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Optintegra
02-21-2008, 08:06 PM
I have a Taig Bench top Mill. I am looking to confirm some of my settings as I’m a bit of a CNC milling noob: My system:

Nema 23 280oz stepping motors
Xylotex driver configured for 1/8 stepping
TAIG Mini Mill with 20 TPI Lead screws
Mach3 Software configured with native units of mm

Thus with 1/8 microstepping on a standard 200 step motor and a Taig 20 TPI screw:

8 x 200 = 1600 (steps/rev) 1600 x 20 (tpi) = 32000 steps/inch

1 inch = 25.4 millimeters. Thus for all axes

32000 steps/inch. = 1259.8425196850393700787401574803 steps/mm which rounds down to 1259. 84252 on the Taig setup screen

Now what’s confusing me is that I found a Mach3 xml file for a similar mill with <Steps0>1282.424009</Steps0> <Steps1>1256.826724</Steps1> <Steps2>1272.309527</Steps2>

Also what do I set Y, Y and Z velocity and acceleration to. I understand Z, because of its load, should be different to the X and Y but seem to see confusing recommendations regarding this. On one hand I have seen a statement that “the acceleration curve of the Z, which should not be anywhere near as high as the X and Y” yet the file I obtained the setting for above shows:

<Vel0>13.86</Vel0><Acc0>88.318017</Acc0>
<Vel1>13.94</Vel1><Acc1>88.318017</Acc1>

<Vel2>3.714</Vel2><Acc2>139.70657</Acc2>

Where clearly the Z velocity is much slower but acceleration much faster? Is this to give it more kick or something? Is it correct?

To confuse matters more imperial XML’s I have found for the same machine show exactly equal Z,Y and Z velocity and acceleration.

<Vel0>0.2016</Vel0><Acc0>2.</Acc0><Steps0>32000.</Steps0>
<Vel1>0.2016</Vel1><Acc1>2.</Acc1><Steps1>32000.</Steps1>

<Vel2>0.2016</Vel2><Acc2>2.</Acc2><Steps2>32000.</Steps2>

I’m perplexed LOL

ger21
02-21-2008, 08:41 PM
I have a Taig Bench top Mill. I am looking to confirm some of my settings as I’m a bit of a CNC milling noob: My system:

Nema 23 280oz stepping motors
Xylotex driver configured for 1/8 stepping
TAIG Mini Mill with 20 TPI Lead screws
Mach3 Software configured with native units of mm

Thus with 1/8 microstepping on a standard 200 step motor and a Taig 20 TPI screw:

8 x 200 = 1600 (steps/rev) 1600 x 20 (tpi) = 32000 steps/inch

1 inch = 25.4 millimeters. Thus for all axes

32000 steps/inch. = 1259.8425196850393700787401574803 steps/mm which rounds down to 1259. 84252 on the Taig setup screen

Now what’s confusing me is that I found a Mach3 xml file for a similar mill with <Steps0>1282.424009</Steps0> <Steps1>1256.826724</Steps1> <Steps2>1272.309527</Steps2>


It's possible that the .xml you found used values to compensate for screw inaccuracies. Start with the 1259 and adjust as necessary.

As for velocity and accel, they can vary from machine to machine, even seemingly identical machines. The best thing to do is adjust them using a trial and erro method, slowly increasing the velocity until you see missed steps, then back off 20-30%. Then do the same for accel.

Optintegra
02-21-2008, 09:48 PM
As for velocity and accel, they can vary from machine to machine, even seemingly identical machines. The best thing to do is adjust them using a trial and erro method, slowly increasing the velocity until you see missed steps, then back off 20-30%. Then do the same for accel.

Being of a scientific background I feel there most be some underlying theory that is being missed here?

phomann
02-21-2008, 09:54 PM
Hi,

Why don't you change the native units to inch. Then you can set it to 32000 steps/inch?


200steps * 8 microsteps * 20TPI = 32000


The native units are for setup. It has no effect on whether you machine in mm or inches.

Cheers,

Peter.

Optintegra
02-21-2008, 11:42 PM
Why don't you change the native units to inch. Then you can set it to 32000 steps/inch?


Because I wanted the Mach3 startup screen DRO to display in units of mm and 32000 steps/inch. = 1259. 84252 steps/mm so it should not matter.

I wanted to know why there is variance on some peoples setup from the above and what underlying principle is behind Z velocity and acceleration setting. i.e should Z velocity and acceleration be greater or lesser respectively to X and Y. I have two conflicting pieces of information.

BTW I'd love a DC motor / Taig mount / speed control package solution for my mill ... I looked at your site but lack will power to find a suitable motor / psu / mill or adapt a mounting plate.

phomann
02-22-2008, 12:06 AM
Because I wanted the Mach3 startup screen DRO to display in units of mm and 32000 steps/inch. = 1259. 84252 steps/mm so it should not matter.

I wanted to know why there is variance on some peoples setup from the above and what underlying principle is behind Z velocity and acceleration setting. i.e should Z velocity and acceleration be greater or lesser respectively to X and Y. I have two conflicting pieces of information.

BTW I'd love a DC motor / Taig mount / speed control package solution for my mill ... I looked at your site but lack will power to find a suitable motor / psu / mill or adapt a mounting plate.


The acceleration and max velocity for each axis is set independently depending on the axis mass. motor size etc. On my Taig I can just get 60"/min on the X and Y and about 45"/min on the Z. How you have th gibs adjusted will also affect the performance.

I set the Max speed on the X and Y to 45"/min and to 30"/min for the Z. As to the acceleration, I set just what seems right. :-)

As to a DC motor, Quite a few use a Sherline DC motor and motor controller. That may be an option. The motor I use is a 400W one with a standard KBIC controler.

Cheers,

Peter.

Optintegra
02-22-2008, 03:35 AM
As to a DC motor, Quite a few use a Sherline DC motor and motor controller. That may be an option. The motor I use is a 400W one with a standard KBIC controler.


Looks like I'll just follow the herd of wildebeast W.R.T. velocity and acceleration then. LOL. If it breaks I'll blame you (only joking).

Sherline looks good value but appears quite light weight at 60 W? I currently have the standard 1/4 HP (186 W) AC Taig motor. 400W sounds quite beefy!

I'm planning on buying a smallish (250W) step down transformer from Jaycar and forgo the 20&#37; speed drop for the interim.

I did hear that the Sieg 7x MiniLathe motor and speed control worked well from a chap in Canberra but have had no luck finding a source or price for them.

To be honest since I'm only planning on machining Delrin and ABS for electronic enclosures I'm not sure I'll need to bother with an upgrade.

Stepper Monkey
02-22-2008, 04:52 AM
The speed is often not as important as the acceleration, as particularly in a machine with such small movements, and depending on the type of cuts you do, you will usually never get to top speed before there is a vector change. I know I don't. Speed of my cuts is strictly an accel limited function, not terminal speed. Get Accel right and you are golden.

When it comes down to it, there is a theory behind it, and there are a number of discrete variables that can be used to calculate maximum acceleration. In practice however, they are many and they interact to some degree, and individual gib adjustment throws a unique value in on top of them all, taken all together they do essentially mean each machine must be tuned individually.

The power supply, drivers power, inductance of the steppers, torque/power curve of the motor in that speed range, driven mass, rotational mass including rotating motor components and screws, and frictional resistance are just a few things that would need to be taken into account. To get an accel/decel curve you would also already need to know top speed as momentum obviously comes into play on vector change. While possible to get close to on paper, honestly it is just easier to get a final value by starting in a good, safe range and moving up until you hear missing steps which is a very clear audible signal. Back it off about 25% or so and you are optimal. That easy.

You must have the Z accel set lower than XY in any case!
Usually much lower than the XY axes for two simple reasons - greatly increased mass and vertical acceleration. Imagine they are free running for a minute with the screws removed, and you are the motive power - it is much easier to push the lighter X and Y and get them moving, and to stop and reverse direction. In the horizontal plane that is all you have to worry about, as it takes the same force to move them either way. The Z is heavier, and as such, more reciprocating mass means a lower max accel. given identical motive power as the XY axes have. This is why you often see a bigger, more powerful motor on top. Given the same type of drivers and voltage as the other axes, however, this necessarily changes inductance of the motor which also then changes max accel. often canceling out much of any gain.
On top of this forces are not the same in both directions, as gravity now comes into play. Unlike with X and Y, the constant is added in one direction and subtracted in the other, which means you actually have TWO different optimal accel curves - one for up and one for down. With Mach you don't have that option so you have to go with the slowest (up) curve anyway.

You can really increase the overall speed of the machine by lowering the Z mass, which most people miss in their quest for more power. Regardless of the theoretical top speeds of the X and Y, they are all interlinked and a slow Z slows down the whole train. Dropping the accelerated mass really helps, and there are motors MUCH lighter than the inefficient stock Taig AC motor with the same range of power. I use a BLDC motor with almost half the wattage of the stock motor but the same effective power output. Particularly for mowing through plastic, even a couple of hundred (efficient) watts works wonders if you want to go lighter.

phomann
02-22-2008, 05:14 AM
Looks like I'll just follow the herd of wildebeast W.R.T. velocity and acceleration then. LOL. If it breaks I'll blame you (only joking).

Sherline looks good value but appears quite light weight at 60 W? I currently have the standard 1/4 HP (186 W) AC Taig motor. 400W sounds quite beefy!

I'm planning on buying a smallish (250W) step down transformer from Jaycar and forgo the 20% speed drop for the interim.

I did hear that the Sieg 7x MiniLathe motor and speed control worked well from a chap in Canberra but have had no luck finding a source or price for them.

To be honest since I'm only planning on machining Delrin and ABS for electronic enclosures I'm not sure I'll need to bother with an upgrade.

I got my 400W motor from Roger Cargill in Canberra. He is the Taig Distributor. Give him a call, he could suuply you with one.

As to the Sherline Motor controller, as far as I know it will take in 240V and does not need to be stepped down.

Cheers,

Peter.

Optintegra
02-24-2008, 11:42 PM
I got my 400W motor from Roger Cargill in Canberra. He is the Taig Distributor. Give him a call, he could suuply you with one.

I actually tried him with no luck. He said he had no idea when or if he may get them in and that he had had them on order for quite a while.



The acceleration and max velocity for each axis is set independently depending on the axis mass. motor size etc. On my Taig I can just get 60"/min on the X and Y and about 45"/min on the Z. How you have th gibs adjusted will also affect the performance.

I set the Max speed on the X and Y to 45"/min and to 30"/min for the Z. As to the acceleration, I set just what seems right. :-)


Wow that pretty nippy. Nearly two orders of magnitude higher velocity than in the xml setup file I found and 1 order of magnitude higher acceleration. You have a dragster! So in metric:

Accel X/Y = 60*25.4 = 1524
Accel Z = 45*25.4 = 1143

Vel X/Y = 45*25.4 = 1143
Vel Z = 30*25.4 = 762

Are you using Gecko controllers? And some kind of custom high wattage power supply?


I use a BLDC motor with almost half the wattage of the stock motor but the same effective power output. Particularly for mowing through plastic, even a couple of hundred (efficient) watts works wonders if you want to go lighter.

Do you think the Sherline will be under powered then at 60W?

phomann
02-25-2008, 01:09 AM
Hi,

No, I'm using the stock Taig controller. Remember these are rapid speeds. Wouldn't dare cut at these speeds.

Cheers,

Peter.