External Rads or Chamfers Preferable

[KENAT]

We have some DFMA guidelines in our Design Room Manual.

One of these is that on external edges/corners it’s preferable to have a chamfer rather than a round/radius, both for breaking edges and larger features.

This is certainly what I’d been taught/led to believe in the past.

We’ve had a number of people ask if this is still true with the widespread use of CNC tools by our suppliers.

So:

1. Are external chamfers still easier/faster to design than radius’?

2. If yes then some feeling for by how much would be great.

Many of the Engineers/Designers here tend to create what seem overly complex parts so we’d like to make sure we’re on firm ground before trying to get them to change.

Thanks for any help.

 

[FACS]

1. Are external chamfers still easier/faster to design than radius’?

2. If yes then some feeling for by how much would be great.

External chamfers are no easier to design than radius because it's just a click of a button on the CAD system.

Machining the part is no different, It's a tool change either way.

How the parts look is the only difference.

Charlie

http://www.facsco.com

 

[KENAT]

Sorry, error in my post.

1. Are external chamfers still easier/faster to MACHINE than radius’?

Also I don't just mean for small 'break edge' type chamfers/rads. I also mean for larger features which would probably be cut as part of the profile.

 

[eromlignod]

For a radius, the machinist has to have the proper tool with the exact radius specified. For an odd-sized radius, he might even have to purchase or make a new tool. A chamfer can be performed by a number of methods with ordinary milling tools and can be made virtually any size.

On manual lathe work, a chamfer is often preferable to a radius, since an external chamfer can be performed by hand with a file, or with a quick diagonal cut with an ordinary lathe bit. A radius requires a tool change and, once again, the tool must specially match the radius called out.

I always design as if parts will be made manually, even if I know they will be CNC. If the part ever breaks or wears out in the field, it might be necessary to have it remade quickly in a breakdown shop, which might not have CNC capabilities.

Don
Kansas City

 

[BobM3]

If they are done on a CNC then a radius is just as easy and fast to machine as a chamfer. A radius often times will produce a smaller (or no) burr as opposed to a chamfer. Many CNCs though can not put a radius on two edges that are anything other than 90 degrees from each other.

If done manually, inside corners of 1/64, 1/32, or 1/16 radii are easily done with different inserts. Outside radii are difficult with manual machines.

 

[frankjconway]

Another advantage of adding a radius is that platings like to adhere better to blended surfaces than sharp transitions.