A two cylinder mill engine under construction

[Brass_Machine]

Looking good Phil!

When are you, me and Tin getting together for coffee?

Eric

[Philjoe5]

Eric,
For sure at Cabin Fever.  Anything else coming up before that?

Cheers,
Phil

[Philjoe5]

This posting describes making the connecting rods.  The con rods in the original plans have the big and little ends silver soldered to the rod.  An admitted hack at silver soldering, I’ve made the con rods one piece.  This means I’ll have a bit more milling to do.  Time spent doing the extra milling could have been applied to a few lessons in silver soldering I suppose but I didn’t want to spend the $ for a proper torch now.  Here’s where I’m starting and also where I hope to end.  The completed con rod is from a previous project.



A few hours later with most of the milling done I have two blank con rods.



Now I have some drilling and boring to do.  Being a believer in fixtures BUT being frugal I try to make as few as possible.  So I’ve drilled and reamed the small end and drilled the big end here to fit the fixtues I have.  Here I’m rounding off the small end on one of the con rods using the rotary table.



After taking the sharp edges off of the big ends on the rotary table it’s back to milling the angles.  I’m setting the milling angle in this picture.  That angle block is removed before milling.



Finally they’re drilled and bored to full size of 0.700” ready for a bronze bushing.  



I use two set screws to hold the bushing in place.  Are they necessary?  I’m not sure but they’re easier to put in now rather than later.  The picture shows two cap screws inserted to emphasize the threaded holes.

Finally the bushings are made from a piece of ¾” bearing bronze turned to size, drilled, reamed and pressed in position on the con rods.  I’m parting one off here:



The con rods are finished.



I’m nearly finished with the stuff that comes right off of the plans.  I’ve done some calculations for the baseplate and I think I have that figured out.  In its final form it will be a plate of 3/8” aluminum but I’m going to make a temporary one out of wood to check my math.  I have lots of cheap wood but no cheap metal.  More later.  At this point if I make the bearing blocks and crankshaft I can finish out the design for the base.  

The crankshaft will have the webs pinned in place so I can remove the flywheel or eccentrics for maintenance.  I’ve made up a design for the webs based upon some other engines of this type I’ve seen.  More details to follow, but right now I’m planning to pin the webs to the crankshaft with 6-32 set screws.  A good idea?

I think I’ll tackle the bearing blocks next.

Cheers,
Phil

[Maryak]

Phil,

Looking good, I agree with you solid is better than silver soldered, or flanged ends and split bushes through bolted.

Best Regards
Bob

[Philjoe5]

Time for my weekly progress report.  Bearing blocks are the topic of discussion this week.

I’ve machined the bearing blocks using a two piece design.  This is a modification from the plans that call for a split brass bearing attached to a steel base.  The sequence of machining is:  mill the steel base to dimensions, mill the brass bearing cap to dimensions, drill and tap the base, drill clearance holes in the brass cap and assemble the cap and base.  Next, drill and ream the brass cap.  Then mill excess off the brass cap and round it off.  Pictures of each step will help you see what I’m doing.  There’s nothing fancy going on here but careful work ensures the crankshaft fits and rotates freely when this whole assembly is mounted on the baseplate.

A short digression here.  I got into this hobby a few years ago and my immediate goal was to build some working engines, display them at some shows and meet some other folks.  Initially I built some engines with fairly simple machining techniques.  An example of one of my first steam engines is shown here.  Note the rectangular bearing blocks.  I hadn’t really figured out how to round the tops according to the plans.



Now, a year later, I’ve picked up a few tricks and have figured out how to do this.  So while I’m working on this engine, I’m going to jazz up the bearing blocks on my older engine using the same fixture and machine setups as my present build.

Starting out I milled two pieces of steel and brass to dimensions.  Then I tapped the steel bases on both sides.  Topside for mounting the brass bearing caps, bottomside to mount the bearing blocks to the baseplate.  Then I assembled caps to bases.



Next, comes the drilling operation for the crankshaft.  I know there has been dialogue on this board about proper drill bit geometry for drilling brass but I don’t have the means to have separate sets of drills for steel and brass.  So, necessity being the mother of etc., I found I can drill a pilot hole on the mill/drill in brass using the quill feed.  Then when drilling larger holes I switch to the fine feed (by handwheel).  The ability of the brass to grab the drill bit is countered by the mass of the mill/drill head and the whole operation proceeds smoothly.



After reaming the ½” crankshaft hole,


the units are assembled and a ½” piece of drill rod is set through the bearing caps to check for alignment.  In my former unskilled life, I would have stopped here at these perfectly functional but unattractive bearing blocks.



Next, the caps are removed and prepared for rounding the tops.  First I drill ¼” holes that define the start and stop positions for the end mill used for rounding.



Holes are drilled and excess material is milled away on the mill/drill.



Then the caps are mounted on a fixture.  The fixture is mounted in the chuck on the rotary table and using a ¼” roughing end mill I find the positions of the start and stop holes I had drilled previously.  I note the positions and keep them handy.  While milling I’m careful not to exceed either limit positions.



Here are all four brass caps milled:



The bearing blocks assembled for the new engine shown here



The bearing blocks for the old engine, shown here, installed.  Nicer than before, no?  Even better, the reassembled engine runs.



The next part I’m working on is the crankshaft.  I’m using a crank web design that’s fairly common.  I cut the two arcs on this steel disk with a boring head.  Although it’s an interrupted cut, it went smoothly enough.  Shown here is a trial cut on a piece of steel I fished out of the “recycle” bin



That’s it for now.  In a week I hope to show you a crankshaft.

Cheers,
Phil

[Maryak]

Phil,

Really like your technique for milling the round on the top half brasses

Best Regards
Bob

[Brass_Machine]

Great idea for those caps Phil.

I should be at Cabin Fever. Don't know if I will be working a booth or not (for CNCzone)... But I should be there.

Eric

[Philjoe5]

The past week was spent making the crankshaft.  My design has five major pieces – a main shaft, two crank webs and two crank pins.  The webs will be attached to the main shaft and pinned in place with 1/8” steel pins.  Since the flywheel and eccentrics are captive between the webs, the pins will allow for web removal when I first assemble (and disassemble) the engine to get it running.  Once I get the engine working I can loctite the webs to the shaft if necessary for semi-permanence.

The crank webs are 3/8” thick steel disks that are center drilled/and reamed 0.375”.  A ¼” – 28 NF hole is tapped at a distance of 0.688” from the center hole.  A ¼”-28 bolt attaches a sleeve to form the crank pin for attached the connecting rod.  There is a small hub on the crank web that’s 5/8” diameter and 0.030” thick.  This prevents the full wall of the web from contacting the bearing blocks in the assembled engine, thereby reducing friction.  

I faced the web disks on the lathe, made the hub, then center drilled/reamed the center hole.  Then I clamped the lathe chuck to the mill table, centered the spindle over the web center hole.  For this operation I use a piece of ½” drill rod in an end mill holder that’s well secured in the chuck that’s loosely clamped to the mill table.  Then, the chuck is carefully clamped to the table and finally the table locks secured.  



At this point, the set screw on the end mill holder is loosened, and the mill head is raised so that the drill rod clears the end mill holder completely.  Now the mill head is lowered so that the drill rod enters the end mill holder.  If there is no significant contact between the end mill holder and the drill rod, I’m done.  Otherwise I start over with clamping.  Other more tedious methods used to center the spindle over the chuck using dial indicators or edge finders never disagree with this method by more than 0.002” so if I can work to that tolerance (like here) I use this method.  Now the crank web is mounted in the chuck and the table is moved 0.688” and drilled/tapped with ¼”-28 NF threads.  



I was contemplating how to cut the arcs in the webs and keep everything aligned.  I can’t trust my eyes to align stuff so I’m thinking fixture.  I came up with this design.  



The center hole of the fixture is tapped 3/8-16 NC and the two ¼” locating holes are drilled.  I bolted the web to the fixture, set the arc diameter on the boring head to 1.50” (a purely arbitrary setting that looked good to me).  Then I adjusted the table x axis so the boring bar just kissed the edge of the workpiece.  I found I could use 0.015” DOC’s without making the machine or me nervous about this interrupted cut.  I cut in a total of 0.625” (again arbitrary), swung the web around on the fixture and cut the other side.  Here is a photo of the setup on the mill with the arc cut on one side:



then the other:



Both webs finished with the fixture used to make them



Then a piece of ½” drill rod was cut for the crankshaft.  It was faced off to length, then turned down to a diameter of 0.375” on each end to fit the crank webs snugly, but not a press fit.   I have heard (can’t remember the source, one of the steam loco groups I think) that one of the most common failures of a joint that is secured by loctite is a fit that is too tight, such as a press fit.  So I typically try for something between “close” and “press” fit and I haven’t had a failure yet.  The overall length of the crankshaft was “calculated” and has to be pretty close to actual dimensions.  I made it 0.020” longer than necessary to accommodate 2 cranks webs, 2 eccentrics and a flywheel and 2 bearing blocks.  This photo shows the crank webs temporarily mounted on the ends



Here, I’ve mounted the crankshaft on the bearing blocks



I’m in the mood for some lathe work so I’ll tackle the flywheel next.

Cheers,
Phil

[Philjoe5]

Since my last post I’ve made a flywheel.  Nothing fancy but functional.  Plans call for a 6” cast iron wheel but I’ll be using some barstock I have on hand.  I have some 4” diameter hot rolled steel and I’ll make a flywheel out of that.  I cut a slice off my stock that’s about 1.5” thick.  Next, I faced it off on both sides, cut a recess on both sides reamed the center hole ½”.  I tapped two holes with 10-32 threads for set screws.  I start these holes at a 30 degree angle from the vertical using a centercutting 1/8” end mill.  



Here’s the flywheel, hub side up with two cap screws in place (not the set screws I’ll be using) to illustrate placement of the set screws.



Now drill some ½” holes so the spinning flywheel looks interesting



Am I done?  Not quite.  A little paint does wonders:



I’ll call the flywheel finished.  Now that I’ve cut the crankshaft to length I’ve pretty much determined the spacing of the two cylinder blocks.  Now I can layout the cylinder blocks and the flywheel and bearing blocks on a wooden baseplate.  With the cylinder blocks and bearing blocks mounted on a baseplate I can hook up the con rods to both cylinders (without any valve operation) and see how smooth movement is (or not!).  

Next up for machining are the eccentric straps and the valve rod bearings.  These are fairly small pieces so I found some stock in the recycle bin and sliced off some workpieces on the bandsaw.  Next, I milled them to size.  Then I drilled/tapped them and finally I reamed some pivot holes.  These are going to serve as pivot points on the rotary table for rounding these parts.



Rounding one of the eccentric straps



One of the eccentric straps being bored out



And the completed straps and valve rod bearings



Now I’m off to visit my brother who just broke a bone in his foot falling off a ladder.  

Cheers,
Phil

[Brian Rupnow]

Philjoe--You are going to love the way that thing runs. Its a totally different world from single cylinder engines.---Brian

[Maryak]

Phil,

Way to go, great cranks and flywheel. 

Best Regards
Bob

[Philjoe5]

I’m working on the valve and its operating parts.  I’ve made the eccentric straps and valve rod bearings so now I’m on to making the eccentrics.  A week or two ago I started making one of the eccentrics.  I was midway through when I realized, NO!, make the part that’s bored out first, then turn the other part to fit.  I finished turning the part to its nominal size but then when I went to separate it from the rest of the barstock I cut it 0.030” too short.  It was almost like when I first realized I was making the “wrong” part first, it was destined to end up in the recycle bin.

So I made two eccentrics this week that differ in minor diameter by 0.001”.  I turned each one to fit one of the straps.  I like a nice close fit here, probably closer than necessary.  I’ve begun to realize making this two cylinder engine that a new challenge arises in a multi cylinder engine, ie, keeping track of what pairs of interacting parts go together.  I’m using witness marks to keep track of mating parts.  Maybe that will be my next engine – a multicylinder with completely interchangeable parts.  Sounds easier than it probably would be.  

With 2 drilled/tapped holes for 10-32 set screws the eccentrics are finished.
Here, the straps are fitted onto their corresponding eccentrics.



Next, I fished some ¼” steel scraps from the recycle bin for making two valve arms.  I’ve deviated from the original plans in making these.  Plans call for filing a ¼” square hole in the arm and pinching it onto the valve end with a 4-40 screw.  My design is all machine work which is easier to do for me.  I milled a ¼” slot in the arm, then made a cap that fits over the slot to hold the valve in place.  The slot is milled 0.010” undersize on the vertical dimension so the cap actually clamps the ¼” square valve end.  The valve arms are pictured here clamping a piece of ¼” square steel bar to test for fit.



Valves were made from ½” brass rod.  I turned them down to a diameter of 0.374” to fit the 3/8” reamed hole in the cylinder block.  Then they are milled to produce two flats near the middle to act as open steam ports for each end of the cylinder, thereby producing a double acting mechanism.  The completed valves are shown here:



Installed in the one of the cylinder blocks with the valve arm attached to the valve



I had one of those Aha! moments this evening.  I’m sure this has happened to some of you out there.  Machining an engine or other mechanical device requires quite a bit of concentration at times.  I’ve been working on this engine for over 2 months and I’ve been in the trees for so long I wasn’t paying attention to the forest!  By golly, I don’t have that many parts to complete.  Steam inlet flanges, crank pins and the baseplate and I’m done.  I’m having déjà vu all over again because it was just about a year ago when I completed my first engine (of this design actually).  

I made two sleeves for the valve rod bearings.  Learned a good lesson making them too.  Wasted time is wasted, no matter how trivial the part.  I turned the minor diameter of my first sleeve to a diameter of 0.249” to fit the ¼” reamed hole in the bearing.  Next I center drilled it in preparation for drilling a clearance hole for a #10 screw (#9 drill).  Then, since I wasn’t reading the plans I put a ¼” drill in the tailstock chuck and started drilling away!.  If anyone needs proof that 0.249” – 0.250” is a negative number, I have the proof in the chip pan under the lathe.

Here’s a pic of the valve trains, one assembled, the other in parts.



My next post will be a completed engine.  I’m making a baseplate from wood to test out my dimensions, then later I’ll use a piece of aluminum plate.  Once I get the dimensions correct, I’ll pin the crank webs to the crankshaft with some #8 set screws.

Cheers,
Phil

[CrewCab]

Phil, this is really looking good  ......... please keep it coming.

CC

[dsquire]

Philjoe5

It sure looks to me like you are doing an excellent job on all the bits and pieces for your engine. I'll be watching for the finished engine when it comes.

Cheers

Don

[Brian Rupnow]

Philjoe---This may be kind of a dumb question, but how are you going to drive anything with your twin cylinder engine. Based on what I see of your photoshopped image at the beginning of this thread, the only way you can take off a drive from this engine is off the outer diameter of the flywheel. When I designed my twin, I considered doing it exactly as you show, but the thing that kept me from doing it that way was the inability to have an exposed driveshaft to put a pulley on.---Brian