Lowcost capable CNC - Make vs Buy?

[JAZZCNC]

Indeed Jazzcnc,
So given I don't have a business case, but want to explore what the capability would bring to my workshop....the choice comes down for me at least to buy a Workbee or build my own for a budget of £1.5 to 2k. This forum shows that this second route is viable and is the route I am keen to take.

Forget the WorkBee or any of those you will be disappointed I promise you that.!
The Budget needs to be 2K to do it right if building DIY.

I should say I want a machine to cut hardwood in my furniture making workshop. 600x600 work area because I don't have the space and have plenty of processes for which this is big enough. Also helps with accuracy keeping small I believe. Want to cut joinery so 0.1mm repeatability. It will be a workshop machine that won't run all the time but when used needs to be reliable and quick (5m/min cutting?). A build I can complete in two weeks full time ideally..(planning, dreaming excluded)

600 x 600 is the perfect size to start your first DIY build. 5Mtr/min cutting no problem, if done correctly you'll double that with a bit to spare.
0.1mm repeatability, again no problem and easily able to achieve better if done correctly.
Building within 2wks could be a stretch for your first build and would require everything to go perfectly and put in some long hours. And obviosuly you have to have everything needed to hand.
For reality's sake, I'd allow your self a full month for fully built and working machines and work shorter hours.
Don't underestimate how long some of this stuff takes, just the wiring alone could take a full week if you are not used to doing it.

Frame
Stiffness directly effects performance so important. Unlike manufacturers, DIYer does not worry about shipping, so a steel frame, welded ideally. Epoxy leveling process allows imprecision to be addressed. However I would like to go Ali extrusion and shimming if possible alternative to avoid epoxy and steel working plus flexibility to extend/change frame in future.

Again Ali extrusion is perfect for first machine as it's easily worked with and accurate. However, you must use the correct type, size and not go with the light duty stuff often found on machines like the Workbee's etc.
It's also very very important how it's all fastened together and plates etc. Done correctly it's very strong and perfect for wood routers.

Mechanics
Linear rails, ballscrews and correct support bearings sourced from good chinese supplier as set. Leadscrews seem possible compromise that many designs accept, attractive as their lower profile nuts allow leadscrews to more easily fit between bearing rails and keep design simole. Guess wear and lower efficiency not a killer for home machine that operates fewer hours or am I wrong?

Don't compromise go with ball screws every time. A quality lead screw and nut that can get close to ball screw efficiency/accuracy will be just as expensive as Chinese ballscrew and won't be massively better in quality.

Dual drive Y axis seems to be preferred for simplicity now electronics can cope with squaring Gantry especially if drivers have stall detection.This especially of value to me as I want to be able to machines end of pieces held vertically through table.

Not strictly required on a machine this size if just cutting woods. However, it is better if you want to cut aggressively or want to cut very hard materials or aluminum, brass, etc.
Not all Drives have stall detection, in fact, very few do, even then they only work in a limited way. A much better solution is to use Closed-loop Steppers which have come down in price massively. Far better than the standard stepper system.

But again going back to usage and Budget, using a single screw setup is much cheaper and if you don't plan on cutting aggressively or harder materials then it could be wasted.
The other thing is that if you design the machine and plan the control box correctly it's not a very difficult upgrade at a later date to just stick another ball screw on and fit another drive in the cabinet.
I've built many machines for people like your self who were on tight Budgets and didn't exactly know what their needs were going to be so this approach was taken (all my small machines are electrically designed to do this). Very few actually found they needed to upgrade and those that did then it was a simple few hours to upgrade which they did them selfs.

Principle design challenge are the plates required to mount the components and join it all together. Aluminium can be machined with wood tools. Aluminium tooling plate is already flat, so either they can be cut and drilled myself or waterjet cut by contractor. Adjustability is principle to adopt rather than precision.

If you cannot make them your self by any of the methods you mention then I suggest you get someone to machine the parts rather than cut them on a waterjet or laser. unless they are thin parts. Both water and laser leave a taper on the edges of thick parts which can cause you more grief than it would to cut them your self with a hand router.

Gantry
Make it L shaped and use stiff large box section or extrusions. Extrusions make fitting everything much easier. Rails on front or top&front. One thing that eludes me is how best to join two extrusions to make L, what fitting works that way?

The best method for the "L" gantry is to bolt into gantry end plates with the ends. On a narrow gantry like what you want you'll get away with just one Bolt in the center which goes from the underside into a T-nut on the upper profile.(or can drill and tap the profile directly) However, it's important that you have a piece of material which is a nice tight fit that goes into the slots between upper and lower profile. This stops movement from sliding and the single-bolt clamps the profiles together. More bolts could be added but on short length like this it's not required.

Electrics
Nema23 steppers are big enough for small/medium machine (exact force and inductance to be determined), matched with proper drivers (digital, stalll detection?) and serious power supply (toroidal). Homing limit switches, inductive for accuracy and reliability. Get shielding and earthing of wiring right. Think through positioning and routing of everything.

Electrics are the KEY to a great machine. Take your time, don't cut corners and if the budget allows use closed-loop steppers, in fact, save up a little, wait a little longer if needs be, it's worth the wait.

Electronics
Mach3 and printer ports are old hat. Ethernet and UNCNC or Acorn seem to get thumbs up, though there are also dedicated controllers and open source solutions based on grbl are getting better.

Again KEY don't cut corners. Forget Grbl or open-source, yes it's getting better but it's still miles away.
If you want quick and good at a reasonable price then go with UCCNC and one of there controllers like the AXBB, there is nothing better for a wood router for the money.
Or if your like a challenge then take a look at Linux CNC and Mesa but get ready for a big learning curve.!

Build challenges
Machine accuracy is determined by build accuracy, so need a dial indicator and know how to use it!

A good design should make build process one of bolting together and aligning ideally, plus lots of wiring.

What have I overlooked?

Design is VERY VERY important and if done with a forward-thinking attitude then you can have a great machine for not a lot of money.

Lastly, let me just say don't get caught up in the "Steel is better than Profile" or " Must use Steel if want a strong machine" because it's often said by those who haven't built a machine using it.
I build machines using both or Mixture of both as is often the case and I can tell you now profile is more than good enough for any router which is to be used in a DIY environment or even a Small/Med business environment where speed and high material movement rates are not required. Accuracy and repeatability can still be achieved with a profile just like it can with Steel, that's down to how it's built the design and components used.

Good luck if you take this route and if I can help just ask.