Edge finder lubrication

[HopperParticipant @hopper]

Posted by pgk pgk on 20/06/2022 10:39:50:

Posted by Hopper on 20/06/2022 09:54:47:

Or just invest 10 Quid in an electronic edge finder. Are they not claimed to be more accurate? (I still use a fag paper and spit so would not know.)

That must gum up the fag paper over time…..😁

I'm terribly wasteful and cut each fag paper into narrow strips and throw each strip away after a couple of uses.

But I have actually ordered an electronic edge finder that is on its way as we speak. Yet to determine if it will work held sideways in the lathe for milling with vertical slide. I know the fag paper works better than the Starrett style wiggler for this. Gravity is a bitch.

[JAParticipant @ja]

I now use a simple edge finder without any lubrication. However I am aware that it is not as accurate as a small length of silver steel bar and fag paper, previously used. Since I do not smoke (anything) ordinary printer paper was used as a substitute. It was always 0.004" thick.

I wonder how accurate a simple electrical edge finder is. It must be affected by oil etc hindering the conduction of the current.

One trades accuracy for speed which is never wise.

JA

[SillyOldDufferModerator @sillyoldduffer]

Posted by JA on 20/06/2022 12:50:15:

I now use a simple edge finder without any lubrication. However I am aware that it is not as accurate as a small length of silver steel bar and fag paper, previously used. Since I do not smoke (anything) ordinary printer paper was used as a substitute. It was always 0.004" thick.

I wonder how accurate a simple electrical edge finder is. It must be affected by oil etc hindering the conduction of the current.

One trades accuracy for speed which is never wise.

JA

In another recent thread I posted this:

One of my books gives figures for some locating methods, unfortunately not all of them.

From worst to best:

Cone into hole (how I do my rotary table) – ±0.005"
Wiggler needle – ±0.003"
Laser pointer – ±0.002"
Electronic Edge Finder – ±0.0005"
Mechanical Edge Finder – ±0.0002"

Interesting how good a mechanical edge finder is, ten times more accurate than a laser pointer! But laser pointers are designed to find cross-hair markings or centre-punch holes, which an edge finder can't do, and a laser pointer is quicker and more accurate than a wiggler needle, which I also depend on.

Note how difficult location inaccuracies make it to work accurately in tenths!

Somewhere else I hypothesised fag paper is better than might be expected because it compensates for the operators slow reactions. The operator winds the cutter in until he notices it's hit the paper. As human reactions are surprisingly slow, any measure based on a visual cue will be late, ie when the surface is detected by your 0.004" printer paper, the cutter is closer to the metal than 0.004". I think how close depends on the thickness of the paper, how slowly the operator moves the cutter, and how quickly he reacts.

All in all, I think cigarette paper is a good way of getting the edge of a cutter very close to the work. I get good repeatability from Rizla Grey Paper which I believe is their thinnest. It's a little under 0.02mm ( 0.0008" ) thick. Ordinary kitchen Aluminium foil is thinner again, but I've never tried it.

Dave

[Tony Pratt 1Participant @tonypratt1]

In another recent thread I posted this:

One of my books gives figures for some locating methods, unfortunately not all of them.

From worst to best:

Cone into hole (how I do my rotary table) – ±0.005"
Wiggler needle – ±0.003"
Laser pointer – ±0.002"
Electronic Edge Finder – ±0.0005"
Mechanical Edge Finder – ±0.0002"

Interesting how good a mechanical edge finder is, ten times more accurate than a laser pointer! But laser pointers are designed to find cross-hair markings or centre-punch holes, which an edge finder can't do, and a laser pointer is quicker and more accurate than a wiggler needle, which I also depend on.

Note how difficult location inaccuracies make it to work accurately in tenths!

Dave

I personally doubt a mechanical edge finder will repeat to .0002", in my book the most accurate method is to 'split the edge' with a DTI, & in reality .001" or under positional tolerance is jig boring territory.

Tony

Edited By Tony Pratt 1 on 20/06/2022 13:44:35

Edited By Tony Pratt 1 on 20/06/2022 13:53:16

[JAParticipant @ja]

Posted by Tony Pratt 1 on 20/06/2022 13:40:54:

In another recent thread I posted this:

One of my books gives figures for some locating methods, unfortunately not all of them.

From worst to best:

Cone into hole (how I do my rotary table) – ±0.005"
Wiggler needle – ±0.003"
Laser pointer – ±0.002"
Electronic Edge Finder – ±0.0005"
Mechanical Edge Finder – ±0.0002"

Interesting how good a mechanical edge finder is, ten times more accurate than a laser pointer! But laser pointers are designed to find cross-hair markings or centre-punch holes, which an edge finder can't do, and a laser pointer is quicker and more accurate than a wiggler needle, which I also depend on.

Note how difficult location inaccuracies make it to work accurately in tenths!

Dave

I personally doubt a mechanical edge finder will repeat to .0002", in my book the most accurate method is to 'split the edge' with a DTI, & in reality .001" or under positional tolerance is jig boring territory.

Tony

Edited By Tony Pratt 1 on 20/06/2022 13:44:35

Edited By Tony Pratt 1 on 20/06/2022 13:53:16

I fear that this posting is being hijacked.

My feelings on the above table are:

1. Cone in hole is better than stated but it does depend on feel.
2. Laser pointer does not approach the stated value because of the diameter of the laser spot.
3. Mechanical edge finder is nothing like that quoted.

As stated I have not knowledge of electrical edge finders.

I would like to know about electronic touch probes, such as those made by Renishaw, which do not rely on the electrical contact between probe and work piece. I know they are very expensive and probably have figures far better than those above. I have no idea if any are sold by model engineering suppliers.

JA

Edited By JA on 20/06/2022 14:47:52

[SillyOldDufferModerator @sillyoldduffer]

My library is unhelpful: it says almost nothing about the basic accuracy of ordinary workshop locating methods, and I can't find anything on the internet either. The limitations of verniers, parallax and micrometers are discussed, but not those of the various edge finding and locating methods.

There's a challenge here! I have a book that quotes numbers that Tony and JA find hard to accept. Two respectable contributors who know their stuff versus one book that might be wrong. The challenge is this: can we settle the argument by measuring the accuracy of our edge-finders?

I don't think opinion is enough. We can't just claim 'Cone in hole is better than stated but it does depend on feel.' even though that might be true. It needs to proved, preferably by an experimentally sound method we can all do ourselves. However, as my workshop doesn't have the wherewithal to measure the accuracy of an edge-finder, I'd be happy with figures from a reputable engineering book. Anyone have one?

All I can confirm is that my edge-finder has better repeat performance than my milling machine's DRO and mechanical dials, neither of which are top-end. Off hand I can't think of a way of measuring the accuracy of any of my location tools. I'm stuck!

Dave

[JAParticipant @ja]

Posted by SillyOldDuffer on 20/06/2022 16:05:41:

All I can confirm is that my edge-finder has better repeat performance than my milling machine's DRO and mechanical dials, neither of which are top-end. Off hand I can't think of a way of measuring the accuracy of any of my location tools. I'm stuck!

Dave

Dave

I think this is crux of the discussion. Most of us use tools that are just (about) adequate. Once comparisons start being made we, model engineers, are only just above where our predecessors were 200 years. After all nations have spent lots of money trying to improve measurements.

JA

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