1/2 Size KyKo Hot Air Engines

[crueby]

Great work!  I like how you held the parts for milling.   

[vtsteam]

Beautiful, both the parts and the photos! 

[Kim]

Your builds are always a pleasure to follow, Dave.  Amazing work, well done.  I always learn something! 

Kim

[springcrocus]

Very much enjoying following this. 
And your photographs are so crisp and clear, they make mine look like they were taken with a box Brownie. 
First-class workmanship.


Regards, Steve S

[Admiral_dk]

Great parts and progress     thank you for sharing 

Per                        

[Dave Otto]

Thanks for the nice comments guys, they are always appreciated.

Dave

[RReid]

Just getting caught up with your build, Dave. Lot's of beautiful work going on, and lots to learn from too!

[Dave Otto]

Thanks Ron.

Dave

[Dave Otto]

Hi everyone,
The next part of the engines that I am working on is the crankshafts. On the original engines the crank was formed from 8mm rod. The factory had tooling that was able to form the throw with a ball bearing installed. I did give this a try with some 3D printed tooling that I had designed. It did kind of work but to be completely successful I would have had to make all the bending fixtures from aluminum or steel.
I decided to just go ahead and make a built up crank as outlined in the plans for the model. I did however make some changes to the crank design. I changed the angle of the webs to better match the angles on the connecting rod, this will show later when I make the rod. The model drawings have the crank pin smaller than the shaft and the webs have some taper from large to small. I wanted the crank pin the same size as the shaft so there is no taper in the webs.


Here is a screen shot from Alibre of the redesigned crank. This will show what I’m working toward.


Starting out I cut one end of the web stock at the 25 degree angle. This will give me a good surface to locate the stock for milling the holes. It was left long to give some stock to clean up when forming that actual profile of the web.


Using the surface machined in the last step to locate the stock, it was set up at the proper angle and the two holes for the shafts were machined using the CNC.


Next a fixture was made to hold the web stock at the proper angle so they could be profiled. Hollow dowel pins were used and also some special tapered washers were made to clamp the stock onto the fixture.




The fixture was set up in the mill and one of the pins was used as a datum for the XY fixture offset.



I ran the tool path without a web installed, the fixture was oversized and this brought it to the same size as the crank web.


The web stock is installed on the fixture and the program run again. I used a full depth adaptive type of tool path to run these parts. This worked out good for these parts.


Here are all the parts for the two crankshafts including a pair of alignment blocks that were made. One crank assembly is threaded to accept the fan hub.


Here is a test fit up of one of the crank assemblies.


All the parts in the proper position and silver soldered together.


After a light cleaning the excess material is removed with the band saw.


All the remaining work was done by hand, the excess shaft material was removed using a file and the webs were given a nice polish.


Here are the crankshafts installed in the bearing A-frames. Even though the crankshafts differ from the original somewhat I’m pleased with how they turned out.

Thanks for checking in,
Dave

[RReid]

My gosh, those cranks are PRETTY!

[vtsteam]

They Sure are! 

[Kim]

Boy, Dave!  Those polished up beautifully!  What material did you use there?  Stainless?  Or just mild steel?  It looks like you chrome-plated it it's so shiny! 

Kim

[Jasonb]

Having fabricated a very similar crank before I got the CNC it is interesting to see your approach, on the manual machines I put the holes into rectangular blocks first and then shaped the webs around them

[Admiral_dk]

Interesting approch + I really like your use of the Alignment  blocks, to ensure parallism (sp?) during soldering 

Per             

[Dave Otto]

Hi guys, I apologize for the long delay to respond your comments. I just got busy and I’m also one of the world’s best procrastinators. So thank you all for taking time to look at my work and the nice comments, as always they are much appreciated. I also need to apologize for some of the very sub standard photos. I’m not sure what is going on but I seem to be having trouble getting good photos. I know sometimes it is hard to photograph highly reflective items.

Kim, I did get a little carried away polishing the crank shaft. At this time I’m not sure if I will leave it as is for maybe blue it, or possibly bead blast it so it does not stand out so much. I used sanding sticks from Micro Mark to do pretty much all the sanding and polishing.
https://www.micromark.com/Softback-Polishing-Sticks?quantity=1&keywords=sanding%20sticks

Jason that would have been a great option that I really didn’t think about, sometimes I get my nose pointed in one direction and without much though that is where I’m headed. Like my buddy Max says “I’m mad now I’m going to do it the hard way”.



The next part I decided to work on is the connecting rod or displacer rod. There were castings supplied for this part but I wasn’t particularly happy with them. You can see in the photo that the un-broke one has the lower bearing bosses at an angle. This was due to either the wax, casting or both pulling in to each other. I tried to straighten one and as you can see I broke it. This part should have been cast with a spreader between the bosses to keep this from happening. Also on the castings there are no oiler bosses as on the original. So I decided that I would be happier if I just made new ones from scratch Not that I had a choice after breaking one of them.


The new connecting rod was modeled in Alibre using an original part to go by. As you can see the cups and the boss for the grease cup have been added.


A couple of blocks were prepared and in this photo the 1st operation has been completed. I used a pocket routine to remove the bulk of the material and then a couple different finishing strategies using a .062 ball end mill to finish it.


Here are the two blocks ready for the second side machining.


Pretty much the same drill on side two, the same corner of the block was used as the datum to help keep things in alignment from front to back.


At this point I’m able to use the picture frame to do the rest of the machining operations. Here the bearing pivots are being drilled and reamed.


Now part of the frame has been band sawed away to allow access to the upper bearing boss. The pin was used to dial in lower bearing and insure the center to center distance was correct.


Then the bore was finished using a boring head to obtain a proper fit for the ball bearing.


The connecting rod was mounted to a tooling block and the clamp features for the ball bearing were machined. Here the hole has been drilled and tapped and the split is added.


Then again a little more of the frame was removed and the lubricator boss machined to proper height. A shim was used to keep from distorting the clamp and the gauge pin to help stabilize the whole thing. The gauge pin was also used to find the center for the lubricator boss.


With the gauge pin removed the 2-56 hole is drilled and tapped.


The little oil cups need some care so they would come out right. First the cup was milled using a ball end mill. Again I’m sorry about the crappy photo, I didn’t realize until after I was done with the part that some of the pictures didn’t come out too great.


The next operation was to drill the passage from the cup into the bearing. This required a precise angle and you can see in the photo my little sine setup. The gauge block stack gave me the proper angle of the set up.
The center drill in the photo has been ground down in the D-bit grinder to keep the body of the drill from hitting the upper edge of the cup. The pin was slid out before drilling the holes theough.


All went well in the drilling operation; that is a .04” hole or just a squeak over a millimeter.


With some needle file work and a trip through the blast cabinet here are the two completed connecting rods.
Thanks for checking in.
Dave