Optimizing Channel Section Tolerances for Pin Jointed Machine Design

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Discussion Overview

The discussion revolves around the challenges of obtaining consistent tolerances for channel sections used in the design of a pin jointed machine. Participants explore the issues related to dimensional variations in standard channel sections, specifically BS10279:2000 Hot Rolled Steel Channels, and seek alternatives or solutions to improve the quality of the materials used.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Mech King expresses difficulty with the wide nominal tolerances of channel sections and seeks alternatives with tighter tolerances.
  • One participant mentions ASTM A6/6M as a reference for variations allowed in shapes and plates, questioning the specific tolerances and problems faced.
  • Mech King highlights issues with the flatness of channel flanges and the variability in flange thickness, which complicates drilling processes and increases costs.
  • Another participant suggests that custom extrusions may offer better tolerances but questions whether steel is necessary for the design.
  • Mech King considers the possibility of using aluminum sections but notes concerns about strength and cost, indicating a willingness to adjust design parameters if necessary.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the availability of channel sections with tighter tolerances. There are competing views on the feasibility of using aluminum versus steel, and the discussion remains unresolved regarding the best approach to achieve the desired tolerances.

Contextual Notes

Participants express varying degrees of concern regarding the impact of tolerances on the functionality and cost of the machine design. Specific tolerances and the implications of material choice are not fully explored, leaving some assumptions unaddressed.

Mech King
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I am deisigning a pin jointed machine that uses some standard channel section. I am having difficulty getting consisitency with the channel section (type BS10279:2000 Hot Rolled Steel Channels) dimensions due to the wide nominal tolerances.

Is anyone aware of any channel/U -Section that has much tighter tolerances over the flatness, height, length, thickness, radius' etc?

I dont' want to resort to welding jigged sheet steel together to obtain the correct dimensions.

If anyone is aware of anything then i would be more then greatful,

Cheers

Mech King
 
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The only thing I know of is ASTM A6/6M which pretty much spells out the variations allowed in shapes and plates.

Just what kind of tolerances/problems are you wanting/experiencing? Could anything be solved by so,e properly selected limited local machining processes?
 
Hi Fred cheers for the reply,

my main issue has been with flatness of the channel flanges - which when drilling concentric holes, has become a more time consuming process with the obvious associated costs. Also, the flange thickness varies by about +/- 1.5mm if i remeber correctly, and if both flange thicknesses are out the the clearence will be greatly increased or reduced. Just wanted to get more consistency with it because each length of channel is widely different from the other it would seem.

I will okk into what you specified and see if i can get tighter tolerances.

cheers again

Mech king
 
Yeah. That's pretty much the run of the mill (pardon the pun). I honestly have never seen anything better that wasn't a custom extrusion.

Does it have to be steel? There are some more expensive, but mass produced aluminum sections that would fit your needs.
 
The Aluminium section will be too weak for the design, its a mechancial lift, i think i may be able to get away with AL section though, if i down-rated the max weight of the lift - which wouldn;t be out ofthe question. I also wanted to keep the lift as cheap as possible, but if it means i need to spend more to get better quality then that might have to be the way forward - i gues you can't have eberything in the quality, cost and time triangle lol.

Cheers

mech King
 

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