Rotary Laser centre finder

[Gary WoodingParticipant @garywooding25363]

I've obviously missed something about the cones and the inclined rotating laser.

I see how the rotating laser indicates when the cone is not directly below the centre of rotation, but I don't see how you place the cone directly over the required datum point of the work piece.

I thought Mr. Gelbart's method of adjusting the laser circle diameter to pretty much coincide with the circumference of an existing hole, reducing the circle to a point to indicate an edge pretty much did it all. As did the edge "V"s for indicating the spot for cross drilling a cylinder.

I'm sure somebody can tell me what I missed about the cone.

[Ian PParticipant @ianp]

Gary

The circle (cone) is created by the fact that the laser is rotating, ergo the cone must be concentric with the centre of rotation which in our case is the axis of the cutter spindle.

The cone is not important in itself, its the described circle that matters. You don't actually see a cone (unless you are in a smoke filled room!)

Also, you don't align the circle to the work, you move the work until the point you want is at the centre of the circle. His method of altering the circle diameter by simply altering the Z height means its easy to position the tool centrally in say a rectangular plate by using it two diameters to set the X and Y separately.

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

Gary,

I think this slight detour in the discussion originated when Michael Williams mentioned Toolmaker's Buttons. John McNamara picked-up on this idea [excuse the pun] and determined that centering on a button would be easier if the button was conical … presumably this would only be the top section, or it would be difficult to set the distances between them. Alternatively a single conical button [or, as I wondered, an Ickey Ball] could be used for positioning a master datum point.

Hope that makes sense, and that Michael and/or John will correct me if I have misrepresented them.

MichaelG.

Edited By Michael Gilligan on 29/01/2014 14:32:11

Edited By Michael Gilligan on 29/01/2014 14:32:55

[John McNamaraParticipant @johnmcnamara74883]

Hi Garry

The cone was discussed a fair bit on the second page of this thread.
**LINK**

My thinking was that a small cone shaped object may increase the accuracy of the devise when locating on marks on the surface of a work piece where the laser strikes at a constant depth.

The cone provides an amplified slope to the horizontal of the laser unless the laser line (Circle) is cantered in a similar way Mr Gelbart shows V when locating over a cylinder.

As soon as I can get my hands on a decent pointer I am going to make one and test the theory out.

This is the first centre finder design I have seen that overcomes the zeroing in problem that laser pointers cantered in the collet or chuck have, and it does not matter if the laser spot is asymmetric when it rotates. Two sources of error eliminated.

Regards
John

Edited By John McNamara on 29/01/2014 14:41:40

[Gary WoodingParticipant @garywooding25363]

Thanks Ian, but as I said in my original post, I understand all that. What I don't see is the use of the solid cone that was shown in the CAD drawings used to illustrate how the laser circle deviated from the horizontal if the cone wasn't concentric with the spindle.. There was discussion on whether a ball would perform any better than a cone – for what purpose? Certainly a ball would self centre in a hole, but would offer no more accuracy than the described laser circle.

Like I said, I don't understand the purpose of a real, solid, cone.

Gary

[Norman LortonParticipant @normanlorton75928]

Thank you to John for pointing us to the Dan Gelbart series. I have watched all 18 and they are excellent. It's a delight listening to someone who understands the science behind why stuff happens.

His part 15 of 18 demonstrates the rotating laser centre finder and I was intrigued, as others in this thread have been. Never mind the theory that has been discussed, I decided to make one and try it out. It uses the commercial laser centre finders that have been discussed (here and ME?) before and fits into a 1/2" collet. I made the angle adjustable but it worked at the first try which is around 10deg from the vertical (20deg cone).

The image worked at around 600 RPM and the polarising cap had to be removed to see it well. I obtained lovely tilting circles on machined steel for upright bar and holes. Dan Gelbart is exactly right (and who wouldn't believe his every word) when he claims 50 micron alignment precision. In my language that is two thou 0.002" and that is my estimate of what's achievable.

I have been using the static, vertical laser to find centres and edges and with the eight thou spot size would have to try hard to get +- 0.004. Now, this device is a magic dream. I have put three photos below to show the device. I have also made a quick video and posted it on this link in case anyone has not seen the Gelbart original film.

Video Link

Who else has just made one?

Norm.

Edited By Norman Lorton on 29/01/2014 15:16:40

Edited By Norman Lorton on 29/01/2014 15:37:54

[John McNamaraParticipant @johnmcnamara74883]

Hi Garry Wooding

Maybe this will assist.

Regards
john

[John McNamaraParticipant @johnmcnamara74883]

Hi Norman Lorton

Well it looks like you get the first prize…. The first Rotary laser pointer off the production line

Nice Job and a good video.

Can you machine up a button cone and test it please?
One with a small angle difference please. I notice you have made the angle of yours adjustable.

Great to see it in action.

Regards
john

[Oompa LumpaParticipant @oompalumpa34302]

"Never mind the theory that has been discussed, I decided to make one and try it out. It uses the commercial laser centre finders that have been discussed (here and ME?) before and fits into a 1/2" collet. I made the angle adjustable but it worked at the first try which is around 10deg from the vertical (20deg cone)."

Thank you for that Norman, the most useful paragraph since page two.

I have ordered a couple of cheap laser "pens" from t' bay so I will crack on when they arrive. Going to make a couple and give them to my friends too.

I would be interested to hear if there is a source of (reasonably priced) good quality lasers as the cheaper models can have a variable quality.

graham.

[_Paul_Participant @_paul_]

Graham,

Which pens did you order please I quite fancy a play with one of these.

Paul

[Gary WoodingParticipant @garywooding25363]

John,

As I mentioned before, I understand how it works, and how, if the conical button is placed in exactly in the right position, the inclined rotating laser beam "magnifies" the displacement error. What I don't understand is how you place the conical button exactly in position on the work piece.

It seems to me that the whole point of using a laser is that it allows you position the work piece relative to some specific feature that already exists: an edge, corner, or hole, for instance. How does the conical button assist in locating that feature?

Gary

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Gary Wooding on 30/01/2014 08:05:29:

… if the conical button is placed in exactly in the right position, the inclined rotating laser beam "magnifies" the displacement error. What I don't understand is how you place the conical button exactly in position on the work piece.

It seems to me that the whole point of using a laser is that it allows you position the work piece relative to some specific feature that already exists: an edge, corner, or hole, for instance. How does the conical button assist in locating that feature?

Gary

.

Gary,

Did you see the comment about Toolmaker's Buttons ?

Although they are also of use in the lathe; these were typically used for laying-out distances on a plate, for "toolmaking" purposes [such as precision Jigs]. In the days before DRO precision; this was the way to achieve accuracy.

Rather than try to explain their usage in any detail, here … may I refer you to this

The gist of it is …

• Mark out various hole positions [approximately]
• Drill and tap at those locations.
• Bolt down the Button[s], just "nipped"
• Adjust the positions by delicate use of a Rawhide Mallet.
• Check repeatedly with Micrometer, until you can get it no better.
• Tighten down the Bolts, and check it all again !!
• Put the plate on the Machine, and centre the Button.
• Remove the Button and bore the hole

That penultimate step is where this device may be especially useful.

Hope that helps …

MichaelG.

.

Edit: inserted the step where you tighten the Bolts

Edited By Michael Gilligan on 30/01/2014 09:08:08

[Ian PParticipant @ianp]

Gary

Apologies for my earlier erroneous reply (I misunderstood your question) but I'm with you on this 'button location' topic.

I suspect you have opened a can of worms here, the rotating laser device is great for positioning the job relative to some known feature but its the position of that feature that is the important thing!

If the job is a blank chunk of metal then the positions is not likely to be very critical but if its a part machined component then the laser has to pick up on some part of that component (possibly on two parts if its an irregular shape). Fixing tapered button/s in place would only work if the job had flat surfaces capable of being tapped or being amenable in some other way.

Earlier in this thread JS brought up the subject of centering a hole for cross drilling a cylindrical object but if I understood his point it was that he relied on his DRO to ensure accuracy. That only works if the job position is already known by the DRO and how he did that was not made clear.

Dan Gelbarts devices biggest advantage is is speed of deployment, By having something that just slips on the chuck body, collet nut, or the spindle itself its a world apart from having to change collets and probably raise and lower the Z or whatever to install a (however beautifully made) pointer shaft.

Buttons (tapered or otherwise) have their uses but in this day of electronics and DROs are only needed for some specialised tasks.

Ian P

[John Stevenson 1Participant @johnstevenson1]

How do you bolt a conical button down into a tapped hole to adjust it ?

No good having a stud on the bottom as it will follow the original hole.

To be honest I think people are over thinking this idea. Not much good trying to achieve 0.00000001" when the average clapped out home workshop Bridgeport is only good to 3 furlongs on a calm day. [ 4 if it's windy ]

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ian Phillips on 30/01/2014 09:28:28:

… but if its a part machined component then the laser has to pick up on some part of that component (possibly on two parts if its an irregular shape). Fixing tapered button/s in place would only work if the job had flat surfaces capable of being tapped or being amenable in some other way.

.

Ian,

At the risk of labouring this, and offending those who just want to get on and make one …

Your comment highlights the reason why I was wondering about its use with an Ickey Ball: This is a 3D version of a "button" and therefore only needs one hole to be drilled "somewhere convenient" on the job [or even on a seperate block if everything is secured properly]. Centering this on the machine gives you a single reference datum for XYZ … and then off you go with your DRO.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 30/01/2014 09:48:32:

How do you bolt a conical button down into a tapped hole to adjust it ?

No good having a stud on the bottom as it will follow the original hole.

.

John,

As I mentioned earlier; I think that "conical" was just convenient shorthand for a Toolmaker's Button with a chamfered top.

MichaelG.

[Oompa LumpaParticipant @oompalumpa34302]

Posted by _Paul_ on 30/01/2014 00:44:09:

Graham,

Which pens did you order please I quite fancy a play with one of these.

Paul

Hi Paul, I posted a really detailed answer to your question – which seems to have vanished?

Anyhow, it was just a couple of laser pointers off that usual auction site costing about £1.20 including postage each.

graham.

[John McNamaraParticipant @johnmcnamara74883]

Hi All

Hi John S
If you study the conical button I proposed There is a plain cylindrical base, In the example given it is a third the total height of 15mm being 5mm. Used as toolmakers buttons the initial location would be done on that surface. I also mention it in text.

It is pretty clear in the CAD drawings I posted, Maybe I should have dimensioned it rather than just relying on proportion I did give the 15mm overall height.

Not all the members of this forum have the facility of using a DRO on their mill. I do not accept your premise that an old machine tool say a Bridgeport as you mentioned is not capable of good work. I have seen old machinists achieve very good accuracy on a machine past its use by date. OK a new machine makes life easy but it still takes skill to achieve accuracy. It is the person on the controls that makes the difference.

Toolmakers buttons are actually quite simple to position, On their own or on a surface plate (Or a just a piece of stone countertop or plate glass if you don't have one not quite as accurate but pretty good) You need a height gauge but they are not that expensive.

The traditional way to centre them was with an indicator held in the spindle fiddly and time consuming to set up, The laser pointer speeds the process considerably.

As I have not yet got a pointer to try the cone button I Cannot say that the device will improve the accuracy rotary laser pointer, However the analysis I have done suggests it will. That is what experimentation is all about you get an idea and you try it out.

Regards
john

 

Edited By John McNamara on 30/01/2014 10:21:06

Edited By John McNamara on 30/01/2014 10:23:01

[Michael GilliganParticipant @michaelgilligan61133]

O.K. folks: Here we have it … What the software people would call "the killer app" for this device … presented with grateful acknowledgement to Dan Gelbart and John McNamara

There have been several enquiries on this forum, about the best way to centre a Rotary Table on the Mill. [Most of these tables have a Morse Taper socket, so let's presume that.]

• First obtain a hard Dead Centre, and check it for concentricity [preferably between centres].
• When you are sure that it's a good one, keep it safe.
• Then; when you need to position the Rotary Table, just fit the Centre and use its "cone" as explained by John.

I cannot imagine an easier way of doing the job.

MichaelG.

[Norman LortonParticipant @normanlorton75928]

Michael, I thought about the rotary table and a centre (cone) sticking up from the Morse taper, and decided to try it on my newly built kit. A few minutes later I realised all this talk about conical surfaces might be off-target.

Let's think about how the basic Gelbart idea works. A laser beam at, say, 10 deg strikes the vertical surface of a rod and draws a horizontal circle around that rod if the beam rotation centre is exactly coincident with the centre of axis of the rod. Displace one of the axes and the drawn circle will be distorted (to some sort of ovoid, but not egg shaped, neither is it an ellipse) and no longer horizontal. As you reduce the angle of beam incidence any misalignment of the two axes will amplify the distortion and further tilt the circle. When the incident angle is zero degrees then the sensitivity becomes infinite.

It follows that if you increase the incident angle, for example by making the rod into a cone, then the sensitivity of the rotating laser, in indicating the centre position, is reduced. My thoughts are that this negative effect of a cone applies to the conical buttons theory (sorry John and Michael). I recon that the buttons will however work well if they are conventionally parallel and stick up about 1/4", but are quite wide, perhaps 1/2" diameter or more.

I played with my rotating laser last night and found it more sensitive at 9 deg than at 11 deg, such that finding a datum point better than +- 0.001" in both axes seemed easier. You also need a target of around 1" diameter to properly judge the laser line being horizontal, at this sort of precision

If I'm wrong on the cones I will eat plenty of pie, but I think they exited stage left with a few Dodos.

Regards, Norm.

I am adding this edit to clarify that all the above assumes you are working in the cone area above the laser point of intersection.  If you want to work in the conical area below that point, then conical metal targets become useable, but only if the the total target cone angle is greater than the total laser conical angle; ideally around 20 deg more so that the incident angle is around 10 deg.

Edit number two: Hmmm, perhaps I should eat some pie as I now see from his diagrams that John was talking about using the laser cone below its point of incidence; sorry John for trying to kill off the cones. The problem with working in this laser cone area is that the distance from machine head to table starts to get a bit bigger.

Edited By Norman Lorton on 30/01/2014 14:43:05

Edited By Norman Lorton on 30/01/2014 14:51:33

[Gary WoodingParticipant @garywooding25363]

Michael,

I know and understand toolmaker's buttons,and how they are used. Essentially they are bolted approximately in the correct position then adjusted until accurate measurements indicate they are correctly positioned. The machine tool is then aligned to the correctly positioned button. This was the method used before the advent of DROs.

Now days we line the machine tool up to some appropriate datum point on the work piece, then set the DRO appropriately. If the datum point was correctly located then the DRO allows us to accurately position the work piece to any other relevant position.

What I don't see is how a conventional or conical button assists in this – how do you place the button accurately in the first place? relative to what? If the required datum point just happened to be a correctly positioned button, then fine, but that is very seldom (never?) the case.

I can see how the spinning laser can position the conical button accurately below the spindle centre, but how do you place it where you want it in the first place? If its in the right place, then fine, if its not then how does the spinning laser help?

Gary

[Mark CParticipant @markc]

Have been watching this thread with interest. I have not seen anyone using green diodes instead of red – the eye is significantly more sensitive to green so this should make resolving the arc easier. I would think spraying the area with NDT developer would also provide a means to better contrast on a reflective metal surface?

Mark

[Michael GilliganParticipant @michaelgilligan61133]

Gary,

I've been struggling to appeciate what it is that you don't understand … but I think I may have "got it" now; so let's try again

The Buttons/Cones are all about an alternative way of working …

Consider, if you will, the guy with an old Mill; with no DRO and with worn feedscrews. … He can't therefore work the way that [I suspect] you would think normal. Instead, he sets-out the work using Toolmakers Buttons and then transfers it to the uncalibrated Mill. The rotating laser alignment makes it very easy to pick-up each of the Buttons in turn.

Using the Ickey Ball is another different approach … It provides a single "point in space" from which you can [with suitably calibrated slides] move anywhere, and machine with no marking-out required. [The drawings should, of course be prepared in the appropriate style, dimensioned from a single datum.]

MichaelG.

.

Edit: Here [final article on the page] is a brief description of a job where the Ickey Ball is useful.

 

Edited By Michael Gilligan on 30/01/2014 22:14:16

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Mark C on 30/01/2014 18:00:53:

Have been watching this thread with interest. I have not seen anyone using green diodes instead of red – the eye is significantly more sensitive to green so this should make resolving the arc easier. I would think spraying the area with NDT developer would also provide a means to better contrast on a reflective metal surface?

Mark

.

Mark,

You are right, of course, regarding the sensitivity of our eyes.

I am an enthusiastic user of Green Lasers … As you will see, I used one to illuminate the Fibre Optic in the photos. BUT that one is capable of "spotting" trees a kilometre away, and I would not use it at close range near any reflective surfaces!

Given the distances involved, I suspect that the humble red dot will be plenty bright enough.

MichaelG.

[Mark CParticipant @markc]

Michael, I was thinking more about the "haze" around the dot – using green would allow a smaller dot or less power or both and make the arc appear crisp to the eye, the same reasoning behind my suggestion of using developer as it dries to a uniform white (matt) film and might improve the edge appearance further?

Mark

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