The Modular Tower Engine - a new, experimental design

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awake

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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:

IMG_8123.JPG

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:

IMG_8118.JPG

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

IMG_8122.JPG

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:

IMG_8124.JPG

IMG_8130.JPG

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:

IMG_8133.JPG


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.
 

Richard Hed

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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:

View attachment 117786
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:

View attachment 117784
A button-head socket screw and a washer secured the blanks in the jig:

View attachment 117785
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:

View attachment 117787
View attachment 117788
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:

View attachment 117789

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

awake

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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 ... !)
 

Richard Hed

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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 $$.
 

awake

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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:

09-Camshaft.png

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

IMG_8180.JPG

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:

IMG_8186.JPG
 

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awake

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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:

IMG_8162.JPG

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).

IMG_8166.JPG

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:

IMG_8167.JPG

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

IMG_8170.JPG

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 ...

IMG_8172.JPG

... 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:

IMG_8174.JPG

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:

IMG_8176.JPG

IMG_8178.JPG

IMG_8177.JPG

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.
 

awake

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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

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

awake

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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

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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:

IMG_8216.JPG

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:

IMG_8218.JPG

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:

IMG_8219.JPG

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

IMG_8220.JPG


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!

IMG_8222.JPG
O
 

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