Messages

1701

Show"N"Tell ( What you have made with your CNC machine.) / Re: Machined an Iphone 5

« on: February 09, 2014, 08:30:52 PM »

Looks nice.....maybe make a bunch and sell them as paperweights?

Rich

1702

General Mach Discussion / Re: Anyone point to an installation manual for usb to parallel breakout board?

« on: February 09, 2014, 08:26:36 PM »

boards i can afford come from china and basically dont have instructions

So how do you expect to get the boards working if there is no documentation?
If there is no support?
What is your tolerance level for frustration?
Suppose the board dosen't even work or the pin out or description is incorrect?

Some things to think about.

That said........
The Chinese make some drive, sell it cheap, sometimes pure junk, then expect someone else to adress the issues a purchaser is faced with,sell or provide pirated software,....should I go on?

May I suggest you save a few more bucks and maybe look at the the lower cost Gecko drives.

RICH
 

1703

General Mach Discussion / Re: Shield grounded at one end only

« on: February 08, 2014, 09:49:10 AM »

Don't have any numerical values. If i get a chance will blow the dust off the specturm analyzer and show / create an actual example.

But in the mean time, here is an example that was a  rather interesting experiment we did a loooooong time ago.
On transmision of low power say 1 watts output from a a transciever so about 6 watts out of the antenna, we would lock up an on line pc. So we put an isolation transformer in the ac line to it, completely enclosed the pc , wring etc, in a solid metal shield, EXCEPT for the face of the monitors glass tube, and provided a separate grounding system for the pc and downstream side of the transformer. The ground wire was actualy a 1" diameter piece of copper tubing and the inside of it was used as the conductor tied to a 10' driven ground rod.

If the transmitted freq was near (don't remember how much) the pc cp operating htz, fundamental overload occured
and the pc screen would first turn blank white and stay that way even after the transmitioin was stopped and pc unplugged
for some time. Placed a wire meshed screen over the monitor screen some distance away from it and tied it to the ground system.
Don't remember the extimated / calculated freq based on screen opening, and it did provide for interference rejection but was not satisfactory, ie; could move the interfering freq a little closer ......signal to noise ratio was down a little.

Here is another un quantified one.
Just do TIG welding near a PC . Say the pc is 15 away, shoot, it wiped the hard drive!

Another little tid bit for info:
Ever read that tag that's on an electronic device that says something like " this device complies with FCC rule ???15"
so the device cannot  radiate signals but must be able to accept them.

Another practical example:
House telephones, cheap ones had no filtering for noise or filtering that was about usless, but you would never have a problem with
a good phone made by AT&T. Not much of a problem anymore as the phones function in the giga htz range.

Then there are rules form a safety point of view that came out some 10? years ago. The field as measured in gauss? had to be within a certain level from a people location point of view......don't remember specifics.

So the EMI / noise,contol & elimination of it is not simply a some value that one can use as a quideline.
So one must measure the values to have a feel of relative intensity and that info  is tied to how sensitve the offended circuit / electrornics is. Also as distance increases from the source the field intensity drops off.

That's why you don't see any qauntification, all is specific to the situation at hand, and also most folks don't have the equipment to measure.
 
RICH

 

1704

General Mach Discussion / Re: tool path way out when loaded in Mach

« on: February 08, 2014, 04:52:09 AM »

Draw in mm, cam in mm/post in mm, the machine should be configured in mm.
Don't mix units.

RICH

1705

LazyCam (Beta) / Re: Lazycam Lines + Arcs

« on: February 08, 2014, 01:50:15 AM »

A few comments:
- Make different layers for the machining tasks that you wish to do in CAD
- always check that all entities in CAD connect
- don't use polylines / break them up in CAD
- save as a version 12 dxf format

After you clean the drawing un-enable layers and check and see if all is connected as the layer should not have much pathing and be continous. I usualy use .0001 for a tolerance but sometimes there is small error on import to LC and thus you need to change the tolerance. In this case .001 ( or even greater as Russ noted) worked.

You really need to think in terms of machining tasks when in CAD. Do not waste time trying to do CAD work in LC as it is only
meant to be an importer.

RICH

1706

LazyCam (Beta) / Re: Lazycam Lines + Arcs

« on: February 07, 2014, 09:07:36 PM »

Can you attach the "lcam" file and I'll have a look when i get a chance.
There may be no answer.......

RICH

1707

General Mach Discussion / Re: Shield grounded at one end only

« on: February 07, 2014, 03:43:48 PM »

Just a clarifcation of what noise is:
Well use Russ's audio analogy since you can hear it.
Noise is just many frequencies over a frequency range which we don't understand. You can hear a single tone or some combination
like an orchastra playing and make sense of them. But all that hiss or crackling is just noise. They both exist and depending on the amplitude of one to the other one may dominate.

The same applies to higher and lower frequencies out of our hearing range.

A good example of noise would be sparking from brushes of a motor which puts out high noise levels ie; many random frequencies
through out the spectrum . Should see what happens when tig welding welding is done and a computer is on and near by.....
heck wiped my friends hard drive.

So if you cut a energy field, say one with a whole bunch of noise, with a wire, a flow of noise electrons will occur on the wire and you can measure the voltage. The noise was inductively coupled from a radiating source. So if the noise level is high compared to the
a signal that you were sending on the wire, the noise would dominate and say a device recieving it could not process it.

Sorry for the crap explainations as most of the tech stuff is saved to memory and just can't seen to find the folder it was place in!

What do you mean by  ...induced into a "SCREEN".

RICH

 

1708

General Mach Discussion / Re: Shield grounded at one end only

« on: February 07, 2014, 11:00:54 AM »

Some thoughts that come to mind.....

some of the explanations have mentioned that it is frequency dependant.

Yes,true if you want the shield to act as low inpedence to some group of frequencies, ie;
it could act as antenna which is tuned to a group or actualy be a high impedance to a frequency and
act a short....but...depends and that's were the famous word "subjective" comes into play

resistor and cap

a resistor and cap ie; rc circuit ( charge up and discharge at a time rate  ) can be tuned and act as wide or narrow filter to ground

black magic

Yes it certainly seems that way since I have known some sharp cookies who realy couldn't explain why something worked
or didn't work

Location / proximity to the source, intensity of the signal, frequency, shield quality, ground quality, type of ground system
etc all have an affect on what may or may not happen. One of the problems with all this is that one can't see it or if it is seen it's  via a device which shows what your interested in in some manner.

RICH

1709

General Mach Discussion / Re: Shield grounded at one end only

« on: February 07, 2014, 10:56:30 AM »

most bizarre source of noise you have found and the solution

Blinking Christmas decorations.
Just need to waite until after the new year. 

RICH

1710

General Mach Discussion / Re: Shield grounded at one end only

« on: February 07, 2014, 06:17:39 AM »

Shielding is done / required / utilized and even custom designed for a lot of different reasons, but, simplisticaly:
- to keep what is inside, inside the shield
- to keep what is outside from interfering what is inside

So now the question becomes......  What are you trying to control with the shield?

Using a crude water analogy... water may be on a pipe. Where do you want  the water to go ?
Go back to the sanitation sewer, air dry, or go to a designated sump which makes it easier to get into the sewer line or a designated sump system, just contain it ( ie; tank to tank ) or even a combination of two or three of them.

So grounding of the shield could be subjective and only the person looking at the big picture for what was considered may know why
what is being done with the shield is appropriate. But generalizations do come about and are not necessarily always true.

From a non-electrical ....and may be all "wet", just some thoughts,

RICH