My Sieg X1 micro mill

[Memran]

I have not done anything on the 4th axis, since last update.
I have been trying to make my Z axis play nice. The leadscrew is being forced out of line by the bearing block at the top of the column, resulting in 'ok' movement when the head is low, and very poor movement when it is high.
I think I need to make a new block with some horizontal adjustment so that I can get it all in line. I think this will reduce the torque needs dramatically. At least I hope it will!
If I reduce friction enough, I'll make a new motor mount and go direct drive, and ditch the gears.

[Memran]

After a lot of investigation, I believe I've found the main cause of the stiffness, and noise: The shoulder of the leadscrew has a small 3mm spacer resting against it, however the shoulder itself is turned directly from the thread, so it is uneven. When I tension my bearings, it is causing shaft deflection, and is not free running. Cheap, nasty, Chinese build quality :/

Options for me:
1) Machine a new shoulder
2) Use a tight fitting, and longer spacer, which cannot be skewed
3) Use a clamp-on collar instead of the spacer
4) Replace leadscrew altogether

[Memran]

Ok what I described in the post above was only a small part of the problem.

The main problem seems to be the threaded hole which goes though the L-shaped section which drives the head up and down, is not perfectly vertical.

When the head is at the top of it's travel, the block which the leadscrew goes through is in-line. When the head is at the bottom, and I remove the bolts holding the block, the leadscrew springs it to the side.

This is not mine. It is just to show the part I am talking about:



Perhaps I could make a wedge to straighten it?

Also, I found that I get more speed from the Z if the motor is direct drive. I made a makeshift solid coupling, and held the motor with my hands while it moved up and down, and it was significantly faster.

I've also ordered some M542 drivers and breakout board, so I can pump more juice to the motors

[fragger6662000]

if you are upping the drives you should up the voltage as well. Also i think you have found the hard way that stepper motor torque curves are not linear with rpm. When stalled they give the most torque and as you spin them faster the torque reduces. So in nearly all cases direct drive is the way to go as it maintains torque and higher feeds. The drive you are going for are the ones i had and i am unsure why you need a breakout board as they are isolated inputs.

[fragger6662000]

Z mount wise i would shim the L bracket till it is parallel to the axis and then adjust the Z mounting plate to suit.

[LUCKY13]

I have a X1 and the way I am doing the Z axis is to move the screw to the back. This is pretty easy by adding another L bracket on the other side, then connecting the two L brackets with a flat plate/bar which could be threaded or simply add a nut to it. This gives more even pull on the head instead of pulling from one side. Plus you can make or buy a derin nut and get the backlash gone.


Also where the bearing is having problems against the thread a simple ground washer could be silver soldiered on to give the bearing a good flat surface to work against. A slip on collar with a set screw could work to. I think I found some at the local tractor supply store when I needed some quick.


Jess

[Memran]

Thanks guys

I took off the L-bracket today and found that the threaded hole is way off vertical:

Top:


Bottom:


The end of the hole are 1mm out of line! So I've shimmed the L-block, and managed to get things straight

The non-square shoulder on the leadscrew has been corrected by making a tight-fitting collar, which extends over some of the thread, preventing any wobble:

That also shows part of my new Z mount.

I've turned the end of the leadscrew and threaded it to be able to fit a bearing tensioner nut:


New motor mounting plate:






Now I am only waiting for my coupling to arrive to join the motor to the screw!

[Memran]

The coupling arrived today, so I fitted it and did a quick test.
With gears, the Z "rapid" was 150mm/min (6ipm). With direct drive, and everything else the same it is 600mm/min (24ipm).

Also i think you have found the hard way that stepper motor torque curves are not linear with rpm.

Yep!

if you are upping the drives you should up the voltage as well.

I will be, probably to about 40v initially. But the drivers have not arrived yet.

There is still some noise when going up, and sometimes when coming down. When moving downward, if the noise starts (it doesn't always), I can stop jogging and start again, and the noise will be gone. I guess this is some kind of resonance effect.

Here's a little vid to show the new speeds:

http://www.youtube.com/watch?v=LT6feqav60k]Better rapids on Z - YouTube

I guess I could still use a counter-weight or a gas strut to improve things further.

[fragger6662000]

I counter weighted mine with the table of an XY table that i had, about 15kg. it was enough to reduce any crabing of the axis.

[Memran]

Little update
My breakout board arrived, which has built in PWM 0-10v spindle control I think I can just replace the spindle pot with this, although I'll probably want a switch in between for the times when manual control is required.

Just waiting on beefier drivers now...

Additionally, I need to start thinking about flood coolant and enclosure, but I am extremely limited on space as you can see in the first picture in the thread.
Anyone have any good suggestions for making a compact enclosure, or something that can stop chips and coolant going everywhere?

[HorridHenry]

Hi Memran
Did you put the two locking washers back on aftewr you fitted the driveband pully?

Anyome noticed on this mill that the headstock is the same from seigs mini-lathe. very resourceful them chinese.

[Memran]

Hi Henry

If you mean the two lock nuts on the back of the 4th axis spindle, then yes, they're holding the pulley in place

The 4th axis is made from a 7x12 (C2/3) mini lathe headstock

You're not wrong about the Chinese!