What type of aluminium are drop outs made of ?

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  • What type of aluminium are drop outs made of ?
  • Another tandem related question I’m afraid.
    I want to modify a 145mm rear hub width tandem frame to take a standard 135mm hub.
    The plan is to cut two 5mm thick shims to the same shape as the drop outs and get them welded to the inner faces.
    I spoke to the guy from the motorbike shop where I will probably get this done today and he said it would be helpful to know what the alloy is so the welder would know what rods to use.

    Manufacturers always state that their frames are made of 6061, 7075, or whatever, but nobody ever mentions the drop outs.
    So, does anyone know what it is likely to be ?

    cynic-al
    Member

    If each alloy requires different rods, won’t dropouts be the same as the frames?

    Premier Icon aracer
    Subscriber

    You’d think so wouldn’t you – and in any case I doubt they’re all the same.

    khani
    Member

    Edit,, non reading me..

    crankrider
    Member

    If they are bolt-on dropouts they will 95% of the time be 6082T6 if the uk has had anything to do with making them or 6061T6.

    If it is a welded frame then as above – the dropout would usually be made from the same stuff….

    The dropouts are welded to the frame.
    I don’t think the problem is that different alloys can’t be welded together, it’s more that he would need to know what the two alloys are.

    So, as I understand it, a 6061 dropout could easily be welded to a 7075 seat stay by the frame manufacturer, using the correct rods, but anyone then wanting to weld to those dropouts would need to know what they are.

    Retrodirect
    Member

    why not just get tiny wee allen-bolts to hold the inserts on? I mean, they’re really only acting like spacers, no?

    Bolting the shims on won’t work.
    I’ll be using a Rohloff hub, which is only available in 135mm width and the axle itself only extends about 5mm beyond the lock nuts each side, so the shims will be taking the full weight.

    Macavity
    Member

    Photos can be a good thing.
    Trying to weld a “5mm shim” onto the side of a comparatively thicker and much larger dropout (frame) could be quite a challenge. To get enough heat into the drop-out / frame and not have the shim just melt away and still make a good weld could be difficult. The bigger the shim the more heat it will take.
    Just to clarify, the shim will need to be of comparable alloy type to the drop-outs. The drop-outs will be of comparable material to the frame tubes. ie 6061 to 6061, or, 7005 to 7005.

    Still quite a challenge to do well.

    What about using epoxy or other glues? I’m sure I’ve hard of motorbike ehadtubes being glued on rather than welded to reduce distortion and save weight, so I’m sure some dropouts would be fine.

    Some interesting links there, Macavity, although I hope the welder will know most of that stuff already.
    A couple of pictures then, which should help explain what I’m trying to do.

    A shim, cut from cardboard just to show the idea.

    The shim in place.

    I’ve found some 5mm plate on ebay, but it’s 1050 grade.
    This is where I need the expert advice, or to speak to the welder himself, to know if 1050 will weld to whatever the dropout is likely to be made of.

    Yes, glue would be another option.
    As I mentioned earlier, the Rohloff axle won’t extend through these shims to the original dropout, so the shims will be taking the full weight and drive load of two people on a tandem.
    I think I would need some proper advice on contact area and shear load before chancing it.

    Premier Icon scotroutes
    Subscriber

    Would it not be better to get the rear of the frame modified so that the dropouts are only 135 mm apart?

    Yes, that would be by far the easiest option, except that reading various forums where people have asked about mixing and matching road and MTB 120, 126, 130 and 135 hubs and frames, it sounds like “cold setting” or bending an aluminium frame even 5mm is not recommended.

    Premier Icon scotroutes
    Subscriber

    I was thinking of cutting/welding rather than bending. Or how about getting some new dropouts machined up and replacing the existing ones?

    Edit: I’m not an engineer, just making sure you’ve considered other possibilities.

    Premier Icon jameso
    Subscriber

    This sounds like an accident waiting to happen.
    2 riders weight and all the brake force reacting against that join? No axle support in the frame itself? High-mileage rider with a rep for broken frames..? : )

    Narrowing the frame to 135mm by cutting and welding would involve cutting off the seat stays and chain stays at the BB and seat tube, shortening the seat stay bridge, then welding it all back together, preferably in a jig to keep it all aligned.
    That sounds like far more work and not something I would trust to anyone other than a proper frame builder. A lot more painting afterwards as well.
    Welding two small plates in is comparatively straightforward. If it was steel, I’d do it myself.

    Jameso, if you look at the potential weld area between my shim and the dropout, I’m sure the force needed to shear the weld would be far greater than the force need to break the dropout away from the seat stay or chain stay.
    I won’t be making the frame any weaker overall than the original design.

    asterix
    Member

    wont you muck up the frame’s heat treatment if you weld new bits to it? I have been warned off welding disk mounts to Alu frames for this reason

    New frame? šŸ™‚

    irelanst
    Member

    I won’t be making the frame any weaker overall than the original design.

    I think that depends on a few factors; first how much of an impact will the welding have on the surrounding area (including the existing welds) and secondly how will the increased torsional loading on the chainstays change the stress distribution locally.

    My own opinion (and Iā€™m not a frame builder) would be cold setting 5mm would be less risky and easier than welding pieces to the frame.

    nbt
    Member

    wrote:

    Some interesting links there, Macavity, although I hope the welder will know most of that stuff already.
    A couple of pictures then, which should help explain what I’m trying to do.

    Looking at that picture, could you not use the existing bolt holes to bolt it in place rather than weld it? looks like they’re rack/mudguard eyelets

    I wouldn’t expect the heat of a new weld about 10mm away from an existing weld would have any further effect on the strength of the existing weld. But then, I’m not a frame builder either.

    I had thought about using those two holes, but it’s a lot of force to put through two M5 bolts. I don’t think they’d take it.
    Drilling more holes for more bolts isn’t really an option either.
    If you look at the other side, there’s not much flat area to put more bolts, unless I replace the hanger bolt with a countersunk M10 bolt an drill a similar hole on the left.
    The inner face of the dropout isn’t flat either, which would make clamping it up with a bolt difficult.

    Looking at those dropouts now, I can’t help wondering if they are cast, not cut from sheet.

    I remember looking at a Chinese site once (XACD, or something like that) selling all sorts of titanium frame fittings, dropouts, BBs, cable guides etc. for frame builders.
    I saw another one, linked to on a thread on STW recently, selling the same sort of stuff, plus lugs, in steel.
    I would hazard a guess that there is a similar site selling aluminium frame fittings, and a small scale tandem frame builder would get their dropouts from them, rather than custom cut or cast their own.
    If I could find that site, I might recognise these dropouts and it might state what alloy they are made of.

    I had thought about using those two holes, but it’s a lot of force to put through two M5 bolts. I don’t think they’d take it.

    They wouldn’t be taking it. Assuming the dropout and new dropout are firmly pressed against each other, my understanding is that the force would be shared by both. Think of how a brake spacer is joined to an IS brake mount, and your dropout has an axle to help on the horizontal plane too.

    Premier Icon jameso
    Subscriber

    They’ll be from one of a couple of large Al fittings suppliers in China and Taiwan I expect. Usually forged and available in 6000 and 7000 series.

    I’d just put a 145mm hub and a mech on it. In all seriousness, I’m no fabrication expert so I don’t know about the join strength or heat affect on that area. You’d need to be an experienced Al frame builder to say with any confidence that it could be fitted to resist the brake (disc?), Rohloff torque, drive and impact forces without affecting the weld that’s next to it. That, and I’ve never seen an Al frame ‘repair’ that’s lasted 5 mins.

    Plus the shortened DH fork that’s headed for the front of a bike designed for 400mm forks.

    All meant with a mix of bodger-spirit respect as well as good-natured ribbing that there’s no way I’d ride your bike : )

    Premier Icon aracer
    Subscriber

    wrote:

    Jameso, if you look at the potential weld area between my shim and the dropout, I’m sure the force needed to shear the weld would be far greater than the force need to break the dropout away from the seat stay or chain stay.

    Are you assuming you’ll get the weld across the whole area of contact? šŸ˜Æ I’m not a welder, but I didn’t think it worked like that – surely at best you’ll manage to weld around the outside of the shim, but even getting a good weld around the whole of that will be tricky.

    At which point, bonding may be a good idea as you will be able to make use of the full contact area. Though I’d be a bit nervous about that given you’re loading the glue in shear, which they’re not necessarily good at. Is there any chance of machining some small grooves in the existing dropouts and ridges in the shims to get a bit of mechanical support (to be honest if you did that well enough it might take the load on its own when clamped up without any bonding or welding)?

    I think your best option is probably belt and braces though – whatever you do you should make use of those bolt holes as well as they will add to the strength. Tricky as you won’t be able to use a flat plate – but then your suggested cardboard shim appears to extend over that area anyway.

    Premier Icon gary
    Subscriber

    Maybe talk to Ben @ Kinetics about this approach – looks more promising than trying to make a convincing bond for a shim

    https://twitter.com/bencooper/status/406468597054464001

    Are you assuming you’ll get the weld across the whole area of contact?

    No, I’m a truck mechanic, so I know a bit about welding steel and the difference between lap joints and butt joints and so on.
    Welding a small plate to a bigger plate with a lap weld on three sides can be incredibly strong. If I was doing this myself in steel, I would expect the parent metal to fail before the weld.

    A bit of searching, and it looks like 6061 is the allooy of choice for dropouts.
    http://www.alibaba.com/product-gs/999135523/aluminum_alloy_bicycle_frame_dropout_Manufacturer.html
    http://www.alibaba.com/product-gs/640431142/alloy_bicycle_dropout.html
    http://www.alibaba.com/product-gs/918004225/aluminium_alloy_bicycle_frame_dropouts_for.html
    http://www.alibaba.com/product-gs/918014774/aluminium_bicycle_frame_dropouts_for_MTB.html

    irelanst
    Member

    I wouldn’t expect the heat of a new weld about 10mm away from an existing weld would have any further effect on the strength of the existing weld.

    Welding temperature of aluminium is about 660Ā°C and the annealing temperature is 300-400. So regardless of the impact on the surrounding area, the plate you get welded on and the new welds will be annealed and weaker than the original structure (The yield strength of annealed 6061 is about 25% that of T6 treated!)

    Macavity
    Member

    “What type of aluminium are drop outs made of ?”

    You can get 6061 dropouts you can get 7005, it depends on the material that they are joined to that will determine the type used.

    http://www.fairing.com/bicycle_frame_depot.asp?subcat=dropout

    Macavity
    Member

    “The yield strength of annealed 6061 is about 25% that of T6 treated!”

    And that is one reason why aluminium dropouts are so big.

    Macavity
    Member

    Now that we have seen the righthand dropout it looks even more of a challenge for a welder to do a neat job.
    The shim idea is horrible.

    The lefthand dropout could have some weld built-up on the inside face to create the 5mm thickness. Build up slightly more than 5mm and then cut it back with whatever implement you choose. Any welder will understand what to do. Have a scrap piece of aluminium shaped to fit in the slot where the axle would fit. Then build up some weld on the inner face of the drop out using 5356 filler wire, then dress it back to the 5mm. Then cut out the scrap piece of aluminium in the slot, there will have been little penetration so it should come out with a bit of drilling etc.
    The right hand drop out looks a bit too delicate for all that though, or atleast would be a challenge.

    Why is the shim idea horrible ?
    I thought it was the neatest, strongest solution.

    Building up with filler wire, then dressing back would put far more heat in to the area and be difficult to get two dead flat parallel faces.

    I’ve spoken to Pinkerton Cycles and the guy there reckons he can do the job.
    I know he builds novelty bikes, so some wouldn’t regard him as a serious frame builder, but if those low riders, cargo bikes, tall bikes and sidecars are holding together with the extra stress that must be on the joints compared to a normal frame, I think I can trust him to weld two small plates.

    Premier Icon porter_jamie
    Subscriber

    5083 material 4043 rod

    I had thought about using those two holes, but it’s a lot of force to put through two M5 bolts. I don’t think they’d take it.

    The bolts dont take the shearing load though, the bolts act in tension only, the shear reaction force is provided by the friction between the shim and dropout. Mill it flat and bolt&glue the shims on, you could even mill some grooves into it and matching ones into the shims. You could even wrap it in epoxy and s-glass or CF.

    I am not a mechanical engineer (but I still think its a better idea than welding).

    The bolts dont take the shearing load though, the bolts act in tension only, the shear reaction force is provided by the friction between the shim and dropout

    This succinctly describes what I was trying to say.

    But I’d still buy a new frame. šŸ˜‰

    or drill out the dropouts to 12mm or larger, and mill the shim to fit into that, you only really need a 4-5mm hole for the QR, so thats quite a solid bit of metal, you could even raise the rear end by 2-3mm to allow for even more metal in the dropout. Might need a custom disk from hope to suit though.

    I just went out to measure the exact dimensions of a Rohloff axle on Mrs MTG’s Kona Big Unit and looking at the sliding dropouts on that, combined with your idea, thisisnotaspoon, I think I may have another solution.

    The Kona dropouts fit within the width of the frame, more or less as I need to do on the tandem.
    They also put the axle below the level of the actual frame dropout.
    Like this.

    It’s hard to describe in words, but I’ll have ago;
    Cut a new dropout from 13mm steel.
    Machine 8mm of it away from all except the axle slot in the frame. It is now a 5mm plate with a 8mm thick boss on one side. This will locate it and support the weight.
    Bolt it to the frame using those two M5 holes. This will also locate it and keep it in place with the wheel removed.
    Cut a 10mm slot below the 8mm thick boss to take the Rohloff axle. This will raise the rear end slightly to match the longer suspension forks I will be using. If I get it right, it also means I can use a 180mm disc adapter with a 200mm disc.

    In fact, thinking about this a bit more, I could probably fabricate this in steel myself.
    I’ll make another cardboard model to show you what I mean.

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