Sheared Edge C Channels 1

[Design-fab]

Hi Folks,

Small time trailer builder here. We use off the shelf hot roll formed C channels for crossmembers. The tolerance of these is not the best, especially the squareness of the flanges, which causes various minor issues during fabrication. They are also locally only available in a zinc coated finish which is not desired as we are in a low corosion environment and the zinc impairs weldability.

Since the length of the crossmembers is always less than 8ft, we are considering the alternate option of having the channels formed from sheet stock on a heavy pan brake. This would hopefully produce a channel with tighter tollerance and allow us free choice of material (no zinc). The opertunity to use non off the shelf sizes would be a huge advantage as well.

It all sounds like a great idea but my concern is that the shop with the pan brake would typically cut the sheet stock on a guillotine therefore leaving the channels with a sheared edge. Is the sheared edge is going to cause a fatigue issue and come back to bite us in the a** later down the track?

I should say that obviously I'm not expecting a definitive answer here but any hints or tips would be greatly appreciated.

John.

 

[MintJulep]

Edge deburring/rounding machine example:

https://www.timesaversint.com/machine/42-rb-series/

 

[WKTaylor]

Deburring sheared edges of sheet metal is not rocket science... there are simple hand tools that deburr one-edge at a time with a 'drawing action; or for thinner metals, there are 'V' blade tools that deburr both edges simultaneously.

I hesitate to recommend mechanical sanding... 'grinds' the entire surface area... along with breaking most/not all of the burrs along the edges.

BTW... NEVER form sheet metal with edge burrs!! Burrs 'make for a poor/irregular-fit in precision bend tools/fixtures'... and can initiate tears/cracks readily... especially aluminum.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
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[EdStainless]

In mild steels the edge burr is usually no big deal.
Yes, it is sharp and hard to handle, but there is little work hardening of the edge and little risk of cracking unless the parts are very heavily loaded in torsion/flexure.
Instead of sanding/grinding the edge use a wire brush on the side with the burr.
The wire brush will also remove any crap that got caught by the burr.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Design-fab]

All valid points, appreciate the input.

John.

 

[mfgenggear]

design fab
just my 2 cents
there is a technique to minimize burr by sacrifice cheap 1018 steel sheet while shear stainless steel.
also proper shearing technique , shear clearance between the blades.
depending on the volume you want the suppliers input for their best way to remove the burr.
as an actual sheet mechanic, getting cuts on my hands and body is not fun.
always allow for burr removal. for safety reasons.
what condition (hardness and heat treat is being used currently,
and yes welding zinc plated steel is dangerous, and people have lost their live trying to do this.

 

[Design-fab]

I agree, I would always at least take the sharp edge off for safety and paint coverage. We are only talking about hot rolled mild steel here, although if we do go down the folded channel route there's a chance we may investigate using higher strength steels in the future for weight savings.

The zinc coating is fairly thin but I'd certainly rather not mess with it if we had the choice!

John.

 

[TugboatEng]

If you're zinc plating the material you can use the acid wash portion of the plating process to deburr it.

 

[SnTMan]

Get it powder coated instead...

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Design-fab]

We're not zinc plating, but that's interesting an acid pickle would remove the burr?

John.