Z axis setter gauge

[JScott]

I'm not sure if this is the right place for this.  I suppose it could go in Projects or Metrology but since it is primarily used on milling machines I plopped it here.

I was looking for a simple, inexpensive way to set a "zero" on the mill in the z-axis for those times when I want to get back where I started from.  There are several models available for sale but none really floated my boat and they cost more than I want to spend.  Searching the net I came across an expired patent for a version that uses a dial indicator and a vertical plunger in a solid body.  It looked pretty simple to adapt to my needs so I made up a drawing of what my version will look like.  I drew it up using a standard AGD 2 indicator like the one from Harbor Freight.

In operation the gauge plunger would be set at a height of exactly 3.000" and the dial indicator zeroed at that height.  Then you place the gauge on top of the workpiece or vise and slowly lower the quill of the mill until it touchs the top of the plunger.  The quill is lowered gradually until the dial indicator reads zero.  At this point the tool in the spindle should be exactly 3.000" above the reference surface.  The mill dial or DRO can be zeroed at this time and allow you to calculate the elevation where you want to start cutting.

I have some 2x2 blocks of 4140 pre-hard steel that should be perfect.  The gauge could also be round but square is vise friendly.  I did not add any magnets to the base because of the tendency to pick up chips.  Also, I did not add any holes to make it lighter because I don't want the overhung load from the indicator to tip it over.

Please be advised that I have not fabricated this item yet but I do not see any glaring flaws in the design that will keep it from working.  I don't know when I'll get to the build so I thought I would throw this out for review and discussion.  Please respond with any comments or suggestions.

The commercial version.  Very nice, but too expensive for me.

  Picture2.jpg (Size: 19.8 KB / Downloads: 107)

The patented version.
   

   

And my version.

  Zaxis gage Rev A-Model.pdf (Size: 106.01 KB / Downloads: 34)

[DaveH]

JScott That is a really nice professional looking drawing .......... were you a draughtsman?
 
DaveH

[JScott]

Thanks Dave.  Actually I am a mechanical engineer but I can do drafting if I have to!  I took several liberties that are not correct for an engineering drawing.  But, I think my shortcuts are not too bad and it all fits on one sheet of paper and is still readable.

[Vinny]

Are you putting a spring under the plunger in yours? The drawing doesn't show it but it looks like it's designed for one.

[ieezitin]

A planer gauge is designed for that exact job, gets you within a thou or two, plus it has dozens of other uses around the shop.

Anthony.

[JScott]

(04-19-2016, 03:15 PM)Vinny Wrote: Are you putting a spring under the plunger in yours?  The drawing doesn't show it but it looks like it's designed for one.

Vinny, yes there is a spring under the plunger but I didn't show it because almost any spring will work.  I did call out the uncompressed length of 0.940" for a spring so the plunger will extend completely.

I have been collecting springs from all the used up pump/spray bottles we go through.  They are typically stainless steel and one of those will fit handily for this application.

The spigot on the bottom of the plunger is 0.188" diameter but it could be smaller to match the I.D. of whatever spring is on hand.

[TomG]

My first impression is that you might need to go with a tenth reading indicator and a shallower taper to get smooth enough operation. The 45º angle in your design will place a fair amount of side load on the plunger.

Tom

[PixMan]

I've never used such a thing because for me the ranges of tool lengths used on my machine in any given job can be so varied that I have to run the knee up & down to accommodate. Does this tool help in some way?

My modus operandi is to get a job done with the minimal motions and/or steps and I don't know if something like that would be a solution in search of a problem.

For ME.

I agree with Tom. If you do create that, consider a mating 45º plunger to mate with the vertical rather than direct to the plunger of the indicator.

[JScott]

Thanks guys, that's the kind of input I am looking for.

The angle of the taper is 63.43° (2:1) and may need to be steeper.  The taper will also require a very smooth surface finish.  If I make the whole gauge taller, then the taper could be steeper.  I wanted to keep the gauge short because my round column mill only has 5" of z-axis travel and no knee.

When I get the time I will set up an experiment to see if I can determine what a reasonable "angle of attack" is for this indicator style.  I really appreciate the feedback.

[f350ca]

What's the mechanism inside a bore gauge? I'd expect something similar>