# Precision Ground Stock?



## wanderer (May 26, 2015)

Good morning,

I am just getting started pursuing my new hobby and am working on trying to retrofit a hydraulic release bearing in place of the old arm and release bearing setup in a manual transmission. 

I need to take accurate depth measurements so I will need a metal bar to lay on the face of the bell-housing to accurately measure depth. 

Is there a particular type of metal that is good for this? I was looking at 6061 aluminum.


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## RJSakowski (May 26, 2015)

wanderer said:


> Good morning,
> 
> I am just getting started pursuing my new hobby and am working on trying to retrofit a hydraulic release bearing in place of the old arm and release bearing setup in a manual transmission.
> 
> ...



Ground bar stock is not necessarily flat or straight.  However, it is usually fairly tight on thickness.  I would use a thick enough bar to eliminate any sagging and mark the contact points with the bell housing.  Make a measurement and carefully invert the bar to contact at the same points.  Remeasure and average the two measurements.  Subtract out the bar thickness and you will have the depth.


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## EmilioG (May 26, 2015)

What about a very accurate parallel? The thicker ones of course, like a Suburban Tools parallel?


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## Joe B (May 26, 2015)

Save the cost of expensive parallels. Regardless of the material, stiffness is related to thickness of that material in the direction of bending. A 1/4" by 4" piece of aluminum is relatively stiffer - in the 4" direction - than a 1" square bar of the same alloy and temper even though they weigh the same and are the same length. Aluminum is fine for what you are doing as long as it doesn't deflect more over the span of the bell housing than the tolerances you are working to.
Straightness is unrelated to stiffness and can be compensated for mathematically. If the bar you are using is the same thickness throughout its length (has 2 parallel sides), take a dimension and record it. Then flip the bar 180 degrees and measure again. The actual dimension will be halfway between the two measurements no matter how much bow there is in the bar.


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## kd4gij (May 26, 2015)

A good 2' or 3' level should do.


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## wanderer (May 27, 2015)

Thanks for the help everyone. Really like the Suburban Tools site. Its another site of all the stuff I never knew I "needed" til now 

I will probably pick up a bar of 6061 for now since its relatively cheap since I am just getting started.

Never thought about flipping the bar and taking the midpoint of the two measurements. I've spent far too much time sitting at a desk...


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