Any tips on cutting TTW fin slots?

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manixFan

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I would say a coupler is good advice for standard tubes, like Estes, which are thin walled. For LOC tubes or Blue Tube, not required. I recently cut fin slots in a LOC airframe without a coupler, no issues.

I do use the gold X-Acto blades as they are MUCH sharper, last much longer and are worth the extra cost for stuff like this. I cut all four ring tubes for my King Kraken with just one of those blades. I use regular X-Acto blades for less exacting tasks, like cutting out balsa fins.
I agree, for HPR tubing, a backer is not really needed, unless the cuts are really long and the tube deflects once several of the slots are cut. But for Estes style tubes, I used a spare coupler to 'back up' the cut. And using several light passes seems to also help reduce tearing/ragged edges.

I suppose you could soak a coupler with CA and then sand it smooth to make a better backer than a plain paper tube.


Tony
 

Back_at_it

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Mark the fin location on the tube. Based on the thickness of the fin, measure and mark locations of the both sides of the center line.

For Estes and other thin tubes, use a coupler inside so you have something to cut against. Follow the lines and make slow repeated cuts. You should make it through in three passes or so. Biggest thing is don't be worried if they are not exact. You're going to cover the cut with a glue fillet anyways.

Here's an example of one of mine. Not the straightest cut but it doesn't matter. The fin fits in there just fine and there is room enough for me to ensure that the fin sits straight. I could sand it if I wanted to but it's completely unnecessary.

TTW.jpg
 

boomtube-mk2

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I've cut a lot of tubes and a bunch of slots for fins and all I've ever used are those $1.00 throwaway snap-blade knives.
They are very sharp and when they get dull you just break off the end and carryon.
 

brockrwood

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Well, not to belabor the point, but actually, you are more likely to cut yourself with a dull blade (for the reason you described), but the cut with a sharp knife can be much worse. A sharp blade can cut you much more easily and deeply with lighter pressure or an accidental brush with the blade, and worse, you may not notice because the cut is so clean. I have a fair collection of knives and can tell you that just during general handling the super sharp ones are far scarier than the dull ones. I was at a gun show once and watched a guy sharpen a hunting knife with a very high end sharpener (I think it was a Wicked Edge). Before he gave the knife back to the guy, he told him "do not test it with your thumb, you will cut yourself". Of course, the guy gets the knife, runs his thumb along the edge, and says he can't feel it. The knife sharpener hands him a paper towel and the guy looked confused. He was already bleeding and did not realize it yet.

Dull knives are bad tools, sharp knives are silent.


Tony
My grandfather said to always “cut away from yourself”, meaning, when cutting anything with a knife, saw, blade, etc., make sure the cutting motion is always going away from your body, not towards your body. That way, even if the knife slips, it slips in a direction harmlessly away from your body parts. Good advice I think.

Of course, with a hobby knife, you may have to draw it towards yourself, just to get the leverage and angle you need. Still position your free hand so the knife is going away from the hand, not towards it. I think that is what granddaddy meant.
 
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brockrwood

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I've cut a lot of tubes and a bunch of slots for fins and all I've ever used are those $1.00 throwaway snap-blade knives.
They are very sharp and when they get dull you just break off the end and carryon.
Any recommendation on the cheap throw away snap blades to use? Dollar store variety ok? Wally World brand?

I have tried to buy only brand name, high quality hobby knives and blades. I like the xcel (spelling?) blades best. Still, I have trouble getting through some material, such as thick cardboard. I think I just run out of patience. After three swipes with the blade, I want to be done. :)
 

neil_w

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Any recommendation on the cheap throw away snap blades to use? Dollar store variety ok? Wally World brand?

I have tried to buy only brand name, high quality hobby knives and blades. I like the xcel (spelling?) blades best. Still, I have trouble getting through some material, such as thick cardboard. I think I just run out of patience. After three swipes with the blade, I want to be done. :)
I use an Elfa knife, and any old blades. IMHO it's more important to have a good solid knife; the blades are so cheap and easy to snap off that they don't matter as much.
 

brockrwood

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I use an Elfa knife, and any old blades. IMHO it's more important to have a good solid knife; the blades are so cheap and easy to snap off that they don't matter as much.
I stole a nice, Olfa brand, retractable utility knife from my girlfriend’s toolbox. I am going to try that first. Better to try the free tool from the love of my life than to buy something needlessly. I only get into relationships with women who have a well stocked toolbox. :)
 

lakeroadster

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I stole a nice, Olfa brand, retractable utility knife from my girlfriend’s toolbox. I am going to try that first. Better to try the free tool from the love of my life than to buy something needlessly. I only get into relationships with women who have a well stocked toolbox. :)
I bet that first date was uncomfortable, you know when you brought up her tool box....

 

brockrwood

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I bet that first date was uncomfortable, you know when you brought up her tool box....

My last girlfriend (before the current one) was a true “Tool Time” gal and proud of it! Great lady. We just weren’t a good fit, chemistry-wise. She rocked the tool belt and the drill press. But her favorite tool was the sawzall. She was a bad*ss doing demo with the Sawzall. The current gf and I are a far better fit, romance-wise. But even she would admit that her tool collection is nothing compared to the last lady. :)
 

manixFan

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I stole a nice, Olfa brand, retractable utility knife from my girlfriend’s toolbox. I am going to try that first. Better to try the free tool from the love of my life than to buy something needlessly. I only get into relationships with women who have a well stocked toolbox. :)
Not to derail the thread, but the first time I visited my (now) wife right after we first met I thought I'd show her how manly I was by fixing something. I asked her if she had any tools, and she just said 'in the closet'. Turns out she had a better stocked toolbox and tools than I did and she also knew how to use them. Later when I asked for a beer she said 'in the fridge' and the only thing in there was beer, bread, and milk. We celebrate our 30th this year.

The really great thing is I never have to justify buying a new tool. She understands the value of the right tool for the job and since I continue to be handy around the house I get a free pass when it comes to tools.


Tony
 

tsmith1315

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Still, I have trouble getting through some material, such as thick cardboard.
You have to take it easy and let the blade do the work. Start with a sharp blade and a gentle pass with just enough pressure to break the surface and establish a line to follow. Score all of the slots first, while the blade is sharpest, before cutting deeper.

Add a little more pressure and follow the line carefully. Repeat, repeat...Back off again when almost through so you don't delaminate the last layer or two. When possible (bigger tubes), I cut the last pass from the inside of the tube, decreasing the chance for delamination.

Like @Bruiser and @Cape Byron above, I prefer single-edged razor blades. Utility knife trapezoid blades without the handle are second choice. Cutting by hand gives me better feedback and less leverage to screw up with.

In this manner, slow and easy, I've done 3 slots with one blade.
 

brockrwood

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You have to take it easy and let the blade do the work. Start with a sharp blade and a gentle pass with just enough pressure to break the surface and establish a line to follow. Score all of the slots first, while the blade is sharpest, before cutting deeper.

Add a little more pressure and follow the line carefully. Repeat, repeat...Back off again when almost through so you don't delaminate the last layer or two. When possible (bigger tubes), I cut the last pass from the inside of the tube, decreasing the chance for delamination.

Like @Bruiser and @Cape Byron above, I prefer single-edged razor blades. Utility knife trapezoid blades without the handle are second choice. Cutting by hand gives me better feedback and less leverage to screw up with.

In this manner, slow and easy, I've done 3 slots with one blade.
These things? Do you use a handle of some sort?


 

Bruiser

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Those are them. Harbor Freight has them in packs of 100. Like the others I use my thumb and finger. I do use an X-acto knife for the top and the bottom of the slot. Take your time and make multiple passes. Use a new blade to start and when it gets dull, use another blade. Did I mention not to rush or trying to make the cut in one pass? Don't do that.

-Bob
 

boomtube-mk2

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Any recommendation on the cheap throw away snap blades to use? Dollar store variety ok? Wally World brand?

I have tried to buy only brand name, high quality hobby knives and blades. I like the xcel (spelling?) blades best. Still, I have trouble getting through some material, such as thick cardboard. I think I just run out of patience. After three swipes with the blade, I want to be done. :)
I've bought mine from ACE Hardware, Tractor Supply, Atwood's, Currell's and a local tool supply store and I may even have purchased some from WalMart.
They all appear to be much the same, about six inches long with a blade about a 1/4" wide with a slight angle at the sharp end.

You can find more expensive versions of the same thing that allows you to refill it with blades sold separately, personally I never bothered with that as I have a tendency to either lose them or drop epoxy on them or otherwise wreck them beyond further use.
 

beeblebrox

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I agree, for HPR tubing, a backer is not really needed, unless the cuts are really long and the tube deflects once several of the slots are cut. But for Estes style tubes, I used a spare coupler to 'back up' the cut. And using several light passes seems to also help reduce tearing/ragged edges.

I suppose you could soak a coupler with CA and then sand it smooth to make a better backer than a plain paper tube.


Tony
Depending on the tube size you could use a spent motor casing... BT-20, BT-50. For BT-60 use a spent 38mm motor wrapped with plain paper until it fits nice.
 

beeblebrox

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The best blades by far and longest lasting are X-Acto 'Z' Series, they are TiN coated and stay sharp much longer. The secret is many light cuts...Don't cut any slots all the way thru until you have made a couple of scoring passes on all of them first. I finish off the cuts with a single edge razor blade since it is big and stiff. (The corners of those get dull too quick for the main cutting. For really large tubes 4" and up I mark the tube then cut with a sabre saw...the rough edge really sucks up epoxy when filleting.
 

NOLA_BAR

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I'm modding my Broadsword build to have 1/8 inch plywood TTW fins. So I need to cut the slots in the BT-80 tube. I haven't done that before so if there are any tips or tricks to it, please share.
BT-80 tubes are very squishy. If you have a sharp(new) hobby knife and a template, then the only thing I would add is a BT-80 coupler to support the tube while cutting.

OOPs someone already suggested this.
 

beeblebrox

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BT-80 tubes are very squishy. If you have a sharp(new) hobby knife and a template, then the only thing I would add is a BT-80 coupler to support the tube while cutting.

OOPs someone already suggested this.
Another option, don't use BT-80, use AeroTech 2.6 tube, it's same ID and fits the same cones, and you can buy a pre slotted tube with either 3 or 4 slots...
 
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