Point Length

http://forums.azbilliards.com/showthread.php?t=311538

Sent from my SM-G920V using Tapatalk

I did the same thing a while back couldn't find and gave up. Then last week I happened by it searching for something else and saved it for future reference

Sent from my SM-G920V using Tapatalk

The answer on normal V points that are 9 to 10 inches long is remove 8 to 9 thousandths of total diameter for every tenth of an inch shorter you want the points..

Busbee Cue said:

Hello,

I have spent a few hours reading the archives and can not find the post that
was on the forum at one time with the formula to figure how short the points would be after turning down the forearm.

Seems like someone said it was roughly 1/10 inch for every .01 you take off. I have a couple of junk forearms with points in my junk box I was going to mess with tomorrow and see if this was right or not but if anyone has a precise formula for calculating this task I would greatly appreciate it.

Thank you.

Click to expand...

FWIW - this can be calculated for any point length, of any point type, on any size cue
or blank, to however many decimal points you care to go.

Thee cheers for Trigonometry.

Dale

Dale,
I get the trig function, but since the forearm is offset when the pocket is cut, wouldn't that also have to be figured into the formula for accuracy? Or maybe the offset is irrelevant, just wondering.

Mildly confused,
Alan

Actually, I believe it's closer to simple Geometry.
Look at the point from the side-view, 'through' the F/A.
It can be either a 'right-triangle' or an Isosceles-triangle,
depending on how the F/A was angled for the cut.
I learned Pythagoras' theorem in High School Geometry.
The Isosceles is basically two right triangles back to back.
Reducing the diameter of the F/A will lower the point PROPORTIONATELY.
The only thing that changes is the length of the HYPOTENUSE.
This is a wonderful little aspect of math because you can do so much with it.
I'm pretty certain Kelly will correct any of my inaccuracies. Lol

KJ Cues said:

Actually, I believe it's closer to simple Geometry.
Look at the point from the side-view, 'through' the F/A.
It can be either a 'right-triangle' or an Isosceles-triangle,
depending on how the F/A was angled for the cut.
I learned Pythagoras' theorem in High School Geometry.
The Isosceles is basically two right triangles back to back.
Reducing the diameter of the F/A will lower the point PROPORTIONATELY.
The only thing that changes is the length of the HYPOTENUSE.
This is a wonderful little aspect of math because you can do so much with it.
I'm pretty certain Kelly will correct any of my inaccuracies. Lol

Click to expand...

If I say anything I will get another request to add point cutting to CueCut. So...I'm not saying anything.

You know, I gave what has to be the simplest overview that could have been given.
Actually, everything changes; not just the hypotenuse but the base and the height/altitude change as well.
While I'm making an attempt at self-redemption, let me add that what I have disclosed should me more than
sufficient in terms of starting points, to allow anyone truly interested to do some independent research.
I also like the 'charge ahead' and trial and error it until you get it right approach.
That will get you results. Just be sure to take notes along the way.
Fact is, I'm not even interested in points.

Kelly, you just know that you'll have to add to your program now. Lol
It should always be evolving. Thanx Bud.

KJ Cues said:

You know, I gave what has to be the simplest overview that could have been given.
Actually, everything changes; not just the hypotenuse but the base and the height/altitude change as well.
While I'm making an attempt at self-redemption, let me add that what I have disclosed should me more than
sufficient in terms of starting points, to allow anyone truly interested to do some independent research.
I also like the 'charge ahead' and trial and error it until you get it right approach.
That will get you results. Just be sure to take notes along the way.
Fact is, I'm not even interested in points.

Kelly, you just know that you'll have to add to your program now. Lol
It should always be evolving. Thanx Bud.

Click to expand...

CuePoints would be a different program than CueCut is. CueCut is strictly a taper design and turning program. It may further evolve in that realm. CueBillet (talking ring billets) is up next. I honestly don't know if I will ever do a points program. I have a GCode program for cutting Vee grooves, and I don't see that as something that changes often so writing a program for that isn't a priority for me right now. I'm writing these programs for my own use first.

To address the thread topic, this is what I think is the theoretical answer:
Point length is dictated by an intersection of two lines, both described in relation to the forearm axis. The surface of the forearm is one line (which changes of course for each specific turned diameter). The other line is the taper of the VEE groove at full depth of cut. This does not change. You can achieve both by taking some key measurements of the blank. Once you have both of those equations, you could derive a receding point length to diameter removal ratio since neither of the two lines in question have a quadratic term. That ratio is guaranteed to be accurate for only those two lines. However, because forearm tapers and Vee groove tapers don't really change all that much (relatively speaking) from one cue to another, a ballpark ratio (such as what Chris gave) gleaned from trial and error and experience is probably applicable to a whole lot of cues.

KJ Cues said:

Actually, I believe it's closer to simple Geometry.
Look at the point from the side-view, 'through' the F/A.
It can be either a 'right-triangle' or an Isosceles-triangle,
depending on how the F/A was angled for the cut.
I learned Pythagoras' theorem in High School Geometry.
The Isosceles is basically two right triangles back to back.
Reducing the diameter of the F/A will lower the point PROPORTIONATELY.
The only thing that changes is the length of the HYPOTENUSE.
This is a wonderful little aspect of math because you can do so much with it.
I'm pretty certain Kelly will correct any of my inaccuracies. Lol

Click to expand...

If you are clever enough - you can calculate using proportions and simple arithmetic.
But I like to use references to Trig for Math.

Dale

Ok I posted the link because it's good info but I think everyone is making this a little too complicated. I figure out my point length by drawing two simple lines in bobcad but Any of the free cad programs can do this too. One line represents the cues taper the other is the path of your cutter where they meet is where the point ends. If you want to know how much they receed just add a third line representing the taper at a larger diameter. Takes a few seconds and avoids any complicated math for the math illiterate like me

Sent from my SM-G920V using Tapatalk

Cody Cash said:

Ok I posted the link because it's good info but I think everyone is making this a little too complicated. I figure out my point length by drawing two simple lines in bobcad but Any of the free cad programs can do this too. One line represents the cues taper the other is the path of your cutter where they meet is where the point ends. If you want to know how much they receed just add a third line representing the taper at a larger diameter. Takes a few seconds and avoids any complicated math for the math illiterate like me

Sent from my SM-G920V using Tapatalk

Click to expand...

IMHO - KJ's method is even more simple, and can be done using nothing more than
a pencil and the back of an envelope.

Dale(who has noodled many specs on the back of an unpaid bill)

KJ method of drawing a triangle is exactly what my lines are in cad only I have a handy little grid and perfectly accurate measurements right at a glance makes it really simple

Sent from my SM-G920V using Tapatalk

aphelps1 said:

Dale,
I get the trig function, but since the forearm is offset when the pocket is cut, wouldn't that also have to be figured into the formula for accuracy? Or maybe the offset is irrelevant, just wondering.

Mildly confused,
Alan

Click to expand...

Good question Alan - and rest assured, no one in history has ever been more confused
than I was trying to imagine how to make a forearm with points.

As noted before, I don't actually use Trig, tho it could be done that way. Bit of an inside joke

But no, the offset doesn't have any effect, nor does any machining technique used to
to create the taper - of which there are several options - don't get me started on Snooker cues

After re-reading, the offset does have an effect in that it determines the angle of the
taper.

But you don't really need to use any angles to calc for point length - you don't
even have to know what the angles are.

Dale(who prefers the rise-and-run method)

MVPCues said:

If I say anything I will get another request to add point cutting to CueCut. So...I'm not saying anything.

Click to expand...

Tell anyone who needs to automate it that for the standard Jim Rockford fee of
$200 per day plus expenses, I'll show 'em how

Wondering how much $200 in 1974 dollars would be today.

Dale

Advancement in technologies can be a wonderful thing but not always.
Using CAD as a design function will get you your answer but it doesn't TEACH you how you got there.
Basic hand-held calculators will give you an exact answer but tell you nothing (learning),
about how the answer was derived. I'd like to KNOW, for whenever the batteries go dead. Lol
There was a time when calc-s weren't ALLOWED in the classroom. They taught you nothing.
As a lifelong student of Engineering, knowing the HOW/WHY to manipulate the numbers matters.
"too complicated"...Sometimes just knowing the answer isn't my goal.

I spoke of PROPORTION. Kelly spoke of RATIO and Chris gave us actual numbers to work with to compliment
the ratio. It's always a privilege to have Dale's contributions. This is what the Forum is about.

The Forum thanks you for your question Randy. Have a thoughtful and reflective day gentlemen.

Cody Cash said:

Ok I posted the link because it's good info but I think everyone is making this a little too complicated. I figure out my point length by drawing two simple lines in bobcad but Any of the free cad programs can do this too. One line represents the cues taper the other is the path of your cutter where they meet is where the point ends. If you want to know how much they receed just add a third line representing the taper at a larger diameter. Takes a few seconds and avoids any complicated math for the math illiterate like me

Sent from my SM-G920V using Tapatalk

Click to expand...

Correct, Intersecting lines. One changes, one doesn't. You just described exactly what I said, you just illustrated how a tool can do it for you.