Surface Roughness

[Tegguy]

Does anyone have any recommendations on how to communicate surface roughness for bonding? Normally I'd just say something like "abrade surface using X grit" however, in this instance I cannot since it's optics I would rather just communicate a target minimum roughness. I have talked to the epoxy vendor and their lap shear testing was done with 2500 grit surface finish (this number seems very fine for lap shear specimens)

 

[drawoh]

Tegguy,

If you specify surface roughness as per the standards, your drawing and part are inspectable. You care what they do, not how they do it.

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JHG

 

[Tegguy]

Drawoh,

I understand but what I'm struggling with is how do communicate this. The epoxy vendor gave me a 2500 grit finish but that's not something I can just push on the print since 2500 grit isn't a surface roughness (I don't think) so I'm struggling with how to translate what the epoxy vendor provided me into something on the print (125, 250, ect)

 

[powerhound]

Why don't you go through the process of polishing the material with 2500 grit, measure the surface texture, then use that value? What parameter are you going to specify?

John Acosta, GDTP Senior Level

 

[drawoh]

Tegguy,

Can you get your hands on a surface finish comparator and a Machinery's Handbook? Take a photo of your comparator sitting on the page with the tables for surface finish. Get your fingers into the photo. This shows what those surface finish numbers mean, along with the English/metric conversions. My photo is IP, so I cannot show it to you. You can do what you damn well please with your photo. My fingerprints are around 125[μ]inches (3.2[μ]m).

Send this to your epoxy vendor and ask them what surface finish they recommend.

--
JHG

 

[dgallup]

For plastic mold making the Society of the Plastics Industry (SPI) Moldmakers Division has a scale for the surface of mold tooling that is similar to what you are looking at. They sell a plastic plaque, the SPI Mold Finish Guide for optical comparison. However, I don't see a grade that I can directly equate to 2500 grit surface finish. The end result will be dependent on quite a few additional variables including the type of material and it's hardness, etc.

I've put surface roughness on drawings for bonding, we usually have a max and a min with a pretty big range in between for process variation depending on how you produce it. Something like 2,4/0,8 microns for bonding rubber.

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