0,0 by Jog or Crank?

[Pretorien]

One of the "wants" on the list that I have for functions and features of a CNC mill is retention of manual control in part because the way I work now with my manual, DRO fitted X2 is to lay out all of my cuts, corners and holes as XY cordinates from a corner (typically lower right), find that corner with an edge finder, zero my DROs and crank to the numbers. My initial reaction was that it would be easier to get to that corner by hand cranking than by using a keyboard or dongle.

After reading the section on jogging in the Mach3 manual, I am reconsidering that assumption. Tapping the 4/6 - 8/2 keys on the numeric pad is pretty easy. I am left with two questions:

1. Obviously, the system must be on in order to do this and it appears, from what I have read, that one does not want to leave steppers, drivers and power supplies on idle 24/7 so start-up time is a question.

A bare installation of XP (no external connections, no anti-virus etc,etc) will start up very quickly - assuming that Mach3 is the only program running - how fast will it boot?

2.The second question should amply demonstrate that my understanding of stepper motors is marginal - but I asking because I'd like to learn. If one does have manual control and uses it to set 0,0 with the sytem off and then powers up the system, will the X&Y steppers move, of their own accord to one of the 200 lock positions that a 1.8 degree/step motor will have? (I don't know, for example, if "microstepping" is a purely dynamic process or also defines rest postions of the motor) In one sense, this is a minor point because, worst case, with 200 steps/rev and a 20 TPI screw, the offset will be about 1.5/10ths (half a step jump = 1/400 rev X 1/20 inch/rev) which will not affect my intended use.

Thanks

EM

[in2steam]

the first question is purely depends upon your system, but in general the cleaner the boot is the quicker the startup will be, my answer otherwise is are you ready to drill or mill a hole in under 20 seconds of you turning on the lights were the mill is kept. I know it takes me at leaast 3-4 minutes just to figure out how to mount it in alot of cases. Just watch your hardware as there are a few computers(dell seems to be on top of that short list) out there that don't power the paralallel port to 5V and on all there models. Modders(the computer gear heads) have contests on how quick they can get there computers to boot, most down into the 10-15 second range(some quicker). I would alot arround 1 minute, this gives you time to turn on the lights, stepper drives, the radio and mount your work, I think you will find your computer waiting for you not vice versa. If you are one that works for 20 minutes walks away for 15 minutes and then comes back, I think you will find it easier on you and the computer just to leave it on, I leave my main computer for the house on. Since I have done that my power billl has gone up around $10 for a 500W power supply.
2. I think you will find that trying to set the machine to 0,0 by hand will be counter productive, esp since you have a button that does it for you. But to answer your question, when steppers power up they almost always cog to the nearest step, typically under 1.0 degree, on ultra sensitive machines you will notice a movement, I think on a x2 it will be next to nothing with stock screws. You will in the end find it alot easier to just not have handles, and rely on Mach to do the work, thus freeing your hands for more important things like, coffee(or soda) and the home shop machinst or local newspaper.
To give you an idea, I have a machine I work with that is an x,y,z,a vinyl die line cutter. It upon powerup if not homed will always move one step, this machine has encoders so it knows that its moved but it often looses that very first step so it often leads to after several(maybe 20) on-off cycles being off by about .005-.010" which is nomial for this app. But if its homed by the operator for what ever reason it returns to its proper alignment. I say this becuase with a stepper controler it only knows were it was, so if has been disturbed since its last known you may have undesired results should it power up and try to home or start a program without first homing. It would be to your benefit to give home limits, and you could also look into an MPG for manual overide, you will find this much easier then using hand wheels which can get caught on things and snap off. You could also create a pulse generator with some simple electronics I suppose, when you don't have the computer on, but would require a means of switching between the computer/breakout board and it. Again alot of redundant work unless you plan on not having the computer dedicated or always present.

I timed my kids smaller p3.0 1gig ram xp pro machine and it took it a marginal 36 seconds to get to the desktop with a password. I cannot even get a drill bit out and in the chuck in that time frame.

chris

[Pretorien]

Thanks for the response - it helps with the decision making.

The system will have a dedicated computer - I change out my business hardware fairly regularly so there is always a spare box lying about (I leave my main unit on as well - only shut down my laser printer)

The "machine" jogging makes a lot of sense especially since after flipping back and forth for about a month, I am currently leaning towards leaving the Sieg as is, with its DROs and adding an off-the-shelf Taig for the CNC function. I have attached a JPEG of the sort of thing that I will be doing - the part is 2.4 X 4.0" and the cuts are primarily with 1/16 and 3/32" end mills in 1/16" brass:

EM

[in2steam]

Originally Posted by Pretorien Thanks for the response - it helps with the decision making. The system will have a dedicated computer - I change out my business hardware fairly regularly so there is always a spare box lying about (I leave my main unit on as well - only shut down my laser printer) The "machine" jogging makes a lot of sense especially since after flipping back and forth for about a month, I am currently leaning towards leaving the Sieg as is, with its DROs and adding an off-the-shelf Taig for the CNC function. I have attached a JPEG of the sort of thing that I will be doing - the part is 2.4 X 4.0" and the cuts are primarily with 1/16 and 3/32" end mills in 1/16" brass: EM

Sounds more like laser work, or water jet, alot of treepaning other wise, my experience with brass is that it will not like the stress of cutting. A taig out of the box is a option, I own a taig lathe and love it to death, deepgroove makes a good conversion for around what it would cost to covert sieg.

chris

[wildcat]

Originally Posted by Pretorien I have attached a JPEG of the sort of thing that I will be doing - the part is 2.4 X 4.0" and the cuts are primarily with 1/16 and 3/32" end mills in 1/16" brass:

Looks pretty neat... what's it for though?

[Pretorien]

It's a set of parts (4 pieces when done) that make up the basic chassis of a 1/32 slot racing car! The 4 sections are hinged and pivoted together and then the temporary webs and waste parts are cut away (makes for easier assembly) - I'll post a photo when it's finished.

EM

[wildcat]

Please do!

FWIW: I use a normal mechanical edge finder in a CNC mill without cranks without problems. As I get closer I slow the jog rate down until it is really slow. To help with this I added a few new push buttons to the Program Run page of Mach3 to switch to slower rates with a push of a button. I also have occasionally use an electric edge finder tied to one of the input lines into Mach3. This makes edge detection a little more automatic but frankly a quicker job can be done with a mechanical one. I've used a laser edge finder though don't find it all that repeatable as an edge finder so it is mainly used for setting up the four jaw chuck now.