X1 Micro-mill with Mardus-Kreutz Drives

[kreutz]

Recently I found some time to do a good PM on my X1 micro-mill (converted to CNC by a friend a few years ago). After a complete disassembly, cleaning, adjustment, blueing, lapping, lubricating, more adjustment... a lot more blueing, a lot more more lapping and a few modifications, my X1 is acting now as precision machine. Of course, the high precision is maintained within a couple of inches around the center of the working area because I didn't map the leadscrews. The temperature of my shop is kept at 76 degrees F.

I kept the original lead-screws and nuts, both were lapped, cleaned, lubricated and aligned parallel with the respective axis and completely perpendicular with other 2 axes respectively.

The motor couplings were replaced by helical couplings and the lead-screws were machined to add new extensions as shown on the photos. The thrust-bearings were also replaced by quality 8x16x5 bearings and a nut was added to control the preloading.

Backlash (measured at 76 degrees F):

y = 0.0002"
x= 0.00015" approx (my indicator is a 0.0001").
z no appreciable backlash.

There is no need for a counterweight on the Z axis. (After a lot of lapping and good alignment of the lead-screw, motor mount and nut).

Rapids on the 3 axes are limited to 30 ipm, more than enough for the size of the mill.

[DRock]

Looks very nice, what do you mean by mapping the lead screws?

[kreutz]

Looks very nice, what do you mean by mapping the lead screws?

There is a feature in Mach3 where you map your leadscrew, that is, you specify the real pitch of the screw depending on the position of the nut along it, so a non precision leadscrew gets more precise results after mapping it on the software. See http://www.cnczone.com/forums/indust...allscrews.html In order to do the mapping it is necessary to have a precise positioning reference (home switches).

Best regads,

kreutz

[DRock]

Thanks for the quick reply!

I assume you are using ballscrews, but you said "original screws" so I am not sure if you meant original to the machine or original to the CNC conversion.

Are they the normal Roton screws?

[kreutz]

Thanks for the quick reply!

I assume you are using ballscrews, but you said "original screws" so I am not sure if you meant original to the machine or original to the CNC conversion.

Are they the normal Roton screws?

Original X and Y axes 20tpi, Z axis 10 tpi leadscrews.

[H500]

The backlash is surprisingly low. I only managed to get mine down to .0007 so far.

[Winnfield]

How are you guys measuring the backlash? Numbers like .0002" seem very optimistic. Is there something about this little mill that makes it inherently more accurate than the larger ones? I have a brand new one sitting on the floor that I thought was a turd, so I never did anything with it. It would be a nice surprise to be able to make a competent machine out of it.

[kreutz]

I use a 0.0001" indicator mounted on a magnetic base on top of the table. Approach the axis to the column until the indicator measures zero, continue advancing a few more mils and return back, re-zero the indicator, zero the 3 axes on mach3, continue advancing from the column to the starting position about 1 inch and send the axis back to zero using the button on mach3 (reversing the direction of travel). I am not using Mach3's backlash compensation at all.

I did a little modification to the original nut. Maybe it makes a little difference.

While adjusting the parallelism on the X and Y axes nut-leadscrew combination I found out that the part of the anti-backlash nut that bends (with the setscrews) was stuck to the base and tilted vertically so I used a Dremel tool to grind 0.01" from the bottom of the adjustable part of the nut so it doesn't touch the base anymore. Maybe a photo will help.

How long the current level of backlash will last I don't know. The modification was done a few days ago as well as the final adjustments.

I will have to partially disassemble the X and Y axes in order to replace the gibs strips. They were also lapped and recesses were drilled for the point of the adjusting screws but a brass test gibs on the Z axis made a lot of difference on rigidity and easiness of movement. I just machined the X gibs strip from a 1/8" brass strip, tomorrow I will make the new Y axis', it took me a while to devise and make a fixture to safely mill the brass strips with the correct angle (55 degrees).

Best regards,

kreutz

[kreutz]

How are you guys measuring the backlash? Numbers like .0002" seem very optimistic. Is there something about this little mill that makes it inherently more accurate than the larger ones? I have a brand new one sitting on the floor that I thought was a turd, so I never did anything with it. It would be a nice surprise to be able to make a competent machine out of it.

There is nothing inherently accurate on this mill, it is just so small that it takes less time and effort to do all the adjustments and lapping required to get good results. Nevertheless it took a lot of time (about 40 hours) to get it to perform decently.

I wasn't expecting so little backlash, tried with a 0.001" indicator and didn't notice any deviation from zero, so replaced it by the more accurate indicator (while suspecting that my 0.001" indicator had a problem..) and found out backlash was really small.

Using a nut to preload the thrust bearings on all axes helped a lot too.

[hoss2006]

Just a thought, Are you using a dial indicator or a test indicator?
Is the indicator showing the same reading as mach as it moves or only when going back to zero.
This video shows how to check backlash with a test indicator.
http://www.youtube.com/watch?v=buXHZ_McbOY&feature=plcp&context=C42effb0VDvjVQa1PpcFMgf1pRyc2Rt3R0soib87806rkk6Bhp3Ss=]Verifying Mach 3 Backlash Comp - YouTube
Hoss

[691175002]

There is nothing inherently accurate on this mill, it is just so small that it takes less time and effort to do all the adjustments and lapping required to get good results.

I'm going to take a risk here (since this is a contentious topic) and point out that lapping does not always improve the accuracy of a machine.

The processes that improve the parallelism and flatness of surfaces all require that the surface is ground, machined, scrapped or otherwise altered in relation to a perfectly flat reference surface (for example, a surface plate).

Lapping can certainly improve the flatness and parallelism of a surfaces (for example if you lap against an already flat surface), but the common meaning of the term where grit is simply used to wear the ways against each other does neither of those.

If you are rubbing two surfaces together with grit you are performing two surface lapping:
Lapping - Wikipedia, the free encyclopedia

Where the mating of the two surfaces is more important than the flatness, the two pieces can be lapped together. The principle is that the protrusions on one surface will both abrade and be abraded by the protrusions on the other, resulting in two surfaces evolving towards some common shape (not necessarily perfectly flat)

Lapping in such a fashion will not remove material evenly and will not produce flat surfaces. If you want to produce a flat surface from rough surfaces, you actually need to lap three plates against each other in a specific order known as Whitworths Three Plate method.

That being said, it is completely possible that lapped ways will perform better than the original ways depending on how well the machine was originally built.

[LUCKY13]

Your electronics box looks very well built, good job.




The little screw nuts on these machines I dont know if your backlash will hold up. With end bearings with no movement it is very possible to get this setup very tight. But the little flap with the set screw will more than likely ware quick.


Finishing your brass gibs will help as you have seen with the Z axis. So this will take more pressure off the screw/nut and may help it last longer. As you have seen these little nuts are not much, it would be possible to turn them into a backlash nut if you had more brass to make the parts to add to them ( using spring washers & screws to hold the second nut to take the place of that little flap).


You might even consider getting some of the derin anti backlash nuts that have the slit end and a spring assembly to take out backlash. The forces on this mill are very low so this kinda nut could work good. You would only need to make mounts for them. They also take less force away, unlike the style the X1 uses so it might even gain IPM. Not that you need it faster but it might help it be smoother , plus hold tight clearances longer.

As small as the screws are on this machine it would not cost much to add multy start screws with better accuracy & friction that can run these derin anty backlash nuts. With the mill run under CNC it would not be hard to make mounts for this setup. All though clearance for nuts under the table & sadle are very thin on a X1, so carefull measurements would need to be taken before so you would know if they fit.


Anyway your mill looks great, would love to see a video of it running. Its not to often you see someone put a lot of time into a X1. I am converting one now, but with a lot of mods. It has leanier rails & ball screws with a lot of axis extentions built in. I am stuck on it for now because of budget but i hope to get back on it soon.



BTW your spindle drive looks very interesting. I am guessing its a belt drive and you have done away with the box that held the electronics & gears. Looks like a nice job.

Jess