How could you determine the radius of the fillet on mechining parts?

[E-stone]

I am very new to mechanical engineering. I wonder if the part is made in machine ship. How do you determine the radius you could put on in the drawing. The last company I worked on just let the vendor decide. Actually, if you are a designer, how do you determine the radius? Would you check any book to see the sizes of common tools in the machine shop? If so, what is the book?

 

[dgallup]

Very dependent on part function. Something like the fillet on a crankshaft journal is critical to not create a stress riser. Not only is it precisely dimensioned and machined but it may be rolled under high load to create beneficial compressive surface stress. If the fillet is unimportant you might not dimension it at all. If you just need to make sure it does not interfere with a mating part you might just put a max dimension on it. It's virtually impossible to machine a truly sharp inside corner so if you need to fit something into that corner which is sharp you need to design in an undercut.

When I need a very small precision inside corner fillet I specify R0.3 mm because the smallest tool radius we use in production is R0.2 mm and you have to allow for some tool wear. This is the type of thing you learn hanging around with a good machinist.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[drawoh]

E-stone,

What radii are we discussing here?

[dt]Corner radii in machined pockets...[/dt]
[dd]You should make corner radii as large as possible. Large radii allow your machinists to select large cutters. Large cutters remove material more rapidly, and they don't bend (much) due to the side loading. You get better quality work at lower cost.[/dd]
[dt]Inside and outside radii of machined edges...[/dt]
[dd]A large bend radius at the bottom edge of your pocket requires a special cutter. Don't do this if you don't have to. The top edge of your pocket will be not be sharp, unless you explicitly specify otherwise. This is a handling and safety issue. Machine shops usually have a set of what look to me like dental tools, for removing sharp edges. I recommend a note on your drawings stating something like UNLESS OTHERWISE SPECIFIED, CORNER RADII 0.5mm MAX INSIDE AND OUTSIDE.[/dd]

This is basic DFMA. I strongly recommend that you add a copy of Product Design for Manufacture and Assembly to your engineering library.

--
JHG

 

[drawoh]

E-stone,

Telephone your machine shop, or better yet, visit them. Ask what tools they like to use. This will never not be necessary.[ ]

--
JHG