Locating center

[T*O*F]

I know how to locate the center of a circle on paper using a compass.  Without buying any new tooling and other than by eyeballing it, how do you locate the center of a 5/16ths circle so it can be drilled. 
Example: drilling the cavity in the nose of a percussion hammer blank.

[Bob Roller]

I know how to locate the center of a circle on paper using a compass.  Without buying any new tooling and other than by eyeballing it, how do you locate the center of a 5/16ths circle so it can be drilled. 
Example: drilling the cavity in the nose of a percussion hammer blank.

In that case I use "High Powered Guessing" and it seems to work.
I use a milling machine and a two or three flute end mill.Touch
off on the surface to be cut and adjust as needed.

Bob Roller

[Chris Treichel]

5/16 is a bit small to use other than SWAG... for larger circles I have a nifty little gauge for measuring angles. You set the edge of the inside angle make a mark move it about a quarter or so and make another mark.

http://www.prestonhardware.com/16ME_POCKET_RULE_GAUGE_p/6938856.htm

[smylee grouch]

I took a piece of thick key stock and drilled a 1/8 hole all the way through and then drilled another hole just over the dia. of the hammer but only half way through using the 1/8 hole as a pilot.

[T*O*F]

In that case I use "High Powered Guessing" and it seems to work.

That's how I usually do it but only have a drill press.  I spot the hole by eyeball, punch it, and drill it.  Then I use an end mill in my drill to square up the bottom.  Using the end mill to do the whole thing is often kinda grabby and usually doesn't work out well. 

Sometimes my eyeball is off a bit and I was hoping for a better solution.

[D. Taylor Sapergia]

I use the old and semi-true eye ball method too.  But I drill the hole to form the cup with a twist drill, and have ground another drill to cut a slightly tapered hole with a flat bottom.  Thus the wall of the cup is thicker at the bottom of the cup.

[Ky-Flinter]

I took a piece of thick key stock and drilled a 1/8 hole all the way through and then drilled another hole just over the dia. of the hammer but only half way through using the 1/8 hole as a pilot.

BRILLIANT!  Stick the hammer nose in the hole and mark the center thru the thru-hole.  Perfectly centered!  Now if I can just remember that trick the next time I need it.

-Ron

[smylee grouch]

Ron, I didnt finnish my post enough but you nailed it. I have used this method for other projects like finding center of ramrod tips, short starters, etc.

[davec2]

Scribe 4 or 5 lines across the nose purpously just off center line. The resulting very small blank area in the center of the nose of the hammer contains the real center. Eye balling the center of this much smaller polygone is much easier. The more lines you use the more like a circle the blank spot will be. Jus takes a minute to do. No tooling although the tooling is the best method.

[frogwalking]

If I need to drill a hole on something round, like a metal ramrod. I clamp a hardwood block in my drillpress vice, drill a hole the diameter of the piece to be drilled, place the piece in the hole (in the wood block) (without moving the block) then drill my hole.  I have gotten quite close this way.  The resulting hole is not only centered, but straight with the axis of the part. 

[Acer Saccharum]

If the hammer nose is 3/8 diameter, put a piece of 3/8 stock in the chuck, and center that on the hammer nose, then clamp workpiece in place. Then withdraw the spindle, and switch to your 5/16 tooling.

[KentSmith]

Two ways. 1.  Find the diameter of the circle.  Mark it off on a straight edge.  Now draw a chord(a straight line intersecting the circle in two places) the length of the diameter.  Draw another one.  Where the two chords meet is the center.
                 2.  Draw a chord smaller than the diameter.  Find the center of the chord.  draw a perpendicular line to the center of the chord.  Draw another chord, mark the center, draw the perpendicular line.  Where the two perpendicular lines intersect is the center.

For the hammer recess I'd use #1 and a scribe to get close enough

[Long John]

I would use my 6" combination square made by Starrett.  It has two slidey-deals, one your conventional square and the other a right angle at 45 degrees.

I would use the 45 degree slidey-deal placed on the side of the hammer and scribe across the face along the beam.  then move the 45 degree slidey-deal about 90 degrees and scribe again.  Where the two scribe lines intersect is the center.  The intersection of two perpendicular bisectors of two cords of a circle define the center of the circle.  Euclidian geometry.

Best Regards,

John Cholin

[Scota4570]

I'd drill a 5/16" hole in a piece of aluminum.  I'd glue that to the part you are working with and carefully center it.  I'd then use my 5/16" transfer punch to mark center.  I'd then pop the aluminum guide off. 

[T*O*F]

Actually, I have a set of thingys for removing studs with an EZ-out.  You slide them over the stud and they have the correct hole for whatever drill size is required for the stud you are trying to remove.  I just can't ever find them when I need them.  I have even used a socket in the past and spotted the hole thru the 1/4" square that fits on the ratchet.  Anyway I just finished doing it by eyeball and it came out good.

Lots of good ideas have come from this thread that might help someone in the future.  I like to see the novel ways that guys come up with to do things.  One the other hand, I think some of these guys must be engineers or school marms.  I mean who can remember those geometry theorems when its been 55 years since you took the class.

[shortbarrel]

T.O.F Centering the hole on the nose is the easy part. What kind of tooling and machines have you got to drill the hole , you didn't say.

[D. Taylor Sapergia]

Here's a series of photos I took while re-cutting the nose of a Hawken hammer.  The lock is a Davis, and the hammer underwent a lot of filing to make it presentable.  But the first step was to recut the cup.  I simply clamped the hammer by the flat part in my drill press vise and leveled the nose.  The drill I used is a re-ground bit to create a slight taper which reinforces the bottom of the cup, and cuts a flat bottom.  The spur of the hammer rests on the drill press table - lots of support.  I simply positioned the bit over the cup, and drilled away.  A light touch.  When I worked for Don Robinson in the late 70's making our version of the Hawken rifle, I made up this bit, and drilled about 180 of these hammers.
This is a before shot...


...and an after shot...notice how much farther the hammer comes down over the nipple, and also moves forward so that the hammer strikes at the rear of the cup.



the recut cup...


And last, here's the re-ground drill bit.  I flattened it first, and then cut some draft on the cutting surfaces.  Then I ground the taper into the bit, again providing some draft so the bit would cut rather than squeal and heat up.

[Bob Roller]

One more thing to be done after the deepening of the hammer nose and that is to
file a "V"slot in the forward edge to vent the debris from the cap.

Bob Roller

[D. Taylor Sapergia]

...like this?

[Bob Roller]

...like this?

Looks fine to me.

Bob Roller

[D. Taylor Sapergia]

The chequered hammer spur is not always seen on original rifles.  But I like it and always cut it, as it ensures the hammer does not get away from you when you are cocking the lock - especially on a hunting rifle.