Best Milling Machine for CNC Conversion

Hi - new member here in Beverley East Yorkshire

I'm looking to buy a milling machine with a view to using it to make parts necessary to convert the machine to CNC

In the price range I'm looking at, there seems to be several suitable but I'm not sure which is more suited to being reliable, convertable and as precise as possible for the price

I'm considering

VM32L from Amadeal

VM27 from Amadeal

Axminster SX3

VM32B from Toolco

Any pointers or advice would be hugely appreciated especially if you have one of these either converted or standard

Thanks

Monty

Personally I wouldn't mess about, if you want a CNC mill buy a CNC mill instead of trying to convert a manual mill. Of course the conversion can be done but you'll need to change most of the guts of the machine and it still won't be optimum.

Andrew

Join The SMEE and read their 23 articles on constructing one of from scratch?

Seems like a shedload of work. Interesting read.

John

https://www.cnc4you.co.uk/MM32L-CNC-FF-Conversion-Factory-Fitted

**LINK**

Converting a mill is a lot of work and you'll need a mill to do it. The company linked to above sells all the bits as well as the converted machine.

I think one of the biggest downsides to converting the type of mills you and John link to is the existing head.

Firstly you have a quill that is not needed and will be a source of play, noise and reduce rigidity

Spindle bearings will not be as good, for example my X3 manual mill has one taper and one plain bearing costing about £20 to replace. My KX3 has a pair of matched high quality taper roller bearings that I'm told could be in the region of £250

Then you have the lack of speed as most only go to 2-2500rpm which will increase run time using small cutters which are what these machines are best suited to

There are ones on the web that have had the whole head removed and replaced with spindle motors which gets round the problem but you are going to have to pay for it. At least the basic machine should be able to make the parts needed for the head swap

Edited By JasonB on 20/01/2022 10:05:09

If you haven't found it already, have a look at *** MyCNCUK ***

John

It's certainly true that a higher spindle speed than usually available on manual machines is very useful. If you look for the articles by Dick Stephen I referred to he published a design for a replacement high speed spindle for the X3. This used an ER parallel-shank extension chuck and (IIRC) poly-vee pulleys.

There are also the high speed spindles available from China which use 3-phase motors and VFDs, but I'm not sure just how good the bearings are in these. Also CNC4YOU have a range of Kress spindles.

Ian

I recently purchase a CNC4YOU converted MM25L complete set up, and although all the previous posts have a point I find it works for all my small projects I expect to use it for. At 4k it was far more affordable than a new dedicated machine at 10k , but it all depends what projects you have in mind, space and budget. I looked at old second hand machines but did not have space, time, transport, or expertise to update the electronics that some needed.

If a machine can make something under manual control then if the handles are turned by computer they can do the same, no less and perhaps more. Maybe not at breakneck speed, may have to to keep compensating for backlash but that should be easier for a computer. Ballscrews are nice to have but not essential, as is the supper fast spindle.

It does depend on the intentions of the OP. Sometimes these 'out of the blue' would be machinists have ideas to mass produce golf clubs or bits for motorbikes.

This might be of interest (as posted originally on mycncuk.com):

https://www.youtube.com/watch?v=pgMnH-LRCY8

**LINK**

Basically a guy in Oz who is fitting DC servos to normal mills with DROs on each axis and has a novel (?) controller to drive the motors closing the loop so that the DROs do the positioning rather than relying on ballscrews. I think it's novel, however I believe that LinuxCNC has the ability to drive DC servos as drives with external feedback in a PID loop. But I have some reservations about this approach.

• "Backlash compensation" isn't as easy as it seems at first sight. The idea is that when the drive reverses the controller "knows" how much it has to turn the screw the other way before the table starts to move. However for a worn machine that might vary along the screw, so quite a complex calibration algorithm is needed (in principle easy if you have DROs fitted anyway).
  
• If the calibration isn't quite right, every time the screw reverses a small error can be introduced, which is cumulative.
  
• Mach 3 has backlash compensation - I use it on my mill which has very small backlash in its ball screws. However you can see that there is still a tiny glitch, for example at an X or Y axis tangent on a circular bulge or pocket, so it isn't perfect. It's not very well documented as a feature either.
  
• I've tried setting it up on the main L/S axis on my Myford which has ~0.3mm lash and it really doesn't work at all. (Cross slide has a ballscrew.)
  
• In principle these problems ought to go away when you have DROs measuring the actual position, but there are some problems. Putting backlash in a servo loop and getting precise control is very tricky and it's all too easy to find the motor oscillating through the backlash. It can be tamed but isn't easy.
  
• Even if you can "compensate" the backlash, this doesn't mean everything is OK. CAM milling programmes can easily generate toolpaths which include climb milling, so the table can be moved by the cutting forces if the feedscrew isn't holding it steady. In the video I linked to above, the machine is shown milling a circular spigot on the end of a square - you can see that where the axes reverse there is a distinct mark left. I guess you might improve things by for example incorporating table brakes to prevent movement while the backlash is being taken up, but then you beging to wonder why you don't just use ballscrews?

As a final point, though the machine might be able to do whatever a manual operation can do, that's missing the point! No one is going to manually mill a circular spigot like in the video - you would put the work on a rotary table. And there are things like profiling gears and other shapes from the flat which would be virtually impossible manually.