Post by: Geezer on 26/01/2012 03:53:38
How does it make the beamy thing draw a nice straight line. It's too small for a spinning mirror, and I'm pretty sure there are no "frikkin sharks" involved.
Post by: CliffordK on 26/01/2012 10:26:57
Don't you hold onto the handle and pull it back and forth... many many times... until the board falls in half?
Post by: Sprool on 26/01/2012 12:22:24
Post by: RD on 26/01/2012 16:40:45
... It's too small for a spinning mirror
But doesn't the mitre saw have a spinning disc blade ? ...
(https://upload.wikimedia.org/wikipedia/commons/5/57/Miter_saw.jpg)
attach a laser pointer to the hub and voilà it draws a laser guideline.
Post by: CliffordK on 26/01/2012 18:24:59
I did find this after-market attachment for sale. (http://www.amazon.com/Irwin-Industrial-Tools-3061001-Miter/dp/B0009XYN4M)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fecx.images-amazon.com%2Fimages%2FI%2F51F6SNGXKVL.jpg&hash=2db4b15690cbc08295bbe452cb91b250)
It appears to be a small disk, probably powered by the initial acceleration in spinning the saw blade. That means that the laser pointer is only turned on when the saw is actually turned on and the blade is spinning. It may also align to one side of the cut.
Post by: Bored chemist on 26/01/2012 20:41:35
http://en.wikipedia.org/wiki/Cylindrical_lens
Post by: RD on 26/01/2012 21:12:06
They spread the beam out with one of these
http://en.wikipedia.org/wiki/Cylindrical_lens
One of those would not produce a line wider than the incident beam.
It would not "spread" the light beam, only focus it into a line rather than a point,
(a line no wider than the incident beam).
Post by: Bored chemist on 27/01/2012 06:47:04
If you pass the beam though a cylindrical glass or bottle of water you will see that it fans out into a line.
You can arrange for a line like that to coincide with the saw cut.
Post by: Geezer on 27/01/2012 08:31:05
I think BC has it right. The "laser" draws the line even when the blade is not rotating.
For an additional twenty bonus points, if the beam is, say, 600 mm long (about two feet), and I try to position a straight-edge parallel to the beam, what sort of angular difference between the beam and the straight-edge could I hope to achieve?
I'm sure it's a lot better than one degree, but how much better?
(If you have not already guessed, there is an ulterior motive behind this question.)
Post by: imatfaal on 27/01/2012 10:41:57
Personally I can align a straight edge to either side or the middle of a .3mm line - so I would guestimate that .1mm accuracy is obtainable by eye in a real world situation. If we double that to be conservative and to take account of other factors (ie it not being aligning a straight edge with a line drawn on sheet of paper with a tech drawing pen) to a .2mm error, and assume that we have compounding errors at each end of the 600mm, we end up with a pair of right triangles with adjacent edge being 300mm and opposite edge being .2mm and the "error" angle in the middle.
I would further widen the range and just give an answer of in the order of hundredths of a degree. I don't think it would be difficult to make it into the thousandths (or lower) with a little extra effort and cross checking.
I have probably fallen into Geezer's heffalump trap by missing an obvious problem - but I am happy to play the fall guy
Post by: Geezer on 27/01/2012 18:20:14
There is no trap here. I have a particular application in mind. 0.04 degrees is not bad, but it's probably not sufficient for what I have in mind.
The eye is very good at judging parallels, so perhaps we can do even better than you suggest. I'll probably need to try it to find out. I can provide more info on the application if anyone is interested, but it's extremely BORING.
Post by: SeanB on 27/01/2012 18:52:39
Post by: Bored chemist on 28/01/2012 00:09:41
Thanks Matt!OK, so check the name.
There is no trap here. I have a particular application in mind. 0.04 degrees is not bad, but it's probably not sufficient for what I have in mind.
The eye is very good at judging parallels, so perhaps we can do even better than you suggest. I'll probably need to try it to find out. I can provide more info on the application if anyone is interested, but it's extremely BORING.
What's the application?
Post by: Geezer on 28/01/2012 04:03:44
Thanks Matt!OK, so check the name.
There is no trap here. I have a particular application in mind. 0.04 degrees is not bad, but it's probably not sufficient for what I have in mind.
The eye is very good at judging parallels, so perhaps we can do even better than you suggest. I'll probably need to try it to find out. I can provide more info on the application if anyone is interested, but it's extremely BORING.
What's the application?
Don't say I didn't warn you!
I have a thing that's called a mill/drill. It's a vertical milling machine - looks a bit like a drill press on steroids. The motor/gearbox part is supported by a large vertical steel tube. It can be raised, lowered and rotated about the tube. During milling or drilling operations, the motor/gearbox bit is clamped securely to the tube.
The motor part accepts various drilling, milling and boring tools. The item that is being machined is secured to a table that can be moved in two dimensions (the x- and y-axes) by leadscrews during a milling operation.
For some operations it is necessary to unclamp the motor/gearbox bit, usually to change the tool. Then you want to return the motor/gearbox bit to exactly the same "z axis". But that's not so easy! There are mechanical methods, but they take a bit of time.
I was thinking I might attach a laser thingy to the side of the motor/gearbox bit and rotate the motor/gearbox bit until the beam was aligned with a large steel square on the table in the y-axis. To be of any use, I have to be able to to return the z-axis to within a couple of thousands of an inch of it's previous position.
Post by: CliffordK on 28/01/2012 09:20:49
If you have some kind of a knee mill, then the table moves in the X, Y, and Z axes. And, then the head may also rotate to give additional planes of cutting.
You wish to return the head to its last position, not necessarily a fixed position with respect to the table (which you move all the time).
If you always keep the head absolutely vertical, then you can add some adjustable stops for the rotation part.
If you only need access to the tools, you can raise and lower your knee (or does your machine have a quill?) That allows all other axes to remain fixed. And, if you've changed tools, you likely have thrown your Z-axis out of whack anyway, so the new tool will have to be reset with respect to the Z axis.
If you computerize your table and/or quill, then the computer should be able to return to the exact same position it was last in (again, realizing that each new tool can change the Z axis, and even other axes if the head is tilted.
I'm trying to think of how lasers might help. If you had two moon shaped lasers, you could mount them to the side of your head, and essentially draw an "X" over the center of where the mill is cutting. (in the X/Y directions). The Z direction is still more complicated. As you moved the head close to your work, a large cutting head would likely obscure the center point though.
A single dot laser could be aimed at a non-moving place in your shop. At the back of your machine, wall, whatever. But, that still is assuming you aren't intentionally tilting the head.
Post by: Geezer on 28/01/2012 09:58:35
On some mills, the vertical movement runs on V-ways, so the z-axis is constant, but on this machine the z-axis can be anywhere on an arc described by the rotation of the spindle about the vertical support tube.
Post by: SeanB on 29/01/2012 06:41:07
Post by: CliffordK on 29/01/2012 07:12:24
You can do it the other way around too.
Attach a round laser to the head. Perhaps design a slit for it to shine through to give you a short, narrow line.
And, a protractor lower down on the back of the mill... to judge the angles of rotation. That way, you get a somewhat larger scale than putting it on the head.
Post by: SeanB on 29/01/2012 09:36:10
Post by: Geezer on 29/01/2012 18:04:45
The idea is to purloin the laser line drawing unit from my mitre saw and attach it to the head of the milling machine so it projects a line on to the milling table. The line would be parallel with an imaginary radial line connecting the axes of the spindle and the support tube.
To align the (imaginary) radial line perpendicular with the X-axis of the table I would rotate head on the tube until the laser line was just touching (really "equally touching") the edge of a steel square making a perpendicular with the x-axis of the table (the y-axis). The square could be jiggled left and right slightly as the head was being rotated to fine tune the adjustment.
I have a hunch that this method will make it quite obvious that the beam and the edge of the square are parallel within some small limit, although I think that's going to depend on the quality of the lens in the laser.
The other tricky bit will be to ensure that the plane of the laser is parallel with the axis of the tube, but that should be a one time setting.
Post by: Geezer on 29/01/2012 20:16:43
I think it should work. I did some experiments with the laser on the miter saw. When I place a square piece of steel on its table and position it so that the laser is just "kissing" the vertical surface of the steel, the laser highlights the raised irregularities on the surface of the steel and they appear as random points of light.
As I rotate the steel relative to the plane of the laser, the points of light become increasingly uniform over the area of the steel surface. At maximum uniformity, I'm pretty sure the surface is plane with the laser. The adjustments I am making are tiny.
The resolution of this method is probably a function of the surface irregularity of the steel. To get the highest resolution I think it should be possible to inscribe a grid on a polished flat steel surface so that only the grid is illuminated as the surface touches the plane of the laser.