Straight Tube Cuts

lakeroadster

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I recently used my 12" Dewalt miter saw with a "DIABLO 80-Tooth Fine Finish Circular Saw Blade" to cut 3" mailing tubes and it was a thing of beauty for the thick walled cardboard. My curiosity led me to try with something much smaller and thinner - a BT50 (.976) tube. While the cut was 90deg, the edge was too rough for my liking despite moving the blade slowly. I had to use thin CyA on the edge and then sanded the rough cut smooth. Given the choice between trying to correct squiggly lines and "frayed" edge due to first/second/third blade passes with the Exacto, I'd actually try the miter saw again.
Thanks for your reply. I have a 12" Miter Saw and a 8" DeWalt Radial Arm Saw... I simply never thought to try them.

I'm betting that slipping in a coupler to stiffen the tube during the cutting operation would also help the saw blade in making a cleaner cut.
 

dr wogz

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Instead of masking tape I use the heavy cardstock that those mail advertisements for windows, Republicans, Democrats, whatever, that come in the mail. Wrap tightly around the tube to be cut, tape in place. It usually takes several wraps (the more the better). That provides a stouter guide against which the knife blade can rest. If the blade cuts into the guide that's usually not a problem because the guide is so thick, the blade doesn't cut through all the layers of the guide.

Sand afterward, checking as to whether the cut is square with a good carpenter's square.w

Best,
Terry
Again Terry, we completely agree!

Exactly what I do. take your time, patients, and a bit of practice. No expensive [power / single use] tools, nor reliance thereof..
 

caveduck

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Hey Shane, for cardboard tubes I like the Kuhn cutter with a coupler or motor casing inside the tube. They work great and are easy and inexpensive to build in various sizes. I also have a couple of original ones made long ago by Howard Kuhn himself. My bigger one is a 3' chunk of 2" aluminum angle stock with a stiff spring clamp and a short piece of 1x2 for the tube stop.
 

Paul Howard

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I use a compound Miter saw. Newish fine finish carbide tipped blade. From 24mm to 4". With blue tube it's a dream. When I've used a razor saw, a coping saw, a hack saw or exacto it never comes out square no matter how carful I am.
Yes, I can see that since I have on occasion re-cut a tube after seeing the first attempt wasn't "true", it's definitely a careful process to be sure!
 

Lee

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Kona razer saw with their miter box. No need to "reinvent the wheel" with a custom jig - this is what the miter box is designed to do. For larger tubes, I use a carpenters miter box. Square cuts every time. Sand to perfection if needed. For tube stiffness, if needed, stuff the tube with rolled up cardstock on the inside.
 

neil_w

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Another general purpose tip: when sanding the edge, keep rotating the tube as you go. That way, if you're not applying totally even pressure it will "average out" as you rotate around, and you want create a new non-square edge due to the sanding.

This sort of advice applies to a lot of different hand-sanding activities.
 

hobie1dog

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Kona razer saw with their miter box. No need to "reinvent the wheel" with a custom jig - this is what the miter box is designed to do. For larger tubes, I use a carpenters miter box. Square cuts every time. Sand to perfection if needed. For tube stiffness, if needed, stuff the tube with rolled up cardstock on the inside.
I found a Zona razor saw, but no Kona brand:
cutting depth is only 1 3/16" , so do you have to rotate your tube?
 

smstachwick

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I bought the Estes guides. I expected them to be next to useless, given the mixed record of the fin alignment jig, but these actually did nicely. I believe the limiting factor is my own skill, so I’ll keep practicing and sand this one down the tiniest bit.

47A80F9E-34DD-4EA1-AA01-91E4571CA33F.jpeg
 

neil_w

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I bought the Estes guides. I expected them to be next to useless, given the mixed record of the fin alignment jig, but these actually did nicely. I believe the limiting factor is my own skill, so I’ll keep practicing and sand this one down the tiniest bit.
I quite like them, and wish I had one for BT50H which I use a lot.

The key technique I've found is keeping the side of the blade pressed against the cutting guide (not letting it drift) without cutting into the guide itself.
 

smstachwick

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I quite like them, and wish I had one for BT50H which I use a lot.

The key technique I've found is keeping the side of the blade pressed against the cutting guide (not letting it drift) without cutting into the guide itself.
Yep, that was my takeaway too. I wouldn’t call them disposable exactly but they will need periodic replacement, as the wear adds up.

Not too shabby of a result on a BT-50 either, the last photo being a BT-60.

ED658306-E1BD-4CCA-8D16-E8D524008FF7.jpeg
 
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bjphoenix

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Instead of masking tape I use the heavy cardstock that those mail advertisements for windows, Republicans, Democrats, whatever, that come in the mail. Wrap tightly around the tube to be cut, tape in place.
I do that too because I usually have plenty of that stuff nearby in the trash. I also cut strips of it for fin marking guides- wrap around the tube and put a mark where the stuff overlaps, divide that distance by 3 or 4, etc. And I use strips of that stuff as a guide for placing masking tape when I'm doing multicolor paint schemes. The hardest part of using cardstock is keeping straight which edge was the factory straight edge and which edge was the scissor cut edge because it might not be perfectly straight. I make my scissor cut edges intentionally wavy so I can tell what's the factory straight edge and what's not.
 

waltr

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Nice, that is exactly how I cut BTs. Have done BT-5 to LOC 2.2" tubes.

Only issue I have had is the ravor blade moving away from the end of the angle. But this just makes part of the cut a little longer which is easy to sand off.
 

BABAR

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Get straight and clean cuts, by using a sacrificial coupler on the inside of the tube being cut especially larger diameter airframes..
for up to 29mm you can “sacrifice” a used motor casing, at least for BT-5, 20, 50, and whatever 29mm is (I rarely go that big.)

biggest thing is getting the line straight. I save face card plaques from Estes rockets (I guess others have them too.). They are pretty much guaranteed to be cut straight. Wrap it around the tube until the SIDE edges (near front and back of TUBE) line up, scrunch it down until tight, tape the Plaque to form a ring, then use it to draw the line.

few wraps of masking tape on one side of the line. I cut by hand, just start shallow and go around two or three times before completely penetrating the wall.
 
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View attachment 538515

I've cut 18mm cardboard to 98mm blue tubes using this method and they are always very square and mostly burr-free.
This is essentially what a Kuhn tube cutter is.
 
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