Simple Z-Axis Design Question

[deleteallusers]

I've had to keep redoing the Z-Axis on my first machine. I've had problems getting it to slide smoothly.

Could someone please explain the trick of getting the Z-Axis alignment
correct ? I've really been having problems with this. I'm not doing somthing the correct way.

Here's a picture of what my Z-Axis looks like. I have three layers. (A Top
a Middle plastic block which is where I mount my tool, and a bottom)

http://img175.imageshack.us/my.php?image=zaxisgk4.jpg

The top & bottom are made up of two rectangles of 1/2" mdf with
5/8" holes drilled into one of them for the rods. The other piece of MDF goes over the top, this holds the rod's in place, and on the top one it serves
as the motor mount.

But no matter what I do, I can't get the center to slide correctly on the brass bushings.

Must I sandwich all three pieces and drill them all at once ?

How do I make it work ? I feel stupid, I know there's a way to get it to work.

I had to take one of the bushings out of this one for it to slide, cause it bindes up with it in. Now there's two much wobble in the movment



Thanks,

[ger21]

You need to attach all 3 pieces together and drill them at the same time. Either screw them together, or use double sided tape. Put the plastic piece that accepts the bushings on top. Use a drill press. After you drill the 2 holes, lower the bit into the hole, and clamp the parts to the drill press table. Then change to the larger bit for the bushing and drill that without moving it. This will get them lined up.

Once drilled, however, you still need to make sure the plates are mounted so they line up perfectly. Bushings are very unforgiving of misalignment.

[deleteallusers]

Thank you,

I'm having fun at this, so I hope this idea works

I'll let everyone know

[jhowelb]

There is a design flaw causing the z carriage to yaw as it begins to slide, it stems from geometry.
You need two more bushings and Dimension B needs to be more than twice Dimension A. (see attached sketch)

[deleteallusers]

@jhowelb

Thanks for your help ! but my simple mind does not understand the solution to your problem statement. Can you rephrase your solution so my mind
can better understand what exactly I'm going to need to do to fix it ?

Yaw is a sideways tilt, right ?

Thanks again,
-Mark
deleteallusers@hotmail.com

[jhowelb]

Point 1 Your z axis slide needs 4 bushings
Point 2 the space between bushings needs to be greater in the direction of movement.

Stated differently, the z slide needs to be taller than it is wide. This is to keep it from rotating clock or counter clockwise.

A sled going downhill has to be longer than it is wide to avoid upset and killing the rider. The same can be said of a boat, a ski or tricycle.

[deleteallusers]

Ok, thanks. I understand now, I got to redo it, cause
I'm slow in the head (I'm not going to admit that to my wife, she'll
just want me to mow the yard more this year)

Good thing it's just a square, if were a circle I think I would be defeted.

Thanks again.

[jhowelb]

Now that we are past that point, this might also be helpful.
There will be an outside piece, top and bottom to hold the rods, pipe, whatever and a top and bottom piece of the carriage to hold the bushings. Making four pieces that need equally spaced holes so that the rods are parallel as well as the bushings.

Depending on the equipment one has available, one might;

Bolt all four together and drill them at the same time (you need more bushings for this because the holes are all the size for bushings), create an adjustment block so that all eight points of contact can be moved to eliminate binding (a real pain to be sure) or use a cnc mill (borrowed or hired) to cut the holes.

I live in Southern California and have offer some assistance to other hobbyists, perhaps someone in your area might lend a hand?

[deleteallusers]

Thanks again, I'm going to redo the Z-Axis this weekend, I've got to
go ahead and do the electronics first and install the limit switches.

It's taken me two long to get to where I'm at on this project. I think
I been working on it a solid month.

Thanks for the help, I can use all I can get.
-mark
deleteallusers@hotmail.com

[jhowelb]

Don't think of it like a job, it is a hobby. Learning experience, release from tension from work, escape from the living room (shopping mall) or what ever.
Just LOVE doing something for SELF!

Good luck!

[CNCkitsandBITS]

Clamping by what ever method and drilling through all the parts at the same time is not necessarily the best way to do things. If your drill press is not set up so that the drill bit is dead square to the table you will have problems.

Imho a better method would be to make a plywood template and use a guide bush on your portable router.

John

[delhierro]

I don't hane a clue but looking at the picture I am sure of one thing
you are not stupid keep trying body