Centre Finder

[steveharris]

:)At the Midland Model Engineering Exhibition, one of the exhibitors had a centre finder for his CNC miller made from a web camera mounted on a morse taper shank. The image could be displayed on the computer screen for setting up.
He said that the information on how to build it was in a magazine. (Model Engineer he thought!)
Does anyone know where I can find this info so I can make one for my miller.
Thanks. steveharris

[baggo]

Hi Steve,

apparently it was in Model Engineers Workshop. I don't have it myself but some-one may be able to tell you which issues. There's also some info about it here:

www.miketreth.mistral.co.uk/centrecam.htm

Hope that helps,

John

PS just looked at the website - it tells you it was in issue 121!

[houstonceng]

drjohn wrote : "how the blazes to you make sure they are exactly in line with the spindle?"

As far as I rember on reading the article, drjohn, the S'ware allows one to "centre" the Cross-hair image wrt the actual centre of rotation. Don't ask me how it does that since I'm not into "web-cams" and image software.

Effectively, you turn the spindle through 180 degrees and - via the software - reduce the difference when viewing an edge.

Personally, I think the Work-shop isn't the place to have a PC. Too cold, too damp, too much detritus and it would get in the way of my loco building because of limited bench space.

[circlip]

Splitting the offset assumes that the spindle is vertical, Not necessarily so with a Bridgeport. Meant to dive in on this subject before drjohn's safety valves started blowing on this one. Looking round some of the American sites just shows what technological lepers we are, while we are playing with DRO's, they are into full CNC. On one of the other threads we were talking about if we had to go back how would we cope? I'm not a Luddite but how far do we want to go? When you've set your cross slides to three decimal places, and centred to a tenth of a thou/ micron, when you've drilled your holes you still have to "fit" the bits together. Some of my mentors words still echo with reference to "A proud 1/16th or a shy 1/64th"

[abby]

I agree with you circlip , chasing half a thou is time consuming and often un-necessary for most model engineering , I have received patterns from US customers ,made by rapid prototyping or CNC, as masters for castings and they look exactly like what they are - digitally produced . This may be ok for some people but personally I like filed or matted finishes.
Some computer logic in the workshop can be indipensible though , I have found a scanner great for inspection, and I used an apple II with home made i/o board and basic software to control my burn-out furnace for several years until the disc drive died ( no hard drives then lol ) It gave the first class service of a "proper" controller costing ten times as much , and printed out a graph too.
A digital caliper clamped to a slide makes a cheap , if sometimes awkward to read , DRO.

[houstonceng]

Circlip wrote "Splitting the offset assumes that the spindle is vertical, Not necessarily so with a Bridgeport. "

I'll agree about the Bridgeport, but not about the effect on the centre finder.

If the true centre of the spindle is "aimed at a point" and the S'ware superimposes cross-hairs on the image, then as the camera is rotated 180 degrees, so are the image and cross-hairs.

Let's assume that the true centre of rotation isn't the centre of the image (which it probably won't be) then the spot that the camera is aimed at, will not be in the centre - but will be a fixed point in space and, consequently, a fixed point on the image. All that you have to do is move the S'ware generated cross-hairs to that point on the image (splitting the difference each time.)

Once set, the cross-hairs will be at the true centre of rotation of the spindle - irrespective of the angle that the mill-head is set at. - - - - - Unless, your Bridgeport spindle rotates around a different centre wqhen the whole head is tilted. If that's the case, it's in serious need of restoration.

[circlip]

Thank heavens for the wonders of electronics.

[houstonceng]

Before circlip deleted his immediately previous posting, I replied as follows.

I still don't understand why you think that splitting the difference repeatedly when adjusting the S'ware created hairs in the centre-finder (subject of first letter in this thread) will not result in them being exactly on the centre of rotation of the spindle - irrespective of the angle of the complete head.

Obviously, you need to do in in both the X and Y planes and more than once for each.

Maybe we're agreeing violently - except that I'm talking about the centre-finder in MEW121/122 and you're talking about a "mechanical" finder. Similar things have happened to contributers in the past.

[circlip]

Megabites rule OK ;D ;D ;D

[houstonceng]

Before circlip deleted his immediate previous posting, I replied as follows

As I said. We are violently agreeing, but our arguements are based on two aspects of the same problem.

drjohn was asking how one made sure that the centre of rotation coincided with the centre of the centre-finder and I answered that.

Shortly after, you wrote about the need for the column to be exactly vertical.

Unfortunately, since there was no lead-in to your mailing indicating a different subject - ie material position - it wasn't obvious that you were talking about the potential error in that position following the use of the edge-finder. That error obviously occurs irrespective of the type of edge-finder employed - be it web-cam, microscope or mechanical - if the column isn't exactly vertical.

I must have missed the reference to "material position" in your earlier contribitions.

[steveharris]

Thanks to all who gave their valuable comments, especially baggo, I'm on the case now and have got lots of info so far.
Sorry to those who do'nt like PC's in the workshop. but for CNC it's a bit of a necessity.
Thanks again

Regards. steveharris.

[houstonceng]

"Cute" edits (aka deletions) circlip, but you've now removed the thread of the discussion for anyone reading this topic in the future.

Nevertheless, I enjoyed the argument when it was there - and by "argument", I use the correct sense if the word, not a series of contradictions.