Compound Radius - details?

[sgainar]

Hey... great forum. Glad so see so many Jackson fans. I’ve searched the net and this forum a bit to try to understand how the compound radius works with the Jacksons. I have a straight 16” on my current instruments but I’m thinking I’d like to try the compound for a bit more chording comfort.

They say 12”-16” is standard for CS instruments... and different sources say different things. Is it:

12” at nut through 16” at bridge?
12” at nut through 16” at 24th fret (which would make it a little more than 17” at bridge)?
12” at nut and 16” at 12th (which would make it 20” at bridge)?

Something other than this?

Thanks... and Rock on.

Scott

[Jack Napalm]

I thought it was 12" up tp 16" at the 12th fret and stays at 16" the rest of the way.

[Axewielder]

Anyone know what year the first one appeared at J/C? Late 80's I believe?

[Spivonious]

I thought it was 12" up tp 16" at the 12th fret and stays at 16" the rest of the way.

I believe this is correct.

[sgainar]

I thought it was 12" up tp 16" at the 12th fret and stays at 16" the rest of the way.

Yeah, I’ve seen that posted as a thought... but I don’t think that could be the case. In order to get the laser close action the Jacksons are known for, it would have to be a consistent conical radius (i.e. a radius cut from a cone as opposed to a cylinder).

This is difficult to explain, but it you imagine a cone with a radius of 12” at the top and 16” at the bottom and cut the width of the fretboard from the side, you would have a 12” to 16” compound fretboard. This is important to understand when setting up the action on a compound radius guitar because you need to imagine the “cone” extends to the bridge... the bridge will actually have a flatter radius than the high fret end of the fretboard.

If it maintained 16” after the 12th fret, you would have (imagine again ) a cone sitting on top of a cylinder. If you cut a fretboard from that, you couldn’t pull a straight line (string) from the top (nut) to the bottom (bridge) without having very high action on the top frets.

I could be wrong with this, but the geometry doesn't make sense to me.

Nobody seems to know exactly, so I figured I’d try you fine folks. If I had the “under the string” radius gauges, I’d head on over to the local guitar shop and measure a few.

I apologize in advance for the confusion I may cause with my hack-job explanation of this stuff.

Thanks for your thoughts thus far.

Cheers!

Scott

[rjohnstone]

An off the shelf Floyd Rose bridge has a 10" radius. I bet 95% are never shimmed to match the radius of the neck.
To make matters even worse, the R2, R3 and R4 nuts all have a 14" radius.

So on a guitar with 12"-16" radius board with a Floyd, the setup is almost reversed.
The Floyd goes from 14"-10" (Nut to bridge).
Real head scratcher aye.

[Axewielder]

An off the shelf Floyd Rose bridge has a 10" radius. I bet 95% are never shimmed to match the radius of the neck.
To make matters even worse, the R2, R3 and R4 nuts all have a 14" radius.

Hehe I just went through this on my Jackson strat. You actually remove the stock shim from the factory Floyd to change the radius from 10" to 16".

[Voyager1000]

OK is the shim under the G string string seat on the floyd?

I saw one there but left it alone when I was putting on a brass big block the other day. I thought the floyd would be shimmed under more of the strings to match the radius, but I guess not.....

[Axewielder]

OK is the shim under the G string string seat on the floyd?

I saw one there but left it alone when I was putting on a brass big block the other day. I thought the floyd would be shimmed under more of the strings to match the radius, but I guess not.....

The stock ones are under saddles 2 - 5 (they are one big shim). If you see a small shim under one saddle, it was prolly added by the previous owner.

[RacerX]

This page is from the 2006 catalog, from Henrik's site:

http://audiozone.dk/cm/displayimage.php?pid=315&fullsize=1

[sgainar]

Awesome RacerX, that’s the picture I was thinking of. Thanks for posting.

Well the official word from a Jackson rep is 12” at the nut and 16” at the heel end (like the picture shows), with the bridge, ideally, needing to be set even flatter. With the floyd, you’re kinda stuck (though it’s probably close enough). Kahlers and other adjustable bridges let you dial this in a bit better. So with a Jackson standard compound, you’re really not playing on a 16” radius anywhere on the fretboard... it would be around 14.5” at the 12th and the bridge should be set a little flatter than 17”.

Here is a link from stewmac that describes what I was trying to earlier but with pictures and more detail than the Jackson photo that make it easier to understand. Another interesting note explained there is that a conical (compound) radius will let you set lower, more accurate action that a straight radius neck.

http://www.stewmac.com/freeinfo/Neck_relief,_building_and_repair/a-compoundradius.html

I wonder if the CS would make a custom compound? Not sure exactly what I would do but I’m thinking I’d like it a bit flatter after the 12th. I’ll have to check this out.

Rock on.

Scott

[Voyager1000]

Interesting that I have two new custom shop guitars without a shim under the string seats on 2-5, i've thought about what would be needed to get the guitar to better match the radius, I'm sure it would allow the action to be set better.

[DonP]

Interesting that I have two new custom shop guitars without a shim under the string seats on 2-5, i've thought about what would be needed to get the guitar to better match the radius, I'm sure it would allow the action to be set better.

You have custom shop guitars with a 10" radius at the bridge? The shim is for changing the radius from the defaul of 16" to 10".

[Voyager1000]

Hi DonP,
My floyd rose trem plate looks flat to me, perhaps the height of the internal sring seats themselves are close to 16"? I did put them back in the same order and I noticed the markings on the bottom of them, so I guess they have some different heights which would correspond to a set radius but I didn't know the original floyd default was 16",

Seems a bit off to me.

I'd like to shim the string seats to better match the neck, I think the action would improve. is that not required?

[Spivonious]

Wait a minute, so the Floyd bridge is set to a 10" radius by default? Doesn't that mean that every Jackson out there would need to have shims under all of the saddles to get it closer to the correct radius?