Need Help!- Behaviour of Edge Finder

[Ashish B]

Hi...All..

Well this thread is for a self observation of the behaviour of edge finder.

Kindly refer the attachment, On the left side u will find the edge finder is clamped close to the neck ( or shoulder ) of the Edge Finder. In this scenario, u will find a less kick.

On the Right hand, u will be curious to know that the kick found is more.

Well the only intention is to find a kick, u will observe that the operator needs a close watch & vigilance over the edge finder…& thats is a time consuming Task...

Well that’s all I have……

Please let me know if my quotes are valid or I am driving myself in the wrong direction…


Also how do you clamp the edge finder…I mean do you clamp by using the Spanner or its just a manual pressure Lock…Well I do it with a manual pressure lock & I doubt that what is the correct method....


Please revalidate all these things.

Ash

Thanks for your time & Patience

[wildwestpat]

Hi Ash

For some reason I can not open your file as it indicates it is an old version and will not let me view it!

From your previous interest in edge finders in other threads I asume this is similar.

The kick on edge finders is a nack that can only be learnt by observation and practice. I do not like them and use a DTI where ever possible comparing the reading from a refference which is part of the machine table. This reference is also a check on the home zero of the CNC which in my case is set with inductive switches as I got variable results with mechanical micro switches and optical ones are a no no with flood cooling.

In my opinion edge finders belong with manual machining and are the province of machinists with a lot of experience under their belts as well as formal trainning where the use of both DTIs and edge finders form part of the indexing of the job to a machines axis in one or more planes.

If you care to send me an uncompresed file I may be able to help further.

Regards

Pat

[Ashish B]

Hi Pat...

I have unzipped & reduce the size of the file and attached it directly.

A lso i wanted you ask that are Edge finders & Dial indicators ( Lever Type ) tighten with the aid of spanner or are they clamped manually.

Well, i know this is a basic question of using edge finders, but sometimes we miss the roots & practice a technique ( which is wrong ) over years. So, just wanted to confirm from All your tech people over there.

[Superman]

Edge finders, wrigglers etc are not a tradesperson best choice for accurate work, these finders are too open for interpretation and cannot be certified for fine accuracy. They are great for a quick initial set-up of rough stock, similar to running a "blued-up" dowel in a drill chuck at low RPM--- it's a rough and ready tool to suit the situation, where close enough is good enough. It also doesn't allow for taper or draft on a face.

If accuracy is needed, then you would use some device that does not require a judgement call, or have any additional factors that may affect the readings

--Most tend to use a dial indicator for general shop work, its spring loaded ( same constant pressure is applied ), dial tells you how far to move, has single point of contact, someone else should get the same result as you

If you wanted greater accuracy, then machine probes, lasers would be your next step, but then the cost of manufacture would also rise to reflect the higher accuracy needed in the part

[wildwestpat]

Hi Ash

Thanks for the thumbnail of your sketch.

I don't think there will be much to gain as the edge finder will self adjust from way out as started to nearer and nearer to alignment as true centring is approached.

The final tweak causes the finder to jump / kick into alignment indicating centring is as accurate as the device is capable of. The operator skill is in slowing the speed of the feed as centring is approached to get the best feel for the snap / kick.

However I am pleased that I am not the only one who thinks DTI or lasers are better as they are not reliant on operator skill.

My preference is always for DTI as visible laser alignment is difficult and relies on secondary reference to the work piece / machine datum as a supplementary action.

In view of the questions you have asked in other threads I suggest you take an overall view of the way the part is machined and the way the surfaces produced relate to the reference points of both the cutting tooling and the 'zero' for each axis. My approach would be to use an accurate DTI to measure from the machine 'zero' or 'home position' to derive the offset of the work piece's reference edge and from there to compute the tool cutting edge position. This means that all the accuracy is provided by the DTI. The DTI being checked and calibrated against a known standard such as a slip gauge.

You must in addition take into account all the other factors that degraded accuracy. There are a lot of other factors that relate to temperature and tool wear as well as basic positional accuracy of the lead screw and its drive mechanism. I strongly recommend a cold towel to the head and a quiet room when you check the tolerance spread (+&-) from the perfect placement. Production spread tolerancing is a difficult subject and needs to be take into account with the percentage reject rates and the fit required to other components. Obviously the other components would have their own tolerance profiles. Whilst rejects can be reduced by selective pairing of parts - this is at the expense of interchangeability and spares provisioning problems at a later date. This will be a problem that needs to be addressed at the initial design stage if you are considering a production run or runs..

Regards

Pat

[Ashish B]

Hi..

I totally agree that edge finders are the secondary choice for everbody. The first choice is always a dial indicator.

In accuracy terms, edge finders do find the centre of the block accurately. The disadvantage is that it cannot express the accuracy as its open to human senses of sensing the kick..


Ash.