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Diamond drag tool

Arbutus

Super User
Premium Member
FWIW, I was digging through the web for an engraving tool for scribing markings on finished parts, I found a number of tools which seemed to me shockingly expensive for what was involved. So I spent 30 minutes saving a couple of hundred beans, and now have a very reliable tool for the CNC mill.

The diamond points are sold on the usual sites - they come in a 90 and 120 degree tip, with a slightly undersized 1/8" shank. Cost was around $25 for two points which will last a lifetime. I prefer the 90 degree which seems to cut more cleanly in steel. The 120 degree point worked better in soft ductile materials such as brass.

Body is 3/8" 12L14. The magnet is 1/4x1/2 from Lee Valley. Spring is 3/16"x1/2" and quite stiff. 1/8" steel ball to pack under the M8 set screw.
Diamond engraver 49.jpeg

Here's the napkin sketch. I drilled 7mm for the M8 setscrew, then used an F drill (0.257") to provide a little clearance for the magnet. The edges were chamfered and the part reversed in the chuck. The hole for the diamond tip was drilled and reamed to match the shank which measured 3.15mm. This last part is critical because the bit must be a snug sliding fit in the body. If there is lateral slop, the tool will simply make a mess of the work.

Diamond engraver 52.jpeg

Here's a design engraved in steel. The lines are less than 0.1mm across and very clean. When cutting acrylic, the edges of the lines were not as crisp due the brittleness of the plastic which left a rough edge. Cutting speed 200mm/min. The Z height of the tool compresses the spring after the tip makes contact. I found about -0.2mm applied enough force to cleanly mark the steel.

Diamond engraver 51.jpeg

Don
 
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DPittman

Ultra Member
Premium Member
So would one of these diamond tips mounted on the end of spinning shaft/arbor in a milling machine be adequate to scribe hash marks on metal for measurement purposes?
 

PeterT

Ultra Member
Premium Member

Arbutus

Super User
Premium Member
So would one of these diamond tips mounted on the end of spinning shaft/arbor in a milling machine be adequate to scribe hash marks on metal for measurement purposes?
The spindle is not rotating, it is the vertical pressure that is doing the cutting. But yes, marking dials for machines is why I made it.
 

PeterT

Ultra Member
Premium Member
I should have qualified that. For deeper cuts and or harder materials, engraving bit 'might' be required. Not sure what the limits of drag are. OP mentioned 0.1mm across so 0.004". Nice results anyways.
 

DPittman

Ultra Member
Premium Member
The spindle is not rotating, it is the vertical pressure that is doing the cutting. But yes, marking dials for machines is why I made it.
Yes I understand how you were using it in a drag fashion but I was wondering about being able to effectively use it in a manual milling machine while spinning.
 

Arbutus

Super User
Premium Member
Yes I understand how you were using it in a drag fashion but I was wondering about being able to effectively use it in a manual milling machine while spinning.
There's nothing except the magnet holding the bit in the shank, the bit is free to rotate. Actually I find this drag cutter is able to produce much finer work than any rotating engraving bit. Theres no chatter and the cut is free from tooth marks. The depth of cut is of course quite limited so for relief work a rotating cutter would be needed.

However for harder materials than CRS, the governing factor is the stiffness of the spring which is applying the cutting pressure. The 3/16x1/2 spring in there is quite stiff - requiring about 1Kg force to fully compress it. I have also played with glass engraving using this tool and the results are quite acceptable in tempered glass.
 

darrin1200

Darrin
These bits are not designed to rotate. Spinning it and running it through metal will destroy it. I used to do pantograph engraving when I was in the army, I tried this once, thinking to get deeper marks, and destroyed my last diamond point. Took me two weeks to get another in, which did not impress my sergeant.
 
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