Which edge finder?

Several types are available including: electronic (capacitive?), wigglers, and split cylinders. Which do you prefer, and why?

I have an electronic and a split cylinder type and mainly use the split type. They are inexpensive and less susceptable to damage. If you over travel the edge of the work piece, the split end just moves sideways. (have gone a bit too far on occasions and the end has come off but easy to re-attach to the internal spring). My electronic edge finder is rigid and would bend if pushed too much.

Paul.

What sort of machine? Manual or CNC? I have a contact-based one for CNC that interfaces to the controller which I often use on the manual mill with a multimeter on "bleep" continuity mode. But for many jobs I find it's quicker to judge contact between the edge and a dowel (or even the tool) by feel on the feed knob.

For rough 'n' ready I use a fag paper trapped between the tool in use and the surface. Using the DRO it's then simple to move half the tool diameter and re-zero. For better accuracy I use a mechanical edge finder by Haimer:

Andrew

I generally use a PEC electronic type but as Paul says it is easy to damage them as the cylinder that makes contact is rigid, this is my 2nd PEC as the 1st got damaged by overtravel.

I also have one of the 20mm stem type with a ball that is held in the socket by a quite strong spring, it works well but is too long for use on my mill unless the work is shallow and fixed to the table.

I do use the spring type with a centre point on some occasions and find all give similar accuracy.

You can see the PEC in use here at 2min 28sec **LINK**

Emgee

I would like to have 1 of those Haimers but it's cost and lack of height that mean it would not always be possible to use it.

Edited By Emgee on 06/11/2020 22:52:35

added the i in Haimer

Edited By Emgee on 06/11/2020 22:53:44

I'm a great fan of the Huffam type wiggler for general use on my DRO equipped Bridgeport.

Given a modest level of care reliable sub-thou accuracies are routine. Maybe under half a thou if I concentrate. Using the 1/2 function of the DRO between two decent smooth surfaces, such as good vice jaws, suggests something around a couple of tenths of a thou. But how realistic that is in the real world given everything else that is going on is open to question. When you get down to that sort of precision variations in technique are seriously important.

A fair few years back I did some comparative tests against my nanometer sensitivity Hiedenhain probe which confirmed the Huffam was pretty darn good and very repeatable.

Unlike the cheap wiggler, probe and indicator holder collet set types the Huffam has a proper bearing surface for the ball to run against and a spring loaded nylon pusher to apply a constant, modest load. Internal frictional forces are both low and repeatable so the ball or cylinder contact probe is able to crawl sideways almost immediately on contact with the surface rather than needing a real offset as the cheaper ones do.

The collet held style wigglers have unavoidable friction so they need more offset to swing sideways. By dint of much patient playing in pre Huffam days I got my cheap set down to around 5 thou error on a good day. 10 thou is more realistic if you just assemble it. The needle pointer now lives permanently in my collet for when I have to pick up on lines and similar. Friction on the ball is an advantage there because the needle stays put when gotten to run true.

Converting an inexpensive wiggler set to Huffam style by making a new holder or two looks to be a relatively simple project and well worth the effort. Geo. H Thomas published a design for a complete unit whose holder could easily be adapted.

I have a Haimer like Andrews which I really must play with somewhen. Grabbed it 'cos the price was far too good to miss.

Clive

Edited By Clive Foster on 06/11/2020 22:54:24

Edited By Clive Foster on 06/11/2020 22:55:34

As Emgee I use a PEC electronic one on the manual mill and rarely get the wobbler out. On the CNC I've been using the cylindrical type recently as lest likely to get damaged by over jogging.

I have s split cylinder type which I got last year and find I use it all the time now. It's very quick to put in the chuck - even quicker if you are using a drill chuck. I find that since I got DRO I seldom mark anything out, just find the edge with the edge finder and zero the DRO. You've got to remember to add half the diameter of the finder.

Another vote for split cylinder and fag paper!

Like Clive I am a fan of the Huffam edge finder. I used one all through my working life even when operating a SIP jig borer. The accuracy is more than good enough.

Using the DRO I now find the edge, zero, move half the diameter, then zero again.

I use a piece of 6mm silver steel rod and a light, I find it simple, cheap, quick and accurate, I bought a wobbler edge finder and couldnt get on with it.

Martin P

I have a split cylinder wobbler from Machine-DRO which I use about the same number of times as a piece of 10mm dia tool steel and a piece of .0015" shim, in conjunction with the DRO. If I have a cutter set up I use a bit of fag paper.  I also have a cheap ebay chinese electronic one that's LED didn't work from new and its beep is at best intermittent, I got my money back for that one...

Edited By Henry Brown on 07/11/2020 10:49:17

I know a friend who had a Chinese 'electronic' edge finder (LED + AAA battery!) - could never understand why his centres were all over the place - until he discovered the 5mm centre was eccentric to the 12mm body by about 0.3mm TIR!

Sticky pin, an Optivisor and LED flashlight!

(the last two items are optional for younger readers!)

IanT

I have for more years that I can remember used a 6mm dowel and the ubquitous cigarette paper, bringing the dowel up until the paper (held in the other hand) is just nipped. Accurate for within a thou and certainly for most of of the time for what we do. It is and was 'needs must' for me on my Linley mill - can't hold the diameter of an edge finder in my drill chuck. Edge finders are there - a left over from working days - just never used

What colour paper - well I use green but not for any specific reason other than that's what I first used all that time ago.

Tug

Not having a DRO I find the split cylinder type easy & reliable on relatively good, flat surfaces. The fag paper in conjunction with a piece of 10mm SS in a good ER collet satisfieas every other situation. Both methods time-proven and cheap! M

I have all of the above including a Haimer, but my go to tool is one I made myself.

It is a small ball race loctitied to the end of a plain shank, with it spinning in the spindle I approach the work until the outer part of the ball race stops spinning due to the contact friction.

I get repeatability as good as a split cylinder edge finder, the Haimer is very good, but takes up too much headroom for most jobs and will not fit my Boley jig borer anyway.

I have a selection of home made ball race types with different shank diameters that will fit whichever collet happens to be in the spindle at the time. Plus some dedicated ones for the Boley that fit directly into the spindle as shown below.

Phil

Edited By Phil P on 07/11/2020 12:25:59

Heidenhain make a rather magic probe that can zero in x y and z and directly interfaces to the DRO to zero automatically, I think the price puts it firmly in the professional tool class. I expect the east have something similar although I have not seen one, but then I haven’t really searched.

Mike

Until recently I have used a small length of silver steel bar and a bit of ordinary printer paper. The paper was always 0.004", 0.1mm, thick. I have now bought two cylindrical wobblers which are no more accuarte but quicker to use.

I recently attanded a Zoom meeting of the local club where a member described making a variant of the Renishaw type touch probe. From what I saw it cannot be beyond a competent model's engineer ability to make such a probe. I think aligning it would give the most difficulty.

JA