Messages

41

General Mach Discussion / Re: Non linear axis measurement...

« on: May 27, 2009, 03:49:38 AM »

I cannot see how your motor gear stays in contact with the pinion - something must move to allow it to work.

If the pinion stays in the same position and some mechanism lengthens the bracket so the motor stays in contact, then the tangent of the angle subtended by the bracket{call this A} is the (distance along the pinion) divided by the (distance of the pinion from the centre {call this C}).

Therefore the (distance along the pinion) = TanA multiplied by C.

If however, your pinion moves to keep in contact with the motor, then the angles are constantly changing, and the calculations become much more difficult.

42

General Mach Discussion / Re: Problem cutting circles

« on: May 25, 2009, 12:23:45 PM »

SteinarN - I am coming in late to this post - it appears finished - but - YES - Mach 3 supports backlash compensation. You cvan measure your backlash on each axis and put the data in Config/Backlash. If you turn backlash compensation on, the Mach 3 will allow for the backlash every time your acis changes direction.

43

General Mach Discussion / Re: Index switch / limit switch

« on: May 25, 2009, 04:27:56 AM »

The two laser modules, which are 2 inches long and 1/2 inch dismater (certainly less that that) run off a 5 volt supply. You can get tham fitted with lenses to give amore focused output. I got mine from Maplin (UK firm) at £10 each. The dtectors are three wire Schmidt trigger devices, giving an instantaneous change fro 5 to 0 v if hit by a laser beam. They drive TTL and CMOS directly.

I have my lasers mounted on the table shining onto detectors mounted on the lathe body. There is no physical contact between the two, indeed, they with work over a long distance if required.

Excellent, repeatable results, to less than 2/100ths of a mm.

44

General Mach Discussion / Re: DRO error in mm

« on: May 25, 2009, 03:18:47 AM »

It stands to reason that not every number can be divided by a whole number and come out to an exact whole number.

It your machine is set up in inches, then usually this is becasue the leadscrew is in inches, so a finite number moves the correct distance. The same applies to a machine set up in metric - where the leadscrew is metric - again a finite number will give a finite answer.

Whe you use one to produce the other , the divisor is 25.4 hardly a simple number, and therefore some rounding up must occur. Mach calculates to 12 places of decimals (depsite what is shownon the DRO's) and the error, as Hood said, is very very slight, and I doubt your machine will cut that accurately anyway - we are way past the micron stage.

45

General Mach Discussion / Re: noob - help on breakout card and parallel port card

« on: May 22, 2009, 02:22:32 PM »

Seems OK to me - I would use 8 microstep position thought. It achieves your required accuracy straight away, and Mach can calculate that fast anyway. You must realise, however, that your accuracy cannot be guaranteed if you are relying on microsteps. Over the eight microsteps, the positions are not necessarily equally spaced between each other. They are accurate at position 0,(within the parameters of the motor) but could vary slightly between the others - but then again - what are you machining that requires that accuracy - aeroplane parts.

Set up your pulses per unit (mm's) at whichever microstep you decide to use, and you should be away.

46

General Mach Discussion / Re: noob - help on breakout card and parallel port card

« on: May 21, 2009, 04:52:32 AM »

Faults are not unknown on new cards - you are obviously quite competant around electronics, therefore I would say you are ready to roll.
I can't see why there should be a hidden "enable" or earth return for 1,16 and 17 especially if 14 works.

The only thing you need, to enable you to at least "dabble" some more in the mysteries of CNC is to set up two axis.
I dont know what drivers you have chosen - if it is a "set" from CNC4PC then the explanation and diagrams from them should be clear enough.

To go back to Mach, then only thing then is to set up your "steps per unit" and "acceleration" on the motor tuning page.
First set up your "master" units on Config/Select Native Units if you have not already done so. This has no relation to what units you might use while cutting, (which can be changed by instruction) but is the units in which you set up the system. If you mill is calibrated in "imperial" use imperial, if "mm s" use metric.

Steps per units (Config/Motor tuning) is worth setting up before you try and get the motors turning. A stepper motor has 200 steps per rev, your driver might use 8 or 10 micro steps (if you have a choice, use 8 or ten) if you have any gearing between your leadscrew and the stepper (I had a 3 to one reduction) and finally the leadscrew - mine was 10 turns to the inch. If you multiply these all out you get 200 x 10 x 3 x 10 = 60,000 steps per inch. Even ignoring the microstep multiplier, I would still have 6 divisions for 1/1000th of an inch.I say ignoring the microsteps, becasue these are an electronic division, not a mechanical one, and while you must add them into your calculation (and they improve the smoothness and reliability), the exact position they settle in cannot be guaranteed i.e. they are not spaced out evenly over one step.

I recently replaced my leadscrew with a metric ball screw, and had to reset all my machine in metric - same calculation 200 x 10 x 3 i.e. 6000 up to the leadscrew, by one rotation of the leadscrew moved the table 5 mm, so divide by 5 - 1,200 steps per millimeter.

Set your velocity at a modest speed e.g. 4 inche or 100 mm per min and then your acceleration at say 1 inch or 10mm per sec per sec which will get you started.

You should be then able to jog you machine up and down, and then enter commands in the MDI line to move the  cutter.

Get up to that and you are almost ready

47

General Mach Discussion / Re: Is laser cross dangerous on aluminum table top

« on: May 21, 2009, 04:03:04 AM »

I would have thought that the reflections from your table would be so diffused that it is unlikely to cause anything to anybody. The "strength" of a laser is in the ability to focus the many beams of light into a single path. No - get on with it.

48

General Mach Discussion / Re: Index switch / limit switch

« on: May 20, 2009, 03:57:12 AM »

The entirely mechanical solution is to alter your "switches". I use small laser modules, shining on detectors - i.e. the "switches" never make physical contact and are completely protected. Another advantage is I can also have several detectors at different positions, to stop the carriage at different points. I have a combined lathe/mill and have a different set of limit and home switches for each "mode" - same lasers (2modules), different detectors (6)

49

General Mach Discussion / Re: Choppy cuts in X-Y direction

« on: May 20, 2009, 03:50:22 AM »

What are you using to create the code.

Most drawing package do not produce arcs and circles, but produce straight lines, to the eye they look smooth, but to Mach they look what they are - a lot of straight lines. You description of getting choppier towards 45 degrees reminds me of the effect I get drawing a diagonal line with too much magnification

Look at your code and see if this is the case. If pockets you are cutting are circular, this shold be a G2 or G3 move, in which case I would expect you to get a perfect circle. If the pocket is square or whatever, is there any way you can increase the resolution on your drawing package. My Turbo cad also has a setting for the number of sectors in a circle, which can vary from eight or so, up to whatever - I usuall use 360.

50

General Mach Discussion / Re: Arduino microcontroller

« on: May 20, 2009, 03:23:28 AM »

I assume you are then using the microcontroller to control some higher function in a robot or something similar, otherwise I cannot see in what way you are expecting Mach to "control" the Arduino.

Mach puts out onlt step/direction pulses for axis and then can put out various on/off signals to control relays etc. As you say it can read on/off signals into the computer as well.

The control of spindle speedhas two different systems, step/dir (as in the axis control) and PWM - pulse wave modulation - which requires additional electronics.

If you use a breakout board on the LPT1 port, you can read the output signals directly (and drive TTL - and therefore a micro controller directly) with recourse to RS232.

Mach does use a USB output to drive the latest "smooth stepper" control card, but I do now know what protocol is used for the link.