Conductive Paint or Tape on the Edges??

[rustnrot]

I am getting ready to find the edges of several boat planks to cut on the ShopBot. I thought finding conductive paint for the edges would be cheap and easy to find. It is $10 a gram or so! So has anyone used marine bottom paint (they say "60% copper") or something like that. How low must the resistance be for the probe to work? If in low ohms looks like will probably have to use tape?

[davidallen]

you can find copper tape with adhesive backing or metal tape for A/C ducts that work well. you'll need to figure an offset due to tape thickness but that's fairly constant.

[richards]

Tom,

I'm no expert on paint or on conductivity; but, I've designed and built enough computer circuit boards to worry about using anything that is not completely reliable.

In my opinion, conductive paint can/will cause problems. Every time the cutter touches the paint, some/most of the paint 'might' be fractured to the point that it breaks the circuit.

Tape 'may' be a better solution. I would think that it could withstand the pressure of the cutter touching it better than paint; however, if it were to be cut, conductivity would be lost.

Would it be possible to 'jig up' some aluminum or other metal in some way that the jig could be placed on the corner of the plank and a xy-zeroing routine run, compensating for the thickness of the metal?

Perhaps this is just being over cautious, but, I've spent hundreds of hours over the years tracing down a 'fractured' circuit.

-Mike

[billp]

Tom,
In the past some of us have tried bottom paint, with NO luck. We then tried the spray on "cold galvanizing", again, NO luck. At the Jamboree last year we tried Sculpt Nouveau's metal coatings, also, NO luck. I think the search feature on the Forum will bring up numerous earlier attempts of looking for a liquid solution, all to no avail. David's idea is probably the most likely solution. If it DOES work for you , please let the rest of us know...
I have a question though; if you have the probe, why do you NEED the paint? Can't you just run the edge finding routine? I use it regularly with good results. You just have to remember to offset your final toolpath (half the thickness of the probe tip I believe).

[mikejohn]

Bill
I'm sure you meant to say:
If you offset the above result by half the thickness of the probe towards the original material, you get the true shape of the original.
To get the final toolpath, you then need to do the normal offset of half the bit thickness.

.......Mike

[elcruisr]

Tom,
remember that 60% copper is really cuprous oxide, not pure copper. As an old shipwright and current 'bot owner I'd say why not just transfer the plank lines to the new stock and cut it the old fasioned way. If it's for a carvel planked hull you'll still need to cut or plane in the 5 degree bevel anyway right? If it's lapstrake a small error wil be unnoticeable.

'Bots are great but some things I can still do much faster the old way.......

Eric

[edcoleman]

Tom:

I've used the metal air conditioning duct tape that David mentioned with good results.

One thing to look out for is the fact that the back of the tape is not conductive; in other words if you try to tape up your part with multiple strips, you will need to make sure the face of each strip is electrically connected to the previous. If your part is small you will be able to get away with using one continuous piece of tape. What I have done to check the final "tape job" with an audible continuity tester to make sure that the tape is electrically connected around the whole perimeter.

Finally, I chuck up a 1/4" dowel rod into my router, run the probe routine to create a DXF file, and then use my CAD program to offset the toolpath. Adjusting for the thickness of the tape has not been an issue for me since my part tolerances are not that critical.

-Ed

[harold_weber]

There are tapes available with electrically conductive adhesive backing. One example is 3M #1181 copper tape; its sometimes offered on EBAY. I've used this tape on several jobs with no problems.

[rustnrot]

Thanks to you all for your testing of what will NOT work. I will use tape. FYI these planks are glued on a dimensionally repeatable and stable substrate (so far it seems to be anyways), a fiberglass plug of a Gar Wood speedster, circa 1934. Since the 1/4" thick planks are for looks only I choose to ignore the 5 degree bevel. My goal is to get the ShopBot to cut the planks and the bung holes ready for installation with, hopefully, minor, and eventually, no trimming. The bung holes are simply to allow a place for fasteners to hold the planks to the hull while the epoxy cures. They are then removed and filled with plugs. The pic is a gen 1 speedster. Gen 2 has all the deck beams etc. cut by the Shopbot. FYI when I said "probe" I do not have the Shopbot pressure probe, I am calling my piece of 1/4" rod chucked in the router my "probe".


2542

[trakwebster]

I make guitars, and must 'shield' cavities that hold the electric pickups. I've used conductive paint, and it kind of tends to flake if not covered with shellac, which would defeat the purpose of creating a contact.

However, copper foil should work pretty good, and although it's available through specialty electronics catalogs (like MSC or Mouser or DigiKey), if there's an OSH (Orchard Supply Hardware) store around, go visit the gardening section, where you'll find adhesive-backed copper foil sold as 'snail killer.' It's worth a try. (I have no idea of how much you will need.)

[ron brown]

Copper foil tape is used in leaded glass work. It might be worth a trip to the stained glass supplier.

http://www.anythinginstainedglass.com/metals/foil.html

Ron

[dingwall]

Hey Arthur. Welcome aboard.

[Mayo]

Not sure if it's still available, but alarms on store windows used to be made with a metal (possibly lead) foil tape. The breaking of the glass would cause a break in the continuity of the tape, which would set off the alarm. Perhaps Radio Shack or electronics supply shops might have it.