I think it is more imporant to get good readings at the edge. I have also noticed the error factor of cheap levels starts really bad then is better over a modest space and then goes bad again over a long run. The marin of error between the not great table and the crumby level may miss the mark altogether. If I have a problem it starts with the base and so a torpedo can at least verify that flatness before moving to the platter and then to the cartridge.
If the readings are non-level in the center and level on the edges is there any possibility that the piece of wood is slightly warped?
That's exactly what I was thinking...I may have to rethink my shelf. It's bizarre...it seems like I check it, rotate it 180 degrees, rotate it again back where it was the first time, and it's not even close to the same measurement!
Try using a "bulls-eye" level. This has a clear dome showing the level for the entire 360 degree range instantaneously , and will make leveling a shelf (or a turntable) MUCH easier!
Do you mean the little $2 Sears circular level, or something else altogether?
While it is important that the turntable be level, how level it has to be depends on what kind of table and arm and what some poeple consider perfectly level.
First off, the most important reason a turntable should be level has to do with the balance of the arm. If the arm is not level, the balances will change slightly, and the less out of level it is, the less it is affected. It is also important the arm be level in relation to the platter, so the alignment does not change according to where on the record it is, and it is important that on a table with a suspension, that it not lean one way or the other so as to change the behavior of the suspension.
Not being totally familiar with the sl-1800 you are having problems with, I will offer this, it could be that dependind on what type of suspension it has, where you place the level could be having an effect on the turntable because of the weight of the level, or you could be getting different readings because the platter or mat is cupped, which some are to better support the record, or your level is not accurate, which is confusing you.
Being a carpenter, I will point out that almost all levels made today are not true. Proper leveling technique is to get the same reading when you flip the level 180 degrees, then you eliminate all variables. In other words, If the bubble is dead center and then you flip the level end to end, and it is not also dead center, your level is out. If the bubble reads slightly to the left, when you flip the level end to end it should read slightly to the right the same amount. That is how to level using a level that is off, and also how to check if a level is accurate before you buy it. It is not really nessessary to have a level that is totally accurate, but one that is easy to read.
I should think that the sl-1800 does not have a separate suspension separating the platter and arm from the table? How springy are the feet? If you are fairly confident that it is stiff enough to not change level by placing a level on it, I would say leveling the table itself is going to be close enough.
Hope this helps.
Two levels are alot easier to use for a four point set-up. Front/back,left/right. "Starrett" machinist levels(4")are very accurate & can be had cheap used.
Just seconding the wise above and even my own that levels are accurate only to their rating.
Aceto, a bulls-eye balance looks like a clear circle with a bubble at the top, and a small marked circle at the top, in which the bubble should be positioned for true level. Makes leveling much easier and more accurate, than having to continually move a linear level! They are very small, too; mine has a base with a 1-1/2 inch diameter, which makes it handy for fitting into tight spaces as well. Just remember, that the bubble move toward the high position
IMHO -- Stabila brand is the level to beat, 'tho they have some econo models as well. The #81S 9.5" torpedo I use is good to 0.5mm/meter in the upside position, which is really hairsplitting. OT, but the other tool I'd pay anything for and never give up, is the Armstrong Tools #64-005 torquing screwdriver for setting receptacle and breaker terminals to correct torque.
I'd check the platter for bearing wobble (run-out). If you can't borrow a dial indicator (I think it's called; ask a machinist or auto engine builder), I'd build my own. Use a RS soldering aid -- the weighted base thingie with multiple arms with aligator clips on the end. Clamp something hard with a smooth finish in one of the clamps, and place it so it just barely touches the platter surface. I'm thinking a toothpick for starters...Slowly rotate the platter by hand and see if the object touches the platter evenly around it's edge, middle, and inside. You might need some other jig to check the inside. You could also build a jig out of scrap in no time...
(What do the black lines on a bubble level indicate? Some kind of tolerance based on the level accuracy, I'd guess...)
Shasta, why is torquing receptacle and breaker terminals so important? Isn't just "tightening the snot out of it" O.K.? (Sort of like Marisa Torme's "balls on" technical calibration standard for the dripping faucet in MY COUSIN VINNY!
I just found that those bulls eyes levels are available at Sears (go where the levels and other measuring tools are) for $ 1.49/ea.
That has to be cheaper than what our local hi end retailer would charge us after painting it gold and putting it in a snazzy wooden box....
Fatparrot, ok I have a bull's eye. But where do you put it? I know i'm being dense again but the spindle is where I would want to put it.
Place the level all along the arc that the stylus will trace from the outer edge of the record to the inner groove. Once you have adjusted it to be perfectly level along that section, rotate the platter 180 degrees. Put the level along the same arc (from the outer groove to the inner groove where the stylus will pass as it plays the record). If it no longer reads level then you probably have something wrong with the platter.
My comment and your inquiry are a bit OT. Sorry to everyone. Having said that, buy a new panelboard, receptacle, or circuit breaker. Look at the instruction sheet and you will see torque specs for all electrical connections. These must be followed per NEC 110-3(b).
Overtightening or guesing at fastener tightness doesn't work. Ask any auto engine builder. On an electrical connection, it screws up the metal due to thermal expansion/contraction cycles, and you end up with a looser connection over time. That's why infrared thermograpy was developed, it's part of industrial PM, and everything is re-torqued on a scheduled basis.