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Author Topic: Datum Zero  (Read 3479 times)

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Offline John S

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Datum Zero
« on: April 15, 2008, 07:23:34 PM »
First load the sound track.

http://www.stevenson-engineers.co.uk...dambusters.wav

or

http://www.stevenson-engineers.co.uk...dambusters.mp3

Now read the history.

http://en.wikipedia.org/wiki/The_Dam_Busters_(film)

Now watch the pictures.



Two cross haired lasers [ no it's not a breed of dog ] mounted either side the router head at 45 degrees. My finger is over one so only the other shows.

The camera is picking the laser line up a lot fatter than it actually is, in real life it's quite fine.



Both lasers shining together, head is too low at this point.



Raise head.
Both lasers converged, bombs away. That is bang on under the centre of the tool and Z hight is exactly 40mm above the work.

Set tool hight, zero axis and open bomb bay doors.

In real life I can get between 5 thou and 10 thou of where I want to be, may not be accurate enough for some in metal but for the router guys who work from the start point then everything from that point is accurate, mostly outside shapes are discarded.

Won't suit everyone but it's very quick.

[Edit] the tracks in the chipboard as the outline of Phenolic brush rings out of large DC motors. It can make a complex ring with curved slots in about 2 minutes.

John S.
Re: Datum Zero
« Reply #1 on: April 15, 2008, 10:55:42 PM »
Maybe I'm not seeing it, how does the cutter height relate to the lasers?  40mm from the part to where on the spindle?  Can't the cutter be set in the spindle/collet up or down a bit, i.e. not the same place everytime?

Monte

Offline jimpinder

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Re: Datum Zero
« Reply #2 on: April 16, 2008, 03:56:05 AM »
This is british genius at it's best. During the last war a chap called Barnes Wallace invented a bomb, which when dropped on water, skipped across the surface, until it hit the dam wall. The bomb then sank to the bottom of the wall and exploded - blowing up the dam - hence the name DAMBUSTERS.

The R.A.F. squadron who made the attack had the problem of dropping the bomb at low altitude, at night, at a precise height. The squadron leader was a bit ***** one night and went off to the theatre. There he saw spotlights on the star artiste - and realised that two spotlights at an angle only coincided at one point - and spotlights were fixed shining at angles from the nose and tail of the aircraft to meet under the aircraft at the precise height the bomb had to be dropped from.

Watch the film - if you can find it - Stiff upper lip and all that
Not me driving the engine - I'm better looking.
Re: Datum Zero
« Reply #3 on: April 16, 2008, 08:14:20 AM »
This is british genius at it's best....

If your reply is to me, I can understand the lasers lining up at a certain height at a certain angle to each other, but the cutter height doesn't directly relate to them.  Unless he's using tool holders with a preset height in the spindle.

Monte

Offline jimpinder

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Re: Datum Zero
« Reply #4 on: April 16, 2008, 12:25:40 PM »
I assume that, once he knows what height his cutter is at, he can use offsets on his tool table - over to you Guy Gibson !!
Not me driving the engine - I'm better looking.

Offline John S

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Re: Datum Zero
« Reply #5 on: April 16, 2008, 07:51:41 PM »
Sorry for the delay, just got back from a bombing run  :)

Because the lasers are remote from the cutter you can keep the cutter in. I drop the cutter onto the work, zero Z,  then raise the head until both lasers converge then move X and Y to line up.

At that point I take the Z reading and enter it into the tool table then re zero all axis.

Because the Z hight is in the tool table for the cutter in the collet a file can be run straight away. If I then swap to a thicker or thinner board just lining the lasers up will keep the tool offset in the table the same.

As this Router has no positive way to swap tools and keep the settings any tool changes have to be re done but not material changes.

John S.
Re: Datum Zero
« Reply #6 on: April 16, 2008, 10:50:39 PM »
Sorry for the delay, just got back from a bombing run  :)

Score any hits?

What you said about setting the tool height clears it up for me.  Thought some manual measurement/setting had to be done.

Monte