Here we go again . . . MK4

[routercnc]

Well, thank you all for the kind words of support. Means a lot, especially coming from the seasoned machinists on here.

I've re-read some of my latest posts and have realised that they paint a glowing picture where everything I do is perfect and works first time. This is misleading for the novices out there so I've decided to include things that went wrong for posts where there is something of interest. Readers have just as much to learn from things that work for me, as well as what not to do!

So here are some things that did not go so well / areas for improvement.

1. When making the bearing holder I'd broken my last good 6mm carbide the day before and a new one had not arrived. So I was stuck with an old blunt one. To give it a fighting chance at the pocket I chain cnc drilled out some of the material using a 3mm drill bit:


But the carbide bit made a nasty noise and was not happy. I switched over to a 3mm carbide and carefully cut it out. You can see the evidence of the 6mm blunt carbide on the top surface:


I had another look through my draws and found a single flute 6mm carbide which I've used for plastic. I cut the outer profile out with that one, plus all of the second part.

2. The 'second part' in the photo was actually the third part:

The real second part went on the scrap pile. On the drawing I'd called for a 36mm bore to take the bearing. After the roughing cut (~1.0mm under) I offered up the bearing and it almost fitted. Scratched my head and measured the bearing and it was actually 35mm. Using Vectric 2D you cannot leave stock etc so the quickest fix was to frig the tool diameter (e.g. telling the software that dia is '8mm' whereas it is actually 6mm gives you 1.0mm stock). Rather than re-draw the part, CAM, etc. I did a quick calc and frigged the tool. Bearing dropped in the new bore with 0.5mm clearance all round. Useless! Thought about making a sleeve, but 1.5 hours later had a replacement made with the proper size bore.

3. The radius on some of the corners is exactly 3mm. This is bad practice with a 6mm bit as there is suddenly a large tool engagement which leaves a witness mark. Better to go with 3.1 or 3.2 if radius is cosmetic. Look at the bottom right inner radius to see the slight chatter. Not a big deal, but one to be aware of.


4. Vectric cut 2D does not have lead in/out. This means there is a tool witness mark at the start / end of the finishing cut. You can help with a ramp in, but the exit goes straight up past the side of the work leaving a groove/scratch. Look at the wall near the top left screw:


Let me know if the bad stuff is as interesting as the good stuff and I'll include that too . . .