Going too fast.
This is something that almost every woodworker learns from experience. Almost every woodworker has at some point of time spoilt a project at a crucial stage because he was going too fast and not paying enough careful attention to what he was doing.
It's almost the same principle as measuring twice and cutting once. Whenever you are at a crucial building stage of a project, slowdown, take a measure of your affairs, ascertain how you are going to proceed from there and only then move.
Remember that while you may want to hurry along, it may actually cost you more time fixing a project when it goes wrong. And even that is not the worst outcome of rushing a job. Rushing is one of the main reasons why accidents and injuries occur in a woodshop. So whenever you are tempted to rush a project, remind yourself that it is extremely unsafe to do so.
Drawers that do not fit
Many times woodworker makes the entire project only to realize that somehow the drawers on the wrong size. This surprises many but shouldn't really. The reason is that you have probably made everything according to a pre measured woodworking plan without taking reference measurements periodically while building the project.
The solution is to leave the building of the drawers after you have finished making the rest of the project. Even when following accurate plans, the measurements can go slightly off and that slight difference is enough to create the problem with the drawers.
Make the carcass of the furniture piece first Then take a measurement of the drawer space available from the structure and build them according to that measurement.
A blotchy finish
Using certain oil-based polishes can end up giving a blotchy finish to certain kinds of wood, such as cherry. The reason is that this kind of wood has pores which tends to absorb the polish unevenly giving the surface an uneven look. The solution is to prepare The surface beforehand using a sanding fill to fill out the pores and then applying the finishing material. Alternatively you can use a finish that does not actually absorb into the wood but stays on top of the surface, for example varnish.
Polish Doesn't Take
The only reasons for wood not to take on a stain properly is either you have used the stain resistant wood filler or the table surface is unclean, usually with the remnants of glue.
It's easier to prevent this from happening but not so easy to recover from it once the damage is done. Therefore make sure that you are using the right filler and the polishing surface is clean before commencing the staining process.
Wood gets fuzzy when sanding
This happens to certain kinds of wood. The fibres tear and create a fuzz on the surface. In order to prevent this do not use a sandpaper finer than 150 grit. If it does happen, use a lower grit sandpaper like 100 to sand off the fuzzy fur. Do not try to stain or topcoat that area otherwise the problem will become unfixable. Even if the fibres settle down with the stain, the texture of that area will look different from the rest.
The joints are too tight
It's important for the joints on a wood project to be tight and well fitting. For example, a mortise and tenon joint. The strength of such a joint depends on it being well fitted. But sometimes it comes to pass that the joint will not fit. It's too tight.
The only way to tell if your joints are going to be too tight is to dry put them together first. If you have to use gentle to moderate tapping with a mallet to get the joint in, you can safely assume that it will be too tight once you put the glue on.
Therefore you need to lose them up at this stage. How you do it depends on the kind of joint it is. For example if it is a mortise and tenon joint, shave of the tenon point with a chisel.
It's also important to assemble joins fully and resist attaching them partially. Attach one joint fully during installation before moving onto the next one. The reason is that you might sometimes experience what is known as a lock-up of joints.
Locked up joint is a stuck joint that might require a heavy effort with a mallet to pry it loose. Sometimes, if it has been locked for a long of time you may not be able to loosen it all. You do not want this happening as it could ruin your entire project.
Therefore to avoid tight and stuck joins always do two things first:
Dry fit them to check if they fit easily and always assemble each joint fully before moving onto the next one.
Joints are too lose
If the joints are not too tight they can be too lose. As we have mentioned before, the strength of a joint depends on how well it fits. Once again let's take the example of a mortise and tenon joint. There are two ways of fixing a mortise and tenon join that is too loose.
Use a special glue to fill up the space. The usual glue you use for sticking the wood will not do. Use an epoxy resin glue that expands on drying.
The second method is to glue additional thin wood on the tenon part of the joint and gradually shave it with a chisel till it becomes a right fit.
There are other things that commonly go wrong in a woodshop like wobbly tables, surface not turning up flat etc. These problems need a more detailed solution. But help is readily available online for many issues through a search engine.
You will probably find several posts on blogs, people sharing information on forums and even uploaded videos giving a solution to your problem. Feel free to add any of your experience with things gone wrong in a workshop and how you fixed them. I'm sure your contribution will be a great point of interest for other readers as well. Thank you for reading.