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Old 04-01-2010, 10:37 AM
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Default PLH- what it is and what it does.

"What is all this PLH mumbo-jumbo that I keep hearing from this nutcase?"
I have been preaching PLH here on DGCR. People keep asking me what it is. Here is an explanation.

This is a picture that Anakha posted on DGR along time ago.
You see the thin horizontal line in the middle of the discs? That's the Parting Line Height (PLH). The parting line is the thin line of plastic that is accidentally left on the disc after it has been injection molded. It is accidental because ideally the molds will be machined with high enough tolerance that there will be no witness of where the mold separates. But in the real world, wear and tear will slightly round the edges of the mold halves. Plastic flows into the rounded off sections and voila! You have a visible parting line.

"Yeah, I hear you but... so what?"
Well... assuming the 2 discs in the picture above came from the exact same mold, the PLH will dictate how overstable the disc will be. Well, that's the extremely simplified way of stating it but that statement still holds up well in practice. I underlined "the exact same mold" because this is very important. No, San Marino Rocs and Rancho Rocs are not the same mold.

Take 2 Wizards. Put them nose to nose. The one with the higher PLH will be more overstable. Even if one is E plastic and one is SSS. If both discs pictured above were Wizards (they're not, one is last year's Ace Race putter), then the yellow disc on the right would be more overstable. That's all there is to it.
Take 2 Bosses and put them nose to nose similar to the putters in the picture. The one with the higher PLH will be more overstable than the one with the lower PLH. I have a Champ Boss and an R-Pro Boss. The PLH is almost 1/8th inch higher on the Champ; guess which is more overstable? Yes, there is a big difference between the weights. But the difference would still be huge if they weighed the same. Even with the 25 gram weight difference, if the lighter R-Pro had a higher PLH it would be more overstable than the Champ. It might not ACT as overstable because you could more easily reach the designed cruising speed of the disc. It is easier to accelerate a 1 pound object to 50 mph than a 20 pound object. Given the identical speed and spin between the 2 Bosses, the lighter disc but higher PLH would be more overstable.
Because of the discs geometry, the PLH will have a larger range of shift on discs with wider wings. This is commonly recognized. Flashes are known for wild inconsistency. Forces vary, Bosses vary, Katanas vary. Even Leopards (relatively thin rimmed driver) will have stablility variations but because the PLH can't shift as much the variations won't be as extreme. This is why Cyclones, GZs, TBs, EXs, XLs, etc. are "more consistant" from run to run when compared to Bosses.

"Okay, that's all fine and good but what practical application does this have for me?"
You can save money. Ever go to the store to buy a backup Boss? It might not fly at all how you wanted it to. Too overstable, too understable whatever. It is tough to do with beat discs but you can try to match your thrower's PLH to a new discc's PLH. It is better to take a measurement before you ever throw that disc. Yeah it's pretty nerdly but it would save money.
Also you can use this technique to pick out specific variations. The first time I bought a Roadrunner I knew I wanted most of the typical RR characteristics but I didn't want a really flippy one. I bought the highest PLH that PIAS had and I'm happy with it. I bought another one online and it is too flippy. The PLH is significantly lower. Not 1/8th of an inch like the Bosses, but every little fraction of a millimeter makes an appreciable difference.

So, to sum up (and I know you are sick of hearing this by now)...
THE HIGHER THE PLH, THE MORE OVERSTABLE THE DISC.
THE LOWER THE PLH, THE LESS OVERSTABLE THE DISC.
But they have to be the same mold.


EDIT: Sorry for any misspellings, I didn't proofread. My post was too long.
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Last edited by Marmoset; 04-01-2010 at 10:40 AM.
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Old 04-01-2010, 10:45 AM
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interesting thanks for sharing.
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Old 04-01-2010, 10:55 AM
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I can definitely vouch for this, as the higher PLH Z predators I have are meathooks, where the lower PLH ones act more like x preds.
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Old 04-01-2010, 11:15 AM
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from DGR...
Quote:
Originally Posted by marmoset
Quote:
Originally Posted by Dave McCormack, owner of Gateway
"The most recent runs of Sabre are less stable, but not JUST because of the lower PLH,, because of the smaller bead,,, which like the PLH, beads and concaves and rim depths are all also extremely important to the stability.

Baby blue Illusions are a perfect example of PLH and again YES, lowering this height is what we try to do when we run E Illusions. It can be done by a WIDE range of variables from temperature of polymer, Temperature of mold, speed of injection, pressure, hold time, how they are stacked on the table and a combination of any more,,,plus a combination of the above mentioned.
...
Several factors effect flight,,,, PLH is certainly one of them."
I had a conversation with Dave and he said he specifically tries to influence PLH to get desired flight characteristics.
Interesting.
I knew it could be done, I just didn't know anyone was actually doing it.
I asked if he could label the runs so we'd know the relative stability of the run but he said no way, Jose.
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Old 04-01-2010, 11:25 AM
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This is interesting. Makes me want to hold off all disc buying until I can get to a store I can sit there and compare the discs to find what I really am looking for.

Thanks
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Old 04-01-2010, 11:28 AM
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Yeah. I know. I used to buy a ton of stuff online but now I really want to fondle before I buy. Maybe I'll make an annual pilgrimage to CDGS, DGC, MS, etc.
PIAS just doesn't have the selection.

I hate bothering the guys at the online stores. I'd rather do it myself anyway; "if you want a job done right, ..."
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Old 04-01-2010, 11:30 AM
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Interesting...what I'm trying to understand is this: How can the parting line move if it is formed by the union of two solid pieces of metal? I could see offset, as I have encountered this in my own occupation, but the up-and down shift is harder to understand.
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Old 04-01-2010, 11:33 AM
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Quote:
Originally Posted by toothyfish View Post
Interesting...what I'm trying to understand is this: How can the parting line move if it is formed by the union of two solid pieces of metal? I could see offset, as I have encountered this in my own occupation, but the up-and down shift is harder to understand.
Nevermind, I get it. The PLH doesn't change relative to the two halves. It moves up and down relative to the wing location...low parting line = bent down wing, high parting line = bent up wing...need more coffee...

Looking closer at the pic, the lower parting line disc also has more slope on top of the wing...
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Old 04-01-2010, 11:43 AM
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you guys are reading way too much into all this. its interesting to know but you shouldn't dwell so much on it. if you fill your head with all this non-sense eventually you wont be able to just play the game. this is the same as the color argument. go out and throw instead of searching through disc after disc and driving miles away. your time will be better spent.
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Old 04-01-2010, 11:44 AM
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Quote:
Originally Posted by toothyfish View Post
Interesting...what I'm trying to understand is this: How can the parting line move if it is formed by the union of two solid pieces of metal? I could see offset, as I have encountered this in my own occupation, but the up-and down shift is harder to understand.
I used to wonder the same thing until I started doing injection molding stuff for my job.
There are literally dozens- if not more- process variables that will affect the PLH. Process variables is just a fancy word that means different ways of doing the same thing during the injection molding process.
Here are a few:
•Using different plastics. This is a biggie...different plastics shrink at different rates.
humidity. Affects how much shrinkage occurs.
•Packing pressure. How much extra material is injected into the mold. The more you cram in there, the denser and stiffer the disc.
•Injection pressure. How hard you squirt your plastic into the mold.
•Clamping pressure. How hard you squeeze the mold pieces together.
•Mold temperature. How hot is the mold?
•Holding times. How long is the molded disc allowed to cure inside the mold?
•Holding pressure. How much pressure is the disc held under during the holding time?
•Cooling methods. Is it allowed to fully cool inside the mold or is it put onto a cooling fixture after ejection?
Etc.

I probably missed a bunch of obvious ones, these are what immediately popped into my head.

Side note... in the "gotta love that secret mix" thread, you see the gateway guy putting the discs dome side down on a table immediately after injection molding. There is a good chance they are doing this to make the dome flatten out as it cools. Dome won't affect stability as much as glide (IMO) but it is an example of Gateway influencing final disc geometry and flight characteristics by modifying process variables.

Even with molding golf discs, everything you do is for a specific reason.

Last edited by Marmoset; 04-01-2010 at 11:49 AM.
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