Author Topic: The Modular Tower Engine - a new, experimental design  (Read 1771 times)

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #15 on: July 14, 2020, 09:18:39 PM »
Interesting and whimsical design! Many thanks.
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #16 on: July 19, 2020, 01:32:16 AM »
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! But 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. The plans are in attachments 1 & 2.

Attachment 3 shows 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, attachment 4 shows a closeup of the gear assembled on the shaft.
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #17 on: July 19, 2020, 02:14:46 AM »
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 attachment 1 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). Attachment 2 shows this in process, and here you can see the size of this 33° jig. On the left you can see the angle milled in what will be the bottom. You can also see another hole in the side of the jig, but it has no purpose - 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. Attachment 3 shows the result, along with the 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 (attachment 4).

A little simple lathe work 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.) With that made, the jig was ready (attachment 5) ...

... 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 (attachment 6).

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 with the help of 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 (attachments 7-8).

Once the tap was started, I removed the gear from the jig to finish the tapping - otherwise the tap would have run into the 1/4-20 bolt holding 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.
« Last Edit: July 19, 2020, 02:20:59 AM by awake »
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #18 on: July 21, 2020, 07:20:04 PM »
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 finished 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.
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #19 on: July 27, 2020, 11:15:04 PM »
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.
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #20 on: July 27, 2020, 11:36:53 PM »
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 (attachment 1). 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 attachments 1 & 2, 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 (attachment 2).

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 (attachment 3).

With the blank secured and the center of the big end known, machining can begin (attachment 4).

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! In fact, I had already used this jig to make the cylinder platform shown in an earlier post - I just made a locating "pin" with the 1.075" diameter needed to locate the center, and drilled the 10-24 hole that you can see in some of these pictures to hold the blank through one of the mounting holes.
« Last Edit: July 27, 2020, 11:40:55 PM by awake »
Andy

Offline cwelkie

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Re: The Modular Tower Engine - a new, experimental design
« Reply #21 on: July 28, 2020, 02:50:10 PM »
That’s a very slick and versatile fixture plate with lots of room for future positions in a ring about Center. Nicely done Andy.
Charlie

Ps
Very interesting project by the way ...

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #22 on: July 28, 2020, 05:12:23 PM »
Thanks! The fixture plate is going to be used one more time on this build - I'm almost ready to cut the cams on it. Coming soon ...
Andy

Offline Craig DeShong

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Re: The Modular Tower Engine - a new, experimental design
« Reply #23 on: August 06, 2020, 07:58:12 PM »
Hi Andy, chiming in  little late here I know.  A potential problem you may have with the flywheel on the camshaft is that any gear lash is going to cause some somewhat erratic movement of the crankshaft, along with a unique sound as the engine runs.  I would take every precaution to eliminate as much gear lash as possible.

 Part of the fun of posting as you go is the humility you get when things don't always go as well as planned.  My just finished Witte is a perfect example, but then we all need to eat a little crow now and again to keep us honest.  Good luck with what is sizing up to be an interesting build.
Craig

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #24 on: August 29, 2020, 07:52:37 PM »
Thanks Craig, and others who have looked in on this. 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.

In this post, I've included the plans and a couple of shots of the finished cams. 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.
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #25 on: August 29, 2020, 08:45:17 PM »
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 (attachment 1). 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 circe 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 (attachment 2), 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 (attachment 3). 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 (attachment 4).

Then it was just a matter of continuing to rotate the RT by a couple of degrees, taking a cut, and repeating until the RT rotated to where the cut 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. When the RT had rotated to this point, it was cutting the "other" flank of the cam, perfectly symmetrical with the keyway as I had intended (attachments 5-6).

Finally the cams were complete, and in attachment 7 you can see the finished cams, the fixture in the plate with its key, and 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!
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #26 on: August 29, 2020, 09:09:10 PM »
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.
Andy

Offline mnay

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Re: The Modular Tower Engine - a new, experimental design
« Reply #27 on: September 15, 2020, 07:16:06 PM »
Andrew,
I have been following along.  What a great design.   Hope to see it run soon.
Also, thanks for sharing your work, methods and plans with us.
Mike

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #28 on: September 17, 2020, 01:23:52 AM »
Thanks, Mike! Unfortunately I have not been able to get out to the shop the last couple of weekends, but I have hopes that maybe I can this weekend ... if so, perhaps there will be some progress to report. :)
Andy

Offline Bearcar1

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Re: The Modular Tower Engine - a new, experimental design
« Reply #29 on: September 17, 2020, 05:29:12 PM »
 :popcorn: :DrinkPint:  Watching along Andrew. I like your drawings :Love:  and really am enjoying seeing the methods you have used in machining. This is gonna be cool...


BC1
Jim