CNC Experts, please help me to choose cutting knives.

[HKPhysicist]

Hello Friends,
I am choosing cutting knife to mill a shallow (0.1mm) logo on plastic enclosures containing PCB; so that my final product looks more attractive and professional. I may be also possible to mill a serial number onto the plastic case as well.

Could you recommend cutting knife to me according to your precious experience? ^^

My CNC will be a cheap China mini GRBL CNC; software will be bCNC for Ubuntu or Candle for Windows.

[Harvie]

It's very important what kind of plastic that is. For example Delrin, POM, HDPE and PVC are much easier to machine than ABS... Go as slow RPMs as you can to prevent melting and gumming things up...

I used to have best succes with straight bladed and single bladed milling bits, especial those "half-straight" ones. basicaly anything that looks like if you grind away half of cylinder. no spiral:

Those are perhaps easier to break and/or cause vibrations if your workholding is bad. But once you tune feeds and speeds in, they can cut very nicely. Some of the plastics need like wd-40 spraying in the cut or something like that (compressed air, mist, cooling, etc...) to prevent gumming up.

They even have v-bits like that:

[HKPhysicist]

Yes, mine is an ABS Thermoplastic with UL94 rated!

I also find it very hard to drill with my ikea hand-held drill.

[MARIOBASZ]

Hi.
The problem with plastic is that it melts. 1. Use a single-edge bit. 2. Low RPM relative to the feed rate: 2.a) The cutting tool cuts by chip removal, not by friction. 2.b) The heat generated during cutting is mostly transmitted and evacuated by chip shedding. The cut should be "granules," not dust. Counterintuitively, to protect the tool, we often increase the RPM, which results in excess heat and premature dulling.
3- There are online speed and RPM calculators that can be used as cutting parameters. 4- From what I wrote before, single-edged tools have a higher chip removal rate (and better heat dissipation). 5- You can spray with water and alcohol (30%) or a mixture of water and plastic detergent. 6- If you provide the tool diameter and the number of edges, I can give you speed values ​​for testing. 7- I'll try to give you the data for a brand (for example, Izar). I'm self-taught, not a professional, so I could be wrong in much of what I wrote, with the best of intentions. Hugs.

[MARIOBASZ]

Hi.
The problem with plastic is that it melts. 1. Use a single-edge bit. 2. Low RPM relative to the feed rate: 2.a) The cutting tool cuts by chip removal, not by friction. 2.b) The heat generated during cutting is mostly transmitted and evacuated by chip shedding. The cut should be "granules," not dust. Counterintuitively, to protect the tool, we often increase the RPM, which results in excess heat and premature dulling.
AI can help you with values

[MARIOBASZ]

3-Spray with a mixture of water and alcohol (40%) or water and plastic detergent
4- One or two edges at most are preferable
5-If the workpiece is thin, you can use a upcut cutter

[MARIOBASZ]

I can't paste the link. In Izar tool, milling cutter 9441, you can see cutting parameters.

[HKPhysicist]

I find this one on Amason, US$10 made in China; should be a good alternative to your Germany single edge knife!

[HKPhysicist]

Hello Friends,
My ABS plastic box is like this one which is about 8cm in length. If I want to cut a nice smooth USB-C slot on its end as this picture, what tools should I use?

As I have found that most cheap China mini GRBL CNC can only accommodate work piece less than 6cm along it z-axis :(

[HKPhysicist]

is it this one? seems to use trapezoidal screws with small motors... i don't like that.

Similar one but I will buy one with all-aluminium frame and motor holders which is double the price.

[HKPhysicist]

Even if the distance from the chuck to the bed is 9cm, I still have to match it with a very short mill bit.

mill bits on the market are almost longer than 3cm :(

[Harvie]

What is the z-height of genmitsu 3030 prover max ?

[HKPhysicist]

What is the z-height of genmitsu 3030 prover max ?

As their diagram shows, z-axis stroke is 78mm. If I can find a very short mill bit, perhaps they will work.

By the way, its power supply is very big! :O

[HKPhysicist]

Hello Friends, My ABS plastic box is like this one which is about 8cm in length. If I want to cut a nice smooth USB-C slot on its end as this picture, what tools should I use?

As I have found that most cheap China mini GRBL CNC can only accommodate work piece less than 6cm along it z-axis :(

I have finally opened this USB-C slot manually with my ikea power drill and a hobby knife.

Now, the next step is to buy a China metal frame CNC to do the auto CAM job on the next 10 stock enclosures! ^^

[MARIOBASZ]

something like that?

[HKPhysicist]

This one seems a good fit to my purpose. Let me check where I can find a cheap one.

[HKPhysicist]

something like that?

Yes, I have found a similar cheap one on Aliexpress. This one is very close to an USB-C slot 9mm x 3mm. If any one is interested in it as well, send me private message.
Thank you very much! ^^

[MARIOBASZ]

Are you milling PCB?

[HKPhysicist]

Are you milling PCB?

only the ABS plastic enclosures. I buy the PCB from another vendors.