Bought it as a roller. Finished it up.
1/3 Scale Ford 289 Hi-Po
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Half step forward, one step back ...
I want to try something different for the fuel tank and thought making a scaled-down 60's Ford gas tank would be fun. Since all the running accessories I've been making will be prominently mounted along side the engine, I started looking at possible layouts. Unfortunately, the just-finished starter solenoid is way out of proportion with the others because it was designed around a standard 40 amp automotive relay. A much smaller one based upon an IGBT will be designed, but in the meantime I'm continuing down what could be a whacky rabbit hole with this fuel tank.
An electric fuel pump opens up lots of possibilities for a tank's shape and its mounting location including those of a scaled-down version of a 60's era Mustang tank. Its cosmetic top surface will require most of the machining time, although the bottom side has a lot of functional complexity.
The fuel pump is the same model RC filler pump used in my previous builds and briefly mentioned in one of the HiPo carburetor posts. It's obsolete and no longer available from hobby stores although they still turn up on eBay. After verifying its long term compatibility with gasoline, I began using it in my engine builds and bought a 'lifetime' supply while they were still available. I also created a SolidWorks model of a reusable mount for the pump assembly that I've integrated into several earlier tanks.
These pumps with their 12V brushed motors were designed for high flow rates. Minimal flow is needed in my applications though, and an operating voltage of 4-5 volts turns out to be adequate. The plan is to power the pump from the 6V regulator module along with the ignition module and add a miniature potentiometer in the side of the tank to fine tune the flow rate.
The current design shown in the photos is still a work in progress. Neither the Oldham coupler between the pump and motor nor the interconnecting hoses and bottom covers are shown. The design of the tank's bottom half is still a bit fluid, but the top half has been stable for over a week,and so machining can begin there. The tank will be machined from a 7"x5"x2" block of aluminum and its finished surfaces left unpainted. It will eventually be mounted with its bottom side flat against the floor of the display stand.
I hoped to use 7075 since its hardness would allow the use of four flute end mills to speed up the tiny cutter machining that will be required on the top surface. Lacking that or any known 6061 of the right size I decided to finally use a chunk of mystery alloy dug out of a landfill thirty years ago. It's been unused in my shop because it looks like a soft casting. After band sawing off a suitable workpiece, some test cuts were made and a few holes drilled to test its machinability. It appears to be usable, but I'm definitely back to using two flute cutters. - Terry
I want to try something different for the fuel tank and thought making a scaled-down 60's Ford gas tank would be fun. Since all the running accessories I've been making will be prominently mounted along side the engine, I started looking at possible layouts. Unfortunately, the just-finished starter solenoid is way out of proportion with the others because it was designed around a standard 40 amp automotive relay. A much smaller one based upon an IGBT will be designed, but in the meantime I'm continuing down what could be a whacky rabbit hole with this fuel tank.
An electric fuel pump opens up lots of possibilities for a tank's shape and its mounting location including those of a scaled-down version of a 60's era Mustang tank. Its cosmetic top surface will require most of the machining time, although the bottom side has a lot of functional complexity.
The fuel pump is the same model RC filler pump used in my previous builds and briefly mentioned in one of the HiPo carburetor posts. It's obsolete and no longer available from hobby stores although they still turn up on eBay. After verifying its long term compatibility with gasoline, I began using it in my engine builds and bought a 'lifetime' supply while they were still available. I also created a SolidWorks model of a reusable mount for the pump assembly that I've integrated into several earlier tanks.
These pumps with their 12V brushed motors were designed for high flow rates. Minimal flow is needed in my applications though, and an operating voltage of 4-5 volts turns out to be adequate. The plan is to power the pump from the 6V regulator module along with the ignition module and add a miniature potentiometer in the side of the tank to fine tune the flow rate.
The current design shown in the photos is still a work in progress. Neither the Oldham coupler between the pump and motor nor the interconnecting hoses and bottom covers are shown. The design of the tank's bottom half is still a bit fluid, but the top half has been stable for over a week,and so machining can begin there. The tank will be machined from a 7"x5"x2" block of aluminum and its finished surfaces left unpainted. It will eventually be mounted with its bottom side flat against the floor of the display stand.
I hoped to use 7075 since its hardness would allow the use of four flute end mills to speed up the tiny cutter machining that will be required on the top surface. Lacking that or any known 6061 of the right size I decided to finally use a chunk of mystery alloy dug out of a landfill thirty years ago. It's been unused in my shop because it looks like a soft casting. After band sawing off a suitable workpiece, some test cuts were made and a few holes drilled to test its machinability. It appears to be usable, but I'm definitely back to using two flute cutters. - Terry
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YUP, that chunk of mystery alloy does look like it was dug out of the landfill 30 years ago. But not for long - right?
olympic
Well-Known Member
I like the threaded stop rod on your band saw vise. Clever!
Gotta make me one of those.
Gotta make me one of those.
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+1 on olympic's comment.
I never even noticed that little doo-dad until he said something. Bet it really helps balance out the clamping pressure, and no more trying to find a piece of scrap the right size.
I never even noticed that little doo-dad until he said something. Bet it really helps balance out the clamping pressure, and no more trying to find a piece of scrap the right size.
A late night labor of love ...
Back in the good(?) ol' days the seamed flange between a fuel tank's pressed-formed galvanized halves was used to mount the tank in an opening in the floor of the car's trunk. Nowadays, it's not unusual to find a plastic tank hanging under a car by a couple straps. In any event, the model tank will be mounted to the engine's display stand with standoffs under its faux seam. This seam also conveniently separates the machining of the tank's top half from its bottom half which was still under design. The tank's top ribbed surface is its most interesting feature, and I was anxious to get started on it even before finishing the bottom side design.
The first step was to face off the workpiece's nasty top surface. The seam and everything above it were roughed in using half inch and eighth inch two-flute end mills. The Tormach Speeder was used to multiply the small cutter's speed up to 15k rpm for a huge time savings. Total roughing time worked out to about 2-1/2 hours. A 5/32" ball cutter also running at 15k rpm performed a three hour finishing pass. Since our Texas daytime temperatures have been near triple digits during the day, all machining was done after midnight while the shop temperatures were in their mid-80's.
The workpiece was then set up on the manual mill where it was faced and the excess bottom material trimmed from around the tank's periphery. With the workpiece clamped on its newly machined surfaces the hole for the filler neck was drilled.
The workpiece was returned to the Tormach for its bottom side machining. However, details of the internal fuel paths including clearances for drilling, tapping, and assembling the internal hose fittings were still being worked out. The design of the tank's bottom periphery was complete, though, and it was finish machined in just over an hour.
After wrapping up the design of the contorted fuel path routing, the tank was returned to the manual mill where the various holes for the fuel paths were drilled. A couple had to be drilled from two sides of the tank and had blind intersections. An extension was brazed onto a 8-32 tap in order to reach a pair of internal holes for hose fittings.
Back on the Tormach, the 3.3 oz. fuel reservoir itself was finally machined along with the groove for its -042 o-ring sealed cover. Final machining operations included the complex recessed mounts for the pump and motor and the nearly two dozen 1-72 tapped holes for the bottom covers. Cutouts for a power connector and a wire routing channel were also added. All totaled these operations took about three hours machining time with quarter inch and 3/32 inch cutters.
Along the way the tank was bead blasted and thoroughly cleaned with Simple Green and hot water and the surface finish left bare. Some bits of hardware still need to be fabricated before it's finally assembled and tested. - Terry
Back in the good(?) ol' days the seamed flange between a fuel tank's pressed-formed galvanized halves was used to mount the tank in an opening in the floor of the car's trunk. Nowadays, it's not unusual to find a plastic tank hanging under a car by a couple straps. In any event, the model tank will be mounted to the engine's display stand with standoffs under its faux seam. This seam also conveniently separates the machining of the tank's top half from its bottom half which was still under design. The tank's top ribbed surface is its most interesting feature, and I was anxious to get started on it even before finishing the bottom side design.
The first step was to face off the workpiece's nasty top surface. The seam and everything above it were roughed in using half inch and eighth inch two-flute end mills. The Tormach Speeder was used to multiply the small cutter's speed up to 15k rpm for a huge time savings. Total roughing time worked out to about 2-1/2 hours. A 5/32" ball cutter also running at 15k rpm performed a three hour finishing pass. Since our Texas daytime temperatures have been near triple digits during the day, all machining was done after midnight while the shop temperatures were in their mid-80's.
The workpiece was then set up on the manual mill where it was faced and the excess bottom material trimmed from around the tank's periphery. With the workpiece clamped on its newly machined surfaces the hole for the filler neck was drilled.
The workpiece was returned to the Tormach for its bottom side machining. However, details of the internal fuel paths including clearances for drilling, tapping, and assembling the internal hose fittings were still being worked out. The design of the tank's bottom periphery was complete, though, and it was finish machined in just over an hour.
After wrapping up the design of the contorted fuel path routing, the tank was returned to the manual mill where the various holes for the fuel paths were drilled. A couple had to be drilled from two sides of the tank and had blind intersections. An extension was brazed onto a 8-32 tap in order to reach a pair of internal holes for hose fittings.
Back on the Tormach, the 3.3 oz. fuel reservoir itself was finally machined along with the groove for its -042 o-ring sealed cover. Final machining operations included the complex recessed mounts for the pump and motor and the nearly two dozen 1-72 tapped holes for the bottom covers. Cutouts for a power connector and a wire routing channel were also added. All totaled these operations took about three hours machining time with quarter inch and 3/32 inch cutters.
Along the way the tank was bead blasted and thoroughly cleaned with Simple Green and hot water and the surface finish left bare. Some bits of hardware still need to be fabricated before it's finally assembled and tested. - Terry
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That is just absurdly impressive work !
This thread just blows me away......
.
This thread just blows me away......
.
Everything he does blows me away !
All I can do is shake my head, but I don't know whether to laugh or cry.
Soooo nice.
Soooo nice.
I did the same to my saw vise years ago. Works good.
Superb work. Leaves me speechless with admiration!
K2
K2
The four hose fittings (and one plug) were threaded into their respective holes and sealed with Permatex 59214 thread sealant. A male Futaba RC connector carrying power to the motor was JB Welded in place and its wiring routed along side the frame of the motor. The speed control pot was also epoxied in place and connected in series with the motor's 6V power feed. A .01 uF ceramic capacitor soldered across the motor's terminals will limit any brush noise fed back to the 6V regulator which will later be shared by the ignition.
The motor and pump were installed in their mounts and retained with several blobs of Devcon epoxy gel. A short pair of 1/8" flexible fuel lines connect the pump to its corresponding tank fittings. The simple bottom cover over the pump assembly wasn't extended over the fuel line connections to prevent fuel from accumulating in a closed space in the event of a leak at either of the hoses.
One end of a short piece of stainless tubing was mitered to match the angle of the drilled filler neck hole before being pressed and Loctite'd in place. With all the time invested in the tank, it deserved a 'fitting' gas cap. A reasonable facsimile of a 60's era Ford GT cap was machined from a piece of aluminum rod stock. The cap is o-ring'd but vented to the atmosphere through a tiny cross hole in the bottom of its outer rim. Its raised logo was machined using a 1/32" end mill. Two caps were made just for fun - one was bead blasted and polished and the other was painted black.
The o-ring'd cover plate over the reservoir is more complicated. It was designed with a sloping floor drain under the pickup to help the pump fully evacuate the tank. Gasoline (its octane package actually) begins deteriorating soon after it leaves the refinery, and it's best to not leave it festering in a stagnant tank. Several years ago I blocked off the carb's rear metering block in the car my son was going to learn to drive in. I didn't empty the rear bowl, though. A year or so later when I restored the 4 bbl carb back to full working order, the rancid odor of the fuel that had been trapped in that rear bowl was beyond belief. It took several hours working with multiple solvents to clean up the mess.
A piece of brass tubing was formed into a pickup and Loctite'd in place with the input just .050" from the bottom of the drain. Final testing included recirculating fuel in a loop some 12 inches above the tank. The drain works really well, and it seems possible to pump the tank completely dry. Several test runs were made and thankfully no leaks. - Terry
The motor and pump were installed in their mounts and retained with several blobs of Devcon epoxy gel. A short pair of 1/8" flexible fuel lines connect the pump to its corresponding tank fittings. The simple bottom cover over the pump assembly wasn't extended over the fuel line connections to prevent fuel from accumulating in a closed space in the event of a leak at either of the hoses.
One end of a short piece of stainless tubing was mitered to match the angle of the drilled filler neck hole before being pressed and Loctite'd in place. With all the time invested in the tank, it deserved a 'fitting' gas cap. A reasonable facsimile of a 60's era Ford GT cap was machined from a piece of aluminum rod stock. The cap is o-ring'd but vented to the atmosphere through a tiny cross hole in the bottom of its outer rim. Its raised logo was machined using a 1/32" end mill. Two caps were made just for fun - one was bead blasted and polished and the other was painted black.
The o-ring'd cover plate over the reservoir is more complicated. It was designed with a sloping floor drain under the pickup to help the pump fully evacuate the tank. Gasoline (its octane package actually) begins deteriorating soon after it leaves the refinery, and it's best to not leave it festering in a stagnant tank. Several years ago I blocked off the carb's rear metering block in the car my son was going to learn to drive in. I didn't empty the rear bowl, though. A year or so later when I restored the 4 bbl carb back to full working order, the rancid odor of the fuel that had been trapped in that rear bowl was beyond belief. It took several hours working with multiple solvents to clean up the mess.
A piece of brass tubing was formed into a pickup and Loctite'd in place with the input just .050" from the bottom of the drain. Final testing included recirculating fuel in a loop some 12 inches above the tank. The drain works really well, and it seems possible to pump the tank completely dry. Several test runs were made and thankfully no leaks. - Terry
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Your work "sets the standard" (- that I fail to achieve!).
K2
K2
As mentioned earlier, I wanted to make a new starter solenoid because the one designed around a 40 amp automotive relay wound up much too big. A new one was designed around a power MOSFET whose heatsink set a lower limit of the solenoid's size. In this simple switching application for a MOSFET, it's the internal heat created by the device's ON resistance that needs to be controlled.
Guesstimates based upon earlier starter tests showed the solenoid may have to handle cranking currents as high as 70 amps. A TO-220 packaged Infineon IPP011N03LF2S was selected for its impressive 200 amp capacity and .001 ohm ON resistance (which by the way is an order of magnitude lower than the relay's contact resistance). At a worst-case 70 amps this would work out to be 5 watts of dissipation inside the Delrin solenoid.
The new solenoid was designed, but only its heatsink was initially machined for some preliminary tests. A pair of screws eventually connect the heat sink to the solenoid's mounting bracket and so the MOSFET must also be electrically insulated from the heatsink.
While waiting for the .001 ohm MOSFET to arrive, I mounted a .012 ohm IRF3205 MOSFET (I had plenty of these on hand) to the heatsink for testing. A 20 amp resistive load was set up to generate 5 watts of heat in the test device. Measurements showed its temperature approaching 100C in under ten seconds. More scary was the 20C temperature differential measured between the device and its heatsink. Ceramic, mica, and Kapton insulators augmented with silver grease all behaved similarly.
Plan B was to machine the solenoid body from aluminum rather than Delrin and to use the entire solenoid as a heatsink. With the test device mounted to a large chunk of aluminum the results were only marginally better with the device reaching 90C after 20 seconds or so.
The aluminum bodied solenoid was machined, but in the process of tidying up the test area on my bench, I broke a lead off my test device. The replacement part performed so much better that I thought the test had somehow changed.
To make a long story short, the first device came from a batch of 3205's purchased from Amazon, while the second device was taken from a batch purchased from Mouser Electronics - an actual legitimate supplier. Three devices from each batch were tested, and the results were essentially the same. Under identical load conditions the Amazon parts came close to thermal runaway while the Mouser parts warmed up to only 43C or so. In addition, the temperature differentials across the insulators dropped to less than 2C with the Mouser parts.
After reading a couple one star reviews among some 400 positive reviews for the Amazon parts, it was obvious that others who had actually used the parts had run into similar problems. After disassembling a couple, one user discovered the die size of Amazon parts was just a fraction of a legitimate part.
After wasting several days in this rabbit hole, the Delrin body was machined and the new solenoid completed as originally intended. The partially finished aluminum solenoid is a paper weight reminder of my experience with counterfeit Chinese parts.
Tests on the completed solenoid with the .001 ohm MOSFET included a repeat of the 20 amp tests which showed essentially no temperature rise. The solenoid was also tested with an unloaded motor, because the earlier torque tests couldn't be repeated since the test fixture had already been repurposed.
OK, but wait ...
So what goes on inside a 40 amp automotive relay while carrying 20 amps through typical .030 ohm contacts and generating some 12 watts of internal heat? I cut one open and connected it to my test bed to find out. Sure enough, the contacts get hot - 65C in fact. What keeps the relay from self-destruction is an efficient internal heatsink that includes the relay's entire frame, coil, and five thick connector blades. The contacts themselves are bonded to wide copper straps that carry much of the heat away from them where it's conducted through the blades and into sockets and circuit board traces. It's a nice design that uses all five blades to conduct heat out of the relay. - Terry
Guesstimates based upon earlier starter tests showed the solenoid may have to handle cranking currents as high as 70 amps. A TO-220 packaged Infineon IPP011N03LF2S was selected for its impressive 200 amp capacity and .001 ohm ON resistance (which by the way is an order of magnitude lower than the relay's contact resistance). At a worst-case 70 amps this would work out to be 5 watts of dissipation inside the Delrin solenoid.
The new solenoid was designed, but only its heatsink was initially machined for some preliminary tests. A pair of screws eventually connect the heat sink to the solenoid's mounting bracket and so the MOSFET must also be electrically insulated from the heatsink.
While waiting for the .001 ohm MOSFET to arrive, I mounted a .012 ohm IRF3205 MOSFET (I had plenty of these on hand) to the heatsink for testing. A 20 amp resistive load was set up to generate 5 watts of heat in the test device. Measurements showed its temperature approaching 100C in under ten seconds. More scary was the 20C temperature differential measured between the device and its heatsink. Ceramic, mica, and Kapton insulators augmented with silver grease all behaved similarly.
Plan B was to machine the solenoid body from aluminum rather than Delrin and to use the entire solenoid as a heatsink. With the test device mounted to a large chunk of aluminum the results were only marginally better with the device reaching 90C after 20 seconds or so.
The aluminum bodied solenoid was machined, but in the process of tidying up the test area on my bench, I broke a lead off my test device. The replacement part performed so much better that I thought the test had somehow changed.
To make a long story short, the first device came from a batch of 3205's purchased from Amazon, while the second device was taken from a batch purchased from Mouser Electronics - an actual legitimate supplier. Three devices from each batch were tested, and the results were essentially the same. Under identical load conditions the Amazon parts came close to thermal runaway while the Mouser parts warmed up to only 43C or so. In addition, the temperature differentials across the insulators dropped to less than 2C with the Mouser parts.
After reading a couple one star reviews among some 400 positive reviews for the Amazon parts, it was obvious that others who had actually used the parts had run into similar problems. After disassembling a couple, one user discovered the die size of Amazon parts was just a fraction of a legitimate part.
After wasting several days in this rabbit hole, the Delrin body was machined and the new solenoid completed as originally intended. The partially finished aluminum solenoid is a paper weight reminder of my experience with counterfeit Chinese parts.
Tests on the completed solenoid with the .001 ohm MOSFET included a repeat of the 20 amp tests which showed essentially no temperature rise. The solenoid was also tested with an unloaded motor, because the earlier torque tests couldn't be repeated since the test fixture had already been repurposed.
OK, but wait ...
So what goes on inside a 40 amp automotive relay while carrying 20 amps through typical .030 ohm contacts and generating some 12 watts of internal heat? I cut one open and connected it to my test bed to find out. Sure enough, the contacts get hot - 65C in fact. What keeps the relay from self-destruction is an efficient internal heatsink that includes the relay's entire frame, coil, and five thick connector blades. The contacts themselves are bonded to wide copper straps that carry much of the heat away from them where it's conducted through the blades and into sockets and circuit board traces. It's a nice design that uses all five blades to conduct heat out of the relay. - Terry
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Very slick Terry:
I've read lots about the quality of Chinese knock off parts. And folks exposing them.
I also had an experience with some small "Mosfets". Tested out that they were just regular transistors.
I'm glad you subjected yours to your usual rigorous testing. Sad that we can't trust Chinese junk.
Looking at the "real" Mosfets - those are very impressive. I may have to order some just to have around.
Considering your usual build quality, that "solenoid" probably won't have to endure any more that a few seconds of activation.
A very nice final result.
I've read lots about the quality of Chinese knock off parts. And folks exposing them.
I also had an experience with some small "Mosfets". Tested out that they were just regular transistors.
I'm glad you subjected yours to your usual rigorous testing. Sad that we can't trust Chinese junk.
Looking at the "real" Mosfets - those are very impressive. I may have to order some just to have around.
Considering your usual build quality, that "solenoid" probably won't have to endure any more that a few seconds of activation.
A very nice final result.
Terry,
Thanks so much for doing and sharing that testing. I have also found that high current semi conductors of questionable origin have a high infant mortality rate and that heatsinks don't help much with high inrush current. Sticking with name brands from a supplier like Mouser or Digikey is the safest route. I have more than one breadboard with a hole burned in the middle of it.
Lloyd
Thanks so much for doing and sharing that testing. I have also found that high current semi conductors of questionable origin have a high infant mortality rate and that heatsinks don't help much with high inrush current. Sticking with name brands from a supplier like Mouser or Digikey is the safest route. I have more than one breadboard with a hole burned in the middle of it.
Lloyd
Solid state is fairly impervious to stink bugs, too.
I would have expected more from 200 amps at 50vdc.
I would have expected more from 200 amps at 50vdc.
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Apparently stink bugs are fairly non-conductive, especially when electrocuted. If that contactor had a 200A feed maybe Edison was on to something, DC is safer than AC?
How did that bug get into that contactor anyway? Doesn't look like he should have been able to squeeze through those slots.
Don
How did that bug get into that contactor anyway? Doesn't look like he should have been able to squeeze through those slots.
Don
Stink bugs love to, and are capable of, squeezing thru very small cracks. And grouping into an infestation, yuck! The contactor is SPST-NO so the stink bug must have been asleep between the 2 terminals while they were open and maybe it had enough resistance in its body to prevent initial continuity. The Li batt pack is capable of dumping more than 200 amps, but apparently did not at that time. No flames and splattered guts.
EDIT- sorry. I realize some of my posts might be leaning in the direction of hijacking the thread, which was not my intention. My apologies. Lloyd
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Piston Rings: Blank Preparation . . .
I've run out of excuses to start working on the piston rings, and so they're now underway. I'm anal about precision when it comes to piston rings, and for me their machining has typically been an exercise in frustration and patience. Asymmetrical stresses left in cast iron after it's cooled can cause parts to distort during machining and even days later. The ring's form factor particularly makes it a problem.
I've experimented with machining sequences, depths of cut, preheating, and relaxation strategies all with questionable degrees of success. The best rings have come from small choice areas in the central areas of finished blanks and sometimes with yields as low as 10%. Blank material that didn't finish up to within a couple tenths of being round or not on the final o.d. target is scrapped, and I've have a collection of shiny cast iron tubes to show for it.
In the last dozen or so years I've used the 'Trimble method' to make hundreds of rings. Fervent discussions about other techniques pop up all the time, but I was won over by the science behind the performance and longevity of George Trimble's rings first described in his 1989 Strictly IC articles.
Trimble's method requires a shop-made normalization fixture that's designed around the rings' exact finished dimensions. Its purpose is to set the ring's final shape so that after installation the ring will apply uniform contact pressure around the cylinder wall. Trimble's 1475F normalization temperature is the only part of his process that hasn't withstood the test of time. I use 1050F which is a compromise of what others with more metallurgical knowledge than I have recommend. Controlling this temperature in a home shop without a suitable oven can be difficult, and this along with a lack of understanding of Trimble's original treatises may be why other methods have found favor over the years.
Trimble's method begins with the ring's o.d. and calculates a width and thickness to produce an optimum cylinder contact pressure. These numbers plus clearances are used to machine the ring grooves in the pistons. These calculations along with those that will be used to machine the fixture are shown in the worksheet in the first photo.
I've used gray cast iron (also known as class 40 cast iron) for all my rings. It's available in centrifugally cast rounds from multiple suppliers. The 1-1/2" round used for the 289's rings was purchased sometime in the 90's from now defunct Enco and has been relaxing in my shop for the last 25 years.
A 3" band-sawed starting blank was prepared with the hope of winding up with two inches of finished candidate ring material. After skimming its entire o.d., the blank was chucked in the lathe and left there for the remainder of its machining. Fifty percent of the excess o.d. stock was removed, the i.d. was rough drilled to 7/8" before leaving the workpiece to relax overnight. The i.d. was bored to its finished diameter the next day. The one inch holding spigot was left solid to avoid clamping-induced distortion in the finished area.
The workpiece was allowed to rest for another day before the o.d. was turned to its finished diameter plus two thousandths. Sharp inserts intended for aluminum and .040" (dia.) depths of cut were used. The o.d.'s last two thousandths were polished away the next day using 220g and then 400g paper. Quadrature measurements were continually mic'd at three equally spaced points along its length during polishing. The diameters were left two tenths oversize and the blank allowed to rest overnight before being remeasured for the final time.
As it turned out this was the first ring blank in my memory that remained well-behaved throughout its machining. The entire finished area wound up round within a tenth and the o.d. within two tenths of my target. I'd like to believe I finally stumbled upon an optimum ring machining process, but the results probably had more to do with the age of the material. After 25 years it had no energy left for hide-and-seek games. Although I probably could have gotten all the rings needed plus spares from this blank, a second one was identically prepared and it too was trouble-free.
The finished blanks were moved to the Wabeco lathe and a simple program written to part 40 rings from each blank. The Trimble calculations had been used earlier to machine the piston groove widths to .027". The rings were parted off with .027" widths and then lapped to their final dimension which was .025" +.0005"/-0".
Lapping the rings isn't for cosmetics. Smooth sides are important because during combustion the bottom face of the ring must seal against the lower face of the piston groove so combustion gasses behind the ring can push and seal the ring to the cylinder wall. Of course, the lower face of the ring groove must also provide a smooth sealing surface. Without this seal, an otherwise perfect ring will have excessive blow-by and compression loss.
A simple shop-tool was used to uniformly grip the rings while they were being lapped. The first thousandth was removed using 400g paper over a surface plate, and remainder was lapped away on a glass plate using 600g grease. The inside corners of the rings were broken using a cylindrical ceramic file, but the outside corners were left sharp.
After a ring is parted from its blank, it's difficult to judge its quality without completely finishing it and running a light test, and all this will be done next. For now, all rings from both blanks are being lapped (half are completed), and at ten minutes per ring, I have another seven hours of mind-numbing work ahead. - Terry
I've run out of excuses to start working on the piston rings, and so they're now underway. I'm anal about precision when it comes to piston rings, and for me their machining has typically been an exercise in frustration and patience. Asymmetrical stresses left in cast iron after it's cooled can cause parts to distort during machining and even days later. The ring's form factor particularly makes it a problem.
I've experimented with machining sequences, depths of cut, preheating, and relaxation strategies all with questionable degrees of success. The best rings have come from small choice areas in the central areas of finished blanks and sometimes with yields as low as 10%. Blank material that didn't finish up to within a couple tenths of being round or not on the final o.d. target is scrapped, and I've have a collection of shiny cast iron tubes to show for it.
In the last dozen or so years I've used the 'Trimble method' to make hundreds of rings. Fervent discussions about other techniques pop up all the time, but I was won over by the science behind the performance and longevity of George Trimble's rings first described in his 1989 Strictly IC articles.
Trimble's method requires a shop-made normalization fixture that's designed around the rings' exact finished dimensions. Its purpose is to set the ring's final shape so that after installation the ring will apply uniform contact pressure around the cylinder wall. Trimble's 1475F normalization temperature is the only part of his process that hasn't withstood the test of time. I use 1050F which is a compromise of what others with more metallurgical knowledge than I have recommend. Controlling this temperature in a home shop without a suitable oven can be difficult, and this along with a lack of understanding of Trimble's original treatises may be why other methods have found favor over the years.
Trimble's method begins with the ring's o.d. and calculates a width and thickness to produce an optimum cylinder contact pressure. These numbers plus clearances are used to machine the ring grooves in the pistons. These calculations along with those that will be used to machine the fixture are shown in the worksheet in the first photo.
I've used gray cast iron (also known as class 40 cast iron) for all my rings. It's available in centrifugally cast rounds from multiple suppliers. The 1-1/2" round used for the 289's rings was purchased sometime in the 90's from now defunct Enco and has been relaxing in my shop for the last 25 years.
A 3" band-sawed starting blank was prepared with the hope of winding up with two inches of finished candidate ring material. After skimming its entire o.d., the blank was chucked in the lathe and left there for the remainder of its machining. Fifty percent of the excess o.d. stock was removed, the i.d. was rough drilled to 7/8" before leaving the workpiece to relax overnight. The i.d. was bored to its finished diameter the next day. The one inch holding spigot was left solid to avoid clamping-induced distortion in the finished area.
The workpiece was allowed to rest for another day before the o.d. was turned to its finished diameter plus two thousandths. Sharp inserts intended for aluminum and .040" (dia.) depths of cut were used. The o.d.'s last two thousandths were polished away the next day using 220g and then 400g paper. Quadrature measurements were continually mic'd at three equally spaced points along its length during polishing. The diameters were left two tenths oversize and the blank allowed to rest overnight before being remeasured for the final time.
As it turned out this was the first ring blank in my memory that remained well-behaved throughout its machining. The entire finished area wound up round within a tenth and the o.d. within two tenths of my target. I'd like to believe I finally stumbled upon an optimum ring machining process, but the results probably had more to do with the age of the material. After 25 years it had no energy left for hide-and-seek games. Although I probably could have gotten all the rings needed plus spares from this blank, a second one was identically prepared and it too was trouble-free.
The finished blanks were moved to the Wabeco lathe and a simple program written to part 40 rings from each blank. The Trimble calculations had been used earlier to machine the piston groove widths to .027". The rings were parted off with .027" widths and then lapped to their final dimension which was .025" +.0005"/-0".
Lapping the rings isn't for cosmetics. Smooth sides are important because during combustion the bottom face of the ring must seal against the lower face of the piston groove so combustion gasses behind the ring can push and seal the ring to the cylinder wall. Of course, the lower face of the ring groove must also provide a smooth sealing surface. Without this seal, an otherwise perfect ring will have excessive blow-by and compression loss.
A simple shop-tool was used to uniformly grip the rings while they were being lapped. The first thousandth was removed using 400g paper over a surface plate, and remainder was lapped away on a glass plate using 600g grease. The inside corners of the rings were broken using a cylindrical ceramic file, but the outside corners were left sharp.
After a ring is parted from its blank, it's difficult to judge its quality without completely finishing it and running a light test, and all this will be done next. For now, all rings from both blanks are being lapped (half are completed), and at ten minutes per ring, I have another seven hours of mind-numbing work ahead. - Terry
