections make them very susceptible to warping that may not be correctable solely by machining. Straightening, after the castings have been allowed to harden, was therefore left to the end-user.
Since this is a totally new experience for me, I felt it would be best to practice on some scrap cast parts I picked up long ago from my favorite scrapyard. My practice pieces, which are louvered vents, were sand cast from 356 and allowed to age-hardened for many years.
I decided to immediately answer a question that was in the back of my mind, and that was just how much could I permanently deform one of these castings without annealing. After breaking two practice parts, I realized the answer was 'pretty much nothing at all.' The rest of my practice was done using only annealed parts.
I eventually developed a process, after cracking a few annealed practice parts, for controlling the pressures I used to bend the castings. I learned to clamp the parts down firmly and to use positive calibrated stops to quantitatively limit the distance that an edge was being pushed. Rather than using a press I typically used my own strength and body weight in combination with fulcrums, levers, and clamps so I could maintain a hands-on feel for what I was doing. I found it was important to proceed in small deformation steps of .005" at a time and continually return to the surface plate to check my progress. I also decided it was best to not aim for perfection but to stop at the point where measurements showed I could machine the remaining defects away without negatively impacting the part's appearance. Since I had decided to not even attempt age-hardening in my shop, I tried to minimize the areas that I annealed. Before attempting any straightening, I located the major axis of the warpage using a surface plate, and I tried to anneal only a narrow region along that axis. I then applied my straightening efforts across this axis. After a full day of experimenting I had gained enough confidence to start on the Merlin parts.
I first selected the three crankcase-related castings. I was able to machine flat the bottom surface of the main casting with respect to the crankshaft bores in order to obtain a reference surface. The front gear case turned out to be the major problem area on this part. It was out of perpendicular by almost .050" over its 5" height. I annealed a line across the gear case just above the top deck of the crankcase. After clamping the crankcase with its reference surface down to my drill press table, I clamped a long piece of wood to the gear case to which I applied the straightening force. With a pencil mark on the wood as a moving pointer I carefully monitored the distance the part was being pushed. After a half dozen tries which included returning to the surface plate to check my progress after each push, I had finally bent the gear case to within .015" of perfection. At this point I was able to machine its cover mounting surface flat and perfectly perpendicular to the reference surface in order to meet the drawing dimensions with no noticeable impact on appearance. I then machined the rear of the crankcase to its finished dimension. The decks for the cylinder heads will be done later, since they can be cleaned up with just finish machining.
The gear case cover was relatively simple to correct because its major warp was also about a single axis. The documentation warned that this rather rigid part might have to be widened, and the drawings included the design of a complex 'stretcher' to attempt this. I'm thankful that my particular cover, which is a fairly rigid part, didn't require this really scary correction.
The oil pan was considerably more complex and problematic. Being rather flimsy by design, it was warped across two separate axes. In addition, it's width had to be spread to match the crankcase. When checked on the surface plate, one corner of this part was initially almost 1/8" higher the other three. This part required almost a full day to correct, and I ended up annealing practically the whole casting. Fortunately, the oil pan is not a structural part, and the loss in strength that it likely suffered is not important. In the set-up for its final flange machining, the pan had to be packed with plastic modeling clay in order to dampen the chatter created by the mounting flange machining. I used high relief aluminum-cutting Korloy carbide inserts for all the machining operations and was able to obtain excellent surface finishes on both the annealed and un-annealed areas of all three castings. - Terry

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pascal

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The Rolls Royce V-12 Merlin, was one of the best known, if not most influential, WWII aero engines. It was deployed in the British Spitfire and later replaced the Allison in the American P-51 Mustang. I recently purchased a set of quarter scale castings from a small San Diego start-up that originally planned to build and sell completed quarter scale Merlins nearly a decade ago.
http://www.quarterscalemerlin.com
The parts I received were investment cast and can be best described as large pieces of (expensive) jewelry. They share most of the realistic features and intricate detail with the equivalent parts on the full-size engine. Photos of the castings are available here:
http://www.quarterscalemerlin.com/castings/
I've no experience in working with castings, and was a little taken back by the notes accompanying them. The notes warned, in several places, that being long, complex, and thin-walled, they will likely require straightening and, in some cases, heat treating.
The set I purchased includes castings for a functional supercharger, but it's not clear whether its scaled development was ever fully completed and just how much of it became a part of the prototype that was produced. The original designers opted for a glow plug engine, and so the magneto development may not have been completed. Finally, the notes mentioned fuel distribution issues with the Merlin's scaled-down intake manifold. The developers eventually designed an alternate configuration with multiple carburetors in order to get a running prototype, but the drawings didn't include information on its design. Over-heating issues were also mentioned, and a prop didn't show up in the published video of their running engine. Working these issues will add some interesting challenge to the project, but I'd rather additional development work wasn't going to involve very expensive and perhaps irreplaceable castings.
I've been able to find online evidence of three other builders who have tackled this project using these particular castings. One posted his crankshaft build on 'the other' forum but he never returned after creating his own piece of art.
My plan is to spend the first few weeks evaluating the castings I have so I can better understand the issues involved with getting them ready to machine. My first goal will be to see if I can get the major crankcase components straightened and fitted together with minimal machining. -Terry

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HI mayhugh1

very impressive work.
I want to build same engine.
Can you help me with or if its avaiable cad, cast and drawin?
thanks
Pascal
 

Bentwings

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I remember this project from many years ago there was an active forum for a while I wanted the casting set as I had machine shop availability atvthe time the castings were just too expensive . There were numerous posts about them being very weak and often breaking or cracking while machining I YHINK there was quite a set of drawings available to I don’t remember if I actually purchased these Atvthe time the general feeling drifted to carving the parts from solid bar stock 6061 or even higher strength alloys. Even then these were quite expensive tonourchbraw materials. If I remember there were probably 3 engines produced that ran . As far as the supercharger , even back then it was well known that model scrolls superchargers and centrifugal ones didn’t work well at best they were great fuel mixture beaters. It’s surprising that mixture issues came up but air with gas or alcohol in it just does not like to turn corners well . Often the fuel drops out and you have a lean condition for one or more cylinders . This happened even in full sized racers. I’ve had supercharged cars for many years as well as race fe cars . This is a common problem even there the Hogson radials have a centrifugal impeller that actually does a good job of mixing furl but I YHINK push comes to shove it would show mixture variation cylinder to cylinder Were I to build this Merlin today I’d make a full set of solid model Assemblies to check the design then look into cnc machining . The oil pan and valve covers are really thin so they would be tough to machine nicely. I YHINK I might look into pressure forming these parts as sheet metal The crankshaft would be a real issue if any serious power were applied
HI mayhugh1

very impressive work.
I want to build same engine.
Can you help me with or if its avaiable cad, cast and drawin?
thanks
Pascal
 

Bentwings

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after reading and posting I looked this up again
I tried to get backninbtobyhecsite but I couldntbitvtookbsvlittlevmessingvaroundcwith quarter scale Merlin and related things but I finally foundvitbibstillncsntvgetvavclickabke site address but muchbofvyhebokd stuff is still yherevifvyoubdidcaround in the Ed this was actruev2/4 scal except for fasteners In my mind it’s a good example of full scale that really does not scale well down to 1/4 or 1/5 if exactness is desired . You end up with wired sizes of hole bores pistons rings bearings. That would be much better adjusted to more or less standard sizes


Then how did that scary wrinkle cream site get stuck atvthe end of this thread yikes!
The site is called scale Merlin .com I YHINK I was not able to cut and paste the site I don’t think the castings are available but there is a drawing set noted . Check it out . I’ll look it up again and see if I can get a tag able site .
HI mayhugh1

very impressive work.
I want to build same engine.
Can you help me with or if its avaiable cad, cast and drawin?
thanks
Pascal
 

Bentwings

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I probably commented this before .

In my opinion I YHINK rather than exact scale. Is probably not the best idea . My idea would be around possibly using parts that you can purchase . Make the model “ about scale”. Look toward using standard fasteners metric or imperial I YHINK a cad model would be essential Then maybe 3 d print the parts and build a plastic model so it could be seen where could be useful concessions . I’ve built amber of large scale Rc model airplanes I subscribe to “ if it looks scale , it’s pretty close “. A good example was a “ semi scale” gun sight I made it had many features that were notable on the real one but in the end it was terrible “ but it look like it was scale to the unknowing “ I had countless good moments on this atrocity . Even real pilots thought it was good . I had a semi scale pilot positioned so he appeared to be looking correctly into the thing if if you were to measure this’ll stuff you would probably just shake your head and walk away . You can scale plastic models an come close but practically being able to make it look scale yet functional is the real challenge As I noted the crankshaft would be a real work of art Eve with modern cnc just machining some thing that small out of 4340 or tougher steel would be a challenge. Just look around at small engines and especially large scale Rc planes. A two cylinder crank is pretty tough most are built up so some pretty close size work involved Look at a Hogson 18 cylinder crank. It’s built up some have mad it press fit others have made it slip fit assembly using various “ fixing” means . I have a 4 cylinder double acting engine it has only mm main and rod bearings I haven’t put it under heavy load yet but I’ve already designed an outer bearing support for the overhung flywheel it’s probably not really necessary as I’ll most likely not power a heavy load no run at high speed for long periods But 6 mm is pretty small shaft I just wanted double hung bearing rather than single over hung bearing .
Just my yhoughts
 

CJD

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It's been a while, as the Stearman project is taking most of my free time, but after 2 years of working here and there, I have managed to measure and digitize all of the Merlin castings. I am now working on machining and building the engine in virtual space. The beauty of this is that any mis-matching in the castings becomes immediately obvious. I can then take care of fixes in virtual space, long before the first CNC cutter touches a casting.

merlin.jpg


merlin lower.jpg


Here is an example. This next picture shows the front gear cover installed on the block. The cover is a bit too large, so the screw holes do not perfectly line up. Some of the screw holes can be seen punching through the block casting! I then have the opportunity to realign the cover or re-locate the screws as appropriate to ensure there is not a problem. The front cover is shown translucent to aid in viewing the internal gears and bolts.


merlin screws.jpg


The pictures above also show some of the machining operations started. In other words, the main bearing webs have been virtually machined to reflect the fit of the bearing caps, and the cross bolt drillings are located in both the block and bearing caps. The cylinder decks have also been planed flat and indexed to the crank bore.

Terry, if you are still out there, this thread is invaluable to me, as I received my castings from an estate sale, so I do not have all the notes and documents. I am depending on your detailed posts to obtain recommended screw sizes and a lot of other important information about this build. Thanks!

My time frame is still infinite. I expect the Stearman to take at least another 2 years. I work on the Merlin project virtually when away from the house on business trips. With luck, I will have the virtual work completed about the time the Stearman is compete, and I can start the CNC machining shortly after.

I'll try to give (virtual) updates now and then...

Cheers,

John

Oh...a quick glimpse of the Stearman...

IMG_2437.JPG



IMG_2419.JPG
 
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Bentwings

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by all means keep up with the cad models I was going to purchase the original drawing set and do as you are doing . Once you make really corrected models maybe you could do 3 d printed models an really assemble as intended . IE make a desk top plastic model
It's been a while, as the Stearman project is taking most of my free time, but after 2 years of working here and there, I have managed to measure and digitize all of the Merlin castings. I am now working on machining and building the engine in virtual space. The beauty of this is that any mis-matching in the castings becomes immediately obvious. I can then take care of fixes in virtual space, long before the first CNC cutter touches a casting.

View attachment 142338

View attachment 142339

Here is an example. This next picture shows the front gear cover installed on the block. The cover is a bit too large, so the screw holes do not perfectly line up. Some of the screw holes can be seen punching through the block casting! I then have the opportunity to realign the cover or re-locate the screws as appropriate to ensure there is not a problem. The front cover is shown translucent to aid in viewing the internal gears and bolts.


View attachment 142340

The pictures above also show some of the machining operations started. In other words, the main bearing webs have been virtually machined to reflect the fit of the bearing caps, and the cross bolt drillings are located in both the block and bearing caps. The cylinder decks have also been planed flat and indexed to the crank bore.

Terry, if you are still out there, this thread is invaluable to me, as I received my castings from an estate sale, so I do not have all the notes and documents. I am depending on your detailed posts to obtain recommended screw sizes and a lot of other important information about this build. Thanks!

My time frame is still infinite. I expect the Stearman to take at least another 2 years. I work on the Merlin project virtually when away from the house on business trips. With luck, I will have the virtual work completed about the time the Stearman is compete, and I can start the CNC machining shortly after.

I'll try to give (virtual) updates now and then...

Cheers,

John

Oh...a quick glimpse of the Stearman...

View attachment 142341


View attachment 142343
 

ajoeiam

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It's been a while, as the Stearman project is taking most of my free time, but after 2 years of working here and there, I have managed to measure and digitize all of the Merlin castings. I am now working on machining and building the engine in virtual space. The beauty of this is that any mis-matching in the castings becomes immediately obvious. I can then take care of fixes in virtual space, long before the first CNC cutter touches a casting.





Here is an example. This next picture shows the front gear cover installed on the block. The cover is a bit too large, so the screw holes do not perfectly line up. Some of the screw holes can be seen punching through the block casting! I then have the opportunity to realign the cover or re-locate the screws as appropriate to ensure there is not a problem. The front cover is shown translucent to aid in viewing the internal gears and bolts.



The pictures above also show some of the machining operations started. In other words, the main bearing webs have been virtually machined to reflect the fit of the bearing caps, and the cross bolt drillings are located in both the block and bearing caps. The cylinder decks have also been planed flat and indexed to the crank bore.

Terry, if you are still out there, this thread is invaluable to me, as I received my castings from an estate sale, so I do not have all the notes and documents. I am depending on your detailed posts to obtain recommended screw sizes and a lot of other important information about this build. Thanks!

My time frame is still infinite. I expect the Stearman to take at least another 2 years. I work on the Merlin project virtually when away from the house on business trips. With luck, I will have the virtual work completed about the time the Stearman is compete, and I can start the CNC machining shortly after.

I'll try to give (virtual) updates now and then...

Cheers,

John

Oh...a quick glimpse of the Stearman...

View attachment 142341


snipped most of the pics/visuals

Hmmmmmm - - - - where did you get your information (drawings etc) for the "Stearman" - - - I'm assuming that its an airplane.

TIA
 
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Hmmmmmm - - - - where did you get your information (drawings etc) for the "Stearman" - - - I'm assuming that its an airplane.

TIA

Wow and a real airplane at that. This must be a restoration project. What is the history of this one? Is the engine running or will you have to tear that down too?
 

Scott_M

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To CJD
You should really start your own thread on both the Stearman and the Merlin. Right now it is at the end of 45 page post. Good luck on anybody finding it again.
Not to mention going "off topic" on Terry's excellent post.

Scott
 

CJD

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Yeah, I hear ya'. I'm only able to post every 9 months or so on the Merlin, and the Stearman is definitely "off topic". I only mention the Stearman to explain my slow progress on the Merlin. Once I am able to work enough to post regularly, I will start my Merlin's own thread. It deserves it's own thread, since it is a completely different approach to the same engine project. Right now I just don't have enough info to start a new thread...plus it serves to "bump" Terry's great thread every few months!

Bentwings...The thought of printing one of these engines crossed my mind. The digitizing I have done is really all that is needed to print. It would be best to "fix" the casting problems that I built into these particular parts, but that is rather easy once the parts are built in virtual space. In fact, I bet 3D printing in metal wouldn't be as pricey as making castings. I am not really interested in printing a Merlin, but if anyone else is, let me know. Unlike Dyno, I would be willing to share my Inventor files.
 
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