Drag Engraving Bits and Simple Math

I wasn’t sure where to post this. I’ve been liking what others have been doing with the Diamond Drag bits and saw a few people ordered their bits from Ebay. I decided to order a 120 degree spring loaded diamond drag engraving bit and the 90 degree replacement bit. I received the shipping notice the same day I ordered and then it actually shipped Monday and arrived Thursday. I opened the package to find a bag with a shiny nice looking tool and a pre installed bit with a blue cap. Another small bag had the additional bit with a black cap and a spring. I pulled the blue cap off the pre installed bit and noticed it was a bit less than a right angle even though it was supposed to be the 120 degree bit. I pulled off the black cap on the other bit and noticed it looked spot on at 90 degrees. I compared the two and came to the conclusion that the pre-installed bit is only 60 degrees. When I emailed the seller he responded that yes the pre installed bit was 120 degree and that “The one with the blue protector is 120 and black is 90. 120 is pointier that the 90.” I responded that I didn’t think that was right, that 120 is an obtuse angle. The last response ended with him telling me to send the it back that he wasn’t going to argue about the angle and whoever I buy from is going to tell me the same thing. He even pointed out that he had a diagram showing the angles, which in fairness I didn’t click on till today and it indeed shows 120 degrees being a sharper angle than his 90 degree bit. I appreciate that he’s willing to take it back, and his ebay page even says returns accepted. He’s got great feedback, and I don’t want to leave negative feedback. But I can’t believe that nobody else has noticed or questioned this before. Am I missing something, is there a alternate degree scale that I’m missing in relation to diamond drag bits?

My reasoning for ordering both 120 and 90 is for the thicker line that 120 is supposed to give in acrylic and glass and I figured 90 would be good for the harder materials. Is it worth keeping this, what I think is a 60 degree bit, or will it go unused? I know loaded question there, but what are others experiences with this pointy of drag bit?

Any help or comments would be appreciated. I’m confused.


This is the picture of the two diamond drag bits. Blue cap is supposed to be 120 deg and black cap 90 deg

Diagram from sellers ebay page.

C3D end mills showing their 90 and 60 deg end mills. C3D’s 60 is what the 120 deg bit I received looks like.

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yes his diagram should show 30 or 60 that being said this was done with his “120 degree” bit

and this

first one on glass second on aluminum.


I think you and the seller are both right…but he is kind of an idiot. With V-bits, sometimes you see them referred to by the full angle value (the C3d examples you gave and your 90 deg bit show this. In some of the CAM/CAD software though you have to enter those mills as half-values; so my 90 deg V-bit in Fusion 360 is listed as a 45 deg angle of taper. Somewhat confusing, because not all software uses the half-value.

Still, I think most people would refer to your 60 deg bit as either a 60 deg (full value) or a 30 deg bit. Technically you can say that the 60 deg angle is also 120 degrees if you are referring to the fact that the 60 deg is the interior angle and the 120 is the exterior angle, but I can’t say that it makes sense to refer to the bit by the exterior angle.


@fiero1 Thank you. They look awesome. Would you mind posting a picture of your 120 degree bit? Did you get the 90/45 bit also? What type of stepover, ipm, etc did you use to get those. Are you setting it up as a .005" tip.

@EvanDay I’m aware of the interior or centerline angles that Fusion uses as opposed to the full side to side angles. It’s a 60/30 vs a 120/60 bit though. His 120 that I received is only measuring 60 total which means the interior angle would only be 30 degrees. He did message me back and said he’s never had someone bring it up but will look into it when he get’s a chance.

I though maybe he was using CAM software logic when he ordered and bought 60 degree bits thinking they were actually double and he was getting 120’s. Who knows.

If you’re getting those results with a 60/30 bit then I’ll may just keep it and the 90/45. I just didn’t want to add exponential paths to something to make a design.

Thanks for your responses.

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My bit looks just like yours, it is 60 degree and should have never said 120 anywhere in the description! I knew what I was buying because I click the diagram. I will be getting a 90 bit also just because :wink:
I think the spring could be a bit stiffer, not sure I’m happy about the results in acrylic. I’ve only tried it with Home depot acrylic and should really be using cast acrylic.
Half of line width, which I set at .01, so step over of .005 and feed of 30 IPM.
My understanding is they make these bits there in Connecticut.


@fiero1 That’s exactly what I was wanting to know. Thank you. I wonder why I’m the first to question it. Everything I’ve read says about using 120 deg bits for acrylic so that’s why I ordered it. I thought that’s what I was getting but maybe I can find a compatible true 120 bit to fit this.

So what is the difference when using te 2 different bits? Do you have some pictures using each? I will order the 90 if there is actually a difference.

Blue is a 30°+30° or 60°. Black is a 45°+45° or 90°