# Easson 12B DRO Bolt Circle Function



## Alan H. (Oct 21, 2017)

My PM935TV mill is equipped with an Easson 12B DRO that Matt/OMT installed as part of the package I bought.

In the past several months there have been discussions on the Easson 12B DRO but not too many specifics on their capabilities.    I thought I would post a specific glimpse into its bolt circle function.  It makes child’s play out of drill and tapping holes on a part.

I am skinning a casting down making a die filer.   It will have a small seal cover plate that surrounds the vertical shaft that drives the file.   This casting is clamped in my PM935 and referenced.  It is getting several operations while in this position in the mill including drilling these six holes for 4-40 screws.

The DRO has a function called “PCD” (Pitch Circle Diameter) or what I might call a bolt circle function.   You invoke the function using the menu on the DRO and then simply scroll through the PCD's menu adding the center reference, bolt circle diameter, no. of holes, starting hole angle, and ending hole angle.   This input of the parameters is quite intuitive.  To drill them, you then toggle through each of the holes, zero x and y on the screen, and punch your hole.  There’s a very nice graphical display on the DRO that shows you which hole you are working on.  I also scrolled back through the coordinates to support the tap with a tap guide.   This makes this sort of work unbelievably quick and accurate.

Thought this might help folks who wonder about the Easson 12B by showing a specific function that I have found very useful.  No searching for a bolt circle calculator on the web, ciphering and capturing it on paper.  The DRO does the ciphering and the process is quick as lightning.

The whole casting for context:






DRO with PCD Function up and running:









Drilled and tapped:





By the way, these 4-40's are on a 9/16" radius.


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## mksj (Oct 21, 2017)

Very nice Alan, one reason why I like the graphical display on the DRO as it it is a bit  of a no brainier the way information is displayed. You can index to each whole and the DRO will give you the new zero coordinates to the that hole. I used this function frequently, most recently drilling the bolt circle holes of my ER chuck to match the back plate. I have an EL700 on my mill, and it has a wide range of similar functions. On a mill, the Eason 12B or C is a wonderful display at the price point. I also feel that the color and graphical numerical display is much easier on the eyes than the traditional LED numerical displays. The Easson 12B and C DRO comes with 3 scale inputs in the standard model, so one needs to decide on putting the Z axis on the knee/head vs. the spindle.  The EL700 and a few others have 4 axis models, but pricey and often difficult to adapt the 4th axis to the spindle. I think you have a very nice setup on your PM935 with the Mitutoyo DRO on the spindle. 

You do beautiful work.


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## darkzero (Oct 21, 2017)

Nice job Alan! Yup, the graphical displays are awesome! I originally wanted a Fagor DRO with graphical display for my lathe, at the time there really were no affordable graphical display DRO available. I decided that I didn't need a graphical display for my lathe, I wanted a lathe specific DRO with out all the.mill functions to keep it simple.

But for my mill, I definitely had to have one. I originally had an Easson ES-8A on my mill. The ES-12 (original version) had just came out but Matt wasn't getting them for a few more months. I waited patiently to get one from Matt & I couldn't be happier. Not just the bolt circle but all the other functions are very easy to use with the graphical display. I really only use the bolt circle & line hole functions though.


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