Bog's Paddleduck Engine

[kvom]

After I posted previously I went and sliced off some 2" brass round and machined a square block from it.  I'll start drilling the holes next.

[kvom]

Today I started on the steam control block, which is the last component needing to be machined and the last assembly that can be completed until I am able to silver solder pieces together.  Here's the block and spool, along with the elements of the eccentric linkage completed since the last photo:



I made several errors in machining the block, none of which I think (hope) will require remaking it. 

The first issue was in drilling the mounting holes for the flanges.  I was using the vise stop to center all of the holes on the edges, and apparently a piece of swarf or something got between the block and the vise jaw, causing these holes to be slightly off center.  To work around this, I will need to offset the mounting holes in the two flanges, but this seems reasonably easy to do.

The second issue was in the size of the 4 steam holes.  I just scaled these up from the 4mm plan spec, which means I drilled them 15/64.  I should have realized that I would be soldering 1/4" tube into these holes.  Since I machined the block out of 2" round stock, the block is slightly smaller than the plan scale would require (1.4" each side vs. 1.47").  This means that the holes are closer to the edge, and enlarging them would make them even closer.  However, it appears that I can enlarge the holes to 1/4" while keeping enough material between the hole and the edge.

Finally, I made the center hole overlarge.  I entended to drill it to 1/2" and then bore to .59".  To save time I drilled the hole using a 1/2" endmill.  At least the shank was 1/2" but the flutes made it a 5/8" endmill.  So after boring, the hole ended up with a diameter of .645".  This can seemingly be handled by making the spool larger to fit, and that's what I did.  I also made the spool shaft slightly oversize at 1/4" as I need to find an o-ring with a matching ID.  Once I get the O-ring the front and back caps can be machined.

[bogstandard]

Kirk,

You might find that the valve doesn't operate quite how it should.

When I designed and made the control valve, the diameter of the spool and porting holes was rather critical when it came to swapping over the inlet/exhaust. Allowing just a small 'dead spot' when in the off position before going to a pressure on position.

You might find that your 'dead spot' will be a little larger before the engine starts to be fed with pressure.

Oh the joys of changing scales and having to wing it.

But at least what you have done is a good job.

The learning curve coming up. Just hope you can get the silver soldering cracked. But if you follow how I did it, and DON'T use too much flux and solder on the joints, you should be ok.

John

[kvom]

John,

After studying the control block during machining, I now understand how it works.  Before I mill the slots I will do some measurements to ensure that they properly connect the inlet/exhaust holes in both positions.  I'm not sure right now, but I might need to angle the slots and/or increase/decrease the depth.

[bogstandard]

You are quite right on that method Kirk.

When the engine is stationary, the slots sit against the dead area between the porting holes, so effectively blocking all movement of steam or air. As you move either way it connects the ports and depending how much it moves, depends on how much pressure is allowed thru, acting like a restrictor, like your finger over the end of a hosepipe.

John

[kvom]

I had a full afternoon in the shop making the front and back plates for the steam control.  It took a lot longer than I expected as I had to turn both pieces down from 2" brass round, and I wanted to keep the waste of material to a minimum.  In addition, the boss on both is a close fit to the block, so some attention and repeated measurements took time.  I had located a 1/4" ID by 3/8" byt 1/16" O-ring at the local hardware store this morning, so I had what I needed.

Here's the assembly:



I didn't have any 6-32 SHCS so had to use these for the trial fitting.  I had been thinking of using stud and nuts here, but standard 6-32 nuts are too large and inerfere with the shaft.

The rear cap turned out to be a press fit to the block, so after screwing it in tio align the holes I pressed it in with the arbor press.  I don't see it coming out again.  I realized at that point that this part is unnecessary if you have the ability to bore a blind hole in the block for the spool.

Once I could measure the depth of the hole and the size of the boss on the front cap I could mill the spool to length.  I probably cut it too close as once the 4 pieces are fastened tightly together there's a lot of friction; I can turn the spool holding it with pliers, but not with finger pressure alone.  I imagine there is friction between the end of the spool and the bottom cap as well as the sides and the o-ring pressing against the front cap.  Once I make a handle I'll be able to assess if it's too tight.

Here's the parts disassembled.  I still need to mill the slots, pending some thoughts on other dimensions.



On the soldering front I located local sources for both firebrick and citric acid, so tomorrow I should have everything needed to get started.  The first joints to be attempted will likely be the eccentric straps to the linkage blocks.

[kvom]

Following the recipe in Chapter 5, I made an attempt to SS two scrap pieces of brass together.  The good news is that they are in fact together.  However the fillet is not as pretty as  could be wished:



In fact it seems that most of the solder remained outside of the joint.  The rod is 1/8", and I created a chamfer on the hole with a deburring pen.  I'm wondering if either the chamfer was too small or I used too much wire, or the wire wasn't tight enough to the joint.  I found that getting a loop or the wire around the rod to be awkward. 

I took the piece out of the pickle after 1 hour to take the pic.  Can I assume that it will be easier to clean up if I leave it in longer?

[bogstandard]

Kirk,

Looking at that, too much flux and maybe a bit too much wire, but because it hasn't penetrated the joint, it might be the correct quantity.

Silver solder requires a gap of approx 0.002" to penetrate down to join the parts together.

With tubing make it a slight slack fit, and very gently flatten the end of the tube into a slight oval. This will make it tight in the hole, but allow the solder to penetrate.

Do the same with solid rod or whatever, but tap the rod with a hammer or centre pop to deform it slightly (only on the area inside the hole, so it will not be seen). Again this will hold the rod tight, but allow the gap.

I normally paint a tiny amount of liquid flux down the hole, and only on the very end of the rod or tube and assemble them all together. You should only see a tiny amount of flux on the surface.

Wrap the wire around the rod or tube like a spring, and cut along it's edge. This will give a series of rings that will easily slide down the tube or rod, flatten them straight before use, you should be able to do it with your fingers, locate it down against the hole. Just use one ring for normal, two rings for a deep hole.

Do not play heat directly onto the flux or solder, only onto the main part, in your case the big bit of brass, somewhere around the other hole, or the end of the metal hearest where you want the joint, and watch the heat travel towards the required joint. As it heats up, the flux and solder will melt and flow into the gap around the two parts. As soon as you see the nice fillet form, take the heat away, wait for a few seconds and then drop it into a quench tank or your pickle bath. Half an hour in the pickle should leave the job completely free of flux and maybe a bit of copper plating over the job, this should easily be polished off.
If the part gets to bright red heat, you've cooked it. Usually a dullish red is sufficient for the main component.

These instructions are for the special flux and wire I have sent to you, other fluxes and solders might react in a totally different way. Especially plain borax, it is not worth even trying, you will never get a perfect joint with it. OK for the 1950's, but not modern day materials and solders.

The main problem with silver soldering is usually too much heat, too much flux and too much solder. Use the minimum you can get away with. If it is not enough, you can always put another drop of flux and a ring of solder and reheat. Just always watch for when the solder flows.

Hope this helps, if not, maybe a change in technique for your style of soldering. You will get it eventually, and once you do, it should be with you for life.

John

[kvom]

Thanks.  I definitely had a lot of flux, and also had the flame too close to the joint.  I'll try again tomorrow.

[rleete]

Kvom,

I've never silver soldered, so take this with a grain of salt.  However, having read Bogs post above, and having done more than my share of "regular" soldering (mostly sweating pipe joints), I think it sounds very similar.  It's one of those things that takes a bit of practice to get a nice looking and solid joint.  It takes time to learn how the heat flows, and where is best to apply it, and how much solder/flux to use.

When my dad first taught me, the pipes stayed together, but they looked terrible.  Scorch marks all over, dripping solder, and the possibility of burn marks on the surrounding materials.  It also took twice as long as he did it.  Nowdays, after 30 years of doing it, I can put most 'professional' plumbers to shame.

The one tip that I took out of Bogs post that struck me the most was the use of flux.  Apply it only where you need it, and use it sparingly.  That, too, will become more apparent with time and practice.

All that said, I thing you're doing a helluva job on this engine, and a very professional writeup.

[kvom]

I finally got back in the shop this afternoon.  The first order of business was to finish up and test something that a lot of people here have made:  a diestock for the lathe:



The small part is 1" CRS drilled and reamed .5" and turned down to .65", which is the largest diameter the lathe chuck can clamp.

The larger part started as 1-3/8" aluminum round, bored 1" x .4" deep for the die, with the opposite end turned to .5" to fit the other part.  Handles are 3/16" drillrod, and screws are 6-32 (I'll cut them down some later).

I also made a second try at silver soldering, and this time it seemed to go a lot better.  Here's the joint after 1 hour or so in the pickle:



This time I used a very little flux and chamfered the hole manually with a countersink.

[bogstandard]

Kirk,

Looks like you have both jobs cracked.

Nice two.

John

[kvom]

Past few days in the shop have been dedicated to working on the Jeep, after breaking a control arm bolt on Saturday that also resulted in a busted shock absorber.   

That said, this morning I took a little while off wrenching to silver solder the eccentric straps.  This is the result after 2 hours of pickle soak:



I used 3/16" drill rod turned down to .150" on each end.

[kvom]

Crawling under the Jeep replacing shocks left not much time for any engine building, esp. as I have a sore back as a reult.  That said, I spent a couple of hours making some temporary air inlets, copied from shred:

 

I also had to re-do soldering one of the eccentric straps.  Seems as if the solder did not go where it was supposed to.

Seems as if the only machining needed to be able to try out the engine under air is to fabricate the pins for the eccentric joint and thread the piston rods for connecting to the crosshead, and then I can try to put it together and do the "tuning".  If I can get it to run then I'll need to make some feet and try to figure out if I'm going to make the bent copper lines like shred or make the straight flanges.  I'd like to make gbritnell's tube bender, so I will investigate that option soon.

[kvom]

I did make the pins for the eccentric joint, but I also screwed up my pistons.     I used my new die stock to thread the ends 10-24 only to "discover" that the crossheads are threaded 8-32.   Not having any Al stock for remaking the piston & rod as a single piece, I decided to try to make them separately as now I have a chance to make straight threads on the rod.  I threaded the 8-32 end on one and it looks pretty good.

Going offroading tomorrow, so no progress until Sunday at the earliest.

[kvom]

I finally got all the parts made that are needed to try to get it running.  I started to assemble everything, and discoivered that one of the threaded holes in a crosshead that connects the piston rod is crooked.     No way it can ever work the way it is.

One option is to make another crosshead.  But I'm wondering if there is a way to fill the hole and redrill it.  Calling John!   

[bogstandard]

Kirk,

The normal way would be to drill out the offending hole oversize, silver solder a little bar of brass in it, then just redrill and trim everything up so that it looks nice.

If you can get a little bit of the same metal into the original but enlarged holes, you can rescue almost anything.

I don't know if you have read the article, but this shows just how to do it. In an hour or so, you should be able to see the finished article after rescue.

http://madmodder.net/index.php?topic=1370.0

Hope this helps.

John

[kvom]

I was thinking it was something along that line.  The hole is about .25" deep, threaded 8-32 and hence ~.160" in diameter. 

Once I drill it out, how much solder needs to go with the plug?  Am I trying to get the solder to flow all the way down the sides of the plug, or just around the top?

[bogstandard]

Make the plug slightly smaller than the hole, say 0.002" to 0.004".

Dip the plug into your liquid flux, paint a bit of flux down the hole, and push the plug down into the hole. If you make the plug longer than the hole is deep, you can always trim it back afterwards. Cut up one coil of solder wire so that it fits around the plug on the surface, it doesn't have to be a super close fit (if you are repairing a tapped hole, use two coils, so that the threads are filled up as well), as long as it isn't too far away from the hole it has to go down. Heat up the main part of the job and you should see when the solder flows down the gap. Take away the heat, let it cool down for a few seconds then quench and pickle for a while.

Dress up the the part to get it looking like it was before the bad hole was put in, then redrill and tap your new hole in the correct position.

All you are doing is filling up the bad hole with metal, then remaking the part from before you made the mistake.

John

[kvom]

I followed the recipe, and it worked like a charm!    Although I was irritated that I needed to do this, I'm glad to know the technique for future use.

Since the hole was both off center (at one end) and angled, I was reluctant to just drill it out, fearing that the drill bit would just follow the hole.  Since I have some 1/4" brass rod, I decided to use a 1/4" endmill centered on the new hole and encompasing the old.  After a slight chamfer, I did the SS thing.   Once I had milled the plug level with the top of the crosshead the repair was practically invisible.

Rather than risk doing the same error again, I clamped the piece in the vise such that the crosshead guide bar chucked in the mill would go straight into its hole, thus ensuring that the new hole would be parallel.  After drilling the new hole, I also used the mill to tap it.  That's what I should have done in the first place.

[kvom]

With all the working pieces fabricated, I wanted to put it all together for a trial fit.  Here's the result:



It's not quite ready to run yet, as it's still too stiff to turn by hand.  The main culprit is the right hand piston rod, which binds in the gland.   I think I will progressively test each eccentric and each piston separately to try to get them loose enough so that the tuning process can be done.  The bottom end (crankshaft) does turn by hand fairly easily, and the valves and one piston slide freely when not connected, so hopefully I can get it to run quite soon.

[Darren]

That is looking real good there, every time you post I think I should do something with mine....

So much to do and not enough time

Like I said, your build is quite something to follow....

[CrewCab]

Kvom  .......... well done wit the fix .......... nicely done 

The rest of the build ain't too shabby either 

Cracking work mate 

Dave

[kvom]

Thanks for the encouragement.   

I just spent the past hour fiddling with it.  The 2nd piston/rod combo is definitely not straight, so I will likely make it once again (#5 if I'm counting correctly).  The one piece design seems more likely to come out; since I now have some steel that's over .5" in diameter I think I'll try that again. 

With everything connected except that piston&rod, I can turn the shaft assembly by hand, although not easily.  I had to quit when my fingers sharter to get sore from pushing on the cranks and crossheads to move them.  I suppose I can hook up the electric drill, but since I heard John bad-mouthing that process I decided to wait for advice.

[bogstandard]

Nice one Kirk.

That is sure one big engine, comparing it to the size of the can.

I think you have now found out, thinking about doing a rescue can be a lot more gut wrenching than actually doing the job. In fact it can be a massive anti climax when you find out just how easy it is.
Now you have done it the once, all that worry shouldn't be there when you do the next one. You will be plugging holes and redrilling every chance you get.

You are quite right that I don't believe in solving problems by mechanically turning over an engine. Most of my repair work is caused by such actions, you only have to look at my latest repair job. So many worn out parts, before the engine is even running.

I am not saying you shouldn't do it in all cases, as I do it sometimes. Mechanical turning over should only be done on an engine that already turns over fairly easily by hand. I do it to align say crank bearings. Gently have it turning and then slacken the bearing and retighten, allowing the components to find their own perfect running positions. This usually realigns it much better than you can do it by feel.

Are you sure it is not the crosshead guide bars that are causing your problems? With the con rod disconnected, you should be able to push the piston up and down fairly easily. If it tightens up after putting the con rod back, it points to your two cross holes in the con rod not being perfectly parallel. In which case, if they are not far out, you can realign things to run by slackening off the two crosshead guide bars and allow them to find their own position, as the engine is turned over slowly, then a slow and gentle retighten until tight again.

It might not be this, I am just trying to help you fault find before you start to make new parts, that might not be necessary.

Best of luck and well done so far.

John