CNC X2 Build
I have just finished my X2 to the point where it functions as a CNC mill. I will show some pictures of the progress form start to finish. I started first be tearing down most of the machine and cleaning it. There were a number of screws that where not even tight! This is my workshop in the back of my apartment. The room measures 3.5’ by 9’. As you can see it has a bench and a tool box and some room to stand. Its tight but it works.
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Last edited by will_eng; 11-14-2008 at 08:45 PM.
Here I made strap clamps a “V” jaw and did some turning and milling. I made everything in this build with the mill itself a 3/8” electric drill a hacksaw and few tools. I should also note I have been a Manufacturing Engineering Tech. for about 3 years and am now back in school for Design and Analysis.
I have been doing this project kind of step by step and as cheap as possible but somewhat upgradeable. I had NEMA 23,125oz/in steppers which I will elaborate on later that I designed the mounts around. I used 3/8” Alu flat for the flanges and 1/2” steel standoffs. Since I had such small steppers I went with a timing belt drive design. I rotated the worm gear drive that drives the Z axis rack and pinion. The stepper mounts beside the head and flush on a flat mount form the bottom.
Here are the assembled motors and mounts. I also removed the torsion spring balance arm which had a different torque effect throughout its stroke. I added a 20lb counter weight which is still under development. You can also see the first wood parts I made under CNC power.
Before I even had the mill I found a design on instructables.com for a stepper drive which I build on a breadboard and did work ok but decided to go with the 4 Axis drive from Mechatronics. I assembled everything in a box and mounted it to the bench. I am now working on a interface box for switches lights and jogging...
The rest of the pics. Let me know what you think or any ideas or questions.
Good job, nice setup!!
Nice work and good pics! That's a very interesting Z drive. Could you give more detail on that please?
CR.
Super nice! I love the dual-chain counterweight and the timing belt drive.
Are you using the stock leadscrews & nuts? How is your backlash?
Ditto. That's brilliant !! Hoss has something similar. Unfortunately the Z drive occupies that space on my machineOriginally Posted by Seb
First time I've seen that exact approach to the Z drive. Original thought or copied from somewhere ?
Anyone who says "It only goes together one way" has no imagination.
Yes the Z axis setup is my design in keeping with the original rack and pinion. I do plan to eventually upgrade to ball screws and stepper motors that ≈300<oz/in<400.
To explain the Z axis drive I first considered the stock setup with the Z dial knob at the front of the head. The knob is slightly offset from the head to allow space for the diameter of the knob which is the reason for the “U” joint that then drives the worm gear assy. It could have been the tolerances on my particular machine but the whole assy was stiff and just plain hookey. So to remove the joint I would have to extend the drive rod out further in front of the head and then mount the motor on its side on the upper part of the head. This would work but I just liked the option of just detaching at the joint and rotating the worm assy 90˚ down and driving from the bottom.
The counterbalance is still under development. The head weighs ≈36lbs. I bought a 40lb dumbbell and cut the cross bar out. I was going to hang the full 40lbs off it but I found that with my small steppers that if I just used 20lbs that the stepper has enough power to lift the resultant load and the weight of the head aids in Z axis cutting. This is possible because of the fact that steppers have good holding torque. Now I will probably remake the clevis for the weight so it hangs nice. With this design backlash is also absorbed mechanically. There was quite a bit of backlash in the table. I’m not sure exactly how much, I think like 0.007-8”. But I am running backlash compensation, which is not perfect. I thing I might work on thrust bearings and split nuts next. As I get into heaver milling the backlash issue will become more apparent.
Another thing I am struggling with setting the gibs. With such small steppers the table becomes too tight when play is totally removed. So I am still playing with adjustment. Too bad there weren’t a ball type gib spacers that would act as a cage for a row of 50-100 small ball bearings.
Will,
I think you're going to find the "bearing" on the Z axis pulley shaft will wear *very* quickly. It's not designed for any lateral load carrying capability, and timing belts need considerable tension to eliminate backlash between the teeth and the pulleys.
Regards,
Ray L.
Yes infact i dont think there is any type of busing at all in that block. If i decide to stay with this design i might make a bearing block to support the shaft.
I would like to change the z axis to a lead screw but i dont know if it is worth it. I know ball screws are the way to go but so far i have been able to do this for pretty cheap and all of the work on the mill itself.
Will,
A leadscrew can work just fine on the Z axis. Backlash is much less of a problem on Z as long as you keep enough weight on the head. The only downside is you'll need a larger motor, but motors are pretty cheap. When I CNC'd my X2, I bought the Z axis leadscrew and nut for an X3, and mounted them behind the column. It worked quite well. The next step is a good anti-backlash nut, which can be easily fabricated. I even kept the leadscrew on the knee of my BP clone, and it is now CNC'd and working flawlessly.
For X and Y, you really do want pre-loaded ballscrews.
Regards,
Ray L.
This is another neat, inexpensive conversion. Always fun to see.
You might consider using the "Hoss" design for your Z-axis. I did a hack job of it, and my Z still hits within <.003" so long as you keep the plunging loads reasonable. I did mine using a non-loaded Roton ballscrew and no counterweight.
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