Here we go again . . . MK4

[routercnc]

I've put off assembling the gantry parts for now and moved on to making the bed rail supports. Here is the basic bed structure and the parts I'm making now are the large RHS sections on top of the uprights (highlighted).


First job is the chop the RHS down to the right length. The Rage saw cut through in about 30 seconds, with minimal effort and just a few sparks. The section is 100x60x5mm wall thickness steel so very impressed:




Light dusting of zinc spray to make the marking out/spot drills easier to see:


Dialling it in as best I could - it bumped around a bit when jogging along the edge but I got it pretty much aligned. From memory I think it was within 0.3mm high to low spots.


Then onto spotting all the holes. It is longer than the machine so I did 80% of them, then pushed the part back and zeroed off the last hole to finish it off. Bit fiddly but actually not too much work.


Then onto the drill press to get to work on it:


I had some M6 holes to tap so used a generic spiral fluted tap but it did not feel good. The effort was high and I could see it twisting. In aluminium it was fine, but this was not going well and the thought of it breaking was too much. So off to ebay to get another yellow ring (steel) tap from Europa tool. Tried it out and the effort was much lower. It made short work of the threading, so ~£7 well spent I think.


Next job was always going to be a bit tricky as one set of the M5 rail mounting holes was on the radius. I spotted them on the cnc and went very slowly to reduce deflection. But drilling them on the pillar drill was not working - the bit was clearly deflecting away.


So I knocked up a drilling jig:

The existing tapped holes help locate the fixture to drill out the holes on the radius. I drilled the holes in the fixture a very close fit to the bolt diameter so am using them a bit like dowel pins - thought about getting some shoulder bolts but didn't need to in the end. Just tried drilling one of the holes (with a cordless drill as a quick test) and it picks up the spot drill mark and works well. Will do them all properly on the pillar drill.




In case you were wondering there will be 5mm epoxy on top of the rails which will 'fill in' the radius to create a flat surface to mount the rail. For now they are supported 16mm rail, but I've done CAD checks for 20mm linear profile square rail and it will fit fine and just needs a simple interface plate to bolt it to the gantry. But at 1100mm they get expensive so I'm not buying them at this point.

Next up is some simple holes in the side (will do these the 'old way' scribe, centre punch, spot, drill . . . ) and then repeat the whole lot as a mirror image on the other one.

I've also cut up all the vertical supports which go between the rail and the bed:

These need the holes drilling out to around 9.0mm to allow 120mm long M8 bolts to pass right through and into a nut / nut plate in the lower extrusion channel (not shown), bolting the RHS rail and the uprights to the bed in one go. I think this will be better than using lots of little L brackets.


All for now . . .