How do you cut your TTW slots?

[MoeFaux]

I'm a noob working on my first MP scratch build. I spent a several hours yesterday just cutting my TTW slots, and I'm hoping the wisdom of the masses here can show me a better way.

The method that finally worked for me (after some trial and error) was this:

1 - mark fin locations on BT (38 mm in this case) using marking guide, extend lines.
2 - wrap paper around tube, transfer fin marks to paper.
3 - unwrap paper, lay flat, center a scrap piece of fin material to each fin mark, then trace edges to get proper slot width while trying *real* hard to hold the scrap bit steady.
4 - measure and mark fore and aft slot ends on paper.
5 - re-wrap paper to tube, aligning all marks.
6 - spend the next hour cutting along marks with hobby knife.

I'm pretty happy with the end result, but it was awfully time consuming for only 4 slots, and I'd really like more precision in my process.

 

[afadeev]

What I found that works for me:

1). Print out the fin marking guide (I always model a rocket in OR first, then print from there) on regular printer paper.
2). Securely tape the fin guide to the paper tube.
3). Using a small metal ruler and a sharp hobby knife, trace the fin slot cut outs until you cut through the body tube.

This only works on paper/cardboard tubes.
For FG or CF ones, I make sure to buy them with pre-cut fin slots.

HTH,
a

 

[dr wogz]

4 fins are easier than 3

1. wrap tube with a strip of paper, mark overlap (Work on the straight edge of the paper!)
2. Fold in half, aligning end edge to overlap mark (this divides tube circumference in two)
3. Fold again (2*2 = 4) 4 fins are easier than 3.. or use a fin marking guide for multiples, or use a calculator & basic circle geometry & Pi
4. make an extra fold in paper , in between 2 of the folds, to make my 'launch lug / button mark (or use a compass & 'how to divide a line with a compass' once teh slots are cut)
5. mark folds, double check they are all equally spaced
6. Mark tube with my fin upper & lower locations (to denote how 'tall' my slot will be)
7. Re-wrap tube with my this strip of paper. tape paper together, not to the tube (yet)
8. make marks onto tube for the fins & LL (Launch Lug)
9. Slide wrapped paper up to & down to the upper & lower fin slot marks. Make a generous mark against the edge of the paper. (or just trace a line about teh tube at the paper's edge.)
10. I now have longitudal marks & teh upper & lower limits on teh tube.
11. use an angle or a door frame to extend those longitudal marks (a al Estes method)
12. I then either rotate the paper wrap the thickness of the fin and make another set of marks, or I use that line & rotate the paper left, make a mark, then right & make a mark, so my original line is now the center of the intended fin slot..
13. Extend these new lines, per the door or angle method
14. I should now have 4 rectangles drawn on my tube, equally spaced.
15. Cut slots.

Cutting slots: I find an angle held / taped to the line helps make nice straight & parallel cuts. Cut these first. then cut teh short top & bottom parts. A sharp blade & several passes. don't try to cu8t the slot in one pass. And I tend to cut a little inside my marked lines. Its' easier to sand a slot bigger than have the fin flop in a big hole

The 'Great Planes' sanding bar is a great tool for marking tube & cutting slots. It also is a good sanding bar! that is, if you can still find them.. If not a 1.5" x 1.5" aluminum angle is a good 2nd choice!

 

[MoeFaux]

What I found that works for me:

1). Print out the fin marking guide (I always model a rocket in OR first, then print from there) on regular printer paper.

I do wish I'd had a pre-made marking guide available. I even pulled one from some of Apogee's free resource and scaled it up. It was intended for 29 mm tube, so took 38/29 = 1.31, then printed at 131%. As you may be able to predict, this came out too small to wrap the tube completely. I assume this is because those numbers are inner diameters, and the difference in wall thicknesses between tubes means circumferences will have a different ratio. If only I'd just measured OD instead. . .

If you print a guide from software, will it only give fin center lines, or does it give the full rectangle based on tab size and fin thickness?

 

[boomtube-mk2]

https://www.amazon.com/Utility-Cutt...hvlocphy=&hvtargid=pla-4583726542710274&psc=1

When it comes to the actual cutting of the tube I have always used the above.
Inexpensive, incredibly sharp, with an angled "Point" that is just perfect for cutting tubes.
And when they get dull, just snap off the leading edge and carryon.

By extending the blade only one "Bit", you'll know what I mean when you see one, you can grip the knife just behind the bade for great control of pressure and movement.
I have never found anything that is remotely as good for this particular job than these cheap throwaways utility knives.

 

[Scott_650]

I do wish I'd had a pre-made marking guide available. I even pulled one from some of Apogee's free resource and scaled it up. It was intended for 29 mm tube, so took 38/29 = 1.31, then printed at 131%. As you may be able to predict, this came out too small to wrap the tube completely. I assume this is because those numbers are inner diameters, and the difference in wall thicknesses between tubes means circumferences will have a different ratio. If only I'd just measured OD instead. . .

If you print a guide from software, will it only give fin center lines, or does it give the full rectangle based on tab size and fin thickness?

Tools on the Payload Bay website include a fin marking guide generator https://www.payloadbay.com/page-Tools.html. Good stuff and fairly easy to use.

 

[afadeev]

I do wish I'd had a pre-made marking guide available. I even pulled one from some of Apogee's free resource and scaled it up. It was intended for 29 mm tube, so took 38/29 = 1.31, then printed at 131%. As you may be able to predict, this came out too small to wrap the tube completely. I assume this is because those numbers are inner diameters, and the difference in wall thicknesses between tubes means circumferences will have a different ratio. If only I'd just measured OD instead. . .

This happens to me too.
The diameters of paper tubes are nowhere near as precise as you might expect, and vary from batch to batch.

This happens not only with scratch builds, but with an occasional Estes kit - you cut out the fin alignment guides, wrap them around the body tube and discover that that overlap tab is either too far, or too close. In other words, paper cut-out diameters did not match that of the tube.

With OR model, you can scale things up or down to match the measured tube diameters, then re-print the guides.
With Estes guides, I just % scale them on the copier. Usually, copying at somewhere between 95%-105% (some trial and error may be required) fixes things.

If you print a guide from software, will it only give fin center lines, or does it give the full rectangle based on tab size and fin thickness?

It looks something like this:

 

[waltr]

Payloadbay or OR fin guides.

Put a second mark equal to the fin thickness next to each fin mark.
Wrap and mark two places for each fin.
Remove fin guide and use an Angle, Alum 'L' or 'T' sander.
Mark the fin cut lengths.
Mark start & stop of fin slot.

Use the metal 'L' again to guide the knife (X-acto) to cut the log slots using multiple passes..

 

[teepot]

I use my Dremel with a cutoff wheel. I use a payload bay tube marking guide to mark the slot center. Then measure the fin width and using an aluminum angle I extend the lines. The cutoff wheel goes thru cardboard like a hot knife thru butter and the cuts are straight. It is very fast. Just a couple of minutes to cut the slots.

 

[Cape Byron]

I do it this way. (Let me know if this doesn't make sense...)

1. Print your Fin Marking Guide from Payload, OR, whatever.
2. Measure the thickness of your fin stock accurately. Lets say 2 mm.
3. Measure the 2 mm from one fin guideline only and mark with a pencil. This is your offset.
4. Wrap the guide around the BT as usual and mark fin positions. Don't mark lug positions yet.
5. Rotate the guide on the BT until one fin mark on the BT lines up with the offset marker.
6. Remark the fin positions and now mark the lug position.
7. Remove the guide and extend your marks up and down the BT.
8. Mark slot ends and cut out.

It only requires one new mark on the fin guide and all your fin thicknesses will be accurate. Worked this out a long time ago.

 

[teepot]

I don't worry about being precise on the fin width. If there is a small gap the filet epoxy will fill the gap. I cut my slots with square ends. But I airfoil the fins. There is always a gap at the front and back of the fins.

 

[K'Tesh]

When I'm scratchbuilding, and need to cut a cardboard tube, I do this:
Using a mechinical pencil, I mark the body tube with an alignment guide for the left side of the fins only. (Left side as the body tube is oriented nosecone end up, fin pointed directly at me). I use a piece of aluminum angle to guide my pencil as I extend the lines. I also mark the top and bottom of the slot to be cut.
Using a brand new #11 Xacto blade, and the piece of angle aluminum as a guide, I make the first cut by lightly doing repeated cuts until the knife has fully penetrated the body tube.
I then press the left side of the fin intended for the slot up against the cut, and make another mark using the mechanical pencil.
I repeat the process of gentle cuts until the 2nd parallel cut is complete.
I then connect the cuts top and bottom, and I'm done.

This makes sure that the slot is tight to the fin, but not too tight (as to drag the body tube down into the slot, forming a "wasp waist"). It it is too tight, I'll use an emery board to sand the right side of the slot only. It it's too loose, I can glue the scrap of body tube to the right side of the fin and tighten up the hole. By sanding or gluing the scrap to the right side only, you ensure that you don't change the angle of the fins.

 

[afadeev]

3). Using a small metal ruler and a sharp hobby knife, trace the fin slot cut outs until you cut through the body tube.

One augmentation to the above - insert a pre-built motor mount inside the tube before you start cutting the slots.
Most paper tubes are too flimsy and will start flexing as you slice into them. Reinforcing them with centering rings glued to the motor mount helps to mitigate the bending and distortion, and makes cutting easier.

a

 

[Back_at_it]

Mark the body tubes using a marking guide then extend the lines. I then lay a fin against the body tube to determine where the the slot needs to be cut. From there I simply cut equal amounts on both sides of the line until the fin fits.

Keep in mind that the slots don't need to be perfect. As long as they are somewhat straight you can always go back and open them up if needed to get the fin straight. Sliding a coupler inside the tube will help and make sure you have a new blade in your knife. Also keep in mind that 80 grit sand paper makes short work of paper tubes so you can very easily open up the slots if needed by sanding.

Below is an example of the slots I cut for my recent Brighton build. Each of these slots took about a minute to cut in BT80 tubing. Of you're working with heavy wall you will need to make more passes but it shouldn't add but a couple of minutes.

 

[bjphoenix]

1. Wrap a piece of paper around the tube, put a pencil mark where it overlaps.
2. Straighten out the paper and measure from end to pencil mark. Divide the distance by the number of fins then measure and mark the additional marks on the paper.
3. Wrap the paper around the tube and transfer small marks to the tube.
4. Measure with a small ruler and put additional marks either side of the first marks to create slots of the desired width.
5. Extend the lines with a straightedge such as a piece of metal angle.
6. Cut the slots. In Estes or LOC type tubing I just use a hobby knife and make a lot of light cuts until I cut all the way through. In heavier tubes I've used an old XActo razor saw that I used to use for plastic models.

I usually don't worry if the cuts are straight because they will be covered by fillets. If the slots are too wide the gaps will be covered by fillets. I make my first fillets as thin wood glue fillets because it is thicker and won't run through the gaps, I think epoxy will run through very small gaps. After the wood glue is dry I will make the real fillets with epoxy.

If I'm scratch building I will cut fin tabs long enough to extend to the motor mount. I glue the fin tabs to the motor mount first, then I mark those locations on the airframe and cut the slots all the way to the end of the tube so the fin can assembly will slide in from the rear. For kits that just have tabs long enough to go through the tube I put the fin in the slot and put the small wood glue fillet on the outside. Then I'll make bigger fillets on the inside.

 

[kenstarr]

I do exactly what teepot says. Works great on cardboard, phenolic, fiberglass, carbon.... I use blue tape as a guide once my lines are drawn then just freehand the cutoff wheel with both hands while the tube is in my tube vice.
Ken

 

[Budro0]

I've never been good enough with an Xacto knife, so I build jigs for the different sized tubes. I generally use payloadbay guides to mark the slots, then slot with a router. It may be overkill on thin-wall tubes, but they are straight and generally right where I need them.

 

[Lee]

I do exactly what teepot says. Works great on cardboard, phenolic, fiberglass, carbon.... I use blue tape as a guide once my lines are drawn then just freehand the cutoff wheel with both hands while the tube is in my tube vice.
Ken

Can I see your tube vice?

 

[kenstarr]

Can I see your tube vice?

It's pretty jankey but it works great! Just some angle iron with a tab welded on the bottom and lots of tape to keep from messing up the tube surface... All this so I can put it in one of my several vices. Works great for body tubes from a couple of inches up to around 6". The clamping action comes from more tape around the tube!
Ken

 

[Rocketless]

I've never been good enough with an Xacto knife, so I build jigs for the different sized tubes. I generally use payloadbay guides to mark the slots, then slot with a router. It may be overkill on thin-wall tubes, but they are straight and generally right where I need them.
View attachment 484837

View attachment 484838

What kind of router bit do you use?

 

[lakeroadster]

I just cut slots through a BT-55 / C-55 yesterday for the sustainer stage of my 2 Stage Ahpla . @neil_w suggested using a piece of aluminum angle as a cutting guide.

I happened to have a piece of 1/2 x 1/2 x 1/16" th. x 36" long.

Once you have the lines marked on the tube you simply grip the angle onto the tube with one hand, and cut the tube with a hobby knife using your other hand.

Great results and it really is just that easy.

 

[Budro0]

What kind of router bit do you use?

I normally use Freud, but do have some Rockler and McMaster. For fin slots, I use a double flute straight bit and almost any of them will work. I think the one in the pic I posted is the 1/8" version of this: https://www.rockler.com/freud-double-flute-straight-bits-1-4-in-shank

 

[bjphoenix]

For LPR I cut slots with standard hobby knife. For thicker tubes such as LOC MPR I use a thin kerf razor saw. The slots don't have to be precise, if the gaps are too big I fill them with a thin fillet of wood glue before I put on the epoxy fillets.
For LPR I make my own marking guides by wrapping paper around the tube, marking where it meets the edge, take the paper off and measure it in mm, do the math, and mark the paper. But for MPR I always build the fins onto the motor tube first, then slide on the body tube and mark it to match the fin locations. Then I cut the slots with the saw.

 

[kyle]

https://www.amazon.com/Utility-Cutt...hvlocphy=&hvtargid=pla-4583726542710274&psc=1

)
Dude, the1000 pack! I like your style, but question your judgement...

 

[beeblebrox]

3D printed guide slides over the tube. Use X-Acto knife to cut tube... This one fits BT-55 for Three slots, two different lengths.



This one for LOC/AeroTech 4" Wanted slot to conform to airfoiled fiberglass fins. (0.03" sheet x 2 halves bowed out with a small piece of balsa.)

 

[boomtube-mk2]

)
Dude, the1000 pack! I like your style, but question your judgement...

Nobody gets to question my judgment . . . my sanity on the other hand is open to debate.
But seriously, I didn't notice when I posted that image that it was for 1,000 knives, I only wanted an image of the type of knife I was using.

 

[GlueckAuf]

I'm a noob working on my first MP scratch build. I spent a several hours yesterday just cutting my TTW slots, and I'm hoping the wisdom of the masses here can show me a better way.

The method that finally worked for me (after some trial and error) was this:

1 - mark fin locations on BT (38 mm in this case) using marking guide, extend lines.
2 - wrap paper around tube, transfer fin marks to paper.
3 - unwrap paper, lay flat, center a scrap piece of fin material to each fin mark, then trace edges to get proper slot width while trying *real* hard to hold the scrap bit steady.
4 - measure and mark fore and aft slot ends on paper.
5 - re-wrap paper to tube, aligning all marks.
6 - spend the next hour cutting along marks with hobby knife.

I'm pretty happy with the end result, but it was awfully time consuming for only 4 slots, and I'd really like more precision in my process.

For the Blue Tube air frames I build, fin slotting is one job I’m very happy to pay Dave Ebersole of Always Ready Rocketry to CNC machine for me when I order the tubes. The slots are always dead-nuts accurate, sharp, and perfectly rounded on the ends. At just $4 to $5 per slot depending on tube diameter, and no worrying over a mistake that could ruin an expensive length of tubing, it’s a bargain at twice the price. (But don’t tell Dave that!)

 

[mtnmanak]

I also like to use a router and I love the fin slotting jig from Macklin Missile Works. You can buy the kit from Apogee (https://www.apogeerockets.com/Building-Supplies/Tools/Rocket-Slotting-Machine-Tube-Slotting-Jig) if you have money to burn ($267 for this jig is insane) or just buy the plans from Ted Macklin and build your own for whatever it costs you for plywood and bolts (http://www.macklinmissileworks.com/...y-and-user-guides-rocket-tube-slotting-device). I built the size according to the plans, which is good for about 3" diameter and up, and then I built a scaled down version to use with my trim router (currently using a Makita RT0701C) for smaller tube diameters. Paying $20 for the plans was money well spent for me, but you may be able to design something yourself like @Budro0 did in post #17.

 

[beeblebrox]

Nobody gets to question my judgment . . . my sanity on the other hand is open to debate.
But seriously, I didn't notice when I posted that image that it was for 1,000 knives, I only wanted an image of the type of knife I was using.

Hmmmm... 1000 knives, death by 1000 cuts...lol

 

[beeblebrox]

I also like to use a router and I love the fin slotting jig from Macklin Missile Works. You can buy the kit from Apogee (https://www.apogeerockets.com/Building-Supplies/Tools/Rocket-Slotting-Machine-Tube-Slotting-Jig) if you have money to burn ($267 for this jig is insane) or just buy the plans from Ted Macklin and build your own for whatever it costs you for plywood and bolts (http://www.macklinmissileworks.com/...y-and-user-guides-rocket-tube-slotting-device). I built the size according to the plans, which is good for about 3" diameter and up, and then I built a scaled down version to use with my trim router (currently using a Makita RT0701C) for smaller tube diameters. Paying $20 for the plans was money well spent for me, but you may be able to design something yourself like @Budro0 did in post #17.

I like that jig idea, My solution is only good for paper tubes. THAT is the bees knees for fiberglass or other hard tubes!