Jill of all trades, but mistress of few !

[Smiler]

Hi Julie,

Welcome to the forum.

Only advice I can give is:

Know what you want to make beforehand and size your machine accordingly. It's pointless having an 8X4 router and then having it only making 18" long house signs.

CNC is really, REALLY good at multi-run jobs, but not for one-offs unless you can price it right. It ISN'T just another tool like a drill or a planer, it is a manufacturing system that can do the jobs of all your machinery in you workshop but I bet 90% of the time you will use the drill or the planer or whatever simply because it is easier and quicker to do than writing the program or generating the CAD/CAM. WHen I first built mine and I wanted to say cut a 20mm groove across a sheet for a shelf to fit into, I would clamp it down and zero the machine, then type in a move to the appropriate distance up the sheet, lower the Z to the required depth and then simply zip the cnc across the sheet, job done. I don't do that anymore, I just clamp a straight edge across the sheet and run my triton router across it by hand like I used to, quicker and easier.

If you want to get into 8x4 size machines and cutting the likes of oak etc. think of getting into welding classes and build it from steel with supported rail on all axes, rack and pinion on the 8' axis and ballscrew on the other two. IMHO an 8x4 from MDF or baltic birch can't hold a candle to a steel or aluminium framed machine for rigidity, Irving will be able to fill you in on the deflection of wood vs steel. If you are thinking of doing this professionally, i.e. to earn a living from, then you really need to be building in longevity and accuracy IMO only a steel framed design will give you that on the scale of machine you are looking at.

You are looking at splashing £2,500+ to get a half decent machine up and running, 8x4 really is getting into commercial territory size-wise and it might be cheaper or more sensible to look at a second hand commercial machine. If you want to build one for the experience, knock yourself out, that's why I built mine and I can honestly say it's the best thing I've ever made and the most fascinating hobby I've ever had.

I don't want you to think I'm trying to put you off but do yourself a favour and decide in the first place what you want to actually DO with the machine and stick to it!

All the above my own humble opinion as always but good luck whatever you do and don't forget if you start to build one, we want to see pictures!

Jeff

[Julie]

Hi Jeff,

Thanks for the reply. I'm not put off by your words of warning and do appreciate all advice and points of view.

I do have some clear ideas on what I want to do. My most immediate requirement is to do engraving on a large number of wooden panels. They will not be very wide, but will be of varying length, with many of them being in the 2 to 2.5 m range. My current solution (which I have prototyped) has been to make up a wooden jig then use a bearing guided cutter in my hand router. It works, but I would expect to able to get better accuracy and finish from a cnc tool. Beyond that, I have other ideas, but nothing so specific yet. However, I think I'm sufficiently clear on my needs and ambitions to decide that if I do this at all, I should go for the size I've suggested. Equally, other functionality that might be nice to have, such as additional axes, are not high on my priority list at present. In summary, yes I do think I''ve got a suuficient handle on what my needs are.

I certainly wouldn't dispute your point that a cnc router would never be the best option for all tasks. I have many other machines and hand tools in my workshop that will continue to earn their keep.

I think welding is a skill too far for me at this stage. However, since my original post yesterday, I've noted one or two websites advertising ranges of extruded aluminium profiles. This has started me thinking. I should be able to handle that, provided I can lock everything together by mechanical means (i.e. brackets or other fixings).

I'm interested in your suggestion to go rack and pinion on the long axis and ballscrew on the others. Is this because rack and pinion is better over such lengths or is on the basis of cost for a ballscrew system with sufficient rigidity at that length? (I'm not doubting your advice, just keen to understand the rationale behind it.)

I was wondering whether anyone was going to come back on me with regard to my idea that the router spindle should be of the order of 2 kW. I note that commercial machines are at this rating or, indeed, much higher. The only DIY offerings I've seen so far though are the Kress models that only go up to about 1kW. I've noticed that large commercial machines often talk about water cooling. I wouldn't want to go to that complexity. I could go 3-phase (off an RPC that I've already installed to drive my saw / spindle moulder) but would probably rather stick with single phase.

I have had a long term search set up on ebay for cnc routers, and while they certainly come up regularly, anything that might fill my wishes (adequate size, not too ancient) still goes for more money than I could contemplate. For example, there's currently a Pacer Cadet on offer. It has only a 1220 x 700 mm bed, albeit with computer and vacuum pump thrown in, but the seller is seeking around £6k.

As you can see, I really would benefit from a good, comprehensive idiots guide if one exists.

Thanks

Julie