This article was originally posted as a possible method to produce props as a response to the closing of Exact Scale Miniatures. With that closing the general ship modeling community and my R/C Warship Combat hobby lost a major source of excellent propellers! A new supplier has now filled that need, SWAMPWORKS Manufacturing. As this source is now available, no further updates will be made to this page (as there is no major reason for me to make up the jigs needed to make my own). Standard disclaimer: I have purchased SWAMPWORKS products and been satisfied with them, but have no other interest in their operations.  I will leave this page available, though, for anyone who may wish to "Roll their Own" props. As I never actually made a prop this information is speculative! It is however a reasonable (in my opinion) method. If someone does make a set of props using these ideas, I would gladly update this page if they are willing to provide pictures and comments!!

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Figure 1

The type of propeller, the construction of which is being described, is shown in Figure 1. This is a concept of how the propeller can be made. The actual machining has not been tried. The original supplier of this type of propeller has permanently stopped production due to the failing health of the owner, and he has stated that he did not pass on the methods or rights to another. This leaves a fair number of modelers with no further source for this type of propeller. I am therefore publishing this in hopes that another supplier will start production. I do require that anyone wishing to start production contact me and work out an arraignment for permission to use this method.

There are two main parts to this type of propeller, the hub and the blades. The hub must be turned on a lathe. The blades need to be punched out of sheet brass.

There are also two related ways the attach the blades to the hub, soft soldering or silver soldering. This method has to be decided on before the production of the propellers can begin. This is due to the different clearances required by the different solders. A soft solder joint requires an interference fit, Silver solder needs about .002 of an inch gap between the parts. Silver solder, however, does produce a stronger joint. Silver solder also requires a much higher temperature 1100 to 1500 degrees as opposed to 500 degrees. This higher heat can not generally be obtained with a regular torch. Sievert makes a larger torch designed for silver soldering. A basic setup would run about $150. A regular torch using MAP gas instead of propane may get the assembly hot enough. In all the articles I have read an Acetylene torch is strongly not recommended. It produces enough heat, but in too concentrated an area. You need to heat the whole assembly, not just an area. True silver solder is not the type sold in most stores, this "silver solder" is regular solder with some silver added to the mix. It is stronger than regular solder, but much weaker than true silver solder. In many cases a silver soldered joint is stronger than the brass parts it holds together!

Figure 2

Figure 3

Figure 4
Note 1: In both types of hub the blade slots (not shown) are cut 0.070 inches deep.

Given that the soldering method has been chosen, the hub can be made. Figure 2 shows a drawing of a completed hub, with a setscrew installed. Normally the setscrew would not be installed until after the blades were soldered on, but due to the vagaries of my CAD program I could not properly show just the screw hole. Two basic sizes of hub are needed for our use: A small hub for 1" and 1 1/4" props, and a large hub for the 1 1/2, 1 3/4, and 2" props. Figures 3 (small hub) and 4 (large hub) give the dimensions of each type. All blades will be made from the same thickness brass (0.025 inch). Table 1 gives the dimensions of the blades needed for each size propeller.

The most critical requirement for the hub is that it provides a centered mount for the blades. If the hub is not centered on the shaft extra stress on the propshaft and vibration will occur. The lathe can be equipped to cut the hub by following a premade removable pattern, held in place by a holder. Figure 5 illustrates this process The holder can be permanently attached to the lathe, such that it does not interfere with normal turning operations. So you position the bar stock, cut the hub to the pattern profile, and then cutoff the part. You then reposition the bar stock and cut the next piece.

Figure 5

The easiest way to make the hub would be to form the hub with the propshaft end toward the raw bar when finished, cut off the hub, and then drill the propshaft hole. If the outer diameter of the hub is a "standard" size, such as 3/8 inch and this area is cylindrical, then a collet with a depth stop can be used to hold the hub for drilling the propshaft hole. Alternately a special collet could be made to additionally have a depression to hold the hub by the tip thus increasing the holding power. This might require fabricating a special tool to form the depression in the collet, though a depression formed by the tip of a regular drill bit might suffice. Two types of collets are shown in Figure 6 a standard 5C collet and a collet to be used in a Morse taper 3 lathe spindle. Collets and their uses are explained more fully in the Equipment Required section at the end of the article. If we can live with a flat rather than pointed tip, these last considerations disappear. The hub can be turned with the propshaft hole at the exposed end. The hole could be drilled first, the hub turned up to the start of the flat tip, and then cutoff.

Figure 6

To produce the hubs the following sequence can be used:

1. Assumptions:

A. We are turning a 3/8" (1 1/2 to 2" prop) hub (instructions are the same for a small hub, but with a different collet and final diameter)
B. We are starting with a 3/8" round brass bar.
C. The hub is a pointed tip type.
D. The collet used for both steps is a standard 3/8" collet. A second dedicated 3/8" collet with preset depth stop or a custom made collet with a depression to hold the tip may be used to simplify the second operation setup.

3. Using correctly sized collet in the lathe spindle insert the raw brass bar and position it for turning.

4. Adjust the tool and pattern in relation to the bar.

A. This is done by moving the pattern follower to the cylindrical blade area section of the pattern. With the pattern follower touching this portion, adjust the tool so that it clears the bat by a couple thousandths of an inch. This insures that this area will always be the same size (3/8") for clamping when the propshaft hole operation is performed. We are relying on the accuracy of the collet, to insure concentricity between the hole and the blade mounting area.

A. As the pattern follower moves along the pattern the cutting tool cuts that profile in the bar. The pattern should be made so that the tool bit does not cut the cylindrical area where the blades will be attached

8. After the required number of hubs have been thus partially formed remove the bar, collet, and initial pattern.

9. Install the second collet, if used, and position the hub propshaft end pattern in the holder.

A. You can dispense with the second pattern and simply lock the carriage in place to face off the hubs at the same length each time. In either case a chamfer should be formed at the end of the hub to clean up any burrs in this area. In the case of just locking the carriage a second tool held in a four way toolpost or a quick change toolpost, or a form tool would be required.

11. Face the end of the hub based on the length built into the pattern.

12. Using a center drill then a standard drill cut the hole for the propshaft in the end of the bar. Tolerances as to the depth of the cut can be fairly loose as long as it is deep enough for the setscrew to engage the propshaft when the propeller is finished.

Alternately you could use a form tool to shape the hub instead of following a pattern. A form tool is simply a cutting bit whose tip is ground to the desired profile to be cut. These tools have to be custom ground (by you) and tend to chatter and cut slowly. The hubs you cut may also be possibly slightly different in size and profile, depending on the care taken while cutting and wear on the tool. The pattern method provides fixed stops, while the form tool relies on you stopping at the same point each time.

We have completed the lathe turning portion of the hub and now need to cut the slots for the blades. For soft solder the slots should be the same width or slightly narrower then the blade thickness. For silver solder they should be about .004 inch wider. The slot should ideally be the same diameter as the blade, but there are no slotting saws commercially available (that I know of) smaller than 1 to 1 3/4 inches in the thickness we need (about .025 inch). We will need a method to position the hub for the correct blade angle (pitch) as well as rotating it the proper amount for the number of blades desired.

This operation will more than likely be done on a drill press (using an auxiliary x - y table, as in a milling machine) or (preferably) on a mill. Depending on the size and model of lathe you have this could also be performed on it. A specially made holder with fixed locating indents or a spin index fixture will be used to rotate the hub the desired number of degrees for the number of blades desired. A spin fixture that uses 5C collets is available from Enco for about $35 to $40. It can be indexed in increments of 1 degree. Figure 6 shows a photograph of the spin fixture. A more expensive $300 to $1000 dividing head or rotary table can also be used. If a dedicated fixture is not made, I think the spin fixture, while a little harder to use than a rotary table, is the better choice. It will do the increments we need for 2, 3, 4, and 5 blade props, and is cheap enough that one can be used in a permanent setup just for this operation.

Figure 7

The spin fixture (Figure 7) is setup on a homemade adjustable (or fixed angle) angle plate set so that the slitting saw will cut the slot at the correct angle. Figure 8 shows a rough sketch of this arrangement. In this case the angle is 30 degrees from a line perpendicular to the propshaft centerline. The hub is gripped in the collet by the cylindrical portion and the assembly. is moved into the saw until the proper depth is cut. The assembly is retracted, the fixture spun the correct number of degrees, and the next slot is cut. A collet with an internal shaft that fits into the propshaft hole may help to steady the hub during this operation. Some experimentation may be needed. Both right and left hand propellers can be cut with the same setup. By feeding the hub from left to right into the saw, you produce one direction prop. By feeding the hub from right to left you produce the opposite rotation prop. A specially machined collet with a longer nose way be needed so that there is clearance between the saw and spin fixture. The Equipment Required section discusses how to acquire a machinable collet for this purpose.

The last step is to drill and tap the setscrew hole. A simple jig with a hole to accept the hub is set under a drill press and the hole is drilled and taped. A simple jig is shown in Figure 9.

This completes the work on the hub, now we need to punch and attach the blades.

I believe the blade punch will have to be fabricated, if you know of a reasonably priced unit commercially available please let me know! My concept for the punch is to use a length of angle iron as the body of the punch. A block is attached to the angle to guide the punch body. A thick plate is attached under the this assembly to hold the die. This plate is spaced away from the upper assembly so as to allow the brass sheet to fit between. An arbor press (possibly modified to accept one end of the punch) is used as the driving force. This setup is diagrammed below. Again no prototype has been built. If silver soldering is going to be used to attach the blades, use a center punch to prick both sides of the section that fits in the hub. This will provide a small area of interference fit to help hold the blade in place, while still providing the needed .002 of an inch clearance elsewhere. Figures 10.11, and 12 detail the punch.

Figure 10

Figure 11

Figure 12

My initial idea of how to make the jig used to hold all the parts during soldering is given below. Figure 13 shows a diagram of the jig. I choose aluminum as solder will not adhere to it. How much of a heatsink effect this will have I do not know. Also how well it will hold up to repeated exposure to the torch flame is not known. Covering the exposed alignment surfaces with an insulating material would be one solution to the problem. A sheet of non-asbestos material used to protect beakers from the direct flame of Bunsen burners might be a good choice. The block is machined using the collet spin fixture as for slotting the hub. The back of the fixture is drilled and taped to accept a bolt with the head cut off. This bolt is held by the fixture. The front is drilled to accept and position the base of the hub with a short length of rod to fit in the propshaft hole. This rod should not be overly long as it will act as a heatsink if it projects much into the hole. An end mill is used to cut the lands. This fixture may be sufficient by itself, or a clamping arm may be needed to hold the blades. One fixture for each of the two sizes of hub may be needed, or perhaps a removable center section for each size hub may suffice. A separate fixture will be needed for the 3, 4, and any additional blade configurations desired. The four blade fixture can, of course, be used for two bladed props. You also need to produce a similar set of fixtures for the opposite rotation props. If we consider only the 2, 3, and 4 blade we need four to eight soldering fixtures depending on whether the fixtures can hold both size hubs.

RECOMMENDED EQUIPMENT REQUIRED

I. Equipment requirements for the lathe:

1. Standard size collets compatible with the lathe spindle taper, a collet chuck made for the lathe, an after market collet chuck (~$300), or custom made collets made by operator. These are for holding the bar stock. Collets are designed to hold (generally round) work pieces to close tolerances. The end of the collet typically has three "fingers" that close on the work piece as the collet is drawn into a tapered seat. As the collet and seat are precision made the work piece ends up precisely positioned each time (generally within .0005 inch or better). Care must be taken that the pieces held by the collet are at most only a few thousandths difference in size than the rated nominal collet size (ie. 3/8ths, 5/16ths, etc.). Attempting to hold parts to large or small will result in damage to the collet and possibly the part!

A standard 3 jaw chuck is not suitable as it is closed by a spiral scroll engaging the teeth on the back of the jaws. This scroll is generally not made to close tolerances (generally just a cast piece with minimal machining) and therefore is typically only accurate to at best between .003 and .005 of an inch. Additionally this error is different for each different size piece you hold with it, as the jaw teeth engage a different spot on the spiral for different diameters.

2. Possibly custom made collets (one for each size of hub) for holding the semi-finished hub during the final steps. In the standard 5C size "Emergency" collets are available these have soft (not hardened) ends that can be machined to hold custom work pieces.

These are not required if a flat end on the hub can be tolerated.

3. Accurately positionable 4 way tool post, or quick change tool post set.

4. Three different lathe bits for a quick change or a 4 way tool post. One to face off the end of the hub before drilling, one to turn the profile, and one to cutoff the semi - finished hub. Additionally a fourth tool to chamfer the propshaft end of the hub may be needed.

5. Multitool tail stock adapter (Tailstock Turret). Figure 14 shows a picture of a Tailstock Turret. This fits in the tailstock and has a rotating disk which holds several different tools. As the disk is rotated each tool lines up with the center line of the lathe and workpiece. Each tool always falls at the same distance each time it reaches its' position. Thus you spin the disk to bring into position the tool you need for the next operation. These cost between $50 (Morse taper 2) and $90 (Morse taper 3) depending on the size of the tailstock taper.

A cheaper method would be to use dedicated drill bits and center drill. These would be swapped in and out of a drill chuck held in the tailstock. Both drill bits would have both a locating collar and depth stop permanently installed. The locating collar are used the position the item at the proper depth in the chuck, and the stop collars to insure that the drilled hole is always the same depth

Figure 14

6. A bar to use in the above tailstock adapter to set the position of the end of the raw bar before the start of the turning operation. If a tailstock turret is not used the methods below may be used:

A. If the single drill chuck method from 5. above is used, a custom made positioning rod can be used. The rod would have a locating collar turned on it so that it always ended up being held at the same depth when clamped in the drill chuck. As the rod will have to be moved back to clear the tool bit during turning a dial indicator may have to be installed to measure the position of the tailstock ram.

B. Alternatively the pattern for the hub could be made such that the tool can be run in past the end of the bar and the side of the tool can be used to position the bar for the next hub during the initial machining operations.

8. Pattern holder and patterns for the hub profile.

II. Equipment for mill or drill press for cutting slots in hub:

1. A home made or commercial adjustable (or fixed) angle plate.

2. Collet Spin Fixture for 5C collets (~$35 to $40). The spin fixture I got from Enco needed a slight modification. The fixture uses a plate with holes and a locking pin to hold shaft at the desired rotation. This plate is held to the shaft by friction only. I drilled the hole through both and inserted a permanent pin to keep these in alignment. As part of the hole had to be drilled through a hardened portion I used a solid carbide drill bit, which Enco had fortuitously sent me by mistake (I called them to point this out, and they told me that it would cost them more to mail it back than it was worth, so I could keep it).

3. Two 5C collets, one for each size hub. If both the large and small hubs have the same size cylindrical section on the propshaft end, only one collet is needed ($6 to $20 each, depending on runout accuracy). Runout is the measurement of how far the center of a piece held varies from the true centerline of rotation.

4. Slitting or screw slot saw, with arbor. The slitting saw can be gotten in a 1" diameter, the screw slot saw in 1 3/4". While larger in diameter, the screw slot saw is designed for this type of operation. The slitting saw is designed to cut a slit in thin tubing. Some trails are needed to determine which should be use in production. Either blade may need a custom arbor for our use. Figure 15 shows a 1 inch X 0.025 inch slitting saw blade.

Figure 15

5. Some means of accurately moving the angle plate and collet fixture into the saw. A milling machine already has this feature. A drill press needs an after market or operator made feed mechanism. This could be made from cold rolled plate for this simple use.

III. Equipment needed to produce blades:

1. Punch fixture.
2. Punch body and die for each size of blade.
3. Arbor press or other means of driving punch body.
4. Center punch for pricking "holding" marks if true silver solder is used.

IV. Equipment need for the soldering operation:

1. A holding fixture for each blade configuration and direction of rotation.
2. A high output torch if silver soldering with true silver solder.
3. An acid bath for removing the flux from a true silver soldered assembly. This may not be needed if a bright clean finish is not needed (if flux marks can be ignored).
4. A cleaner and brush to remove the flux from soft soldered or "store bought" silver solder.

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