can someone please help with hole dimensions

[reefy86]

thank you. just dont want to be making any mistakes in my drawings and want everything to bolt together nicely the first time.

Ash

[komatias]

ok, the precisionist in me is screaming right now because I work with drawings, precision and accuracy on a day to day basis.

Everything has a tolerance, even ground shoulder bolts. A vernier caliper is not the golden standard as it has a 0.02+/- accuracy tolerance. A micrometer on the other hand is the standard. Would you need this kind of precision for your application? That is your decision.

Now when you use a 12mm drill, you are likely to get a 12.1-12.2mm hole. If you want an accurate hole, you need to ream it.

[Clive S]

thank you. just dont want to be making any mistakes in my drawings and want everything to bolt together nicely the first time.

Ash

This is getting silly now just use standard cap head bolts like everybody else dose

[reefy86]

This is getting silly now just use standard cap head bolts like everybody else dose

i dont mean to make this thread all pointless and silly, i have no real experience when it comes to cnc or mathmaticals unless its your typical diy timber frame that any dummy can do. now the cap head bolts was what i was using but then the shoulder screws came into it :). now ive read hundreds of threads and love them all and watched plenty of videos to know that there cant be any play in the machine regardless if its just cutting wood or aluminium so this is the reason why i asked about clearance hole size because when looking at the drill tap and clearance chart it tells me the clearance for an m8 bolt is 8.4mm but the bolt is 8mm so i asked if 8.1mm clearance hole would work and then i got told id get tolerance issues. everyone who is helping me here has their reasons and know what they are doing and i apologise for confusing people :)

Ash

[Neale]

Another way to look at this is that if you have access to high-precision machining and manufacturing facilities, you can make parts to incredible accuracy and just assemble. That's how car manufacturers work these days. If you are building with typical home workshop facilities, build with a bit of slack at key points and then align on assembly. That would never work commercially but with care and a bit of extra time, it can give good results. So I would go for 8.4mm clearance holes, for example, to give a bit more wiggle room on assembly. If you want to lock parts after setup, you could drill and ream through both components and fit dowel pins but I doubt if many do.