# The Modular Tower Engine - a new, experimental design



## awake (Jul 1, 2020)

With some fear and trepidation, I am introducing a model engine that I have designed, and which I am about half-way through building. The fear, of course, is that I have no idea yet if it will work! Below are some CAD mockups of what it will look like. The first three provide different angles on the fully assembled engine; the last picture has the ignition components removed so that you can see the details of the crank and cam gearing.

It may not be obvious at this point, but this design was inspired by Longboy's Side Shafter and Super Tee - though I hasten to say that he is not responsible for the gaffes and mistakes that I am no doubt making! The key element of Longboy's designs are the connection of multiple cylinders through gears rather than through a shared crankshaft. You may be thinking, "but this "modular tower" is a single cylinder design." Quite right ... but you may note that the design includes the placement of holes and features that will allow a second cylinder to be placed at the other end of the tower - at which point, the tower will be turned 90 degrees in a boxer configuration, but the cranks will be connected to each other via gearing with the cam shaft. Now you know why I call it the "modular" tower engine!

One major feature of the design is also the primary source of my fear and uncertainty about whether it will actually work: The main shaft, i.e. the shaft on which the flywheel resides, is actually the cam shaft rather than either of the crank shafts. I've never seen this done ... but I can't think of a reason it won't work. That may simply reflect my ignorance and inexperience! One issue could be the piston having to complete all four cycles for one revolution of the flywheel ... but then again, this is also true of the various Atkinson designs. I know the "Atkinson differential" is a beast to get running, but from what I can tell the "Atkinson cycle" seems to be reasonably easy to get running.

I welcome your comments and feedback, disparaging or encouraging alike! Stay tuned for the build ... I will provide pictures and plans as they become available.


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## kuhncw (Jul 1, 2020)

Andy,
Interesting design.  I suspect the engine will run, but two things come to mind.  You may run into some torsionals between the crankshaft and the camshaft due to clearance in the gear teeth.  Also with the flywheel running at half the crank speed, you'll have less rotating inertia to carry the piston through compression and over top center.  I'm not saying this will be a big problem in a small model engine, they are just things that could give problems in a larger engine.

Good luck.  It will be interesting to see how your design turns out.

Regards,

Chuck


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## awake (Jul 1, 2020)

Thanks, Chuck. Both of those have been on my mind, but especially the first - this thing may strip the teeth out of the gears pretty fast, if I can even get it to run. But maybe, maybe ... ? I decided to give it a go, and if it doesn't work, I'll re-purpose most of the parts into a more conventional design. And if it does work, I'll add the second cylinder and see if it works as a boxer. And if that works ... I have further plans.


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## minh-thanh (Jul 2, 2020)

An interesting design
 Looking forward to the build.


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## BaronJ (Jul 2, 2020)

Hi Andy, Guys,

I tend to agree with Chuck.  Also for the same amount of effort to keep the piston moving will require a flywheel with twice the mass.

Though I cannot see any good reason why it shouldn't run.


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## awake (Jul 2, 2020)

Thanks, all, for the feedback.

Here's the first piece of the engine - the "tower," which functions as the foundation for everything else. Since there is nothing out of the ordinary in any of this, I did not take any pictures while machining - just the finished product.

A couple of notes. First, note that this is fully symmetrical - both ends, both sides, both faces are drilled/tapped/bored exactly the same way. This will allow the second cylinder to be added later one. Second, note that the bores are made to take the common-as-dirt 608 "skateboard" bearings - these will be used throughout to support the crank shaft and cam shaft ... which means that both shafts will be 8mm diameter.


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## Peter Twissell (Jul 3, 2020)

BaronJ said:


> Hi Andy, Guys,
> 
> I tend to agree with Chuck.  Also for the same amount of effort to keep the piston moving will require a flywheel with twice the mass.
> 
> Though I cannot see any good reason why it shouldn't run.


I think you would need 4 times the mass of flywheel. The flywheel running at half speed has half the momentum and then it's geared to the crank, so the crank sees only half of that momentum torque.


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## BaronJ (Jul 3, 2020)

Peter Twissell said:


> I think you would need 4 times the mass of flywheel. The flywheel running at half speed has half the momentum and then it's geared to the crank, so the crank sees only half of that momentum torque.



Hi Peter, Guys,

Ah, yes !  I missed that !  A good reason not to drive a geared down flywheel.


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## peter2uat (Jul 3, 2020)

I have a somewhat fuzzy recollection of having heard/seen of real life airplane engines doing quite that - running the prop on the camshaft to keep keep the revs under 3500 - anybody con confirm this?


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## Bentwings (Jul 3, 2020)

I worked in a large stationary engine plant. One of the really big motors was made up of two smaller motors. The camshafts were two pice per each motor. These had an interlocking joint similar to hooking your left and righ5 hands together. Theis joint had a sleeve over i5 for a bearing surface. The double motor had a similar joint on the two motors. Pluse a larger crankshaft. I forget the hp rating but about 5,000 seems right. These motors were designed to run non stop for years. Most had automatic oil changers. At given time oil was transferred to barrels and fresh oil pumped in. Various alarms were in place. The customers just had to bring oil delivery trucks out occasionally to replentise oil. Most ran on natural gas so fuel was not an issue. These ran very large generators for community electrical power,   Cylinders were designed so one cylinder with piston and rod could be replaced. The blocks had windows in the sides for access. One was in the world trad3 center basement. It was shut off just before the water got to the carb. In other words it was running nearly submerged.  Jyou might want to look at this type of joint also.some model inline motors use this. A variant was used in the ‘60’s twin engine dragsters too.


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## awake (Jul 3, 2020)

Since the flywheel is under discussion, I'll go ahead and jump ahead to show that next. The weight of the finished flywheel together with hub and screws comes out to 2.05 lbs. / 930g.


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## awake (Jul 3, 2020)

I haven't been taking pictures of making most of the parts for the engine, thus far, but I did take pictures of making the flywheel, since this was a new approach for me - the last flywheel I made used a key, but this one uses a tapered, split hub that tightens into the flywheel, and tightens onto the shaft at the same time. It uses 4 screws to attach the hub to the flywheel, and has two set screws to help push it out after it is tightened (the taper is fine enough to lock). There is also an open hole in the hub that may be used for a starter mechanism - that is not yet worked out.

Here is the making of the hub, first as a slightly oversized blank with an 8mm / .315 hole bored through:





Next I mounted this blank on an 8mm (.314+) arbor that was made between centers, affixing it with Loctite:





I mounted this between centers in the lathe and finalized the size of the flange; then I put it in the mill vise, located the center, and drilled the various holes into the flange:





I also tapped the two 6-32 holes that will hold setscrews to use to push the hub out after the taper locks:





With the hub all drilled and tapped, I put the arbor back between centers, set the compound to 4°, and cut the taper:





With the hub finished (except for slitting the slot), I continued working on the flywheel. Earlier I had roughed it close to final size. Once the hub was made, I left the compound set at the 4°, mounted the flywheel, faced it off, and drilled it at 5/16":





Then I began boring, using the compound still set at the same 4°, until the hub just fit:





Unfortunately, there was a bit more spring in the boring bar than I thought, so after the final spring passes, the hub fit loosely. 





Fortunately, there was a ready solution. I went ahead and cut the inset on the face of the flywheel, then faced off the middle hub area shorter until the taper fit snugly as desired:





Once the hub fit securely, I removed the flywheel and began to work on finishing the other side and the rim of the flywheel. I tried to do this with an arbor between centers, but to get access to the face, I would have needed a very long arbor ... and at 8mm diameter, a long arbor was too flexible. So instead I prepared an arbor using a piece of scrap stock in the lathe, cutting a 4° taper until I got the fit I wanted. I drilled and tapped for a central screw to secure it. I neglected to take pictures of this, but it worked well, allowing me to finish the turning of the flywheel. The final step was to put the flywheel in the mill vise, locate the center, and drill and tap for the four 6-32 screws that mount the hub to the flywheel:





I also neglected to take pictures of the final operation on the hub - with it still loctited to the arbor, I put mounted one end of the arbor in a spin indexer and secured the other end with a center. I positioned it to the right orientation and used a 1mm slitting saw to cut the slot through. Then I heated the hub and arbor to break the loctite bond, pressed out the arbor, and cleaned it all up.

The previous post shows the final results. I made the 8mm cam shaft and tried it out - the tapered hub tightens up and locks tightly. I spun it up to 2000 rpm in the lathe, and it seems to be free of vibration.

On to the next part ...


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## WOB (Jul 3, 2020)

peter2uat said:


> I have a somewhat fuzzy recollection of having heard/seen of real life airplane engines doing quite that - running the prop on the camshaft to keep keep the revs under 3500 - anybody con confirm this?











						Continental Tiara series - Wikipedia
					






					en.wikipedia.org


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## Longboy (Jul 3, 2020)

Peter Twissell said:


> I think you would need 4 times the mass of flywheel. The flywheel running at half speed has half the momentum and then it's geared to the crank, so the crank sees only half of that momentum torque.


I'm going to take the other side of this argument! You can leave the mass of the crank as is. You have twice the torque input now from the reciprocating assembly per two revolutions of the flywheel.


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## awake (Jul 3, 2020)

Dave, I have thought it about that way as well. To be honest, I can see an argument to be made on both sides - more mass needed because it has to do twice the work per revolution, or less mass needed because it is getting a power input every revolution rather than every other revolution. I don't know enough to judge between these competing arguments!


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## Longboy (Jul 4, 2020)

I haven't found anything (yet) on the internet about a 4 stroke engine running the crankshaft at half the reciprocating items speed. That you are making it modular for another cylinder will let the project develop as a single to prove viability somewhat sooner.  
I have run my 2-3-4cyl engines on one cylinder to isolate fresh engine combustion issues and the crank had no problem carrying the spark less dead cylinders along at a slower speed of course.......sometimes with the plugs in (2cyl) for compression.


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## awake (Jul 5, 2020)

Next up for your viewing pleasure, the cylinder. No pictures of the making process - nothing unusual involved - so just the finished pictures. I notice that it has got a bit of rust on it - I had the garage door open the other day when it was raining, and I've been paying for it ever since.


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## Cogsy (Jul 5, 2020)

I've found that my digital camera somehow shows up rust that is almost invisible to the naked eye. And I have issues with damp in my shop too.


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## Steamchick (Jul 6, 2020)

I'd  like spell checker to cope with the word pefrectionist?,


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## BaronJ (Jul 6, 2020)

Steamchick said:


> I'd  like spell checker to cope with the word perfectionist?,


 
pefrectionist

Owz that


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## Brian Rupnow (Jul 6, 2020)

I have seen this attempted before. The biggest problem is the wear and associated backlash that results between the crank gear and the cam gear. When the engine fires, the gears get a concentrated load on one side of the meshing gear teeth. As the flywheel carries the load thru and over the points in the crankshaft where the con-rod is not creating power, the meshing gear teeth see some fairly intense loading on the opposite side of the teeth. It doesn't keep the engine from running, but it is a very high wear area.


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## awake (Jul 6, 2020)

Brian, I've been worried about the stresses on the gears. You don't happen to have any links to where this has been done before, do you? (Or maybe I shouldn't ask until after I have presented the complete design - I surely wouldn't want to ruin my concept by seeing any facts actual experience someone else's work. )


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## awake (Jul 6, 2020)

Steamchick said:


> I'd  like spell checker to cope with the word pefrectionist?,





BaronJ said:


> pefrectionist
> 
> Owz that



Actually, the word you're both looking for is "pre-fectionist," where "fection" is a technical term referring to the acquisition of wisdom through experience. Based on that definition, my work is definitely _pre_-fectionist!


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## Brian Rupnow (Jul 6, 2020)

Awake--Sorry, I don't have a link to give you. It's just one of those things I've picked up over the last 55 years.---Brian


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## awake (Jul 6, 2020)

Understood! Thanks.


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## Canyonman (Jul 7, 2020)

Hey Longboy, What is that engine you have in your Avatar?   Might you have plans for it?
Ken


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## ShopShoe (Jul 7, 2020)

Awake,

You said: "Actually, the word you're both looking for is "pre-fectionist," where "fection" is a technical term referring to the acquisition of wisdom through experience. Based on that definition, my work is definitely _pre_-fectionist!"

Do you also know if that means that "feckless" is a actually a word based on this knowledge-gaining, or rather the lack of it. I had always thought someone somewhere had created the word from random thought.

Language can always be interesting......

--ShopShoe


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## Ken I (Jul 7, 2020)

The amount of energy in a flywheel is its polar mass moment multiplied by is speed (in radian per second) squared.
So a half speed flywheel delivers 1/4 the amount of inertial energy - that's non-negotiable physics for you.

I did a write up on scaling issues in this post :-

Reduce engine size.

Regards,
               Ken


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## awake (Jul 8, 2020)

ShopShoe said:


> Awake,
> 
> You said: "Actually, the word you're both looking for is "pre-fectionist," where "fection" is a technical term referring to the acquisition of wisdom through experience. Based on that definition, my work is definitely _pre_-fectionist!"
> 
> ...



ShopShoe, I must apologize - I was saying that with tongue-in-cheek, not meant to be taken seriously. I did not actually know the origins of the root word for- "fection"; I was just making it up to [try to] be funny.

As I thought about it seriously, I guessed that the root for "fection" comes from the Latin _facere_, "to make or do." Perfection would then be to make or do thoroughly and completely; confection would be to make together - to combine things into something made; and so on.  Sure enough, a quick search on the internet seemed to confirm this (from more reliable sources than a trying-to-be-funny hobby machinist!); meanwhile it looks like "feck" may be a Scottish word, so totally different roots.

Again, I am sorry for misleading; I should have made it more obvious that I was attempting to be funny. Or at least, that's what my family regularly tells me ... !


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## ShopShoe (Jul 9, 2020)

Humor is OK, too. And I think we all need it now........

--ShopShoe


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## Richard Hed (Jul 9, 2020)

awake said:


> ShopShoe, I must apologize - I was saying that with tongue-in-cheek, not meant to be taken seriously. I did not actually know the origins of the root word for- "fection"; I was just making it up to [try to] be funny.
> 
> As I thought about it seriously, I guessed that the root for "fection" comes from the Latin _facere_, "to make or do." Perfection would then be to make or do thoroughly and completely; confection would be to make together - to combine things into something made; and so on.  Sure enough, a quick search on the internet seemed to confirm this (from more reliable sources than a trying-to-be-funny hobby machinist!); meanwhile it looks like "feck" may be a Scottish word, so totally different roots.
> 
> Again, I am sorry for misleading; I should have made it more obvious that I was attempting to be funny. Or at least, that's what my family regularly tells me ... !


If you are going to get onto that, then, I am post-fection profectional in my anti-fectual ways.  I notice that ante-fectual, being nearly the same as pre-fectual, that I must be sub-fectual as you must all be superiour to me as superfectuals.  Godz--I thimk I will slash my ankles with a rusty spoon!


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## Richard Hed (Jul 9, 2020)

ShopShoe said:


> Humor is OK, too. And I think we all need it now........
> 
> --ShopShoe


I don't needs humour now--I have crashed my lathe, ruining one of those @#$^&&d**mned plastic gears on the gear train on my crapply lathe.  I wasn't paying attention and did it but even so (I'd like to blame some else or kick something soft), I needs to get the pulley on the main spindle off.  the retainer nut unscrewed easily, but the pulley is thin alum.  and won't come off easily (maybe that is a goo thing).  so . . . any advice?  (besides don't kick the lathe?)  I've been trying to imagine a circular piece of wood around the base, inside the setup and some kind of lever.


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## BaronJ (Jul 10, 2020)

Hi Richard,  A bit of heat might not go amiss !


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## Richard Hed (Jul 10, 2020)

BaronJ said:


> Hi Richard,  A bit of heat might not go amiss !


Goo Idea, I was thimking I might try that, just don't feel comfortable with heat anywhere near the bearings.  I can try it carefully.  Thanx.


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## BaronJ (Jul 10, 2020)

Richard Hed said:


> Goo Idea, I was thimking I might try that, just don't feel comfortable with heat anywhere near the bearings.  I can try it carefully.  Thanx.



I would use a hot air paint stripper !  Much easier to control where the heat is applied.


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## Richard Hed (Jul 10, 2020)

BaronJ said:


> I would use a hot air paint stripper !  Much easier to control where the heat is applied.


Ah, wouldn't you know it?  My son and I were out trying to get the pulley off, thimking of heating it.  Of course, I didn't want to do it, (didn't thimk of a hair dryer or paint stripper) and my son was against it too.  As we were considering what to do, I tried various wood pieces, then I spotted a nail puller, that is, like a crowbar but flat.  I tried it from the side, as I had been trying from the top with the wood,  Well. from the top, it bound the thing, but with the metal nail puller, I managed to get it just right and it slid right off.  Howl-a LEW-ya!  Easy.  Now I have to find some spare plastic or aluminum 80 tooth gears.  Enco must have know what crap they were selling as they had the fore-sight to put in an extra one so for now, I'm OK.  I don't feel secure without a spare, however.  I would like to build my own gears (cut, I mean) but will have to build many pre-cursor tools to do so.  Well, I'm on that track but in the mean time, I suppose, I should try to find a spare or two.







%Thanx for the goo advice.

I've put this CAD drawing in, as I drew it off an old dwg from an old mag.  I don't really like this, but I might try to build it.  I doesn't like the fact that there are so many "wiggle" spots.  I'm thimking that I could maybe weld a few spots reducing the flexure.  Any advice?


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## BaronJ (Jul 10, 2020)

Richard Hed said:


> Ah, wouldn't you know it?  My son and I were out trying to get the pulley off, thimking of heating it.  Of course, I didn't want to do it, (didn't thimk of a hair dryer or paint stripper) and my son was against it too.  As we were considering what to do, I tried various wood pieces, then I spotted a nail puller, that is, like a crowbar but flat.  I tried it from the side, as I had been trying from the top with the wood,  Well. from the top, it bound the thing, but with the metal nail puller, I managed to get it just right and it slid right off.  Howl-a LEW-ya!  Easy.  Now I have to find some spare plastic or aluminum 80 tooth gears.  Enco must have know what crap they were selling as they had the fore-sight to put in an extra one so for now, I'm OK.  I don't feel secure without a spare, however.  I would like to build my own gears (cut, I mean) but will have to build many pre-cursor tools to do so.  Well, I'm on that track but in the mean time, I suppose, I should try to find a spare or two.
> 
> View attachment 117751
> 
> ...



Hi Richard,

Milling on a lathe is not for the faint hearted !   I certainly wouldn't do it any more unless I absolutely had to !


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## Richard Hed (Jul 10, 2020)

BaronJ said:


> Hi Richard,
> 
> Milling on a lathe is not for the faint hearted !   I certainly wouldn't do it any more unless I absolutely had to !


Yeah, I hears ya, but I has no choice.  No access to a real mill.  Was thimkking that if the local jr. college opens this fall, I could take a credit class (1 credit, that is) and have access to good mills and other goo tools for almost nothing.   In my  Soviet  of  Washington, peeps over 60 can go to the colleges for a mere 5$ per credit plus some upfront fees and books.  I doesn't needs books but this is a real cheap way to get access to quality tools that I cannot afford.


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## BaronJ (Jul 11, 2020)

Richard Hed said:


> Yeah, I hears ya, but I has no choice.  No access to a real mill.  Was thimkking that if the local jr. college opens this fall, I could take a credit class (1 credit, that is) and have access to good mills and other goo tools for almost nothing.   In my  Soviet  of  Washington, peeps over 60 can go to the colleges for a mere 5$ per credit plus some upfront fees and books.  I doesn't needs books but this is a real cheap way to get access to quality tools that I cannot afford.



Hi Richard,
That would be a good way of getting access to machinery that you can use.


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## awake (Jul 12, 2020)

Work has been rather demanding, so this is my first chance to get the next part finished. Here is (most of) the crankshaft - I just realized I still need to make and fix the crank pin, but that will be a relatively simple operation.

Here is the plan:





And here are the finished parts (note that the gear/hub has already been loctited into the web at this point):









Here it is assembled:













And in place on the "tower":









Finally, a picture showing things to come - here it is with the camshaft (mostly done), tappet cage, and flywheel in place. The action of the gears is very smooth, with very little backlash:






Hopefully I will get some time this week to finish up another part or two ...


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## awake (Jul 12, 2020)

I'm mostly not doing pictorials of the make - unless there is something noteworthy in terms of procedure. I'm not sure if this is altogether noteworthy, but I thought it might be helpful to show one way of handling the fixturing of the web.

This picture shows the key idea in a nutshell, but obviously there has already been some work to get to this point:






First I stacked two plates, tacked the edges with a few quick bursts from the TIG welder, and machined them to a square just a bit larger than the OD of the web. I then located the center and drilled and bored to .500". I moved over .500" from the center and drilled the .201" hole for the crank pins. While I was at it, I also drilled 1/4" holes that represented the inside corners of the final shape - this made it a bit easier to handle the milling later on.

I then prepared a mandrel with a .499" stub and loctited the blanks in place. After the loctite set, I turned the blank round and to the final 1.496" OD. After removing the blanks from the mandrel and separating them, I had the two blanks shown in the foreground of the picture above. Unfortunately, I neglected to take any pictures of preparing the blanks up to this point.

With the blanks prepared, I needed a way to hold them securely and aligned along an axis in the mill. The answer was to put a piece of scrap stock into the mill, locate the center, drill and tap for 3/8-24", then move over .500" and drill and tap for 10-24. On the lathe, I used some more scrap to turn pins that screwed down into these holes, one with a .499" OD and one with a .200" OD. When I made the larger pin, I also drilled and tapped it for 1/4-20. Both pins were turned just a bit shorter than the total height of the stacked blanks:





A button-head socket screw and a washer secured the blanks in the jig:





Now the milling could begin - with the help of the DRO, it was a relatively simple matter to rough out the cut-away parts, then come back for a final smoothing pass:









A bit of file work shaped the corners and eased the edges. Finally I needed to drill through the center of the larger part of the web for set screws; to secure the blanks in the mill vise, I put a scrap piece of .499" round through to align the blanks, and a couple of parallels to lift them up to clear the rounded inside corners:






Then it was a simple matter to find the center, locate the edges, drill the relief hole, and drill the tap drill through. I then loctited the hubs/gears in place, in which I had already cut the keyways, lining up the keyways as per the plans. After the loctite set up, I put the hubs back in the mill vise and finished drilling through and then tapping 6-32.

Next up ... maybe the cam shaft.


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## Richard Hed (Jul 13, 2020)

awake said:


> I'm mostly not doing pictorials of the make - unless there is something noteworthy in terms of procedure. I'm not sure if this is altogether noteworthy, but I thought it might be helpful to show one way of handling the fixturing of the web.
> 
> This picture shows the key idea in a nutshell, but obviously there has already been some work to get to this point:
> 
> ...


I hate you--I am so jealous (JK).  Wish I had a mill.  Your work is beautiful.  Thanx for showing.


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## awake (Jul 13, 2020)

Richard Hed said:


> I hate you--I am so jealous (JK).  Wish I had a mill.  Your work is beautiful.  Thanx for showing.



Richard, it is certainly nice having a full-sized mill (BP) with a DRO ... but before I got that, I did an awful lot of work with my cheap, low-end mill-drill, some of it pretty high precision - even without a DRO, though it sure is easier with one. All that to say, keep your eyes open - sooner or later a deal will come your way. (I'd sell you my now-no-longer-used mill-drill, if you want to drive to NC from Seattle ... !)


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## Richard Hed (Jul 13, 2020)

awake said:


> Richard, it is certainly nice having a full-sized mill (BP) with a DRO ... but before I got that, I did an awful lot of work with my cheap, low-end mill-drill, some of it pretty high precision - even without a DRO, though it sure is easier with one. All that to say, keep your eyes open - sooner or later a deal will come your way. (I'd sell you my now-no-longer-used mill-drill, if you want to drive to NC from Seattle ... !)


No, but thanx, when I can afford one, I am going to get a cheapo mill in the range of $2000.  This years purchase is a better lathe if I can get together enough $$.


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## awake (Jul 18, 2020)

I had thought this build would go a bit faster ... but then again, my estimates for how long anything will take are invariably off by an exponential factor!

Here is the next installment: the camshaft. Note that this does not (yet) include the cams - this is the shaft with keyways cut and the gear that will drive it:





Here are the parts (with the gear already loctited to its hub - I keep forgetting to take a picture BEFORE doing that step):





You'll see that I made two gears and hubs while I was at it - the second will await a future variation on the engine, assuming this one works. Note also the key - I forgot to mention this in the last installment, but I wound up making the 2mm keys. Presumably they are available from somewhere, but it turned out not to be hard to make several at once - thin a piece of steel down to 2mm, set it vertical in the vise, and use a slitting saw to cut off blanks.

Finally, a closeup of the assembled shaft & gear:


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## awake (Jul 18, 2020)

Once again, I am not doing a full pictorial of the build, but only of things that may be a bit out of the ordinary. In this case, the issue is how to countersink, drill, and tap for the set screw, since the set screw goes in at a 33° angle. The answer, of course, is to make a jig.

I began with piece of steel scrap, roughly 5" long, 3" wide, and 1" thick. I used the bandsaw to rough-cut the bottom of this piece close to the 33° angle, then set my mill vise to 33° and finished milling the bottom so that it was 33° off square. Unfortunately I did not remember to take a picture of this. However, while I had the vise out of square, I went ahead to set it up to make a jig for a later part that needs a 23° feature, and I took a picture of that. The 23° jig is both narrower and quite a bit shorter than the 33° jig, but hopefully this picture conveys the general idea:





Next I set the jig on its side in the vise, located the middle, and drilled out a pocket into which the hub fit snugly (a nice slip fit). Here you can see the size of this 33° jig, and on the left you can see the angle milled in what will be the bottom. (You can also see another hole in the side, but it has no purpose for the jig - it was already in the piece of scrap).





I also needed to drill a small countersink using a 9/16" bit to accommodate the small "lip" in the hub. Here is the result, along with a gear with the hub up; if you look closely you will see the little lip in question:





At the bottom of the pocket, I drilled and tapped 1/4-20 for a bolt that will secure the gear to the jig:





A little work on the lathe gave me a custom "washer" with a pocket in it to fit over the .394" x .040" protrusion on the other side of the gear. (This protrusion ensures that the gear rides against the inner hub of the bearing without any interference.) Here you can see all the parts of the jig, along with one of the gears, ready to put it to work ...





... or not quite. After I took that picture, I realized that I had skipped a step - I wanted a clear center line on the jig that would help me line up the gear correctly. Fortunately, the mill was still positioned for the center of the jig, so I just popped the jig back into the vise and engraved a center line:





_Now_ the jig was ready to use. I set the angled bottom down in the vise so that it rested on the flats. This caused the side of the jig, where I had created the pocket, to be angled back at 33°. I mounted a gear with the hub in the pocket, screwed in the bolt through the custom washer, and after lining up the gear on the center line, tightened it firmly in place. From there it was easy as pie to counter sink (using a 3/16" end mill), center drill, drill, and tap for the set screw:













Once I had the tap started, of course, I had to remove the gear from the jig to finish tapping - otherwise the tap would run into the bolt that is securing the gear to the jig. Fortunately, that worked well, and in fact I am pleased to say that everything about the jig worked well.

On to the next piece ... which will probably be the "platform" that supports the cylinder.


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## awake (Jul 21, 2020)

As promised, the next part to show is the "Cylinder Platform" - this bolts onto the top of the central "tower," and the cylinder bolts into it. No make pictures - it is a simple enough part - but a couple of details of the process: Once again I made two pieces at once by flash-tacking a couple of plates together (giving a quick burst from the TIG welder without filler). I had machined most of the features some time back, but it wasn't until I set the rotary table up last night for several operations that I was able to finish the outside curve.

Other than that, the plans and pictures should be sufficient. I've shown the part by itself, and also the way it will mount on the tower and have the cylinder mounted to it.


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## mnay (Jul 22, 2020)

Awesome work.  Thanks for sharing the plans and for the build log.  My bucket list is getting longer.
Mike


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## awake (Jul 27, 2020)

Time for a new installment on this build - the rod. You'll see that I designed this to accept tiny flange bearings both for the big end and the little end. I'm reasonably confident that the former will work ... not at all sure about the latter. Is a 3mm wrist pin going to be strong enough?? If it isn't, I'll remove the bearings and substitute bronze. The reason I didn't do that from the start is that I'm not quite sure how to get oil to this bit.


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## awake (Jul 27, 2020)

In one sense, there is nothing unusual about the way I made the rod - it is just rotary table work. But I thought it might be worth showing the way that I set up the jig.

I started by creating a plate to mount to the top of my rotary table. I drilled and tapped 1/2-20 in the center, and made a centering "button" (not shown) so that I could remove, remount, and recenter the plate on the RT (which of course first requires re-finding the center of the RT). I wasn't necessarily expecting it to be particularly repeatable on center when removing and remounting ... but surprisingly, it repeats within .002" or so, and just takes a couple of light taps to get it dead-on again:





As you can see in the picture above, I also drilled and tapped another 1/2-20 hole 1.875" from the center. I turned two locating pins, each with a 1/2-20 thread on one end. On the other end, one pin is .3935", drilled and tapped 10-32 through the center; the other pin is .2355", drilled and tapped 6-32. These locating pins will screw into the tapped holes, providing locating pins for the rod blank, which has previously been drilled and honed with .394" and .236" holes, 1.875" apart:





The blank fits very securely and precisely on the pins, so I must have measured right. The 10-32 and 6-32 features allow screws and nuts (and if needed washers) to securely hold down the rod blank:





With the blank secured and the center of the big end known, machining can begin:






What I failed to photograph was the key to this jig - once I machined the big end, I unscrewed the pins, swapped them, and screwed them back in, and voila! Now I had the blank mounted with the little end centered on the RT.

The jig worked like a charm, and should be useful for future projects as well!




O


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## awake (Aug 29, 2020)

It's been way too long since I've posted any progress - part of that is, unfortunately, that pesky thing called work, which has been very busy the past few weeks as we have been starting up the semester. Part of that also is that the making of next part to show, the cams, was a bit tedious.

First, here is the plan:





And here are the finished results:









In the next post, I'll show a few details about how I made them, and explain some of the busy dimensioning on the plans.


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## awake (Aug 29, 2020)

I made these cams using yet another accessory/fixture that screws into the 1/2-20 tapped center hole on the rotary table fixture plate described in previous posts above. This fixture has a .125" thick flange with holes for a pin spanner; the flange is engraved with a center line across the x-axis when the rotary table is set to 0°. The fixture is bored 8mm through and a 2mm keyway is cut on the center line. An 8mm post with its own 2mm keyway is fixed in the bore (using Loctite) with the keyway aligned to the fixture. The top of the post is drilled and tapped for an 8-32 screw:





I also prepared blanks for the cams, each with a major diameter of .825", a minor diameter of .625", an 8mm bore, and a 2mm keyway. As can be seen in the plans in the previous post, the only difference between the blanks is the length of the .625" diameter section, and where it is tapped for the 6-32 set screw. (Sorry, no pictures of the blanks.)

The fixture was screwed into the RT fixture plate and aligned to the X-axis with the RT set to 0°; a couple of drops of blue loctite ensured that it would not unscrew itself during the machining. Both blanks were place on the post, "back to back" (with the major diameters together), and affixed using the set screws. For added assurance, an 8-32 screw through a specially turned washer clamped the parts down from the top.

At this point, the "busy dimensioning" of the plans comes into play. Looking at the plans, you will see that the flanks of the cams are based on a 1.377" diameter with its center offset .174,.333 from the center of the cam. I had been scratching my head, trying to figure out how I would dial in the exact 1.377" diameter on my boring head ... and then I realized that it was easy. I just had to set the table at .177,.333 ...





... and then set the boring head up to run backwards, with the cutting tip facing inward, and initially set to clear the blank. At that point, I could move the boring head in by .005" at a time and start cutting the initial flank:





Once the cut just began to graze the minor (.625") diameter, I was set at the 1.377" circle. Now I could leave the boring head set, and start turning the RT a couple of degrees at a time to make each additional pass. As the table turned and each pass is made, it cuts away the major diameter to match the minor diameter at the tangent point as it steps around:





Now it is just a matter of continuing to rotate the RT by a couple of degrees, take a cut, and repeat until the RT has rotated to where it just finishes off the other flank of the cam. But exactly how far must the RT be rotated to achieve that? That's where another of those busy dimensions on the plans comes into play. If you look carefully, you will see that there is a measurement of 235°, representing the rotation from one tangent point to the other - "tangent point" meaning the point where the .625" diameter transitions to the 1.377" diameter of the flank. Not by coincidence, this is the complement of the designed 125° angle of action for the cam:









Finally the cams are complete, and you can see the fixture in the plate, with its key, along with the special washer that helps to add additional clamping:





Did I mention that this was tedious? It was, indeed, because I settled on only stepping the boring bar .005" at a time to establish the flank diameter, and then the RT 2° at a time to cut it around. Given the way I set this up, I needed a longer boring bar than I usually use ... and the only one I had is a bit spindly. Thus, I just couldn't take off any more than that at a single pass - I experimented with .010" adjustments, and with 4° steps, and I think that these would give me good results if the boring bar were more rigid ... but with this set up, there was just too much spring in the bar. So ... it took a while, quite a while, to do this. Next time I will make sure I have a more rigid boring bar!!

With the cams complete, it is time to work on the tappet cage and tappets ... stay tuned!


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## awake (Aug 29, 2020)

On to the tappets and tappet cage/guides. I had made the steel "cage" sometime back, so just had to find time to turn the bronze guides, loctite them into place, and turn the tappets. I think the plans and pictures should be enough - no need for an extended description of the build, except to note that the steel "cage" was made from a piece of pipe that happened to be "just the right size" with the flange welded on; after welding, I machined it all to size and shape. You can see evidence of the weldment in a couple of the pictures.

I've also included a picture showing the cams assembled on the camshaft, and here is a link to a brief video showing the tappets being activated as the camshaft revolves:



Next will be either the piston or the head ... we'll see which one gets to the finish line first.


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## James Barker (Mar 2, 2021)

I am going to bump this thread to current by asking a question. AWAKE, what is the status of this project to-date? And also, do you have drawings available for the head and rockers, etc? It has been quite some time since this thread went dormant and I just wanted to check in on it. Many thanks.

BC1
Jim


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## awake (Mar 3, 2021)

Hi Jim,

Thank you for the interest and the bump! I have been stalled for quite a while, I'm afraid, largely related to being super-busy at work. (I hate when my job interferes with my hobbies ... !)

I have gotten out in the shop a good bit just in the last few weeks, but I have been working hard on three separate but semi-related projects - related to each other, I mean, but unfortunately not to the Tower engine, or at least not to any significant degree. I've gathered the materials to build a foundry so that I can try my hand at casting aluminum - something I've wanted to do for many years, but I was prompted to proceed by the acquisition of a used water heater tank of just the right size. That tank has also been prompting my wife to ask when I am going to get that ugly thing out of the driveway, since it is currently residing in front of the non-vehicle side of the garage. But I have determined that in order to make it the way I want, I really need to be able to form a metal sleeve to use as a form (yes, I've thought of any number of alternatives, but this seems the best). So I need a way to roll the sheet metal, which means finally going ahead with another long-desired project, a slip roller. The design is complete, and I have everything I need to make it, so I have begun work on the end pieces (.95" thick steel, using some scavenged material that I have on hand). Meanwhile, though, while sorting through my stocks of steel, I realized I had a nice bit of square tubing of an unusual size - 1.75" square, with a 1/8" wall. Why is that significant? Because yet another long-on-my-list project is a 2" x 72" belt grinder, which _could_ come in handy for some part of making the slip roller, and the major reason I had never started _that_ project was needing to have tubing that would telescope snugly but freely. I knew that I have a lot of 2" square 1/8" wall tubing, and 1.5" square 1/8" wall tubing, but mating those leaves way too much slop. But when I realized the actual size of the tubing I re-discovered, and that with a bit of cleanup, it would fit just right ... well, I'm off to the races on that project as well; I've filed out the inside weld seam on the 1.75" tubing, and verified a beautiful sliding fit with the 1.5" tubing; I've scavenged a treadmill motor and controller (actually, I have scavenged more than one over the years ...) and verified that both work as desired; I've scavenged a piece of 4.5" OD pipe and am working on a hub to mount it to the treadmill motor to become the drive wheel. Just yesterday (the last day of a 2-day semi-vacation, allowing me some concentrated shop time!) I made the 1/2-13 left-handed tap that I will need to connect it to the shaft of the treadmill motor. So all is in motion at the same time ... too many projects, too little time ... I need to retire so that I can get some real work done! 

Never fear - I WILL resume work on the Tower, and will continue to post plans as I verify them. I do have plans drawn for the head and rockers, but haven't made either yet, which means I'm not yet sure those plans actually work!

On edit - I just realized that I left out a fourth project in the mix - I need to do a fair bit of welding on both the slip roller and belt grinder projects, and I was tired of how hot my air-cooled TIG torch would get, so I finally invested in a water-cooled torch ... which meant I needed a TIG water cooler. I worked up a designed, bought about $60 worth of parts, and put it together a couple of weeks ago. It works great! Also just yesterday, I finally wrapped up the last bit of that project by completing the filter housing and buttoning it all up to keep the dust out.


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## James Barker (Mar 3, 2021)

Hi Andy, Thanks for the reply. You need to get a job! Lol!! Seriously, you sound like a one armed paper hanger in a windstorm at present. Lol! Things do tend to get in the way thats a fact. I look forward to seeing the finish to the tower engine project. I just did not want to see that thread die off. Be safe.

BC1
Jim


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## Richard Hed (Mar 3, 2021)

awake said:


> Hi Jim,
> 
> Thank you for the interest and the bump! I have been stalled for quite a while, I'm afraid, largely related to being super-busy at work. (I hate when my job interferes with my hobbies ... !)
> 
> ...


I know how you feel.  There should be a law against work interfering with hobby.  Also, understand about those projects being planned for years ahead and never getting it done.


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## awake (Mar 4, 2021)

James Barker said:


> Hi Andy, Thanks for the reply. You need to get a job! Lol!! Seriously, you sound like a one armed paper hanger in a windstorm at present. Lol! Things do tend to get in the way thats a fact. I look forward to seeing the finish to the tower engine project. I just did not want to see that thread die off. Be safe.
> 
> BC1
> Jim





Pent up demand! When I finally can carve out some time, I feel like I've got to go at 90 miles per hour. On the one hand, I love it when I get a bunch of different things moved forward by significant steps. On the other, I do have to watch out for a tendency to start turning the hobby into work by setting goals and timelines and evaluating the results - too far down that road and it becomes a job rather than a way to relax and enjoy.


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