I believe that the heads on standard allen-head cap screws may be taller than space allows for in many of the parts that stack together or for which a recess is provided (e.g. corner pieces that support the conduit rails).
I was able to easily locally source the hardware here in the US even during the pandemic. If you absolutely need to work with the hardware you have on-hand, I suggest you check clearances as you go and be prepared to improvise (e.g. grind down a head where needed) if you find things aren’t fitting.
I think the other problem with allen head cap screws is that the diameter of the bottom of the head isn’t large enough. I think someone built one using them and had to add washers on all the bolts to even out pressures on the plastic.
I built my mpcnc with Allen head bolts. There are 4 (from memory) parts on the gantry that will not accommodate Allen head bolts and normal hex bolts are needed.
Since very few (none?) of the bolts are really, really tightened up, I haven’t had any problems that needed washers yet.
Purge the t. It’s Innensechskantschrauben, also known as Inbusbolzen. Hex bolts are Außensechskantschrauben, JFTR.
And as others mentioned: Their heads are higher than standard hex bolts, but also a bit slimmer. There is an infamous video of a well known YT activist who tried to build an MPCNC in real time in a series of tutorials. He said he refused to use hex bolts, then found out that the allen bolt’s head was where something else wanted to be too. Funny scene then how he used an angle grinder to reduce the Allen head when he found out that that was an exothermic mechanical procedure, making a remake of that molten PLA part necessary.
Stay with hex bolts. They have their merits.
Just my two €-C.
