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Ive seen it mentioned here that one of the Golden Rules for building your own machine is to make sure you have 'built in' adjustments.
Whats the best way(s) of doing that?
Oversize holes or Sloting holes, depending on the application?
Would you over size the holes in Gantry Plates when attaching to Gantry Extrusion?
It seem counterintuitive to me, to achieve a ridgid connection, but I understant to concept and the need.
Steve
I think the answer is - whatever works in that situation! I'm a great believer in the "if you can't build accurate, build adjustable" concept. On my machine, for example, the profile rails are held with (from memory) M5 bolts in 6mm holes to give a bit of wiggle room. In other places, where a component bolts to a bracket bolted to another bracket, I might use slots in both but arranged to give adjustment in two directions. It's a design decision but keep in mind all the time - "How will I be able to tweak this on assembly?" Which also means - "Will I be able to get to the adjustment bolts when it's all assembled?"
One thing I've done to minimise the total slop is to drill all clearance holes to minimal size and then enlarge as required. It's a tedious process and you will need to decide whether it's worth it considering the amount of repeated assembly/disassembly required.
Wherever possible try to design in a way that you can adjust only one parameter at a time and not have to undo one adjustment to get at another. That's much easier said than done.
I certainly don't like the idea of built in slop but I guess it has to be done.
I may use your method Kit. Only drill out the holes one has to.....We will see.
The idea of more adjustability isn't so much about oversized holes but rather not limiting adjustment by machining in groves etc locking plates to other plates.
In an ideal world machining in reference edges etc is how you would do it but this only works if the whole machine is done this way so everything aligns perfectly. In the DIY world, this isn't so easy to do because you really need another machine to do it.
So not limiting adjustment so if you need to tweak alignment etc it can be done by either opening a few holes or thinking about it from the start and putting slots in plates etc.
One of the methods I use in critical areas that need locking is to machine slots into the plates to allow adjustments, then when all setup I lock the plates together using tapered dowel pins.
The key at DIY level is to not restrict adjustment and when designing think about how the adjustment and alignment can be done.
Perhaps one of the most important things to keep in mind when designing a DIY machine is that you cannot just copy a commercially produced design. Those machines are designed to have their components accurately made by another machine as Dean points out. Without that luxury most of us are hand drilling, filing and shimming a bespoke machine which must be designed as such.
On this note I can highly recommend the book I'm reading at the moment... 'Exactly' by Simon Winchester. 'How precision engineers created the modern world'. Fascinating stuff for the likes of anyone likely to be reading this post. Have it delivered by wireless to your Kindle (the best invention since the printing press).
Thanks guys.