Designing an engine

[mu38&Bg#]

I would expect to see a 5.5-6.5mm crank in a ~10cc cylinder. If the engine will never see a load it may be strong enough, but still looks like it will be difficult to machine. Piston proportions look great for a model engine. This isn't a racing piston. Just keep a copy of your CAD. I have 6 versions I kept of a project I'm working on now. There are always new ideas, just after you commit to one.

Greg

 

[Metal_slicer]

My stems are .125"

Steve where did you get those springs? I have been looking but its a jungle out there!

 

[Metal_slicer]

I would expect to see a 5.5-6.5mm crank in a ~10cc cylinder. If the engine will never see a load it may be strong enough, but still looks like it will be difficult to machine. Piston proportions look great for a model engine. This isn't a racing piston. Just keep a copy of your CAD. I have 6 versions I kept of a project I'm working on now. There are always new ideas, just after you commit to one.

Greg

Thats a good idea. I will make a copy before I tear things up.

 

[stevehuckss396]

My stems are .125"

Steve where did you get those springs? I have been looking but its a jungle out there!

Grainger lists a million of them. Worst case they have to get them from the warehouse and you wait a day.

 

[Metal_slicer]

Started on the engine block. The last image was taken seconds before a malfunction occurred. It bent the drill bit and caused slight damage to the hole just drilled. The problem was a set screw attaching the Z-Axis stepper motor coupling to the lead screw. It came loose, therefore, when backing the drill out of the hole it started to free spin leaving a portion of the drill bit still in the hole and then began to jog over to the next hole! I'm tempted to use some blue loctite on this screw, this is the second time this has happened.

 

[Metal_slicer]

Did some more work on the engine block. I milled the block to the proper dimensions today. I was able to fix that damaged hole after all. Turns out 1/8" is to tight for some of the push rods to move freely, so I drilled one size larger. I may need to create some sort of guide but I'm not sure yet. Here are the images of what I have so far.

 

[Ryan]

A shop dog to go with the lathe dogs...

 

[barnesrickw]

Did some more work on the cad design. It's quite a challenge especially when my laptop crashes when I try to do to much. I have included a wire frame picture so that you can see the various parts inside. I created the crankshaft, rods, and pistons. I have started working on the lower portion of the block and I need to make several changes. This design will likely change several times, but here is what i have at the moment.

Is a brave man that uses CAD on a laptop. My hat is off to you and your shared drivers.

 

[barnesrickw]

A shop dog to go with the lathe dogs...

Lost my shop dog a few years ago, and my shop cat recently. Best shop accessories I've ever had. Not a fan of small dogs until my daughter got a Yorkie, Morkie actually. Trying to turn her into the new shop dog. Daughter does not like the aluminum shavings in her coat.

 

[Metal_slicer]

A few more images of todays hour in the workshop. Bottom crank case features machined as well as the bolt holes.

 

[Metal_slicer]

Hello guys,

I have a question about making the crankshaft. Which would be easier? using round stock or flat bar? How can I accurately center drill the journal center lines for both ends? If I can get the center lines drilled correctly, I think I can do it.

 

[stevehuckss396]

You are going to want to use 1144 stress proof steel. It has very little stress internally so it won't warp as you remove metal. It also cuts very nice. It only comes round so I mill a small flat on the end of the bar so when I flip the bar to do side 2, I have a surface that I can run an indicator across.

 

[Metal_slicer]

You are going to want to use 1144 stress proof steel. It has very little stress internally so it won't warp as you remove metal. It also cuts very nice. It only comes round so I mill a small flat on the end of the bar so when I flip the bar to do side 2, I have a surface that I can run an indicator across.

Forgive me, but I don't understand what you are talking about. I understand you mill a flat on the end of the round stock, and I did this on some scrap 12L14 stock to explore using the edge as a reference but that is only good for the Y - Axis, I will need a reference for the X-Axis as well don't I?

I don't have an indexer or any kind of turn table yet. Just my cnc mill and manual lathe.

 

[Swifty]

What Steve was getting at, is you mill the flat as a reference for a dial indicator when you flip the part for centre drilling. You will still have to indicate both ends to find the centre if the bar.

Paul.

 

[kuhncw]

Here is another way to line up the crank centers on a round bar, assuming you have a vee block that will hold your crank blank. After indicating the bar and drilling centers on one end, flip the vee block (don't loosen or move the bar), indicate the other end, and drill.

Hopefully the photo is attached properly.

Regards,

Chuck

 

[Metal_slicer]

Here is another way to line up the crank centers on a round bar, assuming you have a vee block that will hold your crank blank. After indicating the bar and drilling centers on one end, flip the vee block (don't loosen or move the bar), indicate the other end, and drill.

Hopefully the photo is attached properly.

Regards,

Chuck

Thanks for the example image! I like this idea a lot! This seems to be the easiest way to do this. Milling a flat on the round bar and using a dial indicator is still not very clear to me because I don't know what orientation the bar is. horizontal? vertical? is a mill used? how is the part held, etc... I'm sure I may frustrate some of you but I just cant picture in my mind how a dial indicator is used for this particular method. I'm not a machinist, everything I know is 100% self taught.

 

[stevehuckss396]

I understand you mill a flat on the end of the round stock, and I did this on some scrap 12L14 stock to explore using the edge as a reference but that is only good for the Y - Axis

After you flip the stock, the flat will be at the bottom. Align the flat along Y and indicate so it is perfectly along Y. Once done you have rotated 180 and are back in alignment with side one.

 

[Looper7]

Photo of set up
Hope that helps

 

[Metal_slicer]

Thanks Looper7,

I was considering using flat bar, but I wanted to try using round bar instead. I like the idea of using a v-block to clamp on to the round stock and I will likely use this method. My goal is to have crescent shaped counter weights which would be easier to achieve using round stock.

 

[Metal_slicer]

Ok! it's been a while. It's going to be a long process because I need to buy several new tools to do the various jobs. I have taped the head bolts, side inspection cover bolts and oil pan bolts which will double as front and rear crank bearings as well. I bought the A2Z QCTP so now I can swap out tools fast. I got the much needed cut off tool so now I can part off my work pieces. I still need to buy a 4 jaw chuck, indexer, turn table, index boring head, and boring bar. Oh and I will need a v-block, parallel set.... I think I need some aspirin now.

Sorry I don't have any pictures yet. I will try to take some this weekend and share with you all.

A have a question: What would make a light press fit .001" undersized? I'm thinking ahead when its time to machine the cylinder sleeves.