Brass Plaque on the Mini CNC

#1

Hi there!

Im planning a project to make a brass plaque/sign using the mini CNC machine, heres a preview of the project from VCarve:preview.pdf (419.4 KB)

I just wanted to post my plans just in case anyone had any advise on doing this kind of thing:

My process will be:

  1. Make some screwholes in the corners of an oversized brass blank by hand and screw it down to a piece of sacrificial wood.
  2. Run a v-carve toolpath to engrave the letters using a 60 degree v-cut bit
  3. Run a profile tool path to make the actual screwholes for the Plaque using a 2mm end mill cutting 0.1 mm into the sacrificial layer
  4. Run a chamfering toolpath to countersink the screw holes using the 60 degree v-cut bit
  5. Put some screws into the new screw holes to hold down the plaque.
  6. Cut the plaque out using a profile tool path using a 2mm end mill cutting 0.1 mm into the sacrificial layer
  7. Run a chamfering toolpath for the perimeter using the 60 degree v-cut bit

The preview all looks good, I would post the vcarve file, but I dont seem to be able to post in on discord :slight_smile:

Does this all sound sensible, is are there any improvements I could make to the process?

I have a couple of questions, if anyone can help:

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#2

Sounds reasonable to me! @CNCtechs?

Speeds and feeds come from the chip load specified by the tooling manufacturer, if you get generic stuff, see if you can find the chip load for a similar tool elsewhere and use that.

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#3

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I had some reasonable success with this project.

I definitely need to do some work on the tooling and speeds and feeds. I broke the tips on my engraving bits, I’m thinking I need to be way more conservative on the feed rate. The engraving bits I used do seem kind of delicate, reading around maybe using a spot drill bit might be a more robust option.

Either way, it cleaned up nicely with a bit of filing, wet sanding and buffing.

I coloured the letters with some spay paint and then sanding off the paint that wasn’t in the grooves.

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#4

Nice one! Looks really good!! What bits / speeds n feeds (+ resulting chip load) did you use?

#5

So for the hole and the perimeter cut I used this bit:

https://www.rennietool.co.uk/collections/solid-carbide-endmills-slot-drills-for-aluminium/products/solid-carbide-single-flute-dlc-coated-end-mill-for-aluminium?variant=39349395619927

And this configuration:

spiral
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I found this chart as a guide but eared on the conservative/slower side of things to start off with.

https://www.rennietool.co.uk/blogs/news/solid-carbide-router-bits-speeds-and-feeds?utm_campaign=gs-2019-04-16&utm_source=google&utm_medium=smart_campaign&gclid=Cj0KCQjwxYOiBhC9ARIsANiEIfb_Mmdo1iyRmZh1dPW0BTBi2sgm5nsLVePryGbuCnja8zlOMZLKIkMaAjk2EALw_wcB
Those cuts were fine.

For the lettering/chamfering I use this:

I couldnt find any guidance on speeds and feeds for v-bits so I went with something similar to the end mill:

vbit
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Those cuts didnt go as well, ie the very tip of the bit broke of almost immediately. At that point I changed the ‘flat diameter’ to roughly approximate the new/broken tip and re-ran the cut, which went ok although it didnt seem to do a very clean a job of cutting the letters.

I guess I kind of makes sense, the v-bit cutting surface is basically 90 degrees to the surface being cut so probably doesnt cut as well as the end mill.

None of this seemed to be stressing the machine out at all.

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#6

Looks great! I’ve got some brass pieces to CNC in the near future so I think I’ll copy your set up :slightly_smiling_face:

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#7

Great! like I say if you are using a v bit dial it back a fair bit, the 2mm end mill worked well, super interested in hou you get along🙂

#8

Potentially a naive question on my part here with regard to the way you added spray paint to the brass.

I have seen videos for wood projects where a “mask” has been applied to the wood with the design cut through that surface into the wood. Paints/ epoxy fill used to colour the design that has been cut, then the mask is removed so only limited (if any) sanding is required to tidy up the design.

Would that process work on brass too ? I have a long term project in mind where I will make a memorial trophy shield/ plaque where it has a brass plaque like the one you have make in your project giving the pertinent details of the trophy and why it exists so I was interested to read of your process and the outcome. Wondering whether the mask process would work, while I contemplate the multitude of other projects I have on the go before I become a member and get anywhere near this !!

#9

Hi @crafty_creator,

It might be worth a try. The brass stock a got did come with a plastic film on it. Whether that would be cut cleanly enough by the cnc machine to work as a mask Im not sure.

If you could avoid sanding all together you might be able to use polished brass stock and you could avoid the polishing step altogether, which would be a bonus.

Although this might be a bit optimistic as, for me, the CNC machine did leave burs around the cuts it made, these needed to be sanded off too. This is hopefully something that can be improved upon by tweaking the feeds, speeds and tooling.

Like I say definitely worth a try, you can always go down the sanding and polishing route if it doesn’t work :slight_smile:

Let me know how you get along!

#10

Thanks for the reply - I will add a bookmark to your project so I can refer to it when I start to think about my proposed project in the future.

#11

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Had a go at another ‘engraving’ project🎉

This time I used epoxy rather than paint to fill the engraving which looks pretty good.

For fixturing I super glued the brass stock to a bit of sacrificial perspex, I was able to remove it using an iron to heat up the brass and soften the glue. That really worked well!

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#12

Looks good - did you have to sand it much to clean it up, or did you use some other way of cleaning the excess resin ?

#13

Yes just sanded the resin off, it comes off fairly easily.

It does take some time to sand/polish the brass stock up to a nice finish.