Thanks very much jeffmoss- I’d love to see the Cleveland fed door- security would probably end up dragging me away from it come closing time 🙁giggle):
Doug, got timed out 3 times so hope it all makes sense- here goes………
1- Yes pretty much the same- I’d still use a centre drill to start each hole though- especially in steel. They eliminate any flex or deflection, the tiny pilot on the end is a small initial contact area so centres perfectly, and as you feed it in the main diameter enlarges the hole nicely to a size to suit your secondary drill. On a small model where the wall thickness is less you can of course go all the way through with a centre drill- just make sure you flush the swarf out thoroughly as the basic slash flutes on centre drills tend to choke up fast.
I’d also plan it so you cut the boltcase out to leave the inner ring as part of the door- makes it a lot easier not having to fix it in position for all the cross drilling- small parts on small machines means access often gets difficult and things get very confined with dividing heads and rotary tables etc.
2- As to whether you drill or ream the holes, I think that’s down to whether you’re making a working model or a static. No point going to all the extra trouble of reaming them if the bolts are only going to be fixed rigidly in place. On a working model though, yes they should really be reamed to get the holes a perfect fit for the bolts- as I found out long ago the smallest amount of tilt on the bolts when they slide- so small you can’t even notice it- can still be enough with certain designs of boltwork to jam it solid! Don’t forget the smaller you go with moving parts the harder it becomes to maintain accuracy and 20 or 22 tiny bolts being driven by tiny parts still amounts to a lot of friction and contact on the tiny mating surfaces. If there’s the slightest little irregularity on a pin, slot, or tilt, it’ll find it and jam solid on it!
I’ve only ever bothered to ream them on working doors- most of the ones I’ve made more recently have all been detailed statics to sit on the desk or wall, so getting the bolt holes accurately positioned has been more important than the smoothness of the internal bore.
3- As for flattening the end first, I’d say that’s down to the material and the taper on the door- don’t think you’ll need to with shallow tapers if you use the centre drill mentioned before. Once up to a 10 or 11 degree taper in steel it would probably be a good idea, and for up to 20 degrees like the Cleveland fed it’s a must even in aluminium. Make sure you use a centre cutting one though- most end mills don’t cut on the end tip as they are intended for sideways cutting. You can soon tell by looking at the end- one of the cutting edges will be off-centre and one longer to overlap- usually 3-flute but some tiny ones are 2. They are normally called ‘slot drills’ here in the UK and can be used vertically like a drill or horizontally like an end mill.
Hope this helps and makes sense 🙁happy):
