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[4]

Touchdro calibration question

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Kenny G

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#1
So I have the BLU-DRO coming soon and I have watched Yurieys video on calibration but it has me sort of confused. This is his formula



X_disp = the value shown on the display
X_real = the real value of the travel
CPI_start = the CPI value used for the calibration
CPI_new = the calibrated CPI you want to know

X_disp / X_real * CPI_start = CPI_new

it doesn't matter what units you use (inch,metric or Norwegian beard length)



Note X_disp / X_real * CPI_start = CPI_new

but in the video he does not divide by 3 he just used the display value to set his new CPI and it adjusts to 3” what am I missing?



The main reason I am asking is that I am going to be using this on a mini lathe with Igaging scales. and don't have 3" travel on the cross slide so it will be necessary to use the 2" dimension for that axis. Another thing is that he seems to arbitrarily chose 30000 for an initial CPI is there a reason? So do I just go by the formula? Thanks for any help in understanding
 

RJSakowski

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#2
So I have the BLU-DRO coming soon and I have watched Yurieys video on calibration but it has me sort of confused. This is his formula



X_disp = the value shown on the display
X_real = the real value of the travel
CPI_start = the CPI value used for the calibration
CPI_new = the calibrated CPI you want to know

X_disp / X_real * CPI_start = CPI_new

it doesn't matter what units you use (inch,metric or Norwegian beard length)



Note X_disp / X_real * CPI_start = CPI_new

but in the video he does not divide by 3 he just used the display value to set his new CPI and it adjusts to 3” what am I missing?



The main reason I am asking is that I am going to be using this on a mini lathe with Igaging scales. and don't have 3" travel on the cross slide so it will be necessary to use the 2" dimension for that axis. Another thing is that he seems to arbitrarily chose 30000 for an initial CPI is there a reason? So do I just go by the formula? Thanks for any help in understanding
In step 7, he is entering in an arbitrary count of 30,000 (10,000 cpi x 3 in.). His built-in calculator takes the no. of counts recorded in traversing 3" and updates the cpi value.

One thing that was not done was verifying that the 1-2-3 block is actually 3.000" They can and do vary. Even expensive blocks are shipped slightly oversize to allow for lapping.
 

Kenny G

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#3
RJ thank you for the reply so now I can use the 2" dimension and multiple 10,000 x 2 and use 20,000 for my constant when calibrating the X axis on the lathe since the max travel is only about 2.5+/- ". In reasearching this I have also discovered that the native CPI for capacitive scales is 2560 CPI thanks to Al Basset of Blu-Dro. Considering the equipment and its condition I am using i.e. mini lathe, mill and my experience, the variance of the 123 block will probably not be a concern. Knowing the native CPI though may help in determining the slop in the feed screws and nuts due to ware on my lathe.
 
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