Hole Sizes
People who have bought my un-reamed parts often ask what size the holes should be.
I supply the pulleys and gears reamed even in an un-reamed set. The hole for the motor shaft is 5mm and the hole for the grub screw 3.5mm. I ream the hole in the large extruder gear to 3.5mm and tap it M4.
The big holes are 8mm. The rest of the holes in the bot are 4mm and 3mm. You should be able to see which are smaller.
The holes in Adrian's extruder are all much tighter. They are a mixture of 3mm and 4mm, again you should be able to see which are which. The 3mm ones are the motor screws and one in the base and one in the driven holder, which take M3 studding to hold the PEEK support for the PTFE.
I do the three on the filament path 3.5mm to allow for some clearance with oversized filament. I also do the four in the idler holder 4.5mm as it makes it is easer to slide along the long bolts. To insert the nuts in the idler holder I put them on a soldering iron with a conical tip at 200C, heat for a few seconds and then push them in with the iron while holding the bracket upside down.
The counter-bored holes in Adrian's extruder are a pain. I use a 7mm reamer with the end ground flat. I do these now even on my un-reamed sets as it is very easy to go too far with a drill.
Beware that four holes in the carriage lower part are at an angle.
If in doubt of the size look at the assembly instructions and see what size fastener goes through the hole. Although in engineering it is customary to use clearance holes, e.g. 4.2mm for M4, I find 4mm is sufficient clearance on my parts for a nice snug fit. Drills usually produce slightly smaller holes than reamers.
Building
Here are my observations from building mine hydraraptor.blogspot.com/2010/03/making-mendel.html
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My attempts to make a rapid prototyping machine that I will use to make parts for a machine that will be able to make parts for a copy of itself.
