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Author Topic: Help me understand pitches  (Read 3961 times)

nospareball

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Help me understand pitches
« on: June 14, 2007, 07:54:34 AM »
I get the general concept of pitches, but what I'm wondering is how they are actually measured.  I recently went to a 0" reverse on my thumb from a 1/4" reverse.  Obviously the ball feels much different on the hand, and more secure.  It got me thinking, how are pitches measured?

Take for example, 1/4" reverse in the thumb.  I've never drilled a ball, but I assume there are settings on the press for pitches which angle the bit.  So what's that angle?  Is it 1/4" over for every 1" down?  Or some other method?

And really, why don't we go by degrees for pitches?
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Oskuposer

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Re: Help me understand pitches
« Reply #1 on: June 14, 2007, 04:16:36 PM »
The are measured in inches.  Going from 1/4 reverse to zero is a big change.  Did you also change your span too?
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RealBowler

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Re: Help me understand pitches
« Reply #2 on: June 14, 2007, 04:31:21 PM »
Yeah, what Deadbait said.

The drill bit doesn't move, the jig moves the ball.

Setting it at 0 and 0 would drill a hole through the exact center of the ball.

X-axis is left and right, and Y-axis is up and down (fingers and thumb) - if what I was told is correct...I've never been good with keeping my axis stuff straight!

Moving y-axis 1/4 reverse would drill a hole 1/4" away from the center of the ball.
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nospareball

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Re: Help me understand pitches
« Reply #3 on: June 14, 2007, 09:20:59 PM »
Ok, I think I get it now, 1/4" reverse would actually put the top of the thumb closer to the fingers.  So roughly how much should the span be shortened going from 1/4" rev to 0?  I did have my middle finger shortened 1/8" (I think, I'll have to check the sheet), not because of the pitch but because it was too long to begin with.  I asked for the thumb pitch change, and he didn't seem concerned that the span should be shortened.   It feels good so far, but a slug change can shorten up the span some if needed.
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LuckyLefty

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Re: Help me understand pitches
« Reply #4 on: June 14, 2007, 09:48:22 PM »
You have got to be kidding.

OF course changing the pitch does NOT change span length!

The top of the hole is in EXACTLY the same place!

THe bottom of the hole as described perfectly by Deadbait points to a different spot.  For a 1/4 inch reverse thumb hole the center of the hole points exactly 1/4 of an inch of center of the ball.  (using Deadbaits example in the S direction).

A 0 pitch hole drilled on the surface of the ball in the EXACT same place has the center of the hole pointing directly at the center of the ball.

REgards,

Luckylefty
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nospareball

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Re: Help me understand pitches
« Reply #5 on: June 15, 2007, 10:36:30 AM »
Thanks for the clarification.  So let me see if I have it now, the difference is measured at the center of the ball, so for every 6" down the hole ends up 1/4" over?  That angle has to be really shallow, like around 2° as opposed to 0° with a 0" pitch.  Doesn't seem like much of a difference to me, unless I'm misunderstanding again.
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ccrider

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Re: Help me understand pitches
« Reply #6 on: June 15, 2007, 02:34:01 PM »
So, as the jig moves, does it tilt the ball. It would seem to have to if the top of the hole is always in the same place.
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RealBowler

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Re: Help me understand pitches
« Reply #7 on: June 15, 2007, 06:24:36 PM »
quote:
So, as the jig moves, does it tilt the ball. It would seem to have to if the top of the hole is always in the same place.


Depends on the jig.  This one does tilt the ball - http://www.jayhawkbowling.com/Products/Pro-Jig.html

A standard type jig (x & y axis) moves the ball left and right and back and forth.  You set your pitches first, and then adjust the ball under the drill bit to line up the drilling lines.  - http://www.jayhawkbowling.com/Products/Mini-Mill.html



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ccrider

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Re: Help me understand pitches
« Reply #8 on: June 15, 2007, 06:47:28 PM »
Even with pitch gauges, how can you "set the pitch first" with something like an AMF jig? Do you actually have to tilt the table itself?
 
Or does the pitch change by moving the jig back and forth or left to right from zero. In other words, if I have my jig set at 0 to hit the line, and move it 1/4 left, and then turn the ball so that it again hits my mark, want that give me 1/4 pitch?

Charles
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RealBowler

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Re: Help me understand pitches
« Reply #9 on: June 15, 2007, 07:21:18 PM »
quote:
Even with pitch gauges, how can you "set the pitch first" with something like an AMF jig? Do you actually have to tilt the table itself?
 
Or does the pitch change by moving the jig back and forth or left to right from zero. In other words, if I have my jig set at 0 to hit the line, and move it 1/4 left, and then turn the ball so that it again hits my mark, want that give me 1/4 pitch?

Charles


Yes, on the standard jig, the pitch changes by moving the jig.

0 and 0 means the drill bit will hit the center of the ball.  To drill 1/4 reverse on the thumb, you would move your y-axis to 1/8 - the table moves up because you want the hole pitched away from center.  Which ever direction you want the pitch, you move the table the opposite direction.

So, you put the ball in the jig, set your y-axis to 1/8, lower your drill bit to just above the ball and then move the ball until the bit is lined up with your hole markings.  You drill the hole and get the correct pitch.

It's hard to describe.  I had a hard time understanding it until I drilled a couple of balls.  I think part of the difficulty in being able to picture it in your head is that the object is round - most people are used to drilling square (or flat) surfaces.

There are a couple of different types of jigs, but in the end they all do the same thing - enable you to drill into a ball at different angles.

http://www.ultimatebowling.com/equipment.asp



I've never seen the pro style jig, so I don't really know how it works.  You can kind of figure it out by looking at the picture.
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