Bog's Paddleduck Engine

[Stilldrillin]

That`s taking shape nicely! 

David D

[bogstandard]

Kirk,

Coming along great now, you are doing a wonderful job of it seeing as you are making it a non standard size. I think that there is a mention in the text about making the holes in the bottom plate so that the bearing blocks overhang the edges slightly.

He also has a shaper attachment for a BP mill that I can have

I would suggest you take his hand off at elbow level. The slotting head can be used for allsorts, from cutting keyway slots to square holes. Even if it only gets used once in a blue moon, it is doing no harm hanging out of the way at the back of the head ram. If he comes up with a right angle milling attachment, take his other hand off. That is one bit I would like, but finances are stopping me at the moment.

John

[kvom]

I got the shaper head home and did some disassembly to check the working/condition.  It's not a BP, but made by Lilian Co. in Taiwan.  It is missing the clevis that would allow it to mount on the back of the BP ram.  I suspect it was permanently attached to the front of a ram as it had a weird setup on the end of the tool ram that looked like it was some some of textile fixture.

I was going to plug it in to see if the electrics worked, but the plug has a different pin configuration than the plug for my lathe does.  Motor is 3PH 3/4HP running a 5-sheaf pulley.  Stroke is up to 4".  There is a homemade control box with e-stop and jog buttons, in addition to the power on/off switch on the head.  Pictures can be viewed here if anyone is interested:  http://www.pbase.com/kvom/slotting_head.

As for the engine, I did a test fit of the conrods to the cranks this afternoon.  As I mentioned in an earlier post, I had made them wider than spec since my crankwebs are narrower.  Since the crosshead slots are to spec, I will need to narrow that end to fit, and plan to cut a taper in the center.  Not sure that I will get to that today as I have shop class this evening.

[kvom]

Today I narrowed the heads of the conrods to fit the cross heads.  I removed the top section and attached the crosshead guides to check for fit.  The crossheads went on fairly cleanly, even without any extra "wiggle room" with the guide mounting screws.  I did find that one of the guide rods was slightly bent, so I needed to make a replacement.  I found that my rear temporary columns were too thick and interfered with the crossheads; so I needed to turn them down to clear.

Then I made one of the link pins to connect the conrod to the crosshead and put it together with the crankshaft, as shown here:



I am able to turn the cranksahft by hand and move the crosshead up and down, albeit somewhat stiffly.  The conrod is still a bit wide and rubs the crankweb.  Since I plan to taper the conrods this issue will go away.

Progress might be slow the next week as we will have houseguests.

[Brass_Machine]

Kirk,

That is progress so very nicely. I am envious of this endeavor. Keep up the good work.

Eric

[sbwhart]

Coming together nicely Kirk  its always good to get start to get things assembled things will really progress quickly know.

Great Job 

Stew

[kvom]

Only had a couple of hours or less today.  Turned the conrods between centers.  I couldn't taper the entire shaft but got reasonably close:



Here's the setup:

[kvom]

My goal for today was to get the entire bottom end assembled and turning.  I had to remake both of the smaller crankshaft pieces as they were slightly short and as a result some of the crankwebs were not gripping enough.  Lots of disassembly, re-assembly, etc.  I finally got it all together, oiled up, and locked in the mill vise.  Then I used an electric drill to turn the crank.  I ran that for about a minute at a couple of hundred RPMs.  Now it's still a little stiff, but I can turn the entire assemblage by hand holding the flywheel.

I then turned my attention to the pistons and piston rods.  Cut a length of 3/16 drill rod to size, turned on end down to .155 and threaded it 8-32, which is what I had previous tapped the pistons for.  After some polishing on the lathe, I attempted to use the mill to lap one of the cylinders with the piston; all was well for a few seconds until the threads in the aluminum piston stripped out.   

I decided at that point to remake both pistons from steel.   

It's unclear from the plan how much the crosshead end of the rods should be threaded, so I need to do some measurements.

[kvom]

Somewhat frustrating afternoon once again.  I decided to remake the pistons in steel, and spent a fir amount of time turning them and polishing on the lathe to get a press fit.  After parting off I attempted to tap one of them with my Kobalt 10-32 tap (since that will match the 3/16" piston rods), and the tap broke.     Too late to switch to 10-24 as the hole in the other was already drilled too large.  I also failed at cutting the 10-32 threads on a length of drill rod with a die (threads were slightly crooked).  Next time I'll rough cut them with the lathe, and then finish with the die at the end.

Tomorrow is another day.

[Bernd]

Kvom,

Keep the faith, some days ya' just can't get it right.    I find doing something else for a while helps.    Then the next time you get back to the project it all falls into place.

BTW, I can't wait to see this engine run.

Bernd

[kvom]

Better progress today in a short 90 minute session.  I finished the glands for the valves, where previously I had made the gland and screw.  Tonight I drilled and reamed the through hole for the valve stem as well as the two mounting holes.  I was apprehensive about this step, but all went smoothly.



Although I didn't see anything in the plan about where to drill the mounting holes in the steam chest, John's photo shows them fore and aft.  That's a job for another day, as well as lapping the valves into both the glands and the valve bores.

[kvom]

Today I managed to get the valves lapped into the steam chest valve and drilled/tapped the holes for the glands.  Otherwise too much time occupied with family visitors.

[Bernd]

Hey at least your making progress. Mine seems to have come to a hault here.

Bernd

[kvom]

Today I milled the steam slots that connect the steam chest holes to the block holes.  As mentioned in a previous post, it's possible to mill the slots in the block rather than the steam chests, and that's what I did.  I used a 1/8" endmill cutting .11" deep.

I also made V3 of the pistons, this time threaded 10-24 for a stronger joint with the piston rods.  The other end of the rods are 8-32 for connecting to the crossheads.



I managed a better fit on the pistons by taking tiny cuts on the lathe.  One is already a tight slip fit on one cylinder; the other will require some more polishing.  If I can get the pistons lapped I'll drill and mount the glands next.

[kvom]

I lapped the pistons so that I have a good sliding fit.  I tapped the hole in the crossheads to accept the piston rods, and assembled the block and top plate to the bottom with one piston in its cylinder and the rod screwed into the crosshead.  Although the mechanism operates fairly well (able to turn the crank by hand), there is an obvious issue: at TDC the piston protrudes through the top of the block.   

Since I had made the piston rod to the same scale as the rest of the parts, I am wondering if the 75mm on the drawing is correct.  I checked the rest of the critical elements (stroke, length of conrod, height of columns, height of bearing blocks), and all seem correct.  Doing some measurement of the piston postions I concluded that my piston rod is .45" too long, corresponding to 7.5mm off the plan's size.

[bogstandard]

Kirk,

If the engine is built to plans, the measurements should be almost spot on.

No-one has come back with any problems such as yours, and it seems enough allowance was made on the parts to allow the engine to be tweaked into the correct position for running.

It might be that you are not following the plans in the correct order, and are using the wrong measurements, and also because you are scaling up, maybe the allowances are not correct for your engine. This is always a problem which changing scales

If you have a look at the two extracts, it shows there are two different lengths for the rod. The first to allow the rod/piston combo to be made, the second, where the final lengths have been found. Are you using the first measurement?, as that will certainly give a rod that is too long.





If you look at the difference between the two lengths, multiplied by your scaling up, it is showing something close to the error your are finding.


John

[kvom]

Yes, I missed the second part.  Thanks for pointing it out.  I wasn't too worried since it was/is going to be straightforward to shorten the rods.

In the meantime I drilled/reamed the packing glands, and will be drilling/tapping the mounting screw holes next.

[bogstandard]

Kirk,

I am sure you will get it all running just fine.

You still have time to bore it out bigger and turn it into the monster you are after.


John

[kvom]

One step forward, two steps back.   



I drilled the gland mounting holes and the block, as can be seen.  Why the missing screw?  Because there's a broken 5-40 tap in the hole.     So I will get a chance to try to dissolve it out a bit later.  In the meantime it's not holding up progress.

After screwing down the glands my piston rod/piston assembly wouldn't go in; turns out the thread on the piston iend of the rod is slightly tilted, so scrap one piston rod.  In addition, I had a bright idea that instead of cutting an external 8-32 thread on the crosshead end of the rod, I would drill and tap an 8-32 hole in the end and use a bit of 8-32 screw for the connection.  In theory it should work, but the two I tried ended up with the hole slightly off center.  At least the threads were straight.  I still have enough 3/16 drill rod for 4 or 5 more tries at good piston rods.

It's getting "tricky" to figure the sequence for putting everything together.  I believe the best approach to connect the bottom and top sections is to have the crossheads as part of the top, so that you need only bolt the crosshead to the conrod and the top plate to the columns (haven't made the eccentric linkages yet).

You still have time to bore it out bigger and turn it into the monster you are after.

In reality I chose to go bigger so that I could work with bigger parts (I'm still not too confident working at small scales).  Given that the displacement will be 3.4 times the original, it may be a "monster" already.  The air channels will be only 2.25 times larger in cross section, so it will be interesting to see how much air it will need.

[CrewCab]

there's a broken 5-40 tap in the hole. 

Dammit, that's a bug**r ..... hope you manage to get it out Kirk  ............ the build is coming along very well, really enjoy following it, thanks for the progress reports.

CC

[sbwhart]

Ho that annoying breaking the tap  , are you going to try alum to desolve it out ?.

The builds looking very good though    keep up the work, and the post are excellent.

Cheers

Stew

[kvom]

are you going to try alum to desolve it out ?.

That's my plan.

In the meantime I managed to screw up another piston rod (too short, measure twice, cut once).  I think I have enough drill rod for one more shot at getting them right before I need to order another stick.  I'm waiting for another "free shipping/$25" offer from Enco.

So I switched to something less stressful and milled out the sides of the top plate in order that the steam chest can join the block now that the glands are in place.  Other than the piston rods, the main pieces I need to finish for a first run are the valve linkages to the eccentrics and some temporary inlet flanges, like shred made.

[kvom]

Here's my results for the day's activities.  Rather than worry about getting straight threads on both the piston and piston rod using my crappy dies, I decided to experiment by turning the piston and rod from one piece.  The first one worked well so I made the second. 

Because there are fairly tight fits on both the cylinder bore and glands, any deviation would tend to bind.  By turning them together, they're concentric and (hopefully) straight.  I still have to thread the ends for the cross heads, but any issue there can be adjusted by enlarging the mounting holes for the crosshead guide rods to allow "wiggle room".



In any case, I have a good sliding fit on one cylinder, while the other needs a small amount of lapping.

[kvom]

I spent some time in the shop today on "fiddly stuff".  First order of business was getting the second piston to fit its bore.  A few seconds turning on the mill with some fine-grit emery cloth and some scotchbrite got that done.  Then I made another temporary column to replace that one I sacrificed to turn one of the pistons.  Then the boring job of cutting down screws to attach the top plate to the block.  Next drilled and tapped the forks for the eccentric connection, and also milled and drilled the little blocks that go into the slots.  Finishing the eccentric linkage will require me to get ready for silver soldering, which is still on the todo list.

I then spent some time looking at the drawings for the steam control.  I don't have any flat brass stock thick enough to make the block, but using 2" round the block will be only .06" small.  I could possibly use aluminum, although it's not on the "recommended material" list.

Earlier I was cogitating on how the valving works.  It would seem that the main points are as follows, assuming the top holes are steam and the bottom are exhaust:

1) For the power portion of the stroke, the piston is near the top and the valve moves lower, opeing both holes.  Steam or air enters the valve bore and can go in only two places, the cylinder or via the bore in the valve into the bottom of the valve bore.  Since the exhaust hole is blocked from the bottom of the bore by the lower valve disc, all of the work will done by the steam pressing on the top of the piston.

2) For the start of the exhause stroke, the piston is at the bottom moving upware and the valve moves upward.  Now the air or steam is forced by the piston back into the valve bore, where its only path is through the hole in the valve piston to the bottom of the bore.  Now the exhaust hole is exposed so that the steam can escape.  During this time the supply hole is also open, but the stream is confined between the two valve discs.

1)

[bogstandard]

Kirk,

It is because of that swap over period that the distance between the two spools has to be spot on. Otherwise you would be having both pressure and exhaust trying to go into the same chambers. That is the reason I showed how to measure the distance between the porting holes and transferring it to the piston valves. Any more than a couple of thou out and you can start to run into timing problems.

Aluminium would be a difficult material to use for the fwd/rev valve casing because you would have to use mechanical fixings to join the pipes to it rather than silver soldering. You should get away with using a mild steel, if you can get the internal finish good enough. The soldering flux I sent you will cope with anything up to stainless steel, so it should easily join copper to steel.

John