Finding the centre again

[lee hawkinsParticipant @leehawkins46887]

Posted by Terryd on 22/01/2012 21:54:45:

Posted by lee hawkins on 22/01/2012 18:16:28:

It may not work on something as small as maybe down to 6mm or something, but any other size circle it’s perfect.

 

Get yourself a piece of paper+compass, get the diameter of your circle , draw the circle on the paper, then cut it out nice and accurate, fold it twice , you then have a perfect segment of the circle with a nice point, put that on the workpiece you want to find the center of, accurately lining it up, now where ever that point is will be spot on the center

 

Maybe most people already know this way.

 

lee.

We do,

but 5mm dia is a bit small for such methods, even more accurate is to draw the circle in a drafting program and draw the centre lines with the finest lines possible.

T

Edited By Terryd on 22/01/2012 22:02:54

 

Edited By lee hawkins on 23/01/2012 07:06:20

Edited By lee hawkins on 23/01/2012 07:07:57

[Ed DuffnerParticipant @edduffner79357]

Now don’t laugh guys, I’m only a beginner, but how about something like this? (knocked it up in Rhino3D).

 

The circular plate has known sized holes 1 to 12mm in increments of 1mm. This could be swapped for other plates e.g. half sizes or imperial.

 

The lower pin locates the desired hole size, which should be directly underneath the upper pin. The upper pin is then held in the mill chuck or collet. The job is then moved x,y until the marked feature on the job is centred visually in the plate hole. The centre finder is then removed and replaced with the milling tool/centre drill etc.

 

[blowlampParticipant @blowlamp]

A pair of dividers or a trammel with large cone points could also be used to transfer the hole centres from the old jaws to the new ones.

 

 

Martin.

[Jim GreetheadParticipant @jimgreethead]

I’m not laughing Ed, I think that is quite brilliant. Simple, effective and useful. Thank you for sharing.

 

Jim

 

[Billy MillsParticipant @billymills]

Nice Ed, You can also print out a load of circles of different diameters on OHP film with the centres as very fine crosses then prick through the centre. Select circle over job then mark centre.

 

Michael mentioned overkill- well if you are using countersunk holes and fasteners you do need to get things right, some get very upset if the screw is not nicely centred in the countersink, it does not look good. For Wolfie’s job it may be on the inside, if the countersink is to sink the head it still needs to be right.

 

Point that has not been mentioned is that the problem is an order-of-work issue. It may be tempting to cut the countersink at the same time as drilling holes but it could be best to leave it for later after spotting through for other holes.

 

Billy.

[Martin WParticipant @martinw]

Ed

 

How about a small mirror mounted on the lower upright set at 45 deg directly above the active gauge hole. This would make viewing easier and remove parallax errors especially on the smaller hole sizes.

 

I like the idea as it could be put to many uses where a centre needs to be determined, sheered screws, broken taps/drills etc. Get it patented quick and make yourself a fortune, well maybe .

 

Cheers

 

 

Martin

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