measure angle on pcb v-tip engraving bit - how?

[j ferguson]

Guys, I have a real problem.

This is the second board made on my 6040 Chinese Router:



It is as close to perfect as I can imagine. isolation grooves .010, traces .012, and even across the board.  The design is about two inches square.  There were no burrs and no 'slivers.'  It was finished when I removed it from the vise. Normally, I'm not this good, so here's my problem.

I used one of the v-tip  engravers which came with the router.  I used Eagle to design the board and Pcbgcode to generate the g-code.  I'm running my 6040 with LinuxCNC in Ubuntu 10.04. Feed was 8 ipm.  some of it was done at 20 ipm, but I can't see the difference.

Obviously this wonderful bit won't last forever. It was sort of a freebie from the Chinese. I had the impression that the vendor didn't really know anything about these things and might have been a reseller. They were handling a wide variety of stuff, baby carriages to blenders, with an occasional router thrown in.

What do I measure to determine the bit angle? The bit has two angles. I assumed that the shorter one was the one doing the cutting so I measured its length, took 1/2 of the 1/8 bit diameter and using TAN came up with the included angle from the axis of the bit for that edge at 15 degrees. 

These things are pretty cheap so i suppose I could buy sets of 15, 30, 45, and 60 and see which ones are the same.

What would you do?

[sokoloff]

What do I measure to determine the bit angle?
<SNIP>
These things are pretty cheap so i suppose I could buy sets of 15, 30, 45, and 60 and see which ones are the same.

What would you do?

Exactly what you proposed: buy a variety of them, figure out which ones are useful, and then buy more of them.

With a CNC router at your disposal, it's not likely that the others will be irrevocably/permanently "wasted" anyway...

[j ferguson]

Sokoloff, I think you're right. That is the best.  I do have to say that the first board done by this setup was also beautiful but had some routing errors.  I am so unnerved when something works the first time.

[sokoloff]

You can use the mill to help you find the angle.

Take a solid piece of stock and fixture it on the mill reasonably flat.

Cut a short (10mm is probably enough) groove as deep as reasonable in the material by lowering the Z axis and then traveling along the Y axis to cut a groove. Return the Y axis to the middle of the groove (back 5mm in this instance).

Then, use the mill to help you measure the travel needed to just hit the edge of the groove. Record the Z and X travel needed to position the point of the mill at the edge of the groove. Use inverse tangent to determine the resulting angle, remembering to double it after (as you're finding half the angle from this process).

[jpanhalt]

An optical comparator (best) or dissecting microscope with reference angles will get you pretty close.

John

[j ferguson]

I'd been thinking of getting a comparator to get a better handle on trace and isolation groove dimensions.  I have one we used a long time ago for type face sizing, but it's reticule's finest marks are .010 and it's only 8x so pretty much at the limit. I can measure the length of the tip with it and come pretty close to the angle that way.

best,

another John

[ebclr]

A web camera and a graphic software can help, But to know if is 15,30,45 or 60 any naked eye can determine "near" group

[j ferguson]

Many thinks. It's the included angle of the tip. that was what i wanted to know. 

[frogblender]

Quick & cheap & dirty: 

LASER PRINT    a printout, on regular paper,  using your favorite cad program, with a bunch of thin lines radiating from a single point (I think I had the lines in 5° increments, IIR) - like spokes on a bike.

Grab the paper,  the v-bit in question, and have a squiz  (did I spell that right?) under the microscope.

Note that when viewing under the microscope, you must "project" the bit onto the paper;  if you push the tip down to the paper (such that the shank is up in the air), your observed angle will be off  (hard to explain, just try it and you'll see, and don't be fooled by the "roundness" of the bit).


My paper also has a bunch of .005" pitch parallel lines, for similarly measuring distance.   (dang it, that paper has been beside the 'scope for about 8 years.... until today     )

I've always found laser printerouts in general have excellent dimensional accuracy.