triple expansion engine

[peatoluser]

After messing with screw cutting it was good to get back to some simple swarf making.
turned and bored some phosy bronze to 1 5/8 OD by 7/8 bore

to make the steam passages, rather than drill at an angle, i decided to file a large flat (it was too difficult to hold in the 4 jaw) on to cylinder and solder a block on to this.
i milled a groove each end on the cylinder for the steam

I squared up some brass and then milled the steam passages on this as well as the port face slots

here are the two parts before soldering. you can see some centre punch marks to give the capillary gap. get the job hot enough and the solder will flow, so long as there's a gap for it. although I think this job would be ideal for some of bog's silver solder pallions (?)

i figured that this might be a better means of producing the steam passages than trying to drill them at an angle. well at least with my drill anyway!
to clean up , I turned a stub mandrel a tight fit for the bore, gently filed a small leading chamfer on it , and wrung the cylinder on ot it to face the ends

next up will be the chest and valve
thanks for looking

peter

 

[danstir]

A very interesting build. Thanks for posting.

 

[steamer]

Peat! I've done threading like that on a screw cutting lathe....but never with a follower!

Well done! Just the kind of lateral thinking that can get you out of a bind!

I always love watching someone put the beany on and think a way through a problem! :bow:

Dave

 

[peatoluser]

Thanks for the compliment Dave.
I think most of my problems with the scewcutting arose because I didn't quite believe I could pull it off, so wasn't really giving it the full attention I should have.
still, not bad for my first attempt at screwcutting. Only ever used taps and dies before.
definitely going to make another screw though.

peter

 

[bronson]

Just read through this whole thread and found it very interesting. I really like the triple engine one of my favorites. The fact that you are building everything on a taig lathe is very impressive. The engine is looking great can't wait for the next update.

 

[peatoluser]

Slow progress, but I'm then I dont want to start getting things badly wrong at this stage.
I didn't have any material thick enough to make the cylinder bases including the piston rod gland, but I did have some 1/4 brass plate so decided to use this for the bases and solder the gland bosses in seperately. heres the plate being skimmed and bored to take the gland. it's on a shop made faceplate. the screw holes will dissapear when i file it to shape.

the body of the HP cylinder is quite thick , so I wanted to skim it down but couldn't use the lathe because of the port face soldered on. then I remembered seeing somebody on here do a similar job but used a milling machine to take a series of tangental cuts and then cleaned up with a file. So , bolted the cylinder to cross slide, and using various thicknesses of packing, I managed to do the same.

part of the reason I wanted to thin it down was to fit some lagging. I had quite liked the way Dr Jo had used wooden coffee stirers to lag her model , and wanted to do something similar.I also noted her idea of using a tile saw to cut the brass banding. I don't have one but it got me thinking, and I quickly cobbled together this table to use with my slitting saw arbour

the bands came out flat and parrellel and here is the suitably lagged cylinder

I know the drawings show all 3 cylinders as one block, but it wasn't that uncommon for the HP cylinder to be seperate and the IP & LP to be one block, and thats the set-up I intend to model. I guess it would be due to the casting ability of the foundry or the size of the machinery to machine the cylinders.

 

[peatoluser]

When I came to make the valves , I realised i couldn't use the drawings , as i had had to make the port face block slightly narrower. on the plans the valve is moved by a valve buckle as in full size practice rather than a square nut set into the valve as in most models. I liked the idea of the adjustability of the valve buckle so devised my own method of an adjustable bobbin. here are the parts

It was when I came to make the chest that I ran into problems. my drill is a cheap far eastern one, and has quite a lot of play in the quill. it's fine for drilling shallow holes or through ones in thin sections, but anything over 3/8 and it's hit and miss where the drill will come out. so rather than clamp cover, chest and cylinder together and drill as one, I marked and drilled the cover tapping size 7BA and used this as a jig to drill the port face and tap 7BA. everything fine up to this point. I then used the cover as a jig to drill the chest. because of the thickness (9/16), the drill went every which way but straight. even when I opened the holes to 1/8 - and 7BA is only 3/32 dia. - some o them still didn't line up
here's a mock up of the cylinder and valve. the photos poor, but some of those holes are very close to the edge

so, while I work out what to do, I decided to carry on with the IP cylinder. Some of you might have noticed on a seperate thread were I made some jaws for the 4 jaw to allow me hold larger diameters more comfortably
here's the cylinder being bored

i decided to use the same method of making the steam passages as on the HP cylinder. but the problem was I couldn't file a large enough flat on the cylinder to accomodate the port block. so I came up with the idea of having one broad flat face with two 45 degree angled faces either side. this would mean that the block would need two angled wings to suit. but how to file the wingss accurately?
first I decided to make 45 degree marking block. I bought a large countersink and milled down some 3/4 by 1/2 bar to give me the required slope

(I hope to use the countersink to make some v blocks and a cross hole drilling jig for the drill as well)
I bolted this to a piece of scrap to give me a guide as to how the filing was going. I could check it against a light or use a small smear of marking blue.
for the port face block, I milled the centre out of a block of brass, then used the 45 block to check progress as I filed the wings 45 degrees.

one of the few times i use the vertical slide. I much prefer to clamp to the cross slide directly. far more rigid.
here are the parts and block . the black mark is showing the width of the 45 degree slope on the cylinder

the fit is quite good. certainly good enough for soldering. I dont think I could have filed it freehand and got the fit that good.
I now need to mill the ports. But for the LP cylinder I might have to come up with a different tactic. i dont think I have any brass big enough for the port block.

thanks for looking

peter

 

[Ramon]

Hi Pete, I've just had the pleasure of reading your thread for the frst time.

Just like to say you are doing a cracking job given the limited kit you have. The way you have tackled what is, after all, a challenging project with the best of equipment should be awe inspiring to all of us with basic resources and just shows what can be done if you've a mind to it. Your approach throughout is resourcefulness at it's best for me but that in achieving the two start screw is just brilliant :bow:

Good luck with the rest of the build Thm: Thm:- I look forward to more inspirational ingenuity

Ramon

 

[peatoluser]

Thanks for the vote of confidence , Ramon. I guess when machinists like yourself, steamer, deanofid et al make such positive comments, then I must be doing something right!
I've been trying to refine the way I make the thread follower, and came up with this method

I rolled (well, bashed really) from a piece of thin plate one helix of a 4 TPI T thread that was a tight fit over some 5/8 bar and then used it as a guide for a hacksaw, cutting a shallow groove three-quarters of the way round, repositioned the tube, cut a bit more etc. It took a few attempts to get the tube right, but looks far more accurate than filed follower. just need to sort out the tool offsetting , but I think I really should press on with the cylinders in the mean time.

yours
peter