Design and build side shaft hit and miss engine from bar stock

[gbritnell]

The cam doesn't really need to be hardened. You could do the roller. For the amount of time the engine runs it would have negligible wear. Actually when the roller is on or near the lower part of the cam profile it isn't really touching because of the valve clearance. It just skip along on the surface.
gbritnell

[Brian Rupnow]

With cylinder head finished and bolted in place, and cylinder o-ringed and siliconed into water reservoir, this thing is beginning to look like an engine. Very soon I'm going to have to dive into the unknown and make a face cam. George Britnel and Jason have been guiding me along on this. I'm still not certain I have the total picture sorted out in my head, but I'm running out of parts to make. One good thing is that these parts (the cam follower and face-cam) are on the outside of the engine, so if I mess something up, I don't have to tear the entire engine down to correct it.

[Brian Rupnow]

George--I tried to reproduce your sketch. Top view shows cam follower riding against face-cam with 0.157" total lift.
Projected view below shows cam follower on face cam with projected tangent point.  0.344" dimension from centerline to tangent point is a resultant. If I connect center to tangent point, it yields an angle of 32.29 degrees. Then if I move 90 degrees from that tangent line, that should indicate where my other tangent point is. ---I think!!
I realize that there will be a few degrees of movement to get the cam follower up onto the high part of the cam track, so in consequence the valve will be completely open for 180 degrees minus whatever that small amount is, doubled??

[gbritnell]

Brian,
Look at the radian line you have drawn at 32.29*. Now if a cut was made at that line the inner edge would hit before the outer edge therefore changing the timing dramatically not just that but the cam follower would just hit on that corner. You want as much contact area as possible which is made by making the cut line parallel with the cam axis.
gbritnell

[Brian Rupnow]

After much heavy thinking and going slightly crazy in the process, I decided to let the power of my Solidworks software do this face cam thing for me. The area which appears as solid black in the drawing is flat, representing the area where the valve will not be influenced by the cam. I have decided to cut the profile with the side of a a 5/8" endmill and to use a 5/8" diameter cam follower. I greatly appreciate the help I received from Jason and from George Britnell.----Brian

[gbritnell]

Looks great Brian,
Sometimes parts just don't look right but the math never lies.
gbritnell

[Brian Rupnow]

Today I'm going to try something a little different, and make the face cam. It is definitely different than anything I've machined before, and should make for an interesting day. I will post pictures as it develops. First we start out with a solid model, and then using the math data from the model I will machine the part.

[Brian Rupnow]

I know from my drawing that the outside diameter of the face cam is 1 1/4". I found a piece of 1 1/4" dia. cold rolled steel and chucked it up in the three jaw, and took a couple of passes to clean up the end. I also know that the face cam will be 1/2" thick, with a 3/8" dia. hole thru the center. so--I drilled and reamed a 0.375" dia. hole 0.8" deep in the end of the piece of steel. I also know that there will be a 7/8" diameter recess by 0.188" deep in the face, so a 7/8" diameter milling cutter was held in the tailstock chuck and plunged 3/16" deep. If I wanted to, I could now part off the piece to the thickness I need.--However--I know there will be some rotary table work before I'm finished, so I will leave the piece about 3" long to give a "chucking stub".

[Brian Rupnow]

With a couple of dimensions added to the drawing, I can see that a very large portion of the face cam is flat, with no curvature to it. That is the 0.931" dimension on the left side of the drawing. So, with the part held vertically in my rotary table chuck, I will machine that flat area away to a total of 0.157" deep.

[Brian Rupnow]

The part has been set up vertically in the 3-jaw chuck on my rotary table, and all of the "flat" area has been cut away to a depth of 0.157". The small remaining bit that hasn't been machined away is going to become the actual profile.

[10KPete]

I've been keeping my yap shut so far but it seems to me that one would want the cam stock held at 90* to the cutter so the cutter was on the same alignment as the cam follower would be....???

 

Pete

[Brian Rupnow]

Once the preceding steps have been accomplished, it comes down to basically 2 plunge cuts with a 5/8" endmill. Of course there is a bit of head scratching as to just where the plunge cuts have to be. Once they have been completed, the face-cam looks like this. Only one profiling step left, and that is using a file to "break" the sharp corners at the beginning of the remaining "lobe" area.

[Brian Rupnow]

Pete--I think this set-up is the one you are thinking of. The transparent grey thing is the 5/8" milling cutter. The red face-cam part is held horizontally in the 3 jaw on my rotary table. I didn't take a picture of that set-up.

[Brian Rupnow]

-And here is the face cam finished, roosting safely where it is intended to go. Will it work?--Well, probably. I won't know until everything else is finished and I try to start the engine. These little hit and miss engines are pretty forgiving.---Brian

[10KPete]

Yep, that's the one Brian. You're way ahead of me!

 

Pete