This question is for those experienced using dial bore gauges to read cylinders.

Let me start by saying, I've tried to use a dial bore gauge a total of 2 very long sessions, each separated by year(s?). I would also like to mention, I am not confident I've been able to understand how to be accurate with it until maybe this session. This session earlier tonight, is where the method that I will describe below, came to me as the way to located the widest spot of a cylinder while being confident you have centered the measuring tool both on the X axis and the Y axis for any spot you are measuring on the Z axis. Z axis being the height of the cylinder. X axis and Y axis being the planar axes of the Z axis measurement.

The spring loaded dual wheel dial bore gauge is supposed to be self centering. And I know if you are off center the distance measured is shorter (larger number on the gauge) than when you are centered in the bore. I insert the bore gauge into the cylinder and rocking it up to pseudo center. I start rocking the gauge left and right, then introduce a towards and away motion while continuing to rock left and right. I do all of this while trying to allow no more than roughly .0003" variance in any gauge reading (small variations/motions). I do this until I find what I believe to be "smallest" highest reading of the gauge for the spot I'm measuring. By that I mean, when I first put the measuring tool into the bore and start the rocking motion in my pseudo plus formation, it will be reading something like .0472" as the tightest squeeze of the measuring tool and eventually ends reading something like .0460" as being the tightest squeeze of the measuring tool. It has been time consuming to find that .0460" sweet spot, the majority of the time the gauge sticks right around .0470" and I think that is my measurement.

I have spent easily 5 minutes, possibly more, finding this elusive "smallest, largest" number for a single spot.

Is this the best way to be sure you found the absolute center spot of the area being measured?
Is there some method that should be used to efficiently center a bore gauge when taking a reading?
How easy is it, to not be centered when rocking the measuring tool back and forth in short soft movements?
How efficient are the wheels in centering the wheel side measuring point in relation to the opposite non wheel side measuring point?
Should I be tilting forward and backward as I rock left and right?

 

I should provide a picture of how I assembled the bore gauge so left/right and forward/back (towards/away) can be visualized. I agonized over the previous post for hours trying to describe it in a manner that I hoped made sense. And, I do wonder if I'm being overly OCD on this but ten ten-thousandths of an inch is a large variance in readings when it only takes a touch over twenty ten-thousands of an inch to be beyond service limits.



Bore gauge setup

 

 

 

Yeah I watched that video. It still doesn't help with larger bore readings as if you are even just a little off dead center you get a smaller distance or false reading. The larger the bore, the easier it is to be off center with a two point measuring device. The 3 point devices are quite expensive. The wheels are supposed to help the gauge seat on line "A" but it seems it's not difficult to be on line "B" which would be a false reading. And being I seem to have been able to finesse out ten ten-thousandths of an inch in the spot I was reading, it gives me concern.

 

insert at an angle so you don't drag anything down the cylinder.
make sure the cylinder is oiled. doing it dry can scratch the cyl wall, and scuff the tip on the gauge.
ONLY rock the gauge on the wheel axis so the tip rubs up and down, do not rock it on the perpendicular axis.
Pay close attention to the gauge being perfectly straight up and down at all times on the axis you shouldn't be rocking it on.
Use a loose grip on the gauge. Being too tense or too tight of a grip will prevent the gauge from centering itself. This alone is 90% of the error in measurement with beginners. Guide the gauge, don't control the gauge.
When rocking the gauge, you can move it a lot until it centers. Don't try to only move it a tiny tiny bit or that will take forever to center.

 

Thank you. I believe your instruction will be very helpful, I just recently started using a light grip. I will try and take it to heart to guide the gauge not control the gauge.