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Author Topic: Constructing a Low Profile Tool Height Setter.  (Read 49214 times)

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #40 on: May 18, 2012, 01:48:32 PM »

 :)Good one Tweakie
 ;D ;D ;D
 :)
Re: Constructing a Low Profile Tool Height Setter.
« Reply #41 on: May 18, 2012, 06:44:35 PM »
Now you know, Tweak we all want to know how you blamed this on a machine, lol

Don't bring one of those tiny tack hammer sized ball peens.

Hi YNN,
You should never take anything as being inevitable - there is always chance.
A genetic inheritance may skip a generation or a genetic pattern being modified between the combination of both parental sets may resolve a possible problem. Chance is always there.
Tweakie.
From your post/comment/wish to God's ear. Thanks
But in the mean time I should have retired much sooner... I love contract work. More profitable and more control.

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #42 on: May 25, 2012, 02:30:05 AM »
A couple more pictures of the probe parts.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Constructing a Low Profile Tool Height Setter.
« Reply #43 on: May 25, 2012, 07:08:32 AM »
Fine looking workmanship Tweak.

How do you determine overall height of the tool sensor/when it has detected the tool tip? 
Is this a NC switch and your pushing it down to break contact?
Is that a bonded or pressed in insert? of what material, does it keep the plunger in axis alignment or is that left up to the spring to keep the plunger from rocking?

How much travel once the tool contacts the sensor before tool detection?
How much more travel for overtravel?

I follow with great interest.
Keep up the fine work.

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #44 on: May 25, 2012, 09:18:18 AM »
Hi YNN,

Thank you for the kind words, it is much appreciated.

The contact ring, insulator and plate have all been lathe turned and the flat surfaces are as near parallel to one another as I can make them. These 3 items have then been fitted together using Locktite, under a small pressure until cured, making the assembly of the contact ring as plane with the top surface of the plate as I can. The 3 individual contacts have been lapped so that they each protrude from the rear surface of the PCB by exactly the same amount (as near as I can measure using feeler gauges on a surface plate).
The contact ring, plate and the 3 contacts are all made from A4 (austenitic) stainless steel.

The contact ring rests on the 3 contacts under spring pressure and the overall height of the completed probe measured with a micrometer – this dimension being entered into the Mach3 probing script as plate thickness. Any downward movement of the plate breaks one or more contacts for the G31 detection. Although the contacts are ‘normally closed’, the transistors invert this logic so the probe output is normally a weak High and only taken to a strong Low (GND) when contact is broken.

The amount of movement necessary to operate the probe is incredibly small (unfortunately I don’t have the necessary equipment to accurately measure this) but it is largely dependant on the flexibility in the top cover and operational movement is currently smaller than two of my Z axis micro-steps. It does not seem to make any difference if the plate movement is parallel (centre contact) or tilted (off-centre contact) there is never any contact bounce – it either makes contact or it doesn’t.

This type of contact break detection is used in some of the Baumer Electric limit switches – OK they have far more accurate manufacturing facilities than I have but they claim 1 micron repeatability. I don’t think I am anywhere near to that but, as I said, the triggering movement is incredibly small and beyond my micrometer measurement skills.

The over-travel (after contact break) is approx. 2mm but I have found that with Mach3 version R3.043.062 the G31 appears to trigger an immediate stop rather than a decelerated stop and plate movement is not even visible.

One new thing that I have noticed is that the work piece must not have any movement or flexibility when tool height setting – my vacuum table holds engraving laminate tightly but double sided sticky tape has a degree of springiness and this can cause a setting error. I am not quite certain just what is happening here but it needs further investigation.

You would really have to build a similar device for yourself to fully appreciate the accuracy of the operation but, as shown in a previous picture, it has enabled me to engrave 0.5mm high text to a depth of  0.05mm which I struggled to do before using this type of probe.

Hope I have answered all the questions.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Constructing a Low Profile Tool Height Setter.
« Reply #45 on: May 25, 2012, 09:48:25 AM »
You would really have to build a similar device for yourself to fully appreciate the accuracy of the operation

Kind of hoping you were providing the units, so I don't have another project to complete.  :D

Thanks for the details.

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #46 on: May 25, 2012, 11:02:33 AM »
but I have found that with Mach3 version R3.043.062 the G31 appears to trigger an immediate stop rather than a decelerated stop.
Hi Tweakie - do you mind giving me your G31 feedrate, your Z axis accel and your steps per please? I'd like to check this out.

Ian

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #47 on: May 25, 2012, 01:26:35 PM »
Hi guys,

Quote
Kind of hoping you were providing the units, so I don't have another project to complete. 

Go on - make one - you will not be disappointed.

Quote
Hi Tweakie - do you mind giving me your G31 feedrate, your Z axis accel and your steps per please? I'd like to check this out.

Steps 533.3333..., Z axis Acc. 100,  G31 feed  200.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #48 on: May 30, 2012, 11:04:16 AM »
Hi Tweakie - forgot about this but FWIW

if my sums are correct (d=v^2/2a) then it should take 0.0555... mm to decel to stop after trip. Scoping Mach confirms (here at least) that it does exactly this (well 0.0543500044871). Don't know if that's any use to you (or anyone else really).

Ian
« Last Edit: May 30, 2012, 11:11:39 AM by stirling »

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Re: Constructing a Low Profile Tool Height Setter.
« Reply #49 on: May 30, 2012, 11:48:20 AM »
Hi Ian,

Thank you for a very nifty bit of calculation (Hopefully that is the value that gets stored in my Var(2002)).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.