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VCO cont. .fpd drill holes for pots.
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author VCO cont. .fpd drill holes for pots.
satindas
I'm close to confirming an order for my first batch of front panels and just noticed that the drill holes for the pots on the VCO controller are 8mm and 7mm .. rather than the standard 7.5mm for 16mm Alpha pots. This obviously hasn't caused any issues (nothing in the forum) but I thought I'd flag it up just in case. Anyone know any reason why they are like this or can I go ahead and alter them to 7.5mm?
julian
I think that, for my own builds, using the 16mm alphas, i cut the holes to 6.9mm.

Again, on my own builds, I never really see any point in adding the 0.5mm tollerance thats so common. I just measure the parts with some decent verniers (i dont go from the datasheet, as theyre often not completely in sync with the real world) and cut the holes accordingly. I maybee round up to the next 0.1mm or somthing like that to be sure.

Its no way unusual for a good cnc cut to not go outside of 1/10 - 1/20th of a mm on hole diameters. Cutters do ware though, so its hard to get closer than this without constantly recalibrating - but, even at the upper end of this, 1/10 of a mm is still way smaller than the common 1/2 mm tollerance.

I can totally see the reason for 'general circulation' fpd files to have 1/2mm tollerance, but, if you can measure the part well yourself, and the place making the panels has good tollerance, then im unsure of the benfit of adding 'slop' where its not required?
Synthbuilder
satindas wrote:
I'm close to confirming an order for my first batch of front panels and just noticed that the drill holes for the pots on the VCO controller are 8mm and 7mm .. rather than the standard 7.5mm for 16mm Alpha pots.


Well spotted. The VCO Controller was the first of the alpha potted 5U boards so I was erring on the side of caution. As you've probably seen all the other more recent panels are 7.5mm. I now know that 7.5mm is just fine for these boards so I'll change the VCO Controller fpd file straightaway.

Ok, but why 7.5mm and not 7mm. The 5U Oakley FPD panels use a simple grid of 2.58mm because that is what I always have used. It allowed me to match MOTM's imperial based grid well enough but keep the measurements metric. It also allows me to use the same grid for the pots and sockets - the early Scheaffer program did not support multiple grids or offsets.

However, PCBs are made with a 0.1" grid - although I will place with an accuracy of 0.025". To allow for the slight differences in the PCB's 1.625" pot spacing, the panel's 41.28mm and the actual tolerance of the pot legs, the hole is made generously large.

Tony
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