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Attempting to etch my own PCBs... accuracy problems
Hi all.
I hope this thread fits under this forum. The machine I'm using isn't really a DIY, I started with a Hermes V3400 engraver and have been hacking it apart to fit my needs, I began by replacing the electronics with an Arduino and a Raspberry Pi. I also changed out the steppers and limit switches to make it run more smoothly. Now I'm looking to find out what else I need to modify to make the machine capable of milling out PCBs with high accuracy.
Ok with that out of the way. I've attached an image of attempt number 1. Disregarding the uneven cut depth (I think the PCB moved after autoleveling), it seems like I'm having wicked backlash/inaccuracy on my Y axis. I am here because I suspect the design of the machine to be the culprit. The X axis screw goes through the center of the gantry. The Y axis, however, drives the gantry through a lead screw in the left side of the machine, in the housing. It relies on a steel rod in the right side of the housing that the gantry floats on, to keep the gantry straight. This seems like it could cause serious accuracy issues. My thought here was to make a whole new bed for the machine and have it driven by the Y axis. What do yall think?
EDIT: I just noticed that the image appears to be rotated 90 degrees counter clockwise. When looking at the image, the Y acid movement is left to right.
Re: Attempting to etch my own PCBs... accuracy problems
Hi Katemonster,
See this post could be of help.
https://www.cnczone.com/forums/pcb-m...44316-cnc.html
and scroll to post #15.
Cheers,
Hanspeter.
Re: Attempting to etch my own PCBs... accuracy problems
You do seem to have some serious mechanical issues. I don't think the design of the machine is the problem though - it did (presumably) work originally, so you should be able to make it work for engraving PCBs.
Can you feel any backlash or deflection if you try to push the spindle by hand?
Re: Attempting to etch my own PCBs... accuracy problems
Hi,
if you wish to have PCB features as small as 0.2mm then the backlash/accuracy needs to be about 10 times better than that, that is about 0.02mm.
That requires a nice machine and near zero backlash is required.
Craig
Re: Attempting to etch my own PCBs... accuracy problems
The good thing is that a PCB milling machine does not need to be particularly rigid, fast or powerful. It does not even need to be particularly "nice". All it needs is low backlash and low runout. I can consistently mill 0.25mm (10mil) traces with my toy CNC machine made of plastic. That means I can use chips as small as SSOP (0.65mm pin pitch).
Re: Attempting to etch my own PCBs... accuracy problems
If both axis are running on lead screws, just ensure it has anti-backlash nut installed and working.
I'm assuming your CNC is Hermes V3400 engraver.
How do you hold PCB on the bed?
double sided adhesive tape should help on a square and milled bed.
PCB's don't lie perfectly flat, except you have an auto leveling tool/software to do this for you.
Is your CNC controller Arduino or Raspberry Pi?
This was last year, I guess you must have resolve the issues.
Re: Attempting to etch my own PCBs... accuracy problems
Citizen of Dreams I am very curious about this plastic CNC of yours that can achieve this kind accuracy. I always struggled with pcb milling and I have an all metal chinese type CNC. Every new pcb is a headache. I have anti backlash nuts in the x and y axis but I've never had consistent results. Can you share a bit more details about your milling settings, engraving bits and your machine setup?
Re: Attempting to etch my own PCBs... accuracy problems
Hi,
I can second the low backlash/low runout requirement.
While my machine is made out of cast iron and steel, rigid enough for metal milling, making PCBs does not even come close to testing its rigidity.
When I designed and built it I bought and used three second hand ground C5 ballscrews by Karoda. Even second hand they were expensive but
I've never has cause to regret the money I spent, and even after six years use I still find myself thinking 'damn these things are good!'.
Likewise I bought a German made highspeed spindle and have never had cause to regret that purchase either despite the premium I paid at the time.
The backlash is near zero, certainly less than I can measure, but the 'lost motion' due to flex in the couplers is 4um.The spindle runout is 3um by spec
and less than I can measure. I can make boards down to 0.4mm pitch, even if I struggle to solder such chips. In fact I look on 0.5mm pitch as being
a challenge to solder but find that 0.65mm pitch is entirely possible and repeatable.
Low, or even zero backlash, and very low runout make PCB making easy, even enjoyable. I've been designing and making PCBs for sale in the way of
a business for over a year. I would make a new PCB at least daily, and sometimes two or three a day.
Craig
Re: Attempting to etch my own PCBs... accuracy problems
With the exceedingly cheap price of having them made with all kinds of features, cheap, is it really worth it?
PCBWAY cost me $2.00 for 10x 100mm x 100mm boards, doubles died with vias.
Re: Attempting to etch my own PCBs... accuracy problems
Quote:
Originally Posted by
joeavaerage
Hi,
I can second the low backlash/low runout requirement.
While my machine is made out of cast iron and steel, rigid enough for metal milling, making PCBs does not even come close to testing its rigidity.
When I designed and built it I bought and used three second hand ground C5 ballscrews by Karoda. Even second hand they were expensive but
I've never has cause to regret the money I spent, and even after six years use I still find myself thinking 'damn these things are good!'.
Likewise I bought a German made highspeed spindle and have never had cause to regret that purchase either despite the premium I paid at the time.
The backlash is near zero, certainly less than I can measure, but the 'lost motion' due to flex in the couplers is 4um.The spindle runout is 3um by spec
and less than I can measure. I can make boards down to 0.4mm pitch, even if I struggle to solder such chips. In fact I look on 0.5mm pitch as being
a challenge to solder but find that 0.65mm pitch is entirely possible and repeatable.
Low, or even zero backlash, and very low runout make PCB making easy, even enjoyable. I've been designing and making PCBs for sale in the way of
a business for over a year. I would make a new PCB at least daily, and sometimes two or three a day.
Craig
Nice, you inspired me to tinker a bit in my machine, I'll install an extra anti backlash nut that I have lying around in the z axis. I look foward to the day that I enjoy the experience of milling pcbs.
thanks it helped a lot
Re: Attempting to etch my own PCBs... accuracy problems
Quote:
Originally Posted by
Al_The_Man
With the exceedingly cheap price of having them made with all kinds of features, cheap, is it really worth it?
PCBWAY cost me $2.00 for 10x 100mm x 100mm boards, doubles died with vias.
I use it actually for smaller projects and quick solutions (and eventually prototypes), nothing fancy. I totally agree with the accessible price and quality of this industrial manufactured pcbs
Re: Attempting to etch my own PCBs... accuracy problems
Hi,
Quote:
With the exceedingly cheap price of having them made with all kinds of features, cheap, is it really worth
The reason I mechanically etch PCBs is not price.....as you've pointed out getting PCBs made conventionally is very cheap, but its not fast.
The PCB company may turn them around within a couple of days but then you have to wait two-three weeks postage from China.
A customer can approach me in the morning for a new tachometer PCB for his classic XYZ car, I can design the circuit and PCB , make
the PCB and populate it that afternoon, and charge the guy $350 for a custom made PCB. In the vast majority of cases that is the first and last
PCB you will ever make of that exact design, having multiple boards does not make me any more money Tomorrow it will be for a ZYX car, and
you can reuse the electronic design within limits, but the PCB will be different, say round rather than rectangular or something.
I have a catalogue of about half a dozen designs that I do frequently, say 20-30 a year. For those designs conventional PCB manufacture is
worth while.
If you really want to save costs then the PCB is only a small part of the cost. I populate all boards, most surface mount, by hand. If I want to save
that time and therefore cost then I would have to engage a manufacturer with a pick-and-place machine, but that's only effective for
production runs of 50 or more. I don't have the capital to invest in that manner.
Even if I did invest in conventional PCBs and machine populated boards, the customer might see a saving.......but would I make any more money....
probably not, and certainly not enough to justify the investment.
The whole point of customers coming to me to repair/remanufacture instruments is because there is no 'new made solution'....if they want their car
to pass a 'Warrant of Fitness' (New Zealand Road Safety Inspection) for which they require a speedo, and they can't buy new or secondhand
then my remanufactured solution comes into play. Before someone asks....it's not a legal (NZ) solution to use GPS for a speedo......who knows when the Yanks
decide to turn it off.
Craig