How to get 8 rms finish in blind bore with radius

mneuro · Apr 8, 2019

Hey all,

We are working a prototype part that I am being told will be moving to serious production numbers in the near future.

Material is 316ss. Ø1.5" bore to a depth of 3.0". Bottom of bore has a large radius.

We are tying to hold an 8rms surface finish. For the first few small runs we have just been putting the parts in a hand chucker and polishing by hand. This works fine for 25 parts, but wont work well for 25,000 parts.

My first thought was electropolishing. Not sure if that is attainable though. Second thought was maybe a custom diamond form tool to make the final pass after the bore bar.

Any thoughts?

Hazzert · Apr 8, 2019

Possibly a high SFM finish pass with a ceramic or cermet tool. A full engagement diamond tool sounds like chatter city.

edward.santos · Apr 8, 2019

You could try roller burnishing as well. It smooths out all the micro wrinkles and leaves you with a really nice finish. Does the radius of your part need an 8rms finish too?

AARONT · Apr 8, 2019

You could try electropolishing, but you're still going to have to hit at most a 16 before sending out. I haven't tried one, but edward brings up a good point. I know cogsdill makes a burnisher for turning. Burnishing Tools | Cogsdill

Milland · Apr 8, 2019

edward.santos said:
You could try roller burnishing as well. It smooths out all the micro wrinkles and leaves you with a really nice finish. Does the radius of your part need an 8rms finish too?

I'd look at roller burnishing, a ball-type or maybe bull-nose could follow the bore and radius without any issue.

Talk to these guys, or search for other options:

Burnishing Tools | Cogsdill

Edit: Oops, missed #4.

Dan from Oakland · Apr 8, 2019

Electropolishing will require a setup with an electrode(s) in the bore itself. You will still need a good finish prior to electropolishing. You need to contact an established electropolisher for input. Sounds like a marginal design depending on where you need the 8 finish.

mneuro · Apr 8, 2019

Thanks for all the advice.

The radius does not need to have the tight finish. If we are within a couple thou of transition point it would be fine.

The roller burnishing seems like the way to go. We were able to achieve a 22 rms finish out of the machine, but still not good enough for electropolishing. Besides, I would prefer to make them complete out of the machine.

Thanks again!

litlerob1 · Apr 8, 2019

I'm wondering why this is not in the CNC sub.

R

mneuro · Apr 8, 2019

It was more about finding a good manufacturing technique, not specific to a cnc machine so I thought this was a more appropriate sub-forum.

litlerob1 · Apr 8, 2019

mneuro said:
It was more about finding a good manufacturing technique, not specific to a cnc machine so I thought this was a more appropriate sub-forum.

Okay, but RPM and CSS have a lot to do with your question. And your quantity is obviously a CNC thing. You might get better results....?

mneuro · Apr 8, 2019

That is totally valid. I may re-post there if we get a firm order for the larger quantities.

Gobo · Apr 8, 2019

Horizontal mill(CNC)with a D'andrea boring head. If you are lucky enough to have access to one.

athack · Apr 8, 2019

A single pass blind hole hone will do it no problem. Google Bates Technologies

Triaged · Apr 8, 2019

Sounds like a job for a hone if you don't need the finish on the radius.

Milland · Apr 8, 2019

If you do wind up burnishing the finish, add a good filter (5 micron or so) to your coolant system for use with the tool. You don't want particles getting pressed into the surface. You can even set up a bypass for when you're just doing regular machining jobs.

mneuro · Apr 9, 2019

athack said:
A single pass blind hole hone will do it no problem. Google Bates Technologies

Thanks for the lead. I reached out to see what they think.

mneuro · Apr 9, 2019

Triaged said:
Sounds like a job for a hone if you don't need the finish on the radius.

We have an old sunnen hone. It did work and did a great job, it was very time consuming though. In large production numbers we would have to invest in a better hone.

mneuro · Apr 9, 2019

Milland said:
If you do wind up burnishing the finish, add a good filter (5 micron or so) to your coolant system for use with the tool. You don't want particles getting pressed into the surface. You can even set up a bypass for when you're just doing regular machining jobs.

Great thought. Thank you.

How to get 8 rms finish in blind bore with radius

Cast Iron

Stainless

Plastic

Stainless

Diamond

Titanium

Cast Iron

Diamond

Cast Iron

Diamond

Cast Iron

Titanium

Stainless

Aluminum

Diamond

Cast Iron

Cast Iron

Cast Iron

Similar threads