YAP2C - Yet Another Pickit 2 Clone

After a long break from the electronic scene, I've decided to pick up the drawing board again.

Since Microchip dropped support for ICD2 (Cypress based clone) all x64 Windows OS (since Vista at least) fail to recognize it.
The solution is to use it in an other machine with a x86 OS which is not practical, since that is not my main PC.

Pickit 2 (Microchip also is discontinuing) is a fine replacement for now for my needs. It is small.easy to build and is supported in Vista/7 x64.

So I decided to make yet another clone based on many other clones that are out there. Of course, also has many other clones out there, it is made of the most common electronic components found out there.

Pickit 2 has the following pros:

• Microchip has open schematics and software for this programmer.
• Small size form.
• Easy to build.
• Easily customizable.
• Made of common parts and a single 18F2550 PIC
• Can be integrated with several programming/compiling tools.
• Doesn't need to download software each time you have to program a different part.
• My simplified version can supply power to the target without penalty for the USB port.
• It's a single side PCB with only a few shunts on the opposite layer.

Cons:

• Does not support most recent PIC (not a big deal for me at this time).
• My simplified version can supply power to the target without penalty for the USB port but requires external dc adapter.
• My simplified version is for 5V parts only. (although it can be overcome with an adapter between the Pickit and the 3.3v target).
• My simplified version has no leds (visual status of PIC).
• My simplified version has no memory for standalone programming.

So here is the schematic and PCB:

Schematic

PCB

And here is a 3D simulation of the circuit. Some parts are missing (I don't have the model) and others are not exactly the specified format but it can provide a good idea. I'm considering changing the inductor to an axial type to save more board space and give it more room.

Pickit 2 - bottom

Pickit 2 - top

My only doubt right now is if I can reproduce this on CrappyCNC. But first I must fix it (yes I've done a stupid thing with it and broke the CNC...lol). Since it was build from root by be I'm not that concerned. The good thing of doing things your self is that you know how to rebuild/fix in case of an accident. ;-)

For more info on the way the Pickit 2 works check this link.

See you next time...

PCB-GCode tips and tricks for full isolation

My PCB milling techniques are getting better at each trial-error experience.

Going to the SMD area there are a few tricks and adjustments that will improve the overall quality of the work.

By the way I'm now using some 0.1mm @ 60º V-bit for the PCB echting process instead of the 10º I was previously using. The results are a lot more even. I'm now going at 0.02mm of depth instead of the 0.05mm in my last config. Actually my new config has changed quite a bit.

I'm now using these settings:

Milling depth: 0.02mm
Tool size: 0.4mm (I moved the compensations and safety margins to this field. Run-out, vibrations and all unknowns are in here instead of being in the default isolation margin.)
Default isolation margin: 0.05mm. Reflects the changes above.
I still use the double passage method for best results. Maximum and Set Margin should reflect that has explained in an early post.

Also as I stated in early considerations the DRC tool in eagle is very important. And should reflect the given formula (Minimum clearance = Tool size + 2xDefault isolation margin) for all clearances.

Ensuring full PCB routing trick

Some times enough clearance between track simply can't be achieved or is too difficult. Here is a technique to overcome that limitation. (Remember this will ignore the clearance rule so your machine may not be capable of reproducing a good route/via/pad because it is just bellow the resolution it withstand).
You clould "lie" to the pcb-gcode plugin about the size of your tool to achieve until path was achieved, but this would result in poor final qualitty since all routes/pads/vias would become thinner than expected. This should be avoid.

Here is an example.

Check your clearances. Try to fix as many has you can. Remember that if you can't guarantee the given clearance the gcode generated will also reflect that and route isolation will not be fully achieved.
In the following circuit I used the DRC tool and my failed clearances were highlighted like in this image.

Eagle after DRC tool

Generated echting gcode

As you can see the the milling route in the areas without enough clearance is not generated.
To overcome this manually add some milling routes in the Milling Layer (layer 46 of eagle)

Manually added route

Generated milling gcode

Merged gcodes (milling + echting)

Has you can see the highlighted gcode and track are actually the milling gcode. The final result is a single pass routing to perform the desired isolation.
If the echting tool is not too big and the routes are not that thin the achieved result is very acceptable. The resulting route will be slightly thinner but it wont be that bad. This will in almost every situation yield best results.

Here is the output of the above circuit with those tips applied

Milled board with SOIC28, mini USB and SMD parts

NOTE:

I detected a small bug in pcb-gcode plugin. The first routing of the mill gcode file those not go to the default milling depth (the G01 Z-X.XXX FXXX instruction is not being generated). You must added it manually.

Cya next time.

3D preview of a PCB- EagleUP

I just found out about this plugin today. And man is it good.

It's the eagleUP plugin. It allows you to create a 3D view of your PCB design in Google's Sketch Up (my all time favorite 3D tool and the winner award for the most easy and comprehensive 3D software ever).

Sketch Up is designed for even a 3D noob like me to do wonders.

The wonderful thing about this plugin is that the model library is virtually endless. You can practically use any model from Google's warehouse (and there are plenty of them). Many users contribute for this library so it's always expanding.

This blog new background was done with it.

It's worth checking out. ;-)

Pimp my toy

The other day my 2-year old got a brand new firemen car that only played a sound or two and nothing more. The toy was quite dull but my kind was all over it because he loves everything with a siren.

I thought to my self. This ride need to be pimped. I said "Son I'm going to put an emergency light on that truck". He kept on going "Dadd...put...light...truck". Man was I under pressure.
So I did. I started to look at the car here:

Original toy

This is a 2xAA battery powered toy. So 3V doensn't allow me to use a popular 555 IC. To do a low voltage blinking led I needed and alternative circuit. So I remembered a simple oscillator circuit that is even easier to make. It' an astable multivabrator circuit made with 2 NPN transistors.

The circuit is similar to the one in this link.
Since this is such a low voltage application I replaced one of the collectors resistences by the LED directly.
This made the LED glow nicelly. I also changed some of the components values because of the LED blinking rate. The polarizing resistors were 47Kohm and the capacitors were 10uF. The transistors I used were a couple of BC549B I had laying around.

I took some prototyping pref-pcb and soldered the compontens. Don't mind the tallness of the components. I made this so I can (who knows) reuse them.



The astable multivibrator circuit


Looking at the toy there is a 2PDT switch that turns the toy on. The switch has 3 poositions OFF-DEMO-ON. So I will power the "blinker" in that switch for the ON position.



Identifying the ground and power spots



All soldered in place

 Then I took my dremel tool and drilled the roof of the toy bellow the light cover and glued it all in place with a hot glue gun.



Drilled roof top




Glued LED

 And here it is a PIMPED TOY CAR. The firemen truck now has a blinking light. I hope my son likes his "new" toy. ;-P

Toy with the added blinking emergency light

PCB - Post processing

So. Here is a little trick to post process a homemade PCB board.
This is valid for both mechanical and chemical echting.

This is a small USB bit whacker I made for quick prototyping. Well it's not that small but this is a first version and it's a single side board.

1º Step - DRILL
First step if you are not making the drilling with your CNC or you are making an chemical echting make all the drills on the board.

2º Step - DEBURR
Use a very fine grain sandpaper or oil stone do deburr all imperfections off the PCB. That will make it look like this photo.

Deburred PCB

OK don't mind that accidental cut on the pad...uugghhh. Looks very scratched doesn't it?
Let's make it pretty.

3º Step - "KIND OF" THIN PLATING
Hummm..thin plating finish would be nice. Well you can do something very similar. Apply a silver iodide (silver nitrate based compound) used to repair and clean jewelery. Here in Portugal there's a product called Pratex.
This will also ease the soldering work.

Here is a photo.

Finished PCB treatment

Nice!!
Despite the...uuuggghhhh...accident...uuuuggghhh (rush is your enemy). Looks quite good.

Milling PCB in a CNC - The guide

OK. So here is a little resume of my process to make PCB with my crap of a CNC.

I'm using freeware version of Eagle to make the schematic and board and then I use pcb-gcode plugin to generate the gcode for the milling.

My steps are these:-Make the schematic and board in eagle.
-After all is in place use the Drc tool in eagle to check your clearances. To do this go to the clearances tab of the Drc tool and set all clearances according to this formula:

Minimum clearance = tool width + (2 * safety offset from pad/via distance)

Why?
Because using the same formula in the pcb-gcode plugin will allow you to make the PCB using 2 passes (making a PCB in a single pass doesn't always ensure proper isolation and almost always needs deburring and more the two passes is excessive and time consuming). The 2-pass isolation has yield the best results for me with a 10º v carbide bit. I'm still waiting for the 60º bit. I'm hopping it can produce similar results with a single pass. For now I'm sticking with 2.

The above formula is a reference and should be used has a reference only. If overlay occurs it's not the end of the world. The amount of overlay is the problem. Some SMD components might not even comply with the clearances. It's OK. But you should check the generated gcode for those places to see if they where properly isolated.

-Next configure pcb-gcode plugin. If you are going to work in metric units (mm) change the gcode-defaults.h in the setting folder of the pcb-gcode plugin to output the coordinates with only 3 decimal places after the floating point.

This is done by changing this line:
string FORMAT     = "%-6.4f ";      /* coordinate format */

To:
string FORMAT     = "%-6.3f ";      /* coordinate format */

Milling depth = -0.05mm
Remember most copper sheets in raw PCB is 35 microns (0.035mm). 0.05mm should be enough without going too deep.

Tool width = 0.2mm.
In my case I'm using a 0.1mm v-bit 10º. I set this to 0.2mm to compensate for run-out, vibration and bit wobbling (being such a thin bit it bends while trying to remove the copper. It's like forcing a needle to scratch a surface. Bending will occur. Also must compensate for the widening of the tip as it goes deeper.

Default isolation = 0.15mm
this is an other place where you can compensate for all the variables above. I prefer not to do it here. In here I like to put the amount safety margin to apply to pad/via clearance.

Isolation step <= Tool width.

Maximum isolation = Default isolation + Isolation step.
This insures 2-pass milling.

Don't forget to set the feeding speed. I'm using between 60 and 100mm/min. Faster then that bits will brake, deformations in isolation will be produced and you don't want that.

-After a good gcode is achieved It's milling time. Secure the PCB to the table in a way that avoids (un)leveling (usually the PCB is not perfectly flat due to storage conditions).
Two ways to do this.
The pro way. Use a vacuum table.
The cheap and dirty (but totally works). Double side scotch tape. This the one I use. It works (period). Read this.
Home the bit with one of the to procedures I've mentioned in a early post (Eagle2GCode - Part 2).

And you are good to go. You should be ready to start milling.

Good luck.

Eagle 2 GCode - Part 2

OK seems my early considerations where partially wrong. The depth of the engraving bit must be ~0.05-0.06mm.

My initial considerations where wrong because I was not homing the bit properly.

Two ways to home the bit (that are actually almost the same).

Homing method 1 (cheap and dirty) - Use an power source of some kind to drive an LED (in series with a resistor if not adequate to drive the LED directly) and use the contact between the bit and the raw copper as a switch to indicate if there is contact between both.
Here is a schematic.

Homing detection schematic

Homing method 2 (more precise) - Exactly the same but using on of inputs in the CNC control board/Software.

Note: For some reason the EMC 2 is rounding my GCode floats to the 0.1mm scale. Don't know why this is happening but I'm upgrading to EMC 2.5.0 seems to have fixed it. Also I had to reconfigure the gcode-default.h file of the pcb-gcode script to write floats with 3 digits after the dot separator. This prevent rounding errors of the gcode interpreter in the EMC 2 reported in arc movements in mm units.

This is a picture of my first trials.

From left to right - 1st attempt had a bad configuration was doing it half sized, next is 1,2mm deep with multiple passes (excessive), next reduced number of passes (still excessive), next at 1mm with one pass (still excessive but acceptable).

These are my SMD trials (just a simple SOIC8 circuit and a resistor)

1st SMD trial

1st SMD trial detail (depth 0.075mm to deep in the majority of the circuit)

2nd SMD trial detail (depth 0.05mm to shallow in some places)

Here are a few videos from the machine working.








Despite the results are not perfect I'm getting pleased with it. There are still a lot of headroom and some tricks in my sleeve to improve this with minimal changes.
Let's see how far I can take this.

CNC Control Software

For the CNC control software I've chosen the LinuxCNC. It's free, open source, easy to configure and use, and there's a huge community that continuously improves it. There's a ton of documentation about how to configure this software but the quick guide is a good place to start.

For the PCB machine code generation I user the free version of Eagle PCB and the awesome pcb-gcode plugin.

The sync tuning of these two tools can do all the difference between a nice clean PCB and a bad one.

I'll keep dumping my tune-up's here, along with pics of the results.

Cheers.

Eagle 2 GCode

I'm now in a test and trial fase for achieve good PCB boards with my CNC.

After 2 kind of failed circuits, here are my early conclusions:

Engraving at 0.2mm depth is to much. 0.1mm is to shallow in some areas due to CNC table alignment defects and the PCB raw sheet defect (it’s not perfectly flat since the board may be bend due to incorrect storage positions and handling). 0.12-0.15mm should yield the best results (still to be tested).
I'm using a 0.1mm 10º V carbide bit to do routing isolation. Applying the formula for the cutting tool wide in this wiki I should consider a minimum tool size (width) setting of 0.15-0.2mm (that also compensate the above errors plus spindle and bit run out).
To keep it simple and fast I’ll be only performing the isolation routing and skip the copper removing in bigger areas. For this pcb-gcode plugin for Eagle should have the following configs:

Tool depth for isolation and Z Down - 0.12-0.15mm (value to be tested) (Z Down is negative)
Default Isolation (*), Maximum Isolation and tool Size – 0.15-0.2mm (this will insure a single passage – the isolation routing passage).

(*) Default Isolation is the tool offset from the track. For best results this should be the same as the tool size. ALWAYS do the Clearence check in the DRC tool of EAGLE. Set the DRC checking rules in the Clearence tab to at least 2xDefault Isolation + 1xTool Size. This checks for error of overlapping that otherwise may result in the isolation routes not being generated.

Also using Voronoi-Regions gcode generetor software can be a good solution to maximize copper area and conductivity.


I’ll test some more and post the results later.

Wah Wah Mods analisys



A brief history

A couple of years ago I (re)started my guitar playing only to put it aside (dam Battlefield :-P). In that intense rebirth of the guitar passion a acquired a couple of guitar pedals and was even building one of my one.
One of the pedals I bought was a Wah Wah Dunlop GCB 95 pedal with the clear mission of modding the hell out of it.
I never even got it out of the box until recently...lol.
Since I'm into a slow comeback to the electronics field I decided to resume this small project.

The Wah FX

I’m not going to explain how the Wah filter works. You can read it in this nice article, but in resume it’s a low pass filter with a peak on the cut-off zone of the response frequency curve (bode diagram). This reproduces somewhat a kind of vocalization of a “wwaaahhh” sound.
The wah circuit is pretty much the same across all pedals, with slight component variations. It uses a kind of LC filter with a circuit that reproduces a variable capacitor (what makes the filter move forward and backward is this C variation).

Here are some pictures of my GCB 95 circuit board (this is the I version and I believe the latest).

PCB front	PCB back
PCB overlay

The Mods

There are a lot of mods on the web so I decided to analyse them before grabbing the iron.

Here are the more popular:

True bypass mod
Vocal mod
Gain and volume mod
Mid range mod
Sweep range mod

Here are other not so popular:

FatWah mod
Transistor mod
Buffer mod


I’m using LTSpice to simulate de circuit. I’ll be basically be looking at the bode diagram (frequency response) of the circuit. I will not show how the mods are done since you can Google it. There's tones of articles explaining what to do. Next I'll present my findings.

The sound changers

Note: All the following diagrams will be present in relation to the original circuit. This means all the mods a showed alone (one at the time). At the end I'll combine the ones I'll most probably implement. All the simulations where done with the pedal value at one of the ends (heel down - the woo part of the wah sound).

True Bypass (Must have or not depends on you)

This actually is the only I did not simulate. It made some confusion in my mind for the first 2 minutes but after reading this article it all became clear.
Since the signal is not totally disconnected/separated (just the output is routed via a SPDT) you will end up with and filter in the way of guitar signal. That filter produces the effect known as “Tone-sucking”. Basically it filters a portion of the original sound muting some of the frequency components of the sound (usually the low and/or high end of the signal’s frequency).

The solution?

Install a good input buffer or true bypass the signal.
Input buffering resides in putting a high/input and low/output impedance between the signal to allow the effect circuit to draw more current from an outside source and spare the weak signal from the guitar. This is applied not only for isolation of circuitry but also to “give new life” to the original signal, when this runs through long cables (the longer the cable the more resistance exists which makes the signal weaker). See good buffers here (JFET are my favourite It makes the guitar very alive).
True bypass is just that The signal is completely shut of from the effect pedal, by input and output routing. There are several articles about doing this, some removing the input buffer and other keeping it. I chose to keep it because of the next mod.
So this is one I should do.

The FatWah (I’m pretty sure it’s a must have)

This is not very known and probably one of the most dramatically changing mods for wah pedals (from an analytical point of view), strangely not mentioned in many mod articles probably because it requires the buffer stage used in the GCB 95(luck me :-D).
First lets take a look at the original frequency response of my GCB 95.

Original GCB 95 bode diagram

As you can see the response is very more or less what you expected (if you read the wah explanation article). The only thing odd is the lower end of the frequency seems to be quite low (-16Db @ 110 Hz – A2 note playing a loose 5th string guitar in standard tuning I believe). The peak sits near 440Hz (A4).
Doesn't seem so much like the theoretical wah filter showed in the article right? Actually it's no wonder this happens. When you plug you wah pedal the sound of your guitar gets "thinner". This happens because the lower frequency spectrum of the signal is being getting attenuated.

So what does the Fatwah does to the signal. Lets look.

FatWah mod bode diagram

Amazing!! The lower frequency range got a nice bost. The down side (from the graphical analysis) is that the "fatness" came at the cost of some vocal strength of the wah due to the reduction in the Q.

never the less the sound should become much more "full".

The vocal mod (also a must have)

Vocal mod bode diagram

This mod changes the Q of the filter making the "hump" of the signal more pronounced. This makes the wah more vocal.

The mid range mod (already factory available)

I will not apply this one for a single reason. It's already in the GCB 95. Changes the Q less then the vocal mod but is not negligible. The wave signal change is similar to the vocal mod but less strong.

The sweep range mod (if detuned wah or instrument adapting)

This actually makes the "hump" slide in frequency. This is the tuning point for your wah. I read in a post in a forum that the sweet spot for a wah pedal is between 440Hz (A4) and 1760Hz (A6) (to octaves apart. This may be needed if your wah sounds dull. The inductors mounted on these puppies suffer from large factory tolerance (ranging from 300mH to 650mH). To tune it you can unsolder the inductor, measure it, calculate/simulate the best value for this capacitor and change it (by adding parallel or series to the original if needed). This is also used to change (a higher value) the wah to a bass wah.

The more subtle mods

The transistor mod (a maybe)

I've simulated with a pair of BC109C. This changes the signal slightly. Makes the Q higher but the gain is smaller. Making a smother more vocal wah.

The gain/volume mod (will not do it)

That's it. it makes the signal more stronger. if you don't remove the input buffer it's not needed. Can make the pedal pick up noise.

The output buffer mod

This is a double mod. This mod is designed to make the wah immune to the fuzz pedal which allegedly kills the wah effect. I have not given this subject much study (the big why) since I'm not a fuzz man my self. This supposedly suppresses the need of an input buffer (I'll be keeping mine for the FatWah mhuahahahah). If a JFET buffer is performed the changes to the sound will be minimal. The output will be something like output of the signal without the buffer multiplied by a 0.98-0.95 gain (will lose around 2-5% in volume).

My Mod selection

Applying the FatWah + Vocal + Middle (already present) I'll get this

My selected mods bode diagram

Seems a lot like the theoretical wah doesn't it? ;-P

Will give it a try and post the results later.

Note: There's also the fasel red/yellow mod. But I'll get to it in a later post.

Cya next time.       

CNC frame design considerations

The real challenge in building a CNC is to choose right type of CNC for the desired task. Remember something. The CNC will (a homemade low cost at least) not respond well to every situation. It will be good for the main type of work it was created for and be poor for almost everything else.

The lower priorities might change from builder to builder but the main goals are (in this order):

1-Rigidity

2-Light Weight

3-Vibration tolerance

4-Size efficiency

…

After building my CNC I ended up getting a CNC with:

1-Light Weight

2-Size efficiency

…

9-Vibration tolerance

10-Rigidity

In other words my CNC sucks big time lol. It will allow me to do very, very light milling or plastic printing and that’s it. My previous MDF CNC was more stiff than this one although it had other kinds of defects, like to many places where some degree of detuning was induced by vibration.

Despite all defects my CNC is very light weight. The frame itself is about 1/3 of the total weight (the rest is from the lead screw system and motors). Here is a 3D sketch of my machine.

I’ve learned this the hard way: IF YOU DON’T PLAN AHEAD EVERYTHING YOU WILL SPEND ALOT OF MONEY FIXING AND REBUILD THE CNC.

So what are my advices to build a CNC:

1º - What is the purpose of the CNC and what kind of materials are you going to work?

-Think this through it will influence the whole design. What’s the maximum size of the machine, the material it’s made of, etc…The harder and heavier the material you are planning to work the more important rigidity becomes. The bigger the volume of the biggest piece of material you intend to work more efficient the area of work the machine has to be and of course the harder the rigidity is to achieve.

-There are different typologies of CNC. The movable/fixed part (gantry, bed), type axis of support (fully, partial). If you’re not trying to reinvent the wheel check existing CNC plans (JGRO, and others) for references. My constant decision changing during the execution did not helped the final result. There are advantages/tradeoffs in every single option. Google-it, read learn.

Resuming the more popular solutions:

• Small milling jobs, and/or lightweight materials, with very high precision can be done in a movable bed CNC (X axis only). It’s quite easy to build to. Nice rigidity.
• Larger parts, and/or heavy materials call for a movable gantry with partial/fully supported approach. Rigidity harder to achieve.
• For very lightweight materials and very small jobs and small machine size consider a X and Y movable bed design. This design is more sensible to alignment issues.

From my research and trial/fail experience the Tweaky CNC seems to be a good starting point. The way the frame was designed seems to assure a good compromise between all factors and most situations above.

2º What are the available raw materials available to you?

For me this was a major setback. I don’t have access to extruded aluminum or steel profiles (like the T-slot). So I had to make everything from very basic hardware, that allied to my weak experience made a poor machine.

3º Budget?

Don’t fool yourself. It will be expensive no matter what. But it can be more or less expensive after all the design considerations taken.

4º Approach?

Draw, measure, draw again measure, check for flaws, measure and draw some more. PLAN PLAN PLAN. To keep the costs down plan the whole machine before building. This will reduce mistakes and unforeseen mistakes (that will surely happen in custom made designs).

This is a learning adventure. You will become better. Don’t be afraid to fail (and you will fail), but be smart (smarter then I was lolol). Research a lot before committing. It’s very hard to undo a poor decision, once the ball is rolling.

Here are some usefull references to start with:
CNC Basics
Linear Motion Ideas
CNC Forums
Free CNC Control Software
Self Replicating CNC Project
DIY CNC (one of the many exemples in the WWW)

Hope this helps.

CNC Control Box - Part 2

In the previous part I showed how I arranged the electronics for the CNC stepper motors inside a nice and very practical PC case.

I'm now in the process of attaching a plug-panel to easily attach/detach the motors from the control unit.

For this I’m using 4-pin DIN panel connectors.

Custom made connector front panel

4-pin DIN panel connector

For me the best spot to place the panel is right in the front of the PC case where the CD-ROM drive should be. I’m using an piece of aluminium (bought an 1000x25x2,5mm stripe of aluminium) that was cut to form the front plate that I’ve cut and drilled to fit the panel connectors.

After I riveted the aluminium plate in the case all that is left I to solder the wires and rivet the connectors to the plate, but you can get the general idea.

Check it out. ;-)

Riveted front panel

Almost finished box

ATTEN 858D Repair


Yesterday I decided to repair my ATTEN 858D air gun.

This is a cheap chinese hot air gun to solder/rework pcb boards with smd components.

Disassembled air gun (broke pins place)

The first time I use it got broken. This hot air gun comes with 3 tips to focus the air flow that get jammed very easily. While trying to remove one of those tips I 've broken two plastic pins that hold the resistive part of the gun in place (signaled in green in the pic). The broken plastic pins made the resistance stand floppy and potentially slide out the plastic holder.

Refractory glue for fireplaces

 
Man, that day I even chipped my tooth trying to remove the tip in desperation. Since then I've never inserted those tips to the end, instead I just let them sit on the edge of the gun.

So how do you repair a hot gun that reaches temps well above 400ºC?? Some special glue must come in hand for sure. The answer: Refractory glue used in fireplaces and stoves.

The one I used resists up to 1500ºC. More then enough.
 

Standart PC case screw

The idea was simple. replace the plastic pins with to screws (those used in CD-rom drives or disks to fix the drive in the case are fine). I've started by dremel the remains of the old pins and dig a little deeper to make a bed where the screw head would rest in place (alignment) with the holes in the resistance of the gun. Then I applied the retractile glue in the void ring where the resistance rests. I've made it slightly higher so this ring of glue could work as a clamp. If too much glue is applied I would then remove the excesses with the dremel tool.As you can see the glue filled the ring completely. After trimming this ring to make a tight fit I've screwed everything in place.
 

Glued screw to the resistence support

Make sure the 12 hours of curing are respected (I didn't and the glue broke near the screw, and had to (re)glue them).

After that the resistance was tight in the holder and didn't felt flimsy any more.

Hurray ;-)

CNC Control Box - Part 1

Control box (pre)wiring

This will be the control box for my CNC. I bought the kit from Keling Inc. on e-Bay, with the NEMA 34 steppers. The KL-4030 drivers will control the stepper motors in a 1/4 or 1/8 micro stepping configuration. It will all be housed in an old PC case.

Control box wiring final

With a resolution of 1.8 degrees per step (for an 1/8 micro stepping) will allow about 1600 pulse steps per revolution. The motors will by their hand be coupled to a RM1605 ball bearing screw. This means that every pulse the driver receives the axis will travel about 0.003125mm.

The 1/4 or 1/8 micro stepping will be determined by the amount of vibration caused by the motors.

Micro stepping trades torque for vibration and smoothness and even more important trades resolution for accuracy. Make notice I did not mentioned precision because the loss of torque can affect the ability to make the structure move and the motor can actually skid under the force of the unwilling linear motion system. And micro stepping is a real torque sucker. Check this article to see what I’m talking about.

Next will be the wiring of the steppers to the control and testing the micro stepping configuration.

The begining

I decided to start this blog to share some of my ideias and home projects. I usually don't like to waist a lot of time writing but I feel that I have to return some "brainstroming" to the web cloud.

The ideia is to share some of the sucesses and failures (there's nothing like a bad project to teach a leason or two), so that maybe somebody may take advantage of it.

Hope to write soon.