"Break sharp edges" note 4

[mathlete7]

Hello,
I have a pretty simple question - I know that its common to call out "break sharp edges" on machined parts. I'm curious, what tool do they generally use to do this?

Or for instance, on a machined aluminum I-beam, what would be the most common way to remove the sharp edges from the flanges? Would you generally just machine a chamfer along the length of the flange? Or would you just run some tool along the length of the flange to break the sharp edge?

Thanks much...

 

[KENAT]

I've seen different techniques, from a rumbler (like a tumble dryer with special agragate in it that you throw parts in with to be spun around for a while) for small parts to a guy with a file/emery cloth who while the next piece was on the tool was deburring the last one by hand.

I must admit I don't know what automated process might be used on something like you say.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[GregLocock]

I've seen guys hit the cut edge with a bastard file, and I've also seen some custom made tools resembling miniature scythes. Since it is uninspectable I imagine it has no business on a modern drawing.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[berkshire]

The most common tool for breaking sharp edges in the aircraft industry is a small tool called a Burr Wik, it has a receptacle into which several types of scraper like devices with different radii can be plugged.It is simply dragged along the edge of the part and shaves off the corner, it is also used on holes.
Another device common in the sheet metal industry is a scraper with two circular blades that can be set to the thickness of metal you are working, this device removes about .005" from each corner of the edge of the sheet.
B.E.

 

[MintJulep]

A nice selection of manual deburring tools here:

http://www.deburringtools.com/

Power deburring tools include the "burr beaver" and "burr king".

Since it is uninspectable...

Not so Greg.

“Standard for Determination of Sharpness of Edges of Electrical Equipment,” U.L. 1439.

There is a "standard finger" for such things.

http://www.sharpedgetester.com/

 

[GregLocock]

A go no-go gauge? Oh well have a star anyway.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[berkshire]

Good site Mint Julep
You have the types of tool, I mentioned and a few more.
B.E.

 

[mathlete7]

Thanks all for your input. It was very helpful.

 

[tbuelna]

mathlete7,

If you want sharp edges removed in a certain manner then specify it. And the more specific you are the better. Don't leave things open to interpretation by using ambiguous drawing notes like "Break sharp edges". Specify the shape and form of the edge breaks, the permissible tolerances, and the process to be used to produce and validate them. A proper edge break may seem like a rather insignificant feature, but a sharp corner bearing into the fillet radius of a mating part can (and often have) cause big problems.

Adding callouts and notes specifying proper edge break processes on your drawings doesn't take much effort.

As for edge breaks on the flanges of a machined I-beam, the easiest, most consistent, and reliable method would be to program the machine to run a chamfering cutter along the flange edge as a finish operation. That way it always gets done exactly the same on every part, and is usually much quicker than doing it by hand.

Good luck.
Terry

 

[uGlay]

-tumbling
-sandblasting
-deburring tool

i usually call out 0.020/0.030 for structural parts and 0.005/0.010 for small parts that require precision.

It is not uncommon for the fabricators to forget to break sharp edges.

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[debodine]

We have a standard note on our fabrication drawings that says Break sharp edges per BAC5300. BAC5300 is the Boeing spec that controls this, along with some other items it controls.

 

[RPstress]

Re "Specify the shape and form of the edge breaks", be careful that you don't accidentally impose an overly-onerous inspection requirement.

 

[uGlay]

I have made parts that do require an 'overly-onerous' inspection requirement but this is usually justified by the part's function. usually it adds $ to the piece price. and ticks off QA a lil.

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[KENAT]

uGlay, surely in that case where justified by the parts function it wasn't 'overly-onerous' but 'adequately onerous'.

This has been debated before if not on this forum then others.

Putting exlicit limits can create arguably excessive inspection requirements for many applications.

Many use the "Remove sharp edges .005 max radius or chamfer" or similar. However putting 'break sharp edges' doesn't give a pass fail criteria unless you use something like the 'finger simulator' at Mints link.

I've yet to find a true, one size fits all, solution.


KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[ewh]

Speaking of previous threads along this subject line, whatever became of the thread started by wktaylor several years ago in which he asked for reasons for edge breaks and was to give us an answer? I'm still curious as to what his answer would be.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[dicer]

Shot peening and I think sand blasting will make a sharp edge on a sharp edge. For shot peen we always break and radius the edge first.
You can scrape the sharp corner, sand it, use a highspeed rotary burr bit, a file, sand paper, emerypaper/cloth, a grinder, scotchbrite pads, rolled emery cones, etc etc.

 

[Dan320]

Re. OP:
If you, the designer, does not specify how to break the edges, the operator will use what ever tool he thinks is appropriate. And you will, to some extent, loose control over your part. In some cases it will be acceptable but not always.
As long as the part is made iaw the drawing the designer is responsible. That's why you shouldn't allow others to influence the final result by being unclear when writing drawing notes.

 

[KENAT]

Unless the 'how' fundamentally affects end performance you shouldn't spec it on the drawing.

You should spec the 'what'.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[drawoh]

Dan320,

I agree with KENAT. On my drawings, there is a standard note that says to break edges, and there is another note specifying a maximum corner radius of 0.5mm. All of this is "UNLESS OTHERWISE SPECIFIED" of course.

When I visit machine shops around Toronto, I see things that look like dental tools. I assume they use these to take off the edges.

JHG

 

[Dan320]

I was being general in my comment.
I think the designer should know what he is doing when he leaves something for the next guy to decide.
Assuming is not a good word here.
I do not think we disagree, really.

D