GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell

[eccentric]

Dodged a Bullet Today

I made an error this week machining the Block Top Plate and it really gave me pause. The part needs to be .227" tall and I started with 1/4" thick stock that ended up .242" after I had squared it up and fly cut the top and bottom. When I programmed the tool paths in Fusion360 I miscalculated the amount of raw stock to be removed from the top (.242" - .227") and I machined too much material off and ruined it. The top plate is relatively simple and was easy to remake, but what if I had made this mistake on the cylinder block? I have been working on the cylinder block up to this point and have innumerable hours into it. The thought really upset me. I got lucky and dodged a bullet on this one. I need to remain ever diligent and check everything multiple times (I thought I did).

The Block Top Plate seals the water jacket in the cylinder block.


The good part is sitting on top of the block and the bad part is in my hand,



I also machined the back of the cylinder block and the oil pan in the same manner as the front as seen in my last post.



Next up is machining the sides of the cylinder block.

I made the Top Plate wider than it needs to be because I am going to secure it to the cylinder block and then machine the sides of the bock with it in place.

But now I am going to kick back, enjoy the sunset and meditate on my luck.

[eccentric]

Cylinder Block Side Machining

Today I am going to work on machining the sides of cylinder block, but before I do I want to mount the cylinder block top cover plate I fabricated in the last post. This is so the top block plate sides are machined at the same time as the block so I get a good blend.  Screws don't work well when you need to precisely align two parts because of the uncontrollable tolerances and slop of the threads in a smooth hole, so here we use two alignment pins to register the parts.  Real estate is at a premium at the mating surfaces so  a hollow pin is used that shares a couple of the stud mounting holes.  The machining on the lathe is straight forward with the critical dimension being a tight fit in the matching holes in the two parts.



 
Above I am checking the diameter for a tight fit while still on the lathe.  In the photo below the pins are indicated by the arrow and it can be seen that all of the holes line up well.


 
I start on the surface plate characterizing the cylinder block and determining exactly how much material is to be removed.  The camshaft is still our baseline datum and measurements are take from it.
 

Then the machining proceeds with first a roughing pass, a finishing pass on the horizontal and vertical surfaces and finally a finishing pass on the angled surface using a ball end mill.
 

Below is a photo of the finished right hand side.






 

The process for machining the left hand side follows the same work flow.

Checking our dimensions on the surface plate.


 
Final finishing pass.
Here is a short video of the block with all sides machined:
<a href="https://www.youtube.com/watch?v=fKHu8z1_-KQ" target="_blank">http://www.youtube.com/watch?v=fKHu8z1_-KQ</a>

[MJM460]

Hi eccentric, nice work on that block.  I like the hollow dowel pins, must remember that one.

MJM460

[crueby]

Neat trick with the pins. Beautiful work!

[Art K]

I just got caught up. Great work! I remember watching one of those "How It's Made" shows and they were making some V8 Indy sort of engine, it had the same sort of block cooling set up. I've seen the same sort of dowel pin to locate things in automotive applications. Great way to get repeatability.
Art

[eccentric]

Yeaaaaa! I received the last of my metal.  The cast iron for the head, cylinder sleeves and rings; bronze for the connecting rods.  And the steel for my crankshaft I already had on hand.

[Zephyrin]

amazing work with this cylinder block, thanks to share all the steps of the build, the bolt in a hollow dowel pin is to be noted!

[kuhncw]

Very nice work.  Thanks for taking the time to document your CNC methods and setups.'


Chuck

[eccentric]

Intake Manifold
Today I am going to be working on the Intake manifold, it can be seen below in green and indicated by the arrow.  I am going to be attempting Terry's Epoxy Encapsulation Technique (TEET) as the part is machined from two sides and work holding would be very tricky otherwise.
I design the part, then the encapsulation fixture.  I  go to the mill, square up a block of aluminum, then measure it and put the exact dimension back in my model.  There is a runner that needs to be drilled all the way through to create the internal fuel/air passage from the carburetor to the cylinder head.  Then aluminum plugs are turned on the lathe for a snug fit and pushed into position just the right depth. 

 
The drawing below has all the dimensions I need to fabricate the initial fixture/work piece including the through hole and the aluminum end plugs for the lengthwise fuel/air passage.  Note that I have also drilled two 5/16" end mill entry holes into the work piece.  My little CNC router complains when I drive an end mill straight down into the work piece, but if I provide the entry hole then only side mill, I can run at higher speeds without stressing the setup.
 

The tool paths are created and simulated.  I use an adaptive clearing strategy to remove most of the material, a ramp strategy to mill the vertical sides, a horizontal strategy to mill the flat horizontal surfaces; these all use a 1/4" end mill.  A 1/8" ball end mill is then used to create all of the internal and external fillets. 

 
Below is the work piece after machining the top.



 
I then use 5 minute epoxy to encapsulate the intake manifold.  The amount of epoxy used was great enough that the exothermic rectionof the mixed epoxy cured very rapidly and I did not need to wait long to move on to machining the back.  I then repeat the tool path generation and machining of the back side.  When I touch off on the back side I am careful to use the same datum points as I did for the top as it is very important that the two machining operations meet as accurately as possible so the features are not noticeably offset.

 
Below is the back side of the work piece after machining.  I am pleased at the alignment of the top and bottom machining operations.

 

I then heated the whole thing for 1 hour at 275 degrees as Terry did.  The 5 minute epoxy I used did not decompose, but just got soft.  I was able to remove the intake manifold from the fixture, but as the part cooled the epoxy just got rock hard again.  I think I just post cured it.  I had to reheat and then work quickly  with a rag to remove as much of the softened epoxy as I could. I used a "Quick Set" epoxy from Ace Hardware instead of the Devcon 5 minute epoxy Terry used.  Most of the epoxy reside was removed as I did my final filing and hand finishing of the part, and the sand blaster got the last of it.  I did not want to use a higher temperature as I used Loctite 638, which is a high strength, high temp adhesive, but it too will get soft when it gets at higher temperatures.


 

 

All for now, thanks.

[kuhncw]

Well done.  Thanks for posting.

Chuck

[Art K]

Looks great I will have to file that away in case I make a manifold.
Art

[eccentric]

Machining the lobes of the Camshaft

The machining of the Camshaft lobes is done using a 4th Axis on the CNC.  The Camshaft is cut from 5/16" drill rod and uses the OD as the bearing surfaces.   There are bearing surfaces at each end and between each cylinder.  The cylinders alternate between having the intake lobe  closer to the front or the exhaust lobe closer to the front.  This is done to simplify the design of the intake and exhaust manifolds.  I am going to machine a single cylinder's pair of lobes in one machine set up, thus will have four setups on the CNC.
 
A 3D CAD model of the camshaft sections is created for both the intake manifold lobe in front and the exhaust lobe in front.  A feature is added as shown below and highlighted with the red arrow to create a coordinate system the CAM software can use as a reference for the tool paths.  There are four separate tool paths.  I could have gotten away with two tool paths then adjusted the starting rotation of the work piece before each machining operation, but I opted to make the setups as easy as possible even if it required a little more work before hand. 
Then each of the four tool paths are simulated.





All four machining operations will be done as close to the collet chuck as possible to minimize the stick out, so a method needs to be used that allows the work piece to be extended and reoriented before each machine run.  The work piece is prepared as shown below with a flat machined at the far end.



 
A simple carpenter's level is modified with an aluminum guide that rides in the flat, then it is secured to the work piece with rubber bands.


This provides a simple and accurate way to return the rotation of the work piece to a known zero point. I am able to easily discern a tenth of a degree of rotation by jogging the A axis.

The stick out is simply measured with a caliper to the face of the collet.


 
Once the CNC is touched off on all axis, it is ready to run.

 
The cut is done in three passes, two roughing with a .025" step down and .025" step over.   The finishing pass uses a .0075" step over.  Mist coolant is used.
The work piece is stepped out of the collet before each of the four machining operations.




 
 
And the machining of the Camshaft lobes is complete.  The remaining machining and finishing work will be performed on the lathe.

[michelko]

very nice

[Roger B]

That's a neat way of keeping the camshaft alignment     

[fumopuc]

That does look very interesting and impressive too.
It looks like that you have used Fusion for the CAM.
Is it possible to make a screen shot of the browser at the manufacturing area in Fusion with the different tool paths listed and show it here ?
It would help me to understand the details of your operations much better.
Thanks