Author Topic: A Tandem Compound Mill Engine  (Read 29655 times)

Online deltatango

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Re: A Tandem Compound Mill Engine
« Reply #165 on: November 30, 2022, 05:39:27 AM »
With the HP cylinder cladding fixed I could move on to making some of the moving bits, starting with the Corliss valves themselves. The steam valves are from 5/16" diameter FC stainless, the exhaust from 3/8". I added two small details to the original design, an 8BA axial hole for an extractor screw and a shallow transverse skim across the end in line with the valve face. The extractors will allow the valves to be pulled from the outside end which avoids having to dismantle the operating gear to push them out. The indicator for the valve face position will make setting the valve timing a lot easier (thanks to Tug Wilson for at least one of these ideas!):



Then the valve face was milled to depth:



Over the last few weeks, in the background, I've been painting the finished machined castings and assembling the engine to show progress to date:




The engines turns over quite smoothly but it's a bit tight, I guess there's some fitting needed but that is for later. The paint is lots of coats (sorry, lost count!) of Brunswick Green rattle-can enamel over two coats of primer-surfacer and one of grey primer. This was a tedious and frustrating process, but the final result looks good - I hope.

Some of the smaller details will need painting later but I've had enough of the smell of paint for a while. Oh, and I'll turn the flywheel around the next time, the barring teeth should be on the outside. With them on the inside the governor drive would be much too close for comfort when turning the engine.

David
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Offline MJM460

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Re: A Tandem Compound Mill Engine
« Reply #166 on: November 30, 2022, 10:38:31 AM »
Beautiful work, David.  It’s all coming together well.

MJM460

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Offline Admiral_dk

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Re: A Tandem Compound Mill Engine
« Reply #167 on: November 30, 2022, 11:47:43 AM »
Nice pictures and parts - looks good  :ThumbsUp:    :cheers:

Per

Offline vtsteam

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Re: A Tandem Compound Mill Engine
« Reply #168 on: November 30, 2022, 02:00:08 PM »
That's beautiful!
Steve

Online deltatango

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Re: A Tandem Compound Mill Engine
« Reply #169 on: December 17, 2022, 11:55:32 AM »
MJM, Per and vtsteam - thanks and sorry for the slow reply. Life, mostly in the shape of our one-year-old granddaughter, has been taking a lot of time recently.

Vt, I saw your lovely winter pictures on the "View out the window" thread which made me think of Cousin Maggie who lives in Bridport, VT, with a house right on the shore of Lake Champlain. It'll be cold there right now!

Getting back to the engine...
The valves need a 1/8" x 1/8" slot across the end to couple to the drive. I set the valves up in pairs and centered them in the y-direction using an edge finder and the "1/2" function on the DRO:



the brass block clamping on the valve face should guarantee alignment. The slots were cut with a 3 mm slot drill with a slight offset each way to get to 1/8. One pair got a very satisfying fit on a 1/8" thick parallel:



The other two were slightly looser. Both sets were 0.003/0.004 off centre - damn! I still don't know why so there is more investigation to come after Christmas.

The shafts that drive to the valves have a 0.110" square on the end for a positive drive and so the levers attached to them need accurate square holes. There is very little chance that my filing skills would be up to the occasion, so I used a wobble broach made from the Hemingway kit a few years ago. The broaches for this are made from 8 mm silver steel:



and hardened just on the end. As you can see below, getting the broach to start in a well-controlled orientation isn't easy so I left plenty of space around the 2.8 mm holes and then lined up the drawn squares to the holes:



Some work with hacksaw and files will carve the levers from the plate but finishing these off will have to wait until after Christmas:



Best wishes for Christmas to everyone - David
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Offline cnr6400

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Re: A Tandem Compound Mill Engine
« Reply #170 on: December 17, 2022, 02:25:41 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
"I've cut that stock three times, and it's still too short!"

Offline vtsteam

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Re: A Tandem Compound Mill Engine
« Reply #171 on: December 17, 2022, 03:16:00 PM »
David I've never heard of a wobble broach before! I'll have to look into that. There's a YouTuber who lives somewhere near me, not sure if he's in VT or NH, but he must be close to the border like me because I see both state license plates in his videos. Anyway I find his machining videos very entertaining -- a fellow traveller in the learning process while having fun with it at the same time. He has a video on making square holes which I thought was pretty good. His channel is called "Jeremy Makes Things" Me, I usually just file out a round hole with a triangular file, but that's extremely tedious on anything over a half inch thickness steel. I might try Jeremy's method of actually making a broach and mutliple drilling next time I want to make a big boring bar that takes a square lathe tool.

Great work so far! :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :cheers:
« Last Edit: December 17, 2022, 03:19:18 PM by vtsteam »
Steve

Online Kim

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Re: A Tandem Compound Mill Engine
« Reply #172 on: December 17, 2022, 04:04:32 PM »
Clever way to handle the difficulty in orientation of the square hole, David!   :popcorn: :popcorn:

Kim

Online deltatango

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Re: A Tandem Compound Mill Engine
« Reply #173 on: December 18, 2022, 12:04:43 AM »
Thanks for looking in everyone!

The wobble broach (or rotary broach) is on the Hemingway website at: https://www.hemingwaykits.com/HK2570. The broaches are easier to make than ones for use in an arbor press and you don't need a press, just a pillar drill or mill drill. I'll look at Jeremy's videos soon.

David
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Online deltatango

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Re: A Tandem Compound Mill Engine
« Reply #174 on: January 31, 2023, 11:12:41 AM »
I should have attached a drawing of the HP cylinder valve gear a long time ago but left it out. I tried to attach it at the end but even as a .jpg the forum tells me it is too big so we'll haave to do without.

Having made the valves and valve levers the valve spindles are needed to join these bits together. These are the spindle (in two parts as I chose to make them) and a special 6BA nut:



Each spindle has a 5/32" shaft with a short square portion to fit the square hole in the lever and a 6BA thread on the outer end, the other end has a key to fit the slot in the end of the valve. These two ends are places where it would be very easy to start accumulating lost motion for the whole valve gear so it's necessary to achieve good fits. The holes through the valve bonnets are reamed 5/32" and were a nice running fit on stock stainless rod so I chose to use this for the shafts and fabricate the heads for the inner ends. It would be just as valid to turn the whole part from the solid if someone wanted to go that route. The square end was produced by direct indexing to a push fit in the holes in the levers (I don't have many small W20 collets so an ER11 chuck with a plain 12 mm shank serves here):



Having gone to the trouble of making a nice square end, most of it was then turned away and threaded 6BA:



The other end of the shaft was turned to 2.95 mm for the thickness of the head (plus a bit to allow cleaning up after gluing together). The material for the head end was turned down slightly from nominal to give a bit of running clearance, a through hole was drilled and reamed 3 mm (sorry about mixing units, I don't have Imperial machine reamers), and the key milled onto the end:



The parts for the two steam valves then looked like:



To get the alignment of the two ends close to have parallel flats I used two bits of HSS as parallels to hold things in place while the Loctite 638 set:



A bit of fitting was needed to get the assembled parts working smoothly, principally because the valves had distorted very slightly after removing half the diameter of the stock. Not really surprising but I hadn't thought about it until they didn't want to turn freely in the reamed holes. There are O rings in housings behind the spindle heads to give a pressure seal (I hope...):



The keys also had to be thinned by about 0.002" each side before the assemblies would turn freely. I can feel only very slight clearances so far so now the large collection of pinned joints in the linkages have to be made to minimal clearance as well.

There are a lot more details to go on this valve gear, I just have to plough on. Life, in the form of the house, garden, work leftovers, an interstate move by our eldest son and a newish granddaughter from our daughter, has been getting in the way lately so progress has been slow. Hope to speed up a bit now...

David
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Offline RReid

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Re: A Tandem Compound Mill Engine
« Reply #175 on: January 31, 2023, 03:23:24 PM »
Those look like fun little bits to make, and came out great! Our kids and Grand-children do have a way of slowing project progress, but it's a good slowing! :cheers:
Regards,
Ron

Offline cnr6400

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Re: A Tandem Compound Mill Engine
« Reply #176 on: January 31, 2023, 04:44:17 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
"I've cut that stock three times, and it's still too short!"

Online crueby

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Re: A Tandem Compound Mill Engine
« Reply #177 on: January 31, 2023, 04:46:47 PM »
Looking great!   :popcorn: :popcorn:

Offline vtsteam

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Re: A Tandem Compound Mill Engine
« Reply #178 on: February 03, 2023, 03:38:00 AM »
Really nice work. :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :cheers:
Steve

Online deltatango

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Re: A Tandem Compound Mill Engine
« Reply #179 on: February 22, 2023, 04:03:07 AM »
Ron, The parts are fun but there are an awful lot of them! Thanks to all who have looked in!

Right now I'm having to pace myself just to be able to keep going. Here are a few more little bits, this time it's a bunch of pivot pins and the exhaust valve coupling rod.
The rod is just a bit of 1/8" stainless rod with a 6BA thread on one end and 6BA left-hand on the other, I'm hoping that using opposite hand threads will make adjusting the valves much easier when I get to that.

The rod ends were formed on FCSS bar:



and the ends rounded over using filing buttons:



After parting off and facing to length one end was tapped 6BA, the other 6BA LH.

I then made all the pivot pins for both exhaust and steam valve gears from 3/16" rod. First turning down to a nominal 0.115" which should be a nice clearance fit on a hole from a #32 drill. Just to make sure I sharpened the drill and drilled a hole in a bit of steel plate to use as a gauge. The last bit of length was turned and threaded 8BA.



After parting off the hex heads were formed by simple indexing in the mill and given a little chamfer. The assembly needed a pair of 6BA lock nuts, cutting left-hand threads tests my powers of concentration, or maybe I'm getting older and a bit vague? All together the bits look like:



I didn't make the 8BA /9BA AF nuts...

The progress pictures aren't changing much between posts but there is some progress:



David
Don't die wondering!

 

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