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Tool to hold a suspension fork tube - what type of fit?

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  • thaiguzzi
    replied
    Originally posted by old mart View Post
    Seems that a lot of the people posting cannot tell the difference between conventional and upside down forks.
    LOL. Well said.

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  • 754
    replied
    Here us what a lot of the ones sold look like. Click image for larger version

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  • A.K. Boomer
    replied
    JW glad it worked out for you - im just covering the finer details and some may look at it as overkill but I go with the best methods to start with in case they are needed when working on something, iv worked on allot of Mt. bike shocks both front and rear and on some of the internals the shaft material is actually thin wall anodized aluminum, not much room for cinching error if more and more pressure needs to be applied to keep it from slipping while your trying to break something loose,

    good rule of thumb is slightly undersize and also always use a softer material for the mount in fact iv had to use delrin on some in fear of damaging the tubes - and due to delrin being slippery iv had to dust both surfaces with baking powder to get a grip, you do what you have to to ensure not damaging the piece... iv never damaged a piece and always got what I needed to crack loose loosened...

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  • JW1942
    replied
    Size for size worked beautifully. Here is a little video.

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  • 754
    replied
    Well I for one am not suggesting oversize, I run size for size. On my straightening blocks I run oversize, and if I make a triple tree, i am over size.

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  • A.K. Boomer
    replied
    Yup, slightly under actually gives 6 contact areas of unit pressure and they are much more equal and uniform - slightly over gives only two until the hollow piece your trying to hold is the thing that actually does the deforming, then you end up with 6 again although more on the original two than the outer 4...

    I will add --- even if you go same size and then try to clamp the geometry is such at the two halves coming together "out travel" the sides trying to cinch, this results in the two main points still having more pressure on the piece and the sides initially deforming and relaxing --- the more initial cinch up you make them have from the beginning the less of this deflection will be experienced and the more uniform the piece being clamped will remain ---- the devils in the elastic geometry when you know how things work and when you know what your doing...

    the mounts and their design and the piece being clamped and it's design and size and materials all have to be considered when assessing the situation and coming up with the proper undersize ratio....
    Last edited by A.K. Boomer; 03-23-2020, 11:37 PM.

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  • BCRider
    replied
    Exactly AK, everything has some spring to it and to get a better grip going a couple of thou under ensures the greatest area of best contact pressure and the most friction. I wonder too if the size shown by the pic in the OP if dead on or a couple of thou over would benefit from a C clamp squeezing in on the sides to help push the ends inward and that two axes of grip pressure.

    754, if slightly over it's not like the fork would be left deformed oval. That spring again. A hair over will still work but more clamping pressure would be needed for the same gripping force against turning. It'll spring out and go as oval as the hole allows and then spring back to round after the pressure is off.

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  • A.K. Boomer
    replied
    Originally posted by 754 View Post
    You are absolutely right, I WOULD BE AMAZED to we a .002 under bore be cut in half and then pressed on by thumb.. I truly would.
    btw I have straightened more a few fork tubes and never managed to oval one..
    I just wanted to save this post for future reference lol

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  • 754
    replied
    You are absolutely right, I WOULD BE AMAZED to we a .002 under bore be cut in half and then pressed on by thumb.. I truly would.
    btw I have straightened more a few fork tubes and never managed to oval one..

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  • A.K. Boomer
    replied
    Originally posted by 754 View Post

    NOW this talk of holding a tube with a spit clamp pad that is SMALLER than the piece it's CLAMPING to me us a load of crap, if you think its worth trying fine but, I won't recommend it to anyone..
    Worth trying ? for over 40 years of success id say so - running a motorcycle service department and doing hundreds of front forks and then looking at the pic in the OP, I might have stated the maximum of what you would want but the fact is is the jaws are aluminum - and not very beefy at their smallest area of the mount, they will have deflection as I stated --- slightly smaller gets it done every time without harm and in fact is better than "same size" as now your jonesing to ovalize the part.... and greater size is almost a guarantee,,,

    build a mount like in the pic of the OP and build it half what I stated - so just .002" under -- then cut it in half and be amazed when all it takes is just thumb pressure to get it to press on all the way...

    also - tons of work on Mt. biking suspensions from rock shox to Fox with even finer details and more pressures (exceeding 500psi) so only load of crap is coming from your post.

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  • 754
    replied
    Another trick I feel I should mention if you are building anything to clamp that is split in two.
    USE TWO PIECES of material , if it is to be drilled and or tapped, do that first. Some as in these rod clamps, may be ok without or benefit from alignment pins.
    Now when you go to machine the hole put a piece of cereal box cardboard between the piece at the join, or 25 or 30 thou shim. Now when you go to drill and bore you will experience the BEST chip breaking material ever, when hole is finished , no slitting and you have clamping clearance..
    easy peasy... tip for the day..

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  • 754
    replied
    Ditto that last post.
    I have built blocks for straightening forks, and I have worked on blocks for holding bicycle fork components, , I think a lot of people are over thinking this, and thinking wrongly. Things get scratched because you didnt clean it, its your job to clean it off., I have cut Down and rethreaded many brand new fork tubes, using a 3 jaw and I am not scratching them, I use padding and check run out.

    NOW this talk of holding a tube with a spit clamp pad that is SMALLER than the piece it's CLAMPING to me us a load of crap, if you think its worth trying fine but, I won't recommend it to anyone..

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  • old mart
    replied
    Seems that a lot of the people posting cannot tell the difference between conventional and upside down forks.

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  • BCRider
    replied
    The nominal diameter of the fork tube is 48mm,, the actual diameter is 47.92mm.
    What type of fit am I aiming for? I am guessing transitional fit. Shoot for exact size?
    Going back to the first question as using your shop to make such a block is a perfectly fine option...

    I think I'd aim for a size for size fit at 47.92 or maybe 47.91. But an acceptable tolerance would likely be between 47.90 and 47.96.

    A hair tight and the edges of your blocks will flex out a touch just fine and give a nice even grip around a good portion of the circumference. Spot on or just a hair loose and the tube will deform to a slight oval shape as the blocks close and squeeze the tube. But still with good broad large areas of full pressure contact.

    Much smaller and the blocks would rub along the edges of the openings pretty hard on spots of the surface. Much bigger and the tube would need to flatten more to obtain nice large contact patches thus needing a lot more pressure to flatten the tube into the saddles for good contact area.

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  • Bented
    replied
    Measure the bore of the triple clamps and make the tool the same size.

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