# Making Pyramid Engraving bits



## shred (Jan 1, 2012)

Faced with some small engraving needing doing and a lack of intact engraving bits (normally in this situation, I'd just fire up a spotting drill or something else pointy, but that wasn't going to work for the line widths needed), I went searching around the net and ran across the concept of pyramid engraving bits. They are three (or four maybe, I used 3) flats ground onto the end of a tool at an angle. Much simpler to make than the usual single-flute engraving bits, and the one I made worked impressively well in both aluminum and steel.

The grinding setup-- I used an angle-indexer on my surface grinder with a shallow diamond cup wheel. I have a T&C grinder (what the diamond wheel is intended for), but it's buried under piles of junk right now, so thought I'd try the SG, especially as more folks are likely to have one. There are a number of ways to do this setup if you don't have the same wheel or indexer I do-- a Spindex set at an angle on the mag chuck would work, or you could lash something up with collet blocks and an angle vise or something. In a pinch, an AlOx wheel will grind carbide, but it'll take almost as much off the wheel in the process. The indexer is set for 60 degrees since a 60 degree point seems to be the sweet spot between line width and tip longevity for engraving metals.







I chose to use a broken 1/8" carbide end mill shank for a blank. I have a number of them in the 'broken bits' box .

Here I've done one flat and indexed around to the next one (yes, I didn't reset the starting index before grinding like I should have and thus had to do the math on the fly...) With this setup, it's simply indexing 120 degrees and infeeding the grinder to the same number each time. You want to be pretty close, but it doesn't have to be perfect (actually non-perfect might help a little with tool life, see below)






Here's the completed bit seen under 10x magnification (I did both ends of this blank. It seems to be traditional with engraving bits and saves time when you need another point)






And some results. The bottom two engravings are with this bit. The light one on the right is at about .003" DOC, and the left one at about 0.009". The top version under the ruler is the best I could do with a pointed 'drill mill' prior to making this.  These are in alu but the steel piece came out very similar. Inspecting the bit after four runs engraving, it was still sharp and pointed.






In use, you want to downfeed these very slowly (like 1 IPM or less) to avoid chipping the tip. If you got the point perfectly on center, it has effectively zero SFM no matter how fast you spin the bit (and you should spin these bits as fast as you can).

For five minutes effort and recycling a broken bit, I think it's a winner. Anybody else messed around with these?


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## ttrikalin (Jan 1, 2012)

very nice -- which makes me remember... I really should make a cutter grinder...


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## Tin Falcon (Jan 2, 2012)

thanks for posting I see myself wanting to do somthing like that in the future. I have wondered what flks use for engraving on there machines.
Tin


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## RonGinger (Jan 2, 2012)

I have made these, but at a sharper angle, making a 60 degree point.

They do work well, but they are easy to chip the point off.

From looking at your work maybe I didnt need to go so sharp- you have a nice fine line. Ill try one like yours.


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## shred (Jan 2, 2012)

Yeah, the fragile point is why you have to drop the z-feed to almost nothing. I had my indexer set up to make 60-degree points, and they don't look that pointed in-person, but with everything concentric and a 90-degree point, line width = 2x DOC, which would be larger than what I'm seeing, so the point is somewhere between 60 and 90. 

The commercial guys put a tiny (angled) flat on the point of theirs, presumably to improve longevity.


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## Swede (Jan 3, 2012)

Nice, Shred - I recognize that sideplate!  ;D The engraving looks perfect. One of the difficulties that a HSM guy faces with these common 1/8" carbide engraver bits is that the theoretical RPM for clean cuts is waaay up there, probably 40,000 to 50,000 RPM. It doesn't mean it won't work slower, but the cut is often ragged, or the bit breaks.

eBay is a good source for broken or used carbide bits that can be sharpened, for pennies.


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## shred (Jan 3, 2012)

Swede  said:
			
		

> Nice, Shred - I recognize that sideplate!  ;D The engraving looks perfect. One of the difficulties that a HSM guy faces with these common 1/8" carbide engraver bits is that the theoretical RPM for clean cuts is waaay up there, probably 40,000 to 50,000 RPM. It doesn't mean it won't work slower, but the cut is often ragged, or the bit breaks.
> 
> eBay is a good source for broken or used carbide bits that can be sharpened, for pennies.


Yeah, I ran that at 5000 RPM, which is on the slow side (albeit max for my machine), but until you put a 10x loupe on it, it looks good.  I have a router add-on spindle for my CNC but haven't messed with using it for things like this.

As an experiment to see if it was really cutting or just bashing the metal out of the way, I did a single pass in Alu at 0.100" deep (way deeper than I'd normally use). Without flood coolant, the entire cut was packed with chips. With the flood, the finish isn't great and there is some chip recutting, but it's not near so bad.

No coolant: 
	

	
	
		
		

		
		
	


	



With flood:


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## Swede (Jan 7, 2012)

Another guy with an inspection microscope! I thought I was a rarity. I've got a Meiji EMZ binocular scope that I've found to be hugely valuable and a lot of fun to boot. Especially important when you have one of those insanely small stainless slivers in your finger. Even the largest swiss pointed tweezers look like clubs underneath the scope, but it's nice to be able to get those splinters.

How did you get the nice pics? I've tried a number of methods short of buying an expensive adapter, with no luck.


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## shred (Jan 7, 2012)

Those are shot through my Peak 10x Scale Loupe with the #14 (inch and metric) reticle. They are not real cheap, but I had it for other purposes. The scale is handy for measuring small, flat things. I keep eyeing the angle and radius reticles for use as an erasatz tiny optical comparator, but as yet have resisted.
For some reason my camera works well with it for extra-macro while the regular eye loupes are problematic.






I'd love to have a good inspection scope, but around here even the surplus ones go for more than I want to spend.


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