Another Sieg X2 CNC conversion

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Crumbs, dont time fly by, hard to believe that it is not far off a month since my last update.

I have been working on this, but it has been a bit stop-start (more stop than start) as I have been just grabbing a bit of time where I can to work on it, so this post covers a few weeks of stop-starts.

I mounted the x-axis on the mill and it worked great, all it needed was a couple of 1-2mm thick packing pieces to go either side of the ballnut flange to fit neatly into the pocket from the old acme nut, then jsut tighten up the 2 grub screws and it was fine. Testing went exceedingly well and I am very happy with it.

That being done I replaced the X-axis back to the original manual acme nut and screw, and set about making the Y-axis stepper mounting, which is basically identical to the X-axis, so see the earlier pics for the details. Then I mounted the Y-axis stepper and mount onto the mill.

As you can see, there was a slight design flaw in that the gib screws of the x-axis would crash into the stepper mount, therefore limiting the x-axis by about 4-5mm. So as a quick and easy solution I just cut a little ledge into the mount with the bandsaw.

And here's a shot of both axis's

So now I can use the X and Y axis as computer controlled to help make the Z-Axis mount. It certainly is easier to just type in a command to move one direction by 72.3mm than counting turns of the handwheel. And being able to spot-drill all the holes at once and then go back to drill all the holes without worrying that you are drilling in the wrong place is just great. I guess it is like having a DRO, but instead of reading off the coordinates of where you want to be, you just type in where you want it to be.

So, onwards and ummm ....... sideways?!?!?

Well, two updates in one month, I think I may have to slow down and pace myself on this one :D ;D :D

So I have been able to make some progress, I have managed to grab a few mins here and there to escape to the workshop.

I have been working on the Z-axis stepper mount. The Z-axis ballscrew is powered via a timing belt reduction of 3:1, so 1st of all I made up a baseplate that had a pocket milled in it for a ballrace so that the stepper-motor's shaft and it's own bearings are not taking the strain by themselves. Then I made up a couple of stand-off's to support the stepper motor itself.

holes drilled and tapped and some partial assembly,

And with the stepper on board,

I then turned to what I thought was going to be one of the easier machining operations, drilling the steel timing belt pulley 10mm for the shaft of the stepper. In fact the drilling was really easy, the problem was I was holding the pulley by it's little spigot in an ER32 collet, and I failed to make sure that it was running true before drilling, and so the hole turned out to be a little askew. When I put it on a stepper and spun it, the pulley wobbled more than my uncle Joe after a night on the black soup ( guinness )

When I then bored it true and parallel it was 0.66mm too big. So I turned up a piece of brass to a sliding fit, mixed up some flux and silver soldered it in place. Then I re-bored the hole, this time I used my 3jaw chuck and used a Dti to make sure that the pulley was held true. Then I drilled it out to 8.5mm and then very gently bored it out to match the spindle of the stepper with a boring bar.

In hindsight I should've bored out the pulley a bit more before soldering in the plug, I had to go pretty gently while I bored out the remainder after drilling to 8.5mm for fear of breaking through the brass or if it collapsed any. I say this because the brass was only 0.6mm bigger than the stepper shaft, so the wall thickness would be only 0.3mm thick and I wasnt sure if the solder had worked its way all the down the brass plug, the last thing I wanted was to go too rough and then end up having to redo it all again.

Actually, in hindsight I should have made sure to drill/bore the pulley in the first place ???

So next I will be working on the base that will attach the stepper mount to the top of the column.

I also want to chase down some backlash that I have noticed (about 0.2 - 0.3mm) on the X and Y axis's's's's's's's, I think it is coming from where each of the ball-nuts attach to the mill table.

Well here's the latest update on this one, actually this is the combination of about 3 updates rolled into one ( to save the postage you know :big: )

I worked on making a top hat adaptor for the Z-axis, I turned it out of a lump of Ali', and bored out the centre to 17mm ( so that the 16mm ballscrew will slide through without binding ). Then I drilled and tapped 6 holes M5 to match the holes in the ball-nut.

Here it is with the Angular Contact bearing that it will sit in.

and with ballscrew and nut posed

I then clamped the large timing pulley onto the mill, and using the PCD hole wizard in Mach3 that I used for drilling the holes in the TopHat above, I drilled the same pattern of holes in it. Then it was over to the lathe to bore out the ID large enough to allow the ballscrew to go through it easily.

and the obligitory posed shot of how all these bits will stack together.

Then I turned back to the stepper mount, or rather the base that the stepper mount will sit on. I needed to have some means of adjusting/tightening the timing belt, so I made an arced slot in the base and used one of the mounting screws that the stepper is held on with. The screw on the left is the pivot point, and you can see the M5 socket head screw on the right in its arced slot. ( again using mach3 wizard really helped in making that )

And that's as far as I've got today. Next will be boring a hole in the base for the TopHat assembly to go through, along with a recess for the big AC bearing, then on to some mounting options for fixing the stepper mount and base to the column.

Just to do things a little differently, I'm making todays update in reverse!!!

So to show you the assembly of all that I've got done on the Z-Axis,

Then to break it down a bit, here's the ballnut removed showing the 6 holding bars that are threaded M5 on each end.

And with the timing pulley removed.

Then whipping the remaining assembly over we have the washer that holds the thrust bearing on to the TopHat.
I made the washer out of some 3mm steel plate, firstly drilling the 8 fixing holes and then holding it on the tophat and then turning down the outside diameter, then I held it in the 3jaw and bored out the inner hole, and then bored a little recess.

And the obligitory shot of everything in bits.

Well I have been a naughty boy, I have been chipping away at this one without taking any in-progress pics. So now I have a glut of photos to show today. As of today the mill has all three axis' cnc'd and working.

So here is a pic of the Z-axis in place. As you can see I have used a couple of side "cheeks" to hold the Z-axis stepper mount in place.

To attach the Z screw to the top of the mill head casting I chose to turn a M8 thread onto the end of the screw and then use a locknut to grip it tight.

When I drilled and tapped the mill head by hand, some idiot ( me ) drilled the hole slightly off centre, by about 1.5mm

So the solution that I came to was to make a little off-set adaptor,

and secured both adaptor and screw with locknuts.

With that done and the whole mill now working on computer control, I am now turning to looking at converting my Rotary Table.

My RoTab is just a real cheap one, so what I do may not be the way I would do it if it were a more pricey model, but I am just working with what I have.

I started by breaking the rotab down into its seperate pieces, and then I took the shaft that the worm is fixed to and shortened it and turned down a section to 6mm (to fit the bearing and oldham connector).

As you can see here I have left just a smidgen of the 10mm diameter sticking out.

This is for the bearing to rest up against,

Then the oldham connector is attached ( when final assembly is made I will clamp the oldham on the shaft while it is under some pressure, thereby gripping the inner race of the ballbearing which is in turn held up against the 10mm part of the worm-shaft, clear as mud eh? This is hopefully engineered so that when everything is tightened up in place, the worm will be held away from the inner face of it's guide just enough so that it will not bind up (as it had been doing at a certain point each revolution under manual activation) but the bearing will take up any lateral movement, or so the theory goes )

Then I made a steel washer that slides easily over the oldham coupling but butts up against the outer race of the bearing.

Then I turned up an Ali' spacer

The reason for the hole will become clear,

Spacer in place, showing that the hole allows you to tighten and release the oldham coupling that mounts to the stepper shaft.

Then I made a stepper mount out of some 10mm ali plate, This was done via semi-cnc using some of the wizards in Mach3 and also by just using single G-Code commands.

This is the side that the Ali spacer fits into. The outer 4 holes just need to be tapped M5 for the screws to hold the stepper, the inner 4 holes are for threaded rods to hold all the stepper mount pieces together and to the RoTab itself.

This is the side the stepper mounts to, you can see the circular recess for the boss on the stepper, and the 4 large counterbores are to allow clearance for the nuts to tighten the whole stepper mount onto the rotab.

And here is the obligitory mock assembly of the whole lot. I just need to make the threaded rods to hold it all together.


Looking good sir, your doing a real clean looking job!

What are you using for a mill while your doing the conversion? I found that to be the biggest problem while doing my mill and lathe conversions. You always seem to need to "touch something up" as soon as the machine is torn down.

Best of luck,
Thanks Matt

1hand said:
What are you using for a mill while your doing the conversion? I found that to be the biggest problem while doing my mill and lathe conversions. You always seem to need to "touch something up" as soon as the machine is torn down.

Well, I'm just using my mill, I just have to build it and rebuild it a lot!!! I have made a heath-robinson affair for a couple of jobs where I had to mill actual parts of my mill, for this I used my lathe, a cordless drill and a corded drill, and a number of files.

It can be an exercise in frustration trying to do all this with just the machines that you are converting. But on the other hand, it really makes you know your machine inside out!

I still have some bits and pieces to get done on the mill, some home switches, a permenantly mounted E-Stop, spindle speed control, and some backlash to chase down as far as practical ( X 0.3mm, Y 0.2mm and Z 0.13mm. If I can get them all down to 0.1mm I'd be quite happy, any less than that and I would be ecstatic! )

I had a little time this afternoon and so I took some 4mm stainless rod that I had and cut 4 lengths and threaded both ends. Popped on a few nuts and then assembled everything together.


I am very pleasently surprised how this has improved this little table. It no longer rocks on its axis, and the backlash is much reduced too. Even if you dont want to convert one of these to cnc, putting in a angular contact bearing will really reduce the backlash even in a manual machine. A reasonably cheap way to make a big improvement on a cheap Rotary Table.

Contrary to popular belief, I havent been doing absolutely nothing since the last update, just doing very little :big: :big: :big: :big: :big:

I have been using the mill in a semi-cnc mode, mainly using manual commands, and even have used some of the wizards in Mach3 which are very handy.

For the last few days I have been making a couple of mounts to make the connection between the X and Y ballnuts and the mill table.

This was where mach3's wizards came in very useful. I used one that cuts an arc of whatever radius you choose and from whatever start point for the desired degree of cut. Then I used a circular bolt hole drilling wizard that does exactly what it says on the tin.

The result:-

and it fits in here for the X-axis

Then using the above mentioned wizards as well as a hole boring wizard, to make a larger mount for the Y-axis.

Then I had a bit of whittling to do as the slot in the mill base casting was slightly narrower, so once I had broken down the mill to get at the Y-axis ballscrew I put the mount on the "bandsaw" diet and trimmed down the sides. A few mins with a file had it fitting ok. A bit more filing to get the fit right and it was time to fit the ballnut into the mount.

This presented another problem, the little space in the casting of the mill that this mount will fit into is only about 2-3mm bigger that the mount, so how was I to fix the ballnut firmly to the mount. I am able to use 3 cap-screws at the bottom, but for the top I trimmed down some cap-screws and then filed a couple of flats to use a spanner. And whatya know, it worked!!

The result of doing all this is that my backlash has reduced from 0.22mm to 0.1mm on the X-axis and from 0.34mm to 0.15mm on the Y-axis. I think that it was worth it. I still use the Backlash Comp in Mach3, but when I want to do some small scale engraving with the mill it should make it much better.

Hi Tim,
This is a nice thread. I am in the middle of converting my X2. How is yours working after all this time?

Again, thanks for posting.


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