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PMR Mill Engine 3A

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DOC123

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Dear All
I am only a beginner at making engines. I have successfully made a sterling engine and a wobbler noted here
http://www.homemodelenginemachinist.com/index.php?topic=11053.msg120953#msg120953
For my 3rd attempt I am making a PME 3A mill engine from a casting kit that I bought at the same time as the wobbler.
I haven't tried to take pics as I'm going before but will give it a try.

The kit comes nicely packaged with all the needed parts including screws etc. It is in imperial measurements that I find confusing but I can easily convert them. All of my taps etc are metric so I will just adapt most of them. The exception is that most of the screws in the kit are 5-40 so I bought a tap to match.

I started by mounting the base casting on my little mill and evened the base. I then turned it over and milled the crosshead to height and drilled the 4 holes.
 

DOC123

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Next step was to mount the base on a right angle bracket and face and drill the end where the cylinder will sit. (no pic) :(

I then attacked the cylinder. First I made it a vertical as I could in my milling vice and faced one end. Using that end as a reference I mounted it in a 4 jaw and faced the other end on the lathe. I then drilled it and bored to 12mm. I only have 12 and 13mm reamers so that determined the size possibilities. I then stuffed up reaming it with the 12mm reamer so had to enlarge the hole to 13mm.
I then returned the part to the mill and drilled the valve hole and reamed it to 6mm.
Next step was making the holes for the steam ports. These were just done on the mill.


The angled holes were first milled with a 3mm end mill and then drilled through to the matching hole.

 

DOC123

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Next step was making the inboard head.
This is a little casting that isn't easy to grip on my little lathe.
I gripped it by the protruding end in the 3 jaw with a washer between the jaws and the part. This made it possible to true up the outside without hitting the chuck. I then and faced it and made the step to neatly fit the cylinder. I then drilled a 1/8" hole in it.



It was then turned around and pushed up against partly closed jaws and held in place with a live centre in the tailstock. I found that I couldn't use the dead centre as it is shorter and it fowls the toolpost.
This allowed me to machine the outside to fit in the hole in the base casting and to reduce the thickness of the head.



I then had to move the tailstock away to drill the part out. I carefully put it inside the jaws and drilled and tapped it to 6mm. This worked well but made little marks on the outside of the part. I may try again with a piece of bar stock.
 

NickG

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Nice work Terry,

I came across a supplier for PM Research engines the other day and they seem well priced. DId you go for the iron and bronze version of the 3A - I quite like the look of the larger engine which is about $108. The only annoying thing is the large postage cost I'd have to pay and import duty to get it into the UK - it still works out cheaper than stuff on offer over here though.

Do the kits come with instructions? The quality of the castings looks pretty good?

Nick
 

b.lindsey

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Looks like you are off to a great start Doc. PMR does a nice job with their casting kits and are great folks to deal with too. Keep us posted on the progress.

Bill
 

DOC123

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NickG said:
Nice work Terry,

I came across a supplier for PM Research engines the other day and they seem well priced. DId you go for the iron and bronze version of the 3A - I quite like the look of the larger engine which is about $108. The only annoying thing is the large postage cost I'd have to pay and import duty to get it into the UK - it still works out cheaper than stuff on offer over here though.

Do the kits come with instructions? The quality of the castings looks pretty good?

Nick
Dear Nick
This kit is the aluminium one that I bought as a first attempt at machining.
I have since bought 2 cast iron and bronze engines from here
http://www.modelmachinist.com/index.php?osCsid=4810bdc00ba248836ad70f78b2412d3c
as the Aus dollar is high at present. Even with substantial postage costs it is still cheaper than buying similar items locally. I will finish this before tackliing the new ones.

The castings seem to be pretty good with no obvious holes and not much flash.
Only limited instructions come with them but very detailed drawings are provided and I am working from them.
 

NickG

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Thanks for the info Terry, can't wait to see it progress.

Nick
 

DOC123

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A little bit more progress.
The next step was to drill the holes in the cylinder to mount the inboard head. I first marked out the holes on the inboard head and drilled them to size. I could then put the head in place on the cylinder and centre dot the position of the holes. I then drilled the holes in the cylinder and tapped them.


The next step was to make the outboard head. It is only thin so I decided to only clean up the inside and leave the outside as the raw casting.
It was held in the 3 jaw and faced to size to make it just fit in the cylinder.



I then had to drill the 4 mounting holes. I decided to do them all at once with the cap on the cylinder. I was able to hold it on the mill table with 2 clamps and still get enough clearance to drill the holes.



The end cap holes needed to be enlarged to allow the screws to fit so I mounted it on a bit of scrap ali and enlarged the holes. Perfect accuracy isn't needed and it worked well by just eyeballing the drill above each existing hole.




 

DOC123

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The next bit I made was the piston rod but I didn't take any pics of it. I decided to make it out of 3mm silver steel rod rather than the brass supplied as I only have metric dies to make the threads. It is a simple rod with threads on each end. I also made the little nuts out of brass hex.

I then tackled the piston. It is made from brass. I first drilled the 2.5mm hole in the middle and bored it out to take the 2.5mm hex nut that I had made for the piston rod. I made the bored end a bit too big. The result was that I couldn't make a deep enough groove in the cylinder to take the first teflon ring. The second groove was made deep enough.
To compensate I carefully thinned the teflon ring with a craft knife so it fits the shallower groove.
The outside was turned to fit the 13mm cylinder and then parted off.



This is it for now. Hopefully I will get more time tonight to do more. I just have to remember to take more pics as I'm going. ;D
 

DOC123

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I was able to do a little more to the engine last night.
I have been working my way down from the cylinder making the parts as I go. The next part is the cross head. As I mentioned in another thread I have misplaced or never received the bit of brass for this part. I decided to make it out of cast iron as I don't have any brass thick enough. This will be my first attempt at machining cast iron.
The cast iron I have is a 30mm rod so I cut a small disk off it with a hacksaw. I was amazed at how soft it is compared to steel that I have cut in the past.

I put the disc in the lathe and faced one end to create a flat surface. This was then clamped to the mill table. I them reduced its thickness down using an 8mm end mill leaving the bit under the clamp unmachined.



When it was the correct thickness I just cut the thick bit off with a hacksaw.
I then put it in the vice on the mill and cleaned up the sawn edge. I then rotated it 90deg and milled another face. This gave me 2 edges to measure from and I marked it out.
I then made it the correct width to fit the slide where it sits on the engine base.
It was then turned 90deg again ready to mill a slit in it.



Using the same 8mm endmill I created the outside grooves.
The centre slot is suppose to be 1/8" but I decided to just use a 3mm 2 flute endmill and not try to expand the hole to 3.18mm.
The part is 19mm wide. I wanted to have the slot as close to central as possible so I measured from the edge of the piece using an edge finder and advanced the carriage 9.5mm. This seemed reasonably accurate so I made the slot with the end mill. It measures within 0.01mm of centre.



I am yet to drill the holes needed but the mostly finished part is pictured here where it will slide on the engine base.


 

DOC123

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A bit more on this engine.
My first stuff up.
Having made the cross head from cast iron I broke it. As pictured above it still needed to be drilled. I marked it out and centre punched it. I have one of those auto punches that you just press on the item and a spring releases it. Well I used it on the side of the crosshead and one of the arms broke off. This meant going back to the start and remaking it. This time I drilled it before I milled out the centre. The only good news is that practice makes perfect and the new one is a better fit than the first one.



The next step was to make the little retainers that hold the crosshead in position. They are small castings seen here held upside down in the mill vice. They have a casting pip on them and the bottom needs to be milled flat.



I just milled to base level.

 

DOC123

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The next step is to make the little spacers to fit under the crosshead retainers.
These are made from brass rod. It is just drilled out to 1/8" on the lathe and turned down to a reasonable size. I then parted them off to length. This left a little metal that needed to be faced off. I did this carefully on the lathe so as not to reduce the length of the piece as I had parted them off to the same length.



Here are the completed spacers and the crosshead retainers ready to be drilled.

 

NickG

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Nice work Terry :bow:, sorry to see the cracked cross head but all sorted now. Does look a nice kit, I could be tempted by one of these PM research kits.

Nick
 

Kmot

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This is an awesome thread! I have looked at those PMR casting kits and wondered about them. This is the first time I have seen detailed machining photos of one of these kits. I am learning a lot from your photos! Thm:
 

Deanofid

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You're going right at it Terry, and looks like you're doing well.
This kit is the first casting kit I ever built, a long time ago. The kit was under $25 at the time, so
it's been a while. Mine still runs like a champ after many, many hours on it. A nice little engine.
PMR puts out a good product. I'm working on their #7 now, and they're all good quality castings.

Good luck, and keep up the good work!
 

NickG

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Dean, I like the look of the No 7 and No 1 - are you doing a build log? They do seem better value than Stuart's and the like, even with the import duty and large shipping costs to UK.

Nick
 

Deanofid

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Nick, I'll do a build log but won't start it until I get more done, (and I have to ask the owner. I'm building
it for someone else.)
I have a good deal of the work on the base done, which is cast iron. One of the best quality iron castings
I've ever worked on.

Dean
 

DOC123

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Thanks for the encouragement guys.
Taking photos as I go is certainly making me think more about how I machine the bits of this engine.
Next step was to make the connecting rod. This is a thin casting that needed to have both ends milled to clean up the casting and give a smooth surface as simple bearings.

I did this on the mill and then drilled the holes in it. The plans ask for a 43 hole in the thin end but after I had done this I found that the pin supplied doesn't fit through the hole. With persuation ;) it will probably expand the hole enough to be a very tight press fit but I would never get it out again. This may be OK when I assemble the engine. The other option is to enlarge the hole and use loctite to keep the pin in place.



I have just been making the bits in order from the piston out so the next part was the crank bearing. It is made from CRS and is a simple bit of machining on the lathe. The kit has a 5/8 round bit of CRS to use for the bearing and for the eccentric hub. I decided not to use this but used a smaller piece of steel that I had rather than machine lots of metal off.

 

DOC123

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Next came the crank.
It is a casting with a big casting lug on it. I just held it in the 3 jaw and faced it flat.



I then drilled out the centre. This became my second stuff up for this engine. I picked up the wrong drill and made the hole too big for the crankshaft. It is 1/4" CRS and the hole was 6.5mm :mad: -about 0.2mm to big.



To solve this I drilled it out further to about 8mm using a little home made small boring bar made from an old drill. It is too long to be very stiff but as long as I only take 0.025mm cuts it cleans up the hole very nicely. I only have metric 6mm and 7mm reamers so this had to do.



I then made a brass insert from a bit of brass I had already. I bored its hole to a close fit for the crankshaft and made the outside of it a tight press fit with the crank. The finished item is here with the crankshaft.



Now I just need to get more time to work on this model. :)
 

NickG

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You're getting on well with this Terry, great work.

Dean that's good to know and I'll watch out for it in case you do a log.

Nick
 

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