DGR Homework: parting line height and relative stabilities

[Spike]

Another thing that is considered giving the disc stability, apart from a high parting line, is the bead. Not many new discs have those anymore, and when they do they are described as old-school (…Stalker). Isn’t the bead just another way of adding distance below the parting line to make it more stable? …or does the shape of the bead itself create some kind of air flow that makes it stable?
This may be off topic (unless it has something to do with the parting line), but I was wondering about the point of adding a non-streamlined shape to a discs profile, such as a bead.

[marmoset]

IDK, that's a good question.
My knee-jerk reaction is to say that beads make a disc more overstable by adding more material under the parting line. I want to say that there is a ratio of material above and below the parting line. In theory a really understable disc could become overstable if you put a big enough bead on it, big enough to adjust the ratio into the overstable disc territory.

It also adds weight further out adding to the gyroscopic-ness. The weight distribution is changed but IDK how that alone affects flight.

But when it really comes down to it, IDK. All I can do is guess.

[Dogma]

Glad you started this thread. You definitely should have called it 'Parting Lines' though. I didn't read it for a day and half because I thought it was going to be about how I should be doing more drills. I'll bet a lot of people are overlooking it.

Gazelles - I have a pretty good DX Gazelle collection. Most are pretty consistent, but I have two that are freak overstable and have always perplexed me. Sure enough, normal Gazelles are all about the same, but the two freaks are substantially higher than the others. Even more interesting, one of the freaks is 146g (the rest are mid to high 160s), so apparently parting line is not a function of weight. Just for fun I looked at two beat Gazelles. Their flashing is long gone and they're pretty scarred up, but when I put them side by side I could see that the more stable one was higher. The most understable one had more "droop" to it's nose (it's hit a lot of stuff).

Xcalibers - I checked two Xcalibers. The more overstable one was higher.

Bosses - The only discs where I saw no difference were two R-Pro Bosses. The parting lines were the same, but one is a little more overstable. However the more overstable one is 10g heavier and brand new, while the less overstable one has taken a lot of hits (big divets in the rim actually) from hitting a chain link fence numerous times so take what you will from that.

Valks - I compared two DX Valkyries that fly about the same. The parting lines matched up. Then I wondered how they would compare to premium plastic. So I pulled out a Star Valk that has a little more stability, and the parting line was higher.

I suspect that parting lines as a functional measure of relative stability will become part of the core of DGR knowledge. It will certainly change the way I shop for and evaluate discs. And it opens up tons of possibilities for intentionally choosing discs of varying stability within the same mold. Or for trying to find the flight properties of a DX disc you like in a more durable plastic. And of course, for finding a good backup for a disc you love (assuming you remember to do it before you lose the disc).

Excellent work Marmoset!!!

[marmoset]

I posted this on the other thread; all measurements are taken with dial calipers and the discs are on a flat surface.

Comets.
Several examples of each plastic were sampled and the average measurement is recorded. All are unthrown. Measurements were taken from the lowest parting line- it looks like the mold uses a spacer.
old Z 175 grams→ .272" high
new Z 175 grams→ .268" high
ESP 175 grams→ .26" high
X 175 grams→ .255" high
This seems to fit the common trends in Comet stability.

[marmoset]

Glad you started this thread. You definitely should have called it 'Parting Lines' though. I didn't read it for a day and half because I thought it was going to be about how I should be doing more drills. I'll bet a lot of people are overlooking it.

Done.

[Spike]

The profile of the Predator is a good example of a VERY overstable disc with a VERY high parting line: http://www.discraft.com/prod_predator_z.html

...Stratus on the other hand is understable but still has a high parting line: http://www.discraft.com/prod_stratus_x.html

So, the theory seems to be one of many aspects.

[Dogma]

The profile of the Predator is a good example of a VERY overstable disc with a VERY high parting line: http://www.discraft.com/prod_predator_z.html

...Stratus on the other hand is understable but still has a high parting line: http://www.discraft.com/prod_stratus_x.html

So, the theory seems to be one of many aspects.

I think you're missing the point. No one is saying that parting lines are the sole factor that defines stability, nor is anyone saying that parting lines are comparable between different molds. The idea is that parting lines give a visual indicator of relative stability when you compare two discs OF THE SAME MOLD.

[Spike]

The profile of the Predator is a good example of a VERY overstable disc with a VERY high parting line: http://www.discraft.com/prod_predator_z.html

...Stratus on the other hand is understable but still has a high parting line: http://www.discraft.com/prod_stratus_x.html

So, the theory seems to be one of many aspects.

I think you're missing the point. No one is saying that parting lines are the sole factor that defines stability, nor is anyone saying that parting lines are comparable between different molds. The idea is that parting lines give a visual indicator of stability when you compare two discs OF THE SAME MOLD.

Yes and no. The initial post was regarding differences within the same mold, but there are also posts that compare different molds (see the image with the Wizard and the new Discraft putter). If we make the discussion wider the parting line will be important as a quick guide to how a disc may fly, but there are also models where the parting line would indicate overstability but in practice flies understable.

[Dogma]

Yes and no. The initial post was regarding differences within the same mold, but there are also posts that compare different molds (see the image with the Wizard and the new Discraft putter). If we make the discussion wider the parting line will be important as a quick guide to how a disc may fly, but there are also models where the parting line would indicate overstability but in practice flies understable.

No one is talking about comparing different molds by using parting lines. There are too many other variables that affect stability to do that. Did you read the post that goes with the picture of the two putters? It says:

I realize these are 2 different discs but if they were the same mold then the one on the right should be more overstable.

The purpose of parting lines is to be able to compare discs of the SAME mold, and determine which is more overstable. For example, if you were at the store looking for DX Teebirds, you should be able to line several up on the counter and accurately predict each one's stability relative to the others, by comparing parting lines. You CANNOT line a Teebird up next to a Predator and do the same thing because you would miss numerous other factors (speed, wing shape, bead, diameter, rim width, and others).

If you want to compare different molds, use the flight chart.

If you want to compare discs of the same mold, use parting lines.

[marmoset]

Sorry for the confusion, I should have clarified this in the beginning.

My theory is for discs produced from the same mold.

This is not intended for comparisons of TBs vs. Preds, not Focus vs. Wizard, not TB vs. TL, not even Sannies vs. Ranchos vs. Ontarios. Not even between the different Rancho Roc molds which theoretically should be identical but are going to have some variance.

I am not yet prepared for a discussion on rim configurations, wing configurations, weight distributions, etc. between different molds.

[Spike]

Sorry for the confusion, I should have clarified this in the beginning.

My theory is for discs produced from the same mold.

This is not intended for comparisons of TBs vs. Preds, not Focus vs. Wizard, not TB vs. TL, not even Sannies vs. Ranchos vs. Ontarios. Not even between the different Rancho Roc molds which theoretically should be identical but are going to have some variance.

I am not yet prepared for a discussion on rim configurations, wing configurations, weight distributions, etc. between different molds.

Now that’s a disappointment I thought this was gonna be the absolute super-thread, that explained why discs fly like they do. All discs!
No, it’s very good the way it is. Good observations with the parting line!! It makes sense.

[elnino]

well the aerodynamics are cleary changed by the parting line being different....now what makes the parting line so different?

different colorants?
different cooling times?
different molds? as in how many do they mold at a time?

[marmoset]

I believe the parting line height is affected when the disc cools and shrinks. The are dozens of variables in this process.
Temperature, humidity, weighting agents, cooling time and process, how full the mold is packed, etc.

[Jeronimo]

Check out the visual results of my latitude 64 parting line home work:

http://www.discgolfreview.com/forums/viewtopic.php?f=5&t=5420&start=780

[marmoset]

A+!