Drum tolerances

Netz Ausg

Silver Member
I've seen many threads discuss 'tolerances' in roundness on drums, but I can't recall see anything about flatness of edges.

I checked out the edges on my new Meridians and if I place the 12" on a flat surface with a light inside it then there is some difference in the amount showing. There is an equal amount of light showing through on two opposing 90 degrees. There is pretty much no light showing through on the other 2 opposing 90 degrees. I can pass a single sheet of paper under the edge on the light showing edges but can't slide it under the dark areas. I cannot slide a folded sheet under any of easily.

The actual edge is consistent and sharp, with one little nick that is less than 1mm wide/deep.

How is this for a bearing edge? Is this acceptable or will it affect the performance of the instrument?

As a note - the shell is nice and in round!
 

mikel

Platinum Member
The roundness of the shell probably has more influence on tuning/sound than the slight bearing edge anomalies your shell has. I don't think the difference you mention would have much effect.

Check the hoops, they are probably less consistent than the edges on your drums, especially if they are triple flange, so don't sweat the edges too much.
 

Andy

Administrator
Staff member
Hoop evenness, especially in cheaper triple flange hoops, is often not so good. Even in the best ones, it's not as diametrically stable as other more rigid forms. There is always a trade off between rigidity & mass. You can also sight the head hoop as being another source of poor tuning tolerance. Even on the best brands, it's never that accurate. Both of these elements, & especially when they conspire together, make even head tuning more challenging. In the worst cases, this can equate to significant reduction in head sustain, but tuning evenness can still be achieved around the head.

The bearing edge is a different matter. You can't adjust for discrepancies in bearing edge evenness. Variations in the actual profile (e.g sharpness, angle, etc) will alter the way the head responds, again, usually equating to a reduction in head sustain. A small indentation of the scale you highlight isn't desirable, but, in isolation, will be of little detriment to the overall drum performance. These are the lesser issues relating to a bearing edge. The two biggest factors are roundness and variations in bearing edge head contact peak height. To a lesser extent, concentricity of the bearing edge form has a similar negative affect to the shell being out of round. Unevenness in bearing edge height is a significant issue, depending on magnitude. It significantly reduces tuning ease, & ultimately head sustain. It also propagates unwanted overtones.

So, what's an acceptable tolerance? Well, that depends largely on the price of the drum. The following assumes you're testing on a known perfectly flat surface. Do not assume a commercial pane of glass is perfectly flat. On a budget drum, being able to slide a folded piece of paper under the edge is probably reasonable & typical. On an intermediate drum, a single sheet in maybe one position, or two opposite positions, is maybe acceptable. On a new high end drum, anything less than absolutely zero light spill should not be tolerated. When testing edges for accuracy, the age, use, & typical application environment of the drum, as well as the shell construction should be taken into account. Shells move, even modern ply ones, so don't be too hard on a shell that's seen plenty of action or was made 30 years ago.

If your drum is new & high end, that's poor in my estimation, & certainly by the standards we employ at Guru. If it's an intermediate drum, then I wouldn't be completely happy, but I wouldn't be too surprised either. If it's a budget drum, you snagged a good one :)
 

pork pie

Member
One thing to keep in mind is this. How sure am i that the flat piece of whatever I am using is truely flat? At my shop i bought a piece of granite that is made for a machinest to make sure parts a flat. This cost me about $1000.00 and it weighs about 700 pounds. It is huge but it is very flat.
 

Netz Ausg

Silver Member
I am aware that most 'flat' surfaces are not exactly flat, so I accounted for this variable by rotating the shell 45 degrees and checking it for light, wobble and with a piece of paper every time. The result was that the light showing moved with the shell, so any inaccuracies with the surface didn't affect what I was seeing.

I'm checking out the 10" and 14" tonight to see how the edges are on them. I've managed to tune them up, so I can't imagine that they're particularly bad. One thing I have noticed on the 10" though, is that the head seems to 'bulge' a little between two lugs (half an inch deep and two inches long running around the edge). Could this be due to a high spot, or more likely just a dodgy head or out of round hoop?


Thanks for the advice so far!
 

Andy

Administrator
Staff member
One thing I have noticed on the 10" though, is that the head seems to 'bulge' a little between two lugs (half an inch deep and two inches long running around the edge). Could this be due to a high spot, or more likely just a dodgy head or out of round hoop?


Thanks for the advice so far!
By "bulge", do you mean slack? This could be due to bearing edge issues, or more likely inaccuracies in the hoop or head. To remove the bearing edge from consideration, rotate the hoop & head to different positions, & see if you still get the same thing happening on the same part of the shell.

Ultimately, you say they're tuning up ok, & that's the bottom line really.

BTW, what drums are we talking about?
 

Andy

Administrator
Staff member
These are Mapex Meridian Maples.
Ok, I think what you're finding so far is both reasonable & fairly typical in an intermediate kit. The "bulge" in the head of the 10" tom being potentially an unwelcome issue though. You need to investigate that further, as I describe in my previous post.
 

Netz Ausg

Silver Member
Ok, cool. I've have another experiment tonight with the 10" - I have a silly number of heads and the hoops from my old kit that I can play with. If I try the heads in question on both 10" toms, exchange hoops and all manner of things then I can confirm 100%.

Thanks for the help again, Andy, your wisdom is appreciated!

I'll keep you all updated!
 

Netz Ausg

Silver Member
Ok, all is happy. Got a new set of heads and it's all sounding great!

That 10" G2 is screwed though, simply won't tension flat =/
 
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