Machining CZ120 on a light CNC mill/router

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Hauk

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Long time no post, but I have finally started some modelling projects that involve machining.

I have aquired a light Heiz CNC mill/router with a Kress spindle. I hope that this is a setup suitable for relatively light, mostly cosmetic jobs.

The most important thing for me is surface finish. I have made some test pieces in CZ120 engraving brass, but I am not satisfied with the results.

I used a "fishtail" 3mm 2-flute carbide cutter at around 12500RPM, and a feed speed of around 10 cm/sec. No cutting fluid. 0,4mm deep cuts.

How does that sound?
Any suggestions for getting a better finish? I want to get as possible to a smooth finish with no machining marks.

All comments are welcome!

Best regards, Hauk
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Try an HSS cutter at a lower speed and stone the corners ever so slightly. CZ121 can sometimes appear "torn" or grainy. Soluble/coolant will help.
 
seems fast. i looked up sfpm for brass and i'm thinking 6-10,000 rpm and .5-1.0 cm/sec if i'm doing the metric conversions correctly.. i know engraving is usually done fast, but is that usually done with a 2 flute cutter? ofcoarse i'm looking at it like a milling operation so if th eengraving tool geometry is very different then perhaps that wont work.
 
Thanks for the replies!
I might have been a bit unclear in my original post. I am not doing just engraving, but milling down to a depth of 3mm.

A lot of what I want to do is profile milling 2mm and 3mm sheets of brass

To reach this depth I use passes of 0,4mm.

So the finish of the sides of the cut is also very important to me.

Regards, Hauk
 
Did some milling this weekend, and here are my toughts.

The machine is a standard Heiz High-Z 400 with a Kress 1050W spindle with a top speed of 30.000 RPM. All milling was done with a flat tip (fishtail) 2-flute 2mm cutter.

The best results was obtained with a feed speed of 4mm/s, full speed on the Kress and shallow cuts of 0.3mm. It also seems that the cuts became a bit smoother after some milling time, could it be that the carbide cutters are a bit too aggressive when new?

Here are some pictures. The subject is an end beam for a model railway wagon in 0-scale. The pictures are fresh from the machine, I smooth out the parts with files and emery cloth before assembly.

endebjelke_frest_05_w.jpg


endebjelke_frest_06_w.jpg


endebjelke_frest_07_w.jpg


endebjelke_frest_04_w.jpg


All suggestions for improving the results are appreciated!
 
What do you use for lube / coolant? You never mention anything in regards to coolant.

I'd also try lowering the spindle speed and increasing feed. 30k is very fast for all but the smallest end mills.


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What do you use for lube / coolant? You never mention anything in regards to coolant.

I'd also try lowering the spindle speed and increasing feed. 30k is very fast for all but the smallest end mills.

I run dry, no cooling or lube. There is no system for cooling/lubrication on this system. Maybe a little WD-40 could do the trick?

Regarding increasing the feed/reducing the RPM, my experince tells me that this give rougher cuts. I think that due to quite bad runout on the Kress and a lack of stiffness in the machine, what actually gives the best results is a sort of grinding rather than actual milling.
 
I run dry, no cooling or lube. There is no system for cooling/lubrication on this system. Maybe a little WD-40 could do the trick?
You could try it but my experience is that WD40 seems to only work really well on aluminum. The little bit of brass that I've done has been manual work and frankly I used whatever was handy at the time.
Regarding increasing the feed/reducing the RPM, my experince tells me that this give rougher cuts. I think that due to quite bad runout on the Kress and a lack of stiffness in the machine, what actually gives the best results is a sort of grinding rather than actual milling.


That has to be hell for your tool life, I'm trying to picture what a Kress spindle is in my mind, is this somewhat like a Dremel? If so your only long term option would be a spindle upgrade.


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That has to be hell for your tool life, I'm trying to picture what a Kress spindle is in my mind, is this somewhat like a Dremel? If so your only long term option would be a spindle upgrade.

Never thought about tool life, but it is a good point. Quality endmills are not exactly cheap.

The Kress is *somewhat* like a Dremel, but of far better build an quality. From what I have heard the Kress has far better TIR.

But a better spindle is worth considering. I have heard a lot of praise for water cooled "China Spindles", but I would like to hear suggestions for where to go from a Kress.

Best regards,
Hauk
 
Check your runout now, if it looks good no point in upgrading. A quality ground collet as balanced nut will be the cheapest way to reduce tool vibration. Technik offers high quality mini collets that can be had for a good deal on eBay. Don't cheap out on Chinese end mills either. Spend a couple extra bucks and buy American micrograin carbide endmills. Call your local machine shops and ask them where the local cutter and tooling distributer is in your area, they always have great deals since they usually have good volume of sales. Your parts look good though! Here at work we don't use any coolant or oil on brass. Alcohol in a small mister works great to sap the heat away from the part though if your getting mixed results.
 

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