I already have more project then I can do but...

A while back I posted about a guy who figured out how to connect an inexpensive digital caliper to a PIC.

At school we have a loft of dead computers junk that includes a few printers. I was thinking that one could salvage the carriage and drive motor from two printers to make the XY table for CNC drilling PCBs. Connect one caliper to each axis for feedback.

The drive motors I have seen are brushed DC motors that one could drive with an H-Bridge. The motor drives a toothed belt without gear reduction. With some amount of work one should be able to come up with software. The hard part would be driving the motor such that you did not over or undershoot the desired position. Perhaps on would need to replace the motor with a gear reduction motor aka gearmotor.

I do not know a lot about PID but I think most algorithms are intended for use with continual feedback. The interface only provides 3 reading per second. It could be interesting.

What do you think?

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I think you would be better off using steppers and dead reckoning. I'm pretty sure that the motors in printers are mostly steppers any way. Have you seen www.cnczone.com/. A very informative site.

Mike.

 

Yup, CNC zone would be a better place to ask about this.

EDIT:
But I am fairly sure that they are very much into steppers and would say exactly what you did.

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i've got more old/redundant pc's and printers than i have counted in a while. i have stripped a few of the printers with a view to doing just what you're describing, minus the feedback [at first at any rate ] all of the motors i've salvaged so far are steppers.
the head traverse is commonly driven with a direct drive to a toothed belt, to which the head is fixed. i want to go with leadscrews because i think it will allow for lower powered motors, and i'm not even slightly worried if that means low speed.
i may counter-balance the high speed drill to facillitate satisfactory vertical movement.
i'm also thinking about adding a rotary table of sorts, powered with a stepper, which would allow the engraving of cylindrical object such as napkin rings or maybe a cylindical, spherical or even 'mobius' pcb....
it will be a fun and interesting crossover project of electronics and light engineering.
like you i've got too many projects ongoing or waiting, so i hope you'll share your progress on this forum as well as the other.

 

Don't do it !!!!

You'll find yourself on the long expensive downward spiral constantly upgrading and building new machines to improve on what you've already got

I've still got to finish mine off but every time I start working on it again, someone offers me money to do some work for them and it gets put on the back burner again.

I've spent around £300 on mine so far and its almost finished but not in any state to actually do anything productive yet lol.

 

That is called a money pit.

There is a CNC mill at school that I can use for milling so there is no need to have this do anything other then drill holes in PCBs. My thinking was to attempt to build a $100-$200 dollar CNC PCB drill mostly from old parts.

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I agree.

First you'll be satisfied drilling a few holes. Drilling different dia holes you start thinking about something more practical like a KAVO-drive with automatic tool change. At that point at the latest your salvaged stepper motors are getting useless because of the weight of the drive. With the KAVO drive you don't plan to drill PCBs of match box size. So you need new spindles and and, and ....

 

The problem is that you will get the CNC bug and want to build bigger better machines lmao.

On a serious note, with a few dead printers (preferable large carriage dot matrix printers) you could easily build a machine that would suit your needs for under $50 if you're carefull with what you buy.

CNC "experts" will slate your accuracy and repeatability with their machines which drill and mill to 0.00000000000001" tolerances but if you take a step back and look at what you need it for (drilling holes in PCBs) then a 0.1mm accuracy (which you will more than easily achieve) is going to be more accurate in most cases than drilling by eye/hand.

A couple of other hints. If you use MDF then its possible to drill and tap holes.

Just drill the hole slightly undersized, tap it, soak the edges of the hole with cynoacrylate (superglue), allow to dry overnight and retap it.

I've had very very good results using this method on my machine.

Heres how mine went:

http://www.cnczone.com/forums/showthread.php?t=37790

 

I have already been bitten.

All I need/want for this unit is a small machine that can drill a 4x4 PCB. The $50 price tag sounds good. I assume there are people at cnczone that have done this?

The little CNC at work is a MAXNC which can only do non ferrous metals. If needed I could use it to help build the PCB drill.

The teacher that runs the shop at school is a machinest. Maybe I can talk him into getting an old bridgeport and converting it over to CNC. That would save a few of the intermediate steps

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The 15 Minute Printed Circuit Board! (+drill time)

 

http://www.engadget.com/2006/06/29/h...achine-part-1/ uses plastic kitchen cutting boards for the frame

 

Since you're using the MaxNC machine to mill the board, why aren't you using it to drill the holes too? Just curious ...
Jeff

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