Edge finders

[Randy]

Many YouTubers use edge finders that look like this.


I'd like to try one. Looks like it might be more useful in certain cases than my common Starrett and General edge finders. They're readily available and inexpensive, but the only ones I see are metric. Nothing wrong with that, but all my collets are sized in archaic units. Have you ever seen them in old world sizes?

I suppose it woud be easy enough to turn or grind one down from 10mm to 3/8". The probe offset wouldn't be a round number in old money, but that's managable. Or I could just make one from scratch. I have some 3/4" drill rod which would serve nicely.

[mklotz]

https://littlemachineshop.com/products/product_view.php?ProductID=1959&category=

https://littlemachineshop.com/products/product_view.php?ProductID=1822&category=

[Randy]

Thanks, Marv, but I've got plenty of those.

[Toolguy]

You could get a metric collet to go with it.

[Davidhcnc]

I have one. It works well. I did cut off the 4mm end so now it is 10mm only.
I would like an 8mm end ,my dial on y axis travels 4mm per turn so then it would always be on zero to the rear vice jaw without any adjustments or calculations.

you could put a ring on to make it an imperial size.

[rickyb]

The one I have is 10mm so it just sits in a drawer.

[npalen]

Why not run the edge finder in a Jacobs type chuck?

[MichaelP]

IMHO, all the headaches associated with use of a metric edge finder in the non-metric world are very hard to justify.

[MyrtleLake]

What is the draw? Three diameters?? Why? Who cares. You're finding an edge. Pick one that matches your leadscrew dial if you want "easy." I don't get the draw...

[Paul Alciatore]

This IS a good idea. At least as a temporary way to evaluate if you like the finder or not. The body of the edge finder does not need to be gripped with any accuracy. It is only the tip that needs to have a precise diameter/radius.

But, something needs to be said here. When choosing an edge finder the first consideration is not the diameter of the shank.

Edge finders of this type are designed to change with an audible click when their center line is OFFSET from the edge being probed by the radius of the TIP. This offset is the first consideration in choosing an edge finder. Why? To make the math simple; well not just simple, but not needed at all. When the edge finder clicks it's tip's center and the center of rotation of the spindle is offset from the edge by the radius of the tip. So, in order to place the center of rotation directly above the edge the mill's table must be moved by that radius.

Of course that can be done no matter what the radius (diameter) of that tip is. But, if the radius is made equal to one or an integer multiple of single turns of the feed screw of the mill, then the setting process is easier. You simply set the dial's scale to zero when the edge finder clicks and turn the dial one or several WHOLE turns in the appropriate direction. No math is needed. Just set and turn.

So the first choice in an edge finder is a tip that is compatible with the FEED SCREWS of the mill it will be used on. That is why so many edge finders sold in the US have a tip that has a 0.100" radius. That radius matches a 10 TPI screw and 10 TPI screws are very common on milling machines in the US. Then you need to find one with a shank that can easily be gripped. But an extra collet would be an inexpensive purchase. And the edge finder CAN be gripped in a Jacob's chuck with no loss in accuracy. The tip clicks when the above condition is reached. The runout of the shank or the body of the edge finder has no effect on it. The edge finder's accuracy does not rely on being held in a collet.

Why not run the edge finder in a Jacobs type chuck?

[MichaelP]

The body of the edge finder does not need to be gripped with any accuracy. ...When the edge finder clicks it's tip's center and the center of rotation of the spindle is offset from the edge by the radius of the tip. So, in order to place the center of rotation directly above the edge the mill's table must be moved by that radius...
...And the edge finder CAN be gripped in a Jacob's chuck with no loss in accuracy. The tip clicks when the above condition is reached. The runout of the shank or the body of the edge finder has no effect on it. The edge finder's accuracy does not rely on being held in a collet.

It depends on what you're doing. If the edge finder body axis is away from the spindle axis, the offset from the spindle axis will be larger than the radius of the edge finder tip. So if the edge finder is held in a high TIR Jacobs chuck, a milling cutter held in a good collet will not be where you want it to be.

You can find center between two opposing edges with this approach, but you cannot properly indicate a single edge (you'd need to add TIR to the radius).

[Mike Burch]

When the edge finder clicks its tip's center and the center of rotation of the spindle is offset from the edge by the radius of the tip...The runout of the shank or the body of the edge finder has no effect on it. The edge finder's accuracy does not rely on being held in a collet.

Sorry, Paul, but this has me baffled.

For the tip to touch the edge at exactly its own radius from the centre of the spindle's rotation, the tip's centre and the spindle's centre must surely be exactly coaxial, i.e., there must be no run-out in whatever is holding the finder. If the centre of the pre-click tip is not absolutely aligned with the centre of the spindle then the radius of the tip will not in fact be the difference between the edge and the spindle centre.

So what am I getting wrong here?

[LKeithR]

Talk about complicating a simple subject...

[djc]

Have you ever seen them in old world sizes?

There is this one:

https://www.ctctools.biz/3-8-edge-finder-d61/

Note, however, that although it has a 3/8" shank, it states the tip is 4mm dia.

The worst of both worlds...

Maybe drop them a line and get them to confirm if the web page description is correct or not.

[Mcgyver]

I'm curious what is the point of this is? Is there some advantage to the "middle aged" edge finder shown in the first post over an edge finders usual form factor? (middle aged as it comes with the midriff spare tire)

if it has to be more accurate than an edge finder, us a haimer or better still an 10th's indicator and a chair.....or is there something I'm missing?