MDF door split after fitting hinges on the face

[jacoscar]

I have built some MDF doors using strips of 18mm MDF in 2 layers, so total door thickness is 36mm, and 3mm hardboard panels (see pictures)

I have bought a bifold door ironmongery kit which comes with normal hinges and 1 inch 7G screws
https://www.screwfix.com/p/henderson-bifold-b20-4-4-door-folding-track-system-silver-2134mm/8195j

The instructions say to use hinges on the side of the door but I avoided this as I was sure that drilling on the edge of MDF would split it, so I decided to screw them on the face of the door

I have used this hinge drillIng kit to make pilot holes
https://www.screwfix.com/p/hinge-drill-bit-set-3-pieces/6163V?tc=RT4&ds_kid=92700048793290430&ds_rl=1244066&gclid=CjwKCAjw2a32BRBXEiwAUcugiHYyoMrjp4TxNAyAi3bmPgXOaeHl49w5Trc8ih4DbzctiGpWNe8gwxoCi04QAvD_BwE&gclsrc=aw.ds using the biggest drill

However, after drilling all the hinges I’ve realised that the MDF had split even before I tried to hang the doors
How is this possible and how can I fix it?

I suspect as the screw was slightly longer than the hole made by the drill, it might have pushed the MDF apart, so I was thinking about drilling a longer pilot hole and using longer screws (30mm) (making sure the hole is deeper than the length of the screw)

 

[Deleted member 174758]

Drill out the holes carefully to 8mm using a brad point twist drill ( i.e. a dowel drill, not a metalwork twist drill). Glue-in 8mm hardwood dowels with D3 PVA. Leave to set 24 hours minimum. Flush off the dowels (flush cut saw or sharp chisel or block plane). Repilot with the correct size drill bit, holes drilled into the dowels. Reattach the hinges with screws taking csre not to overtighten. This is a well known workaround/fix for dealing with spitting in chipboard and MDF

MDF is awful for splitting if not piloted correctly (and the pilot holes thoroughly cleaned out). I'm sure that at least part of the reason they developed 35mm cup hinges for kitchen cabinets, etc is that chipboard and MDF are equally bad in that respect - neither hold screws well.