Another Radial - this time 18 Cylinders

[mayhugh1]

Sparky,
Thank you for the complement. The bender that I'm using is a handheld unit from Rigid. My wife got it for me two years ago for Christmas when I was doing the piping for the H-9 I was building at the time. Its not stocked in the usual home supply stores. She had to look up a Rigid dealer on line. You have to buy the unit for a particular diameter tubing.
Here is Rigid Youtube demonstration videos of it in action:

[ame]https://www.youtube.com/watch?v=ATrDYYPsXaw[/ame]

Terry

 

[cfellows]

Really Pretty, Terry. Not only your usual flawless work, but highly pleasing to the eye as well.

Chuck

 

[vederstein]

That bender looks exactly like Swagelok benders I use at work. The only difference is the color of the label - but the text and font is the same. I wonder who the actual manufacturer is?

...Ved.

 

[mayhugh1]

I spent a few more days playing with my CAD models and mock-up parts looking for a way to avoid splicing the intake pipe assemblies. I made some small changes to the area around the flange recesses on the test heads and played with the flange thickness, but the fits of all the involved components are just too close.
A very thin flange with lots of clearance around it is the only way I can see to make it work, and I've convinced myself that's what the Chaos guys did. I modeled a thin flange mounted in a shallow recess to maintain the current appearance I want to keep, but I soon remembered the deep recesses weren't there just for cosmetic reasons. They have to be deeper than the fin grooves or their remnants will pass through the sealing surface and create leaks. I considered adding a second gasket and spacer to fill in a portion of the recess, but with the minimum gasket margin I have around the tube openings the risk of creating a leak is just too great. So, a splice is now part of my design.
A short Tygon sleeve looks like it will work, but a better looking solution that I'm thinking about is a stainless steel sleeve. If I build the pipe assembly as a single unit and then cut the long straight tube into two pieces with a thin slitting saw there will be room between the two butted ends for a small compressed o-ring. After installing the two sections and slipping in the o-ring, I should be able to slide a thin stainless sleeve over the joint to hold the ends in alignment and the o-ring in place. With the right amount of compression the friction of the o-ring may keep the sleeve in place. I mocked up a splice and vacuum tested it with some o-rings I had on hand. It looks like the o-ring selection will be a compromise between ease of assembly and amount of friction generated to hold it in place.
Since the flange design was no longer a variable; and since I want to make some progress on the high volume work, I made a run of 28 flanges using my original design. One of my $10 end mills cut for nearly 8 hours while making those parts, and there is still life left on it.
Since I only have about half of the scrap 5/16 stainless tubing on hand that I need for this project I had to order a length from an online vendor. I specified 316L (low carbon) annealed tubing because I may have to tig weld the 'Y' in the assemblies. It arrived just as I was deburring my run of finished flanges. I discovered the new tubing measured .316" in diameter while the scrap tubing I had been designing around measured .310". So, it looks like I'm going to have to re-ream the flanges. For deburring I ran the parts in my little vibratory tumbler with tiny (approx. 1/8") ceramic ball media for about 10 minutes. I can only run 3-4 parts at a time because the parts seem to find one another and sometimes scratch up already polished surfaces. When I manually de-burr the edge of a reamed hole I use the nose of larger reamer as a deburring tool. For instance, on the .312" flange bores a .355" reamer with a nicely beveled six-fluted nose works great and gives a nice smooth finish. I typically don't use my good reamers for this, but instead I use specialty-size carbide reamers that I occasionally run across in surplus sales.
Continuing with the high volume work, I milled the clearance slot in the rear row test head for the front row intake pipe using a 7/16" ball cutter to clear a worst-case 3/8" diameter splice sleeve. After verifying the fit with a Tygon sleeve, and while the setup was still in my manual mill, I went ahead and cut the clearance slots in all the rear row heads. The flange recess cutting program is the last head operation to be done on the heads, and it will be run after the valve cages are installed. Now, I also know I'll have to adjust the bore size for the larger intake pipes.
At this point, the most logical step would probably be to install the valve cages so I can completely finish up the heads. Since the intake assemblies have gotten hold of my interest, though, I think I'll continue with them for a while. -Terry

 

[mayhugh1]

I definitely ran into a difficult and frustrating phase of this project. I spent dozens of hours and used up all the tubing that I had to wind up with only two rear intake tubes having a reasonable fit between a rear head and the crankcase plenum. This tube has two bends that are orthogonal to each other. One end of the tube extends into the plenum through a close-fitting reamed hole in the center of a nut and is sealed with an o-ring to the crankcase by the compression of this nut. The other end passes through a .300" thick flange/gasket combination and protrudes into the head about 1/16". The flange at this end will eventually be hard soldered to the tube in a fixture, and then the flanged assembly will be bolted into the close-fitting recess in the head. I have net clearances of only about .003" at each end of the tube to work with, and so the final shape of this tube has to be very accurate. The lengths of the close-fitting bores into which each end is inserted are long enough that it is also important that the tube ends wind up precisely perpendicular to each other.
My CAD model has been useful only as a starting point because so many second order effects creep into the process of bending this tubing, and I empirically found the bends need to be accurate to less than a quarter degree. And, even accounting for spring-back, my bender doesn't seem to make perfect constant radius bends probably due to uneven work-hardening stresses induced in the tubing during bending. I eventually wound up with two reasonably fitting tubes, but the yield of my free-hand bend-and-tweak process was only a few percent. Even using the special tools I made, my hand tweaking usually distorted ends of the tubes beyond usability.
The challenge then became making a set of fixtures and templates to make the process repeatable. Since I'll likely need several practice parts to use while coming up the learning curve for joining the two tubes, I probably need more than a dozen finished parts. The clearances I'm currently working with are probably unrealistic for the final assemblies, but I want to maintain them while making the individual parts.
I used red oak for several of the fixtures and templates. Their creation, for the most part, was by trial and error; and working with wood let me iterate more quickly and cheaply than with metal. I was also never able to characterize the actual shape of my bends to the precision that I needed, and so I took advantage of the compliance of the wood which didn't mar the tubing.
I ended up with 10 fixtures and templates just to create the single rear row intake tube. This number could have been greatly reduced by combining the fixtures (used to verify bends and rough cut lengths) with the templates (used for checking finished lengths). But, once I had a working fixture it became 'gold', and I didn't want to make any changes to it. Two overly complex fixtures eventually emerged to hold the small irregularly shaped tube so it could be safely cut to length on my vertical bandsaw. My fingers ended up in the saw blade several times during my initial bend-and-tweak phase.
The most interesting fixture was CNC'd in aluminum, and it is the final rear tube fixture that is used to cut the notch for the 'Y' with the front tube. It was created in CAD from my engine model, and it precisely determines the position and shape of a milled tube notch. The intersection was designed for a wide flat interface between the two tubes which, hopefully after joining, will become invisible. The closeness of the fit-up of this joint will help determine the actual process I later use to join them. The clearances in this fixture are significantly less than those in the other fixtures, and so it also serves as a final go-no-go template for the rear intake tube.
The first photo shows the scrap I generated while characterizing my bender and coming up with only two usable hand-bent-and-tweaked tubes. Some of this scrap will hopefully be useful later for welding/solder practice. The next photo shows the series of tools and fixtures I created while coming up with a repeatable process for making the rear intake tube. The last photos show a test run of eight parts I made using this process. Only one of the eight parts was rejected due to a poor fit.
The next step is to create a similar process for the simpler front tube and to see how precisely I can fit-up the joint between the two tubes. -Terry

 

[jaggus]

Thats kol. lot of work there.

 

[gbritnell]

Although my perseverance is quite good when working on my engine projects I think that the tubing bending and fitting would come close to wearing me down. Wonderful job on the engine!
gbritnell

 

[mayhugh1]

After a lot of geometry and some machining I finally had a fixture to make the front intake tube. This tube is long and straight with a simple 90 degree bend. But, it's complicated by the fact that one end needs to be machined to fit into the notch of the angled rear intake tube. The goal is to match the rear tube notch as closely as possible while maintaining parallelism between the right-angled front tube and the three axes of the engine. As the photos show I was lucky and got pretty close. I did, though, have to make a small modification to the rear tube notching fixture and then re-work the run of rear tubes that I had already made to correct for an error I had made in that fixture. Fortunately, I was also able to verify similar fit-ups in the other head positions around the engine. With fit-ups this close, one of the options for joining the tubes becomes a thin (.005") disk of silver solder inserted in the interface between the two tubes. An ideal soldering fixture will exert a small force on the joint to push the tubes together and into final position just after the solder melts so my hands can stay completely out of the process. According to feeler gage measurements, the two faces at the interface seem to be parallel to better than .001". The surface area at the interface is .057 in^2, and the silver solder tensile strength is 16 kpsi. If the soldering goes well I could end up a strong (900 lbs), vibration resistant joint.
For testing, I've ordered minimum quantities of two hard solders that are compatible with 300 series stainless. The first is Silvaloy 355 which is a popular 56% silver (probably with nickel) alloy designed for stainless and sold by Brownell's and others in .005" sheet form. Since it doesn't contain cadmium it's marketed as a good color match to stainless. The second is a similar silver/nickel alloy that does contain cadmium, is also available in .005" sheet, and is sold by McMaster-Carr. This solder may flow more easily than the Silvaloy, but the cadmium will give the joint a yellow tinge if I don't manage to keep the solder wholly within the interface. For flux, I still have a double lifetime supply of Brownells 'Ultra Flux' left over from my H-9 project.
After verifying that random tube pairs fit up similarly in the other head-pair locations around the engine, I went into production mode and made the 40 tubes needed for 20 assemblies even though I really only need 9 completed assemblies. I'm anticipating a steep learning curve with the soldering, and I expect some finished assemblies may fit better than others. So, I want plenty of parts to work with.
I also created a fixture for making, what seemed at the time, the much simpler exhaust pipes. Because I didn't have a plan when I started this one it took me five iterations before I had a final fixture. In order to avoid interference with the heads, the exhaust pipes have to turn upward at a sharper angle than my minimum bend radius will allow. I had to cheat some and move a portion of the curved section pipe into the straight bore of the flange. This required increasing the diameter of the flange bore; and, later, a fixture will be needed to hold the pipe in proper position during soldering. I then made enough exhaust pipes also for 20 assemblies.
The next step, while waiting for the solder to arrive, is to create the last fixture to hold everything in position while the tubes are being soldered into a final assembly. This fixture needs to faithfully replicate the positions and orientations of the tube flanges and plenum compression nut bore that exist in the actual engine.
For now, I've all but given up on tig welding the assemblies even though, with the fit-up I have, I would get away without using filler rod and probably end up with a nice looking result. After my experiences with the fits of these parts during the past few weeks, though, I'm afraid the stainless will move around too much under the heat of welding. And, designing the holding fixture for access around the entire joint will greatly complicate its design. If the sheet solder approach doesn't work, my current plan B is to wrap a ring of solder around the exterior perimeter of the joint and flow the solder into it with an exterior fillet. For that reason, I've also ordered some 1/32" diameter color-matching Silvaloy. -Terry

 

[barnesrickw]

I'm blown away. Your jig and fixture use is very inspiring.


Sent from my iPad using Model Engines

 

[petertha]

Hi Terry. Awesome work as usual. I'm not sure if you are already familiar with Kent's offerings, but thought I'd point it out in case. Last fall I treated myself to his OA torch class. (A long haul from Canada, but beautiful part of California & big checkmark off my bucket list . Anyway, I'm pretty sure this is one of the goodies we got to try. I recall the solder color being very close to native stainless, but not 100% & obviously its wire not sheet if that was a requirement. I'm sure he'd be happy to provide details.

https://www.tinmantech.com/html/silver_solder.php

 

[mayhugh1]

Peter,
Thanks for the info. Yes, I'm familiar with that particular solder. I bought the identical product from McMaster Carr a few years ago and just checked, and I still have it. I didn't realize the tensile strength was that high, and so I wasn't considering soft solders for this application. It's now a definite possibility for me to try. I was thinking earlier that even if my hard solder sheet idea works the joint appearance might be improved with an exterior fillet. The lower temperature of this solder might be perfect for adding it.

Thanks,
Terry

 

[mayhugh1]

All my tubing work literally comes together in this final soldering fixture, and so it deserves its share of thoughtful planning and careful construction. It has to present mounting surfaces for the two intake/exhaust flanges that accurately match those in the engine while supporting the bottom end of the rear intake tube in a precisely simulated plenum bore.
The flange mounting surfaces and their orientations were computed from my model, and their dimensions were checked against measurements on the engine mock-up that I've been using to test fit the tubes and validate the numerous fixtures and templates.
I used hot rolled steel for the entire fixture rather than more easily-machined aluminum in order to reduce heat conduction away from the joints during soldering. The wide range of heights among the three mounting points made it impractical to machine the fixture from a single piece of steel, and so I decided to make up a welded assembly. Even though the pieces were only tac-welded, the welding left stresses in the assembly that had to be relieved. I did this by heating the weldment to 1200F for 2-1/2 hours and then allowing it to slowly cool in the oven overnight. If the stresses had not been relieved prior to machining, the silver soldering temperatures would have eventually relieved them, and the dimensions of the fixture would also have creeped over my run of parts.
Construction started by squaring up a half inch baseplate of steel. Three pieces of 3/4" thick steel plate were cut and squared up for the mounting surface columns. Some material was drilled out of the columns just below where the flange mounting surfaces will be later machined in order to increase their thermal resistances. Shallow pockets were milled into the baseplate to locate the positions of the three columns prior to welding. The columns were also rough machined to within .030" of their final heights before welding because of the difficulty in removing large amounts of material later. The components were tig welded, and the entire assembly was then stress relieved. For this step the weldment was sealed in a stainless steel foil package that was filled with argon welding gas to prevent scaling. After cooling, the bottom of the baseplate was re-ground flat. Keeping the baseplate flat and square will become important if the assembly has be returned to the mill vise for re-work after the machining has been completed.
On the mill, the top surfaces were drilled and tapped for the flange mounting screws. Shallow bores were drilled and reamed on either side of the mounting holes to match those on the flange mounting recesses in the heads. These bores allow the tubes to extend slightly through the flange and into the fixture just as they will when they are mounted to the head. Since the ends of the tubes are slightly beveled, though, they can't be used to accurately locate the flange on the fixture during soldering. Therefore, an alignment edge was incorporated into each flange mounting surfaces.
A square slot was milled into the fixture's highest surface to position and support the plenum end of the rear intake tube. The square slot offers a minimum contact patch with the tube and minimizes heat conduction away from the 'Y' joint. The wide range of fixture heights over the rather small base area complicated the machining and required the tools to be set up with very long stick-outs that limited their depths of cut to about .005". This was the reason the three columns were roughed so close to their final dimensions before welding.
I was very happy and, to be honest, a little surprised with the final result. As the photos show, the fit-up appears to be identical to what I have on the actual engine. I won't know for sure, though, until at least one tube assembly is actually soldered together and trial fitted into the engine.
My solders should arrive any day now; and after some practice, I should be ready to start assembling them. - Terry

 

[mayhugh1]

The Silvaloy 355 sheet solder arrived immediately after my last post, and I couldn't wait to see if my solder disk idea had a chance of working. I decided to make a quick and dirty test using my new soldering fixture and a pair of notched intake tubes that I had previously scrapped just to see what kind of learning curve was ahead. I used a pair of my flanges to hold two of the three ends of the assembly in the fixture, but I decided to not solder and waste them in this first attempt. At this point I was only interested in the critical 'Y' joint. I really don't expect problems with the flange soldering as the ones in this engine are very similar to the ones I designed and soldered for my H-9 build.
I cut a disk out of the .005" solder sheet to roughly match the outer profile of the joint, punched a 1/8" hole in its center, and then bent it 90 degrees. For flux I used UltraFlux which is a creamy white water-based fluoride+borax product popular for brazing and silver soldering. I painted both joint interfaces as well as the disk with a light coat of this flux before inserting the solder disk between the tubes. An serendipitous design feature of my soldering fixture is that when the flange mounting screws are tightened down, the fixture pinches the two tubes together at the 'Y' joint and captures the solder disk between them. However, I had some trouble adjusting the height of the front tube at the interface to the exact height of the rear tube because the solder disk between them made it difficult to tell when they were perfectly aligned. I continued, though, and heated the tubes on either side of the joint with a mapp gas torch. After several seconds, the flux began bubbling just before the solder melted and flowed nicely around the joint. The first photo shows my first 'Y' joint attempt while it was cooling in the fixture. After it had cooled to the touch, I dipped it in a pickling solution of sulphuric acid (purchased from Lowe's as drain cleaner) for about ten minutes to remove the flux residue. I used a small stainless steel brush to swab the interior, and then I neutralized the remaining acid by dipping the assembly in a solution of water and baking soda. When the fizzing stopped I lightly buffed the joint with a fine ScotchBrite pad. One of the photos shows the final result. The joint looks great except for the misalignment of the two tubes, and so my alignment technique needs some improvement.
I leak-checked the assembly by plugging two ends and pulling a vacuum on the third. I was then curious about the strength of the joint. The test I did was not at all quantitative, though. I just tightened the long front intake tube in a vise with its ID backed up with a piece of drill rod. I then grabbed the rear intake tube with a pair of locking pliers and pulled until the joint separated. It was difficult to tell for sure, but even though I put a good bit of my weight behind it I probably pulled with less than a hundred pounds. In any event, the tubing at the joint appears to have distorted before the joint separated. The joint strength was certainly less than my estimated 900 pounds, but it feels adequate for this application. The third photo shows a close-up of the distorted halves of the separated joint.
The entire surfaces of both tubes at the interface are wetted with solder, and it appears that it was the solder itself that yielded rather than the solder separating from the metal. This would seem to imply that the metal was adequately cleaned. There are a significant number of gas bubbles, though, in the solder itself visible in the interface where the two halves of the joint separated. These voids total about 25% of the interface area are for sure partially responsible for the lower strength joint. I need to do some research, but these bubbles may be related to an over or under heating of the joint. The solder flowed so nicely in the outside fillet, though, that I wouldn't expect it to be an under-heating problem.
On a more positive note, the flux seems to have been completely removed from the interior by the acid bath. A clean interior is very important for the intake tubes so that foreign debris doesn't eventually end up becoming embedded in the seats of the intake valves. - Terry

 

[Swifty]

Very nice looking soldered joint, I'm following along with interest.

Paul.

 

[mayhugh1]

I did some research and found that Silvaloy 355 actually contains 56% Ag, 22%Cu, 17% Zn, and 5% Sn for a flow temperature just over 1300F. My first thought was maybe the gas bubbles were caused by me overheating the joint and perhaps causing the zinc to outgas. During my first attempt I left the torch on the joint for several seconds after I saw the solder flow on the outside. Zinc boils at 1664F, but I know in it its free state, at least, it can actually start fuming just above its melting point at around 800F. If this is also true with it in a solder alloy the bubbles may be a fact of life.
I soldered up two more sets of practice tubes and tried my best to limit the temperature so as not to go any higher than necessary to melt the solder. In both cases I immediately removed the torch just after getting a beautifully flowed external fillet. But, during my pull tests, both pairs of tubes separated with noticeably less effort than that of my very first attempt. The first photo shows one of my results. In both attempts the solder inside the joint had not gotten hot enough to fully melt and wet the entire area of the joint. This caused a large portion of the solder to separate cleanly and easily during the pull test. For what it was worth I didn't see any bubbles, though. This seems scary to me since it looks like it may be very difficult to judge the proper temperature for an ideal joint.
I also discovered there are basically two types of fluxes used for silver soldering. The first is a "white" flux, and is the one I've been using. The second is a "black" flux which is pretty much the same as the white variety except that it contains more borax for better joint protection. It's also useable up to a few hundred degrees higher than the white flux. So, I soldered a pair of tubes together using a sample of the black flux that I got from a friend. I used enough heat to get a nice exterior fillet and then "a little more." This pair of tubes required noticeably more force to separate them than my very first attempt. The second photo shows there are still gas bubbles in the interface, but maybe not quite as many as there were in my first attempt with the white flux. It's also possible the flux made no real difference, and the slight improvement I saw was due to something else.
At this point I began looking to see if there were other hard solders recommended for stainless steel that do not contain zinc. To my surprise, I found that zinc is a common component in all of them - even in those containing cadmium.
Before I do anymore hard soldering, I want to experiment with the soft solder that Peter mentioned in his post. It is 96.5% Sn and 3.5% Ag and contains no Zn. Surprisingly it has about the same tensile strength as the hard solders and melts at a much lower temperature. I have some of this solder on hand, but I don't have the flux for it; and so I'll have to wait for a delivery to arrive. -Terry

 

[mayhugh1]

I received the flux for my Sn(97%)-Ag(3%) soft solder, and it appears to be mixture of zinc chloride and hydrochloric acid. The solder I have is .093" diameter wire; and so, I used my hydraulic press squeeze a half inch long piece into to a .010" thick disk. I also used a jeweler's ring expander to draw a length out to about .063" diameter. After fluxing both surfaces of the notch as well as the center-drilled and 90 degree bent disk itself, I used a mapp torch to heat the joint in my fixture. The solder wetted the interface and flowed nicely throughout the joint with negligible heat discoloration of the tubing. I didn't trim the disk close to the size of the joint as I had been doing with the hard solders because I wanted gravity to over-fill the underside of the joint so I could metal-finish it as a test to see how it might look. The first photo shows the joint cooling in the fixture. The next two photos show the raw topside and the final metal-finished bottom side of the joint. Disappointingly, it took about the same effort to pull this soft-soldered joint apart as it did to pull apart my original hard soldered joint. The fourth photo shows the nice looking interior of the pulled joint. The solder thoroughly wetted both surfaces; and the joint cleanly separated along a line entirely within the solder. I don't know why I seem to consistently get joint strengths that are nearly an order of magnitude less than what I calculate from the solder's tensile strength. In this particular case, though, the solder line may have been too wide.
I decided to continue using soft solder for my 'production' assemblies since the lower temperature is less traumatic to the metal, and the achievable strength of my particular joint seems to be similar with either solder. I like the appearance of the heavier fillets that I'm able to sculpt with the soft solder even though the manual metal finishing adds another hour of work. If I have to re-solder a joint before things are just right the soft solder seems to be easily re-worked. One might raise a question about the lower service temperature of soft solder in this application, but previous measurements on my H-9 exhaust pipes (150F) tells me this shouldn't be a problem. The flux residue was simply removed from these parts by boiling them in water.
I added a spring to my soldering fixture to help pull the two tubes closer together at the 'Y' just after the solder disk between them melts. I did this to help reduce the thickness of the solder line in the joint just in case it was a limiting factor in my joint strength. I didn't do anymore pull tests, though, to verify any change in the results. I cobbled up some simple fixtures to hold the two exhaust pipe turn-ups in proper position, and then I soldered my first complete assembly. The last series of photos show the final results. It took about three hours from the time I pulled the pre-formed tubes out of their storage bags to when I finally inserted the completed assembly in the engine. The good news was that it fit as expected in random head positions around the engine. As expected, but unfortunately, I also verified that a splice will definitely be required on the long front intake tube. The soldered assembly is too rigid and the clearances are too tight for it be wiggled into position inside flange recesses of both heads simultaneously. The color match of the tin-based solder is pretty close to that of the stainless tubing, but it's not perfect. It's noticeably better, though, than what I observed with the Silvaloy.
Pre-fitting, cleaning, and fixturing the parts and preparing the solder is necessary, but takes much longer than I expected. My current plan, though, is to continue with this process for the remainder of the parts. - Terry

p.s. Thanks Peter, for your suggestion.

 

[petertha]

Thanks Peter, for your suggestion.

My pleasure. (Lucky rookie suggestion!). Your joints are a work of art. I hope they provide many hours of trouble-free, rumbling, radial service!

 

[kuhncw]

Terry, thank you for all the work that goes into your posts as they are very educational. I especially enjoy your fixturing.

Regards,

Chuck

 

[Swifty]

Well I have to agree, they are certainly a work of art, those fillets are amazing. It brought to mind a job that I did for one customer years ago, we had to machine a very high temperature resistant stainless steel material, flat plates with circular grooves in different positions, and tubes machined to length that fitted in the grooves. They were made up into top and bottom plates, with the tubes like pillars between the plates. The assemblies were air freighted to the US for specialised soldering and then returned. The assemblies were all part of a gas powered generator set.

Paul.

 

[mayhugh1]

I can't say that finishing up these tube assemblies has been one of my favorite parts of this build. It seemed that no matter what I did to try to make the process more efficient it still took me three hours to complete each one of them. More than half of that time was metal finishing with a file. To save some steps I tried cleaning (Scotch-Brite'ng) all the parts at one time, but I then found the solder didn't seem to wet as well as when the parts were cleaned immediately before the fluxing/soldering. Evidently, the surface oxide on stainless reforms pretty quickly after machining. It was really tempting to call it quits after completing only the nine assemblies I actually need, but since I had the extra parts I went ahead and finished out 15.
As solders go, this one is reasonably easy and safe to work with since it contains no lead or cadmium. The flux, though, is another matter. After soldering the first few assemblies my fixture had become badly corroded, and the registration surfaces had to be Scotch-Brite'd before building up each assembly. Even though I was running an exhaust fan, all the hand tools on my bench within a couple feet of the soldering fixture also ended up with surface corrosion. And, I came down with an unusual (for me this time of year) chest cold which makes me wonder if chlorine fumes from the flux changed the balance of bacteria in my lungs.
I took some photos of the metal finishing steps used to form the fillets at the 'Y' joint mainly to break up the tedium, but also because the process might be of some interest in other's projects. It seems like a useful tool to have in one's bag of tricks - not only for manually creating complex surfaces but also for repairing accidents to high value parts.
This type of metal finishing is very similar to blending auto body seams with body solder. The biggest difference is that body solder contains a large percentage of lead which separates its melting and flowing temperatures a bit to aid in 'buttering' a vertical surface. The solder I'm using, though, flows like water as soon as its melting temperature is reached. A practiced hand with the torch was even needed to keep excess solder from flowing off the top of the relatively level joint that I was working with. The trick became getting the surface to just the right temperature so the solder melted but then was immediately chilled by feeding in additional solder. It was also important in my particular case to not mechanically clean the interior of either tube in order to discourage solder from flowing beyond the joint and sticking to the tube's interior where it would reduce its i.d. Examination of the sections in my pull tests showed it was easy to keep the i.d.'s open.
After buttering the solder around the joint and allowing it to cool, the assembly was dipped briefly in a pickling bath of diluted sulphuric acid, neutralized in a baking soda solution, and then boiled in water for ten minutes to remove any flux residue. A belt sander was used to knock down the tall blobs of solder that liked to form on the underside of the joint.
A 3/16" circular rasp file was used for most of the metal finishing. It was used to create the fillets and feather their edges into the stainless. A rasp is an effective tool for this first step because it's capable of removing large amounts of solder with little effort and without loading up with solder. Because of the difference in hardness between the solder and the stainless it's very easy to stay within the solder and minimize gouging or severely scratching the tubes. A medium 3/16" circular file was then used to remove the filing marks left by the rasp and to fine tune the blending. This was followed by a fine 1/8" circular file which removed the medium file marks, and smoothed the smaller radius between the two tubes that wasn't reachable by the larger files. A piece of 200 grit paper was then wrapped around the 1/8" file to removed the remaining file marks. The whole assembly was then burnished with a medium (red) ScotchBrite pad followed by an extra fine (white) pad.
Each assembly was completed and checked for proper fit in random positions around the engine before starting on the next one just in case something went wrong. The assembly with the tightest fit was marked for identification. This one will be used later to determine any needed changes in the final clearances of the CNC program used to complete the exhaust flange recesses as well as the bores in the plenum compression nuts.
The next step is to finish the design of the front intake tube splice and to modify the tube assemblies accordingly. - Terry