In real racing we referred to 4.11 as a low ratio while 3.50 would be a taller ratio. Taller gives you more top end speed.
I refer to the same in slot cars.
7/29 4.14 Lower 8/29 3.62 Taller
If I say I want a taller gear in the car..... I go to a smaller spur/crown or a bigger pinion If I want to go lower..... bigger spur/crown or smaller pinion.
If you were running 8/29 and I said "throw more gear in that car" I would be suggesting you go to a 7 tooth pinion. Can't run a bigger crown gear as you would have clearance problems.
Here is a good example 7/26 3.71 8/29 3.62
Both are pretty close in the overall ratio.
The 7/26 will give me more brakes, more punch, run cooler and will have less top end compared to the 8/29 which will have less brakes, less punch, run warmer and have more top end.
Short tracks and flatter tracks will like the 7 tooth pinion better than the 8 tooth pinion. Longer and more banked tracks will like the 8 tooth pinion better.
There has also been time where I have went to a smaller pinion due to concern of how hot the motor ran. I would rather sacrifice a bit of speed versus smelling smoke in the middle of the race.
The pinion size ( from a 8 to a 7 or vice versa ) change will put the motor in a different RPM/torque curve even if the overall ratio was identical, you could still see, hear and feel a difference in the motor performance.
It gets even crazier when you throw in the tire diameters also. A taller/bigger diameter tire gives more top end versus a smaller diameter tire.
Example 29 divided by 8 equals 3.62 divided by .825" ( tire dia ) equals 4.39 overall or roll out ratio 29 divided by 8 equals 3.62 divided by .815" ( tire dia ) equals 4.44 overall or roll out ratio
Remember as your tires wear out, you lower the overall ratio of the car. This is what is referred to as roll out of your car. I will cover how you figure that out in a min.
Adjusting Gear Mesh
Like most things with slot cars, there are a few ways of achieving the same thing.
These are 2 suggestions that work, and will at least get you going.
The process is pretty much the same for setting in-line Crown and Pinion, or Spur and Pinion setups.
For this exercise, we will describe the sidewinder and angle winder set-ups using spur gears.
For inline set-ups, the motor is screwed or soldered in position first, then the Crown gear is adjusted in the same manner as described below for setting the motor, by pushing the Crown gear towards the pinion, etc.
A: By Feel
Set the side clearance in the axle and lock the gear and wheel/s, so the axle spins freely with excessive side play.
Hold the motor in position and engage the pinion with the spur gear, then rotate the wheels in the normal forward direction and find the tightest point of mesh. Most gears are not perfect and will sit on the axle at a slight angle which makes the gear run slightly out of round.
Once you have found the tightest position, adjust the motor for clearance so that you can feel a slight back and forth movement in the spur, but the movement is hard to see. A bit hard to explain, but you can actually feel the backlash more than you can see it.
In my simple terms, set it so that you can just feel the movement, but can't see it.
Once you get to that point, screw or solder the motor in.
Check the clearance to make sure nothing has moved, and away you go.
B: Using a Spacer
Set the side clearance in the axle and lock the gear and wheel/s, so the axle spins freely with excessive side play.
To set the backlash in this method we will use spacer made from a thin piece of paper, or flexible plastic sheet about 0.05mm (0.004") thick. You will need a piece about 6mm wide x about 25 long (or longer) so that you can handle it OK. Have it ready for the next step.
As in the first method, hold the motor in position and engage the pinion with the spur gear, then rotate the wheels in the normal forward direction and find the tightest point of mesh.
Once you have found the tightest position, make note of where the grub screw in the gear is positioned, so that you can return the gear to that same point, move the motor away from the gear, then insert the spacer between the pinion and gear.
Push the motor firmly towards the gear clamping the spacer between the gears, while ensuring that the grub screw in the gear is in the same position as noted before.
Once you get to that point, screw or solder the motor in.
Remove the spacer, check the clearance to ensure it is OK, and away you go, ...hopefully.
It may take a bit of practice to work out what thickness spacer to use, and how hard to push the motor against the spacer, but once you get it right, you will be able to repeat the process without thinking about it too much..
This is a insiders tip I was told about a number of years ago by a team drive while I was running R/C carpet oval pan cars. Knowing this makes your car fast and more importantly stay fast all the time lap after lap if your times are dropping rerun the numbers and that will show you why!
Definition of rollout: Rollout is how far a car will travel with one revolution of the armature, often referred to as the rollout ratio. A larger number indicates a faster top speed/less torque and a smaller number indicates slower top speed/more torque.
Formula: Rollout = ( Tire Diameter * pi ) / Final Drive Gear Ratio pi is 3.141592654
To keep things simple, all you really need to know is: Roll out is how far a car will travel with one revolution of the armature.
Roll out Calculator
The calculator block above will allow you to better see the numbers in a simpler form to determine the roll out ratio, as well as the gear ratio, based on just a few inputs.
What The Results Mean
The tire circumference is the distance around the tread of a tire. In the default example, the results show it's 2.551 inches around the outside of an .812" diameter tire.
The 8 tooth pinion and 27 tooth spur gears in the example results in a 3.375 to 1 gear ratio. An 8 tooth pinion gear will turn 3.375 times in order to turn the spur gear one time. To put it another way, the motor will turn 3.375 times to turn the axle and tires one time.
The rollout ratio number given is not actually a ratio. It's a distance. In the example, 0.756" is how far the car will travel with one revolution of the armature.
I hope I didn't loose anyone with this! Its basically a set of numbers that you would get off of a chassis dyno! Its the numbers of where the motor contacts the ground in the car! Dyno stands for slot cars or real cars are a bit of a joke you can make the numbers up to look great and put that same motor in a car and never see the same results! Stands are Ok just not willing to bet the farm on the number print outs in most cases you will never see them on the track like you will with chassis numbers ,same motor different car different numbers every car is different! Hope this helps and keep it to your self or you may get beat!
General Soldering Information
Cleaning A good soldering technician observes the following stages of preparation for each job.
Cleaning all components, circuit boards, tools, and materials to be used for the soldering process.
Selecting the flux.
Determining the heat to be used and the length of time to do the job, which are based on the thermal mass of the parts to be connected.
Selecting the solder.
Choosing the flux remover.
Ask an experienced soldering technician, "What is the most important task to perform before soldering?" Many technicians, even those who have been soldering for years, will probably answer, "heat," "iron tip," "solder." They usually miss the most critical task of all: cleaning.
Clean the soldering iron tip, component lead or wire, the item that the component is being soldered to (board or terminal), tools being used to form the wires/leads, and even the solder itself.
Cleaning the Soldering Tip The soldering iron tip should be bright silver with no flux residue or solder on it. Any major buildup of oxide on the tip is removed by wiping the tip on a damp sponge before applying it to the area to be soldered. This shocking action steams off the oxide and leaves the tip pristine and in the proper condition for soldering. To start, you need the correct soldering iron for the job. For the majority of electronics work, this means a 25-to-30-watt pencil type iron with variable heat control. This makes is easy to ensure that the proper temperature is used for the work at hand. Soldering guns or irons with magnetically controlled heaters can possibly damage the very tiny and sensitive integrated circuits or ICs because of the electromagnetic fields radiating from these types of irons.
Tip Maintenance If a soldering iron does not have a thin consistent layer or solder over the entire surface, the tip has not been properly tinned. If the iron tips is not properly tinned, start with a cold iron, turn the heat on, and hold the flux cored wire solder against the tip as it heats up. Wipe off the excess solder, then shock the tip on the sponge before soldering. Do not wipe the excess solder, burned flux residue, and other contaminants onto the sponge. The purpose of the sponge is to shock the iron. If you keep dumping your excess solder, burned flux, and other residue onto your sponge, the sponge quickly becomes useless. Every time you then touch the sponge, you pick up the dirt you put there earlier. This adds contamination to the solder connection. The sponge should remove the thin layer or oxide that builds up when the iron is heated. Find another means and another place to remove the dirt from your iron. One method is to use a paper or cotton wipe, ones that will not be shred and leave particles behind, and very gently wipe the dirt from your iron. Then shock the iron tip to touching the dampened sponge. Some solder stations now have sponges with openings in the middle that allow you to wipe the excess solder off into the opening leaving the sponge free of contaminants that would otherwise end up on the tip of the iron. (Practical Hint: When you are not using your iron, make sure you leave a large lump of solder on the tip. This maintains the tinning on the tip, and the tip will last much longer. Many technicians mistakenly clean the tip before they put the iron into the holder. Leave the solder on the tip to protect it.)
Board Cleaning In a manufacturing facility, a relatively clean board is generally available, but this should not be taken for granted. If boards have been stored without protection against oxides and other airborne contaminants, cleaning may be required before you do any soldering. Wire terminals may need to be pre-tinned to remove oxides before a wire is installed. Dirt films on metals may consist not only of oxides, but sulfides, carbonates, and other corrosive materials from the environment. These will hinder solder flow or wetting of the solder onto the surfaces being soldered.
Component Leads and Wire Cleaning Component leads should be tested periodically for solderability. Take items from stock at random and test them to ensure that problems will not be encountered when components are installed onto the board. If necessary, re-tin the leads, then clean them off. Wire, tinned by hand or solder pot, should have the burned flux residue removed. If this residue is not removed, this contaminating material will be included in an unreliable connection. Clean the wire with a liquid cleaner. Items such as a pink eraser, steel wool or similar types of cleaning tools are not a good idea. The eraser leaves a gum residue which you now have to remove and the steel wool could actually remove the tinning, ect. Some technicians feel that the heat of the soldering iron cleans off the area to be soldered. This is a very common misconception. Some of the techniques used actually increase the oxidation rate. Make sure everything you use or solder is clean.
Flux A second very important item in preparing to solder is the flux. Flux has a very definite purpose: It prevents oxidation and removes the thin layer of oxide and the atmosphere gas layer from the area to be soldered. When the flux is applied to the area, it permits the solder to flow, or wet, smoothly and evenly over the surface of the lead, wire, or pad being soldered. It also improves the flow of heat, resulting in faster heating of the items are area being soldered.
Types of Flux There are various types of fluxes available. (Caution: Some types of flux should never be used on a circuit board because they corrode the board and the lead parts if the flux is not removed immediately. Acid- or zinc-based fluxes should not be used on a circuit board. Fully activated rosin flux, known as RA, also is not recommended for use on a circuit board.) The acceptable types of rosin flux include the pure rosin and the mildly activated rosin (R or RMA). This later flux is in common use today, with some inroads being made by so-called low residue and no clean fluxes. It has been found that some residues left behind from flux becomes water absorbent and should be removed within a maximum or thirty minutes after the connection has been made. RA flux is acceptable for use in tinning bus wire or component leads, but should not be used on a circuit board or even kept in the same room, in case it gets picked up and used by mistake. Activators will degrade the board and cause problems that would otherwise not occur. Most boards operate in an enclosed environment where there is considerable heat, moisture (relative humidity), airborne bits and pieces or dirt. The environment softens the flux left on the board, turning it into a gooey, particle-attracting, water-absorbing blob or useless material. This mess will become conductive as it absorbs moisture, resulting in leakage paths that cause problems in the operation of the equipment. In late 1992, a new water-soluble flux, developed originally by Huges Aircraft, received acceptance: final approval for its use was made in early 1993. The flux is made from lemons. This makes it very easy to clean, but the cleaning must be very thorough, or residue may cause corrosion.
Wetting If the correct flux is properly used, it will greatly assist all aspects of soldering and desoldering. It improves the intermetallic bonding and consequently the solder flow, which is one of the important areas of inspection. Poor wetting is usually the result of poor cleaning procedures or lack of sufficient heat. De-wetting problems relate to the material that is being soldered as a result of the intermetallic compound reaching the surface of the tinned area. The feathering out of the solder on a connection indicates that wetting has occurred.
Heat, Time, Mass The third item in preparing to solder includes three very important factors to be considered. These are the heat to be used, time on the connection, and the mass of the joint. Because not all connections are the same, consideration must be given to the differences in the mass of the joints and adjusting the heat and/or time accordingly. You should not use the same heat and length of time to solder a diode to a small pad as would be needed for soldering a wire onto a terminal. The diode would be would be damaged, the pad area where the lead is being soldered could be damaged, and the solder will be overheated. An iron that is too cold will result in a mush type of melt and poor wetting action. The maximum time from when a soldering iron comes into contact with the parts that are to be connected until the joint is finished should not exceed two to five seconds. In some cases just one second is the maximum allowable time. One other thing to keep in mind as far as heat is concerned is the oxidation rate of the soldering iron tip. At a normal temperature of 600 degrees, there is a certain amount of oxidation produced, depending on the time it is left unused and without any solder on the tip. At 700 degrees the rate is nearly ten times the level of oxidation and at 800, approximately hundred times. This oxidation acts as a barrier to the transfer of heat and therefore the proper flow of solder. Because we are not robots and because people work and react differently to what is happening, it is beneficial for personnel to be able to easily regulate the amount of heat being applied. Changing the heat of the tip of the iron should be the simplest task possible; for example, turning a dial. People should be able to recognize what is actually occurring as compared to what they feel is going on. Experienced solders have a genuine knowledge of what happened to a particular joint. They know by observing what has happened and can judge whether a joint will be reliable or will break down in a short period of time. To inspect solder connections, a 10X stereo microscope should be made available for managers and supervisors. They should also be trained to know what they should see during inspection.
Solder Types The fourth point in preparing to solder is to consider the type of solder to be used. Most companies and technicians use 60/40 solder. There is nothing wrong with 60/40 solder, but there is a better one- 63/37 or eutectic solder. Note that for the 60/40 solder, there is a time when the solder is neither liquid nor solid. It is in a plastic state during this period. It is very important that there be absolutely no vibration or movement of the connection when the solder is going through this plastic region, otherwise a disturbed joint will be the result. The 63/37 solder has no plastic period and reduces the possibility of a disturbed connection.
Heat Sinking Heat sinking is a method used to prevent the overheating of components, wires, or circuit boards. It usually is a small metal clip or clamp which is attached to the area between where the solder connection will be made and the item to be protected. The use of a heat sink for soldering some components is not required if the proper technique for soldering is followed to the letter. However, if the proper soldering technique is not followed, heat sinking becomes an alternative, but not a good one. Heat sinking is used mostly by persons who are unaware of the proper procedures. Compensation has to be made for the additional mass of the heat sink by increasing the heat and possibly the length of time. If this concerns a diode in a double-sided board in a plated through hole will a small pad area on each side, the chances of lifting a pad becomes greater by the millisecond. The heat sink would have to be placed on the top of the circuit board attached to one of the leads. Because the solder and iron are on the bottom of the board, it will be difficult to get the solder to flow throughout the hole and wet onto the component side pad - which is what should happen for the lead to be soldered correctly.
Cleaners and/or Flux Removers Item five is preparing to solder involves the selection of a good chemical cleaner. When it comes to the cleaner to be used for removing flux and cleaning in general, there is a wide variety of cleaners from which to choose. The cleaner must be able to remove ionic and non-ionic residue from anything that is being, or has been soldered. Check the contents of the cleaner, then check the Material Safety Data Sheet (MSDS) for information on the various chemicals involved. See if anything in the cleaner is carcinogenic (cancer causing). Even if carcinogens are present in only small quantities, you should try something else. Isopropyl alcohol (IPA), also known as isopropanol, is a decent cleaner; but there are others that contain blends of alcohol that are even better. The key is to find a cleaner that will not harm your work or - more importantly - yourself.
Various techniques have been tried ever since soldering was first used in electronics. The old saying "the bigger the blob, the better the job" can no longer be accepted. What was considered too meticulous and fussy is now the standard. Soldering can no longer be taken for granted. It is an art, and there are very few gifted painters. In 1989 a person who received two weeks of formal soldering training in 1981 said, "Soldering sure has changed in eight years!" This comment underscores the need for training from knowledgeable instructors who keep up-to-date with soldering techniques. The usual soldering technique is as follows: First apply the solder to the tip of the iron, then apply the iron to the area to be soldered. If the flux is not put onto the lead and pad first, the purpose of the flux in the wire solder is defeated. The flux dissipates over the iron tip and turns into carbon pieces rather than going onto the lead and pad to remove the oxides. So much for a clean, oxide-fee surface; so much for the wetting action; and so much for a good, reliable, problem-free connection.
Solder Application There are a few exceptions, but the following is a tried and proven technique. Believe it or not, it has been known for decades.
Before the iron is applied, solder of the proper size is placed beside the lead or wire and on the pad area or terminal to be soldered. A clean iron is applied, and no pressure is exerted on the area being soldered. Only contact with both surfaces is required.
The proper iron tip - clean, oxide-free, and heated to the correct temperature - is brought to where the solder has been placed, commonly referred to as the "point of maximum thermal mass." As soon as the hot iron touches the solder, the solder melts, permitting the flux in the wire solder to clean off the surface, as well as creating a solder or heat bridge that heats up the joint area very quickly.
The wire solder is now moved to the opposite side of the lead or wire, and the proper amount of solder needed to complete the connection is added. In either case the exposed copper end of the lead or wire must be sealed by solder to prevent oxidation of the copper, which occurs very rapidly. How do you know if you have the right amount? If the solder is concave and has an angle of wetting between 0 and 20 degrees, it could be a good connection.
For double-sided and multilayered boards this is the required technique, to ensure that solder has gone through the board onto the component side and wetted the appropriate area on that side. If this technique is not used, the chances of the solder flowing to the component side, without excessive heat being applied, are from very poor to none. Solder should only be applied to the solder side. The solder fillet on the component side of the double-sided or multi-layered boards is never applied on the component side. Some technicians might have learned that the best soldering method is to apply the iron to the item being soldered and then to add the solder. This method can reduce your chances of making a good connection in two ways:
When heat is applied to any metal, the metal oxidizes at a very rapid rate. The higher the heat, the faster the oxidation. This oxidation creates an insulating barrier that will not allow the solder to flow easily into the surfaces being soldered, thereby preventing good wetting action needed.
Flux in the wire cored solder should remove the surface gasses and oxides from the surfaces being soldered. If the solder is applied after the iron, the overheated flux becomes small pieces of carbon-type material that sit on the soldering iron. The flux never gets to do what it is supposed to do. Worse still, it flows into the connection area, causing the joint to become contaminated - a poor connection.
By applying the solder before the iron, you make proper use of the available flux and form a heat or solder bridge. This technique heats up the surface faster and allows you to complete the job properly in the shortest possible time. As you reduce the amount of time needed to do the job, you also reduce the probability of board damage due to excessive heat and time.
Amount of Solder When soldering a joint, it is not how much solder is added but the technique used to make the joint. Very little solder is needed in most cases. Usually about one-half to one-third of what is usually considered necessary is all the solder needed. The larger the blob of solder, the more difficult it is to determine if proper wetting of the soldered surfaces has taken place.
Reflow Soldering A second method of soldering is referred to as reflow soldering. This is normally used where plated through holes are not involved, such as the installation of surface mount items or repairing circuit board traces. The technique is relatively simple.
Unreliable Solder Joints Some examples of poor and therefore unreliable connections to watch out for are:
Overheated - de-wetting; lumps; dull; crystalline-like; looks as though sand has been thrown into the joint.
Cold - poor wetting; stretch marks between the pad and lead.
Fractured - poor wetting; stretch marks between the pad and lead.
Non-wetting - solder balled up around the joint.
Excessive solder - lead or wire contour is not visible and the shape of the solder is convex.
Insufficient solder - hole is not covered; copper end is not sealed; it is not as wide as the wire or lead.
De-wetting - usually excessive heat; solder balls up. This also occurs if an intermetallic compound is involved.
Other defects to watch for include:
Pinholes or voids - from dust, dirt, flux gas, improper heat, or other contamination.
Lumps and large holes - improper presoldering cleaning and outgassing from flux gas.
Damaged wire insulation - excess heat and/or wicking of solder under the wire insulation.
Characteristics Of A Good Connection
A good solder joint has very few things to look for compared to a poor one. A good solder joint shows the following characteristics:
Concave solder fillet
The end of the wire or lead covered with solder
Commonly known as "Donuts"
Mounting tires 101...ring the bell... class is now in session.
DO NOT USE CA GLUE to hold donuts on wheels. They will come apart.
1. Clean old wheels of old glue. Soaking them in laquer thinner will do the trick.
2. Clean wheels, both new and used in Acetone..... this gets rid of any oils from thinner, old glue or newly machined hubs.
3. Use 3-M Weatherstrip Adhesive.... the yellow snot stuff. The best trick is to squeeze some into a class jar then add 25 to 35 % Laquer thinner and mix. This stops the "stringing" of the glue when putting on wheels or donuts. This also thins so the donut will absorb the glue into the pores. Better adhesion.
4. Get some pipe cleaners...fuzzy stuff on a piece of piano wire.... you know what I am talking about. Craft stores sell them and they are longer and thicker. Bend the fuzzy stick in half and in half again. Now you have a real nice thick swab. Dip this into the glue and then slide in and out of the hole in the donut getting the glue to fully coat the inside of the donut hole.
5. BIG STEP HERE... put donuts on a sheet of WAX PAPER and let the glue dry. The donuts and glue will not stick to the wax paper. They will stick to your workbench if not using wax paper.
6. Coat the out side of the rim/wheel with glue mix. Stand on end with the set screw up in the air. Again set onto wax paper. let dry.
7. After a hour or two of the donuts and wheels drying, you are ready to insert wheel into donut. Get a small container and fill with some laquer thinner. The quickest way is to dip the donut into the thinner and let it sit for about 5 seconds or so then quickly slide wheel into donut. Leave set on wax paper and dry
It is preferred to dip the wheel, but for first timers, soak the donut. If you don't get the wheel "wet" enough and it locks up while trying to slide it together, you will have to soak the wheel and donut to get them apart. What a mess.
8. Another Big Step...let assembled tires set for at least 24 hours before grinding/truing to size.
You have lots of fun and possibly get quite a buzz making tires.
Cost only a few cents to do and your tires never wear out or dry up!
I use them mainly to make wider tires than are available other than by special order from the silicone tire makers. I like as wide a tire as I can get to suit my needs. I use old worn down sponge tires with the big and full hubs such as made by JK, HTK, or Alpha on my 1/24 cars. This gives me at least a .450" inside diameter for inserts. I like them worn down to about .750" for rears or trimmed down to that size. Adjust for your needs by trimming. I make them about .030-.040" smaller than the desired finished size. That allows about a .030-.040" coat of silicone. I have found this brand of silicone to work the best so far: Permatex black silicone sealant available in 3 oz tubes at the local auto parts store.
I prepare the tires by truing to exact size on a tire truer of commercial or homemade type, or a handheld drill motor and sandpaper block. When truing, make sure they have a true tire shape with rounded sidewalls and a rounded edge to resist grabbing the slot or braid in corners. It also makes the silicone stick to the tire better and resist peeling at the edges. Very important point in keeping them intact for awhile while racing them. After truing them up, now you must clean them very well. I use lighter fluid and a clean rag. Wet them down several times and wipe off any truing dust or tire goop material, so the rag shows clean when done.
Mount them on a spare axle near the end so you can easily grip them by the axle without touching the tire.
Mount the tire and axle in a lathe chuck or use a small drill press or hand held drill motor, held in a vise to have control, of how they get worked on. Make sure the motor does not spin them too fast or you will not get the silicone to stick and get some thrown off in your face (messy).
Once mounted in the chuck, open the tube of silicone, and with a clean dry finger, apply a 1/4 inch long, ribbon of the silicone as it comes out of the tube to your finger and then rub it in vigorously into the tire surface working the first coat in firmly to get seated it into the tire surface completely. It will take at least three to four applications of the same size amount of silicone to coat the tire well enough to build up a coating of at least .030 -.040" to come to the desired diameter of the tire.
When all coats are applied, clean your finger off well. I recommend a finger wetted with spit or (water) to be applied to the tire surface to work the silicone now on the tire surface into a smooth and complete coating. Especially working it down around the sidewalls to the rim. Make sure the sidewalls have a good coating front and rear.
The spit or water will keep it from sticking to your finger, so it can move the silicone around where you want it. When it looks good to you. Stop and get out a smooth flat surface such as the recommended Lexan sheet, 1/8 inch thick by at least 6-8 inches long. A piece of glass or a mirror will work as well. The sheet is then wet with water or (spit) and applied to the tire surface either by bracing the bottom side against the nearest hard surface, or as I prefer just hand-hold it against the tire surface and lightly press against the tire to make a good true flat surface. If you press too hard, you will run the silicone over the edge too far and have to work it back to the center again. This will take some practice to get it the way it looks best. If you get a sharp edge, wet your finger again and work the sharp edge back to the middle and use the sheet again to flatten and true again.
Once it looks right and true, watch the run-out, remove the axle and wheel from the chuck without touching the tire. Place the axle end, in an upright position in a hole drilled in a block of wood so it will stand upright by itself. Then when both, or as many as you have done, are mounted in enough holes, place the block of wood under a 60 watt lamp to warm them up for at least three hours to dry the silicone out. When dry, you can true the tire up, or just run them in. I find as I get practice at it I can get my tires to within .010" enough for racing purposes.Many of them are ready to run right after drying and just a few laps of track time will true them right up.
I realize this is quick and dirty, so if you have questions please ask and we will try to give an answer. It looks easy but does take some practice. Don't attempt this on wheels with inserts as the silicone will tend to wrap around the sidewalls and get into the inserts and get messy. On plain wheels it is easy to clean it out and then add the inserts after.
Lucks of luck,I have some of these tires still around and usable from some I made in the middle '80s. The silicone tends to seal the sponge rubber from the air and does not allow it to dry out as it normally does. They stay soft for quite a while while fully coated.
Later on I found I could make a fixture out some old aluminum I had access to. It fit in my lathe and does make it very easy to get the tire diameter very close to each other using the lathe hand dials. I then mounted a piece of Lexan in it to smooth the silicone out and and keep it very close to level from side to side.