Help with calibrating

[tierman]

My problem: I have a board that is 96" long, when measuring the board length, my machine only measuring 95.624". when I go to calibrate the length measurement my default is 890.368, I have calibrated it to 874.368 to get to where it measures now(the 95.624"). In trying to get to the 96" measurement, the machine will not let me go below the 874.368, I get "Calibration Range Error". The project requires a measurement closer than 3/8". Thanks in advance, any help is much appreciated. Rog

[bergerud]

If it is out of range, you should suspect something physically going wrong. That is a long board.

You may be interested in:
http://forum.carvewright.com/showthr...685#post156685

[bergerud]

I calculate 890(1+(95.625-96)/96)=886.5. Are you sure you need to go out of range?

[tierman]

Bergerud, it took me to the limit to get the machine to measure the 95.625". It was almost 2" short to begin with and I now have it down to 3/8". I am staying in contact with the brass roller all the way through the measuring process. It is consistently measuring the 95.625. Any suggestions on how to get it closer ?

[JLT]

I calculate 890(1+(95.625-96)/96)=886.5.

Dan, how did you arrive at this means of calculating the adjustment to the calibration. The manual (Rev 1.54, 01/07/13) states...

====================
To find the magnitude of the change to the current value subtract the two numbers (Length difference - _________inches). Although not an exact correlation, you should change the current value setting by 1 unit for every 0.03” (or for every 1/32nd of an inch).

So now you have a direction (add or subtract) to change and a magnitude (number of units). As an example: say you have a board that measures exactly 36” long by your tape measure and the machine measures board at 35.875”, adjust the X axis cal number by -4. If the current value was set to 890.000, change it to 894.000. Or if the machine measures 36.125”, adjust the X axis cal number +4.
====================

...so I had arrived at the following means of adjusting the calibration...

[New_Cal] = [Cur_X_Cal] + 32 * ([Measured] - [Actual])

...but found that upon measuring the length afterwards a few times, and continuing to recalibrate, that I was bouncing back and forth between too short and too long.

But your method was spot on (thanks!), and implies that the calibration is a ratio associated with the value of 890, and not an adjustment to the current calibration by 1 unit for every 1/32" the measurement is off.

Tx, Jon

[bergerud]

It must be something physical. Do you have the rubber damper under the tracking sensor? Try it without the O ring.

(Other things like head level, squaring plate square, O ring rubbing on rubber belt,...)

[tierman]

I'll keep trying and let you know.Haven't tried without o ring

[tierman]

Does not get a consistent measurement without o ring

[fwharris]

Does not get a consistent measurement without o ring

Roger,

How close is your calibration on a 3 to 4 foot board?

Is there any remote chance that your long board is loosing contact with the brass roller?

[tierman]

Roger,

How close is your calibration on a 3 to 4 foot board?

Is there any remote chance that your long board is loosing contact with the brass roller?

Floyd,Bergerud,, Sorry I was out all day yesterday. I have measured the long board 5 ties and all are within .006 on all measurements but I will give a short board a try today, will also take out the brass roller today and check for the damper as suggested bergerud, thank you both for your input