Surface Finish Inspection on small surfaces

[stalbertsteve]

We are a bearing manufacturer who have recently started manufacturing very small bearings. Each surface on these bearing is requiring at least an 8Ra but each surface is very small, in some cases less than 0.040" long. All published standards require an evaluation length which exceeds this length (0.16"). Does anybody have any guidance as to how to approach this to ensure we are getting the correct measurement in such circumstances, with some form of basis to back it up should our customers question our methods?
We are using an SJ-410.
Thanks
Steve

 

[Ron Rompen]

Surface finish measurements are frequently specified by engineers who never consider HOW to measure them.

I am running into a similar problem on parts which we manufacture for an automotive customer........very difficult to achieve an accurate measurement.

 

[John Predmore]

One suggestion is to contact Mitutoyo tech support for assistance. According to page 14 of SJ-410 specifications, there are sampling length options as small as .003 and .01 inch, which is the range you are looking for.

Beyond your existing equipment, there are Interferometry and confocal methods which can measure nanometers. I personally have limited experience with non-contact methods.

 

[ScottK]

I would think that using a stylus type of surface measurement device on such a small part would present some operator related challenges in an R&R.
I'd be looking into a non-contact device. And you would get much greater throughput with a non-contact.

 

[Golfman25]

We are a bearing manufacturer who have recently started manufacturing very small bearings. Each surface on these bearing is requiring at least an 8Ra but each surface is very small, in some cases less than 0.040" long. All published standards require an evaluation length which exceeds this length (0.16"). Does anybody have any guidance as to how to approach this to ensure we are getting the correct measurement in such circumstances, with some form of basis to back it up should our customers question our methods?
We are using an SJ-410.
Thanks
Steve

You have a challenge. Been there, done that. Find something that works for you and if your customer challenges it, ask them how they would do it. It's easier to question than to do. Good luck.

 

[stalbertsteve]

Cheers John but the settings in the machine are not arbitrary, they are governed by the surface finish...and for anything more than 8 Ra it requires that 0.03" is used, which is too big for the surface we are measuring. Ironically you need to know the SF to know the setting, but you don't know what setting to use until you know the SF lol.
I think i may have to take your advise there Golfman. I've contacted the Mitutoyo expert who's advice was to do some testing...which doesn't work if you don't have a baseline. I'd like a non-contact method but unfortunately some of these races are internal with an ID of less than 1.

 

[Scanton]

I was training on a new piece of measurement equipment at (UK) Mitutoyo's head office last month and we had a conversation with them about their new non-contact surface finish measurement equipment and it looks impressive so definitely worth a conversation with their experts.

 

[Golfman25]

I was training on a new piece of measurement equipment at (UK) Mitutoyo's head office last month and we had a conversation with them about their new non-contact surface finish measurement equipment and it looks impressive so definitely worth a conversation with their experts.

You buying?

 

[Scanton]

You buying?

We have just purchased a Roundtracer and a Quick Vision, I doubt I will be allowed to spend any more money for a while although we will will need to replace our surface finish equipment at some point as it is showing its age and can sometimes be temperamental (like the rest of us)

 

[JanKees]

Is your Ra 8, or 0.8? When 8, do you really need measurement results? I am asking because when we have a specified Ra =/> 1.6, a visual check is sufficient. So when indeed Ra8, find visual samples, pictures and clarify if measuremnts are really needed. You can purchase visual sets with different Ra values anywhere.