Four options for an unwilling builder

[Maurizio]

Bah-humbug.
I'm sure everyone has their own greatest pleasures, and for me it is using tools to make concepts, rather than making tools (CNC).

As such, I was hoping for some advice on the following four options for my given use.

My use(mm):
A 400X 300Y 100Z working lengths (plus a bit extra Z clearance)
Hardwood or Aluminium
Precision - +/-0.003 seems to be the goal for journal bearings for making bicycle brakes. I suspect there is quite a bit of leeway here, and tool wear will be important. (Calculated using an ISO online calculator for hole tolerances) - as my important tolerances will be holes, it might be possible to circumnavigate machine precision milling in favour of precision drilling.
Resolution - Using a 0.2 end mill to do small carvings on a 17x17 square (keyboard caps)
Repeatability - I would like to do some small production runs (if that evolved then there would be the self generated funds to invest in something truly industrious)
I have a max budget of £1600, plus a bit extra for end mills/making a table to mount it to.

Option 1. Buy it. Doesn't seem feasible, the budget machines represent poor value for money and poor accuracy and to cap it off are geared towards sheet goods.

Option 2. Buy it second hand. Solely dependant on a machine being available. Potential risks with wear.

Option 3. Convert a Mill (used or new) - very very tempting. As my work surface isn't very large this could work, the frame rigidity and slides are already taken care of. I'm a bit concerned about adding the appropriate steppers and balls crews in case clearance is a problem. Additionally I'm not wholly settled in my current place, so moving with this could be a nightmare.

Option 4. Build it sticking to a KISS mindset. I've drawn up plans and budgeted it - it works! However, a fair amount of work, with potentially variable outcomes. I would also have to settle on the 'best' compromise, which after 17 different machine plans so far might be tricky.

I'm posting this because I'm already a few hundred hours into option 4 and I can see it growing arms and legs before it's done. As using, rather than building, is my goal I wanted to check whether to nix it now, rather than down the line.

I would love to hear from anyone who has gone through a similar experience, has experience with the different machines, or insight into my (perhaps incompatible use goals).


Mille Grazie,

Maurizio!

[Doddy]

Just to pick up on some points...

Hardword or Aluminium.... journal bearings? are you sure?

Journal bearings at the accuracy that you're looking at (3 micron) is a job for a rigid lathe and toolpost grinder, not to mention the surface finish. You'd blow your budget just buying a ball screw that supports that accuracy for a mill/router.

Keytop engraving?, that's a completely different use case, and you now need a bed of 17x17?, and with 0.2mm dia end mill you're looking at a 30k-100k spindle - sounds like a very different machine.

Option 3 - you're not going to get a mill with 400x300 that fits in a small work surface with bed travel of this size.


Question if you're looking at the right machine for your use case. And whether you're really looking at one machine.

[Maurizio]

Hi Doddy, perhaps I don't. To me journal bearings has meant oil lite/bronze/synthetic bushings.

Likewise although that was the quoted tolerance, I suspect I have got mixed up. After all, they work even with a small amount of slop in them!

No, not a bed, I was just giving a size of the piece to give context! So a 17x17mm piece, with some engraving on top. I just wanted to check that this level of detail was feasible. Good point on the spindle speeds!

You're right! There is definite flexibility in my designs however, so looking at e.g. warco wm 16, it has 400mm by 170 of table travel, so could work if I just segmented the bigger designs.


Overall - you're quite right! It might not be possible to have a machine to do the wood/art projects and the aluminium/technical projects. But I'll shoot for the moon first, and if its not possible so be it. And only then will I start buying things

[Maurizio]

Right. It appears that dream was short lived! I got too caught up in designing the frame and mountings for things to think about wether the base use was achievable with one machine. It's not. I wonder if there is a nice graphic representing use Vs machine design for CNCs somewhere. If not maybe I'll sketch one..

Moving forward:
I'll send cad files to machine shop for the mechanical prototypes.
The machine and budget have been reduced to wood only, I wonder how much precision it's possible to wrangle out of a 3040 machine..

[pippin88]

0.003 inches or 0.003mm?

25.4x difference!

Don't expect to circular interpolate even the 0.003 inches on a home build or manual mill conversion.

At your budget, bearing journals are a job for a boring head or lathe

[Maurizio]

Hi Pippin,

I had done them on the lathe before, and has assumed (incorrectly) that the job would be transferable. Alas.