Machining / grinding brass

[JohnBp]

Hello,

I'm new to this forum, so please forgive me if I made any mistakes in posting wrongly.

To start off, we have recently tried to test diamond tools to improve surface roughness on brass.
We have to improve the surface roughness of the brass slots, which are 1.5mm in diameter. The current surface roughness achieved now is 0.4Ra.

After trying diamond mounted points, the surface roughness only got worse. We also tried searching for lower grit sizes, but after further analysis, it turns out that lower grit sizes may load the part more than it machines it.
Does anyone know if diamond end mills would be more effective in improving surface roughness compared to diamond mounted points? And what roughness values can we get from diamond end mills?

Thank you.

John

 

[MikeHalloran]

I think the diamond turning of copper optical surfaces spun on air bearings is done with cleaved diamond single-point tools, at very low feed rates and very small depth of cut.

Diamond grit, as in mounted points and such, is basically a bunch of rocks.

Have you tried High Speed Steel?



Mike Halloran
Pembroke Pines, FL, USA

 

[JohnBp]

Hi,

Thanks for the reply.

We are trying to do jig grinding using the KERN Pyramid Nano, and perhaps possibly milling for the finishing cut.

For High Speed Steel, we have not tried it yet, as we want to test diamond tools first as they have longer tool life, etc.

So using diamond mounted points are not suitable for improving surface roughness on brass?
If so, would diamond end mills achieve better results?

Thank you.

John

 

[MikeHalloran]

I have never used diamond grit tools on brass, and I had not imagined that anyone would try.
I suspect that whatever published data you relied on to select diamond abrasives was based on working with steel or harder materials, not something as naturally machinable as brass.

I would not expect _any_ statistically valid tool life with diamond grit on brass; I'd expect the grit to immediately clog with soft brass flakes, stop cutting, and then the shanks to snap with continued feed.

I have seen nondiamond abrasive wheels used in a surface grinder to put a flat finish on the edges of aluminum bars. It was done while the workpieces and the bottom few mm of the wheel were totally submerged in a soluble oil/water coolant. The finish was good enough for the application, but I'd expect the immersion to recycle some swarf into the cut area, so mirror finishes would be unlikely. ... and I haven't seen anyone grind aluminum successfully with other than total immersion of the workpiece and the cutting edges.

Ask your KERN supplier for some lower-tech cutters.







Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

Brass is soft and easy to machine with very, very little "tearing" so its final surface is smoother at high cutting speeds, and, the high speed tool (used actually at much higher feed rates compared to using on regular machined steel surfaces since there will be less heat build up on each cutting stroke) will last a very long time.

I'd recommend going to high speed tool steel, used at a low or modest feeds but high rotations. But the tool steel edges need to be itself very, very close toleranced.
Air blast rather than liquid cooling? Don't know for sure.

 

[JohnBp]

Interesting, I'll see if we can test it out with high speed tool steel.

However, meanwhile we still have to test diamond end mills for milling the slots.
Would this course of action be recommended, since we are now using diamond end mills instead of diamond mounted points?
Or should I go straight for high speed tool steel? We would prefer the diamond end mill due to its long tool life, but unsure what roughness values it would produce after machining.

Thank you

John

 

[JNieman]

Diamond end mills only have long life when they are the right tool for the task. Using them outside of the situations they are designed for will not give you long tool life. No tool is a "one size fits all" solution, no matter the price tag.

The vast majority of brasses being machined are quite easy and pleasant to cut as previously stated. HSS should be more than enough. Since you haven't stated what type or alloy of brass you are machining, I assume it's nothing terribly exotic or difficult that would be worth mentioning. Correct me if I'm wrong.

 

[Compositepro]

For a really smooth finish the final machining pass would be a burnishing pass. For material removal you want a sharp edge tool. For burnishing you want a round edged tool. Diamonds crystals are not sharp edged.

 

[JohnBp]

Hi JNieman, so if the diamond end mills are used for other purposes other than milling their tool life will be shortened?
Will this also apply to using them on the wrong materials?


I've also read that to obtain better surface roughness after milling, grinding with black silicon carbide mounted points is highly recommended for brass.
We might also try that solution.

Has anyone tried to machine brass with diamond end mills before?
What are the roughness values that can be achieved through the diamond end mills?

Thank you.

John

 

[MikeHalloran]

In my experience, grinding brass with _anything_ is a bad idea.

If I have missed some new development in machining, I'd sure like to learn about it.

Please tell us _where_ you've been reading about grinding brass.



Mike Halloran
Pembroke Pines, FL, USA

 

[JohnBp]

Hi Mike, I've been corresponding with some tooling companies and they have recommended black silicon carbide mounted points for grinding.
Other than that, other companies have also tried to dissuade me from grinding brass.

We've tested diamond end mills on brass material yesterday, and achieved a roughness average value of 0.3801 microns. We will be trying HSS later.