Messages

4611

G-Code, CAD, and CAM discussions / Re: G code Sub routine

« on: May 21, 2010, 08:07:33 AM »

You could also use one of the wizards.
RICH

4612

General Mach Discussion / Re: What Steps/ Units Settings for Z-axis (Quill) of CNC Retrofitted Radial Machine?

« on: May 21, 2010, 07:53:47 AM »

KHALID,
You could make a circular paper template of know size and tape/attach it to the shaft of the stepper. Then see how far along the circumferance it takes to move the Z a mm by jogging the stepper ( i am assuming that it's double shafted). You can get rather close on the number of steps. Then just check over a longer Z travel.  The bigger the template the more accurate.
That will give total ratio ( would include the rack and pinion ). Poor mans encoder.

IE: 6" circle  C= 6x 3.14= 18.84"        18.84/200=  0.094"  so that distance along circumferance equals one step

RICH 

4613

General Mach Discussion / Re: Need Guru input on an idea: Using Mach as dynamic balancer

« on: May 20, 2010, 09:48:25 PM »

Balancing a rotating object is done to reduce the loading / forces that the machine will see. Need to really  call it a system. In that light the bearings will have greater life,
 improved machining, etc. You can run in an unbalanced condition as long as the forces can be tolerated by the system configuration or the task at hand.

You ever wonder why they put that adjustable collar on an Albrecth chuck? What do you do with it?
Why level a lathe? Don't they use them on a ship at sea?
Is the mill table leveled such that when a horizontal 4 th axis is used as a  component of the system, if balanced, takes advantage of the additional efforts done to it?
Why balance the rotor of a motor or the impeller along with it's shaft for a pump?
How come some machines are massive and some are not but they have the same stated turning capacity?
What happens when you add all the unbalanced crap onto a balanced HP car engine? What do you get for all that additional money and effort?
Why spend the money for a hand spindle foriegn made and not spend an extra bunch of money for a name brand ( could be as much as 5X in cost)?

Just some things for ya to think about.

Lets give some vibration and resonance examples form true experiences:

- 10 foot diameter x 60 foot high vessel filled with liquid lifting it's base ring and shearing the anchor bolts.
- Watching a 8" schedule 40 stub end on a 20" pipe sheer off
- a heat exhanger still attached to it's  concrete base shear the pad and bouncel up and down when resonance occured ( 4 ft dia x 10 foot long heat exchanger )
- my favorite and relative to what Steve mentioned about a unbalance during turning:
So the 1200# lathe is leveled and anchored to a 4" thick table which is bolted to a steel frame which is anchored 5 places to a concrete block wall.
An odd shaped piece  is mounted to a face plate and the tail center used to add some hold / rigidiy. I will guess about 5 lbs for the piece and turning off center some 2".
Slowly machine off some of the casting, crank up the speed and refine the cuts, ok, hech turn up the speed and lets get her turned ........
Well before i could  reduce the speed, the inbalance created vibrations which happen to hit a resonant frequency of the sysytem, and in about 3 seconds,
the lathe lifted the base and pulled the anchoring out of the wall. Not something you want to be standing by or experience.

Even if the piece was counter balanced before starting, the eccentric loading while spinning, the balance will vary as mass and rpm change
thus the affect  relative to vibration or resonance is not constant due to a changing natural frequency of the system.


RICH

4614

General Mach Discussion / Re: Need Guru input on an idea: Using Mach as dynamic balancer

« on: May 20, 2010, 02:03:38 PM »

has a 4" steel disc brake on it that is not balanced, so even with the lower RPM, it is a larger problem.

The spindle should be balanced as a unit, thus it would include the disc brake.

no harmonics

Yes it does, the spindle has a natural frequency ( all things do even the human body) and a critical speed, and whether you get vibration or worst yet resonance can be
 dependant on the dampening effects of the mounting, bearing, machine frame, runout,  etc, and could be influenced by repetative driving forces and transmissions.
Usualy you deisgn the part or system to not operate near a harmonic, in some analysis it is looked at to the 16th mode and design
changes made to move the natural freqeuncy away from a resaonant point for a given or fixed rpm. In the analysis, the harmonics of the system are used
and it is important to go through the resonant points / modes in a timely fashion such that resonance cannot occur.

You can have a spindle balanced to satisfy some spec, ( there are ISO and ASME spec quidelines for rotating machinery ). As you have become aware, as soom as you
add a different component  the balance changes, runout changes, leveling plays into this, the natural frequency has changed. As a component in the makeup, a good
example is the addition of say a set screw / screws, or weight additive attachment can be used, or even a movable balance plate can be used to advantage, but ,
like all things it becomes a matter of degree and what your trying to do ( your unlikely to be removing material to accomplish it).
The 4 jaw chuck can be balanced, but then as soon as you put something into it there goes everything  to poop again.

From a practical viewpoint, lets use consider what we do instinctively on say a lathe. If the lathe starts to get some vibration while we are trying to turn
something mounted off center, we slow it down and take cuts to make things symetrical and at some some point we crank up the speed and do more finishing to the piece.
Instinctively we deal with balance, runout, and vibration.
Now if you were to do some study on a part relative to it's natural frequency and as compared to degree of out of balance / loading conditions you could probably
relate back to some calcualted  speed and balanced adjustments. Not something you would want to invest into if not in a large production quantity.
Time spent trying to follow a procedure may not pay when an additional roughing cut may be quicker.

I guess my viewpoints are more from a design point of view but the topic is of interest.

Back to the sidelines......
RICH

4615

Forum suggestions and report forum problems. / Re: Where is the wisdom accumulating?

« on: May 19, 2010, 01:37:08 PM »

ksangus,
Don't have a direct answer for you. CNC covers so many related topics that it takes a book to just cover one topic.
Many times that is what happens in a thread, since the answer to the post needs to address a number of related issues.
For example, G code, you may want to consider the Smid series of cnc programing books as additions to your library of info
yet still save replies when found to be of interest.

Yes, you see similar questions asked, but when stumped isn't it nice to have an answer to suite a particular need in a timely fashion and yet get insight
on the issue at hand.

I could say that the Mach manuals could be improved and expanded upon and would reduce the questions asked, but, the manual may turn into a 1000
pages and thus the intent of the manual would be lost or still wouldn;t cover "everything". It's really tough to do and one of those manuals took 6 months. Mach is so configurable and finding a focused summary on something requires a lot of understanding.

The Members Docs provides a place to post summaries on a topic manner of common occurrence.
Maybe you can do a write-up on something that strikes your fancy?

RICH
 

4616

General Mach Discussion / Re: Parrallel Port Help Request

« on: May 18, 2010, 05:28:41 PM »

Are you sure that your have the steppers wired properly?
Is the current settings correct? Too low or too high ( if too high they will get hot and won't run correctly, if right at the max the steppers can act weird etc.)

Can you attach a bunch of info and maybe we review and find someting you have overlooked.
Post info on the stuff so we don't have to look everything up....
Even a crappy pc will move the steppers, maybe will not sound very good, but at least they will work.

Provide the following:
- xml file
- controller info / drive type
- motor info - manufacturer, etc
- how do you have the motors wired - can you attach some pictures or draw a schematic

Do you use Skype?

RICH

4617

Tangent Corner / Re: Welding a motor mount

« on: May 18, 2010, 05:03:09 PM »

Echo Tweakie's reply. And if you buy it check the windings for your safety  before putting power to it, and even then make sure the motor frame is grounded properly. Hmm ....on second thought i would pass!,
RICH

4618

G-Code, CAD, and CAM discussions / Re: 3d cam

« on: May 18, 2010, 04:55:02 PM »

Hmm.....
I would recommend you invest some time and think about what you want to be able to do and then ask users about how software is limited, likes and dislikes , etc and then master the use, for example of CamBam or whatever.
As the saying goes, "Jack of a thousand trades but master of none".

Sorry no 3D to recommend as i am still learning the thousand trades..........   
RICH

4619

General Mach Discussion / Re: Parrallel Port Help Request

« on: May 18, 2010, 04:41:10 PM »

Is there a recommended computer that works best?  Used IBM and Dell computers are a dime a dozen

My experience with Dells are that they just plain suck as a PC for CNC via PP! They work fine if a SS is used.
You asked ....i just give "my" experience ....you be the judge.

I had a pc made up about a year ago, frankly even knowing what i knew, I realy couldn't define to myself a pc combination
that would guarantee a nice pc for cnc. So, I explained to the technician what it would be used for and he agreed to
find, swap out anything ( motherboard, power supply, etc) until it worked to my satisfaction. What a deal.......and offer!

Here is what i ended up with first the time and it was satisfactory. Very stable and close kernal speed and that was nice when doing the thread
testing.
- Asus motherboard - M2N68-AM SE2 ( this motherboard didn't have a PP port )
- 2 GIG Ram
- AMD  64X2 Dual Core Processor 5200+ 2.7 Ghz
- Asus graphics Card - EN9600GSO
- Rosewill PCI pp card - RC302 ( a cheap card but it works fine )

I am sure there are a lot of combinations that are solid, and frankly, still can't say that there is an "ideal" computer to use.
Notice that it is not top of the line as i wanted to keep the pc cost down. No optimization or any other kind of crap was required.
I should of done this in the first place and applied the SS money towards it. The SS still has advantages in use, but, this pc has
provided excellent results and can run my steppers at the higher feed rates similar to the SS with the PP.

SO it's my dedicated pc for running my cnc machines. I would not buy a used pc today with the prices of available new pc's and would again
have mine built.

FWIW,
RICH


MODIFIED: NOT PUT TOGETHER IN SOME RETAIL STORE AND DEFINITELY NOT A  DELL , HP, or AMD.

4620

Show"N"Tell ( Your Machines) / Re: Fast sherline

« on: May 18, 2010, 03:36:16 PM »

That clamp may restrict the flapping around of the screw some but it's not doing the intended job.
But if your happy what more can i say. 
RICH