Thread: Here we go again . . . MK4
Cheers Clive, good method.
Had a go at sorting out the beams today. I set the front beam using the datums I'd left on the bed:
I used some shims to take out the slight rocking on the underside and get a better clamp:
I then started to skim the face of one of the beams taking off as little as possible. I'd hoped this would only need to remove the high spots but in the end I had to machine back the entire face to get back to a level surface everywhere. Probably had a slight twist in it.
Looked good. Actually this is the first bit of steel I've machined on this CNC and I did get covered in tiny showers of swarf. As it is hot today I had a T-shirt on and they were very hot!
Anyway, then I offered it up to the gantry and as I tightened the bolts I watched for any movement - there was none. I tightened all of the bolts then tried to rock the assembly and unlike before it was solid, there was no rocking on the base plates which means success! Very happy and back on track. Hopefully the other beam is just as straightforward.
Looks quite nice although the steel bits will all get painted.
Looking good, good luck with the next beam!
Well I haven't moved onto the 2nd beam yet for 2 reasons. Firstly I've decided to do all the work on the first beam and make sure it is all going to work out. Secondly, although the outer face is now machined flat, I realised that the lower face is not flat enough. So I started by machining that square to the outer face (part is upside down):
It now sits properly on the base plate and is square to the outer surface:
I then flipped it over and spotted all the rail fixing holes in the top surface for the rail.
Next up was to add the reinforcement plate on the inside. I chopped 2 bits to length using the new Rage saw - really easy and quick:
I used metal epoxy to glue the strip in having first sanded and de-greased both surfaces. I then knocked them both with my knuckle and the epoxied strip one doesn't ring like the other beam. Although I'd added this strip to give reinforcement and extra depth to the rail bolts it has also helped with the resonance. Might help with the cut finish a bit:
Then opened out the small spots made on the cnc machine and then drilled and tapped the rail mounting holes to M5:
I haven't machined this top surface yet as I will do it as a pair with the rear beam to get them exactly the same. Although they will have 5mm deep epoxy on top to mount the rails on, and therefore don't need to be machined, the 'MDF mould' I'm drawing to pour the epoxy into needs to sit on a very flat surface. I'll show more when I've finished the design of this mould part.
Then a trial fit and it sits squarely on the base plate too now:
There is another bolt to go inside on the lower face, plus 2 holes to drill in the inner vertical face to add another connecting block. Basically the RHS will be supported on all 4 sides so should be a pretty good joint when done. Then the end plate will go back on with the stepper mount in.
Finally, something I wondered about recently. All the spot drills I've bought and used have been 90 degrees. The twist drill is 118 degs so when it goes into the hole it contacts only a 2 points until it gets going which is a bit hard on the drill cutting edges. Centre drills are 60 degrees so same problem. I had a look specifically for 118 deg spot drills on ebay and they only came up on the american ebay site and there weren't that many. I didn't look for long so could be me but are the 118 deg spot drills not popular? Or are 90 deg spot drills designed to give good centering alignment on 118 deg drills?
Last edited by routercnc; 24-06-2016 at 10:04 PM. Reason: pictures fixed
Other jobs around the house mean slow progress in the build. I've managed to get the second beam machined.
Drilled and tapped the M5 holes. I bought this spiral fluted tap which has different colour bands for different materials. I thought I'd try this yellow one (for steel) and it works really well.
I've sprayed them with a light dusting of zinc galvanising spray (screwfix) just to keep the rust off and make them look presentable. I've found this sticks well to metal and resists scratching. (Note Spitfire languishing in the background )
Next job is to put it all together, shimming if required, then set it aside. Then move onto making parts for the bed.
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 . . .
Last edited by routercnc; 02-09-2016 at 08:38 PM.