Waveboard Panel

This is what I've been busy with lately...

Solid Nyato timber door panel.

Children Study Desk & Chair Set

Carving, Engraving & Profile Cutting is fun & the product are pleasant to the eye. BUT mostly useless... Very much like having sex...
This doesn't satisfy my natural crave to build something useful...
I've seen many furniture we made with CNC router... but can this really be done without any further human inteference?
It is unevitable that I set out to build a set of functional furniture... eventually... & that "eventually" came sooner then I could anticipated...
The choice of the month is a Children Desk & Chair set. Why Children furniture you may ask... They are no less difficult then any other furniture & they are smaller (that means less material to buy...) period...
Took some serious effort into research of suitable joineries... After over 2 weeks of toying with various design combination in my head... I conjure enough energy to keep myself nailed infront of the computer monitor for 2 full days to come up with the 1st version...

After a not-so-satisfied prototype & some alteration on the original version. This is my final results. A chair that is ergonimically correct, light-weight & assembled (easily) without glue straight out of the machine. AND (most importantly) they look right to my eye too...

"Flat-packe" profile cut

Now... How should I paint this thing...

Alignment

Now that the Chinese New Year celebration is over, & the main machine structure is up. It is time to proceed with the critical rail alignment work.

This is the most dreaded part of the build. Why so? We all know that we can ride smoothly on a bumpy & winding  road. It is the same with machine. without a through rail the machine can never travel straight & smoothly.

What is the primary objective ?
1) line the rail as straight as possible. Here, I set out for within 0.1mm which is equivalent of +/-50micron. which is about the diameter of my hair (which I had just measured...)
2) straightness of within 0.2mm along the 4.4m length x-rail & 1.73m y rail
3) parallelism between the 2 x-rail of 0.2mm

Secondary objective?
1) Using the most primitive tools & equipment I can lay my hands on in my tool box.
Tools I used
1) Filler gauge with 0.05mm to 1mm
2) 30 lb fishing line
3) Aluminium shim salvaged from Coke can.
4) Hole punch
5) a few clamps
6) an aviation straight cut snipplet
7) some spanner
8) a 3lb hammer

No rullers, no micrometer, no dial gauge, no vanier calipers...

Can this be done? Oh Yes.
The last time I lay my hands on similar work was like 2 decades ago, after which I get to supervise/instruct others just by pointing my fingers + a bit of shouting when it calls for ;) . While they slough it out in tropical heat, I get to take refuge in nice air-conditioned office sipping coffee. The for another few year, I don't even get close to job like these...

It was tough at the beginning when I got rusty over the years, but like riding a bicycle, everything came back after a little fiddling.

Will post more on details... once I get everything organized...

Why The Stepper Motor

We have to look back to the type of control system that we select.

Two main types of control system, Open-Loop & Close-Loop.
Open-Loop control:-
The Brain send an instruction to the Muscle and expect the instruction to be carried out perfectly. and never bother to go back to check if the job had benn done properly as told.
Close-Loop Control:-
Commonly named Servo-System. The Brain will send instruction to the Muscle, after completing the instruction, by using encoders the Brain will cross check if its been done correctly,  if there is error, the brain will instruct the muscle to make the correction/adjustmet, & repeat the cross-checking until the brain feels happy.

Another advantage of a Servo system is they can move much faster then steppers.

The first reaction for most will be to use an close-loop system, error correction, faster speed... simply because that is how a healthy person will think. BUT after a quick search, one will learn that a close loop system will cost an arm & leg.... Not willing to hurt the pocket & further complexity, one normally settles for Open-Loop System...

Anyway, most CNC router employ a stepper system as their muscle and they had been proven competent mostly.

A compromise must be made, Generally,

1. One must not skim on specification of the motor, such as power & torque.
2. Eliminate or minimise backlash in the system.
3. One must tune the machine to ensure the motor doesn't

•  loose step, i.e. motor turn but the machine doesn't move. The cause are generally asking the motor to perform acceration which the motor torque are not sufficient to achieve, mechanical friction, Load of machine too heavy.. etc.
• Backlash, this is the term to describe the "free-play" between the to & fro motion, one can introduce mechanical solution to minimise the error or use software to compensate.
• Electronic inteference, one must ensure the instruction signals are transmitted uncorupted by external noise such as EMI, RFI... etc.

There are no free lunch! Stepper motors system is generally a fraction of the Servo-system, so more brain-juice & body sweat is required to compansate the situation. BTW, servo system do have their unique sets of headache to tackle... but that is another story for another article...

When looking at the Stepper motor specs sheet these are the things to look

• number of phase, the modern steppers are normally hybrid 2-phase.
• number of wires,
• 4 wires means 2-coils,
• 6 wires means 2-coils with choice of Bipolar in series or uni-polar (half coils)
• 8 wires means 4 coils with choice of Bipolar inseries, Half coils or parallel half coils.
  

• Coil inductance of each coil. Lc
• Torque.
• Max. Current rating of each coil.

Stepper motor normally runs over 10 times the rated Voltage, so the voltage rating isn't important. To find the actual motor Voltage rating, here is a simplified and safe estimate.

Stepper motor rated DC voltage = 32 x sqareroot(Lc)
where, LC is in mH.

Actually, if the motor doesn't heat up too much, one can go for higher Voltage.

Don't ask me why as the answer will come in a few pages or tech ladden write-up which I am too lazy to do.

Generally,

• Higher the V, we can get higher speed from the motor, if high speed is a necessary, seek out ahigh coil inductance motor.
• Higher the A, we can get higher torque from the motor, check out the coil rating.
• The limiting factor is always the heat during operation, IMHO it is always desirable to have as low a Coil Resistance no matter what...
• Sufficient Torque, too little can't do the job, but too much doesn't always better. just be rational.