Jewelry/Gift engraving

[dano9700]

I've recenlty started learning to use a Roland EGX 360 for various jewelry and other gifts (all metal). I'm picking up things here and there, but not usually getting the quality results I want, and I know are possible. Most of the cutters we have are half-rounds, steel or carbide, from .010" and up, none above 30 deg. cutting angle.
Can someone tell me how to determine the feed rates and RPMs for a given material? Generally I'm engraving silver, gold and nickel -plate, and rarely stainless steel. Right now I'm getting a lot of burrs and ragged edges and wasting a lot of time.

Thanks,
Dan Owen

[Tweakie]

Dan,

I isolation route quite a few PCB's. The copper is pretty soft stuff and will, if given half the chance, make incredible burrs. I have found that the RPM needs to be as high as possible and the depth of cut shallow. I only use moderate to slow feedrates and machine dust.
But the most important thing by far is that the tool is sharp. If there is any shiny reflection from the cutting edge when viewed with an eye glass then the the tool is dull and needs replacing.
I use solid carbide 30 degree points and they don't last long, especially after they have been into fiberglass.

Tweakie.

[dano9700]

Thanks for the reply, Tweakie.
Lately I've been trying high RPMs and low feed rates, like you said, and getting better results but still not good enough. Then again my cutters might be in bad shape from misuse, since the past three weeks for me has been one experiment after another.

Mostly we do personalizations and I'm having no success with anything but single line fonts. Anyone know if true type fonts can be engraved on metal in fine detail, say 2mm - 4mm height?

[mjiko]

Hi I very love a jewelry gift specially with a nice engraving. It so romantic.

[Zig]

Dano,


Pushing the spindle is not the answer.

Lets start with some basics. See if You can determine the cutting speed of the material You are machining.
This is not RPM and Feed rate cutting speed which is what You require .
This is cutting speed in lineal units per minute ...say .

This is the speed with which the tool cutting edge scores the material.
So now that You know what the tool edge speed is for the material Yo need to convert his to rotary speed and linear feed of the rotating tool.

This holds true for large diameter tools.

In the area of micromachining ( this is what You want to do when You engrave with small tools) this relation breaks down due to the fact that the cutting edge of the tool has a radius comparable to the size of the chip the tool is cutting off.

A good rule of thumb is to run Your spindle at its sweet spot where the spindle runout makes least excursion from true, and then pick a linear feed rate for the tool such that the tool will cut 1 to 2% of its diameter per cutting edge of the tool.

The reason for selecting minimum run-out speed ( which is never the fastest RPM the spindle can do ) is to obtain least loading on the tiny tool tip and prevent tool breakage and at the same time get minimum burring on the cut.

I too do a lot of PCB engraving with an Alfred Jaeger spindle ( running up to 100KRP) but i only push the spindle when drilling 0.3mm holes. Otherwise i operate the spindle at 40 to 60 KRP typically.

So as the very first step... determine where the sweet spot of Your spindle is.. listen to its song as the revs go up. Yo will hear it.
Next do the calculation based on "nice " RPM and the material cutting speed.

And last and equally important chuck the tool so that there is as short a protrusion as is practicable to minimise tip wonder.

Experiment with feed rate between the 1 to 2 percent chip load per cutting edge.


Good luck