OK, I don't have any equipment to measure arrow weight.  i'm looking for a predictable/repeatable way to produce a 500 grain arrow.  so my draw is 28".  if i buy a 29" cedar arrow, 3 feather fletch, classic nock and 125gr broadhead, will that add up to 500gr?  if not, what needs to change?

What weight of bow and spine are you shooting? Wood is a natural product,you can have a matched set weigh when finished 550 grs..And you get another set same spine weigh around 500 grs.But most of the wood arrows I've made up usally weigh from 525 to 600 plus grs.You can usally predict the finish weight from the starting weight of the raw shafts.You can pick up a digital scale from 3Rivers or Kustom King for $20 to $25,I've got one and they work great.

Cedar shaft weights vary widely with spine and shaft diameter, over 100 gr, so a simple answer is going to be elusive.  With a 23/64" shaft tho, you will be at or over 500.  

With a 29" arrow, you will come pretty close if you add point weight to the full length bare shaft weight.  Spend the little bit extra for good matched shafts and your supplier will be able to send you pretty close to the weight you need/want, and you will end up with much better arrows.  That is my suggestion.  Tapered is also worth the extra, IMO.  Good Shooting!

If you are looking at wood and a predictable/repeatable way to produce a 500 grain arrow with out a scale you are going to have a hard time. It can be done with alum or carbon. Like JRY309 said scales are not to expensive

I shoot arrows that match that description.  Mine are 11/32", 5 1/2 shield feathers and spine 50-55 with three coats of wipe-on polyurethane.  When I use Douglas Fir they all are 500 grains or over (some just barely, but all at least or more).  I have not found cedar to be as heavy, usually around 475-485 or so.  

Your best bet to make sure you get what you want is to buy an inexpensive Hand Held Grain Scale from Kustom King or 3 Rivers.  They can be purchased for $6-$9.

RonP

thanks guys!  i'll buy a scale!

I bought a small hanging scale form either 3 Rivers or Kustom King for around $100 that works great.  It works best if you hang the scale from something instead of holding it.

Use a heavy broadhead to get the weight up there I have 29" arrow with a 160 gr head weighing 570

I shoot 11/32 cedar shafts cut 28" to back of point spined 50/55  5" fletch with 125 gr point they come in around 500 to 525 pretty much all the time. I just have a cheap scale from 3 rivers around 10$.

According to my electronic scale, my 11/32 cedars cut to 29" BOP with 5 1/2" shield cut, 3 fletch feathers and 125 grain points weigh 495 grains...usually. I had one that kept hitting low, so I weighed it...550 grains. Without a scale, you are just guessing with wood shafts.