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  1. #1
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    Advice for welding brake bosses on Hotrock 16"

    I have a friend who is a welder and is going to tig weld bosses on my hotrock frame and fork. Only problem is, I don't know to much about frame building. I would like to have everything all set up for him and ready to go. Has anyone done this? and possibly able to offer some advice. I am going to make a jig like this one

    Installing Cantilever Brake Bosses

    The part I am most unsure of is which bosses would best suit the fork and which for the frame?

    Bosses

    I am thinking L7 and J3.

    Thanks for any advice!

  2. #2
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    Is this a newer hotrock with aluminum frame? If so, you will need aluminum bosses not steel. If it is an aluminum frame, you need to know the alloy series to match the boss. 6000 series aluminum require a post weld heat treatment regime that is impractically expensive for a single frame.
    If the frame is steel (and for the steel fork) it is a much more straightforward job to add steel bosses. You generally want the bosses set around 80mm apart so measure your fork width and try to determine the miter style that will be needed to achieve that separation. You can always use a file to alter the miter as needed to achieve exact fit if the pre-cut miter is not correct.

  3. #3
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    Thanks Grayjay!! Yes, you are right. It is a 2007. The series is not clear on Specialized site but after a bit of research everyone seems to agree that it is a 6000 series. I had also read about the post heat treat but was didn't realize it would be necessary for this procedure. If that is the case I def. would not do the fork and maybe abandon this altogether.

    You are also right about those bosses. Do you know of a source for 6000 series bosses?

    Thanks for your insight!!

  4. #4
    CJH
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    Quote Originally Posted by bikin222 View Post
    I had also read about the post heat treat but was didn't realize it would be necessary for this procedure. If that is the case I def. would not do the fork and maybe abandon this altogether.
    There are a lot of discussions about this on the web but most of them have to do with adding disc brake mounts to older aluminum frames. The consensus seems to be that heat treating the frame is necessary. Same rules would apply to welding on V brake bosses.

    I'm sure you already know your other options but I'll mention them anyways. A few here have done disc brake conversions with homemade or after market disc brake adapters. New hub required.

    There are also the V brake adapter from Dan's Comp (no longer carried but maybe on Ebay) and the bolt on adapters from Evolution Bike Company which aren't supposed to be in stock until the end of the summer, at least the last time I checked. I wouldn't run either with the stock coaster hub save for maybe a short learning period where both brake types were available. After that you could either do a new hub (cheaper, lighter and more options than the disc brake hub options) or convert the existing hub to a free coaster.

    If you welder friend has access to a machine shop he might be able to come up with some sort of adapter for less overall money than having the frame properly heat treated.

  5. #5
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    6000 and 7000 alu bosses are available from Nova;
    CANTI AND "U" BRAKE BOSS :: ALUMINUM SMALL PARTS :: BRAZON/SMALL PARTS :: Nova Cycles Supply Inc.

    Looks like the hotrock fork is hi-tensile steel, not aluminum like the frame. Hi-ten steel is usually thick an heavy, an alternate way to upgrade the fork would be to start with a decent CrMo rigid fork and cut it down to shorten then add new fork ends to fit the 16" wheel.

    unanealed 6061 aluminum has only 1/3 the tensile strength of T6 treated. Probably a fair chance that the frame is sufficinetly overbuilt for a sub 40 pound rider that it would survive OK if the bosses were welded to the seatstays but this would be ill advised for modifying a bike for a full size rider.

  6. #6
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    Yes, I am aware of all the mods. As well as all the different bikes available, like the banshee, which would make more sense. He just turned three so I have a few more months but I really like projects like this. I found the Hotrock on CL for $20 so I have room in the budget for things like bosses. I also bought a Pitboss on CL for way to much $ but it is an awesome bike. The BB height on the Pitboss is much higher than the Hotrock. When he gets a bit bigger my thought was, that the Pitboss he could use at the track and the Hotrock can be made more like a Mtn bike.

    Thanks once again GrayJay! I am going to see what I can do for a heattreat? The fork is an aluminum blade with high ten steerer. I live in a big boatbuilding town and I might get lucky.

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    read-up on frame heat treating in thread;
    Cracked frame, what should I expect?

    concensious is that it it cost prohibitive to have a single frame heat treated, would likely cost hundreds of dollars to have the necessary treatment performed. Frame manufactures are able to have the treatment done in large batches of frames so the per-unit cost is reasonable.

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    Very good reading, thanks! Surely the people on here that had disc tabs welded on did not do a heat treat. I would not do it to a fork but I wonder how catastrophic of a failure would occur? Especially from a sub 40 pounder. Those bikes are so overbuilt.

    Well anyways, thanks for the help and maybe I will just make an adapter. Much simpler.

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    Just stumbled on to this thread by accident, but I do have some input that may be of value.
    I have 3 kids, my middle daughter has been riding without training wheels since right after her third birthday. The biggest challenge was (and still is, now that she is 8) brakes.
    Brake levers for kids are crap.
    Bars and grips are so big that small children can hardly wrap their fingers around them. Then reaching the brake lever isn't possible unless you get the wheels absolutely true, the v-brakes set super close, and then dial in the lever reach adjuster until it is bottomed out. Then there is the spring force in the v-brakes and friction in the cables that add to the challenges.

    I have been hoping and wishing I could find an affordable frame with disc mounts. That would boost her confidence levels immensely.

    Good luck!

  10. #10
    CJH
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    Quote Originally Posted by bikin222 View Post
    The fork is an aluminum blade with high ten steerer.
    Just curious but does a magnet stick to the fork blades?

    Our 2013 Hotrock 16 is listed as having an "Alloy blade w/ 1-1/8" Hi-Ten threaded steerer" but a magnet sticks to the fork blades.

    I haven't taken it apart to check the steer tube.

  11. #11
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    Pictures certainly look like the HR16 has a steel fork. Perhaps they garbled the specifications and meant to say that the blades are a steel alloy (such as CrMo). The blades look to be welded directly to the steer tube which wouldnt be possible if they were aluminum and steel. Joining dissimilar metals would require that the steel steer be pressed into a separate aluminum lug which the blades are welded onto.

    Much simpler than adding V-mounts or disk tabs, you might consider using long-reach sidepull brakes, might just need to drill the fork crown and frame bridge for the mounting bolt.

  12. #12
    CJH
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    Quote Originally Posted by GrayJay View Post
    Pictures certainly look like the HR16 has a steel fork. Perhaps they garbled the specifications and meant to say that the blades are a steel alloy (such as CrMo). The blades look to be welded directly to the steer tube which wouldnt be possible if they were aluminum and steel. Joining dissimilar metals would require that the steel steer be pressed into a separate aluminum lug which the blades are welded onto.

    Much simpler than adding V-mounts or disk tabs, you might consider using long-reach sidepull brakes, might just need to drill the fork crown and frame bridge for the mounting bolt.
    I just looked up the spec for the 2007 Hotrock 16 which the OP has and the fork is listed as:

    A1 Premium Aluminium blade, 1" threaded Hi-Ten steerer

    Our 2013, on the other hand, is listed as:

    Alloy blade w/ 1-1/8" Hi-Ten threaded steerer, 3/8" axle dropouts

    Since a magnet sticks to the fork leg on ours I'm guessing you're correct, by alloy they mean a steel alloy that can still be welded to a high tensile steer tube.

    I'd be curious to know how they did it with the 2007.

  13. #13
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    On my fork the blade is riveted to the steer tube. That being the case I am sure that it is aluminum. The unfortunate part about that is, that if I was to do any kind of post weld heat treat it would anneal the steer tube. It is such a heavy walled tubing though, I am not sure it would have a huge impact?

  14. #14
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    The steel steer tube would not be effected by the 1000F aluminum heat treatment regime. Plain steel is commonly brazed together with silver at 1200F and with bronze at 1600F without needing to be further heat treated. I might just be worried that there could be some epoxy adhesive used in the "riveted" joint between the legs and the steer tube which might be affected by heat.

  15. #15
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    Advice for welding brake bosses on Hotrock 16"-screen-shot-2014-07-10-09.20.17.jpg

    I've just welded a disc adapter onto the HR16 I'm currently building for my son. First time tigging ally so not perfect but it'll do.

    Not convinced about the effects from the heat on such a little frame, under so little stress - i.e. being ridden by a 5 year old. But nevertheless I'm considering sending it off to be heat-treated anyway. AHT are happy to do frames.

    Suppose I could see how it goes and if the rear stay cracks, re-weld and then send it off.

    Either way... this thing now has some decent stopping power. Onza trials disc hubs on the way. Need to weld up a seat post as 22mm posts seem to be all but extinct.

  16. #16
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    That looks great. Nice job!! I am very curious what effects this have? If you are looking seatposts all the BMX micro mini posts are the right size.

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