Digital edge finder

I am at the minute considering buying an edge finder and I am keen on the idea of the digital type.

Has anybody any advice about them. Are they worth the extra money ? Are they any more accurate than the conventional type.Are there any specific makes to consider or avoid, Recommended suppliers even.

Any advice gratefully recieved thanks.

Dave c

Hi Dave,
I think the type of edge finder you are referring to is an electrical contact type. (I do not see how it can be described as digital.) They only work with an electrically conductive work piece. It is just an insulated probe that completes the circuit and lights an LED. I have made one and it works quite well. I think the bought ones have a ball which is held into a conical depression by a spring. This means that they are not damaged if they are pressed hard against the work piece. (The ball just moves out of its conical depression.) I find it just as easy to use a feeler gauge between the tool (Or a piece of rod.) and the work piece. The electrical edge finder is useful for finding the centre of a hole where the feeler gauge method cannot be used.

Les.

I use my electronic one a lot, it has a cylindrical end that is rigid so you do need to watch what you are doing. I got mine from Greenwood tools but not sure if they do them now.

Dave

I use the standard rotating mechanical, analogue for want of a better description, edge finder and find that it seems to be accurate with good repeatability. Not only that but as the contact body is only retained by a spring then there is no problem if it is wound in to far, just back off and try again.

While this doesn't answer your question directly I would, if you haven't got one already, buy one of these mechanical varieties and give it a go as they are only a 'few squid each' , as Bogstandard would say .

Cheers

Martin

PS

With the mechanical edge finder there are no batteries to go flat and they can be used on plastics and insulating materials as well  !

Edited By Martin W on 28/06/2012 21:57:11

Edited By Martin W on 28/06/2012 22:00:50

Les,

Strictly speaking, I suppose it IS digital

One or Zero, On or Off

... But one-bit digital isn't very interesting.

MichaelG.

there are electronic types available which dont rely on conductivity of the material, but on movement of the contact probe.

In fact, one of the members of MSMEE (melbourne SMEE) has built his own based on his interpretation of a patent found 'on the net'. Cant remember the patent owner right now, but big in measuring tools...

It has 3 pairs of contacts (ball bearings) arranged in a circle (120 deg apart) and a spring loaded disk with contacts which sit between the balls. All is connected in series with a lamp. ANY movement of the probe, which is perpendicular to the disk, breaks the circuit.

he checked it against a 'real' one, with fine results. (he used a commercial probe, as for any edge finder its essential to know the precise dimension of the probe...)

- russ

Just had a thought...as its not 'spinning' when in use, its clearly essential the probe is concentric with its mounting spindle.  I dont think that is a consideration with the mechanical 2piece spring loaded one, so it probably requires more care to build...although the last 'how to' article i read on making one suggested that a cylindrical grinder was an essential tool in its construction.)

Edited By russell on 29/06/2012 04:51:42

He is using it for more than simple Edge-Finding, but this may be what you have in mind, Russ.

MichaelG.

He is using it for more than simple Edge-Finding, but this may be what you have in mind, Russ.

----

Damned interesting stuff, his picture of a NZ coin is really impressive, quite high sensitivity

Glue a broken part back together, touch-cad it, then cnc a new one...

The making-moulds industry would love it too

Make a complicated object out of wax etc and touch-cad it?

Edited By Ady1 on 29/06/2012 12:21:36

As Bogs says some have quite large shanks, mine is 1/2" so easily fits in a collet or drill chuck.

I do give the finder a half turn between taking pairs of measurements just to even out any possible eccentricity.

J

Hi All,
Here is my home made electric edge finder.

It is just a piece of 5 mm ground rod pressed into a hole in the insulator. The insulator was made from nylon (I think). The outside was first turned to about 10 mm diameter. A length of about 5/8" rod was mounted in the lathe chuck and bored out so the insulator was a press fit. the insulator was pressed in to the bar and then bored out so the 5 mm rod was a press fit. Without removing it from the chuck the outside of the 5/8" bar was turned down to 1/2" It was then cut off from the end of the bar that was in the chuck. The 5 mm rod was then pressed into the insulator. making it this way should ensure it is concentric. The indicator was just an LED bicycle rear light (Bought from a £ shop.) with a single transistor amplifier to drive the LED's The connection to the 5 mm rod was just made with a crocodile clip.

Another very simple edge finder is a ball bearing on the and of a short piece of rod. The rod is mounted in the chuck / collet. The outer of the bearing is marked with a felt tipped pen so you can see if it is rotating. With the mill running the bearing is moved towards the work piece until the outer just stops rotating when it makes contact with the work piece.

Les.

I would advise the purchase of the rotating 'wobbler' type of edge finder over the stationary digital type.

Unless you can guarantee the accuracy of your tool-holding and condition of the spindle tapers, any

perceived advantage gained by electronic wizardry will be lost.

I use the cylindrical type most frequently, which will repeat to within .01mm.

The ball type takes a bit more care to use accurately, but offer a choice of probes

which can allow you to take a datum position from a narrow slot or small dia hole.

Neither of the above are any where near as expensive as the electrical circuit type,

and are a lot more forgiving. (Over travel can cost you £60!!

Current electrical jobby is same as Jasons, got mine special offer from J&L some years back. Repeat accuracy i reckon is 0.02mm with differing intensities and runouts.

Previous had another 1/2" shank easily collapsable throwing errors every time put in a chuck. Gave up the ghost when spinning it was already gone.

A mechanical dial would be better even the Wigglers. In saying that i do use the electric to set vices etc and the laser type to line up marks in plates.

Ady 1,

There is another Digitizing Probe, very nicely drawn-up by Shaun Wainford; available via Lester Caine's website.

MichaelG.

Edited By Michael Gilligan on 30/06/2012 08:12:27

cheers

Thanks for the information and advice from all.

I think I will stick with the conventional mechanical edge finders after all.

Many thanks

Dave C

A quick thought has sprung to mind, if you are not familiar to using edge finders then don't forget , depending whether you are advancing or retracting the table, to add or subtract half the diameter (or radius) from the reading to get the true edge. On my mill one turn advances/retracts the table by 2mm so a 4mm diameter tipped finder means I only have to rotate the setting handle by 1 complete rotation to get to the true edge which is convenient. That is just over one rotation in the appropriate direction then back in to the the same dial reading to take up the backlash; edge measurement and zero setting made turning the table handles in the same direction.

If you are familiar with using edge finders then ignore most of the above 'Granny and sucking eggs syndrome'

Cheers

Martin

The company referred to above by Russell is Renishaw plc - bit of an unsung hero of Britich engineering IMHO - worth browing their website. The touch-trigger probe was their first product, the first device to allow a CNC machine to automatically orient itself relative to the workpiece I believe. It was patented internationally, e.g. US 5146691.

There have been a couple of home-made interpretations, e.g.

**LINK**

and a recent one in the Digital Machinist mag.

My preferred method is a fine sharp needle held in a pin chuck. It does need care in selection to get one that's true to the axis - I discarded about a dozen bent ones! Use that and a 10x or 15x loupe and it's pretty well good enough for most things.

There are quite a few edge finders on the market, many include centre finders. Does anyone have any favourites or recomendations? I currently use a feeler gauge and a bar in the mill chuck/collet with a bit of maths, but sometimes this is fiddly.

Thanks,

Dave

If you use any edge finder, don't take the size for granted, measure it. The spherical probe on mine is 0.248" diameter...

Neil