Author Topic: Arnold's take on the MEM Corliss  (Read 134606 times)

Offline NickG

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Re: Arnold's take on the MEM Corliss
« Reply #300 on: July 15, 2013, 01:11:40 PM »
Looking good Arnold and sounds promising.  :ThumbsUp:

Offline arnoldb

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Re: Arnold's take on the MEM Corliss
« Reply #301 on: July 20, 2013, 07:09:52 PM »
Bob, Hugh, Jerry, Bill & Nick - thanks Gents  :praise2:

Bob, thinks look on the up; today's bit gave me a good view, and though I still have to make some of those nitty-gritty parts,  things seem to pan out by eye  :ThumbsUp:

Jerry, I like your optimism in "...just one more step..."  :ROFL: - That's still quite a bit of work to do!

This afternoon I re-made the valves, and yes; I pulled the "Lazy Arnold".  On the full-size engine Corliss, the valves are made from two pieces like in the plans.  The reason for that is that the valves are actually fairly loose-fitting in the bores, and depend on steam pressure to keep them sealed to the steam ports when closed.  This also allows any water that's condensed in the cylinder to force the valve off the seat and prevents damage to the engine in cases where there's water present in the cylinder.  This does away with the need for drain cocks like found on other engines.

My model will most likely never run on steam, and even if it did, the valves are too close-fitting in their bores to allow for hydraulic lift.  So it does not really make sense to make the valves in two parts - so I proceeded to make them as single units.

I just turned the thin sections of the valves using the collet chuck on the lathe.  Next, on to the mill, and I set up things to prevent last weekend's disaster:


All the steps were pretty much the same, so I didn't take any photos.  I ended up with the four valves:


Installed in the engine - and out of shop time for today:


The smallest bits for this phase of the build is up next.  Hopefully I can get some shop time tomorrow and make a start on those.  So close, yet so far...

On leaving the shop, I looked up, and lo and behold; we had a crisp clear dusk with a minimum of dust in the atmosphere.  So I had a go at making the camera take a photo of something without macro mode for a change  :Lol: :


Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline vcutajar

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Re: Arnold's take on the MEM Corliss
« Reply #302 on: July 20, 2013, 08:54:44 PM »
What a lovely photo of the moon.  I guess yuo used a zoom lense for that shot.

Nice set of valves.  I was wondering why the plans where showing it made from two pieces.  I might do the same and do them in one piece like you did.  Did you make a slot at the back end of the valves like last time?

Vince

Offline ths

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Re: Arnold's take on the MEM Corliss
« Reply #303 on: July 20, 2013, 10:19:36 PM »
Glad the valve issue is sorted, and a good explanation as to their full size manufacture.

Great moon shot. I think I could see my neighbour there, I believe he often visits.

Cheers, Hugh.

Offline NickG

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Re: Arnold's take on the MEM Corliss
« Reply #304 on: July 20, 2013, 10:59:36 PM »
Amazing photo!

Offline Captain Jerry

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Re: Arnold's take on the MEM Corliss
« Reply #305 on: July 20, 2013, 11:00:23 PM »
Arnold

Great pictures, engine and moon!  The valves look nice as well!  I don't see any advantage in making the valve and spindle in two pieces and I think that you have avoided some alignment and friction problems by making it in one piece.  Just my opinion, no evidence.

If you have not slotted the back end of the valve, I would highly recommend that you do so.  The slots should, of course, be in line with the flats on the valve and I would also recommend that you  mark the end to indicate which side of the slot is the open face of the valve.  Without some indicator it is no way to be sure of the orientation of the valves at the various phases of the cycle.

During the set up and adjustment of the valves, it is possible to leave the back covers off completely so that you can observe the orientation of all four valves simultaneously.  If the valves are a good fit in the bore and there is a good oil film on them, the air loss will be minimal or non-existant at low pressure.  The back and front covers do provide axial positioning of the valve in the valve bore but if you add a collar to the valve stem outside of the front valve cover, that will hold the valve in place.

The original published plans, without the release trip mechanism shows the valve arm held in position with a grub screw.  In my opinion, a grub screw, particularly at these dimensions, is both unreliable and likely to damage the spindle and since the position of the arm is the primary means of adjustment, a flat on the spindle cannot be used.  I would recommend that you use some kind of split clamp attachment of the arm to the spindle.  Another option would be thread the end of the shaft for a retaining nut, which would require extending the length of the spindle, or taping the end of the spindle for a retainer bolt.  In either case, the end of the spindle would need to have either a shoulder, and or a tapered land for the arm.  My preference would be a tapered land.  From experience, you will likely make numerous adjustments before you are satisfied with the performance, and I have found a tapered land to be much more reliable.

I also would advise you to first run the engine without a quick release mechanism of any kind until you are satisfied that the valve train, from the eccentric to valve edge are properly adjusted, and running smoothly.  If you then want to add the complexity of trips and governor control, you will have the confidence in the basic adjustments to deal with the added complexity.

I have not seen any instructions on how to set the valves for initial testing.  It is not difficult.  Here is how I would start out.

  • Set the crank horizontal - either TDC or BDC.
  • Set the eccentric at a 90 angle to the crank, placing the high point off the eccentric up.
  • Adjust the length of the eccentric rod so that the lever is vertical.
  • Adjust the length of the rod from the lever to the wrist plate so that the wrist plate is vertical (12 o'clock)
  • Adjust each valve so that valve edge is at the edge of its respective port.
  • rotate the flywheel so that the crank is vertical.
Give it some air!  If it doesn't start, it should at least move enough to show you which way it wants to run and you can give it a little help.

I'm not there with mine yet but I will be soon. 

Best wishes

Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Maryak

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Re: Arnold's take on the MEM Corliss
« Reply #306 on: July 21, 2013, 02:01:26 AM »
Hi Guys,

Jerry and I have been exchanging ideas on release mechanisms and he is way ahead of the rest of us when it comes to the various problems encountered at such small sizes.

So yes the one piece valve is a good idea and is how they were conceived in the early days.

I  agree that a grub screw has the potential for problems, the alternative of loctite is suggested. In the case of Jerry's own design the clamping of the governor release arm is great and I will investigate this idea for the latch arm on the Reynolds Latch release.

So......................watch this space  ;D

Best Regards
Bob
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline vcutajar

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Re: Arnold's take on the MEM Corliss
« Reply #307 on: July 21, 2013, 04:45:57 AM »
Thanks Jerry and Bob. Great information.  Definetly, the valves will be made in one piece.  Just in case I come to the stage of making the trip mechanism, would the spindle need to be longer?

I was wondering how to do the initial setup for the engine. Thanks for the info.

Vince

Offline arnoldb

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Re: Arnold's take on the MEM Corliss
« Reply #308 on: July 21, 2013, 07:04:18 PM »
Thanks Vince.  Yes, I added the slot at the back; it will be pretty essential for setting the timing, as it gives a visible cue of the valve's position, as well as a place to stick a screwdriver in to rotate the valve while adjusting.  No lens change on the camera for the moon shot; it's standard lens goes from 5 to 100mm giving macro to 20x optical zoom.  It also has digital zoom to 80x - that's what I used for the moon photo.

Hugh & Nick, thanks gents.

Thanks Jerry; great info!  I pretty much had the same ideas in mind for setting the timing; in fact what is there already of the valve train was set up exactly like you described.  I've already figured out which way the engine will run - currently in the wrong direction, so I need to rotate the eccentric 180o - I want it to run "over" to prevent the crank screw from unscrewing if it comes loose.
To set the valves, I was just going to disconnect them all, set the engine up exactly as you mentioned at either TCD or BDC, apply some air, and then close both inlet and exhaust valves on one side, open the inlet fully on the other side, and adjust the exhaust til it's just closed by listening to the air passing through.  Then disconnect that exhaust valve, open it, and adjust the inlet till it's just closed.  Then repeat for the other side's valves.  This should set the timing pretty well from the get-go.

Thanks Bob.  Though I didn't get to finish them today, I changed the design for the valve arms to work with a slot and small screw to set them; I seem to recall seeing full-size Corliss engines using a similar arrangement.  I'll see how that works out; it'll look slightly more bulky on the model, but should be OK...

I only had a short shop session this afternoon; some other matters needed my attention earlier on.  These bits of 3mm brass plate came from the scrap box, and was fairly close to the size needed:


These were tidied up a bit; milled to width, and one end squared up.  Then I set up the vise stop so I could drill the holes - and for the small hole tap it to 10BA in each workpiece with a minimum of fuss:


It doesn't look like it, but there's two hours of work int this lot:


Unfortunately, I only realized they're wrong once I took that last photo  :facepalm2: .  The holes are too far apart; they should have been 7.5mm apart, and I made them 12mm apart for some silly reason.  The silly reason being that I calculated the position of the 10BA hole from the end of the workpiece, but had the DRO zeroed on the 3mm hole...
Fortunately, I can salvage that in my next shop session; the mill setup is still exactly as I left it when I took the workpieces out, and there's more than enough clearance to move the 10BA hole 4.5mm closer to the 3mm hole and still have enough meat left on that side to round over the end.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline Captain Jerry

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Re: Arnold's take on the MEM Corliss
« Reply #309 on: July 21, 2013, 10:04:43 PM »
To set the valves, I was just going to disconnect them all, set the engine up exactly as you mentioned at either TCD or BDC, apply some air, and then close both inlet and exhaust valves on one side, open the inlet fully on the other side, and adjust the exhaust til it's just closed by listening to the air passing through.  Then disconnect that exhaust valve, open it, and adjust the inlet till it's just closed.  Then repeat for the other side's valves.  This should set the timing pretty well from the get-go.


Arnold

Your method should work just fine for you kids with good ears.  If you have trouble hearing the air flow, as I would, here is another way that I have used.  Pipe the exhaust into a glass of water and watch the bubbles.  You can be very precise.

Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline arnoldb

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Re: Arnold's take on the MEM Corliss
« Reply #310 on: July 27, 2013, 06:21:21 PM »
Thanks Jerry.  I forget I'm still blessed with good hearing, and your idea of using the exhaust through water is a brilliant solution for those that can't hear well any more  :NotWorthy:

As always, making small bits can take just as much - if not more - time than making bigger parts.  I only managed to finish the valve arms in today's session.

First, I fixed up the booboo I made last weekend - drilled and tapped new holes in the workpieces at the correct center distance:


Then I had to think a bit about the next machining operations.  There was some fairly fine work to come; drilling holes at 1.1mm to tap M1.4, and adding 1.4mm clearance sections, with a 0.5mm slit in between the sections.  So, the issue was: slit first and then drill and tap or drill and tap first then slit.  The first option was the most convenient, but ran the risk of having some flex added to the drilling operations.  All of my small drills are basically brand new and sharp, so that mitigated the possible flexing a bit.

Off I went, and added a 0.5mm slit to each workpiece:


Then, using the vise stop again so I could finish the same set of operations that follows on each part, I first drilled it 1.1mm (tapping size for M1.4):


To add the screw clearance, I used a sliver of drinks can inserted into the slit and drilled the 1.4mm clearance - once the sliver moved, the hole was through into the slit:


The M1.4 tap followed:

The brass I used here comes from a strip of 3mm plate I got "somewhere", and unlike most brass, it is tough and gummy to machine and tap.  Where most brasses would machine and tap with tiny bits of swarf coming off, this lot leaves long strings when drilling it, and a lot of burrs - much like soft aluminium, but kind of tougher.  This nearly bit me while tapping it; on a couple of occasions the swarf would make the tap want to seize up, and I had to to-and-fro carefully quite often to try and break up the chips that caused this. In the end, things turned out well though.

To accommodate the screw head, I milled a pocket for it.  A true counter bore would have been nicer, but at 2.6mm diameter for the screw head, I had no easy way to do that, and I was in no mood to try and make up a counter bore from silver steel for a hole this small:


Those steps were then repeated for the other three workpieces.  After trimming off the excess length of each workpiece wit a junior hacksaw, I set about tidying them up a bit, using a drill bit and a long 10BA bolt to set the side angles:

For rounding over the ends, I just kept the same height setting on the mill, and milled facets using the 10BA bolt as pivot pin.

Next followed a couple of licks with a small file, some M1.4 screws, and I ended up with this lot:


I was concerned that adding the short section for the screw might be a bit clunky, but it looks OK installed in place on the engine for now:

Rounding the ends over around the axis of the screws, and replicating the pocket on the other side will most likely look even better, but I'll leave this as-is for now.

Kind regards, Arnold

Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline vcutajar

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Re: Arnold's take on the MEM Corliss
« Reply #311 on: July 27, 2013, 06:46:21 PM »
Good progress Arnold.  I am so not looking forward to do those small fiddly bits.

Vince
« Last Edit: July 27, 2013, 09:02:42 PM by vcutajar »

Offline Don1966

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Re: Arnold's take on the MEM Corliss
« Reply #312 on: July 27, 2013, 07:27:14 PM »
She's looking good Arnold, still following along here. Looks like you are not far from completing it. Don't those small parts take up a lot of time?

Don

Offline Marinus

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Re: Arnold's take on the MEM Corliss
« Reply #313 on: July 27, 2013, 09:42:38 PM »
Looking good Arnold. I like seeing skillfull model engineers making small parts.
Kind regards

Marinus Kruger

Online b.lindsey

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Re: Arnold's take on the MEM Corliss
« Reply #314 on: July 28, 2013, 01:11:01 AM »
Just amazing stuff Arnold. Those assembly shots are most inspiring!!!

Bill