||Model Rocket Motor Ramming Tool
This tool is used to make nozzles from Bentonite clay. They are
rammed directly inside the paper motor tube. Tubes are made from
posterboard and white or yellow PVA wood glue.
It can also be used to make rammed-propellant motors. These
motors are less powerful than rcandy motors, but are very quick and
easy to make, and work fairly well.
The rammer project starts with ordering tube. Here is a link:
0.5" OD x 0.125" WALL x 0.25" ID 6061 T6 TUBE
This tube came from Online Metals where it cost $6.00 per linear foot as of yesterday. One foot will make two rammers.
As you can see, it is 1/2 inch outside diameter, 1/4th inch inside
diameter, which leaves 1/8th inch thickness for the walls.
There is a light imprint on the tubing itself: "Kaiser Aluminum, Chandler, AZ"
This will be used to ram nozzles in a rocket motor casing of 1/2 inch
inside diameter. The nozzle throat will be 1/4th diameter.
2. 1/4th inch steel screw, 3-1/2 inches long. The last 7/8th inch is
threaded, the rest of the shank is smooth. I will cut off the
threaded part and discard it. OK, I'll put it in a jar with the
delusion that I'll use it for something, someday. But I won't use
it on this nozzle rammer. It doesn't need it.
3. Wood block. I like a nice piece of maple, oak, or other
good hardwood. But a sturdy softwood should do OK too, provided
it can stand being whacked with a mallet a few thousand times.
4. Epoxy. This is needed to glue parts 1, 2, and 3
together. I've found 5-minute epoxy to be adequate for this purpose, but slower
epoxy should be sturdier, and is preferred.
5. Varnish, to make the wood pretty and protect
it. Alternatively, you could spread the whole thing with epoxy,
but it's hard to get a smooth finish that way. I use Minwax polyurethane, but any good varnish should do.
Here is the collection again. Unmodified aluminum tube and screw
at top, cut and polished versions below. Wood block has been
drilled with 1/2 inch diameter hole.
The procedure includes cutting off a 1/2 inch section of the aluminum tube.
Heads-up on where we are heading... the short section of aluminum tube (hereinafter called: "the bushing") and the
cut-off-screw (which will be referred-to as: "the spindle") will be glued into the wooden block with epoxy to make
the spindle base. The remaining 5-1/2 inches of tubing will be trued-up and polished to make the rammer.
A short section of the bushing, 1/16th inch, is left protruding from
the wood. This serves to center the motor casing and hold it in
place as the nozzle is rammed.
The screw is a nominal 1/4th inch by 3-1/2 inch machine screw. I
don't think the strength matters much, but be sure to get one with a
Note that the depth of the screw head is not included in its nominal
length. This "3-1/2 inch" screw is 3-5/8ths inches in total
length. The last 7/8ths inch is threaded. The threaded part will be
removed, and the unthreaded shank used as the rammer spindle.
2. Flat file, for squaring up the ends of the hacksawed pieces
1. Hacksaw with a fine blade, 32 teeth per inch or so.
A vise is nice, but you could cut the tube while standing on it
with one foot. Watch those toes!
3. 220 or 320 grit wet-or-dry sandpaper, to smooth the filed ends, remove burrs, and make things pretty.
4. Optional, 400, 600 or 800 grit wet-or-dry, to put a nice polish on the metal parts.
I ordered the tubing in 1-foot sections.
Here I'm cutting a section in half to yield two 6-inch pieces. Each piece will make one ramming tool.
The hacksaw is aptly named. It leaves the end of the tube rough
and not flat. Gotta fix that. We need flat, smooth
ends on both of the ramming faces.
A flat file is used to square up the end and smooth it somewhat.
Critical observers may note that this is actually a half-round file.
Astute observers will realize that "half round" means that one side is flat.
Wise observers will understand that since you can see the round side, I must be using the flat side.
After a few minutes filing, the end looks a lot better. Flat, but still not very smooth.
For greater smoothness, wrap the file with fine wet-or-dry paper. I recommend 220 or 320 grit for this purpose.
Use the sandpaper-wrapped file to sand the end of the tube. This will smooth it considerably.
While you are sanding, be sure to go around the edge to remove any burr left by the sawing and filing.
If you wish, sand it again with finer paper. Here I've used 600 grit to get it fairly smooth.
We could go on to finer and finer papers until the face has a mirror
finish, but that is unnecessary for this purpose. The 220-grit
finish is good enough.
The tube is relocated in the vise so that we have a good shot at the next mark, 1/2 inch from the smoothed end.
This will be our next cut.
||So cutting proceeds, slowly and carefully, as straight and
flat as possible, to minimize the amount of filing that will be
So now we have two more rough cut ends to deal with. But only one of
them needs to be "nice."
The other end will be buried in the
block, anchored with epoxy, where only the maker will know how ugly it
Therein lies the rub. I'm the maker. I'll know it. So I'm compelled to
make both ends "nice." Darn.
So these ends get the treatment too. Here is another shiny one;
The lighting gives us a clue that the filing and sanding has resulted
in a slight "crown" or convex surface. That's OK. In fact,
I think that might be a good thing, as opposed to a perfectly-flat end.
Cutting the screw.
All we want from this screw is the non-screwy part. The threaded
section will be cut off. Last thread makes a nice starting groove
for the hacksaw. but watch your fingers! I think I've been
injured with hacksaws more than any other tool.
As you might expect, sawing off the threads has left a rough end. File it flat and smooth.
And while you have the file out, chamfer the end so that the shoulder
is not sharp. This will help the rammer "find" the spindle inside
the motor casing.
If you happen to have a grinding wheel, this is a good time to use it!
You an round off the end of the spindle, or even make it a point.
Shape doesn't matter much, as long as the shoulders don't have any burr
that will compromise your nozzles as they are removed.
Moving on to the wood block...
Here I've cut a little piece of red oak
2-1/2 inches wide, 4.116 inches long (golden rectangle!) and it came
3/4th inch thick.
A hole is drilled in the middle of it, 1/2 inch diameter, and 9/16ths
inch deep, or a little deeper. This depth is to accommodate the
length of the aluminum tube bushing we cut off recently (1/2 inch
length) plus the length of the screw head (1/8th inch) minus the 1/16th
inch that the bushing will extend above the surface of the wood block.
Whew! OK, I'll illustrate all that.
Or you can forget about drilling to a precise depth and just cut the
hole all the way through. Glue the spindle assembly at the proper
depth, then fill the hole on the bottom with epoxy. That's a lot
easier, so we will do that here.
By the way, you don't need a Forstner bit to drill this hole, although
that is the best bit for drilling clean holes in wood.
Here are the options, in descending order of preference:
0. Forstner bit
1. Brad-pointed wood bit
2. Spade bit
3. Metal-working spiral bit
4. Steel rod and propane torch (heat rod, burn hole)
5. Small fire. Place glowing coal on wood, blow on it to
burn hole, scrape out carbon now and then, replace coal and blow some
6. Fingernails. Recommend using a softwood if you intend to try this.
7. Teeth. I don't even want to think about it.
Mix up some epoxy. 5-minute epoxy should be OK for this purpose.
Coat the inside of the hole in the wood block, coat the screw
head and bushing, and the lower 1/2 inch of the screw shank. Be
generous with the epoxy - we will wipe off the excess later.
Since the screw shank is a loose fit inside the bushing, the extra
epoxy will make the assembly rigid once it hardens.
Insert the screw head and bushing into the wooden block. Use the
rammer to press it down until the bushing is only 1/16th inch above the
surface of the wood. Tap it lightly if needed, to get it to
the right spot.
OK, that looks about right. Now we must get rid of that excess epoxy before it sets.
A paper towel moistened with a little rubbing alcohol works well.
And while you are at it, give the spindle a good rub with the wet towel, to remove any epoxy that might be on it.
Much easier to get it off now than after it hardens.
OK, now we need to fill that open hole on the bottom. Let's hope our epoxy hasn't set yet....
Too late! It is globular. Downside of working with 5-minute epoxy. Oh well, just mix up some more.
The spindle is placed in a hole in the workbench, so that the base lies
flat. Epoxy is dripped into the hole until it is filled....
... plus a little. I intentionally overfilled this hole a bit.
Once the epoxy has cured, I will sand it off flush.
One more step. This one is optional, but I like it. Varnish the wood.
This block is small enough that I can just dip it in the can. It
will take awhile to dry, but this provides a very deep coat in one fell
It is hung out to dry. Look! It has a friend! Maybe they will mate...
No. This one already has a significant mother.
The rammer should be polished too, just to make it look nice.
Go over it well with that wet-or-dry paper to remove all the gray stuff
Pinch it in the sandpaper and twist, twist, twist to give it that "brushed aluminum" look.
||The Drill Press Alternative
The drill press is optional. But very useful.
Hacksaws don't cut straight. At least not when I'm using one. They tend to run off to
one side or the other as I cut, requiring more filing to get the end trued up.
Here I've chucked a 1/2 inch tube inthe press to cut it in half.
The idea is that I will hold a hacksaw against the tube as it
rotates, so the drill press does the sawing. It's not so much a
work-saver, but it should allow me to cut an orthogonal kerf.
"Orthogonal" is a big word for "straight."
But can you imagine the amount of vibration that I would encounter with
this setup? Lots! It will shimmy and rattle and be less
than optimal. I'd be better off with the hacksaw.
So I clamp a 1/4th inch screw firmly in the drill press vise, align it
with the tube, and crank it up until it is inside the tube. The
screw provides a crude sort of bearing, supporting the tube at the
lower end. With two-point support, there is little vibration, and
the tube is much easier to cut.
First, I cut the foot-long tube in half. Then I remove the bottom
half, crank the vise up to the remaining tubing, and cut off a short
section, 1/2 inch long to serve as the spindle bushing.
While the tube is still in the chuck, I take advantage of the spin and
hold a piece of 400-grit sandpaper on it. Gives it a nice
"brushed aluminum" look.
No, I'm not using my finger to wipe off the epoxy. I'm pointing at something.
So. The drill press is a really handy thing, and I recommend
having one. But in a pinch, these tools can be made with a
hacksaw, a hand-held drill, a file, and little more.
The resulting set can be used to make rammed-clay nozzles in 1/2 inch
diameter motor tubes and rcandy grains inserted afterward and sealed
Please check out the web page and the movies on making these motors.
Alternatively, this toolset can be used to ram dry-mixed propellant in
small motors. I have also made a few black powder motors using
this set, and they worked fine.