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Forum Index : Windmills : - NEW ALUMINIUM BLADES -
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fillm Guru  Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi All, Recently after the failure of the blade arm on my Ax Fx I was contacted by OEM who kindly offered to replace my blades with the new aluminium extrusion . The new set of 1.5mt blades arrived about a week ago and to look at are of good quality and have the same proven airfoil as the pvc . The major differences are of course being aluminium are the improved rigidity and strength in the blade its self and of course with the sheer strength with using rivets/bolts to attach the blade to the tube . The other major difference is the 4 c channels in the extrusion , allowing the end caps to be screwed on , the other major advantage of these is being able to align shorter sections during assy ( allows freight costs to be kept to a min with Aus Post ) and could also be used to house small pieces of 2.5mm ( welding rod ) in place for balancing . There are quite a few advantages that these do have over the PVC , not affected by UV , painting is a lot simpler or could be used unpainted with leading edge tape , the overall weight is slightly lighter . Along with extra advantages all so comes the disadvantage that the price is going to be a little higher . I have been offered to distribute the new blades here in Australia , the production of the PVC blades has stopped due to the development of the new blade . Glenn has put the order page onto the "kits and parts" link next to the PVC order link and people will be able to choose between Aluminium or PVC , Anthony / Jabar is still holding stock of the PVC Blades and I assume that will stay there until he is sold out . I will be taking pre orders at present, as I do not expect the first shipment until later in December. The cost per mtr is expected to be $40~$45 + Freight . At present I am also in the process of designing two different blade hubs to suit , one being a more DIY type that does address the loading that these blades can exert and is based on s/s tube and high tensile 4140 solid bar , more info will be posted here and my page in kits and parts over the coming month. Pics of New Aluminium Blades 
Link to order Here PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
awesome. Luck favours the well prepared |
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Warning: unpleasant message about to follow. I don't know who this OEM is, but I hope he has good liability insurance - he may need it. So may you, in case there's a risk of a blade damaging other property or people than your own. (update: I just read you are actually about to sell these blades - in which case you *definitely* need to look into the liability issue, for your own interest). Aluminium extrusions are great for static loads. But aluminium is also notoriously prone to fatigue due to dynamical stresses. Unlike steel, it has *no* minimum stress level below which fatigue will not occur. When aluminium is dynamically stressed (as in a windturbine blade), it is nearly guaranteed to suffer from fatigue. The only question is how long it will take - one week, one year, one decade, one century.... Taking amateur construction and design into account, where concentrated stresses are to be expected due to large transitions in cross-section and stiffness of the construction (e.g. where the extrustion is shoved over the shaft, at the point where the shaft stops) I really fear for this construction. Not to overdramatize the issue, but, how to say it... I *really* fear. To give an idea: if you were my neighbour and I knew what you were doing, I'd at first tell you orally to please cease and desist. If no reaction, I'd send a written official letter. If that failed too, I'd have my lawyer send an official letter so an official trackrecord of my concern would exist. It would be of use in future litigation that would likely occur in the case of one of those blades breaking and damaging my property, me or my loved ones. That's how strongly I feel about this issue. Sorry, don't intend to rain on your parade, those extrusions look very nice - but they're not suitable for this purpose, in my opinion. If you live in the middle of nowhere and your house is 500m away from your turbine, then by all means play with those blades. But if your local situation is different from that ideal one though, then I'd be extremely careful and cauteous about those blades and how you mount them. If you do intend to use these blades (I think I've made it clear that I would never use them myself): [quote=Fillm]The major differences are of course being aluminium are the improved rigidity and strength in the blade its self and of course with the sheer strength with using rivets/bolts to attach the blade to the tube .[/quote] Using rivets or bolts would not be smart as they introduce very defined point-stresses that are likely to start fatigue cracks when not done properly. Glueing or crimping are much more suitable. Also, make sure that there are *no* abrupt transitions in cross-section or stiffness. If the final construction is stressed (e.g. pushing down on a tip), if nearly all the bending is at one particular point (e.g. where the round pipe inside the extrude profile stops), then you have a problem. That point (and the places where fasteners are attached, screws, rivets,etc.) are likely to be the failure points of the construction. You may want to polish the entire blade to remove all scratches that could start as crack initiators. Please read up on proper design and construction methods for aluminium to at least reduce fatigue problems. Prevention is impossible, but you may succeed in postponing failure to beyond your lifetime. Only after writing the above I noticed you are even about to sell those blades. I do not know how legal liability situation is in Australia, but I'd *really* look into that matter before I would start offering these blades to the general public. You may be unkowingly exposing yourself to serious risks here. I don't see what's wrong with those old-fashioned wooden blades. Unlike aluminium, it has excellent fatigue strength. It's much better suited for the application in windturbines than aluminium. No wooden aircraft ever crashed due to fatigue. The above may come off overly dramatic, but it is how strongly *I* feel about this issue. Let everyone inform and decide for himself. With apologies to Phill, as I have no intention of destroying his sales, but I think it's in the best interest of everyone (buyers and seller) to fully realize what they are getting into. Peter. |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
does depend on the condition of the aluminium. if its soft T0-T3 then it would probably be OK with fatigue as the shaft is taking most of the load My only concern was the stainless shaft is further up the galvanic scale (than steel) and will cause corrosion. If you can paint both stainless shaft and inside of blade and wet assemble with polysulfide sealant, corrosion will be solved. The sealant is also a pretty good glue and should reduce point load stresses (ie around the rivets) to a minimum. Corrosion on the outside caused by weather is OK as you can see it and monitor it, from the inside out is a problem. As with ANY windturbine it should be reasonable distance from a dwelling. Imagine the shaft being flung out from the hum at 1.5KG+ at full speed.... Similarly be it an aircraft or a windmill you should never stand in line with the blades whilst in operation. Luck favours the well prepared |
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| anteror Senior Member Joined: 06/10/2009 Location: FinlandPosts: 189 |
Do not use aluminium for windgenerators or their blades. It has so low endurance limit, fatigue resistance. Read my story "Factory made... Antero |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Peter , If the same guidlines that are outlined in the proceedure for providing a structial support for the PVC section as for these blades then I do not see to many problems , the aluminium blade is a section and not designed as a structual member it is like the skin of an aircraft wing and needs be supported . It is designed to have a tube inserted into it for support , modern aircraft designers/engineers seem to think that aluminium over a frame can handle the loads exerted by the worlds largest of aircraft . I would think that a rivet through aluminium opposed to pvc into either steel or stainless tube would have a far greater sheer strength than glueing a blade on to a tube as a way of mounting , due to differences in material expansion and contraction in the sun , a blade could go through many cycles in one day . As for the legalities of putting a windmill up in surburbia , whether it has wood , fiberglass , steel , carbon fiber or aluminium blades there is always a risk of failure ,and damage or injury through failure , that is why you should see you bylaws before erecting one . To be specific that only aluminium blades will fail makes me concerned about aircraft propellers and a multitude of applications where aluminium is used in high stressed applications in todays world . I am not sure with what you are trying to say with regards to having a windmill with aluminium blade with in 500m of your house , if a windmill with aluminium blades let one go as did one with a timber blade and both weighed the same , then which would travel further ? Which would do the most damage if it hit something and would the legal responsibilities be different , and as for the person who built them either in wood or Al , is the liability that different for either material? Obviously you are a big fan of timber blades . PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| frepdx Newbie  Joined: 16/11/2009 Location: Posts: 7 |
It's true that Aluminum doesn't have a fatigue limit, but that doesn't mean it's unusable. Steel, too, is often loaded above it's fatigue limit if the application calls for it. Look under your car's hood an you'll see all kinds of aluminum castings. In this application, however, I'd be a little weary of using thin section aluminum blades without looking very closely at the loadings. It has high cycles, large loadings, and the blades will be moving at tremendous speeds when they fail. Also, bonding a steel shaft to an aluminum blade can be tricky; they have different thermal coefficients of expansion, different Youngs Moduli and galvanic potential. I'd look at some type of structural aerospace adhesive with a couple of mechanical fasteners as backup. Another thing to consider when it comes to fatigue loading; you mostly worry about tensile stresses, not compressive stresses, along with the number of stress reversals. Just thinking out loud here ... is there a way to mount the blade so that it runs mostly under compression? Maybe a high quality adhesive between the shaft and the blade, and a mechanical keeper at the outside radius, possibly a cool looking spoiler? If you're really clever you could pre-stress the joint while gluing such that the aluminum is under compression during operation. |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
These blades as with the pvc are not designed to take the load exerted at the root , where it attaches to the hub , ALL the loads MUST be carried by the support rod , this is why I am going to high tensile 4140 solid steel 30% of the blade cord encased with s/s tube to 75% of the blade cord . All retaining of these two will be done at the blade hub so no welding or undersizing is needed in high stress areas . Karl , The point you have made with corrosion in dissimilar metals , internal inspections could be carried out at times when one had there windmill down for maintainence , the end cap is easy to remove to allow a visual inspection , I would think with corroson you would get a residue , and this would be built up in end cap as a tell tale sign if it was starting to happen . However I am verifing the grade of aluminium used and will post the info . PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Hello Phill, I'm not going to argue this issue, I've expressed my concern and that's enough for me. I'll leave the rest of it up to others. This will be my final response on the topic. [quote]the aluminium blade is a section and not designed as a structual member it is like the skin of an aircraft wing and needs be supported .[/quote] I don't recall reading that in your original post or on Glenn's sale page. I'd make this *very* clear to any buyers of this product if I were selling these blades. I must admit that most of my initial concern was because of the idea of using an internal steel rod that didn't go through the full length of the extrusion, i.e. people using the rod only to conveniently connect the blade and the hub. Using a full-length rod may change the situation for blade bending, but the issue of blade torsion and other bending modes remains. In your original story (and on the link to Glenn's sale page) I notice talk about sheer strength (hardly a relevant performance indicator for a windturbine blade material) and total absence of things like fatigue strength. Ask yourself: what kinds of loads do aluminium extruded profiles normally see, in the majority of applications. Or: for what kinds of products are aluminium extrusions normally used. That will show that your application lies pretty far out of the normal realm of where such things are used, which leaves you with little experience of others to fall back upon, making you (and any buyers) in effect a beta-tester of an experimental product in an experimental application. [quote]due to differences in material expansion and contraction in the sun , a blade could go through many cycles in one day[/quote] A windturbine blade may go through many hundreds of cycles per second. Not because of thermal expansion, but just by whirring around. Windturbines excell as fatigue testers of a construction. [quote]I would think that a rivet through aluminium opposed to pvc into either steel or stainless tube would have a far greater sheer strength than glueing[/quote] I wouldn't put my money on that statement. (and as a sidenote, sheer strength is hardly relevant for dynamic loads, fatigue is likely to be a more stringent and thus relevant limit.) I put more faith in modern adhesives than rivets. So did Fokker for many applications in their aircraft. Look into the specifications of something as simple as Loctite 638 and be impressed. Rivets can yield sound constructions too - when the joint is designed and fabrication executed properly. But adhesives benefit from usually large contact areas, that spread the loading over a large area and reduce concentrated stresses at, say, holes and rivets. [quote]To be specific that only aluminium blades will fail makes me concerned about aircraft propellers and a multitude of applications where aluminium is used in high stressed applications in todays world .[/quote] Any material that doesn't have an endurance limit (or a product that doesn't stay below this limit) *will* fail in a dynamically loaded application. The question is just how long it will take. If you hold an aircraft propeller, you'll notice it is solid - not an aluminium extrusion. Aircraft propellors are also subject to a very regular inspection regimen where they regularly get inspected for defects. Also, propellors (at least in small aircraft) are at eye height, making routine inspection easy. Aluminium windturbine blades are unlikely to get the similar treatment as those propellor blades: unlikely to be regularly inspected, not massive but extruded (though the steel rod hopefully compensates for that), and many turbine users will only lower their windmill (or climb up the tower) when there's no other option, i.e. it has an obvious defect. [quote]I am not sure with what you are trying to say with regards to having a windmill with aluminium blade with in 500m of your house , if a windmill with aluminium blades let one go as did one with a timber blade and both weighed the same , then which would travel further[/quote] I wasn't thinking about just distance travelled or weight, I am thinking of *risk*: the probability that something goes wrong, multiplied by the damage/cost of that. I estimate the risks of an aluminium blade as higher than that of a wooden blade. If only because anyone can buy an extrusion and 'sort of' fix it on a hub, whereas it takes someone skilled (and thus probably educated, i.e. read windturbine forums for a while) to make a wooden blade. [quote]and would the legal responsibilities be different , and as for the person who built them either in wood or Al , is the liability that different for either material? [/quote] Yes, the responsibilities may be very different. Most builders fabricate their own wooden blades, so responsibility and liability rests entirely with them. You sell a blade (or at least, a half-fabricate that's only manufactured and sold with the intent to use in a windturbine blade, thereby suggesting 'fitness of use' for that purpose) to another party. This greatly changes the situation. [quote]Obviously you are a big fan of timber blades .[/quote] I'm a fan of using the most suitable material and construction method for the task at hand. Wood (being a natural composite) is far superior to many a man-made material (including many GFRPs) when it comes to taking dynamic loads. I certainly consider it superior to both steel and aluminium w.r.t. fatigue properties. With this response I end my participation in this discussion. I'm not looking for a discussion on the internet with anyone on the (de-) merits of wood vs. aluminium vs. ....., or proper construction methods. I have expressed my concerns of aluminium (extruded) blades and that, to me, settles it and eases my conscience. I have done my duty, the rest is up to others. Peter. |
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| JimBo911 Senior Member Joined: 26/03/2009 Location: United StatesPosts: 262 |
Phill Why not mount the new Alu blades on your two mills and give them the chance to do there thing? Follow your up grade ideas and make some wattage, that's what where here for right? Jim |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Blades have been crafted from many different materials over time, and some have stood out from the others for different reasons. Wood as Dinges has pointed out has outstanding qualities and this is probably due to the fact that wood stands up to these forces naturally, as that is their job when they busy being a tree. Other materials that are favourites are fiberglass and carbon fiber..... etc etc..... Aluminium has been trialled by a few with mixed results. Aluminium is a fabulous material, and can work as a blade in this application as well as any other chosen material....... but only if it incorporated in the design... taking into account it's inherent properties. I have no problem at all with aluminium used as a blade material, provided it is used knowing it's frailties, and designing around them. A blanket fear of the material used in this application is unfounded and unjustified in my opinion. In this designs case, I have no query at all with the blade itself. It will not fail if used properly. The blade set will fail if it is used as if it were some other material. It's that simple. If it is used like wood, and you expect it to suffer the same abuse as timber can..... then prepare or failure. In this case, provided it is mounted correctly, it will last indefinitely... just as an aluminum dingy or boat can. (now there is a stressful environment). I entertain maximum concern if they are mounted as were the plastic ones... and they will fail the same as the plastic ones did..... not the blades per say, but the mounting system. Simply mount the blades so they don't suffer the bending forces, and the aluminum cannot fail..... ever. A solid rod/ heavy wall tube right up the middle with an end cap, means that the blades cannot fail, and cannot fly off. Torque forces from twist are feeble, and the center rod takes all the forces, the blades are just along for the ride...... so much for the anti aluminum argument... just design it out The weak link is then the steel rod..... and if the mill is kept to a reasonable diameter, and the rods mounted with thought, should last forever as well.... the Al blade cannot get away... even if they were to fracture and crack/split So whilst I agree with Dinges, that aluminum has short comings if used as a substitute for other materials, it is quite possible to use it sensibly for blade applications. I would not use Macgyvers mounting system for anything other than the small scale blades he uses. To strap a set of that kind Al blades to a hub for a 4 meter set like mine would be suicide, as they simply replace wood, but these blades, properly mounted should pose no threat.... and I would use glue to stop them rotating around the rod/ heavy tube, and maybe a rivet near the tips to hold them at the right pitch till the glue dried. The Al is not the problem, it is the mounting system. When DanB's wooden blades fell to bits on his 20' mill, no-one pointed to the wood substrate... they rightly pointed to the design and manufacture by the craftsman who built them..... yes even wood fails if used poorly... there are plenty of busted wooden blades sets out there as well......all design faults... not wood faults..... this includes mine  .
Steel sheet is another no no material.... even for tails (dire warnings on fieldlines). But sensibly mounted lasts for over 60 years on a pumper mill. It eventually rusts away over here, but does not fail from fatigue... It's not what you use but how you use it. So I would heed Dinges warnings.... and then design it with these in mind...... you would need to do this with plastic any way..... which wasn't done ( and we have seen the results), and plastic bends and twists without all the nasty Al fatigue issues no problems... so that wasn't the real worry... was it. ...........oztules Village idiot...or... just another hack out of his depth |
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| Jarbar Senior Member Joined: 03/02/2008 Location: AustraliaPosts: 225 |
I'm inclined to agree with Oztules summation.And as Jim said let's get some up and flying.Macgyver mooted the idea of leaving the endcaps off reasoning the airflow over tip could help reduce overspeeding.The air flowing through the blade might be better than long periods of condesate accumulating inside closed cavity. Anthony. "Creativity is detirmined by the way you hold your tounge".My Father "Your generation will have to correct the problems made by mine".My Grandfather. |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
LOL 'tules said it better than me. polysulfide sealant remains flexible PRC desoto sell it but may be able to get a cheaper alternative perhaps SikaLastomer® 710. leaving the tip caps off to prevent overspeeding looks to me like wishful thinking.. furling is the go!! Luck favours the well prepared |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I certainly would not like to be within earshot of hollow ended blades. Think about how a siren works. Keep the ends closed. Gordon. become more energy aware |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5124 |
Apparently some testing was done by OEM on leaving the end caps off, and there was no noticeable increase in noise. But I would have to hear it to believe it. Besides, little critters will want to take up residence inside a hollow blade. I have heard of a turbine going out of balance when a hornets nest was built on one blade, and I have problems with tree frogs camping inside my F&P hub. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| dsmith1427 Newbie Joined: 21/07/2009 Location: United StatesPosts: 5 |
A turbine with a 3M diameter has a circumference of 14.1 meters. If the cut in speed is 150 RPM, which is 9000 revolutions per hour, the velocity of the tip is 127 Kilometers per hour. At one meter from the center of the turbine, the speed will be 56.5 KPM. The skin IS a structural member. At 127 KPM, the skin of the blade will see a lot of sheer force which will transfer into the fasteners. The shear force could couple with the bending causing the blades to flutter which leads to fatigue. Anyway, these are my thoughts. Don |
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Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
A 3 meter Dia. Turbine will have a circumference of PI * Dia. I get ( 9.42 meters.? = 150 Rev's * 9.42 = 1413 meters minute. divided by 1000 = 1.4 Kilometer per minute, 60 minutes times 1.4 = 84 kilo per hour tip velocity. Don't regard this as a slap in the face. believe me, I've been corrected many times on the net and it hurts. Now I try to be very careful what I publish. Note; You can edit your post when you see an error or don't like the way it looks, If You do it before anyone has replied to it. just log on and find your post, click the edit button and make your changes. Your Point was well illustrated. Time has proven that I am blind to the Obvious, some of the above may be True? |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi All , I aggree totally with what Oztules has said on the previous page with regards to the design of the mounting for these blades , as I have stated they are not a structual member . I have pretty well come up with my new design for how I will be mounting these when they go onto the Ax Fx . I have completly eliminated the need for welding on the tube , the 22mm solid does not need machining in any criticial load area . I am now using a higher grade solid 4140 which is much stronger than normal steel rod and the system if used will allow a high degree of adjustibility with regards to blade pitch , tip run out and also tip to tip measurement which are all as important as each other to getting smooth running blades. Before this mounting system will be offered to mount these blades I will be load testing for sheer limits in my press , I may even look at getting an engineer to look at it as well . Karl , the aluminium grade that is used is 6303-T5 which is commonly used fo extrusions . With regards to not using end caps , I do think the noise would soon make you put them on . I drilled a 6mm hole in my PVC end caps to allow any water to escape as I dont seal root ends , they started to whistle at certain rpms so I closed them to a smaller hole with silastic . Keeping the root caps off does allow ventilation but if you have a frog problem it might pay to use mesh . There has been some coments made with regards to glueing the section , I do not have knowledge or experience in this field but feel if glue was used then I would still be using some rivets as well. A lot of valid points have been made with regards to these new blades , and we have learnt a lot of lessons on what not to do with the PVC Blades and hopefully we now don't have to many more lessons to learn PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
T5 is pretty hard stuff ie in a hard state of tune so to speak as far as aly goes. but as you suggest its there to maintain the blade profile and nothing more. I'd suggest making the load path taper by drilling a hole into the centre of the solid bar at least 3/8 diameter and a couple of inches deep so the loads dont basically stop at that point but rather transition. this should solve/help the abrupt loading change that will occur at this point and cause fatigue. Karl Luck favours the well prepared |
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| frepdx Newbie Joined: 16/11/2009 Location: Posts: 7 |
solid 4140 seems like overkill, very expensive. Unfortunately, hiring a registered professional engineer is expensive too. They are taking legal responsibility and sometimes have to buy malpractice insurance, all of which you pay for. Nevertheless, creating a 'best mounting practices' for this blade is a good idea. You might consider cold drawn seamless tube (it's called CDSM in my part of the world). Very strong and accurate stuff, and probably less expensive than solid 4140. Certain loads will be reduced with less mass spinning, although I don't know how its fatigue strength compares to solid 4140. sounds prudent. |
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