Cutting a cylinder

Factual Questions
1

I have a large cardboard cylinder 10 inches in diameter and about 5 feet long. The cardboard is about 1/4 inch thick and it weighs about 30 pounds. I want to cut a bit off one end so that the cut end is a perfect circle whose plane is exactly perpendicular to the axis of the cylinder. Since the cardboard is so thick, I think I will have to cut it with a saw.

What is the best way to mark the cut line as accurately as possible? I know about the trick of wrapping a large sheet of paper around the cylinder and marking along one edge. Is there a better / more accurate method?

ETA: The current cylinder end is jagged and irregular, so it would be pointless to use it as a guide.

2

How about not marking it at all/
Just use a band saw, or a chop saw, or any saw that can has a 10" opening – place the cylinder side against the back guide, and cut the whole end at once.

3

Are we permitted to know why extraordinary precision is required?

Where would you find such a saw? The OP could check with local custom carpentry shops and see if they could cut it I suppose,

4

Well, anywhere that sells wood - Home Depot.

5

Any bandsaw should be able to handle a 10-inch cylinder with ease. For best results, build a right-angle circle-holding jig and use the miter slots on the bandsaw table.

6

Set your bench against the wall such that the end of the bench is flush with the side of a door. Lay the tube over the edge of the bench and saw it. The side of the door will help you maintain perpendicularity.

7

A circular saw with a 10" capacity is enormous.

8

Probably a band saw at Home Depots (or any lumber yard) I think.

9

Believe it or not, this is probably best done with… a hand saw.
Make a jig (custom miter box) that fits the tube, and has a slot for the saw blade, and then use it to guide the saw and make a perfect flush cut.

10

The very best way is to put the cylinder in a lathe and cut it with a tool moving radially.

11

You’d need a ten-inch holder-thingy for the lathe tho.

12

I would probably make a jig. A piece of wood 10" wide with another two pieces screwed to it to make a channel - all three pieces to have at least one square end.

Put the cardboard tube in the channel and hold it firmly in place while cutting it with a sharp fine-tooth saw using the square ends as a guide. To minimise tearing on the outside, put some sticky tape around it where you are going to cut and work gently.

13

One trick for cutting large diameter pipe straight is to wrap a hose clamp around the pipe. The hose clamp “wants” to be perpendicular to the pipe’s axis.

Alternatively, wrap a string around the tube snugly. The shortest distance around the tube is a path perpendicular to the axis. If you pull it tight, the string should find the shortest path around.

14

Yes, but will they allow you to use their equipment for any purpose except actually cutting something you are buying? I think I would put a rubber band on it, line it up as accurately as I could and then mark around the band. I might instead try to maneuver with a mitre box even if the diameter of the cylinder is larger, but not too much larger, than the height of the box.

15

I think the “wrap something around it and mark the line to be cut” scheme is the most practical one.

The best thing to wrap might be a steel tape measure. The best way to get a clean cut might be a “whiz wheel” (high-speed abrasive disk).

16

Jack up rear of car, attach cylinder to rear wheel. Put in drive and hold utility knife against rotating cylinder and press until cut through.

Actual procedure/tooling is left as an exercise for the student.

17

Welding supply stores have pipe wraps but you said you didn’t want to go that route so…

Put it on a closet rod, press it lightly against the wall while slowly rotating it. Fix a pencil to a nearby thing to make the mark as you rotate it.

18

You can use a marker to mark the Cylinder and then cut it. Though I am not sure marker will be helpful. But you can with this one.

19

Does it have to be that specific cylinder that you cut? You can get similar cylinders at the hardware store that are used for concrete footings. I’ve seen 8" and 12" ones. They’re called concrete form tubes. The factory ends look pretty square.

20

You don’t say what tools you have access to, but here’s a good way to do it on the cheap.

Youtube

Just be aware that cutting a cardboard tube this way will result in a fuzzy end. If you want a clean, sharp cut you’re probably going to have to have access to power tools.