I am making the carcass for a kitchen pull out wire larder and am having trouble getting a good joint using the Kreg Jig which I have just bought for the purpose. The material is 19mm laminated MDF which I have had professionally cut to get perfect edges. On scrap pieces I have not been able to get a good joint. Using the 3/4" settings from the jig and No7 Kreg coarse screws 1 1/4" long and a very low setting on my cordless drill (No 4 out of 18 max setting), the Melamine erupts slightly proud of the original surface when the screw exits the pocket and drives into it, making it impossible to get a nice tight joint, or even a 90 degree joint.
I have tried predrilling the melamine itself to remove the brittle material where the Kreg screw enters the 2nd piece and I have used a substantial batten clamped to the work top, with the two pieces to be joined pushed hard against it but to no avail. I hope someone can help. I am sure it is a matter of technique I have to learn,
This is just my experience and opinion with MDF. Maybe someone else with more smarts than me can solve your problem.
Several years ago, my wife and I decided to do a built in bathroom vanity. While shopping at HD we saw Melaine Coated MDF and said it would be easy to clean and bought 2 sheets.
I laid out and cut the sheets and started to assemble the bottom and sides when I noticed that I could not get a tight fit using pocket hole joinery. The screws would strip the MDF before I had a good fit.
I went back to HD and asked if there was anyything I could use to solve the problem. They sold me some screws that were made especially for MDF, not usable with pocket holes. These scerws were about 3/8" diameter and had large threads to get plenty bite, these also did not work well. If you have ever assembled anything made of MDF, they use cam lock fastners to pull joints tight because of this fact.
I ended up cutting Dados in the side walls to slip the bottom and sides in, glued and nailed them in the dado. For the back I glued and nailed with ribbed nails to keep the carcas square. I was able to use pocket holes to install the face frames to the carcas because the screws in the wood face framd pulled the assembly tight, but you still had to be careful not to colapse the ridge in the hole.
In about 4 years the cabinet was falling apart and I replaced the vanity using plywood.
In my opinion MDF is too soft a material to be screwed to make a good strong joint, not the fault of the Kreg Jig. You bought the right tool but the wrong material.
I referenced MDF in another posting. I am VERY opinionated against the stuff. I use it for backing and holding the targets at the rifle range. My list of usefulness stops there. The problems you have are part of the reason I dislike it so much.
The Kreg Jig is a very good tool, but in my opinion MDF is for looks only and not much looking before your eyeballs will wear it out. Zero durability. That is my biased, prejudiced opinion.
I get very good rock solid, tight joints with dimension lumber, or plywood and the Kreg Jig pocket holes. I always use glue on every joint. Not because you have to, but the insurance is cheap.
Do you have a drawing or photo of the "wire larder", I don't believe I am familiar with the term. I live on the West Coast and we may call something different than you do. Just a curiosity thing.