tricky hole saw cut

[gordon todd]

I'm needing to drill 3-1/4" hole into side of 24" diameter plastic drum off center (not square to side of drum). I've put a longer pilot bit on but think a little less than half of teeth will be all the way through before the rest contact the surface. Has anyone done anything like this? Thinking maybe attach block of wood on inside to keep pilot bit and hole saw teeth boring. I'm inserting 3" pipe into opening, coming into it at an angle with resulting hole somewhat egg shaped. Thanks for any insight or ideas.

[Bruce Volden]

I'd use the drill press and drill desired diameter at the angle you're shooting for.
Then affix the "guide" to the plastic drum. I'd prolly go with at least a 2+" chunk of off cut.
If I understand what you're going after?

Bruce

[Jerry Bruette]

If you're coming in at a tangent you might be better off making a pattern like would be made for sheet metal work and then cut the hole with a jigsaw.

[gordon todd]

Thanks Bruce, that's a good idea though i need to see if that will work on my drill press. Only problem I see is mounting guide block to curved surface without alot of fabrication. Maybe curve it with grinder to fit side of drum

[gordon todd]

Thanks Jerry, that would probably be a more forgiving using jig saw.

[Bill Dufour]

My Uncle George was a rocket scientist first for the Navy then for Lockheed. He earned at least one patent that he sold for one dollar and other valuable considerations. He said the only time he used more then high school algebra was to run a round pipe into a round fuel tank at an angle. There is math to draw out the hole shape on a flat piece of paper then tape it to the tank and cut it with a jigsaw. Weld in any boo bo's. Of course on a rocket weight matters so a more accurate hole uses as little welding rod as possible.
Bill D

[gordon todd]

Thanks Bill, I need an Uncle George. Luckily my tolerences are not that critical. I'm working with plastic drum and pipe, so going slow with jigsaw should do it.

[Bill Dufour]

When he got enough years in with the Navy they told him he had earned six weeks of vacation and he had to take it each year. He quit and went to Lockheed with two weeks a year of vacation time. He asked and they told him he could come in and work for free on his vacation days if he wanted. But he had to claim he took those days off. A syou can tell he loved his job.
Bill D.

[Floyd Mah]

Here's a different way to look at the problem. Suppose that you fix a 3-1/4 inch pipe to a board (along its' length). Make a 24" circle and then lay it on the pipe at the proper entry angle. Use an adjustable square on the 24" circle and project its' outline onto the pipe. After you've established enough data points, take the assembly (pipe and board) and cut into the pipe with a bandsaw until you've removed enough to press it against your plastic drum. The board will keep the cuts on the pipe parallel to the axis of the drum. Now you can trace your pipe's outline onto the drum. If the pipe is too jagged, just repair the irregular areas with tape while it is pressed against the drum. You should be able to get a perfect fit. Alternate plan is to tape the pipe to the drum (after the above steps) and use a scalpel to cut the intersection of the two tubes.

If you cut the hole in the plastic slightly small, then taper the end of a sample of the pipe, cover the taper with sandpaper and use it to enlarge the hole in the plastic drum to the exact size and fit.

[Alex Zeller]

Replace the 1/4" drill bit in the hole saw with a 1/4" metal rod and drill the 1/4" guide hole before trying to use the hole saw. You'll find it's a lot easier. I usually use an old 1/4" drill bit inserted into the arbor backwards (so the smooth part that normally goes into the chuck goes into the pilot hole). It's a lot less 'grabby' and chances are if you go slow you can drill the hole without doing anything extra.

[Bruce Wrenn]

To make a template, using bandsaw and a circle jig, cut the end off a piece of pipe. The radius of the circle jig needs to match the radius of your drum. Use cut end of pipe for an exact template. Mark on drum, and cut inside the line. With some drafting, you can do a mock up using the intersection of two circles. Quicker for me to cut pipe on bandsaw, Remember scrape of pipe only needs to be about 6" long.

[Tom M King]

Sharpen a regular holesaw, and use a rod like Alex was talking about, and it will go right through. They don't come sharp, but can be made with sharp points that last long enough for this job. A variable speed drill at low rpm will increase control. Regular steel holesaws are easy to sharpen with a small triangular file. Each tooth doesn't even have to be pretty, but don't change the height. I wouldn't bother with making any kind of guide. I would run a piece of tape across the top at the angle you want to follow, as a visual guide.

[gordon todd]

Thanks to all for your replies. This is exactly what I needed: different methods to look at the same problem. I now think that I'll take a scrap piece of the pipe, cut it at an angle to match side of drum, trace it and then cut with jigsaw.

[Tom M King]

I figured there was such a thing online:

https://cq.cx/tubejoin.pl

[Rick Potter]

OK, I am an idiot, but I think I would try to position the pipe and the drum somehow, then with a flood light at the other end of the pipe, use the shadow to draw directly on the drum.

Before I get blasted, remember this is free advice. Probably properly priced.