I just got a bow drawing machine from Apple Archery. It is the one that you can use a scale with. Question: Why, when I use the scale does the reading come up 4-5 pounds lighter than the traditional way of checking draw weight? I even turned the scale upside down and tried it that way - no change. I also tried moving the rollers around to change where the bow is held - no change again. The bow is centered and the pulling point is always where the string loop is located. So, any ideas? Thanks!

Man Id check with the dealer you got it
from dosent sound right to be off that much![8D]

Are you sure its that scale and not the " traditional" ? Have you checked them against a known accurate weight? May be dumb questions but often the simplest answer is correct. If it' s definitely off , send it back!!!

Twig69:

I don' t think your questions are dumb at all.

I asked Silksy on another forum what he considers " the traditional way of checking draw weight" ? How are the scales being used? Also, has he done some sort of ' standards' check?

In my shop we periodically check all our scales (3) by hanging a known weight on them. We even had one customer challange our scales by bringing his own ' test weight' . He found that our scales were correct within 1/2 pound.

This is why I don' t believe ANYONE (no direct offense intended) when they tell me their draw weight, arrow speed, etc. The only way to ' comment or compare' any units through measurements is through using CERTIFIED test units that are CERTIFIED regularly, using test methods that have explicit CRITERIA that is universally accepted by the industry.

The only way we have found, without the criteria means mentioned above, is to do a comparative analysis. We test several to many bows at the same time and compare the test results to the advertised data. We test them all at the same time on the same scale, with the same chronograph and with the same arrow. It is through these methods that we soon realize who lies and who does not.

Twig, great questions!

Len, I answered you on the other forum but I' ll repeat it here:

Len, I was hoping you were out here in web land somewhere! The way I, and most other people I have seen, typically check bow poundage is to secure a scale (mine is a 100lb Hanson) from a fixed structure, hook the string, at the nocking point, onto the bottom " S" hookof the scale and push the bow down until the peak weight is achieved. I usually grip the bow at the same point that the machine would contact it. Any help would be greatly appreciated as I need to work out an accurate Force Draw curve in the near future.

Silksy:

I' ll hold on any further comments until we resolve some questions that I have detailed on the other forum.

the scale could be off take it to the department of weights and measurement at your local county blg. and they can check it for you for a small fee.

Silksy:

Sorry I wasn' t in when you called today. I would have enjoyed talking with you.

What my Store Manager explained to you was correct. What he didn' t relate was the following. When using a Hansen ' spring' scale, the weight of the scale itself, which you see is between 4-5 pounds, is compensated/calibrated with an adjustment screw at the bottom of the scale. You can easily see this by turning the adjustment screw to a minus feature. If you would put the bow on the scale, the total weight will be indicated by the cursor. That weight will now be less than what you will get with the cursor starting at zero. When you turn the scale other than vertical, let' s say horizontal as we' ve done on one of our machines, the pointer will automatically move from 0 to a minus poundage depending on the angle. This is the scale weight being reduced.

Since the springs are now not necessary to measure/compensate the scales weight, they are free to measure draw weight. This will result in (guess what?) 4-5 pounds less draw weight. Remember, the cursor moved to minus and therefore has to travel to 0. This will result in the cursor not traveling as far and a subsequent lesser reading on the scale.

If you were to put the bow' s riser onto the scale and then pull the string, you' d have to recalibrate the cursor due to the weight of the bow. Turning the scale upside down; well, I' ll have to take a look at that situation. The reason I say this is that I have a theory that is not proven. My theory is that the weight of the scale would have to be accounted for in the final cursor reading. In other words, the point of the scale' s spring engagement would have to be know to know where to set the cursor.

Keep in mind that this is a ' spring' scale and that all measurements are to be considered by spring engagement and movement. The length of that movement is so indicated by the cursor. The weight of the scale has to be considered and therefore the manufacturer (Hansen has installed a calibration screw into the bottom of the scale. Also note that these scales, like all scales or measurement devices, are only as good as their calibration. Calibration is determined by using a ' standard' (or a ' golden' model) by which all units should be compared.

This is why I' ve always questioned, and rightfully so, the readings/specs that are given by anyone on the forums, those who come into my store, and even the manufacturers. What ' STANDARD' did they use? This is also why we always do a comparative study by examining several to many bows at one time to do a comparative study. This will tell us who is farther from the TRUTH where advertising is considered. You' d be surprise at how much variance we see from what is advertised.

This again is not to say you don' t have a faulty scale.

Hope this helps.

I have one of the Apple set ups you mentioned and my scale will read about 4 or 5 lbs light when using it that way. So regardless of if it is correctly calibrated it still shows a difference between the " standard" way of checking draw wt and using the Apple machine with the scale hanging. I believe Len is correct in that this would be due to the weight of the scale would have to be added to the reading or the scale calibrated with the set screw to compensate .