Messages

511

Tangent Corner / Re: About Motors

« on: February 25, 2014, 09:49:30 AM »

Russ,
The multi-V belts as used on a treadmill would likely give you a much more constant speed.  You'll notice that the treadmill motors all have the motor pulley made as part of a very heavy flywheel which I would think really helps stabilize the speed. That type of pulley is easy to make too.

512

Tangent Corner / Re: About Motors

« on: February 24, 2014, 09:22:42 PM »

Russ,
I think a V-belt drive is problematic too. As you apply a load the belt pulls down into the V and changes the effective diameter.  This might cause a fairly large speed change.  The real problem all the way around is that in thread cutting you load and unload the motor at the beginning and end of the cut.  What you really need is for the X axis (carriage) to follow the A (spindle axis). Think of it as a linear move using the X and A together. I am adding a little lathe attachment to my mill and I am driving the spindle with a stepper so I can use it as a fourth axis and I am thinking threading too.  Don't know how that will work. However I have a large driver on the   A axis and I have 960 in/oz stepper and can get a 1600 oz/in stepper driven at 68 vdc so that should be too bad for a mini lathe.

513

Tangent Corner / Re: About Motors

« on: February 23, 2014, 09:08:32 AM »

The two things that affect the rotation speed are line frequency and load.  I once installed a large diesel generator for a customer because he was monitoring line frequency and it varied from 59 Hz to 61 Hz all the time.  This was affecting his process, and when he complained to the power company they told him they don't guarantee 60 Hz continuously, they provide an average of exactly 60 Hz over the course of a year! Load is the big variable, because the motor needs the slip to work.

If you need a really constant speed you will need feedback or a stepper motor. Microstepped motors will run at a very constant speed because the step frequency is typically crystal clock controlled in the drive.  Another way to get a very constant speed is with a motor and an encoder.  Then it doesn't matter to much what kind of motor it is, DC, Servo, 3 Phase with Inverter etc. As long as the drive has an encoder input you can get very steady speed. Lots of choices, and modern electronics has made this pretty cheap to do.

If you tell me what is you are trying to do I can make some suggestions.

514

Tangent Corner / Re: About Motors

« on: February 22, 2014, 08:13:22 PM »

If you are talking an induction motor, one without windings on the armature, then the motor will always run less than synchronous speed. For 60 cycle AC a 2 pole motor will not run at 3600 rpm it will run a little less at no load. The 'slip' is needed so that the armature is moving through the magnetic fields to generate current and magnetize the armature. If it turned at 3600 rpm there would be no relative motion and no magnetization so no torque. This means an AC induction motor will run at a different speed for every load.

There are sychronous motors with wound rotors and slip rings that will run at 3600 rpm on 60 cycle power. However it only pays on really big motors.

Hope this makes sense

515

Newfangled Mill Wizard / Re: Rectangular pocket vs cutter diameter

« on: February 21, 2014, 06:14:37 PM »

Russ,
Go get a 0.240 regrind and a put radii on your toolpath!  No chatter marks no programming problem.

516

General Mach Discussion / Re: Mach as a linear indexer help

« on: February 21, 2014, 06:11:10 PM »

Gary,

Please send links to the Direct components you reference.  There are numerous hits on DL06.  I like the concept . .  we built a PLC controlled edging cross-cut saw.  I outlined the ladder, but we used outside resources to actually program it.  We also have other PLC stuff and have just as much trouble with them as anything else.  I actually have a PC that has been running since 1998 without failure. It runs DOS and a CNC Router. If the grid is up, it's up.  However, I am on my third high buck touch screen panel mount PC for the current router project.

The fence we are working on weighs about 500 pounds and has about 12 inches of travel. Although it would be nice to count pieces, it is not a feasible task.  What did you have in mind for the HMI?  The fence has a variable zero and a fixed Zero.  The operator would need to set the variable zero and then enter the desired offset values from that zero . . . usually not more than 4 total.  The fixed zero has 5 negative values.            

      

Look at: http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/DirectLogic_Series_PLCs_(Micro_to_Small,_Brick_-a-_Modular)/DirectLogic_06_(Expandable_Micro_Brick_PLC)/PLC_Units/D0-06DD1  This will do pulse and direction up to 7 Khz without any other modules.

Add: http://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/DirectLogic_Series_PLCs_(Micro_to_Small,_Brick_-a-_Modular)/DirectLogic_06_(Expandable_Micro_Brick_PLC)/Motion_-a-_Specialty_Modules/H0-CTRIO2  This will go up  to 250Khz or read a quad encoder.

Add: http://www.automationdirect.com/adc/Shopping/Catalog/Operator_Interfaces/C-more_Micro-Graphic_Panels/3_inch_Panels_-a-_Accessories/EA1-S3MLW
This give you some buttons and a pop up keypad plus data display.

You might be able to use a DC gearmotor and an encoder along with a drive like this: http://kbcontrols1.reachlocal.net/KBMG-212D-8831-SCR-Chassis-KBMG-212D-8831.htm  This will give you almost servo like performance of a big motor for low cost. You approach rapidly then slow way down for final position. If you always approach from the same direction you can remove backlash too.

Your fixed zero would typically be designated by a home limit switch. When you start the system it would move slowly to the home switch, then typically reverse until the switch reopens, that being your exact zero. Then all subsequent moves get calculated from there.

517

VB and the development of wizards / Re: Machining bolt heads

« on: February 21, 2014, 05:53:18 PM »

Joe,
Take a look at CamBam for like $150.  Life is too short to manually write G-Code.  I've written tons of G-Code by hand years ago. Damn I'd have given the thumb on my right hand for a simple program like this back then!  I am of course left handed.

518

Mach3 and G-Rex / Re: Need some assistance PLEASE!!

« on: February 21, 2014, 05:47:43 PM »

You need to pick up a known location on the part, edges, center and an edge etc.  That means a dial indicator, edge finder etc. As you are may be a wood worker you may not have those. So use known size smooth pin in the spindle and a feeler gauge or even a piece of paper that you know the thickness of. Jog close then jog in real small increments until the pin traps the feeler gauge or paper. You are then the radius of the pin plus the guage away. Type that into the DRO for that axis, watching if it is plus or minus.  For a hole eyeball the pin to center then move one axis until the pin traps the guage or paper. Hit zero for the axis you moved.  Move in the other direction until you trap again. Look at the DRO and move away by half the amount shown and you will be on the center of hole for that axis.  Now do the other axis while you are center of this one.  I usually do the first axis a again to be sure.

To prevent this problem in the future.  Use a post it note.  When you have x y and z zero look at the dials and write down the values on the post it.  IF you need to get back to zero on an axis move close to where it is and use the dial for final location.

Buy an edge finder and a dial indicator.  Life is too short to always use a pin and feeler gauge!

519

Newfangled Mill Wizard / Re: Rectangular pocket vs cutter diameter

« on: February 21, 2014, 05:33:23 PM »

The real issue here is that inside corners smaller than the tool are likely to chatter badly in the corner as the tool suddenly increases.  So I always try to design using a  radius about 0.010" larger than a standard tool so the clean up pass sweeps smoothly through the corner.  When I had to deal with on size radii I used to head to the tool room for an under size regrind. They were always sharp because no one else wanted to use them, and the tool guy really liked that I preferred them.

520

Mach4 General Discussion / Re: New people welcome !! Come in here and introduce your self!

« on: February 21, 2014, 08:55:23 AM »

Carl,
Welcome to the forum.  I also use CamBam. I think you are doing it backwards though. I haven't hand coded anything in quite a while as it is nearly always faster to do it in CamBam.  For instance, zig zagging back and forth to clean off the top of a part. Easy to hand code, but even faster in CamBam, by drawing one line a little longer than the part and entering about 5 other numbers. You see the too path drawn out and you are good to go.  I cut metal all the time now without air cutting to to test the program as my confidence in CamBam is very high.