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Michael Henriksen
08-18-2017, 7:11 AM
Someone on a FB group claimed that a laser is more precise than a router because the laser can do an (almost) square corner. I argued that this was just a feature of the laser and has nothing to do with precision. IMO, a CNC router can work to much tighter tolerances than a laser can. What is your take on this?

Gary Hair
08-18-2017, 7:26 AM
It depends... Are you talking about repeatability or precision material removal. Either one can be extremely accurate in repeatability but the cost to make a cnc that has the same repeatability as a laser is fairly expensive because the cnc typically has more mass to move around and it takes $ to keep tolerances tight. Once you have repeatability the same on either then the cnc will definitely be more precise in Z depth control but the laser will give you better X/Y precision due to the fact that the beam is a few thousandths wide vs the diameter of the cnc bit. The actual work you are doing will also play a big factor in precision - are you cutting material and have corners with a radius smaller than the smallest cnc bit? If so, the laser will be the only way to go. Are you cutting thick material in rectangular shapes? If so, the cnc will be the way to go. So again, it depends...

Michael Henriksen
08-18-2017, 7:34 AM
Precsion to me means the ability to remove material to tight tolerances. I consider ability and precison to be two separate things. I don't think you can argue that a laser has higher precision because it can cut an almost square corner.

Scott Shepherd
08-18-2017, 8:01 AM
The answer would be "It depends". Precision is based on the motion system of the machine. Are you comparing a servo controlled, ball screw driven motion system to a stepper motor, belt driven system? If so, then obviously the ball screw driven machine CAN (not will, but CAN) be more accurate.

Precision has so many factors. Is the CNC router a hand held router mounted on the head, with .010" runout? Or is it a precision spindle with .0002" runout?

You'd have to specify a lot more information about which two machines you are comparing, because one is not more accurate because of the machine type, but rather the built quality. I'd say that the best lasers are far more accurate than the worst CNC routers, but when you get into big money on the routers, and you are comparing ball screw driven systems against belt driven systems, then you are going to see the results improve for the CNC router.

Then you have materials, work holding, and skills. Push a router bit too hard and the deflection would be a problem on precision. Conventional vs. Climb cutting is going to push the bit in a different direction. All those things add up. You'd need a lot more specific information to compare two systems.

Michael Henriksen
08-18-2017, 8:06 AM
Well, the person claimed laser was more precise because it can do a near square corner - end of argument. As you point out Steve, it's not as simple as that.

William Adams
08-18-2017, 8:12 AM
A workaround for this is to use two different endmills:

- a V-carve engraving cut along the surface which will allow an even sharper corner than a laser affords since it will lift out
- another endmill to cut out profiles and so forth --- one ends up w/ small uncut areas under the surface at tight corners / angles, but these can be removed w/ a file if desired

Larry Alles
08-18-2017, 11:59 AM
Don't say "depends" around old people

Kev Williams
08-18-2017, 2:23 PM
A screw driven laser will be pretty dang accurate, but a belt driven laser can only be as precise as the belts. And they're simply not all that precise...
I had to mark a hypodermic needle cutting gauge once-- or I should say, SEVEN times. That's how I figured out lasers aren't that accurate. There were 31 hashmarks needed at very specific locations, with only a .0025" tolerance either direction. Any 'bulk' adjustment messed up all others. Of the 31 marks entered per print measurements, only about 5 of them were actually within tolerance. On the 7th run I ended up blue-tape testing every hash mark, measuring with calipers and a loupe, adjusting and testing until it was dead on. Took about 3 hours, but that's what I should've done in the first place.

My most accurate machines are both of my Gravograph IS machines, both of which are ball-screw driven machines. They will make a square corner, and I can make accurate rulers with them. Rulers made with my lasers are in the 'no cigar' category ;) (although they will make them accurate to themselves, and that helps actually)

And if FB guy is talking "sharp" corners, when you cut a box with a tool or laser beam, it doesn't matter how small the tool or beam, the outside corner will always have a radius, and the inside corner will never have a radius. "Square" is dependent on how accurate the gantry's X axis is in relation to the Y axis. Perfectly right angles and parallel lines are hard to achieve...

For giggles, this is a piece of plex my LS900 did before it was a year old, the top 3 lines are rastered at 50 lines per inch, at differernt speeds, slower then faster IIRC...
The bottom line is just lines drawn at 50 per inch and vectored. NH said the wobbly lines were 'on purpose' to aid photo engraving. All I've ever noticed they do is cause banding when they overlap :(
And this is my most 'precise' laser machine.
366293

Doug Griffith
08-18-2017, 3:10 PM
In my opinion, a CNC and a laser might be close if cutting a very thin substrate. After that, the CNC takes over by a mile because the kerf of the laser is not straight but hourglass shaped.

Jed Lawrie
08-22-2017, 3:34 PM
Could you DIY one that had both? Would it even be useful to do that?

Kev Williams
08-22-2017, 5:12 PM
I have a job come in that speaks to this issue-- it's a simple piece of 1/8" plex, kind of double-L shaped (has a second step), and it's to be a go-nogo gauge. The 2 steps must measure to within .003" tolerance from a common edge, and as you turn the part 90 another measurement comes into play... I tried making one of these with the laser last year, and it took several adjustments, only to have one of the dims off by .004"... part of the problem being the laser won't cut thru 1/8" plex perpendicular enough, so one side of the part may be in tolerance but the other side not. And part of the problem is machine accuracy, although with enough patience, that can be compensated for...

However, if I chuck a 1/16" endmill in my IS7000, I can cut these out dead to rights all day... :)