ETW's Wyvern Gas Engine

[Jo]

Thanks Rod,

I might just take up up on it 

Jo

[tangler]

I thought I'd have a go at the flywheels next.  The iron castings have some flash and the registration between the 2 halves isn't great, as we shall see.



A bit of work with a file got rid of the flash and the worst of the mis-registration step on the spokes



The flywheel was mounted on the faceplate, resting on 3 ally pads and centered so that the inner edge of the rim was running as true as possible, since I don't want to machine that.



There is a generous machining allowance on the casting, with about 1/8" to come of each face and the radius.  The rim was turned in the highest backgear - this seemed the most comfortable speed.



I had to use some old school methods to measure the diameter



The rim and the hub are reasonably centered and concentric on this side, which will be the outboard side of the flywheel when mounted on the engine



After machining one side I turned the casting around and centered it on the rim outer using the DTI



As I mentioned above, the 2 sides are not well registered, so the inboard side of the flywheel looks rather eccentric

<a href="https://www.youtube.com/watch?v=aPh2Z8CkD3Y" target="_blank">http://www.youtube.com/watch?v=aPh2Z8CkD3Y</a>

The flywheels are mounted on to the crankshaft using a split, tapered collet so the bore was drilled and then turned with the topslide set over to 5 degrees.  I left the topslide at this setting for making the second flywheel and the collets



So, I've now got a pair of flywheels that look OK from the outside, a bit of Dremel work will blend the various radii

[tangler]

The collets are a simple turning job.  The job was drilled and then bored 3/8" and the taper turned.



I then transferred the job in the chuck to the mill and split the collet with a saw



The job then went back to the lathe to be parted off.  I thought I might have trouble parting across the slit but it was trauma free.  There's another one to make.

[Jo]

Commiserations on the flywheel miss alignment is a common problem

  Ok Rod forgive me it must be late.. what are the collets for?

Jo

[Dan Rowe]

The flywheels are mounted on to the crankshaft using a split, tapered collet so the bore was drilled and then turned with the topslide set over to 5 degrees.  I left the topslide at this setting for making the second flywheel and the collets

Rod, will it be a plate and screws that secures the collets to the flywheel?

Dan

[Jo]

 

[tangler]

Sorry, should have been clearer.

The ends of the crankshaft are turned 3/8" diameter up to a shoulder inboard and threaded on the outboard side.  The collet slides over the plain portion with small end of the taper towards the thread.  The taper hole in the flywheel fits over the collet and is pushed tight by a nut, which then pushes the flywheel to tighten the collet on the shaft and the flywheel on the collet.  ETW claims that this is a more positive method than a key.  It is similar to the way that prop drivers are often fitted to model aero engines (well, the 2 I've built anyway).

Thanks for looking.

Rod

[Dan Rowe]

Rod,
One of the diesel engines I worked on had tapered collets for the cams. There was a nut on a threaded section of the small end of the collet so a very similar system.

Dan

[Dave Otto]

Nicely done Rod,

The flywheels look great!

Dave

[tangler]

Hello again.  What I thought would be a trivial job turned out to be more difficult than I expected - making the retaining nuts for the flywheels.  These need to match 3/8" 26 threads on the ends of the crankshaft.  I have some 3/8" Whitworth hex steel which looked about the right size to make a neat job.  So - chuck, drill, tap, chamfer and part.

Drill was straightforward




My usual set up for tapping is to use the mandrel  handle and hold the tap in the drill chuck



The first problem was that the handle, which grips in the mandrel with an expanding collet wouldn't hold after the tap had gone had gone in about 3 threads.  OK, I could pull the belt round by hand.  Then, after another thread depth or so, the tap was spinning in the drill chuck, even after I changed to a keyed chuck.  The solution is to cut the thread first, which is what I always do on threads bigger than 1/2".  I found that I don't have a threading tool small enough to go in a 3/8" hole  .  I resorted to a tap wrench guided by the tailstock to start with - always a bit of a juggle while pulling the mandrel around with the belt.  I really must make a spring centre (and grind up a small internal threading tool)



Parting was trouble free




and I stopped part way through to chamfer the edge (so that the nicely machined surface was against the flywheel

[tangler]

I  had a go at making the cams next.  These have flat flanks (for a roller follower) with 1/8" lift.  The inlet has a 120 degree lobe and the exhaust 130.  I used my cam generating program to print out a set of co-ordinates to mill the cams in the vertical mill with the blank in the dividing head.  The program actually generates cams with 3 radii, the base, flank and nose.  By putting in a very large radius (10000") for the flank, this is essentially flat.  The calculated values for velocity and acceleration will be nonsense because of the roller rather than a flat follower but the the profile is correct.  I first turned the blank with a 15/32" boss and an OD of the base circle (1/2") plus the rise (1/8")



This is the set of co-ordinates for rotating the blank.  I've used 3 degree intervals, which is half a turn of the handle on the dividing head.  Slightly concerned about this since these cams are larger than I've made before and there may be some faceting - we shall see.



The blank was centered on the Y axis, because I shall need to drill a hole through the boss, and the Y axis zeroed on the DRO.  The Z axis was the zeroed with the cutter touching the OD of the blank and then slid out of the way before lowering it by 1/8" and re-zeroing



The first cut was taken across the blank at a tangent to the base circle.




The blank was then rotated by 3 degrees, the table lowered to the displacement read off from the table of offsets and a cut taken.  I settled into a rythm - rotate, cut,  mark off.  The lobe is finished here and the rest of the rotation cuts the base circle back at the zero offset.  Each cam took about 40 mins.




The Y axis was zeroed and the pin hole drilled  1/16"




After returning the chuck to the lathe the cam was parted off.  There is a hint of faceting here, about the same roughness as the machining marks.  This was easily removed with a dead smooth ( 6 cut) file




The pair of cams.  These will be case hardened.

[Don1966]

Beautiful work rod, I like the lobs they came out great. Is that an excel spread sheet you used to do the calculations with?

Don

[tangler]

Don, 

Yes,  the program's current incarnation is an Excel spreadsheet.  It's the one I attached to my comment in Nick's CamCalc thread.  I pasted the calculated  values into word for printing.

Cheers,

Rod

[tangler]

The pivots for the rocker arms and the roller cam followers are similar straightforward turning jobs.  The rocker pivots have an eccentric spigot to allow for clearance adjustment.

The 3/8" blank was mounted in the 4 jaw independent and roughly centered before turning the 2 diameters. 




The drawing calls for the spigot centre to be offset by 10 thou but I doubled this to give a greater range of adjustment - the smaller diameter is still wholly within the larger.






The head was tidied up and then the screw slot was cut in the milling machine in similar manner to splitting the collets.



ETW designed hardened steel rollers rotating on hardened steel pivots for the cam followers but I found these in my collection of ball races



The OD and ID are the same as the design but they are a bit narrower.  I therefore kept the pivot design the same but in un-hardened mild steel.  I will put washers either side of the ball races to bring them to the middle of the cams

[Lofty76]

Rod, is your dividing head not a standard 40:1?

I make half a turn equal 4.5 degrees, not three.

Just checking