wotayottie
Well-Known Member
should know this but have forgotten. how do I find the centre point of the end of a piece of bar - I need to drill and tap it.
the centre of a circle
- Thread starter wotayottie
- Start date
Boo2
Well-Known Member
You can take a pair of dividers and set them to very slightly larger than half diameter by eye. Then use the point to draw 3 intersecting arcs at 120 degree angles, again by eye. Then punch in the centre of the triangle formed by the 3 arcs.
Or if you have a surface plate and a height guage you can use those in the same way.
Boo2
rivonia
Well-Known Member
From the outer edge draw apencil line to the other side, say 2" down. Then do the same again the other side. Where they cross is the exact center.
Peter
Peter
TWINSCREW
Well-Known Member
With a compass, draw a circle the same diameter as the bar on paper or card, carefully cut out and glue onto the bar end using prit stick or similar, then centre punch through the hole made by the compass.
Salty John
Well-Known Member
Bisect two chords.
MASH
N/A
Don't you need three position lines to make a fix?
srp
Well-Known Member
Not if you bisect two chords.
Many of the above methods are fine on paper, but not very practical in the workshop. It's almost impossible to locate the point of dividers or compasses on the edge of a bar. Ideally you need a centre square,
http://www.ebay.co.uk/itm/Small-Engineers-Centre-Square-/330515737683
or a combination square
http://www.toolstation.com/shop/Han...Combination+Square+Set+300mm/d10/sd150/p10432
Failing that, a decent flat surface, a block exactly half the diameter of the bar, and a sharp scriber.
Or stick it in the lathe, and drill the hole.
Steve C Cronin
N/A
Accuracy depends somewhat on the dimensions we are dealing with. If diameter is less than, say, 10mm, we will be struggling. The theory is that where two perpendiculars at the points of contact of any two tangents cross, is the centre. So if you can drop the rod into an engineer's vee blocks with the square-cut end in one of them, and, using an accurate square, scribe perpendiculars from each of the points of contact on the end of the rod, where they cross is the centre.
Poignard
Well-Known Member
Little Sam
Well-Known Member
Finding the circle center is easy enough as mentioned above.
What i'm curious about is how the OP intends drill the hole square on, otherwise he's highly likely be entering the realm of broken tap-dom, which only a a wire eroder or new piece of bar is gonna solve.
Best to take it to your local engineering shop and have the Center lathe turner do it, which he will for a couple of cans in less time than its taken me to write this !
What i'm curious about is how the OP intends drill the hole square on, otherwise he's highly likely be entering the realm of broken tap-dom, which only a a wire eroder or new piece of bar is gonna solve.
Best to take it to your local engineering shop and have the Center lathe turner do it, which he will for a couple of cans in less time than its taken me to write this !
