I just had this great idea, but unfortunately I have not been able to try it out so far. It requires the plastic kind of pencils. It used to be difficult for me to find wooden pencils. All I could find was plastic pencils, which I never cared for. Now I went to three different stores, and all they had were wooden pencils.

You can kind of tell a plastic pencil from a wooden one because the 'wood' is a light uniform color. They break more easily. You can bend them somewhat. You can also melt them on lightbulbs. I used to make mushrooms out of the graphite all the time, when I was bored with my homework.

Well, here's the idea. I have some nice old potentiometers (thanks to Peter!!)...some of which are good and some of which are faulty. Also, I have a need for 1 and 2 meg potentiometers, none of which I have...or I do have some new Alpha ones, but they are terrible. The beginning and the ending of the resistance is really abrupt. They are for all practical purposes junk.

I took a pencil and an index card. I drew a nice black area about 1.5 inches long and 1/4 of an inch wide, and then measured it with a multimeter. It measured about 2 or 3 megs. Some of the potentiometers actually have carbonized cardboard strips that are easily removable. The type of control I am talking about has a high pressure wiper that presses against a stainless steel ring (or some other shiny metal that doesn't corrode easily). My idea would be to take a plastic type pencil and draw a resistance as required on an index card. Then cut it to size. Measure it. Bake it gently in the oven for a few minutes at about 200 degrees, which would melt the plastic type graphite into the index card material. Then re-measure the resistor and apply more graphite as needed. It sounds like a great idea. Resistors could be made and cut to size for other kinds of controls, too. Where an actual wiper comes in contact with the graphite, the pressure isn't that great, so I think that it would hold up well. I have to try it and see how well it works. It could be an answer to everyone's problems (for those who have the time and patience). For the riveted type of resistance material, the rivets would have to be cut with a sharp razor. Then the new resistance is inserted. New rivets are inserted with the pre-flanged side in contact with the resistance. The other side of the rivet is peened over--the side opposite to the resistance material. That way no damage is done to the resistance material.

Also, I bought that rear window defogger repair kit everyone talks about. The stuff is great, but it has no resistance. It would be perfect for adding taps to a volume control. Also, the glue sold in the package might work well for cementing on extra terminals for taps. According to the package, it, too, has very little resistance. Great stuff!!!

T.

Thomas, I think the idea should work. You could make linear or audio taper pots, depending on how you draw the resistance. I do wonder if, through use, the resistor will hold up to the abrasion of the wiper?

Old grid-leak resistors from the '20s were essentially made like you suggest. Some were even adjustable - by pulling out a little plunger that changed the contact with the carbon substrate.

The biggest problem with the old grid leaks is that they tend to increase their resistance. Ones that were originally 1 megohm are often wide open. I'm not sure why. Maybe over time, some of the graphite particles fall off the paper substrate?
Doug

:I just had this great idea, but unfortunately I have not been able to try it out so far. It requires the plastic kind of pencils. It used to be difficult for me to find wooden pencils. All I could find was plastic pencils, which I never cared for. Now I went to three different stores, and all they had were wooden pencils.
:
:You can kind of tell a plastic pencil from a wooden one because the 'wood' is a light uniform color. They break more easily. You can bend them somewhat. You can also melt them on lightbulbs. I used to make mushrooms out of the graphite all the time, when I was bored with my homework.
:
:Well, here's the idea. I have some nice old potentiometers (thanks to Peter!!)...some of which are good and some of which are faulty. Also, I have a need for 1 and 2 meg potentiometers, none of which I have...or I do have some new Alpha ones, but they are terrible. The beginning and the ending of the resistance is really abrupt. They are for all practical purposes junk.
:
:I took a pencil and an index card. I drew a nice black area about 1.5 inches long and 1/4 of an inch wide, and then measured it with a multimeter. It measured about 2 or 3 megs. Some of the potentiometers actually have carbonized cardboard strips that are easily removable. The type of control I am talking about has a high pressure wiper that presses against a stainless steel ring (or some other shiny metal that doesn't corrode easily). My idea would be to take a plastic type pencil and draw a resistance as required on an index card. Then cut it to size. Measure it. Bake it gently in the oven for a few minutes at about 200 degrees, which would melt the plastic type graphite into the index card material. Then re-measure the resistor and apply more graphite as needed. It sounds like a great idea. Resistors could be made and cut to size for other kinds of controls, too. Where an actual wiper comes in contact with the graphite, the pressure isn't that great, so I think that it would hold up well. I have to try it and see how well it works. It could be an answer to everyone's problems (for those who have the time and patience). For the riveted type of resistance material, the rivets would have to be cut with a sharp razor. Then the new resistance is inserted. New rivets are inserted with the pre-flanged side in contact with the resistance. The other side of the rivet is peened over--the side opposite to the resistance material. That way no damage is done to the resistance material.
:
:Also, I bought that rear window defogger repair kit everyone talks about. The stuff is great, but it has no resistance. It would be perfect for adding taps to a volume control. Also, the glue sold in the package might work well for cementing on extra terminals for taps. According to the package, it, too, has very little resistance. Great stuff!!!
:
:T.

Thomas,
You can do the same thing much easier with a thin cardboard substrate, double sticky tape and powdered graphite in white or black from most local hardware stores.

marv

:Thomas, I think the idea should work. You could make linear or audio taper pots, depending on how you draw the resistance. I do wonder if, through use, the resistor will hold up to the abrasion of the wiper?
:
:Old grid-leak resistors from the '20s were essentially made like you suggest. Some were even adjustable - by pulling out a little plunger that changed the contact with the carbon substrate.
:
:The biggest problem with the old grid leaks is that they tend to increase their resistance. Ones that were originally 1 megohm are often wide open. I'm not sure why. Maybe over time, some of the graphite particles fall off the paper substrate?
:Doug
:
:
::I just had this great idea, but unfortunately I have not been able to try it out so far. It requires the plastic kind of pencils. It used to be difficult for me to find wooden pencils. All I could find was plastic pencils, which I never cared for. Now I went to three different stores, and all they had were wooden pencils.
::
::You can kind of tell a plastic pencil from a wooden one because the 'wood' is a light uniform color. They break more easily. You can bend them somewhat. You can also melt them on lightbulbs. I used to make mushrooms out of the graphite all the time, when I was bored with my homework.
::
::Well, here's the idea. I have some nice old potentiometers (thanks to Peter!!)...some of which are good and some of which are faulty. Also, I have a need for 1 and 2 meg potentiometers, none of which I have...or I do have some new Alpha ones, but they are terrible. The beginning and the ending of the resistance is really abrupt. They are for all practical purposes junk.
::
::I took a pencil and an index card. I drew a nice black area about 1.5 inches long and 1/4 of an inch wide, and then measured it with a multimeter. It measured about 2 or 3 megs. Some of the potentiometers actually have carbonized cardboard strips that are easily removable. The type of control I am talking about has a high pressure wiper that presses against a stainless steel ring (or some other shiny metal that doesn't corrode easily). My idea would be to take a plastic type pencil and draw a resistance as required on an index card. Then cut it to size. Measure it. Bake it gently in the oven for a few minutes at about 200 degrees, which would melt the plastic type graphite into the index card material. Then re-measure the resistor and apply more graphite as needed. It sounds like a great idea. Resistors could be made and cut to size for other kinds of controls, too. Where an actual wiper comes in contact with the graphite, the pressure isn't that great, so I think that it would hold up well. I have to try it and see how well it works. It could be an answer to everyone's problems (for those who have the time and patience). For the riveted type of resistance material, the rivets would have to be cut with a sharp razor. Then the new resistance is inserted. New rivets are inserted with the pre-flanged side in contact with the resistance. The other side of the rivet is peened over--the side opposite to the resistance material. That way no damage is done to the resistance material.
::
::Also, I bought that rear window defogger repair kit everyone talks about. The stuff is great, but it has no resistance. It would be perfect for adding taps to a volume control. Also, the glue sold in the package might work well for cementing on extra terminals for taps. According to the package, it, too, has very little resistance. Great stuff!!!
::
::T.

Sounds good. I liked the plastic pencil idea better because it could be melted to the cardboard (index card), though I will give both methods some thought and experimentation. Also, the benefit of the plastic pencil method would be a smooth and fine grit resistance.

As far as durability is concerned, I've scraped away at some of the old controls. Some use a really hard material, and other use a somewhat softer material. The plastic graphite in a plastic pencil is somewhat durable. Only actual use will tell. I hope that it is a good idea. I can see the kind of potentiometer where the wiper wipes over a stainless steel ring lasting longer than one with a direct contact wiper, but, again, the direct contact wipers often use much less pressure. Some are quite delicate. The trick is to have no sharp edges. The kind of control with the stainless steel ring is under a lot of tension, and damage is done to the carbon even though no direct contact is made with the wiper.

.....We shall see. I wish I had endless hours of time. This could be pretty awesome. I'm going to try Target for plastic pencils...and maybe some other stores.

T.

Thomas,
Do you recall the old time drafting pencils (pre CAD)having plasticized lead inserts? I have 5 ea 5 inches long specifically called plasticized (FILMOGRAPH leads). They're about the same diameter as a normal wood pencil lead. They measure infinite resistance. The others (not plasticized) I have measure different resistance depending on their hardness. I measured an "H" and "6H" One was 8 ohms and the other was 16 ohms for the 5 inch lengths. I have several boxes and will share, if you can't find what you need locally. If you give me dimensions of the element you're trying to create, I'll even coat a piece of paper/cardboard with lead and measure the resistance of the 4 different hardness I have. As for wiping action, I repaired an old graphite rheostat a while back. The wiper was not a wiper, but a wobbling disk that simply made contact around the perimeter of the element as the shaft was rotated. This method would be ideal for an element that is simply coated instead of impregnated with carbon.

marv

:Sounds good. I liked the plastic pencil idea better because it could be melted to the cardboard (index card), though I will give both methods some thought and experimentation. Also, the benefit of the plastic pencil method would be a smooth and fine grit resistance.
:
:As far as durability is concerned, I've scraped away at some of the old controls. Some use a really hard material, and other use a somewhat softer material. The plastic graphite in a plastic pencil is somewhat durable. Only actual use will tell. I hope that it is a good idea. I can see the kind of potentiometer where the wiper wipes over a stainless steel ring lasting longer than one with a direct contact wiper, but, again, the direct contact wipers often use much less pressure. Some are quite delicate. The trick is to have no sharp edges. The kind of control with the stainless steel ring is under a lot of tension, and damage is done to the carbon even though no direct contact is made with the wiper.
:
:.....We shall see. I wish I had endless hours of time. This could be pretty awesome. I'm going to try Target for plastic pencils...and maybe some other stores.
:
:T.

Hmmmm.....well I'll have to work on this one for a while. I'm rather disappointed.

I was able to obtain plastic pencils. My parents had some in their multitude of pencil jars. One resistance I made (about 2.5 inches long and .25 inches in width) measured at about 100K, and varied fairly respectably. However, I was expecting a higher resistance. I drew another. I was aiming for 1 meg. A gray haze reads infinite. At a certain point it starts reading continuity. I finally got it to about 1 meg, but it'd only go down to about 100K when I brought the two leads really close to eachother (dragging one down the strip while the other remains stationary at one end). That's not what I want for a volume control.

T.

Thomas,
Interesting. I tried all the drafting leads I have, but could not get reliable coatings and mostly infinity measurements. A plain #2 wood pencil gave consideably better readings, but its difficult to make the coating reliably thick/thin over any given area. I also used coarse paper. One a linen finish and the other was matt card stock. I'll try the double sticky tape and powdered graphite later. When I did the graphite rheostat a couple years ago, I used messy craft glue on the substrate. At the time, I tried to get info on log/linear controls and when they were introduced, but finally gave up and concentrated on end value only

marv

:Hmmmm.....well I'll have to work on this one for a while. I'm rather disappointed.
:
:I was able to obtain plastic pencils. My parents had some in their multitude of pencil jars. One resistance I made (about 2.5 inches long and .25 inches in width) measured at about 100K, and varied fairly respectably. However, I was expecting a higher resistance. I drew another. I was aiming for 1 meg. A gray haze reads infinite. At a certain point it starts reading continuity. I finally got it to about 1 meg, but it'd only go down to about 100K when I brought the two leads really close to eachother (dragging one down the strip while the other remains stationary at one end). That's not what I want for a volume control.
:
:
:
:T.

I take it that your method worked well.

Earlier I actually used one of my strips in a control. It worked alright. I didn't actually test it in a radio. Still some reliability issues. What should be available is a lacquer carbon spray. Then anyone could either repair or rebuild potentiometers. Have it available in a couple of general 'resistances,' and include two types of spray heads--one fine and one spread, depending on whether it's needed for repairs or for a complete remanufacture.

T.

Thomas,
Tried the double sticky tape/powdered graphite method. Started with a 3 inch x 1/2 inch strip of tape. Just shook off the excess graphite, and measured about 300 ohms. Scraped it with an xacto knife several times, measuring after each, but never got above 3k. Started cutting away strips of the 3 inch length, and it got higher each time. Got down to about 1/16 width x 3 inch long with about 1.5 M. It might be worth a try, but tedious and time consuming. Can't imagine a 3 inch long pot though. When I did the graphite rheostat, I got about 50k with about a 180 degree arc x 1 1/4 inch dia, and maybe 3/8 inch width.

marv

:Hmmmm.....well I'll have to work on this one for a while. I'm rather disappointed.
:
:I was able to obtain plastic pencils. My parents had some in their multitude of pencil jars. One resistance I made (about 2.5 inches long and .25 inches in width) measured at about 100K, and varied fairly respectably. However, I was expecting a higher resistance. I drew another. I was aiming for 1 meg. A gray haze reads infinite. At a certain point it starts reading continuity. I finally got it to about 1 meg, but it'd only go down to about 100K when I brought the two leads really close to eachother (dragging one down the strip while the other remains stationary at one end). That's not what I want for a volume control.
:
:
:
:T.