Setup Spacing For Holes To Be Drilled

Keith, yes it sounds like you did it right. The .250" is a smoking gun. Did you measure with calipers or did you use the DRO with an edge finder?
 
Also, was the distance you calculated too short or too long?
 
If you measured with calipers, that could be an issue. I have a set of cheap calipers that, for whatever reason, sometimes "skip" counts and I end up with a grossly inaccurate number. They usually give me dead-on accuracy or left-field dimensions. I only use them for rough measurements and still double check with a scale.
 
RJSakowski said:
The practice of measuring outside to outside of a pair of bolts and subtracting the diameter of the bolt should get you much closer. The error arises because on clearance between the bolt and threaded hole tilting the bolts slightly so the measured distance is slightly short (To compensate for this, I try to run short socket head cap screws instead and measure the head diameter and the outside to outside of the heads).
Click to expand...

Whenever I need to do this I usually measure the bolts outside-to-outside and then inside-to-inside and average the two measurements to remove the errors to due bolt angle and fit. I have had great success even when matching an unknown bolt circle.

Keith, it sounds like you have the right approach, but just made a mechanical error somewhere during the process.
Perhaps a scale drawing would get to the root of the issue.

-brino
 
It sounds like your math is correct, but maybe you miss-measured. Check the center to center distance with a scale and see what you get. Either that or you zeroed the DRO and moved over 3.25 inches rather than 3 inches. Yeah, I've done that;)
 
mzayd3 said:
If you measured with calipers, that could be an issue. I have a set of cheap calipers that, for whatever reason, sometimes "skip" counts and I end up with a grossly inaccurate number. They usually give me dead-on accuracy or left-field dimensions. I only use them for rough measurements and still double check with a scale.
Click to expand...
I have a pair of HF calipers that will add .200" to the reading for no reason that I can see. I don't use them for that reason. If your calipers do that trick, check the zero setting. I have never seen them reset so if the zero is off, reset and remeasure.
 
The easiest way to accomplish this is to use transfer screws. If you don't have transfer screws, you can use set screws. They work pretty well.
Your math process sounds correct. Measure over the 2 screws and deduct one diameter from your reading.
These types of things are generally nominal dimensions. Measure with a scale (ruler) and see what it should be. Compare that with the dimension you measured with your calipers.
Practice makes perfect. If we knew all of the answers, we wouldn't need this forum!

Bill
 
Could just slot one hole to fit. Sounds like your process was correct, and usually gets pretty close, if not darn near exact.
 
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