Mega/Pololu machined circuitboard build

Hey,

Not sure if this is the appropriate section- so let me know if its not!

I've been learning kicad and building an Arduino Mega/Pololu shield for my metal mendel build. Laying out these traces is a fun but tedious little puzzle. I know you can 'autotrace' but I don't like to cheat :p I'm also aware that several people are going this route but I wanted to do it myself mostly for the learning experience.

I have a cnc machine that I plan to use to cut out the pcb board but I have never made a circuit board on the mill before so any advice is welcome! I have researched it a bit, but not gone in depth yet. If people are interested and the board works well, I could do a small run of them.

The pololu drivers are situated in a way that I will be able to use a little cpu fan for cooling. I've got 5 drivers- 3 for movement and 2 for the extruders because I will have a support extruder!

I'm not sure what connectors I am going with- anyone have suggestions? I still have some flexibility in the layout there.

Thought I'd share and get some feedback.

Thanks,
Adam

I would set the Y stepper to something else then 1/16, but that is my opinion :-) I have 4 pololu's X,Y,E on 1/16 and Z on 1/4

You mean the Z stepper, right? Interesting point.

We create a gear reduction with that Z lead screw but I don't understand why that would mean you'd want to get rid of the microstepping. Seems like the higher resolution the better. The downside is speed? But why do you need rapid movements with the Z? It just steps a layer thickness as the model builds.

I'm trying to equate this to my cnc machine, which uses slightly bigger motors and have ballscrews on all axii. I use microstepping on them but now that I think about it, the stepper drivers I use are good quality gecko drivers and they "morph" from microstepping to full stepping as the speed requirements change.

mhensen, have you tried running your mendel with 1/16 on the Z and felt that 1/4 was working better?

Thorp,

I keep thinking how much easier it would be to have something like a Mendel drill all the holes for me (I still design mostly through-hole devices). Then I think of registration errors and how neat it would be to have the Mendel mill out the traces. Then I start looking at some numbers.

The standard 'small' through hole for DIPs and such is 0.030". A via can be half this size, or larger. So just to drill any through holes and all the vias that your design uses, you will need one or more 0.030" drill bits (they break fairly easily, don't buy just one). Next, with 0.030 holes for DIP pins, and 20 mills around that for pad, leaves only 50 mills between pins for traces. If you make your smallest features 10 lines and 10 mill spaces, that is more primitive than even the homemade Toner Transfer PCBs are doing these days. But it means you will need several 0.010" mill bits, and these must do a great deal of work under side loads, so are more likely to break as well as being smaller. If you can find some that are not more that twice the width long until reaching the thicker shank, they may last awhile. You will need to tune up you Mendel to make sure it can handle 5 thousandths of an inch, or 0.1mm accuracy to keep from cutting though traces made early on by cuts finishing the other side later in the process.

You may also want to check the archives of a Yahoo group formed specifically for making Home Made PCBs. I believe that they cover all home methods, from photo-resist to iron on or laminator based toner transfer to CNC drilling and milling.
HomebrewPCBs

Mike

Hi Mike,

I don't plan on using a mendel to make a pcb- I have a mill for that. I also don't plan on putting traces in between IC pins- baby steps First a working circuitboard, later I will see how small I can make things. Nice link. I will register.

I am having a bit of trouble generating the gcode with pcb-gcode and will explain. The board was designed in kicad. Gerber files were generated using 'plot' in kicad. I then used the "gerber to eagle script" found in Eagle PCB power tools so that I could open my pcb in eagle. Now able to open the PCB in eagle, I am using pcb-gcode (v3.5.2.11). "run pcb-gcode" runs the script, produces a plot with only the holes visible, not the traces. I also don't actually get a .nc file. I have tried putting a location after: "run pcb-gcode C:\..." and have run the setup. Nothing seems to do it.

I am also posting in a pcb-gcode forum as well and will report back.




Thanks all.

another thing you have to keep in mind when micro stepping is not just speed, but also torque, i forget if it is after 1/2 or 1/4 but after that you start to loose allot of torque, and also from what i have read repeatability can also be an issue with micro stepping, those are some very key issues you have to remember, that is why i am trying to just use .9 deg stepper motors. verses going to micro stepping

Hi

I had no end of trouble producing machined PCBs from gerber files. I must have spent hours on it. In the end I bought Coppercam. [www.galaad.net]

It has worked perfectly and whenever I have had a difficulty they have responded by return email. They even altered the software to cope with some strange requirement in the CNC I originally used. No connection other than a satisfied customer.

---

Regards

Ian

... i'm using Eagle with the "pcb-outline"-ulp or Target with the inbuilt exporter to my Isel-CNC-mill ... Eagle for free is only capable of 100x80mm-PCB's, Target can output all sizes and is 'only' limited to 2-sided and 250 pins ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

dissidence,
Interesting. Can you tell me what the x,y,z steppers are set to on the stock electronics? Full 1/2, 1/4, 1/8, 1/16

Even with 1/4 step on the x and y axis, 200steps/rev, .350r pinion the resolution is still almost 3 thousandths (.0027") which seems real high to me. 1/8 were looking at .0013" and with 1/16, .00067". 1/16 seems like the only way to go assuming the torque is sufficient, and its pretty easy to adjust that torque with the pololu drivers.

The Z axis is another story with that lead screw and gear ratio. With full step I am getting a resolution of .000134. I wouldn't run anything but full step on the Z.

emt,
I understand the difficulties you went through. I went through many of that same last night, and am still knee deep without a working solution yet. I'm not sure if I will press on with the current software or bit the bullet and get some software dedicated to the process.

VDX,
I will also look into target- though I hate limitations.

Or I could pull a dxf of the board into mastercam and be done with it.... That really doesn't seem like a whole lot of work to me.

here is what i could find micro stepping mendle is stock set to 1/2 step.

also keep in mind the more torque you add with the little pot the hotter the steppers run and the drivers too. so that is also an issue too.

Thorp, how far along are you?

1: Can you mount an extruder on your cnc machine?
2: Mendel is sort of a cult object; it is very good to make from plastic, but metal-mendel or wooden mendel is non-optimal compared to wolfstrap or Eiffel which are optimized for wood or metal.

---

-Sebastien, RepRap.org library gnome.

---

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

Dissadence, thanks and good point. I've designed my pololu board in a way that I can mount a heatsink/fan and am not worried about the drivers overheating.

Sebastion, I contemplated mounting an extruder to the head of my mill but decided to go the long route for several reasons. I was looking for a good project to get additional practice running parts with the mill and I found it I was intrigued with the design and open source concept an so it seemed the logical step.

Here are a couple pictures of my build. Extruder and heated bed are all that is left mechanically to do. I've been trying to take pictures along the way and will get a blog up once I've finished the build. I might also add that this isn't a standard Mendel. I've made my own design changes to make it easier from a machining standpoint and will go into detail with that in the blog.

[img409.imageshack.us]

[img299.imageshack.us]

I've made my own design changes to make it easier from a machining standpoint and will go into detail with that in the blog.
Want to tack them up in the wiki?

---

-Sebastien, RepRap.org library gnome.

---

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

i like your work though, you did make the board i was trying to make, but was unable to with my version of eagle. but i do like your board allot though, i would like to try it some time. but for now i should work on getting my beast running.

but over all good work on yours looks cool at the very least.

[ultimachine.com] you may find these handy they will help at the very least, i have ordered a set for my self from him, along with a few other things that i have found much harder to find. here in canada.

Edited 1 time(s). Last edit at 07/25/2010 10:48PM by dissidence.

Also, have you gotten the mega-pololu boards to work?

i have a board similar to his and i have been able to get it to work, though, my reprap is still a work in progress

i have a board similar to his and i have been able to get it to work, though, my reprap is still a work in progress
What's the MTBF, and how does it compare with RepRap's Gen 3 boards?

I'm trying to figure out if they're "official" or not.

---

-Sebastien, RepRap.org library gnome.

---

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

oh, i think there still out there on the edges, though they do seem to be gaining more momentum and more people do seem to be using them so far.

though i do think they will make it into the hardware soon,

though i do think they will make it into the hardware soon,
You're an official reprap developer, you're using them, the files are in the wiki, and the community is developing and supports them, therefore they are in the hardware.

I'm just wondering how much I should tell other people to use them.

---

-Sebastien, RepRap.org library gnome.

---

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

me i have no issues with recommending the pololu boards to other people. but i am not on the core team has far has i know, i know i have made my contributions on the wiki and so can you if you have anything to input.

SebastienBailard Wrote:
-------------------------------------------------------
> I'm just wondering how much I should tell other
> people to use them.

I was able to solder a wiring harness, wire up the stepper/Pololu/Mega, modify the code, upload it, and do a successful bench test in 5 hours. Then we put together this the next day... safe to say we are not using it cause it is "slow as shist".

But I think the Mega/Pololu combination will really take off if Ultimachine or someone offers johnnyr's board as a plug and play kit. It will put you in the 100USD - 120USD range for electronics, which is killer.

---

-Steve

i must say you are the first person who has ever commented on the speed of the pololu the guys at ultimachine use them on there reprap,

I've finally rounded up all the ingredients!

My attempts to mount the pcb in my vise proved futile as it wouldn't stay flat.

I made a tooling plate to mount the pcb to to keep it down.




And clamps to boot.



Without using the clamps.

Lifting in the middle.


I needed to clamp the pcb on all four sides and my tooling plate was a wee bit on the small side for that.







Looks to have about three thou runout.


The cutters I bought come to too much of a point- I think about three thou- not sure what I was thinking when I bought them. And so it broke.

Down .006" and try again

Opps- decrease that feedrate. Lower the Z another .004" rezero and rerun the program


Finally we get what we want


I now need to drill the thru holes and order the components :p

... i glued a piece of PU-foam on the bed, milled a flat with the size 161x81mm (for EURO-PCB's) 0.5mm deep for a really even base and fix the PCB's with sparx-screws simply in the foam.

I milled some twenty PCB's and engraved some pencils and nameplates with the foam-plate and could have done some more without exchanging, but then i needed the bed free again for my laser-experiments and removed the foam ... next time i need this again, i simply glue a second block on the bed and mill he even flat ...

My engraving bits are made from broken mill-bits and i use my first two of 10 since a year without loss ... for drilling holes i ordered a set of 25 hard-alloy drills with diameters from 0.5mm to 1.2mm.

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Interesting method of mounting.

Can you snap a picture or two of your engraving bits? I have lots of broken bits and a grinder to boot

1mm diameter is the smallest drill I have and I believe that that will destroy my pads. Everything is so much bigger on the computer screen!

Are the drills any different from a normal drill bit?

edit: I'm out to lunch. This first board was just a trail run. It's a singled sided pcb and the pcb I have designed is double sided.

Edited 1 time(s). Last edit at 08/13/2010 11:10AM by Thorp.

... i have to find my digicam for the images, maybe tomorrow

The millbits are shaped similar to the Gravograph-bits: first grind a half-cylinder, then a sharp cone-tip not complete around ...

The drill-bits have a shaft with 3mm diameter, so i can insert them in my millhead ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Hi

I had a similar problem with the board bowing. I eventually made the the pads and tracks as big as possible. I used 20 degree cutters from ebay #260606147316. They were sent from Hong Kong very quickly at a fraction of the UK price. The very tip broke on the first one I used but still cut a very narrow slot. I was able to machine deeper to cut the tracks at the edge of the board but as the angle was steep the extra depth in the middle did not destroy the tracks. For drilling I used a carbide PCB drill. I bought a box of reground bits some time ago and I believe they are also available on ebay.

When you build your board note that the 100K resistor for selecting micro stepping is too high. It took me a while to figure out why the motors were not moving the correct amount. I see Adrian has changed them to 47K on his latest drawing. That works fine.

---

Regards

Ian

... here i atached a photo of my engraving bits, a friend made from broken mill-bits ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]