Muncaster Joy Valve Steam Engine 1/2 scale

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raveney

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Hello All,
Last weekend I machined the sand casted flywheels. There was a fair bit of filing required to clean up the spokes, but the rest of the machining was straight up lathe work using a faceplate to bore the shaft, taper the hub, and cleanup a few spots where the pattern didn't pull cleanly on the inner rim.

Then I fastened each one to an 7/16" arbor and trued up the outer diameter. I had to use the boring bar upside down and run the lathe in reverse to get this to work on my 7X14 mini-lathe but got a very good finish using auto feed at 500 RPM with copious spraying of WD-40. The aluminum that was remelted to cast these is giving a very nice surface finish so far, unlike other extruded melts that I have done which were gummy and smeared.

Then I broached the keyways, primed the centers and set aside to dry. I will polish up right before final assembly as the aluminum seems to scratch easily unlike cast iron.
Faceplate.jpg
arbor.jpg
finished_FW.jpg
 

raveney

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Hello All,

The base casting was de-gated using a table saw by clamping it to a wooden sled and raising the carbide tipped blade in small (0.1") increments. The underside was then machined flat using a 2" fly-cutter after leveling up on the mill. A few passes on the surface plate with wet-dry 150 grit paper gave a good stable part to work with. I then clamped and aligned it on the table using the hold down bosses and a transfer punch. I set some clamps and parallels to allow repeated removal and replacement as the work progressed. This also allowed offsetting so the tooling could access as sides and features as the Grizzly hobbyist lathe has very limited Y travel.
align.jpg

The main standards, valve standards and cylinder pads were then decked, drilled and tapped. I used #10-32 for mains and mounting, #6-32 for cylinder and #4-32 for valve standards. The casting machined very nicely, not gummy at all. The defect cleaned up well where the sand didn't fully pack at the inside corner. There are a few seams that might show up after painting, and will need filling with either JB Weld or body putty. Someone also accidently drilled two 1/16 holes in the wrong spot while laying out the galleys. :rolleyes:
deck_tap.jpg

mains.jpg

galleys.jpg

I enjoy setting the travel stops for removing inside features like these galleys. My mill comes with X-axis ones, but I added the Y-axis ones. One can see the front stop next to the handle. The rear one is mounted on the right of the column. The "stop" rods are removed and stored on the tool rack when not in use. A post below covers some details. I use them frequently


A semi-finished base below. Still need to drill and tap the guide bars, side mill the main standards, minor fettling and restore the pebbly finish. I have a small sand blaster, and have had some success by striking the surface with a stiff wire brush.

Anyone have other tips or tricks?

finished_base.jpg
 
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peterl95124

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someone else has also drill holes in the wrong locations, you can loctite in some aluminum rods or aluminum screws if the holes are threaded, or if they are blind holes cut them 1/16 taller than the hole and peen them in. What I found building my Merlin is that while there's some machining mishap on almost every large piece of aluminum in it, once its all put together no one (not even the builder) notices. There's even some big blunders recovered from by epoxy'ing in a new chunk of aluminum (hobbyist "additive machining" :) !!!). Do obsess about things like bearings and journals, but don't obsess with things that are "as cast" surfaces. great progress, keep up the good work !
 

raveney

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Hello All,
Glad to have you following this project. We all make mistakes, but in this case it was recoverable. I loathe breaking taps in things that I have spent days making. Yesterday I enjoyed some time off work because of the Thanksgiving weekend and puttered on some small parts for the base. Bearing caps and valve standards were patterned using high density foam so they were a little rough, but machined nicely. The casting was done last month, but included some reference photos. Machining foam with accuracy is a bit weird.
foam dowel.jpg
foam profile.jpg
as cast parts.jpg

I reckoned that the bearing dowels were the most important feature so located them, drilled for 10-32 studs while clamped high enough to side mill the finished width and then flipped to cut out the bearing gib/recess. I also milled the square oil reservoirs off camera
index cap.jpg
side mill.jpg


The valve linkage standards were treated similarly. Sand one surface as reference, clamp to rotary table centering on the journal, drill & bore for bearing. Then sweep the corners while rotating the table and side mill the base to finished length. I also radiused the bores and removed some cast boogers under the bored hole inside the recess. Next I finished the width to match the mounting pads on the base. This left one of the recesses too shallow, so I roughed it out lower to match the first one. When I made the patterns I cut a stack of three profiles with the center being whole, and the two outer layers having cut outs. Wasn't considering the depth at the time.

I also cut the lengths while clamped and true so I could later flip, clamp and measure and drill the #4-40 clearance mounting holes
ream bearing.jpg
mill base.jpg
finish width.jpg
restore recess.jpg
 

raveney

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Up next are the guide plates that were cast into the base on the original engine. Because I only have aluminum & brass casting equipment I omitted these from the pattern as aluminum wouldn't wear well under sliding friction. I searched for suitable cast iron remnants, but only came up with a chunk of 1" hot rolled steel as a donor. With a new blade in my bandsaw we were in business. Squared up the stock and milled the locating features on the bottom first.
A36 for guides.jpg

mill bottom guide.jpg

I love using my Florida Flywheelers flea market depth mic for checking dimensions while clamped down. Really appreciate using old tools. :)
I wanted to have the oil dams like the original, so machined them next using an 1/8 end mill. Then I cut the bearing slide areas, and drilled the stud holes. After trial fitting to the cast base I realized that some shimming was needed and added some counterbored mounting holes that will be hidden by the top plates later. This should allow the guide plates to be secured to the base rigidly and the stud/nuts on the top plates to be adjusted for bearing slide wear as I imagined Mr. Muncaster intended.
oil dams.jpg


extra counterbores.jpg
locating and shims.jpg
stoning guides.jpg

I don't have a 1/8 radius bit so just filed the corners using a template
radius corners.jpg

finished base.jpg

Progress so far with the aforementioned parts secured using non traditional socket head cap screws because they are so easily removed. The plan is to make scale taller hex nuts and studs eventually. Plan is to work on the main bearings next so all other dimensions are based on that center line
 

raveney

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1" bearing bronze was sized, drilled and reamed 7/16 which ends up .4385 with my tooling. I then squared surfaces, rounded over corners and milled out the races. Achieved a snug fit by removing and checking insitu. Concentricity and height is dead on (well.... relative to me). Now we have the main reference for all other machining. The last photo shows the ugliness in surface finish left on the base casting just below mains and other areas that were machined. I was thinking of attempting to mix sifted fine sand or blast media in the metal primer and paint again in an attempt to restore the pebble finish. Anyone try this before?
square up bronze stock.jpg
mill out races.jpg
7_16 shaft.jpg
 

raveney

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Hello all,

This weekend I'm attempting to fabricate the cylinder block by TIG welding materials that I had on hand rather than purchasing a billet of cast iron. I had some 1/4 A36 hot roll plate and a piece of 1-1/4 SCH 80 A106 GRB pipe from the dumpster. I bought some silicone bronze filler rod to avoid distortion as much as possible. I sketched it on paper, and the only challenge I see is sealing where the steam enters the cylinder. I think I will be able to tell when I get that far if I get full "penetration" of the passages. If not I'll use a 1/16" electrode to fill any areas that might leak.
raw material.jpg
concept.jpg

Started by rough cutting the plate with the grinder, machined edges and lightly abraded the surface using a flap disc. Then I bored the recesses in the end plates to hold the pipes in alignment. Cut and trued the ends of the cylinders (pipes) and sand blasted all pieces. I have never used silicone bronze tig filler, so I made some test welds to dial in the amperage settings. I used 95 amps with a foot pedal for most of the welding (brazing?). the most difficult spot was the circumferential segment between the cylinders. I was using a gas lens #8 cup and had to stick the electrode out about 1/2" to reach this area :oops:. Here's where I was glad that I chose bronze filler rather than attempting straight welding. I still got some warpage/misalignment of 0.017" on one of the cylinders as witnessed by the taper when I skim-cut the top of each cylinder to receive the base plate and passageway plate. Hopefully this cleans up at the target bore, if not I'll go bigger or sleeve it.
bore recess.jpg
parts for welding.jpg
weld circumference.jpg

It all seems pretty good at the end, and ready to line bore on my "big" lathe (a Harbor Freight 9x20) I will repurpose a 1" boring bar I already made for the Panther Pup and Otto-Langen engine. Just need to sort out a rigid and repeatable support for the cylinder block.

flycut machining.jpg
ready for line boring.jpg
 

peterl95124

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I have used silicon-bronze with my TIG, especially for inside corner fillets as you did, but bronze doesn't penetrate so there won't be any joint where the cylinder butts to the end plate, I would have used a mapp gas torch and silver-braze which penetrates everywhere there's enough heat and flux. There's obviously no strength issue in your build, just a crevice that might rust, but probably not in your life time so probably not a real worry, just a thought.
 

raveney

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Hello again,
this weekend we line bored and honed the fabricated cylinder block. In hindsight my choice of dumpster offcuts of steel pipe was not my brightest. It did not machine well cutting through the red oxide and cleaning up the pitting, but managed to slog through it and ended up with 1.447 bores after lapping. I had a 7/8" boring bar with a 3/16 round HSS cutter that I had to lengthen. I had cross drilled this on a 45 degree to reduce the bending stress in the middle and used leftover diver's lead weights to dampen the chatter. The bit feeds out about 0.004 each 1/8 turn so it was fairly accurate to control the cut. Had to side track and make a batch of tee-nuts for the cross slide to clamp it all down. The 123 block and small angle plate allowed me to just switch bores without realigning it all.
Not the best finish though 😒 A106 Grade B has 0.3% carbon, 0.4% Chrome and 0.4% Nickle so a tad hard to bore with HSS
setup.jpg
boring bar.jpg
lead damping.jpg
before lapping.jpg

A honing/lapping was needed for this, and I wasn't [patient enough to order a nice ACRO lap this size. Let's just make on up I said.... Look at my sketch and one can see why this didn;t work to well. The slotted segments of the barrel are so thick they really resist bending and increasing the barrel OD. Never came across this before with smaller ones. I guess there must be some undercutting (green line) on the store bought ones?
lap drawing.png
lap.jpg

It still ended up doing the job though. Same picture after lapping
after lapping.jpg

Thanks for watching!
Next weekend, I'll drill and machine the steam passageways and tap the end plate holes. I have some 304 SS 3 mm sheet for the valve plate left over from the heat treat oven job.
 

Richard Hed

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Hello again,
this weekend we line bored and honed the fabricated cylinder block. In hindsight my choice of dumpster offcuts of steel pipe was not my brightest. It did not machine well cutting through the red oxide and cleaning up the pitting, but managed to slog through it and ended up with 1.447 bores after lapping. I had a 7/8" boring bar with a 3/16 round HSS cutter that I had to lengthen. I had cross drilled this on a 45 degree to reduce the bending stress in the middle and used leftover diver's lead weights to dampen the chatter. The bit feeds out about 0.004 each 1/8 turn so it was fairly accurate to control the cut. Had to side track and make a batch of tee-nuts for the cross slide to clamp it all down. The 123 block and small angle plate allowed me to just switch bores without realigning it all.
Not the best finish though 😒 A106 Grade B has 0.3% carbon, 0.4% Chrome and 0.4% Nickle so a tad hard to bore with HSS
View attachment 142753 View attachment 142754 View attachment 142755 View attachment 142756
A honing/lapping was needed for this, and I wasn't [patient enough to order a nice ACRO lap this size. Let's just make on up I said.... Look at my sketch and one can see why this didn;t work to well. The slotted segments of the barrel are so thick they really resist bending and increasing the barrel OD. Never came across this before with smaller ones. I guess there must be some undercutting (green line) on the store bought ones?
View attachment 142758 View attachment 142757
It still ended up doing the job though. Same picture after lapping
View attachment 142759
Thanks for watching!
Next weekend, I'll drill and machine the steam passageways and tap the end plate holes. I have some 304 SS 3 mm sheet for the valve plate left over from the heat treat oven job.
They ended up looking good, What is the end diameter? End to end good?
 

raveney

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Thank you for asking.
Using dial calipers
Left cylinder front 1.448, 1.447 rear 1.448, 1.448
Right cylinder front 1.447, 1.447 rear 1.447, 1.447

using telescopic bore gauge and 1"-2" micrometer
Left cylinder 1.4491
Right cylinder 1.4490

I have never calibrated the 1" micrometer since I bought it used, but checked a 123 block using a fairly new 0"-1" Mitutoyo mic and the 1"-2" mic read 0.0005" larger, so the readings make sense to me. the telescopic bore gauges feel pretty good traversing the bores. I will make the pistons and test the fits by releasing them on the surface plate and watching them slide down end to end. I plan to make CI rings also.:D
 

kvom

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Thank you for asking.
Using dial calipers
Left cylinder front 1.448, 1.447 rear 1.448, 1.448
Right cylinder front 1.447, 1.447 rear 1.447, 1.447

using telescopic bore gauge and 1"-2" micrometer
Left cylinder 1.4491
Right cylinder 1.4490

I have never calibrated the 1" micrometer since I bought it used, but checked a 123 block using a fairly new 0"-1" Mitutoyo mic and the 1"-2" mic read 0.0005" larger, so the readings make sense to me. the telescopic bore gauges feel pretty good traversing the bores. I will make the pistons and test the fits by releasing them on the surface plate and watching them slide down end to end. I plan to make CI rings also.:D
My engine runs very well without rings and with less accuracy in diameter. Your fabrication method is cool.
 

raveney

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My engine runs very well without rings and with less accuracy in diameter. Your fabrication method is cool.
Thank you sir! Your build log is a great reference to me as I stumble through this hybrid scale/dimension build.

This week I drilled and tapped and milled the cylinder block where needed. I skimp on a lot of tooling except for taps. I love my swap meet Starret tap holder, and brought out the USA quality Kodiak taps that I purchased when I started the Demon V8 engine block. Breaking small taps in some part one spends days on sucks. The tap holder is engraved "Bernie", and I say a prayer to him every time it works out. 😇 I did manage to break the tips off my #1 center drill and had to pick them out carefully.

kodiak taps.jpg

After the cylinder block worked out well, I started the end caps so I can work on the pistons next week. I had a nice piece of 1.75" cold rolled steel and took it to size on my 9x20 harbor freight lathe. Its very nice having two lathes because i can leave the 4 jaw setup on one and a collet chuck on the little one. Used a 1/16" parting blade to carefully remove all the metal behind the gland and that took most of the day in low speed with lots of oil. I had two 1" thin
offcuts of bronze that were rattling around forever and broke out my adjustable chuck spider to help hold them true while I dialed them in. I set the cap screws on the surface plate based on how thin the part is.
grooving endcover.jpg


chuck spider.jpg

thin brass gland.jpg

The steam gland is a nice looking oval and I debated using filing buttons, but thought the rotary table was best. First I made a morse taper centering pin that a member showed us on his build log. I had a junk drill chuck that I softened and drilled for a 1/4"-20 thread in a past job so I repurposed that. Unfortunately the hole ended up at 0.2525 instead of 0.250 so I had to carefully machine some special pins out of 3/8 drill rod. I made two and the 0.2525 x 0.250 one was used for this job.
rotary table arbors.jpg

indicating table.jpg

gland radius.jpg

I calculated the angle as 33 degrees and 40 minutes and made a roughing cut at 0.460 and final at 0.455 using an apparently semi-dull 1/4 4 flute end mill.
It filed out nicely but I ran out of steam to go on and finish the next one.
I verified squareness and perpendicularity instead and took a group shot of the progress this weekend. My surface plate is a bit small for this model and I'm eyeing up the wife's expensive granite tops. Maybe when she goes to babysit the grandbaby....🤫

progress shot.jpg
 

raveney

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Hello again,
Finished the other cylinder steam gland and made cylinder head covers using the same CRS material. Had some HSS bits that were used with the recess. The bifurcated one avoids chatter when trepanning, and the spoon bit radiused the corners for cosmetics. Once again the rotary table pin and arbor was used; this time to ensure bolt holes were concentric with the cylinder insert part rather then the outer diameter in case of error.
grooving tools.jpg

Locating hole.jpg
cover plate holes.jpg

The next part up that I would like to make is the crosshead. I made the guide plate slides from bronze and located the centers using the cylinder block to make up for accumulation of errors by setting the assembly on the mill. The right cylinder is 0.003" offset and the left is 0.009" offset. I think that came from truing up the sides of the fabrication after boring. Easy enough to compensate for by centering on piston rods and drilling crosshead holes based on those measurements.

The crosshead bearings as depicted by Muncaster are square and require a square hole. A bit unusual, but the plan is to accept this challenge and broach the inside corners (blue arrow). I will also make the bearing faces proud of the sides (orange arrow) to avoid rubbing on the connecting rod. I have to make a broach and will need to practice some on this technique. Two approaches may be a 1/4 HSS square blank ground and held in a split round, or a 3/8 round of O-1 hardened. I'm going to cut the faces by using a square collet block held in the vice at 7* relief. Here's one of those cases where a D-bit grinder would be nice.

Muncaster Joy Crosshead.png
 

raveney

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Successfully made the square broach out of 1/2" O-1 drill rod and hardened and tempered it. The crosshead blanks are nearly 3/8" thick 1018 steel and the tool worked fine! I predrilled and milled inside using a 1/4" four flute endmill. Next I need to make the radius feature where the piston rod threads in. As this feature is purely aesthetic, I'm hoping I don't push my luck and botch these parts🤞

The only square broach tools I could find online cost hundreds of dollars, and I watched a youtube by advanced Innovation where Joe made it look easy. Thanks Joe!

First a 6" long blank was faced off and held in square collet block on an angle for relief. I used a 3 and a 4 degree angle block stacked and stopped in the vice for repeatability as I rotated the part. Did the "maths" and estimated 0.0655" depth of cut to achieve the target of 5/16" square. There was some deflection, so it ended slightly larger (0.317").
Why is it that math is plural in the UK? I thought it was slang, but i saw a textbook with it on the cover on the "tellie"☺️
milling relief.jpg


Relieved the part on the lathe so less surface needed sharpening and then heated red hot and quenched in oil. Honed some more using 1000 grit and then tempered to straw color. Honed again and then it passed QC and was ready to use
sharpen.jpg

carefully indexed it using the edges of the part to be broached and started in the middle area and worked towards the corners. in hindsight, a 1/4" broach would have been kinder to my mill spindle bearings an quill rack.
alignment.jpg
still need snout cut.jpg
 

Sprocket

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You had linked to "Tin Barn Tools" and the little toe clamps like you have on the rotary table. I made a set (not quite as short as those) and they are a real help. Makes it feel like lots of room and lots of possibilities on the rotary table. Also made the "sine plate". Another really useful tool.
Thanks for that reference!
Doug
 

raveney

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You had linked to "Tin Barn Tools" and the little toe clamps like you have on the rotary table. I made a set (not quite as short as those) and they are a real help. Makes it feel like lots of room and lots of possibilities on the rotary table. Also made the "sine plate". Another really useful tool.
Thanks for that reference!
Doug
I do enjoy Mr. Lee's videos.

Finished the cross heads and pistons this past weekend.

I chose to mimic what KVOM had done on the "snout feature" as it matched the curves and squareness of the parts better in my opinion. Also much easier to machine. The square bearings and wedges were fiddly to make and I soldered the wedges to the mating bearing as I machined to width and length, then un-sweated and sanded solder off each face leaving a nice gap. They lock into place using a #2-56 SHCS "permanarily"? Scale #2-56 hex nuts are 1/8 hex and I can't find that size in steel. Lot of work to make QTY(30) hex nuts. I will try a few at a time and see how it looks.
crosshead bearings.jpg

crossheads.jpg

The piston material is cast iron and I got some hellacious chatter when cutting the ring grooves. I performed lathe maintenance and readjusted the gibs and cross slide adjustments and it was no better. The grooving tool width (1/16) is just too wide for this mini lathe so I suffered through it by using some old diving weight bags (lead shot).
grooving pistons.jpg

I bored the piston rod holes so the machine thread wouldn't dictate concentricity. Then trued each piston to the rod as assembled and tried in the block. They are interchangeable between cylinders as hoped, but I stamped each one (L & R) as I have been doing with each part so far.
boring piston.jpg
 

raveney

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Hello again from sunny and warm mid Florida,
Carried on with the workshop puttering and focused on the crankshaft next. I chose to fabricate this one and kept the throws square to aid in assembly of the two planes. A lot of fuss making all the throws equal width, length and thickness but I had 7/16" drill rod and a close fit chucking reamer so all went well. Assembled using green Loctite and let set 24 hours before staking. I used brad nails and a #51 drill, as I don't have taper pins or reamers. The zinc coating on these nails works really well at making the hole disappear. One does have to sort through the nails using a Micrometer to find suitable donors though.
51 size brad nail.jpg

Next the main bearings were trimmed as these function as a sort of thrust bearing (side to side). Anyone know the correct term? Didn't have an adjustable 7/16" stub arbor, so I made one up at the expense of my 1/16" slitting saw blade. Everything was cutting well on the first two slots, and the last one started vibrating and wore the relief of of the teeth. They are only $9 online, so I just added it to the wish list rather than attempt to sharpen.
trim bearings.jpg


Made some fiddly little keys out of brass to hold the wheels to the shaft. Please ignore the drywall screws holding the base down; I have proper hex stock ordered for studs and nuts 🙄
keys.jpg

Some easy parts next were the four guide-block gibs? I used my "tin barn time" sine fixture plate clamped in the vise and set to 14 degrees for the chamfer on these. Here is where the short toe clamps worked well. Thought it proper to sweep the parallel being used as a fence, and use a strip of grit cloth as a precaution for clamping with just two points of contact. Used a nice sharp 1/4 carbide end mill, and was rewarded with a nice even chamfer.
guide gibs.jpg

bevel.jpg

I made a few 0.010"shims for the RHS bearing, and the LHS gib cover plates so everything rotated and slid freely. May have twisted the base when clamping down on the mill table to machine these surfaces in the Z direction. If you can't make it right, make it adjustable! No shame here

Spent some quality can't sleep time reading up on joy valve linkage

Carefully reading this treatise, I understand the dimensions a lot better now. I modeled it in conFusion and kept stumbling on a certain item again and again. I was certain that when the crank throw was vertical that the piston would be dead center. It is not....Can't understand why, but maybe someone smart here can explain it.

Anyway, the pivot, R, in the link QK for link RS needs to line up with the valve trunnion center W, when the piston is dead center. Page 256 gives a step by step way to do this and a few good parameters to ensure slide valve symmetry and prevent binding. link RS will be vertical when piston is dead center, and link FS should be horizontal as possible when this occurs.

I'll start with the connecting rods using dimension QR= 2.280" and QK= 5.466". OK = 0.9" and WO= 3.214" for my scale version
Joy Valve Ratio_2.png
 

peterl95124

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Raveny, don't know if this will help or just confuse the issue,
mine is based on this drawing, but after reading your comment
about criteria to avoid binding I'm not sure mine does, will have
to investigate.

Anyway, the keys to FWD/REV, and TDC/BDC, symmetries are
have the offsets I've labeled 1-1/8 and 1-1/8 be the same, and
the lower link be divided approx 1/3 - 2/3 for where the upper
link pivots on it, and the radius rod and the lower rod (parallel(-ish)
to it) be about the same length (Muncaster design both the offsets
of these two rods from the central axis, and their lengths, are unequal
so this isn't all that critical, but Simon's simulator shows an improvement
in symmetry if they are).

while you're trying to decide if this is useful information, I'll try reading
the google-books reference you found and try to decide if I think it is
useful information. then we can compare notes.
 

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raveney

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Raveny, don't know if this will help or just confuse the issue,
mine is based on this drawing, but after reading your comment
about criteria to avoid binding I'm not sure mine does, will have
to investigate.

Anyway, the keys to FWD/REV, and TDC/BDC, symmetries are
have the offsets I've labeled 1-1/8 and 1-1/8 be the same, and
the lower link be divided approx 1/3 - 2/3 for where the upper
link pivots on it, and the radius rod and the lower rod (parallel(-ish)
to it) be about the same length (Muncaster design both the offsets
of these two rods from the central axis, and their lengths, are unequal
so this isn't all that critical, but Simon's simulator shows an improvement
in symmetry if they are).

while you're trying to decide if this is useful information, I'll try reading
the google-books reference you found and try to decide if I think it is
useful information. then we can compare notes.
Thank you Peter, that is very helpful

As I am disciplined to use three part communication, please allow me to confirm the information given and elaborate on the binding hint given in the cited resource.

The angle drawn on attached should be less than or equal to 90 degrees.

When the connecting rod is at dead center, DC, the intersection to the valve standard centerline defines where one must place the attachment pivot for the lower link. This is defined as L1. This should prevent interference between this link and the guide-plate oil wells.

The radius rod length, L2 should be as long as practical to model vertical motion of the lowest pivot of the lower rod on valve standard centerline. The pivot distance below cylinder centerline should mirror the distance of the valve standard pivot above cylinder centerline.

Have a happy Holiday!
Screenshot 2022-12-24 074358.png
 

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