Here we go again . . . MK4

[routercnc]

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?