5bears制作Wren MW54涡喷发动机
本帖最后由 超级盾 于 2016-5-10 20:19 编辑听说Wren Turbines Ltd雷恩涡喷发动机倒闭了，发这个贴也算纪念一下。
（官网Wren Turbines Ltd和http://www.wrenturbines.co.uk/都打不开了）
5bears是谁不太清楚。
Wren MW54大家都熟悉吧，论坛里也能找到图纸。
5bears自己整理了图纸，重新标定了尺寸。由于部分零件自己加工有难度，他购买了这些零件，其他的两件都自己加工。
实在懒得翻译了，直接转帖过来吧，英文也不复杂，对付着看吧
内容有不少年头了，可能现在看起来会有点老，不过参考价值还是有的，看看吧
下面开始
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自制电焊机
The Home-BrewSpot Welder
A spot welder is a necessity for the production of a homemade gas turbine, unless you can accurately and easily TIG weld a LOT of very fine stainless steel, on the order of 0.5 mm. Commercially produced spot welders have several things wrong with them... first, they are rather expensive, typically $250-$500 U.S. Secondly, the welding tips, where the actual fusion occurs, are relatively thick, and difficult to squeak into tight crevices like the bottom of a combustion chamber. They are also mostly hand-held devices, which would make the spot-welding of small parts challenging. So I guess if I was welding up a bed frame, a commercial welder would suit, but not a 2" dia. combustion chamber.
Thus, the need for a custom spot welder. Desireable attributes are a high quality, repeatable weld, ease of use, and low cost.
All of the parts for this welder (except the transformer) are available from MSC. The transformer must be scrounged from an electronics/industrial surplus outlet. Look for a BIG 115VAC transformer (700 Va or better) with the secondary windings on the OUTSIDE. Listed below are MSC parts numbers, and current prices.
Timer Relay54023122$58.26
Octal Socket54038666$7.40
Foot Switch54097191$17.10
Solid State Relay54050372$56.06
TransformerSurplus
Schematic diagram. For simplicity, I depict the Timer control relay as a box with the necessary pin numbers depicted. Use at least 16 guage stranded copper and crimp or solder suitable terminal connections. The octal socket is required for the timer.
Please, please don't attempt something like this unless you truly understand the hazards involved. You must be adept at basic wiring, and must understand how a transformer operates. There are lethal voltages involved!
An overall view of the completed welder. Plans were "created" on the spot, using knowledge gleaned from the internet on such a project. The basic concept is to find a big 115VAC transformer which has the secondary windings as the outer layer. The secondary is carefully (but tediously) removed, and replaced with enough coils of #4 copper cable to create a secondary voltage of ~4 VAC. a DeStaco clamp is adapted for the upper arm, while the lower arm is fixed, but insulated.
There are two relays... This one is a control relay, c/w microprocessor, variable timing, and variable logic. This little jewel costs $60, and is worth every penny for the excellent functionality it delivers. A foot switch activates the selected cycle. I am using the one shot logic which simply energizes the entire welder for the chosen interval, then shuts it down. This produces excellent and repeatable welds in thin sheet steel.
A second relay, not shown, controls the amperage flow through the transformer primary, which in turn energizes the secondary and produces the very high welding current.
A closer view of the modified transformer. After the secondary was removed, there was enough room for 5 turns of #4 copper, insulated cable. You can use welding cable, or you can cannibalize the cable from a set of automobile battery jumpers. Be sure it is heavy #4, and flexible enough to wrap around the transformer.
I got very lucky... the same surplus store I found the transformer at (Bill Williams Tool, Ft. Worth), had a supply of extra-deluxe surplus aerospace copper cable. This stuff was made for aircraft wiring, and cost me all of $1/foot.
The small black box on top is a fuse box for a 20 amp prmary fuse.
The arms are pinching a little SS test sandwich prior to applying current. I originally got cute and tried a tungsten electrode in the top arm rather than the brass one shown... not a good idea. The tungsten sputtered and welded itself to the steel. The arms are 1/2" dia brass, and the tip is turned to a 90 degree cone from 5/16" brass.
And now for the not-so-funny tale of woe... I completed the welder wiring at roughly 10:30 A.M. one Saturday. I anxiously inserted the first test piece, and applied the current. NOTHING!! I began a painstaking trouble shooting which took hours - I rechecked all the wiring, checked the secondary voltage (O.K. at 4VAC), checked everything. Arrrgh! About 4 hours later, I scared the heck out of myself when I closed the energized pincers without a sample, generating a hot spark. Wow, it works. Suspicious, now, I checked the "samples" I was using, only to find there was thin film of transparent plastic on the stainless steel which insulated the whole thing!!!!! It is always the simple things which bite us in the butt.
In use, the clamp arms and the cable heat up, but not frighteningly so. This does limit the duty cycle... after roughly 10 to 15 welds, I found it was best to allow the unit to cool for a couple of minutes.
The weld quality is excellent. Destructive testing pulls a nugget off of one sheet, and requires a surprising force even with .010 stainless. The entire cycle takes only one second. Neat stuff!
本帖最后由 超级盾 于 2016-5-10 20:21 编辑
The Grizzly Roll Former
Another essential tool is a roll to form sheet stainless into relatively small tubes, later to be welded. MSC carries a nice American-made bench roll for $349. Being cheap, I bough the Grizzly bench roll for $149. In typical fashion, I learned once again that you get what you pay for. The box arrived with parts rattling around inside. Initial cleanup and inspection revealed a roll which was absolutely worthless. The adjustments couldn't get the rolls together closer than about .080", way too wide for the work I was going to do. Rather than send it back and admit my error, I decided to fix it. This took almost an entire day and my entire machine shop to repair. What a pain. DON'T buy this roll unless you enjoy fixing the mistakes of the poor Chinese prisoners who produced it.
Wow, it looks OK, doesn't it? I had to completely tear it down and rework the fit. The rolls' gears had to have .015" removed to allow the rolls to mesh to flush. The cam pins which adjust the rolls were WAY undersized, a floppy, sloppy fit, and had to be replaced. The roll clamp (upper right) didn't exist! This allowed the upper roll to raise upwards when inserting sheet stock, and as the crank was turned, the eccentricity was terrible.
A clamp was engineered and added. A lot of paint in the bearing areas had to be scraped. Overall, a piece of junk!
A view of my quick and dirty roll clamp. After sufficient work, the roll is now just adequate for the task of creating the gas turbine. 本帖最后由 超级盾 于 2016-5-10 20:22 编辑
Purchased Components
I chose certain components to bepurchsed rather than machined for a number of reasons... eitherthe cost was low, or the part in question demanded exoticmaterials or was simply unmachineable on manual tools. JDEnterprises is thedistributor, and Dennis apparently maintains a good stock. He wasknowledgeable and a pleasure to work with.
Part 035: Cast Nozzle Guide Vane (NGV)
This is an excellent investment casting of stainless steel. The guide vanes cause the hot exhaust gases to flow at the correct angle onto the turbine wheel, and also support the combustion chamber and shaft. The casting will require boring and turning to size, as well as drilling and tapping.
Part 003: Thecompressor
A stock Garret turbocharger wheel, this little guy comespre-balanced and bored to 6mm.
Part 007: Thediffuser
CNCmachined of aluminum alloy, the diffuser is a critical component which "collects" the compressoroutput and straightens the radial, turbulent airflow into a well-behaved straight flow for introduction into thecombustion chamber area. A small amount of the air is also used to cool the bearings through the tunnel shaft,and simultaneously drag a metered fuel/oil mixture intothe same for lubrication.
This is a complex partwhich could be machined at home but only with a hugeeffort and time expenditure due to the airfoil-shaped vanes along the periphery, hence it is a wise purchase.
Part 025: The Turbine Wheel
Another part which really needs tobe purchased is this turbine wheel, investment cast from Inconel 713. Early model gas turbines used a sheelstainless steel wheel formed into the correct shape withhand bending of the blades and grinding to shape. This ishow far this segment of the hobby has come, that you canbuy a certified, x-rayed wheel cast of inconel in thissize! The wheel will still require boring, balancing, anda final grinding to size.
Various Combustion Chamber Parts
Probably the true bargain is a setof pre-spun and sized, laser-drilled SS sheet steel partsfor the combustion chamber. The low price justifies thispurchase!
本帖最后由 超级盾 于 2016-5-10 20:23 编辑
Part 009: The Filter Cover
I decided to start theengine here, as I await the delivery of a nice supply ofnecessary stock from Online Metals, an excellent source with goodprices. I highly recommend the metal "Packs", whichreally give you a lot of metal for the money. You saveconsiderably buying in bulk.
This small disk holds avery finely meshed SS screen, and is used behind the compressorto filter the air which helps cool the bearings, and keep themfree from grit. The operations sheet from the plans has this thin(1mm) disk turned from a piece of sheet aluminum bolted to aplywood face in the lathe. I elected to turn it from round stockso as to more easily locate the holes, via coordinate drillingusing a DRO, in my mill. This way too I can make several at once.
The 2024 is turned to size, and the interior bored using in my case a nicecarbide shanked boring tool to minimize chatter. I madethe stock 1.5" in length which will allow me to partaway up to 10 of these covers.
Long experience in the construction of the radial engine has proven to me again and again the excellence of using a DRO and mathematically derived coordinate holes to locate thenecessary drilling spots. The cover has 16 holes spacedevenly on a 48mm bolt circle, 8 of which are 4mm and the others being 2.5mm.
Here, a centering device is being used to locate the stockexactly centered beneath the mill spindle. This widget can easily and repeatably center to within .0005". At this point, the DRO is set to X0, Y0, and a drillchuck is installed.
The 16 holes are started with a center drill, and preliminarily drilled about .010" smaller than the final diameters. Deepdrilling in aluminum is very tedious. The drill must bewithdrawn frequently to clear the chips. After the holesare started, the correct drill is used to open up theholes to their final dimensions. Any attempt to drill the holes to size in one pass is doomed to drill an oversizehole due to the accumulation of chips and abrasion as thedrill is inserted and withdrawn repeatedly.
Back in the lathe, thecovers are parted with an ISCAR blade...
...and the holes, as well as the ID and OD are deburred. An ultra-fine wire brush gives them a nice, satin finish. 本帖最后由 超级盾 于 2016-5-10 20:24 编辑
Part 022: Case Rear
The Case Rear does nothing more than contain the Nozzle Guide Vanes and connect the same to the outer casing. The plans called for a mild steel... since the part is roughly 3.5" diameter, and I had only brass on hand, I elected to use it. It is exposed to significant heat, but not much stress, so I think the brass, especially after I heavily plate it with nickel, should do fine. The exhaust stacks on my radial are nickel-plated copper tube, and these have withstood high temperatures nicely.
The brass will expand very slightly more than steel and will also transfer heat better to the outer case. This may be beneficial or detrimental, I'm not sure of which! If necessary, I can replace this part at a later date with steel.
A stub of stock is held in a 6" 3-jaw chuck, and the basic shape is formed via normal turning and boring practices.
The 8 holes which allow this part to be secured to the NGV are drilled via DRO coordinates. I am converting the metric fasteners to their Imperial equivalents; in this case, the holes are drilled 4-40 through rather than M3. The NGV will eventually be drilled and tapped 4-40 to receive this part.
The outer casing, a thin sheet of SS, is fastened via 6 radially drilled and tapped holes. The plans called for M2.5, which I converted to a 3-48 thread. The setup is quick and very dirty, a rotary table (with attached chuck) is simply clamped in my permanently mounted Kurt vise. After the edge is located and the stock centered, the six holes are drilled and tapped.
Back in the lathe, the case rear is parted to the correct width. The old stock is removed, and the case rear is returned to the chuck for final cleanup.
Using my Caswell plating kit which worked so successfully on the radial engine, I gave the part a deep plating of nickel. The part is first scrubbed thoroughly with common dishwashing liquid, then soaked in hot TSP for perhaps 10 minutes. Plating was at 3VDC, 0.85 amperes, for one hour. 本帖最后由 超级盾 于 2016-5-10 20:25 编辑
Part 035: Cast NozzleGuide Vanes
The NGV came as a nice lost-wax stainless steel casting. This particular alloy machined reasonably well, but did call for a rigid setup and very sharp new tooling. Certain portions of the casting were turned or bored with ground HSS bits, while others were turned with indexable carbide tooling. In any case, be sure the bits are either new inserts or carefully honed HSS. Like most stainless steels, the casting will work harden, which means if your tool dulls, or the feed isn't reasonably aggressive, the steel will toughen and harden, causing your bit to rub and make the situation worse!
Concentricity is vital, and as the casting must be reversed to machine each side, some method of centering in the lathe is crucial. I used a Buck Adjust-Tru chuck... a 4-jaw chuck will do the job as well. A normal 3-jaw chuck simply will not have the accuracy for this procedure. You cannot unchuck a part, reverse it in the lathe, and expect anything better than .003" or worse out of concentric truth. I selected the shaft tunnel boring, which was complete during the first chucking, as my "datum" to center the part for subsequent turning operations.
The plans called for some lightening cuts/undercuts in certain areas which I chose to forego. This was a personal and not an engineering choice, as I don't mind an engine which weighs a few ounces more than spec. Additionally, as I had the combustion chamber rear of spun SS on hand (purchased), I turned that portion of the NGV casting to fit this part, which turned out to be ever so slightly (.010") undersized.
The casting is first chucked with the aft side out. Centering was done with an indicator using the turbine shroud portion of the casting. The plans called for a skim cut only to clean up the casting. After a most careful centering, the skim cut, just enough to get to bright metal and form the turbine shroud area, ended up .010" oversize. WOW! As soon as I measured that ill-fated cut, I grabbed my cast turbine wheel, and with the casting still chucked, checked to see if the tip clearance would be excessive. The turbine JUST slipped in, so I think I may be OK. Excessive clearance between the turbine blades and the wall would be fatal unless I could add a sheathe of SS to close the gap. Anyway, I think Wren needs to add a bit more meat to the casting in this critical area.
With the turbine shroud bored, I faced off and cleaned up the rest of the rear of the NGV to print.
Next, the center hole which mates with the shaft tunnel is bored. Again, concentricity is critical. Take great care with your boring tools to assure a fine, accurate finish. With as much as possible to be machined off of the rear accomplished, the plans called for the NGV to be reversed and lightly gripped on the thin turbine shroud or rim, neither of which is by this time very stout. As the forces involved in machining this SS are high, I elected instead to drill and tap the periphery for 8 x 4-40 holes, which allow the NGV to mate with the case rear. My plan was to bolt the casting for subsequent machining to a strong, beefy ring to be held in the lathe chuck rather than the casting itself.
On the mill, the NGV is centered and the 8 4-40 holes are drilled and tapped, and the burrs cleaned. Tapping is scary in this material. Use a new tap, preferably a set of 2 new taps, one taper and one plug. The taps can be swapped out as necessary to finish the job, alternating the taper and the plug tap. Don't break a tap! Go easy.
Back in the lathe, you can see the NGV casting is bolted to a ring of mild steel. I could then aggressively tighten and center the casting for the coarse operations on the front without fear of slippage or damage to the thin steel walls on the rear.
On the front, 2 critical diameters are turned, the larger for the combustion chamber outer, and the other which will grip the inner. The paths for the exhaust gasses are turned to a 30 degree angle, and in general the NGV is machined to print.
Four separate pictures of the same casting are seen here. On the left is the rear of the NGV. Next is the front, and thirdly, the front half with the spun combustion chamber rear slipped into place. You can see the 12 holes for the sticks pre-drilled. Lastly is the rear of the NGV, this time with the unbored turbine wheel slipped into the turbine shroud. A close check shows the current tip clearance to be perhaps .002", which is not optimum but which should allow the engine to run fine.
本帖最后由 超级盾 于 2016-5-10 20:26 编辑
Part 011: The Shaft Tunnel
The Shaft Tunnel is a very improtant part of the turbine and must be made with care and precision. It provides support for both front and rear ceramic cageless bearings, allowing the shaft, which carries both compressor and turbine, to run smoothly and true. Inside the tunnel is a pre-load spring for the bearing set, a tube to distribute the pre-load forces, and of course the shaft itself. Additionally, it provides a tight seal and support for mounting the diffuser, and also locates the NGV assembly during final assembly.
It is critical that the bearing recesses be truly axial, square, and parallel with each other, or forces induced in the shaft will ruin the expensive bearings in short order.
A blank piece of 6061 aluminum, 1.375" dia. is cut and faced to length. Held in the three-jaw chuck, it is then drilled through 1/2" and bored to the correct minor diameter of 14 mm. The recess for the turbine bearing is bored to be a light, sliding fit, and an o-ring groove is also machined. The o-ring lightly grips the rear (and front) bearings allowing them to flex and seat to optimum running positions.
After the aft portion of the tunnel is correctly bored, a mandrel needs to be used to finsish the compressor end as well as the exterior of the tunnel. I elected to use an expanding mandrel rather than a solid mandrel. These are extremely handy to have as a set, as they can be turned to whatever diameter or shape is needed, in situ, to be a very close sliding fit to the bore of the part. After a thorough polishing and deburring, the mandrel is cleaned and coated with oil. The shaft tunnel blank previously bored is then slipped carefully over the mandrel to avoid marring the rear bearing seat, and a couple turns of the hex wrench grips it securely.
Red marker is used to lay out the different flanges and diameters. The forward bearing recess and o-ring groove are machined to print. A heavy parting tool roughs out the external shape of the tunnel. Be careful not to heat the tunnel up too much, as this may cause it to expand and slip on the mandrel.
A form tool is inserted in the lathe, and the 2 radii which form the front and rear flanges are turned by jogging the cross and slide feed by hand as necessary.
The completed tunnel still in the lathe after polishing with steel wool. All that remains now is drilling and tapping the holes in the flanges for both the diffuser and the NGV.
本帖最后由 超级盾 于 2016-5-10 20:27 编辑
Part 025: The TurbineWheel
The turbine wheel for the Wren 54 is one of those items best purchased. Early in the days of model gas turbines, the only way to get a functioning turbine wheel was to make one yourself, a very tedious, hit or miss process which starts with a sheet of stainless steel. The blades are bent and shaped by hand with a grinder. While I could theoretically do this on a larger engine, the Wren is small enough to require a turbine wheel matched to the compressor throughput and of the correct material, in this case Inconel 713. The turbine wheel can be had unmachined, or you can purchase it bored and balanced for an extra $75. A few hours work saved me that extra $$ when I bored this wheel myself.
Like many machine tool operations, the creation of a special jig and the setup for this operation consumed 5X the time required to actually execute it. The Wren operations sheet details a clever and effective fixture to hold the wheel. I could not think of a better way to do it with accuracy. I considered a pot chuck (a combination of 5C collet and expanding plate) but the simple act of closing the collet lever is enough to throw the fixture out of truth. So in the end, I followed the instructions.
First, a large aluminum round is drilled and tapped for securing cap screws. The Al round is chucked, bored, and a large ring is parted off. The remaining stock is left in the chuck and carefully faced with the carriage locked for best accuracy.
A recess is bored to accept the wheel for a sliding, accurate fit. This was tedious, as it is difficult to measure the diameter of the wheel with its odd blade number, so I had to sneak up on it a few tenths at a time.
At the root of the blades is a ring which becomes the surface contacted at the bottom of the shallow boring. This ring can be seen here, with the wheel successfully placed inside the fixture.
The previously parted ring is reattached with 10-32 SHCS and snugged moderately and evenly tight. I first gave the wheel a deep center drilling. The Inconel is tough, even more than the SS from the NGV, and one must be sure to keep cutting pressure up and the chip-flow continuous.
I then chucked a bit especially purchased for this operation, a straight flute, carbide drill of 15/64" diameter. With trepidation I applied the drill, but it cut nicely in one continuous plunge.
From what I could measure, there was no run-out of the drill, and I could concievably have reamed it straight away to 1/4", bit I elected instead to bore it for 1/3 of its depth to .245"... this would start my cobalt, spiral-flute reamer properly, and any remote eccentricity would be corrected.
The spiral reamer worked properly. After facing the other side of the bore, I slipped the wheel onto a 1/4" carbide end mill shank, a perfectly ground diameter of .2498. When rotated, I could feel a stop-and-go stuttering left over from the reamer flutes. This is an inevitable result of reaming rather than boring to size, and I have seen it in many other pecision reamer operations. While the wheel probably would have worked fine, I elected to lap the bore to perfect concentricity. This was done by charging a brass rod of scant .250" with 500-grit clover compound, and using a pin vise or VERY slow speed drill, to "pump" the lap into the bore. The resulting bore was perfect, with a flawless feel when mounted on the carbide shank.
I DON'T recommend lapping unless you have considerable experience with laps, as it is possible to bell-mouth the bore, or worse, freeze a too-aggressive lap in place.
本帖最后由 超级盾 于 2016-5-10 20:28 编辑
Part 012: The Shaft
The shaft is a deceptively simple piece to make. It is easy to produce a beautiful, polished shaft that to the eye is flawless, but unless absolute concentricity is maintained, unless the diameters are perfect, imbalance, eccentricity, and bearing damage will eventually occur.
If you are making a shaft for the Wren 54 or any model gas turbine engine, take the time to read the text - it just may save you as much scrap as I generated!
Turning of the shaft must take place between centers. Be sure your headstock center is running truly concentric by testing The relatively cylindrical portion just aft of the 60 taper with a sensitive dial indicator. Use a .0001" indicator if you have one, or at least a .0005" capable indicator. In my case, I ended up having to chuck a center in my 3-jaw, and then adjust the chuck to generate a perfect rotation. An aluminum collar engages the center barrel for dog rotation.
The material is 4140 steel. 4340 would be a better choice but since the material is used in the annealed state, and the mechanical properties of 4140 is very close to 4340, I elected to go with it.
For the tailstock, be sure it is perfect. Use a dial indicator, or take a very light cut along the entire length to check for perfect parallelism. If there is any taper (perhaps >.0004") correct it now. I had to shim my tailstock with .002" SS foil to achieve this, as it has no provision for set-over.
Begin by roughing out the dimensions. The steel is quite tough and stringy. As the cut occurs, especially with any cut greater than perhaps .005", the shaft will spring away and result in a tapering cut. Measure frequently with a .0001" capable mike. Rough out with carbide or similar all surfaces (except the tapered portion) to perhaps .010" oversized.
Grind a HSS bit to the correct form for 0 degrees lead, and give the tip a slight radius. I use a diamond hone to clean up the ground edges. This will be your "finishing" tool. Use this tool at the tailstock end only and get the critical surfaces for the bearing and the compressor shaft to perhaps +.001" If you are confident you can get a decent finish with accuracy, go for +.0005". But beware, with this steel, light cuts can produce a hit-or-miss action which may cut undersized. Better safe than sorry!
Next, take a piece of ground flat stock. Failing that, use a 3/8" blank lathe tool bit. Don't use a file! Wrap 400 grit wet/dry paper and evenly and carefully clean up the critical surfaces. Now mike the shaft portion being polished. If there is no taper, fine... if there is, a bit of "leaning" with the steel-backed paper can remove it. I have easily corrected tapers up to .001" with this technique.
When you are within .0004" of the desired diameter, switch to 600 grit. Knock it down another .0002". Now unleash some 1500 or 2000 grit paper. Check the fit as you go! My 688 bearings (these are regular bearings used as guages) had a perfect sliding fit at .3148". For your compressor or turbine, you must remove the shaft and check the fit, as no reamer made will consistantly cut to .2500". They tend to go oversized, especially in aluminum. I reamed my compressor to 1/4" as I wanted to screw-cut the threads fo accuracy and my lathe is 100% Imperial.
My compressor ended up with a tight but wringing fit at .2506". GO SLOW. Once the surfaces are undersized, that shaft is done. Trash it!
Here are THREE shafts, only one of which is acceptable. The shaft on the left had a turbine bearing surface cut too small due to a dull tool and material springiness. Into the scrap-box it went. As for the very promising middle shaft....
When you are ready to reverse the shaft and work on the turbine end, don't automatically assume that your precious compressor-end surfaces are concentric after the end-swap!
Much to my chagrin, I found after I had cut and polished the turbine end surfaces of the middle shaft that the compressor-end bearing surface was not running true... TIR was .001", absolutely unnacceptable. I know this shouldn't happen, but it did on my otherwise well-behaved Hardinge. So CHECK your runout and correct as necessary BEFORE working on the turbine end surfaces!
One other caveat: Use a high-quality live center. Realize that when you are roughing out, the work will heat and you may need to relieve expansion pressure on the tailstock. Before the critical cuts and polishing, let the shaft cool, and EVERY time you re-insert it, dial the tailstock barrel back to the same position for consistency. The light cuts and polishing don't heat up the work very much.
Once all of the bearing surfaces are perfect, cut the tapers with the top-slide... this procedure was not photoed. Use the same care when swapping the shaft end-for-end, and take the time to correct eccentricity even for the taper cuts. An eccentricity during the taper cut will induce an imbalance in the shaft.
The screw-cutting procedure was cake after the other surfaces were finished. I cut both ends with a left handed 1/4 x 28 thread, using a scrap of brass drilled and tapped with an appropriate tap as a guage. You want a fairly snug fit of the female to male threads.
The shaft with compressor and turbine slipped on, after much sweating and angst. The critical surfaces are true to within .0001" of taper, and total runout of any surface relative to any other is maybe .00015 max. I say this not to toot my own whistle, but to show what can be done on a manual lathe with wet-dry paper and some care.
Cylindrical grinding machine? We don't need no stinkin' cylindrical grinding machine!
After I had posted the page seen above, I discovered still additional flaws in the shaft, which I described on my Home Page as dated updates. I have copied them here so others may learn from MORE of my mistakes.
23 Sep 2000: After struggling with the shaft turning, I had a lot of fun "spooling up" the compressor/turbine shaft assembly by squirting some shop air over the turbine blades. I did notice that installation and removal of the turbine, compressor, and standard 688 bearings scored the relatively soft steel of the shaft and actually loosened the fit of these parts very slightly. Having had much success with my nickel plating setup on other projects, I decided to see if I could actually build-up one of the scrapped shaft bearing surfaces with nickel and at the same time protect it both from corrosion and abrasion, the nickel surface being harder than the polished steel. I degreased and plated shaft #2 after carefully measuring the finished surfaces, and plated at .300 amp for the approx. 5.6 square inches of the shaft's surface area.
The result was enlightening... the shaft came out like a jewel. More importantly, the compressor portion of the shaft, which went in at .2503" came out with a dead-even .2514" plate, roughly .001" of nickel in one hour. This was heavier than I expected. I did some experiments... back in the lathe, I discovered the nickel was hard. An effort that would have removed .0005" of steel knocked down the nickel only .0001". I then took a propane torch and brought it up to a dull red heat, which would have produced a measure of scaling on bare steel. The result, a pretty blue/purple nickel, no signs of cracking or oxidation. This could have potential!
I am tempted to reduce my one good shaft to perhaps .0005" undersize, plate it for 45 minutes to get it back above the correct diameter, and then oh-so-carefully work these surfaces to perfection for the bearings, the compresor, and turbine wheel. The result should be a hard, durable, and perfect surface for the shaft components.
24 Sep 2000: I lied, I admit it. Grrr. A double-check of the surviving shaft among the trio already produced revealed worse runout than I had thought. I know that I initially measured around a tenth (.0001"), but a more careful check revealed runout over .001. I don't know how I missed it. The culprit resides in the action of flipping the shaft end-for-end during machining between centers. Another shaft is being turned, and this time I am simply going to chuck the stock and work the entire shaft in one setting. The right side of the shaft will be easy, but for the left I am going to have to gouge out a bit of stock below .2500" and attack it left to right with some left-handed turning tools. I know the dimensions of the critical areas, and I am going to polish them down to -.0005", and try the nickel plating procedure described below.
Stay tuned, this will either fail miserably as well or work like a champ!
1 Oct 2000: The nickle plating experiment was a success. I turned a new shaft with all surfaces at -.0008" or so, and after a very light polishing with 400 paper, I prepared the shaft for plating. I made absolutely sure that the shaft would rotate evenly in the solution so that the nickel would be deposited evenly as well.
I calculated that 1.3 hours in the tank would deposit a little over .001" of nickel, and should provide .0005" or so for final polishing of the bearing, turbine, and compressor surfaces. The shaft came out exactly as planned, perhaps a bit too much nickel but that is O.K. Back in the lathe, I worked the compressor end to perfection, but the turbine end gave me some problems. When I reached a dimension that produced a wringing fit, I found that the Inconel would seize and gall a bit, even though the bore of the turbine appeared very smooth. I was forced to take the shaft diameter down a bit farther so that the turbine wheel would install without excessive grab and gall. The bearing surfaces I have kept fat by about .0003" while I await delivery of the ceramic bearings. I do have some SS 688 bearings on hand, but at this point I am paranoid about using them as a guage, not knowing if the tolerances between these and the ceramic bearings are tight enough to warrant their use at this time. The ceramic bearings should arrive very soon! 本帖最后由 超级盾 于 2016-5-10 20:29 编辑
The Combustion Chamber,part 1
I may be wrong, but a lot of machinists are intimidated by any sheet metal work. I'd rather machine a tray from solid than try to bend one up from sheet metal. But there was no way around the fact that the gas turbine would take a bit of work with stainless steel sheet. Fortunately, with the purchase of the combustion chamber pack of parts, most of the hard work is already done. All that remains is rolling, extruding the air holes, and assembling the chamber.
There are three stainless cylinders which must be formed or rolled into tubes... the combustion chamber (cc) inner, cc outer, and the outer case. Each of these requires an overlap seam be formed in the end of the sheet. Note the green plan print which shows the overlap. This can be done with a lot of beating with a hammer, or it can be done neatly and elegantly with a die.
I constructed a die from the crs rectangles shown. This is a simple mill-drill job, with the step being milled on both sides of the die, so the steel is shaped into somewhat of a "z" shape when pressed. A scrap with a successful seam is show.
When you make your die, make it long enough to do all three parts. If you size it for just the combustion chamber, it will be too short for the case outer wrap!
With the seam in place, the trusty (but crusty) grizzly roll came into play. This was a lot easier than I thought it would be. Rather than roll it in one pass, I slowly crept up to the correct diameter through several passes. I was afraid that the roll would press out the seam, but it doesn't hurt the seam too badly.
Here, the cc inner is being rolled to the rather tight diameter required.
Ahh, thank goodness for cable ties! I was having a devil of a time wrapping up (and holding) the tube to the correct diameter for spot welding of the seam. The idea was to hold the tube stationary and at the correct diameter, and then deliver a couple of preliminary welds. A pair of cable ties did the job perfectly. I was even able to cinch the cable tie down rather tightly around the flange spun into the cc front, shown to the left as the disk at the bottom.
The first spot weld of the seam. Note that I am delivering a single spot as close to the cc front as I could get. Next, the cc inner was tested for size with the nozzle guide vanes, a portion of which grips this from the outer diameter of the tube.
After the second spot, the cc inner seam was welded along through its length.
The two larger sets of holes in the cc inner must be swaged out to a larger diameter. The main purpose of the swaging is to create a "crater" in the steel which will inject the air deep into the combustion chamber. Note that this is the cc inner, which surrounds the shaft tunnel, and is open through its middle to pressurized air from the compressor output; hence, the holes must be swaged as shown so as to inject the air into the combustion chamber.
I turned a 1/4" square of CRS into the required male 60 degree cone, and clamped it into a big boring bar, which I then held in a bench vise. The cc inner hole is positioned over the punch, and a female die is used to swage the hole. Note the shape of the resulting swage. Two rows of holes are completed in this fashion in the cc inner tube.
Now, we can proceed with welding the cc inner to the cc front. I had to modify my spot welder a bit to get into the tight confines of this joint. A couple of welds start the process, and then, when alignment is verified, the entire seam is welded tight. It is important to minimize air leaks in the chamber seams, especially at the front.
The cc outer is produced in much the same way as the cc inner, including a set of swaged holes. Once it was sized and seamed, it too is welded to the cc front. Still required on the cc outer are the swirl jets, and the two plug bosses. I plan on using a 1/4 x 32 spark plug for ignition rather than a glo-plug.
Here is a cool shot of the actual weld taking place. Each spot weld takes exactly one second.
Overall, the chamber is proceeding nicely, and is actually a lot easier than I thought it would be.