I'm hacking a decent hobbyist machine as I learn my way around CNC routers, and I was looking at it tonight and one of the things that bugs me is that if I can't really use my entire z-axis with a router -- if I were to theoretically bottom it out it with my longest endmill it would go through my spoilboard and probably cut through the table underneath... I don't want to chuck the router too high up, that seems dangerous, it's already bumped up a bit in the mounting bracket to accomodate the dust shoe.... so I'm looking at v-slot rails and the potential to expand the height of the frame (20x20 v-slot rail -> 20x40 or maybe even 20x60 or c-bream rails to increase stability of frame??) and then mount that on top of spoilboard... it all seems fairly straightforward and should yield an extra couple inches of z-axis range, but is there some problem with plunging the z-axis too low below the x/y housing?
From your description I gather you are suggesting raising up the entire machine. Raising up the entire machine (or dropping the spoil board down) does not fundamentally change the rigidity of the existing machine structure and is usually the best way to make the most of what Z travel you have. As long as the new structure placed under the machine X-Y frame ro raise it up is 'appropriately solid', then it all should be ok. That is, if I park my car in a car park, it could be now raised up by a few storeys and I would happily still sit in it, but if the same height increase was acheived by putting the car on bricks, I would feel less comfortable being inside ...... How 'solid' it needs to be really depends on the exact machine geometry and the material being machined. For the router clamp aspect, the further the tip of the router bit is from the machine main frame sections, the more leverage there is acting to twist the machine. Again, it really depends on machine geometry and material being machined as to what the combined effect will be, but in general, having the clamp closer to the collet-end of the router (but still clamping properly on the router body of course) will improve the overall machine rigidity. If you are milling foams, then a light-weight structure to raise the machine may be fine. For machining metals or especially some plastics that like to 'grab' the bit, then making sure the machine cannot rock on its new mountings becomes far more important.
Evan, thank you so much for your reply. To your point: If I'm understanding you correctly, it sounds like you're saying the opposite of what I initially assumed, and that having the router fairly high up in the clamp is preferred. Most images I see of routers in CNCs show them clamped at the top / furthest point from the collet, ie: and I assumed this was therefore the default / safest setup currently my router is mounted more like this, about halfway thru the bracket; I previously said I had it lifted it as in the second photo to accommodate the dust shoe but that was late night newbie brain mis-speaking, I did in fact raise it to yield more workable z-axis, the dust shoe prevents me from raising it much higher... and of course my fear of introducing stress on the frame prevented me from raising it as high as I possibly can... but it sounds like you're saying higher is better, and this final image is the "ideal" height in the bracket? Thanks again for patiently explaining to this n00b
This one is more marketing for the adapter, thats probably not even tightened down. You do want to clamp lower usually, but not so low on the body, that your shortest endmill can't reach the spoilboard
I found with my old machine that to get a small bit to reach the spoil board, I had to slide the spindle so far down, I was at risk of just clamping around the cable! The worst was drilling PCBs where the drills are short and the PCB's are thin. At least for the PCB work with the small bits, the cutting forces were really low in comparison to when I had a long 1/2" shaft bit in and was roughing out a 3D tool path. The low cutting forces did not pull the spindle sideways much, so having the spindle dangling low was not a problem. With the longer heavier bits for 3D roughing, because my Z travel was limited, I had to push the spindle up in the clamp as close to the collet as possible in order for the bit to clear the workpiece. Luckily having the collet as close as possible to the clamp was also the strongest configuration, and did best to resist the heavy cutting forces. There are a few 'gotcha' situations though where high cutting forces occur with the worst-case configuration of the spindle pushed right down in the clamp. I was cutting some thin plastics that had a tendency to 'grab' the bit and I accidentally set the toolpath to be climb milling, causing the bit to catch an edge and dig deeper, with unpleasant consequences (conventional milling for that situation would have saved the bit...)
