Torch Pantograph / cnc

[Dawai]

I am building a torch pantograph similar to what Lowbuck tools used to make.

They will cut a straight line like a saw, or follow a pattern. I didn't get thier plans thou I wish I had.

TO cnc it, well since it is a supported bearing mounted very light load it could be done with printer or plotter motors simply. Turbocnc or other light duty cnc software, I have Mach3 on the cnc mill and love it. I may put it on the same computer and just pendant/lcd run it.

If there is interest I can post pictures of my build. Bearings were simple 7/8" outside, 3/8" inside, pressed into 1" tube after drilling on the lathe. A simple H looking affair on the back yoke, a simple loop on the front yoke. Top arm thou I wish now I had used tube is a open piece of track channel from a paintline trolley. If I had used a tube, I could have swiveled the cnc out of the way in about twenty seconds and back to motor-tracing..

Just as a simple saw to cut perfect straight lines it is worth building. I have been clamping a flatbar to my sheet to cut straight lines with the plasma cutter.. My plasma of late has the hiccups thou.. I have to open it up and blow the metal grinding dust out of it perhaps?

I'm dying to mount the henrob on it too.. ya seen it cut yet? It is directional like a swivel knife thou.

This whole deal will cost less than $100 to build.

David
ibewgypsie@hotmail.com


Warning... Unproven design yet: preliminary sketch.. cut list at metalillness site on the cutting forum..

[Lewis Gillies]

So post already!
Inquiring minds want to know!

[Boogiemanz1]

David, I would very much like to follow the build. I have always wanted on to cut brackets and stuff with. I have a torch burning place, and a Hi-def plasma withing 10 miles, but that still don't mean it is fast. Are you building a small barrel-top machine?..........john

[rockflyer]

Hi David,
I'm interested in seeing it done. Will you be posting the electrical interface to CNC it? In any case I'm sure there are a lot of people here that would like to follow along. Be fore warned I will have questions Thanks for sharing! Dick

[Dawai]

Maybe, if it has enough torque..

Two small airpax steppers, two opto22 ttl level boards tied directly into the parallel port.. Using wave (phase coil) drive on turbocnc.

It works on the bench. We'll see.. I got two gecko servo drives and 6amp motors/gearboxes. But I hate to use them on a easy to control system. I bought them for a gantry table I started about a year back. It runs on skateboard wheels on 1x2 channel, uhmw steering blocks keeps it centered on the track.. I got it started and the parts piled in the corner.. Hate to waste the drives.

I'll try these first since I have about four hundred in the drives and motors, these I only have about ten bucks in.



By the way, that is no workbench, it's our supper table about a hour after we finished eating, Don't I have a understanding wife?

[Dawai]

I used to use a Nand chip, tied into the pins from the parallel port, then off to tip120 transistors.. whole board if I can find the diagrams cost about twenty dollars to build.

There are tiny stepper drives on ebay, ($25?) thou I have not used them. Geckos are about the best Hobby type drive. I didn't have much luck with them running my bridgeport, the inertia of the massive table would generate voltage back into the bus bump it over the 80 volt chip limits on the geckos and fry them. LIL bitty motors and smaller cnc's never see that much generated voltage. It was pretty darned amazing that the 1000oz motors would run by a drive smaller than a pack of cigarettes. I got larger, regular chip style Larken drives on that bridgeport now. Now everyone has went to Bipolar drives, it basically push-pulls the coils reversing current directions through them, makes a motor stronger and faster.. THE old style Like I am doing here Unipolar coil energization is simple and cheap.. the cheap drives on ebay are unipolar..

www.geckodrive.com has the best explanations of drives, different motors and styles of running them.. Look to the stepper pdf files Marriss wrote there..

www.artofcnc.ca is Mach2/3 Art, the author of Mach software has the best cnc software explanations and manual on the net.. thousands of people contributed to the manual. He is a good guy.. So is Marriss of geckodrive. Both will take the time to answer questions of hobbiests.

About blind.. can't hardly read the sony LCD, gotta go off to bed.

I'll get some pictures of my loops and mast for the barrel top cutter tomorrow.. Easy to build.. if it works like I think.. I should've bought the Lowbucks plans.

[Bill B]

David,

Thanks for posting some thing (of many) that would never have occured to me. The dynamic braking of the motor would feed back to the circuit board!

I'm calling a friend that is building one to share this right now.

Can you disable braking or make the circuit open when power is not applied with programing?

[Dawai]

Basically you add a diode in, a transistor that turns on when the power in front of the diode is less than the rear, making the base of the transistor flow, dumping buss voltage to a "dump limit" resistor.. This only turns on when the motors are generating more than the transformer and bridge is supplying.. excess voltage dump during reverse flow through transistor, diode keeps all current from bypassing...

THIS is the way Marriss of Geckodrive did it.. His drawing.. I forget where, perhaps on the Turbocnc group at Yahoo, or the Geckodrive group.. or the Mach3 group?? I frequent them all, and forget where his schematic is..

I posted this during a discussion to a "member" who is using gecko drives on his bridgeport, along with a picture of a fried gecko.. He basically laughed in my face on the post and told me he knowed more about it than me.. I was polite. http://bbssystem.com/viewtopic.php?t=707 He will learn his own lessons the hard way, instead of from others.

The table on my 1976 cnc bridgeport weighs in excess of 300lbs.. when it is accelerated to 120ipm, as I have a few times and you stop, it pumps the voltage on up there.. THE 10 watt zener diode I had in there turned black and melted the terminal strip.. WOW.. When I fried the geckodrives the first time I was using my JOYSTICK program in visual basic.. cutting metal.. AND it was writing the movements to gcode for future repeat of the part.. Very little and improper accel-decell.

By the way, there is no reason to run my bridgeport that fast.. Silly actually.. Cutting UHMW or aluminum possibly, with the flood coolant going..

Back on the torch: Hooked to the opto22 boards TTL side.. Board 1. parallel Pin 2,3,4,5 motor #1 phase connections, moved coils around till in turbocnc 0111 , 1011, 1101, 1110 steps motor.. Has .5 amps going to motor.. you can hold it with two fingers, but I estimate about 50-100oz inches torque.. It takes about 250 for a XY drill slide to make a cnc pcb board driller, ask me how I know that?? ( my first cnc was a craftsman table top drill press)

TURBOCNC is one of the only programs I know that still supports coil phase drive.. You input XXXX for the other bits in the port output in the configuration file.. example... 1011XXXXXXXX is the 2,3,4,5 pins.. since the port is inverted, 2 is off, 3 on, 4 is off, 5 is off...

This may not be enough for the torch..

Can anyone do some soldering 16 pin chips in? My eyes are still buggered up.. I got a single chip that does the breakout board job..