My E30/R5Turbo track car - Gearbox MkIII

[GeoffBob]

Time for an update.

I stripped the gearbox output shaft this weekend, meaning that I progressively pressed off the gears that "float" on the shaft, along with the various clutch-hubs and bearings. For reasons that I have yet to discover, 1st, 2nd and 5th gears ride on needle bearings, but 3rd simply rides on the hardened surface of the shaft (with grooves for oil to penetrate and lubricate). 4th Gear is a whole different kettle of fish since it is part of the spigot shaft, so ignore 4th. Anyway, why Toyota in their wisdom decided to do it this way I have no idea, because, when I pulled the gears off the shaft I discovered that 3rd gear had tried to seize itself to the output shaft ! The shaft was visibly burned and burred, looking much like a big-end or main shell bearing does after a seize. Not a pretty sight. The inside surface of the 3rd gear didn’t look much better TBH. In its defence, 3rd gear probably wasn’t designed to work as hard as I have pushed it. Keep in mind that the output shaft was one of the few pieces I retained from the original gearbox. I can’t see how this seize could have contributed to the demise of the 3rd dog-ring, but I am sure there has be a connection somewhere.

And so, as well as having the dog-rings remanufactured I am having the output shaft turned down, the gear ground out, and a needle bearing fitted. Once I have the new dog-rings I’ll loctite them in place as per Keri’s suggestion. Keri PM’d me his personal guarantee that his Loctite idea would work or he’d refund my money spent ”¦.


”¦. on the bottle of loctite

Other news is that I have finally, after goodness knows how long, started to assemble my Quaife ATB differential into an E30 final drive casing, along with a 41:10 ratio crown-wheel and pinion salvaged from an E32 differential. It is going to be so nice to get away from that horrible 40:11 final drive ratio that was only ever supposed to be temporary while I got the Quaife put together.

[keri-WMS]

HAHAHAHAHAAAA!

[GeoffBob]

I received the modified output shaft with the added needle bearing today. Should be less likely to seize now. I am, however, not at all happy with the new dog-rings. The quality is poor compared to last time so I have decided to send them back. The chamfer on the edge of the dog teeth looks like it was done by a drunk wielding a hand-held grinder. Is it any different anywhere in the world these days? Businesses are so anxious to attract new clients that they couldn't give a toss for the existing ones. I can see myself rapidly becoming an ex-client.

[billgatese30]

Is it any different anywhere in the world these days? Businesses are so anxious to attract new clients that they couldn't give a toss for the existing ones. I can see myself rapidly becoming an ex-client.

It sounds like its pretty universal around the globe then. Usually the only way to solve these sort of problems are to run up a tab each month that looks more like a telephone number than a price

[GeoffBob]

It sounds like its pretty universal around the globe then. Usually the only way to solve these sort of problems are to run up a tab each month that looks more like a telephone number than a price

Agreed. If I built gearboxes on a more regular basis then that might be the case. But since it's only my hobby my custom is worth little or nothing to anyone .

I have thus decided to abandon the whole "press-fit dog-ring" idea in favour of a "shrink-fit". I have been assured by a colleague that the shrink-fit technique has been reliably used by a number of gearbox manufacturers on protoype gearboxes, the advantage being that it allows gears to be heated, removed and replaced while experimenting with ratios. This time around the gear will take the form of the "ring" and will be shrunk fit over the now substantially meatier dog ring. Any chance of breakage should be alleviated since both parts will comprise a fair volume (roughly 50% each) of material (whereas it was roughly 80% gear, 20% dog-ring before). I'll post up the new design for comments when I get that far. This time round I am going to handle the heat treatment process PERSONALLY. Luckily I have a colleague here at work who used to work on big gun barrels and is an expert on both virgin steels and their subsquent heat treatment. I wish I had known this earlier on in the process, but we live and learn

[billgatese30]

It sounds like its pretty universal around the globe then. Usually the only way to solve these sort of problems are to run up a tab each month that looks more like a telephone number than a price

Agreed. If I built gearboxes on a more regular basis then that might be the case. But since it's only my hobby my custom is worth little or nothing to anyone .

I have thus decided to abandon the whole "press-fit dog-ring" idea in favour of a "shrink-fit". I have been assured by a colleague that the shrink-fit technique has been reliably used by a number of gearbox manufacturers on protoype gearboxes, the advantage being that it allows gears to be heated, removed and replaced while experimenting with ratios. This time around the gear will take the form of the "ring" and will be shrunk fit over the now substantially meatier dog ring. Any chance of breakage should be alleviated since both parts will comprise a fair volume (roughly 50% each) of material (whereas it was roughly 80% gear, 20% dog-ring before). I'll post up the new design for comments when I get that far. This time round I am going to handle the heat treatment process PERSONALLY. Luckily I have a colleague here at work who used to work on big gun barrels and is an expert on both virgin steels and their subsquent heat treatment. I wish I had known this earlier on in the process, but we live and learn

That could come in handy...a 105mm artillery barrel poking out of the front of the car should prevent anyone from holding you up on a trackday ever again, although you may need to recalculate your COG.

[GeoffBob]

That could come in handy...a 105mm artillery barrel poking out of the front of the car should prevent anyone from holding you up on a trackday ever again, although you may need to recalculate your COG.

LOL, not for me thanks

Well, I have finally finished the redesign of the 1st, 2nd, 3rd and 5th driven-gears plus dog-rings. No more splines for the dog-rings to slide off. I hereby declare that hence forth the gears will be shrunk fit over the dog-rings. I have also spent a bit of time reading DeGarmo's Materials and Processes in Manufacturing in order to brush-up on the hardening and tempering of carbon steel. If I had my own furnace I'd do the heat treatment of the new bits myself - seems a reasonably straight forward process.

[MillRat]

I have also spent a bit of time reading DeGarmo's Materials and Processes in Manufacturing in order to brush-up on the hardening and tempering of carbon steel. If I had my own furnace I'd do the heat treatment of the new bits myself - seems a reasonably straight forward process.

Haha, yeah that's why most of us have furnace in the back yard... because it is dead easy

Only you could think that Geoff.

[billgatese30]

The principles of heat treatment are relatively straight forwards, its things such as vacuum hardening that become more difficult on a "back garden" level. But a straight forward furnace that you can control the temperature of, and can stay at that temperature long enough to allow the material to "soak" then its fine. Quenching is even more straight forward so long as your method isn't just dropping in the tank.

Most steels come with hardening specifications from the manufacturer, they give approx soak times per inch of thickness, soak temperatures, quench mediums and then temper temperatures to achieve various hardness levels.

That being said, it'll never be as good as somthing that has been vacuum hardened though as doing it in a regular furnace will always allow oxidisation to form and then the quenching can induce quite a bit of warp-age compared to an industrial vac-hardening setup.

[GeoffBob]

Haha, yeah that's why most of us have furnace in the back yard... because it is dead easy

Only you could think that Geoff.

Reminds me of a book I read at Christmas, Look Me in the Eye by Jon Elder Robison. He recounts how a mate of his built his own furnace in his garage for smelting various materials. That ended nastily with magnesium fire (from an old Beetle gearbox if I recall correctly) that the fire-brigade tried to put out with water, which resulted in a magnesium explosion!

[GeoffBob]

The principles of heat treatment are relatively straight forwards, its things such as vacuum hardening that become more difficult on a "back garden" level. But a straight forward furnace that you can control the temperature of, and can stay at that temperature long enough to allow the material to "soak" then its fine. Quenching is even more straight forward so long as your method isn't just dropping in the tank.

Most steels come with hardening specifications from the manufacturer, they give approx soak times per inch of thickness, soak temperatures, quench mediums and then temper temperatures to achieve various hardness levels.

That being said, it'll never be as good as somthing that has been vacuum hardened though as doing it in a regular furnace will always allow oxidisation to form and then the quenching can induce quite a bit of warp-age compared to an industrial vac-hardening setup.

You are quite right Chris. The workshop next door to my lab here at work has a very nice furnace (electric kiln) that I had thought of using, but it would never give the same result as professional vacuum hardening.

Superstition has it that the best quenching medium for hardening carbon-steel is urine from a red-head. That reminds me, what happened to Gareth, he seems to have dissapeared off the zone?

Chris, looking at the cross-section of my broken dog-ring under a microscope reveals what appears to large crystals of Martensite, which may have been why the ring broke (Martensite being brittle). I can't help wondering if they forgot to temper the parts after hardening them? Or possibly the tempering process was rushed?

One thing is for sure, I have to be part of the manufacturing and treatment quality control process to make sure the job is done properly this time around. Trust No One is my new motto.

[GeoffBob]

For those interested, you can download a PDF showing my new gearbox design here. I finished drawing this up yesterday (Sunday). Everything remains the same with the exception of parts 3, 4, 5, 6, 9, 11, 15 and 16 which must be remanufactured. The major change to the design is that the gears now fit over the dog-rings, as opposed to the previous design where the dog-rings pressed over the gears. I really should have done it this way in the first place. With each dog-ring now comprising a great deal more material than before (and provided they are hardened and tempered correctly this time around) they should remain intact. The other major change is that I have done away with the splines between the dog-ring and the gear. The gears will now be heated and then shrunk onto the body of each dog-ring. Since this technique has been used with success by gearbox manufacturers, I suspect that it will hold up better than my spline idea.

Other news is that I am busy searching locally for a more diligent gear-cutter. I have thus far asked SKS-Gears of Benoni to quote for the job. I was going to give ARMA gears another chance but then decided ”af*ck ”˜Em”a.

[billgatese30]

Where were you seeing the martensite formations Geoff? Was the heat treat constant throughout the material or was it on the outside/inside. I'm curious if they hardened and tempered the entire assembly then case hardened or flame hardened the outside face to give a good balance between toughness, dimensional stability and wear resistance on the working surfaces (and then went too deep which made them brittle) or if they cocked up the tempering by not allowing them to soak for long enough which means too much of the core was still hardened and made them brittle, even though they would pass any non destructive surface hardness measurement. Or alternatively if it was consistent all the way through and they just haven't had the temper temperature high enough (or they have cooled too quickly for the temperature they tempered at etc).

[GeoffBob]

Chris, the old design dog rings were very thin, with a cross section of just over a 1cm^2. Martensite appeared to cover the full cross-section on nearly every fragment of the ring I examined. I doubt that they hardened the entire assembly as I received the parts separate from each other. I suspect that they could have cocked up the hardening of the rings in one of two ways:

• 1) They didn’t soak the rings for long enough during tempering. I somehow doubt this though, given how thin the rings are. As I understand it (I could be wrong), its the soak temperature, not the soak time that is critical during tempering, provided the timer is set for sufficiently long for diffusion to have occurred throughout the volume of material. If the timer is set too long its simply energy wasted. Set too short however, and it can leave the material brittle inside where pockets of martensite remain.
  2) They overcooked the rings while flame hardening them. The heat from the flame would have most likely gone straight through the ring, making null and void the tempering process, causing martensite to form over again. This is the most likely cause imo.

Either that or they never tempered them at all. The new rings that were delivered the other week are like glass. I'd be scared to use them as coasters for fear that they'd smash if they fell off the table and landed on the carpet . I work a lot with ferrite made from scintered iron alloyed with other metals, and my goodness is that stuff hard but brittle. It's impossible to machine, virtually impossible to grind, and chips like mad. That's almost how these rings feel.

One other thing that has occurred to me is that the poor quality (loose) fit of the splines (where the ring pressed onto the gear) was likely due to some degree of permanent expansion of the rings brought about during heat treatment. The further I get away from the old design the better.

[GeoffBob]

'Had some spare time today so I have been phoning around trying to get the inside story on exactly how and by whom my gears were heat treated. In a nut-shell, they were case-hardened (see here for the process). According to the bloke at Bohler Heat Treatment, the fact that martensite formed all the way to the centre means that the material was not EN36, and could have been EN19 or EN24. Only way to truly tell is for me to grind a sample of the broken ring flat and then do a hardness test. If it was made from EN36 then the centre of the ring should be around 30 to 35 on the Rockwell-C scale. If it was EN19 or EN24 (higher carbon content) it would have hardened all the way through.

FYI, case hardening is employed to harden the surface of low carbon steels (such as EN36) and requires that the sample is placed in a furnace with a ”acarbon-pack”a. The carbon thus diffuses into the surface of the material, resulting in the formation of martensite along the surface. The inside of the piece remains martensite free since EN36 is a low carbon steel to start off with. It’s pretty obvious then that you’ll have a problem if you use a high carbon steel to start off with. I got this information after I spoke with Bohler Heat Treatment. When I confronted Veron Pappas back at ARMA gears he admitted that ”athere may have been a mix up in my materials”a, but he insists that it was only on the dog-rings. Would you trust him if you were me? I doubt it.

I have located a reputable supplier of carbon steel locally and I will in future be buying my own certified materials and taking them for hardening (post manufacture) myself. Now all I need is for someone reputable to do the manufacturing for me. I have thus far had two local gear companies turn my work down today because the application is ”aautomotive”a (they only do industrial low-speed gears ”“ IE: work for the local mines). I get the feeling that a number of people have had their fingers burned on this type of work before. I even had one tell me that ”ait is impossible to have gears of sufficient quality for the auto industry made in South Africa”a. The deficiency, he claimed, is in the hardening process where quality control is absent. Tell me about it. Doesn’t help much if you start the job with the wrong grade of steel either

[billgatese30]

I find it hard to believe that there is no one in South Africa who is capable of hardening them properly. Its hardly like you live in the dark ages. The guy you spoke to about the case hardening sounds like he knows what he's talking about. Sourcing your own materials sounds like a good idea too.

Sounds like the failure of the dog rings has been a mix of bad material and poor heat treatment. Although with the flame hardening your previous design will have been prone to heating up with such little mass of its own if the fit between the splines wasn't that great as there will have been very little contact to transmit the heat away into the main body of the gear, although the low carbon steel meant that, that shouldn't have been too much of an issue on its own.

I work with a lot of tungsten carbide everyday, and as good as it is for what we need (metal pressing/stamping punches and dies) its a bitch to machine. Rough machining can be done with turning and milling with specialist cutting tips (bloody expensive so we don't use them). All of our finishing work is then either done by surface or cylindrical grinding and/or spark erosion (EDM).


It would be interesting to see how hard the different rings are. Both the old vs new rings (that you fear are too brittle), and the outer edge vs the centre of each ring. I am assuming that you have access to some hardness testing equipment of course. I would offer to do some Vickers Microhardness tests on them for you, alas I fear the cost of postage for you to ship some samples would be prohibitive. Unless you prepared some small cross sectional samples so they fit into a very small/lightweight package.

[GeoffBob]

Thanks for the offer Chris, but I'm pretty sure I can get someone in our metalurgy lab to test a few of the new and broken pieces for me.

I agree that it should be possible to have the pieces both manufactured and hardened locally - All the materials, machines and equipment to do the job are here. One does, however, have to be careful in choosing a service provider (machine shop, materials processor etc) who takes pride in their work. When I phoned Bohler yesterday the bloke on the end of the phone readily answered all my questions and kept calling me "sir", even though it eventually transpired that my work-pieces had been sent to Universal Hardeners and not Bohler (another fact that I wasn't aware of). He instilled me with such confidence that he will get all my work in future.

I am currently struggling to find a gear-maker who is prepared to take on my work. They all want big jobs from the mines and have no time for small jobs from individuals like me (mining is BIG business here). I may very well have to go back to Veron at ARMA gears. Luckily I haven't yet burned that bridge. He's basically a pretty decent person, just sloppy. Somehow I have to get him on my side so that he will enforce quality control upon his artisans. Now that he knows I am prepared to decline sloppy workmanship he'll either pull it together, or decline my custom like the others. I have considered asking a generic machine shop to do the work for me, but a generic shop is unlikely to have a hobbing machine, and would likely use a wire cutter (since my gears are straight cut). A NC hobbing machine is a much more accurate solution. Of course the machine is only as accurate as the operator sets it up, and so once again we come back to the issue of pride.

I am of the opinion that industry in South Africa is progressively turning into a clone of British Leyland. Quality workmanship is not the norm, and poor quality is always countered by a list of demands and excuses. Whatever happened to getting fired for not being able to do the job? The US is still very much like that to this day (or so I am told).

[billgatese30]

No problem Geoff, if there's anything I can do to help then don't be afraid to ask.

Unfortunately the problem is choice.....and trust. That I will leave down to you, but I certainly don't envy your decision

depending on the machine shop you could always enter some form of contract where by you pay for any materials up front and only pay the balance upon verifying the final quality for yourself. I suppose if you were a mining company that would be easy, but they may turn you away as a 'civilian' as you therefore have no credibility when it comes to credit/payments made after delivery/completion unlike if you were a registered company.

[GeoffBob]

I just spent the morning with Dr Segran Govender from the Materials Lab here at the CSIR where I work. He had no comment with regard to the use of EN36 vs EN19 as the base material (he appears to be an aluminium, magnesium and titanium alloy specialist) but he referred me to someone in the industry who is. Dr Govender did, however, speak volumes with regard to the design of my dog-rings. He did not like the dog-teeth, specifically commenting on the lack of radius at the root of each tooth, exactly as per Gareth's earlier comment (well done Gareth). He was even more concerned, however, when I told him that the small radius that is there was applied post hardening with a grinding tool. He commented specifically that any radius must be applied pre-hardening and not as an ”aafter thought”a. I left the broken ring with him to perform a "micro-vickers" test on it. Unlike my other colleague, he wasn't prepared to comment on the coarse texture of the fracture, saying only that we wouldn't know that the material core was excessively brittle until after the micro-vickers test had been performed. Clearly a wise man who only puts his neck on the block when he has the scientific evidence to back his diagnosis up. I now await the result.

In the mean time I phoned his industry colleague, Dr Jeff Ferreira (who specialises in the post manufacture processing of steel), for advice on the base material and subsequent hardening process. EN36, as it turns out, is the correct material for the job. He does however recommend that we specify the exact process of hardening and tempering to be followed in order to prevent any furture failure. He commented that the process of carburising such a small part can easily go wrong, especially if my parts were thrown in the furnace with a batch of someone else’s parts. I can well believe that’s exactly what happened.

I will thus be delivering my gears and dog-rings to Dr Ferreira post manufacture, and then return them to ARMA gears for final surface grind and polish (post hardening). It seems that I am slowly getting to grips with this problem.

[keri-WMS]

Superstition has it that the best quenching medium for hardening carbon-steel is urine from a red-head. That reminds me, what happened to Gareth, he seems to have dissapeared off the zone?

Hahaha, I'll let him he's needed. I know what happened to him.......she's tall......and blond!

(The Great Ginge will be back, don't you worry. )

[GeoffBob]

Thanks Keri, it would be good to have him back. I wonder what happened to Mikey_Boy as well? A lof people dropping off the zone these days - quite sad. I almost did at one point.

[keri-WMS]

I'm sure most people will come back - this place (usually! ) has a touch of class that's missing in many other forums...

Gareth says he'll be try to get on here tonight, but by being offline for a while he's in a pickle in terms of reading / catching up on all his threads in one go!

[UweM3]

GeoffBob, I am sure that I teach a grandma sucking eggs but if you need to really cool something down for shrink fit you can use ACETON and DRYICE. as a cooling bath.
That's as cold as it gets for "home-use", approx -70degC.
You can substitute the Aceton with white spirit but it will loose you a few degrees.

[GeoffBob]

GeoffBob, I am sure that I teach a grandma sucking eggs but if you need to really cool something down for shrink fit you can use ACETON and DRYICE. as a cooling bath.
That's as cold as it gets for "home-use", approx -70degC.
You can substitute the Aceton with white spirit but it will loose you a few degrees.

Thanks Uwe, I appreciate your input. I need a temperature difference of roughly 200'C to get over the 0.1mm difference between the diameter of the two pieces. I was going to use my oven at home to raise the temperature of the gear to roughly 150'C, but was stumped as to what to use to cool the dog-ring down the other 50'C. The process of fitting the two parts together will have to happen after the parts have been hardened, so I can’t raise the temperature of the gear over 200’C or I could begin to anneal it.

Acetone I have plenty of, and dry ice I am sure I can get. Thanks for the tip.

[gareth]

Did someone say my name?

I've got 81 pages of posts to read... err, this may take some time!

Looks like i've missed lots of excitement Geoff. I'm loving your approach to this... you're a stubborn bugger aren't you

[UweM3]

GeoffBob, I am sure that I teach a grandma sucking eggs but if you need to really cool something down for shrink fit you can use ACETON and DRYICE. as a cooling bath.
That's as cold as it gets for "home-use", approx -70degC.
You can substitute the Aceton with white spirit but it will loose you a few degrees.

Thanks Uwe, I appreciate your input. I need a temperature difference of roughly 200'C to get over the 0.1mm difference between the diameter of the two pieces. I was going to use my oven at home to raise the temperature of the gear to roughly 150'C, but was stumped as to what to use to cool the dog-ring down the other 50'C. The process of fitting the two parts together will have to happen after the parts have been hardened, so I can’t raise the temperature of the gear over 200’C or I could begin to anneal it.

Acetone I have plenty of, and dry ice I am sure I can get. Thanks for the tip.

Your're welcome. The better you can stop your cooling container to lose temperature to the surrounding air, the longer the Aceton/Dryice mix will last. I would suggest something made from Polypropelene, maybe an old 10liter oil container cut in half?
Clad the outside with polystyrene sheets and put a lid on top, that will give you some hours of cooling.

[GeoffBob]

Did someone say my name?

I've got 81 pages of posts to read... err, this may take some time!

Welcome back Gareth, how's the blonde ?

Looks like i've missed lots of excitement Geoff. I'm loving your approach to this... you're a stubborn bugger aren't you

Oh yes, quite stubborn! I will eventually get this one sorted.

FYI, now that my dog-ring has so much more meat on it I have the room available to put in the radiused edge that you recommended. I'll post up a drawing later for comments. I recon that I'll have the new drawings and certified materials to the gear cutter by next week some time.

[GeoffBob]

Your're welcome. The better you can stop your cooling container to lose temperature to the surrounding air, the longer the Aceton/Dryice mix will last. I would suggest something made from Polypropelene, maybe an old 10liter oil container cut in half?
Clad the outside with polystyrene sheets and put a lid on top, that will give you some hours of cooling.

Thanks Uwe, will do. Glad to see you're still around on the zone too

[GeoffBob]

Well, I did some very basic calculations to determine the shear force applied to the dog-teeth of the old design. I assumed 550 Nm of torque (worst-case) at my flywheel, which is 100 Nm higher than that recorded at the wheels during the recent dyno session. Following the torque path through the gearbox this results in (assuming zero frictional losses) an output torque of 1100 Nm, 856 Nm, 678 Nm, 550 Nm and 444 Nm in 1st though 5th gears respectively. Given that there are twelve dog-teeth that engage with each selector ring, given that I know the mean radius (to the centre-line through the teeth) of each dog ring, and given that I know the area of the root of each tooth, I then determined a shear stress of 42 MPa, 33 Mpa, 30 Mpa, 24 Mpa and 32 Mpa on the 1st through 5th dog-teeth respectively. Note that the 5th gear value is greater than, not less than, that of 4th gear since the 5th dog ring is located on the lay-shaft, not the output shaft like the other dog-rings.

Now, these values are calculated assuming a torque of 550 Nm applied (by the engine) to the spigot (input) shaft of the gearbox. In reality we can expect values up to three times higher than this due to the backlash between the selector-ring and the dog-ring. With that said, that still only gets us to a peak shear stress (on the 1st dog ring) of around 120 MPa. As a rule of thumb, the shear strength of a material is around half its tensile strength. Ordinary mild steel, for example, has a shear strength of around 150 MPa. So, given that my dog-rings were manufactured from case-hardened carbon-steel, why did my 3rd dog-ring fracture and fail? The answer is quite simple: Stress lines concentrate on sharp corners. Even though the mean (average) dynamic stress (over the area of the tooth) may not have exceeded 120 Mpa (as estimated for the 1st dog ring above) the stress at these concentrated points can be many times greater. I would estimate the shear strength of my dog-rings to be around 300 to 400 MPa, a figure easily exceeded given that I failed to radius these edges as Gareth recommended I do. An examination of the broken dog-ring shows quite clearly that the fractures formed at the sharp corners where the stress would have been at its greatest. When my third gear started to seize on the shaft it was the straw that broke the camels back and the 3rd dog-ring simply came apart.



My new design thus includes:
1) A proper bearing on the output shaft under the 3rd gear (same as the others), and
2) A proper radius at the root of each dog-tooth.

Sorry I didn't take your recomendation more seriously at that time Gareth. Until I had done my own analysis of the problem (and consulted with Dr Govender) I was really in no place to comment.

See here for the new dog-ring design. Given that the new rings are larger than the old ones I have the room to include a decent radius at the base of the teeth.

Opinions and comments, as always, most welcome please.

[GeoffBob]

Shown below is how the new design dog-ring will engage with the selector ring.

[GeoffBob]

One 550 mm long by 100 mm OD bar of Bohler M120 carbon-steel on its way from Sheffield, England to Johannesburg, South Africa. I couldn't find what I needed locally, so I opted to import it. Should be here in a few days time.

BTW, with the exception of the "regulars" does anyone actually read this thread? What I mean is, is it still worth me posting up here? Is my work of any interest to anyone, or should I just f*ck off down the zone pub and take up bickering as my new hobby? I get the feeling I'm talking to myself these days.

[baptie0]

Hi Geoff, keep posting the progress, I am reading

[GeoffBob]

Thanks mate, much appreciated

[e301988325i]

I have no doubt many are readig this, with 99% of us learning and hence have little to add. I'm amazed how inefficient helical gear teeth are at full chat, based on your flywheel dyno figure being way too high!

Home designed gearbox. . . That's just bloody awesome!

I use bohler for a lot of material at work, specifically, hardenable M340, 22CR Duplex and 25Cr Super Duplex.

[billgatese30]

Sorry Geoff, I forgot to reply to this the other day. I read it in work on my phone whilst in a meeting but didn't get chance to reply as I got brought into the conversation (you've got to love conference calls...although I should have been paying more attention )

That new design looks much stronger with the teeth facing in-over rather than out over (or is that the selector and the dog ring is still the inner with the larger radii). As you have mentioned previously if you keep an eye on any radii then they should be pretty much indestructible for what you need. I'm pretty sure there is some math which I have never learned (or have forgotton) which will help you calculate the most effective radii (without removing too much material) but I'll leave that ball well and truly in your court as your way smarter than me when it comes to that (I rely too much on SolidWorks to do the hard work for me).





and if you do leave the forum, I'll swim to S.A and kidnap your heat treatment guy (assuming no body beats me to it at the traffic lights...or kidnaps me at the traffic lights) and I'll hold him to ransom until you post another update.