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Rotary Laser centre finder

An unusual design centre finder for the mill

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John McNamara25/01/2014 04:29:31
1331 forum posts
122 photos

Hi All

I have so far not been inspired to build a Laser centre finder for the mill because of the difficulty of reading the fuzzy spot and the difficulty of keeping it truly on the axis of rotation of the machine when removing it and replacing it.

The design shown in the video below overcomes these difficulties by angling the beam through the axis of rotation and rotating the spindle when taking a reading. Thanks the human eye's persistence of vision this forms a cone of light that shows up on the surface of the work as a ring.

It also uses the eyes ability to centre objects between two points, By raising the quill you can make the lasers fuzzy edge just touch the points being compared your eyes make excellent comparators in this situation.

The video shows various ways of using the tool. I particularly like the way it shows on a circular object as a ring that is angled unless the axis is truly perpendicular to the object.

Looks like I will have to build one of these........

Link below (the device shows at 2 minutes 10 seconds from the start)


I have not seen videos from this man ,Dan Gelbart before.. They would be a good start for beginners to learn about workshop processes. I have not seen them all maybe there are other gems like this one inside.


Thor 🇳🇴25/01/2014 05:03:39
1483 forum posts
41 photos

Interesting concept John, thanks for the link.


Andrew Moyes 125/01/2014 06:07:50
142 forum posts
23 photos

Fascinating. Just what I need for centring holes etc. Strange it isn't commercially available yet. I've got to make one...

Further on, he makes the case for a 4 jaw SC chuck which is my preference too for normal round and square stock. I'd always thought the 3 jaw was really for hex stock but I hadn't realised you could hold hex in a 4 jaw as well. The angled hole in the nut is a great idea too.

Thanks for the link from me as well. I must watch some more of his videos.

Andrew M

Michael Gilligan25/01/2014 08:46:21
19601 forum posts
997 photos

That's very neat, John ... thanks for the link.

Incidentally, it is possible to improve the spot from a LASER by using "Spatial Filtering" in a collimator. The unit would probably be too big to fit on the Mill spindle; but you can work magic with Mirrors.



P.S. I do envy Mr. Gelbart's Clean-Room / Workshop.

Edit: added hyperlink

Edited By Michael Gilligan on 25/01/2014 08:51:50

MM5725/01/2014 09:29:22
110 forum posts
3 photos

Great idea.

Come on you 3D printer guys - find a commonly available laser pointer that you can gut to get the parts, and design a casing that they will fit into. 3D print away and start selling the pair of them (purchaser does the gutting and fitting)...

...that'll be £1000 + VAT for the idea please - send to the normal place

JasonB25/01/2014 10:13:20
22017 forum posts
2540 photos
1 articles

All those suggestions to speed up working and he has to walk round the mill to the wall to adjust his VFD?


Chris12325/01/2014 10:28:19
121 forum posts

Can't you just use a 1" square aluminum bar, attach a short round bar to fit into a collet, then drill an angled hole to hold a cheap laser pointer?

The hole would have to be angled towards the chuck otherwise you wouldn't get the angle right.

Edited By Chris123 on 25/01/2014 10:28:45

John Stevenson25/01/2014 10:37:44
5068 forum posts
3 photos

I built one some years ago using two laser pointers at an angle to the spindle and at 90 degrees to one another.

These were just cheap ones from Deal extreme in China but they had a built in collimator to give a line and not a dot.

They were a permanent fitting at the side of the head on the router and set up onto a known centre. They also gave the centre hight when lined up.

Got some pics somewhere but can't find them at the moment, I'll look later.

Got the idea off the Dambusters film.

Douglas Johnston25/01/2014 10:47:48
763 forum posts
34 photos

The Dan Gelbart video on coating is very interesting, particularly the information about surface preparation before painting. I have often used acetone for cleaning before painting or glueing and I now see why this is not a good idea. Much food for thought in these videos.


Oompa Lumpa25/01/2014 10:48:11
888 forum posts
36 photos

I the twenty or so years (give or take) that Laser Pointers have been freely and cheaply available this is the first time I have considered buying one because I have a real use for it. Brilliant idea.

I also like the idea of the camera on the toolpost to see the work, really neat. Another forthcoming project.


Michael Cox 125/01/2014 10:53:12
548 forum posts
27 photos


This is a prototype of a laser centre finder that I have been playing with. It works on exactly the same principle as the Gelbart version. It is designed for mounting in a collet on the mill spindle. The small plastic collar on the laser pointer is just for holding the on button in the on position.

It works very well but it is a little too sensitive because the angle of the pointer is too steep. I shall build another version will angle the beam at around 45 degrees.


Ady125/01/2014 11:02:50
4910 forum posts
726 photos

That laser idea is one of those "why didn't I think of that" moments

Ian P25/01/2014 14:50:10
2552 forum posts
113 photos

I had not heard of Dan Gelbart before today but having watched the video (shame about the audio quality) found his demeanour and explanations a cut above so many of the so called 'instructive' YouTube videos and have started to watch his whole series.

A bit of Google research shows he is quite an exceptional chap and the video is made in his own home workshop with his own machines.

Interesting how he discusses tolerances in microns but uses imperial tools, also likes to make things the most efficient way yet does not have the VFD pot where he can reach it.

Ian P (still looking for a laser pointer but cannot remember where I put it)

Thor 🇳🇴25/01/2014 16:05:45
1483 forum posts
41 photos

Hi Michael,

Your version looks simpler (and cheaper ?). Is the angle between the laser and the centre line of the mill adjustable?


Michael Cox 125/01/2014 17:36:44
548 forum posts
27 photos

Hi Thor,

On the prototype gadget shown above the angles are adjustable. Everything can swing about the two pins in the blocks. I made it this way in order to investigated the effect of the angle. I thought that it would work best with a steep angle so I cannot pull the angle to much less than 70 degrees with the arrangement shown. In fact I think that the angle should be much shallower.

I have built a really simple version with an angle of 45 degrees and this seems to work well. I will photograph it and post a photo soon.


Michael Cox 125/01/2014 17:59:09
548 forum posts
27 photos

Hi Thor,

Here is the Mk2 version:dscf2687.jpg

The aluminium block is 14 mm square and drilled through at 45 degree angle, 9.5 mm diameter, for the laser pointer. One end of the block is drilled out and tapped M5. The sliding bar is 6 mm diameter and reduced in size and threaded M5 at one end. This screws into the aluminium block. The spindle is 10 mm round steel cross drilled 6 mm for the bar and drilled and tapped axially for a 3 mm screw to retain the bar. In use the working distance can be increased by sliding the bar out from the spindle or decrease by sliding it in. The only other adjustment is to twist the aluminium block to make the laser beam line up with the axis of rotation of the mill. This is adjusted to give the smallest circle of light projected onto a surface.

I hope this helps


John Stevenson25/01/2014 21:37:22
5068 forum posts
3 photos

Don't underestimate the MKl eyeball though.

Believe it or not it's accurate to 0.001" unless registered blind that is and then you can use your white stick as a wiggler wink

The pip on the left is done by an endmill / slot drill and has been very accurately been placed on centre using a DRO.

The pip on the right has been done with the same cutter but the work has been wound in 0.001" according to the DRO.

The difference is noticeable.

Ian P25/01/2014 21:58:27
2552 forum posts
113 photos


Wound in 0.001" In which direction?

It looks like the depth of cut might be that but without knowing the work diameter its hard to be sure.

If its distance is to the centreline what was the DRO referenced off?, or how can you be sure its so accurate?

As you infer eyeballs are pretty good, and yes you can observe 0.001" differences but its then working in comparator mode, if you are trying to crossdrill a round bar the unaided eye is only going to achieve that accuracy if the bar is maybe 0.25mm diameter and the drill is 0.01 diameter (watchmaker sized parts)

Ian P

John Stevenson25/01/2014 22:03:56
5068 forum posts
3 photos

Ian, Does it matter ?

Can you not see that the pip on the right is not in the centre ?

Ian P25/01/2014 23:08:52
2552 forum posts
113 photos

No it doesn't matter but what I was trying to say is that I can see they are not in line but how do we know which one is correct?

The laser device looks to be a good way of getting it on the bar centre without even having to know what the diameter is. What is not so obvious is what degree of accuracy can be garnered from the usual irregularly shaped laser spot.


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