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Ask DocSk8 (Expert Indoor Skate Building Advice) This forum is different then the other SkateLog forums in that it is not a discussion forum, but rather a place you can ask skate building expert Fred "DocSk8" Benjamin about building and repairing indoor speed, derby, and jamskate quad roller skates. Please start a new thread for each new question.

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Old April 30th, 2014, 05:29 PM   #21
Kennedy
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Kennedy, you where correct the bolt was over drilled on manufacture. The odd flanges I mentioned are in reality burrs left from cutting a round hole to be hexagonal. They are not/where not designed to fail at any specific torque, though I swear I have seen this done somewhere before.

There are any number of ways to create the hex shaped hole. The most common that I know of is to forge the hex shape into the solid stock using a die shaped like an allen wrench. The other is to pre drill the hole and then forge the hex shape. I am guessing with the Arius, the hole was pre drilled and then the shape forged. The problem with this method is it leaves the burrs behind and makes measuring and visual inspecting the parts difficult. My ASSumption is that someone set up the die and measured the depth without removing the burr. Just a guess.

Torque limiting fasteners have their applications, but I am pretty sure this is not the case. I had one bolt fail as I was tightening it. It failed with just a few ft-lbs of torque, like it was made of plastic instead of steel. The torque was way below what it should have been to cause a failure.


The axis-pin still has an oddly placed groove at the base of the head which still looks like a shear point to me but I am no longer holding onto this accretion.

I think the relief you are seeing is a tool relief and not much more than that. IMO, designing the axis pin to fail would be a recipe for disaster, ie: massive lawsuits.

Wishful thinking on my part. Though I still feel the pressure required to fix the toe-stops into the plate is excessive. I am accustomed to the feel of tightening a toe-stop screw on cast alum SG Competitors. This difference, I suppose, could be chocked up to harder heat treated 6061 Alum resisting bending more than the softer cast alum.

Any sense in that last statment Doc?
Another cause is that the threads could be oversized. Some of the cheap import tooling does not perform as expected. In theory, taps are supposed to cut when going in, then back out. With cheap Chinese / Taiwanese tooling, they cut going in and going out. The cut while going in is typically to size, but when it is backed out it cuts the threads again causing them to be oversized. Been there, done that.

The difficulty of getting them to tighten is more like related to geometry than material. The range of modulus of elasticity for aluminum alloys doesn't vary that much. Despite what aluminum alloy & heat treat is used, the stiffness is going to be about the same. Like I said above, the toes stop threads could be oversized. The pinch bolts could be threaded incorrectly, the geometry of the plate could have something to do with it.
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Old April 30th, 2014, 06:13 PM   #22
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Default Hex Broach

I'm sure its as Kennedy described. The screw is drilled and a hardened hex-shaped tool is forced into the hole creating the hex. I would think the screw would be annealed at that point and hardened later. If the hole is too deep, there isn't enough meat left between the head and the threads, and it just failed.

Essentially, this. This is a rotary broaching tool that does fundamentally the same thing but it actually cuts instead of just cramming its way in.



Let's apply Ockham's Razor - which is the more plausable reason for the failed screw? Did Powerdyne spend time designing a "torque fuse" or did some overseas factory produce a flawed product?
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Old May 1st, 2014, 03:51 AM   #23
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This one becomes more educational by the post.. Keep it up folks.. I love learnin' !!
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Old May 1st, 2014, 08:30 PM   #24
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This one becomes more educational by the post.. Keep it up folks.. I love learnin' !!
I am going to have to research a rotary broach. Never heard of such a thing before. Something new to me!
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Old May 2nd, 2014, 01:29 AM   #25
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Excellent explanation here
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Old May 2nd, 2014, 01:29 AM   #26
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This one becomes more educational by the post.. Keep it up folks.. I love learnin' !!
Yeah, not a bad discussion from a bunch of old guys sittin' around millin' plates.
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Old May 5th, 2014, 11:35 PM   #27
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So the new toe stops arrived (trashed a gumball and decided to replace the set instead of new gumballs), put in some crazy Big Bloc stops (the big 57mm). They where a tight fit going in, firm pressure needed to turn them in (adjuster screw was removed entirely at the time). Ran a practice and spun a stopper (adjuster was still tight). I had that screw cranked enough the boss's slot was touching or at least darn close to. Still spun under hard toe stop running but couldn't do it by hand.

Using a blue thread-lock as a temp fix (though I hate the idea of doing that to the threads). Seems to be working for now.
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Old May 12th, 2014, 08:36 PM   #28
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Using a blue thread-lock as a temp fix (though I hate the idea of doing that to the threads). Seems to be working for now.
Not working... Still spinning the stops. Going to try to make it to the shop and have the tolerances checked by the shop owner.
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