I need to ask did you try to cut this with a hack saw shown in other photos if so this will happen again you need a hand saw not a saw for cutting metal.
see this link
Also if you try score and snap with the amount of material on the edge it will happen as there is not enough supporting material
I have seen it on telly when people work with wood tgey use some sort of equipment to lock it and then it doesn't move.
In my case, the 1st few inches were great and I was kinda chuffed that its coming along and just then it went pear shape.
Will get the correct tool.
It's great to see @r23on has recommended the Irwin 550mm Fine Tooth Handsaw, which is fantastic at cutting straight lines. However, I believe you'd still find it quite hard to use that saw to cut the curved corners. A jigsaw with a fine-toothed blade is what's really needed for this job. You don't happen to have a jigsaw, do you? We're obviously trying to keep costs down for you, but sometimes, as you've experienced, projects can run into issues without the correct tools.
Like all DIY / handyman there are a lot of things that need to be taken into account such as tooling materials and abundance of information / ideas solutions plus endless supply of YouTubs, I did it this way, which in the end it boils down to experience or the lack of. This project of your is the perfect example where having the correct tools would have made all the difference, as Mitchell has stated, having a jig saw would be of great help but make sure you do watch some YouTube and learn a few tricks and how to use it and clamps to hold the material down other wise you will be heading out for more material.
If you are going to continue down the track of the DIY I suggest you have a supply of clamps and good quality clamps for holding parts in place or clamping down.
Unfortunately DIY is not a cheap exercise as you are learning.
Most of all I am looking forward to seeing the job completed.
@newfastfrom the photo, it looked like the piece broke due to lack of support... I am guessing that the back and forth pull of the saw caused the (hand held?) sheet to flex and break at the point where it was being held. As you noted earlier, it is a bit flimsy.
Ideally you would put the sheet on a bench (or table if you can stop it being damaged), clamp it and then sawing is done very close to the benches edge. That stops it being able to flex when the blade pushes and pulls on it. Clamps help, but if you don't have any, then holding the sheet down against the bench/table close to where you are cutting (not so close that your fingers at risk, of course) will stop it moving and flexing (and breaking). Having another person holding the sheet still so it can't move around is big help too. If it slides about you are at risk of cutting into your bench or table edge.
Keep trying and learning, but mostly, be careful not to damage yourself or your home!
Masonite sheets can be replaced much more cheaply and easily than fingers and good furniture.
Hi @newfast while you are checking how-to s online, here is a link to a video with some good tips for making clean cuts using your Multi-tool (although the video maker has a pretty super-dooper model, but the uses are the same).
The most useful parts are in the first half.
I hope your door repair project is coming along ok. For less money than you were quoted for the repair, you get some tools that you can keep for future projects as well as the experience of learning skills, also useful for future repairs, and the satisfaction of knowing you fixed it.
How’s the project going I haven’t seen any post to the progress of the door repair?
Have you finished it?