Foam Lathe For Large Foam Rockets

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ThirstyBarbarian

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I built a rocket out of pink XPS foam insulation board a few years ago using a very labor-intensive technique of cutting many, many foam rings of different diameters, stacking them into the rough rocket shape, sanding down the steps by hand, and hand-laying fiberglass to toughen up the skin.

F0320D7B-A91A-4AEA-88BA-1B6854B7C64E.jpeg

It worked, and I really like the resulting large, lightweight rocket. But I’m never building one that way again! Too much labor, too much dust, and a relatively rough final result.

Instead, I want to build a foam lathe. I want to be able to mount the foam on the lathe and cut the rough profile of the rocket using hot-wire foam cutting tools and a template. Then I want to be able to use the lathe to spin the foam plug and sand it smooth using the template. I want to be able to fiberglass the rocket in place on the lathe and then use the lathe and template to sand the glass smooth.

Here is a really nice example of the kind of setup that can do the things I’m talking about:

http://speedmotionrockets.com/Foam Lathe.html

His results turned out great!

@David Schwantz built a very similar lathe shown in his thread: https://www.rocketryforum.com/threads/12-foam-nc.162415/#post-2057624

In that same thread, @3stoogesrocketry built a much simpler lathe setup powered by a 7 year old! https://www.rocketryforum.com/threads/12-foam-nc.162415/page-7#post-2105172

I don’t have a 7 year old, so I will probably need a electric-powered lathe. But my budget and the kind of lathe that my wood-working and mechanical skills might come up with are probably closer to the one made by @3stoogesrocketry than the one made by @David Schwantz . Not that there’s anything wrong with that, and it might end up being the alternative I go with.

To start, I’d like to get together a parts list, sources for parts, and figure out what it would cost to build something like the nice electric foam lathe. I’ve never built anything remotely like this and do not have the parts laying around or much understanding about what the correct parts are, correct terminology, or how to put it all together. I am also concerned about cost, so alternatives are definitely welcome. Any advice is appreciated! Thanks!
 
Hi Thirsty. Glad to see you are giving it a go. Really wasn't to bad to do.
First, there was hardly any dust other than on the floor right in front of the lathe. And I used my big Craftsman belt sander at times :)
I got a brand new motor off Craigs list for 10 bucks.
Pulleys from Fleet Farm. And belt. Any farm supply store will have them.
2x4's any lumber yard, don't even have to be the best.
Lag bolts to join everything, easy to use. Just screw them in. Although I do drill pilot holes to keep the wood from splitting as they are close to the edges.
3/4" cold rolled rod and pillow block bearings as center shaft. Bearings again at farm supply store. Got the shaft from a metal supply and just asked for the straightest one they could pick out.
I did build a movable center support for the shaft otherwise it kind of chatters.
Used a 3/4" collar, again farm store, and welded 3/8" x 4" bolts on it for the drive mechanics. The bolts just shoved into the foam.
Made a foam cutter. Details on other thread, but just ask what you may. I will answer if I can.
I used pink foam, the thicker you get, the less glue joints.
Used epoxy to glue foam together. Others have suggested other glue, but what I knew. It is hard to hot wire through, but just go slow.
I glassed with 6oz cloth and epoxy resin. many layers. Left foam in NC, removed it for the tail section.
My next one I will make the center section of the NC a body tube with CR's to both support the foam and center it on the shaft. This way you do not have to try to cut anything out when done, and you already have a great tunnel for adding nose weight.
Made a bass wood NC tip, epoxied on and then glassed over it.
Bought a stinkin big motor and let her rip:)
Any questions please ask. Happy to help.
PS, have you seen the videos of the V 2?
Dave.
 
Hi Thirsty. Glad to see you are giving it a go. Really wasn't to bad to do.
First, there was hardly any dust other than on the floor right in front of the lathe. And I used my big Craftsman belt sander at times :)
I got a brand new motor off Craigs list for 10 bucks.
Pulleys from Fleet Farm. And belt. Any farm supply store will have them.
2x4's any lumber yard, don't even have to be the best.
Lag bolts to join everything, easy to use. Just screw them in. Although I do drill pilot holes to keep the wood from splitting as they are close to the edges.
3/4" cold rolled rod and pillow block bearings as center shaft. Bearings again at farm supply store. Got the shaft from a metal supply and just asked for the straightest one they could pick out.
I did build a movable center support for the shaft otherwise it kind of chatters.
Used a 3/4" collar, again farm store, and welded 3/8" x 4" bolts on it for the drive mechanics. The bolts just shoved into the foam.
Made a foam cutter. Details on other thread, but just ask what you may. I will answer if I can.
I used pink foam, the thicker you get, the less glue joints.
Used epoxy to glue foam together. Others have suggested other glue, but what I knew. It is hard to hot wire through, but just go slow.
I glassed with 6oz cloth and epoxy resin. many layers. Left foam in NC, removed it for the tail section.
My next one I will make the center section of the NC a body tube with CR's to both support the foam and center it on the shaft. This way you do not have to try to cut anything out when done, and you already have a great tunnel for adding nose weight.
Made a bass wood NC tip, epoxied on and then glassed over it.
Bought a stinkin big motor and let her rip:)
Any questions please ask. Happy to help.
PS, have you seen the videos of the V 2?
Dave.

Thanks for replying to the thread!

That motor was a good find. That’s looking like one of the pricier items. What do you think the size of motor should be and the rpm? Some of the smaller motors I’ve seen are around 1/4 hp, and they turn about 1700 rpm. I kind of think it would be better if it were slower. Like maybe a LOT slower. It’s not the same as a cutting lathe, and it doesn’t need to be that fast for sanding. Maybe slower might reduce vibration too. I know I can reduce that speed some with pulleys, but what do you think the rpm ought to be?

Below is an example of the smaller kinds of motors I’m seeing. Is this on track? Or are there other alternative that might not cost as much?

https://www.surpluscenter.com/Elect...C-56C-TEFC-Leeson-Motor-C4C17FK4B-10-2696.axd
 
Oh ya, now what the h3ll do I do with it???

Lol! That can be a problem. I don’t have a very big garage, so being able to break it down for storage might be good. The best thing would be if I could find someone local who already had one they would let me borrow, or stored away like this, and they just wanted it gone.
 
This one is 1/4 hp and 1725 rpm. I know I figured out the shaft rpm, it is in the other thread, I want to say it was around 300 after the reduction by the pulleys.
 
You can use mine. Are you close??

Thanks for the offer, but I’m not close.

This one is 1/4 hp and 1725 rpm. I know I figured out the shaft rpm, it is in the other thread, I want to say it was around 300 after the reduction by the pulleys.

Ok. That’s what I’m seeing most of the time for smaller motors.
 
I did see the V2 flight video. Awesome! It was a really nice flight.

What I have in mind for the next foam rocket is sort of a lunar lander type design for J and K motors. I’ve built a few super light rockets for long burn motors that fly extra slow while under thrust. Light, but lots of drag. I was given some long-burn K motors, and I have a long-burn J. So I’m hoping to build a short 12” diameter rocket under 10 pounds for these.
 
Looks like the only difference is mine is 4.7 amps yours is 5.3.

That seems ok then. There is some kind of note in the description that says something about a letter designation that indicates a non-standard shaft or a non-standard frame. But it doesn’t seem to say in what way they are nonstandard.
 
What do you intend for the inside structure of the nosecone to be? If you're planning on, say, a 38mm tube with a bunch of foam discs glued to it, I think you can avoid using a long steel axle and use just the headstock and tailstock with the 38mm (or similar) tube as the shaft, basically how every wood lathe works.

If the intent is to use a hot wire to cut discs, laminate them on the shaft and then sand to shape, that should work. If the idea is to do the previous and before sanding to shape using a hot wire to get a 'near-net' shape, you'd need to be able to spin the lathe by hand with a friend or very slowly somehow.

When foam is involved, I prefer to minimize sanding, but maybe I haven't done it right in the past.

Also, as far as finishing goes, if you can get the foam smooth (likely by sanding. . . arrgh) but it has a lot of voids/air bubbles/rough sanding, a really thin/light-weight fiberglass will make most of those sins go away and not add much weight. It will also survive all of the road rash for moving and storage very well.

Hope you find the right plan and get the results you're looking for.

Sandy.
 
What do you intend for the inside structure of the nosecone to be? If you're planning on, say, a 38mm tube with a bunch of foam discs glued to it, I think you can avoid using a long steel axle and use just the headstock and tailstock with the 38mm (or similar) tube as the shaft, basically how every wood lathe works.

If the intent is to use a hot wire to cut discs, laminate them on the shaft and then sand to shape, that should work. If the idea is to do the previous and before sanding to shape using a hot wire to get a 'near-net' shape, you'd need to be able to spin the lathe by hand with a friend or very slowly somehow.

When foam is involved, I prefer to minimize sanding, but maybe I haven't done it right in the past.

Also, as far as finishing goes, if you can get the foam smooth (likely by sanding. . . arrgh) but it has a lot of voids/air bubbles/rough sanding, a really thin/light-weight fiberglass will make most of those sins go away and not add much weight. It will also survive all of the road rash for moving and storage very well.

Hope you find the right plan and get the results you're looking for.

Sandy.

Thanks for the suggestions!

In this case, I’m making the whole rocket out of foam, not just a nose cone. So the internals will include a 54mm motor tube, 5.5” chute bay, and 29mm nosecone core, plus some plywood rings and bulkheads to keep everything aligned.

I’m planning to cut the right diameter holes in the appropriate-sized squares of foam sheet to slide over the internal tube core for each section, and then cut off the excess using the foam cutting hot wire and template to get the rough shape for each section. That step is going to be similar to the way @David Schwantz roughed out his nosecone plug. For that, you just need to be able to hand rotate the plug into position for the next cut. It doesn’t need to rotate during the cut, which is great.

After roughly shaping the plug, then the lathe comes into use as an actual powered, rotating lathe. I will spin it up and use a sanding board for smoothing the plug. Hopefully, sanding will be minimal. I agree that sanding foam is awful. The more time spent with the hot wire, the less sanding there will be.

Given that the foam will be mounted on the internal structure of the rocket (motor tube, payload bay, nose cone core), I think the steel axle might be the best option. I’ll make some rings to keep the various diameter internal tubes supported against the rod.

This is definitely a work in progress, with plenty of trial and error involved. So please keep any suggestions and feedback coming.
 
Given that the foam will be mounted on the internal structure of the rocket (motor tube, payload bay, nose cone core), I think the steel axle might be the best option. I’ll make some rings to keep the various diameter internal tubes supported against the rod.

I haven't done this with rockets and I may be missing a specific step of your process, but I'll argue a bit, just to either point out an issue you might need to consider or to learn more myself.

I do pen turning which often uses a mandrel and bushings to center and turn the pen. For people who are OK with 1/32-1/64" misangle between joints on a pen, this is quick and simple. Errors that size on something 3/4" in diameter look horrific to me, so I tried different methods.

On a pen, if you make everything super square and then turn between centers, you get a much better result, IMO, using my equipment. There are guys who do great work with their own methods, but that's what works for me.

Turning a rocket in the size you're talking about seems to be similar in ratio of ID vs OD. I *think* if you make your tube cuts practically perfect, then all your turning will be 'perfect' without the steel mandrel/axle. You can even do each segment by itself instead of trying to do the whole rocket in one shot - just match the mating diameters. That should make the foam lathe much shorter.

Again, just thoughts, not facts and throwing them out to seed concepts/ideas. Obviously existing successful designs should be considered first.

Sandy.
 
https://www.rocketryforum.com/threads/level-3-project-black-brant-ii-scratch.64431/This is from my level (2.9) rocket I built. Not hot wire cutter but it worked great for the nose cone. Look about half way down on the first page I think. After using this technique, however well it worked, I'd advocate the hot wireyfoam cutter. Pictures don't do the mess justice...
-Ken

Holy wow! That’s a lot of styrofoam dust!

My first foam rocket, I also used my Dremel with a circle cutter to cut all the rings for the entire rocket. More than 50 rings! Plus all the rings that weren’t quite right and had to be tossed out. And I also used the Dremel to cut the inner circle to go over the internal tube. The rings alone made a lot of dust. And then I sanded everything down, and that was even more dust. This time, the hot wire cutter should save a lot of time, and a TON of dust.
 
I haven't done this with rockets and I may be missing a specific step of your process, but I'll argue a bit, just to either point out an issue you might need to consider or to learn more myself.

I do pen turning which often uses a mandrel and bushings to center and turn the pen. For people who are OK with 1/32-1/64" misangle between joints on a pen, this is quick and simple. Errors that size on something 3/4" in diameter look horrific to me, so I tried different methods.

On a pen, if you make everything super square and then turn between centers, you get a much better result, IMO, using my equipment. There are guys who do great work with their own methods, but that's what works for me.

Turning a rocket in the size you're talking about seems to be similar in ratio of ID vs OD. I *think* if you make your tube cuts practically perfect, then all your turning will be 'perfect' without the steel mandrel/axle. You can even do each segment by itself instead of trying to do the whole rocket in one shot - just match the mating diameters. That should make the foam lathe much shorter.

Again, just thoughts, not facts and throwing them out to seed concepts/ideas. Obviously existing successful designs should be considered first.

Sandy.

Sandy,

As a person who has never turned a thing in my life or used a real lathe, I’m definitely open to suggestions from people who have.

I imagine the design of the lathe tool and the technique are connected. Did you take a look at the Speedmotion link I posted and the technique used by @David Schwantz in the thread I linked to? Those are examples of the type of lathe design I had in mind and the techniques I was planning to use.

I’m open to other ideas. Can you give me some specifics on how you would design the lathe you are describing? If there is no shaft down the center, how are the two ends of the part anchored to the lathe, and how can you be sure different sections of the rocket are perfectly collimated with each other, and the faces of each section are perfectly square with each other?
 
Brad Vatsass built some amazing designs using foam.
This is from the archive of their now defunct web site... You can poke around and find more of their construction techniques.
Hope it helps.

https://web.archive.org/web/2015091...as.org/rtv/construction/styrofoamfixture.aspx

Thanks!

The Vatsass guys made some really amazing foam rockets. It’s too bad their website went by the wayside. Their projects were among those that first inspired me to try building with foam. And I think the rocketeer who built the lathe in the Speedmotion Rocketry link I provided used their template fixture idea in his own lathe design.
 
Here's a picture of what we used in a 2010 project. The nose cone outline is glued onto and then cut out of plywood. Those pieces form the sides of a box. The foam gets glued onto a replacement broom handle, with a crank attached to it. The router rides along the templates while someone else cranks away. Worked like a champ but required lots of cleanup to get rid of all the tiny pink bits. 😁 Ed's Amazing Nose Cone Machine.JPG
 
I made several using a drill for lathe power, using the bandsaw to cut rings of 4" foam to close and glues them together and used 60 grit sandpaper to rough and 220 for smooth
 
Here's a picture of what we used in a 2010 project. The nose cone outline is glued onto and then cut out of plywood. Those pieces form the sides of a box. The foam gets glued onto a replacement broom handle, with a crank attached to it. The router rides along the templates while someone else cranks away. Worked like a champ but required lots of cleanup to get rid of all the tiny pink bits. 😁 View attachment 479175

A basic box design like this might work for me if the other ideas don’t work out. I have the wire cutter, so I would not need the router, and probably would not end up with as much dust. Did you sand it freehand, or use the template somehow? And how about the fiberglass? Hand laid and hand sanded?
 
I made several using a drill for lathe power, using the bandsaw to cut rings of 4" foam to close and glues them together and used 60 grit sandpaper to rough and 220 for smooth

If I had a corded drill, I think I would give it a try. I don’t think my cordless would be great for this. And are drills supposed to run continuously? I would not want to mess it up.
 
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