[Rabs2014]

Hi everyone,
I have a 1980s vintage benchtop CNC milling machine from the UK (Conect Contour Major) that I picked up very cheaply. The axes are in good condition but the spindle is shot. There is noticeable play between the spindle nose and the quill housing which results in ~0.3mm of play at the end of a typical length tool.

I'd like advice on what to do with the spindle.

This is a benchmill similar in size to a Grizzly G0704 or a Sieg X3. At somewhere between 100 and 200kg it's not tiny, but nothing like a full size mill.


I want the machine to be capable of accurately machining fairly small parts (<100mm in any dimension) in plastics, aluminium and occasionally unhardened steel. I have no current need to machine stainless or any hardened steels. I don't need it to be fast. I don't need it to last forever and I don't mind if I don't get optimum cutter life. I generally do 1-off modifications to relatively expensive prototypes where the value of the work makes fast machining or replacement cutters a non-issue. I'm rarely using the machine for more than and hour or two a week so it's not a production machine. I often want to use small diameter tools (<1mm). In an ideal world I would like to be able to use a 10mm diameter endmill, small flycutters and small shell facemills (<50mm) but having a spindle suitable for the smaller tools is more important to me than the larger end of the range.

I don't need ATC.

I could repair the existing spindle. The motor is in good condition but the spindle itself would need new bearings and quite extensive rework. This would probably be the cheapest option but I'm not keen for a few reasons. 1) The spindle taper ground to a weird taper for the Coventry Easychange system, which is uncommon and expensive. 2) The speed is limited to about 3000rpm and I want to be able to use small cutters in aluminium (although I would be happy to use a secondary spindle for this if necessary). 3) I'm not particularly confident that I could disassemble and reassemble the spindle with new bearings to achieve a low runout.

After that it seems like I have a few options:

1. A Tormach Bt30 spindle cartridge and modify the existing belt drive to operate it (Page Not Found | Tormach Inc. providers of personal small CNC machines, CNC tooling, and many more CNC items.). This will be expensive to import and is limited to 6000rpm, so I assume that I would still need a secondary spindle for small cutters in aluminium and plastics.
2. A replacement headstock for a common mill like a sieg or grizzly and find a way to mount it. (such as The Page Cannot Be Found - LittleMachineShop.com) This would probably be even more expensive than the tormach but would come with a motor and be easier to retrofit to the machine. This would probably be even more limited to about 3000rpm, so again I'd need a secondary high speed spindle for some of my work.
3. A chinese 2.2kW or 3kW high speed spindle. I imagine that I will need a better VFD to get anywhere near decent performance from it at lower revs. This seems like the lowest cost option and the only one that I've found that has any possibility to deliver everything I need in a single spindle. However, I would be restricting myself to small diameter carbide tooling for working in steel to keep the SFM up in the working range because my minimum speed will be ~8000rpm.
4. One of these: http://www.skyfirecnc.com/picshow2.asp?id=18. Which seems like a pretty good value option but I know nothing about them - has anyone every tried one? How is the quality?
5. Something like this: Page Not Found - Aliexpress.com. Only for low speed and then a separate high speed spindle. But again, absolutely no idea about the quality of that.

So, does anyone have any other suggestions?
Can I do the work I want to do with only a high speed spindle if I choose the right tooling? Or will I need something that can run slower?
What do you all recommend?

Many thanks

[awerby]

High speed spindles aren't recommended for cutting steel, at least with cutters over a half mm or so. If steel is still in your plans, then fixing the existing spindle or replacing it with something similar would be advisable. None of your links seem to have worked except the Skyfire one, but that looks like the sort of spindle that would work for that. Setting up an alternate spindle to use for soft materials sounds like a good idea too, particularly if it can be easily swapped out for the standard one. Here's a fellow who's restored one of those mills to health; perhaps he could advise you further: Contour CNC mill upgrade | CNC Milling Machine | CNC Router Systems