Surface roughness symbol (in drawings)

[drodrig]

Hi there,

I got some parts machined from the workshop. In the drawings, I have detailed the surface roughness: 0.1 with the "tick" symbol.

The parts are rough, I can fill the valleys/peaks with the nail.

I'm thinking maybe I was not accurate enough with the drawing. Attached a capture. Should have I written Ra0.1 or was it clear?

thanks
regards,

 

[ctopher]

Symbol is clear.
Some info on it: Link

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[drodrig]

yes, but is it understood I mean the Ra?

 

[IRstuff]

If your machine shop doesn't understand the symbol, you should run away, fast. The symbol is described in ASME Y14.36M Surface texture symbols:

4.3 Roughness Average (Ra)
The principal parameter specified for roughness is the roughness average, R,, defined in ASME B46.1. Its value is shown in position "a" of the surface texture symbol in Fig. 3

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[grunt58]

You called it out correctly other than metric lol. With .1Ra you are looking at polishing/lapping to achieve that finish. You are not going to machine that finish.

 

[IRstuff]

The only thing that might be questionable is whether the horizontal bar should be there. According to Figure 1, the horizontal bar implies there are conditions or methods to be further specified. The bar is technically a bit short, compared to Y14's "3x approx"

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[XL83NL]

Based on the snapshot and user profile (German based?) I doubt this drawings was designed to comply with any of the ASME Y standards. A lot of the members here at engtips, experienced included, often assume all and everything is ASME, which in fact a lot isnt (at least for all that doesn’t originate from the USA).
What (typical) standard does your drawing call out for surface finish or other related topics? Is this drawing ISO based?

 

[handleman]

No bar just means "I don't care how it happens, I just need this finish". The bar means "You have to machine this face", but further specifying how it's cut is not required.

Of course, you're not going to get Ra0.1µm without machining... However, if the item in question were die cast etc, you might get Ra25 or so straight from the casting. Therefore, if you wanted Ra25 but also a machined surface, you'd specify the bar.

 

[drodrig]

Hi,
I didn't mention, but yes, I'm based in Germany. So things are specified in milimeters, but I understand in the case of the finishing it is microns.

 

[MintJulep]

The drawings looks fine.

.1µm is lapped, honed, polished supper smooth.

Are you sure that you really need that finish on what appears to be the outside edges of a plate?

 

[XL83NL]

I think it doesn’t (per se) matter if you use millimetres as a unit for length or distance, what matters is which standard your drawing is made up to. I assume you have no specific standard for surface roughness?

 

[dgallup]

We frequently specify Ra 0.1 micron surface roughness. In IRstuff's image above, I will also frequently specify b) the production method (LAP) and c) the cut off length even if it's the default 0.8 mm. Cutoff length will have a huge impact on the measurement. In some cases you might not want to call out the production method but if you know it needs to be lapped then you are more likely to get what you want if you specify it.

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[drodrig]

We are using the parts for carbon fiber moulding, we need good finishing. The symbol is out of the face, but with the line connecting (this is what the Catia drafting module does).

Non defined dimensions must follow DIN ISO 2768

Yes, 0.1microns. I am thinking that the person who manufactured the parts thought it was 0.1mm

I wrote to the company asking about this

thanks to all