Messages

1

General Mach Discussion / Re: My CNC build

« on: June 27, 2009, 01:59:25 PM »

First, no fuse!

If the fuse were to blow the back EMF wave from the motor might kill the drive. Dont use a fuse. They say this in the instructions.

The driver will never make more than 3.5A. It would be nice if you could get 4A from them somehow but you just cant. Set the resistor to 3.5A and you are done.

Most steppers are wired in parallel. You will gain top end speed but loose about 30 to 40% of your low speed power. If you are cutting soft material then you may want speed more than just 12 IPM power.

You did not say if your dropping steps all the time and if it is at high speed or low speed.

With an parallel connection you will have more power above about 800 PPS or 400 RPM than you do now but almost half the power at 200 PPS. There is no danger to this hookup, the only question is if it is a better way or not for your use.

Do you need to cut at 80 or 100 IPM?

2

General Mach Discussion / Re: My CNC build

« on: June 24, 2009, 02:35:12 PM »

You still might try hooking up the steppers in parallel.

You will only make around 500 OZ of torque but your top speed will be more than double. I would think of 150IPS rapids and cutting at 80 or 100IPS.

With less torque the motor tunning will need to be changed to allow more time for the motor to change direction. There is always a price to pay, faster cutting, faster rapids but slower change of direction.

Glad things worked out.

3

LazyCam (Beta) / Re: Lazy Cam tool offsets. Do I need Lazy Cam Pro?

« on: June 12, 2009, 01:52:15 AM »

Thanks for the reply.

I didn't know that "object offsetting" was the same as tool offset. I did do a search for tool offsets.

So it looks like the free L-Cam wont do a standard tool offset so my choice is to draw the work over or under sized to cut a round hole. I do have the wizard pack add on but we want to make a pattern to cut 10 or 20 repeating hole pattering in plastic boxes and it might take some adjusting to get the holes in just the right place and I don't see an easy way to edit a wizard file without a cam program. I don't know any G code yet, I'm just starting out.

They stopped development of L-Cam because of "some other low cost cam software". Was that CamBam?

I grabbed the demo and there is a beta release that looks to work OK. I would rather spend $75.00 for L-Cam but it would be nice if it was still supported. I'm learning everything for the first time and I would like to stay with the same cam software for a year or two. If I run into a bug with L Cam It will never be fixed.


Thanks
Dave

4

LazyCam (Beta) / Lazy Cam tool offsets. Do I need Lazy Cam Pro?

« on: June 10, 2009, 03:08:05 AM »

I can't seem to get the tool offsets to work in the free version of Lazy Cam. I did some searching but the answer is still not clear. Does anyone know for sure that the tool offset function does not work in the free L Cam but does work in the pro?

Thanks
Dave

5

General Mach Discussion / Re: My CNC build

« on: May 27, 2009, 09:12:18 PM »

I'm fairly new to a lot of this stuff so I'm not sure if you should wait for instructions but I will give my 2 cents worth.

When driving a stepper, Current = low speed torque. Voltage =  speed.

For your steppers any power made past about 1000 PPS and higher is determined by the voltage. The current could be set 20A and the motor would make no more power.

Below around 900PPS the power and current is set by the driver.

If you are loosing steps at a low speed then you need more power from the steppers or driver. If you are losing steps over about 1000 PPS then the power supply voltage will help.

It sounds like all will be fine when you go to a 48V supply. The drive will die with a 67V input so you can't over volt much.


The motor tuning is described in the Gecko instructions but I think they use the term low speed and don't give a exact PPS # because it is different for every type of motor.

In Mach3 I have been tuning the motors using the servo motor function. Go to Diagnostics tab then click the Servo Freq Gen button. You can set any PPS rate from there. There is no ramp up or slow down when changing direction so you will lose steps at higher frequencies using this function.

Enter a # of PPS in the Hz box, some will be much louder than others. Try 700 to 1500 in 100PPS steps and you will be able to hear the "ring" Leave the setting there and adjust the Gecko trim pot so the motors makes the least amount of noise.

6

General Mach Discussion / Re: My CNC build

« on: May 26, 2009, 09:09:28 PM »

I can get 300 IPM with the 400Oz steppers and 60V and 5TPI but I will lose steps if you let it run long enough. I have only just started cutting parts but I have slowed things down to 150 IPM for rapids and have not lost any steps.

The 48V supply will give you a 50% speed increase so it is worth doing. To make sure you don't drop stepps you will need to slow thing down more than you think. I would be happy if you got a good strong 60 IPM cutting.

I am still curious about how a single coil behaves with lower or higher current. Can you use twice the current and still get 400OZ out of it? Your motor was a 1.2A for a series connection? Correct. If you run it at 2.4A then you still should make close to 400OZ of torque. Does this happen?

The adjustment on the Gecko drive is to get ride of the inductive ring from the motor. It should happen around 900PPS.  Set the motor to 900 PPS and adjust the pot until the motor makes the lowest amount of noise. You will only need to do this once.

7

General Mach Discussion / Re: My CNC build

« on: May 26, 2009, 01:12:27 PM »

It was not my idea to only use one half of the two coil but MachineMaster. I have not tried the idea myself but it should help and the price is right.

I think the Gecko current drive resistor is the same as the current made, so a 2.2k= 2.2A which should be over driving the steppers some.

I have over driven some steppers and they did not improve the power much and got really hot. I have not read anything about coil saturation effect on steppers so I don't know what gains might be had by overdriving a single coil. The motor will run cooler with a single coil being used so heat should not be a problem. If you can run 2.4A and the performance is fine and they don't get too hot you might be OK just leaving them set that way.

Did you up the voltage?

The little Geckos don't need much heatsinking and at 2.2A almost any heatsink will cool them enough. A slice of 5" x 1 1/2 AL angle stock should work fine and bolt it to the box. You could go all out and get a 10" piece.

8

General Mach Discussion / Re: My CNC build

« on: May 24, 2009, 12:35:14 PM »

In the electronics world inductors are called "chokes". They are often used to stop high frequency's from passing through a circuit. For steppers with slow screws we don't want high inductance. You motors have a vary high inductance and voltage rating. This will allow them to  work with a low current driver like the Mectronics but the price is speed.

28mH is a huge value. Your inductance if you use a single coil should be around 7mH so the speed will be close to what the the 45-8A stepper would give.

A 50V supply and a 7mH coil should give you over 500 RPM and still hold 200 inch of torque. You might be able to get 50 IPM before the torque starts to fall off with that setup.

Your motors would be happier with a 100V supply or a unipolar driver or faster screws.  In the long run I would look at getting the much faster screws. They are more efficient and will let you use your existing motors just fine.

You might take a look at the Roton #60986 lead screws, 4 start and 2 TPI with the dumpster nuts.

You want to use the lathe anyhow!

9

General Mach Discussion / Re: My CNC build

« on: May 24, 2009, 04:22:29 AM »

You will never have a fast machine with steppers and a 10TPI lead screw.

I am running   5 TPI lead screw's and a 60V supply and low inductance 400 OZ NEMA 34 steppers and I can get well over 1,000 RPM, but if you watch the  little 1/2" lead screws  go 1200 RPM you know that this is not a vary good idea for a 34" long screw.


Go to a 50 V supply first, it goes with your stepper driver.

I would think with your current 420 OZ steppers at 1.2A that they will start to loose power at about 125 RPM. 50V will make that 250 RPM. Your max speed should be around 12 IPM.

Faster steppers will help but you might want to think first if you ever will want to cut at 80 IPM or so. To do that you will need faster screws.

As for new steppers you might look at the KL34H280=45-8A 640 OZ stepper or the KL34H280-45-4A

The 4A runs at 4.5A so you will have to give away about 25% of 640 OZ of torque but it has a little higher voltage that will let you run it in parallel to get better speed. The inductance is 6.8mH. I would think you could get 750 RPM.

The KL34H280-45-8A is a 8 wire motor and for a series hookup will give you a 8.8mH of inductance at 3.1A. You will get the full 640 OZ of torque but gain two mH of inductance so you will lose some speed.  The 8A would work nice with some faster screws like the 4 TPI ACMI or even the faster 2 TPI.

You current steppers should perform fine If you go to a faster screw. With 250 RPM from the stepper and a 2 TPI screw you would have around 125 IPM cutting speed. You have a lathe so turning the screws should be no problem.

Could you elaborate? "Center tap and one end of each coil" is not possible with six motor wires and only four Gecko connections. Oriental motors instructs that the center tap is not used for Bipolar serial connection of the motors. (And since they are six wire motors, parallel connection is not possible). I am confused about the center tap. Is this in essence energizing only HALF the coil?

By center tapping you will lose half your torque but double your speed(more than double). The current will be the same but you might be able to bump it up some and still have the motor stay cool. You will have a lot more power at 250 to 500 RPM. With a 10 TPI screw I would think 200 OZ might be OK but you will need to find out by testing.

They say not to use the center tap for bipolar but you can if you are willing to give away some power.

To center tap means to use the center tap and only one of the other two wires.

10

General Mach Discussion / Re: My CNC build

« on: May 24, 2009, 04:15:09 AM »

You will never have a fast machine with steppers and a 10TPI lead screw.

I am running   5 TPI lead screw's and a 60V supply and low inductance 400 OZ NEMA 34 steppers and I can get well over 1,000 RPM, but if you watch the  little 1/2" lead screws  go 1200 RPM you know that this is not a vary good idea for a 34" long screw.


Go to a 50 V supply first, it goes with your stepper driver.

I would think with your current 420 OZ steppers at 1.2A that they will start to loose power at about 125 RPM. 50V will make that 250 RPM. Your max speed should be around 12 IPM.

Faster steppers will help but you might want to think first if you ever will want to cut at 80 IPM or so. To do that you will need faster screws.

As for new steppers you might look at the KL34H280=45-8A 640 OZ stepper or the KL34H280-45-4A

The 4A runs at 4.5A so you will have to give away about 25% of 640 OZ of torque but it has a little higher voltage that will let you run it in parallel to get better speed. The inductance is 6.8mH. I would think you could get 750 RPM.

The KL34H280-45-8A is a 8 wire motor and for a series hookup will give you a 8.8mH of inductance at 3.1A. You will get the full 640 OZ of torque but gain two mH of inductance so you will lose some speed.  The 8A would work nice with some faster screws like the 4 TPI ACMI or even the faster 2 TPI.

You current steppers should perform fine If you go to a faster screw. With 250 RPM from the stepper and a 2 TPI screw you would have around 125 IPM cutting speed. You have a lathe so turning the screws should be no problem.