Halls Rotary Engine

[Jo]

In the original write up of boring the cylinder the lathe they were using was a bit small so they mounted the cylinder on the saddle and bored it between centres. Big C does not have that problem so we mounted the cylinder up in a four jaw 

Having squared up the outside and used the bore to centralise the casting the outside face was lightly skimmed before boring. There was a bit of porosity along the edge of the casting but it looks to be either in the valve area that will be machined away or under the end cover so I am hoping it will not be a concern.

Once bored the face for the covers can be taken so that it is 3.2mm from the already machined face on the end of the cylinder. The cylinder can now be turned round and mounted using a parallel to make sure the cylinder is square. It matters little if the cylinder is perfectly centred to take the other cover mounting face to the correct distance.

As you can see with the finished cylinder the mounting flange for the covers is going to have to be cleaned up and made round at some point - but not yet... 

Jo

[Admiral_dk]

Neat solution using the Four-Jaw Jo 

I suppose that the ends can be solved with gaskets and that the inside doesn't matter as you mention -> you can move on to the next step (nice progress).

Interesting project     

[Jo]

Thanks Per,

The two covers are simple castings, which have been well thought out and the centre boss is long enough to use as a chucking piece  And of course these are made of gunmetal so they have the same strength as soft cheese if you over tighten a chuck round them so I thought it might be worth going through the detail of turning up covers as it is not as obvious as you might think 

You may have noticed I like to use collets to hold my work items, these do not mark the work, if you don't have any then its best when working with gunmetal to use aluminium packers between the chuck jaws and the casting (you may have seen these when I machined the cylinder just now). The first stage is to use a hand file to take off any lumps and bumps around one of the two bosses that can be used as chucking piece. Then hold that to turn the other round, I turned mine to accurately match a collet I had. Turn round and turn the other end circular.

Now holding the cover with the inner face pointing outward we need a reference face and this is going to be the middle boss against which the piston is going to rub. Face it and turn the central boss to the 17.5mm diameter outside. After this it is easy to take the central boss down to length and to machine the face that will clamp against the cylinder and to turn the outer diameter. But before being tempted to remove it we also need to bore the centre the 12.7mm diameter for the crankshaft bearings.

Once all of the inside turning is completed then the outer face can be machined providing the correct distances but now you have to be really careful as you are holding on finished surfaces which will mark given any chance so if you have not got a collet then this is a good time to make yourself a pot chuck to hold the cover with in the three jaw. The only tricky bit in machining the outer face is the half circular feature which of course is too deep to be able to use a profiling tool on  so it needs a tool with adequate clearance under the cutting face, I use a piece of tool steel I have ground down and while it is not the right diameter it can be used to make a good approximation of the required diameter.

I am pleased to say both covers fit on the ends of the cylinder, a bit tight but that is all to the good as I will be planning on honing the cylinder after it has the steam valve port cut. I will wait to drill and tap for the cover studs as I am going to need the vice that is currently set up for a couple of other jobs first 

Jo

[Laurentic]

Nice work on the cylinder machining Jo, as you say, nightmare, clamp it, machine a little bit, move the clamps, machine a bit more, etc, etc, on and on, what a game!  Good job you have a 'proper' 4 jaw chuck for the ends/internal stuff, you really do need the right gear for some jobs, and you are well kitted out!  Liked your set-ups but.

Chris

[Jo]

Thanks Chris 


At the other end of the engine is the crankshaft bearing stand. After checking the features on the casting sat true the top can be milled flat, the groove for the bearing made the right width and depth and finally the outer faces against which the bearings will sit faced. Having considered the 2BA nut size I decided that they looked overly big and chose to make the two studs smaller at 4BA.

Comparing the casting with the original engraving it was quickly obvious that one of the features on the casting was missing  So that was milled in which I think makes it look better

I also decided I did not like the rather odd looking narrow keep plate. The choice was to make it wider to match the main bearing and having checked on the engraving the keep does look to be the same width as the bearing but I suspect the entire bearing is too wide. However as it is the only crankshaft support I would prefer to keep it wider than find out it is too small later so have left it at the 15.6mm wide of the original casting (the drawings say it should be wider but the casting was too narrow to start with  )

Jo

[Bluechip]

Looking good, Sarge .....    

Dave

[Roger B]

Still following along     

In IMG_3210 are you holding the home made profiling tool in an ER chuck. How is the the ER chuck held in the toolpost, a collet block?

[Jo]

Thank Guys, nice to hear someone is still following along   

In IMG_3210 are you holding the home made profiling tool in an ER chuck. How is the the ER chuck held in the toolpost, a collet block?

Hi Roger, one of the types of multifix tool holders is designed to take round tool holders. So I have a 20mm diameter shank ER32 tool holder mounted in a compression sleeve in the tool holder. when I first acquired those round holders I was a bit puzzeld by them but over the years they have proven very useful. 

Jo

[Roger B]

Neat  I've not seen those before 

[awake]

When I first acquired those round holders I was a bit puzzled by them

Are these tool holders intended to hold boring bars, perhaps? In any case, nice combination of the tool holder and ER collet!

[Jo]

For the main bearing they provided a slab of gunmetal. It seemed to be rather too big but there was a number of marks on the surface which only went after machining off 2mm on each side 

The first stage required machining the slab of gunmetal to 11.1mm thick, Yes I know the drawing calls for the bearing blocks to be 9.53mm thick but I like to have a flange all the way round rather than just on either side of the blocks. I also machined the two sides flat but not to size.

Having hacksawed the piece in two the two pieces are soft soldered together using in the joint some solder paste topped up with solder when hot enough. Once together I machined the block so that not only was it 22.22mm one way but so it was the same in the other. This means that it can be mounted up in a four jaw self centering chuck  for facing and boring.

In my design for the bearing block there are equal grooves all four faces ( the drawings showed no groves on the bottom and a narrower one on the top ). I started by milling the two sides making sure that the groove was milled equally on either side before milling the top and bottom faces. The trick here is to make sure the parallel which the bearing is sat on does not sneak into the groove and mess up all your distances when you turn it over  The other important thing to do is keep taking off the burrs as you turn the bearing over as they can also mess up the distances 

A quick check that it all fits together 

Jo

[Jo]

The crankshaft started out as a piece of  12.7mm (not the 303 that I had ordered but something horrible) Stainless Steel. This was roughed out to leave the wide part for the piston and the two tapers, the same distance as the length of the cylinder plus 25.4mm for the two tapers, before heading over to do the two main bearings.

The main cylinder bearings do not come as a casting but they intend on you using a piece of bronze bar. Thankfully I had some 23mm diameter Bronze which was ideal.  To avoid problems the machining of the main bearings is being done back to back so a piece 35mm long was used with either end turned to 12.7mm to fit the cylinder covers. Both ends were then centre drilled before drilling through with a drill the same size and the centre drill centre and then enlarged sufficiently to enable reaming. A quick check it fitted on the crankshaft before going further 

To taper the bore the top slide is angled to 10 degrees and then using the top slide to provide the tool advancement the taper at the outer end was turned until the outer diameter of the taper was 12mm. This leaves a reasonable thickness on the outer rim and no sharp edge.

Not moving the top slide it was then an easy job to turn the two tapers on each end of the wide part of the crankshaft. I saw nothing to be gained by supporting the long length of the crankshaft with a fixed steady as all of the machining is done up close to the nose of the lathe.

Finally the two main bearings can be separated and faced before seeing if it all fits together. 

About this point I have realised I do not have the two bronze balls for the governor    but I may yet change that bit 

Jo

[samc88]

Thats taking shape nicely Jo

[Jo]

Thanks Sam 

The piston is supplied as a cored casting. The core is a bit smaller than shown on the drawing so this means the crankshaft hole will need to be bored to size not reamed.

Having held the piston in a three jaw one end was faced off and I started doing the other but things were getting a bit tight on the measurement so I decided it was time to check how much extra metal was on the outside of the piston. It needs to be 31.75mm diameter and the casting is 34.6mm diameter with a .3mm out of squareness, which can be corrected when it is on its jig for turning the outside.

The hole bored 12.7mm indeed did cut into the inner bore more than shown on the drawing. I was pleased to find I had two broach guides 12.7mm diameter which meant I could broach the slot in the top of the crankshaft hole

Jo

[Jasonb]

Was there any specific reason for cutting a wider keyway and also making the seal slot wider?