Is it acceptable to leave an internal sharp corner undimensioned? 1

[KirbyWan]

So in a lot of drawings there are internal sharp corners that I'm fine with as is. The stresses are not critical and there are no clearance issues. I want to leave the internal sharp corner as is and I don't care about the dimension of the corner. This gives me a dilemma. If I leave it as is, a machinist might take that sharp corner to be critical and add cost to ensure it's accurate when I don't care. I could also put a radius in there and dimension it loose enough so that it's clear that a sharp corner or a small radius would be acceptable, maybe make it a reference dimension. This adds to the complexity of the drawing without much benefit other then having it fully defined. I could put a note that says undimensioned internal corners are not critical. I don't know of a decent way of saying this.

Is there a standard way of handling this that gets the design intent of not caring about the dimension/accuracy of an internal corner?

I tried searching for this but I'm not sure I could find what I was looking for since I wanted to not dimension something.

Thanks all,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[KirbyWan]

Also, this is for one-off tooling, and I talked to our machinists about it and they just would like it left undimensioned, but we may also send our tooling drawings out to be fabricated elsewhere if our machinists are busy with production work.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[mfgenggear]

call out a max radii, for example R .040 max, will cover most machining tools, that is more clear to inspection

 

[chez311]

To piggyback off of the above, you can either explicitly model a radius and directly dimension with a maximum radius ie: R .040 MAX or model your corners sharp and provide a note along the lines of "ALL INTERNAL CORNERS MAY HAVE R .040 MAX" or similar. The former seems to suggest that the corner should have a radius by default and the latter seems to suggest the corner should be sharp by default - when in reality both options allow for a maximum radius of .040 and a minimum radius of 0.

Of course any real part made by real machine tools will likely have some infinitesimally small radius in a so called "sharp" corner, even if not practical to measure, but thats sort of besides the point.

 

[KirbyWan]

Thanks!

Both ways make sense, and for modeling and drawing simplicity I like the note.

Best regards,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[drawoh]

KirbyWan,

Everything on your drawing must be dimesioned and toleranced. I strongly recommend chez311's note. You need to control outside corners too.

--
JHG

 

[TheTick]

When the time you spend worrying about it exceeds the time it takes to document it... Document it!

 

[MintJulep]

You say that you don't care what radius, but that's only because you have so far been lucky enough to have reasonable machinists, with reasonably unworn tools.

Of course the machinists don't want it dimensioned. Because then they don't need to inspect it, or worry too much about it being inspected.

If you put a radius dimension, then it should be inspected. And inspecting small radii is a pain.

I sort of like the idea of a max radius as a reference dimension. It seems to most clearly communicate the design intent of "This doesn't need to be a sharp corner, and I don't really care too much what radius is here, as long as it's not outrageous.

Back in the day, when the machine shop was on the other side of the wall, we just drew sharp corners. Because it's easy. The machinist would come and ask, do you really need a sharp corner? And we'd say, no, but use a new mill, or no, I don't care, or yes, really.

But those days are gone.

 

[KirbyWan]

As I was about to put the note in our default tolerances section, wording it like chez311 suggested when I saw this line already there:

R .030 DEFAULT RADIUS

And I just stared at it for a bit and thought, "that's it, that's how we constrain the corners without making confusing drawings." I'd say I'm sorry for wasting your time, but I have found the discussion educational, going beyond how do I dimension something to why, and why there are standards for it.

Best regards,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[ctopher]

Call out a standard machining radius, max.

What is "R .030 DEFAULT RADIUS" ? Compared to non-default?
If I was a machinist, I would question it.
Knowing machine shop practices and drawing standards will help, and save $$.

ctopher, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[mfgenggear]

Kirby

what you have to keep in mind
if there is a stress point in that corner
does it have to clear an other detail of assembly. corner interference.
if it does not have a stress point and no interference with other parts.

than a max radius makes since. however most of the time it will be .015-.040 R.
machining tools are purchased with standard radius.
for example .007, .015, 030
the most popular is .015 or .030 R on turning tools, and it can be the same for milling tools.
drill points should be .040 R max, on the inside corner.
turning with super sharp tools have a tendency to chip easily, so a .015-.030 radius is preferred. But a larger radius is stronger.
it is important to always specify a radius and do not leave it up the shop to decide, inspection needs to know what the radius is.
the shop can suggest what radius to use, that is a standard tool. making possible to use off the shelf tools. makes every ones job easier.
radius can easily be inspected with dentist cast or wax stick when heated and pushed into the radius can then be inspected on an optical comparator.
or if it's wide open radius gages.
edit: milling highh speed tools are normally sharp but can be modified, indexable milling tools the above can be applied.

 

[ewh]

How about a default max edge break note, eliminating the form requirement?

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV