Isolation
 

So I posted in another thread that we were having some isolation issues upon the start of the torch, and Mike asked me to say something about it here.

What we believe was happening was, as our torch is a high frequency start unit, the high frequency was passing through the ground on the table. This made the inputs on the BOB card trigger random inputs. Sometimes it would be estop, sometimes feedhold, sometimes limits. We were somewhat expecting this, and isolated the material we were cutting with some 2x4's. This fixed the problem immediately.

So the solution was to isolate the cutting surface from the rest of the frame. We made the entire cutting surface replaceable, so that if it got damaged in normal use it could be easily re-made. It is simply attached with two 1/4" bolts. Our simple solution was some 4" wide strips of fiberglass in between the table structure and the cutting surface, and some cool non-conductive fiberglass bolts from mcmaster to attach them together. This has effectively solved the problem.

I also think that if either the computer or the plasma machine had an isolated ground, it would help even more.

Edit: We also cut the MechMate logo, with our serial number, to attach to the side of the machine.

-Cody

Additional isolation note:
The control cabinet has a very unique BOB (MP3000) unit from CandCNC. This board, albeit performing well, is being used instead of the standard PMDX series board. The size of the control cabinet was a "little small" being a found item, thus the class moved the 56v toroidal transformer to a location just adjacent to the control cabinet and routed the 56vdc/12vdc/5vdc via conduit back to the box. This additional wiring practice helped eliminate the erratic flutter on the BOB inputs. The flutter was mostly eliminated by debouncing the inputs to a higher setting, but to be certain, the additional wiring was used and transformer moved.

Today is commissioning day and the local business BOB KING automotive group, which the project would not have been possible, will be present for a "cutting ceromony"!

Thank you to all that made this possible and for the continued generosity of the MM community for a design that is scalable and transferable to other cutting technologies.

Best Regards,
Sean Reish

Cool we need videos of that !!! THat would be greeeeaaaat !!!

Was there a reason for using this board instead of the PMDX ?

we wanted a torch height controller and went with a package from c and cnc. our torch unit lacked thc and arc good signal so we used the arc good transformer from them as well. both of these features really make the functionality of a cnc plasma, without them i would not be as pleased with the machine.

all in all it works well for the torch function. the machine moves like a dream. the torch is cutting very well.

I see that you used prox switches on the Z axises but did you also use them on Y and X?

Bryan that a look at the pic. http://www.mechmate.com/forums/attac...1&d=1272743890

top mid. and left corner.:)

Sorry I did not see the one on Y.

yep prox switches all around.

Ya thanks Mike #27 pointed it out. I had one of those can not see the fourst for the tree's going on. I get that way sometimes.

Couple questions
 

Hopefully, someone from this build still monitors this thread..

How heavy was your base table once completed.. Could a couple guys pick it up and move it?

Also, why did you choose to go with the dual Z slide system as opposed to some sort of 'change out' design on one slide? Is it too difficult to switch between router and machine torch? Is there some reason a single slide could not be used? Or was it simply a 'convenience' issue for you?

Thanks,
Mark

Mark,
Sean here...the University students are still on summer vacation, but I will be glad to answer your questions.

1 - heavy - yes. The material used for the 5' x 5' table was 2x3 - 1/4" wall rect tube. Table was lifted and rotated by an overhead chain hoist. 4 people can move it, flip it, etc....but NOT a 2 man job.

Dual Z slide was so the primary use of the machine was not violated. A plasma machine requires a special break out board and electronics not centric to the MM design.

Additionally, the Plasma can only do certain operations on steel plate.

The machine was designed to fabricate other machine components that require layout lines (like the laser parts you order for the MM).

The layout lines are "engraved" by the Z2 spindle head and center marks pointed for critical marking, then, the plasma head cuts the "not so critical" areas of the part, the rest are drilled by hand or otherwise. The Z2 spindle has a quick disconnect plate (per the MM Plans) for use of a single speed/purpose airdrill for center marking as well.

Plus, the aluminum sheet cutting is to be done on this machine.


You "can" do wood routing on the table, but not specifically designed for that purpose. Wood and sparks don't mix that well together.

Plus, the University has a 5'x10' SB ALPHA for wood cutting of stuff about 200 ft away in another part of the shop.

Sean

Beat me!
 

You beat me to it!

However, I could not have said it better!

Some of us are still here, lurking, and I will be sure to keep adding photos as time goes on, and school starts again.

-Cody

What do you mean by 'breakout board'? Don't see anything named that in the plans, but maybe I missed it...

Thanks,
Mark

Mark.

Break out Board (BOB) A computer board that allows for machine I/O to communicate with Host computer.

PMDX-122 is the design standard for the MM, but many others are allowable.
PMDX-125
CNC4PC (many options)
Custom boards
M3000 - DTHC , BOB integrated controller (which was used on the MechTorch)


...read the threads on Controller basics......read, read, read. :)

Cody and Jon,
I don't see any pictures of all the work you and Dr. Miller produced last week.......No slacking while the "other" professor is absent.

Thanks in advance.

Sean

my bad
 

Yea... this last week has been a liiiiiiiiiiitle hectic. But i will get a photo up tomorrow, two actually, we are cutting knives for a foam carver tomorrow! basically making big shaper bits.

Good to hear from you!

-Cody

Photos!
 

As promised, the first few files that we have cut on the machine this year.

Attachment 10424

Attachment 10425

Attachment 10426

More Cutting!!
 

Test cut using the foam knives, and some M-16 sideplates and clips for props!!

Cody,
Nice progress photo's. So, when are you installing the water pan that Dr. Miller suggested now that the machine has a home!

Nice cornice. How many passes under the cutter with the foam blanks?

Keep up the great work and photos.

Sean

about that...
 

Yea... well the machine will get a water table, as soon as the machine HAS a home. It is still in flux, certain people do not want to give up the space... So for now we are still dragging it out onto the loading dock to cut.

Just one pass with the foam cutter, final product was made with pink EPS, instead of blue, as it is a little denser, and had a finer finish.

-Cody

Update
 

So we were cutting our first real project for the automation department, and we ran into a small issue.
It seems that our plasma power supply has a problem, it is not putting out the correct amperage, and will no longer cut through plate, except at very slow speed.

So as it stands the mechtorch is down, but not out.

As a part of our troubleshooting, we are looking into re-working our control box, which could use some tlc. In working out the bugs and the particular setup for the DTHC the box was made to work, but it did not get documented, and became a bit messy in the process.

We are still having a much reduced, however still present, isolation issue. When the torch starts we sometimes see our spindle light turn on, and hear the contactor fire.

While a multimeter does not indicate continuity from the cutting bed to the machine frame, I am thinking that the high frequency start is still affecting us.

We are also still working on finding a permanent home for the mating, but encountering significant resistance, for reasons that are beyond my understanding. Once the machine gets a home, there will be some more rework, relocating the control box, etc.

-Cody

Out of touch for a while...
 

Hey guys. I know another round of students is leaving for the summer (tomorrow, i believe...) I was just wondering how the machine is doing. I hope someone is still around on campus for next year that knows about the forums. I heard through the grape-vine about the problems that came up, I hope they get fixed.

It's cool to look back on the build and see how far we came!

Rob V also says hey.

Video have been made private?
 

I like this build and its video was fun to show to show friends now its been made private?

http://www.youtube.com/watch?v=aKOLjw6q0Hs

follow the link

Hi all,

Just checked the videos, they should be all good to go now!

http://youtu.be/OSvdGoM5hTs
http://youtu.be/4cMzAEfQX0s

Let me know if they don't work!

-Cody

Thanks Cody!
I hope all is well and you had a good Christmas....

Best,
Sean