A Simple Uniflow Engine

[propforward]

Hi Gary,

Some excellent work here as always. I think you are very critical of your own work. It’s all looking like great progress to me. Is that piston made from a cast iron bar, or is that steel?

[gary.a.ayres]

Thanks Stuart - very kind of you.

It's cast iron, as are the cylinder, the crosshead and the big end.

[gary.a.ayres]

There will be a spigot protruding from each side of the big end, the faces of which will run against the crank webs. The lines scribed on the assembly in the photo below are set apart at a distance which is a little bit wider than the final overall width of the big end from the face of one spigot to that of the other:



I milled down to these lines with the face mill, then again with the height gauge and surface plate marked out the final width of the big end minus the length of the spigots. You can probably just about make out these two new lines in the photo below. The assembly was transferred to the independent 4-jaw chuck in the lathe. A short length of 12mm silver steel bar was held in the tailstock chuck and pushed through the split bearing in order to help with centring, to lend rigidity to the setup and to test whether or not the miniscule degree of runout in the bearing hole (discussed a few posts back) was likely to cause problems. I'm pleased to report that as far as I can now ascertain the amount of runout over the short length in question is insignificant.

A turning operation was then embarked upon to narrow down the body of the big end while leaving the spigot on each side standing proud of the face:



I'm using a circular carbide tool to leave a radius where the spigot will meet the face. This should look good but it will also be stronger than would a ninety degree angle, as per a suggestion from Jason further back in this thread.

This turning operation is not one to rush, what with the unbalanced weight of cast iron spinning in the chuck, so it is taking a while to do, over several sessions...

[propforward]

Nice. Looks like a solid approach - excellent finishes too.

I suppose you could have opted for a faceplate mounting, then added some balance weight if you had really need to go with higher rpm's, but this set up looks like it worked out really well for you. Easier than setting up on  a face plate for a start.

[gary.a.ayres]

Hi Stuart - yes, I did consider using the faceplate but on balance (no pun intended) I decided to just go with the 4-jaw. It's a slow job but there's no rush really. I'm away from home until Friday but hope to make a bit more progress over the weekend...

[gary.a.ayres]

The main body of the big end in progress has now been more or less slimmed down to final width, though the 'spigots' projecting from the sides still need to be brought to final dimensions. After that there is still more work to be done on the overall shape of the part, both for weight reduction reasons and for looks:

[crueby]

Nicely done, coming along great!

[propforward]

Nice work Gary!

[gary.a.ayres]

Many thanks guys.

[gary.a.ayres]

In order to check that the two spigots were the same length, I clamped a couple of parallels on to the assembly and measured the gaps with the inside jaws of the calipers:



The difference was negligible so I considered the part to be symmetrical. Measurement of the overall width told me that I needed to remove 3mm for the assembly to fit between the crank webs, so I took facing cuts with an endmill to reduce each side by 1.5mm. I will confess to you that I have a photo of this operation but the mill is so covered in cast iron swarf at this point that I'm ashamed to show it. I am, however, pretty pleased with the result, which is a smooth-running fit, snug but not tight:





I'm quite pleased with this, but you can see that even when I have reduced the size of the big end (which is the next step), the flywheels will still be quite small by comparison. As discussed somewhere above, I have no clue as to whether or not this will be a problem. The plan is to press on with the build and find out when I first test the engine on air. If I have to enlarge them I will do so.

Meanwhile - iron age digital compact camera?



There's a lot of cast iron yet to remove from the big end, and even these rounded corners may yet disappear with some closer machining to reduce the size. But still, progress...

[crueby]

.......
Meanwhile - iron age digital compact camera?

Mil-Spec iPhone! 

[gary.a.ayres]

 

[propforward]

.......
Meanwhile - iron age digital compact camera?

Mil-Spec iPhone!

    

I literally LOL’d at that. 

[MJM460]

Hi Gary, more great progress.

The main effect of the size of that big end is on engine balance, and as I believe it will be a relatively high speed engine, a large unbalance will get exciting.  However, the big end mass can be balanced by weights added to either the crank webs or a smaller mass at the rim of the flywheels, and then it just adds to the moment of inertia of the flywheels.  If my memory serves me the maths says you balance the weight of the big end plus about one third of the connecting rod as a starting point.  You would divide this and put half each end of the crankshaft.

However, as you add your trademark wonderful artistic touches, it is worth considering detail that  reduces the remaining mass in your design. 

For my part, the best piece of material to use is one you already have, or can easily source, that is big enough and regular in shape so it is easy to hold while you drill and tap for the securing bolts and that all important bore.  Then you can make as much swarf as you fancy in trimming away the bits you don’t need.

It appears that in doubling the original plan size, you have also doubled the bearing cap bolts and spacing.   As it is not a scale model, you probably could have got away with leaving some of those details a bit smaller, but that is an idea for the next engine, no need to change now.  I find that each successive engine, I am prepared to makes bolts a little smaller and clearances between features a little tighter, though having tried 2 mm bolts, I think further progress in that direction will be limited, and I prefer 2.5 mm and larger.  Not sure that I will ever get to 1 mm like others on this forum.  They show amazing skill that I can only admire.

MJM460

[steam guy willy]

Hi Gary, Talking about nuts and bolts... here in The Uk we have EKP Supplies that make BA nuts and bolts with a smaller head size... This gives you a larger stronger thread with a more scale size bolt head,  these bolts go down to 10 BA with 12 BA heads. here is a small part from the catalogue !!

Willy