Point Length

pdcue said:

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)

Click to expand...

You don't have to know what the actual angles are, but you need data describing the taper of the bottom of the Vee groove. Rise over run is a slope, which is the results of an angle.

Take two forearms that are exactly .925 diameter at the end of the points and the point length is exactly 10 inches for both. Take a cut on both, say .050" diameter removal. If either the taper of the cut is different on the two, or the taper of the bottom of the Vee groove when it was machined is different on the two forearms, the points will now be different lengths (saving both tapers are different and you got lucky because the differences canceled each other out). How much different will they be? Almost not measureable because the two tapers don't vary much between cues.

Advancement in technologies can be a wonderful thing but not always.<br />
Using CAD as a design function will get you your answer but it doesn't TEACH you how you got there.<br />
Basic hand-held calculators will give you an exact answer but tell you nothing (learning),<br />
about how the answer was derived. I'd like to KNOW, for whenever the batteries go dead. Lol<br />
There was a time when calc-s weren't ALLOWED in the classroom. They taught you nothing.<br />
As a lifelong student of Engineering, knowing the HOW/WHY to manipulate the numbers matters.<br />
"too complicated"...Sometimes just knowing the answer isn't my goal.<br />
<br />
I spoke of PROPORTION. Kelly spoke of RATIO and Chris gave us actual numbers to work with to compliment <br />
the ratio. It's always a privilege to have Dale's contributions. This is what the Forum is about.<br />
<br />
The Forum thanks you for your question Randy. Have a thoughtful and reflective day gentlemen.

That's exactly why I posted the link I felt knowing how was important but that if you get confused easily like me with all the math you can simplify things and have a shortcut. It doesn't have to be cad either graph paper and pencil work the same

Sent from my SM-G920V using Tapatalk

Bobcad file, .984 oversized blank to .840 finished size, 10 inch point reduces to 8.624 inches if point pocket is .050 from centerline. Offset of forearm when cutting the point pocket is irrelevant.

Not quite as confused,
Alan

aphelps1 said:

Bobcad file, .984 oversized blank to .840 finished size, 10 inch point reduces to 8.624 inches if point pocket is .050 from centerline. Offset of forearm when cutting the point pocket is irrelevant.

Not quite as confused,
Alan

Click to expand...

If your offset of the forearm is different when you machine the grooves (and you don't change the cutter path) you would have a completely different diagram. You would have different point lengths at .984 and .840, and you would have a different rate of change of point length per diameter of stock removal. How is that irrelevant?

Kelly,
Of course the offset is relevant, maybe what I should have said is that it irrelevant to the bobcad drawing above since the diagonal line from .050 to 10 inches represents the offset. For someone with a fixed taper or offset, after cutting the blank all you need to do is find where the point pocket exited the forearm and you are able to see where the point will be on finished size. Reversely, if a finished size point is desired, the entry point on the oversized blank can be easily found. With a few other added lines in the drawing, other information can be gleaned also.

Not minding the confusion,
Alan

aphelps1 said:

Kelly,
Of course the offset is relevant, maybe what I should have said is that it irrelevant to the bobcad drawing above since the diagonal line from .050 to 10 inches represents the offset. For someone with a fixed taper or offset, after cutting the blank all you need to do is find where the point pocket exited the forearm and you are able to see where the point will be on finished size. Reversely, if a finished size point is desired, the entry point on the oversized blank can be easily found. With a few other added lines in the drawing, other information can be gleaned also.

Not minding the confusion,
Alan

Click to expand...

OK. Understood.

OP originally said he had some "junk forearms with points in my junk box". I don't think OP used Bobcad to draw with and cut the point grooves in the forearms he asked about. I entered the discussion in the general sense of how to determine what OP asked for by only taking a made blank and measuring it and then using math to get the answer he wanted for his specific blank without taking test cuts to observe a change.