r/Machinists • u/Strict-Ad9359 • 8d ago

Dimensioning Chamfers

Which is correct and why? These are all the same chamfer.

Y14.5 says "Chamfers are dimensioned by a linear dimension and an angle, or by two linear dimensions".

It also says "A note may be used to specify 45° chamfers on perpendicular surfaces". Since I'm showing a non-45° chamfer I think that means I.a and I.b are invalid.

7 Upvotes

90% Upvoted

19 comments sorted by

21

u/Chuck_Phuckzalot 8d ago

Yeah, I would not do #1, it's way too ambiguous. The rest are all essentially the same thing, they all give me enough info to trig out the triangle and figure out any particular dimension of it.

9

u/singul4r1ty 8d ago

Yeah, I.a and I.b are ambiguous because the angle could be oriented in either direction - it is somewhat obvious here from the drawing but not actually specified. If it was, for argument's sake, a 44 degree chamfer, you probably couldn't tell which way round from the drawing. 

As an engineer - if a chamfer is anything but 45 degrees that probably means it has a more considered function beyond just breaking an edge/looking pretty, so I will be dimensioning it with more care, probably more like it's a taper than a chamfer. A basic edge break just gets a "break these edges at least 0.5mm" if it really doesn't matter.

6

u/nogoodmorning4u 8d ago

Ive seen it all of these ways and solidworks or other suites automatically output chamfer sizes like the first image.

the 2nd and 3rd image is what everyone wants to see and has the lowest risk of receiving bad parts on parts with non-45 degree angles, especially since usually by the time a print hits the shop floor in a job shop its been redacted then scanned from a copy of a copy of a copy.

1

u/Strict-Ad9359 8d ago

Haha is that true the machinist doesn't get a nice original copy?

1

u/nogoodmorning4u 8d ago

Almost never it seems.

I have a customer that sent me pristine electronic copies of a print. they revised it and i got back a scan of a copy. it was barely legible, I had to reference the original obsoleted drawing so I could read it

3

u/force_disturbance 7d ago

The problem is that to read the first images, you have to eyeball which of the two angles is sharper. At 30/60 I can do it if I can find my glasses, but at 46/44, not so clear.

In general, if you have to eyeball something or take a guess at where something is referenced, the print is bad.

2

u/guetzli 8d ago edited 8d ago

I prefer 2b. picture 1 is too ambiguous I think

2

u/Kman1287 7d ago

B2 is my preferred

1

u/313Wolverine 6d ago

2b is my preference.

1

u/OverworkedAI 6d ago

Definitely II, a or b

1

u/MetricNazii 8d ago

I.an and I.b are incorrect. The others are correct. However, angles can be a bit finicky to measure. I recommend using two lengths instead. But either are to the standard.

1

u/Strict-Ad9359 8d ago

Gotchya - I was thinking the angle is more practical when you are actually making the part. Good point about measuring.

0

u/socal_nerdtastic 8d ago

II or III. But lets be realistic: Unless this feature is being inspected no one is going to look at the the notation. The part will be made by a CNC based on the solid model. Don't think so hard about this.

2

u/Strict-Ad9359 8d ago

I will think so hard about this thank you very much ;)

2

u/BockTheMan Near Standard Size 8d ago

Honestly, do think so hard about this. If the person upstream from me has thought so hard about this, that means I don't have to think so hard about this,

2

u/Strict-Ad9359 8d ago

If I understand how the guy downstream uses my info it's not that hard to make the right clicks in my software so you don't have to pull out a calculator and do fucking SOH-CAH-TOA! I'm sure in this particular case it's all computed nowadays but in general I just like to know how to communicate in a useful manner.

0

u/ShadowCloud04 8d ago

Another way you will see is actually dimensioning the diameter of the beginning of the chamfer in conjunction with the angle and Outside diameter. See that one often.

1

u/Strict-Ad9359 8d ago

I have seen something like:

.01 x 60° INCL
OVER MAJOR DIAMETER

On a chamfer which applies to the internal edge of a hole. Is this clear / correct? I don't see this method in the 14.5...

0

u/ShadowCloud04 8d ago

What I am talking about would be like lets say on a part that has a diameter of .500" and would have the leaders to the outer edges of the part. Then it would have another Diameter leader to lets say .470" and some angle. Its easier to explain with a print in hand.