Finishing cutting tools for engraving mats...

[Jason]

This post is largely going out to Andrew D, who I know is at about the same spot as I am in terms of learning how to cut mats, and both he and I have been wrestling with how to finish our cutting tools. Both of us have decent grinders to get the tools to a zero point (Andrew has a much nicer one than I have), but we were both stumped on how to consistently and accurately finish the tips to predetermined specs.

While what I came up with today is still very crude and pretty much entirely unreliable, the cutting tools I made today worked much better than my first set.

First off, I found in Ed Rayher's book on cutting the Cherokee type that he finishes his tools with a "screwdriver" tip: that is, the cutting edge is across the centre of the cutter tip, with the two outside edges back-cut (to clear chips). I remember Micah Courier showing me this when I visited him in New Jersey, but that was on an ATF cutter/grinder, the same one that Ed has (lucky jerk!). This style of tip is contrary to Jim's method of simply dragging the cutter on a stone (because that's all Jim was able to do), which can only result in a cutting edge either on one side of the tool (if the tool was dragged with one of the flats facing the stone) (which means the cutting edge would spin in circles) or the at the very corner (if the tool was dragged with one of the corners facing the stone (resulting in a pointed corner that would also spin in circles). With Ed's approach, the screwdriver tip rotates (rather than spinning), thereby cutting with a flat edge, which would vastly cut down on swirl marks on the floor of the mat.

To me, this meant dragging the cutter twice, with the flat of the tool facing the stone, then flipping it 180 to drag on the opposite side, resulting in a cutting edge in the middle of the tip.

Doing this by hand has seemed crazy, so I came up with a plan.

First, I cut a piece of 1" x 1" brass bar and drilled a hole through the middle (length ways). Of course the hole wasn't quite in the middle, or straight, so I then spent a lot of time on the ATF fitting machine machining the block again and again until the hole was level through the block and exactly in the middle all the way through. I measured this by putting a cutting rod through the hole and measuring with a gauge (measuring the rod on each end, turning the block a quarter turn, measuring both ends again, and so forth on all four sides of the block).



I then drilled and tapped a hole down the top to put in a set screw so that I could secure the cutting rod in a given position.



This block allowed me to position the rod in the block and place it in the ATF microscope. I can now turn the block over 4 times to view each side of the cutter, and the tip is in the exact same position each time I turn it, so there's no fussing with moving the microscope table or re-focusing.





Next up, I had a crazy idea. Could I use my glider saw to run the cutter against my diamond plate? After mucking around for a while I managed to mount my plate on-edge on the saw and get it fairly secure, with a very slight angle to its alignment, so the plate will move closer to the tip and drag progressively more against it. I then used a piece of 6pt leading with a serious magnet to create a 45 angle to the plate, against which I position the block with the cutter locked in it.





Obviously, I'm still totally guessing at how much to drag, but after a few attempts, running the plate against the tip on one side, then flipping the block and doing it again, I ended up with a pretty good edge in the middle of the tip. I then rotated the block a quarter turn, and did a verrrrry small grind to create one back-cut corner (where chips can fly out).

From what I can tell, this is much more accurate and easier to control than simply holding the tool and dragging it, and with some practice I think I should be able to get fairly accurate at repeatable results. The mat I cut today, with the new cutters, has a much cleaner floor to the mat, but we'll see how it casts and prints tomorrow.

Jason

[Val Lucas]

Thanks for posting this! I am at the same point as Jim R, just dragging the point across the stone to create a bevel. Jim Walczak's method too. He aims to get a 15-degree or so angle, but it's all guesswork. It has given me good results on the large flat areas  (as long as the tip didn't break halfway through!) I may need to look into setting up a similar system some day too.

[Andrew Dolinski]

Hi Jason

Sorry for the delay in replying.

I have read and re-read your interesting article a dozen times and have tried to imagine the tip you are aiming for and the method you employed.

It definitely is a huge step forward and I can well see how the tip you describe is a huge improvement.

The benefit of your brass block is indeed key to the manner in which you are able to repeat the process accurately.

I do like how you can use the block under your microscope to see all four edges. I must replicate this for my microscope. I might though use an ER32 collet block, being dead accurate and ready made.

In light of your experiments I have been looking at how I could use my Universal Cutter Grinder (Deckel SO clone) to replicate your success. With its compound angles etc I should be able to set the angles you show on your Hammond saw and then gently hone the tip by turning the diamond wheel by hand. It might just work?

Dragging the tip is definitely not the best way, as we all agree. Interesting to read that Val and Jim Walczak also use the dragging method, but admit to it being guesswork.

Are you able to take a closeup photograph of the ground tip that you have been able to grind?

Andrew

[Jason]

Hi Andrew,

I attempted a photo through the eyepiece of my mic, but it just didn't work. I should get myself one of those digital microscopes for the purpose, but for the moment I'll see if I can figure something out.

As Kevin discussed in another point, the real trick is keeping the screwdriver tip totally level, which is pretty much impossible by hand, etc. Also, I think I need a smoother stone, as mine is leaving a cutting edge with a bit of tooth to it, rather than a perfectly smooth edge.

I did, however, as carefully as possible, make two new cutters yesterday, at .002 and .003, so I'll be eager to see what sort of marks are left on the floor of the next mat I cut.

I've come to realize the tips on the bulk cutters (for the first [.020], second and third [.010] cuts) aren't that important, as long as they cut clean. It's the last two cuts (to .049 with a .005 tip, and then to .052 with a .003 or .002 tip) that really matter.