View Full Version : Concept Z axis

10-02-2003, 09:59 AM
This is a prototype for a 5 Z axis. The parts are motor, timing pulleys, Acme lead screw and nut, 8020 1.5 extrusion, and an 8020 slide. The nut turns not the screw.

Are there any obvious problems with this approach? Comments? Has anyone tried this?

Gary :D

10-02-2003, 10:26 AM
I like the idea Gary.

Will your router/spindle clear the pully at the top of the travel?

What kind of bearing surface will the nut turn against and will it have backlash?


High Seas
10-02-2003, 10:36 AM
Thinking outa the box eh?
I might turn it sideways and use that idea on my gantry - same question - clearance, and in a gantry would it be stable enough? I like it though.
If I do the gantry that way, I might go 2x height with 80/20 on the gantry to increase the moment of inertia.
:cheers: Jim

10-02-2003, 11:06 AM
That is a similar idea I used on my Z axis conversion for my Drill/mill. :D

10-02-2003, 12:03 PM
How are you going to kee the nut from creeping on the screw or from locking down against the plate? You'd have to come up with a thrust bearing arrangement to keep the Nut from moving any direction but in radial motion.

Also how are you going to attach the leadscrew to the slide?

A spacer would be able to be used to move the spindle away from the slide's face so that it could clear the timing gear.

Just a few of my first reactions.

10-02-2003, 01:13 PM
All good questions. I can answer some of them. A short piece of extrusion like this would be very rigid. The clearance is in the art not the mechanics. My pulley is likely to large and there will be a tooling plate mounted to the slide. The problem area becomes the nut. I can make a very complex bearing housing using 2 nuts and thrust washers. I would like to find a simpler solution.

This Z axis is to be mounted on an 18x18 fixed gantry. The size was determined by the most economical use of a 12 piece of 1.5 8020 extrusion. When the design is complete the whole works will be available free. This design started at another forum and for now will remain there, but it hasnt got much response. For me it is as much an exercise in 3D modeling as it is tool design.

Gary :D

10-02-2003, 03:37 PM
Hi Gary,

You could sandwich the pulleys between an upper and lower plate, to provide the thrust surfaces. I would probably suggest that you provide room for a thin layer of polyethylene sheet (or cut some disks out) to serve as the bearing surfaces.

10-02-2003, 06:14 PM

Yes you could, and I like it. Back to the drawing board.

Thank you

Gary :D

10-02-2003, 09:00 PM
Might as well show you the rest. I havent given much thought to motors or controls yet.

10-02-2003, 10:08 PM
From down under.

Gary :D

10-02-2003, 10:16 PM
And one more.

Gary :D

10-03-2003, 02:32 AM
Duluth I like your idea.
You could try making a couple of lazy suzan type bearings running in a circular groove, one above and one below the nut.

10-03-2003, 09:14 AM
Why are you going with rack and pinion drive? With a small machine like this 5/16" threaded rod through a tapped piece of 3/4 Delrin plastic for a nut would be cheep, easy, and have close to zero backlash. You would also be able to drive the screw straight from the stepper without the need for the gear down.

Have you used the 80/20 linear slides before? I have not, but I wonder about their stiffness, rigidity and friction. I defiantly want to hear how they work out.

Is your extrusion 1010 or 1515?

I gather that you will be welding the tube frame? AL or steel? Make yourself a jig to hold the pieces in perfect alignment when welding. Bolting things together has the advantage of adjustability.

Is that ProE that your modeling in? Looks good, I like their graniteized surface renderings.


10-03-2003, 01:41 PM
What material is used for the linear slides on these 8020 extrusions? I have used the extrusion for machine frames before, but have never seen their linear bearings in action. Is it simply a piece of UHMWV that slides across the extrusion? If so, is there any use in polishing the top face of the extrusion?

Oh yes, I am also curious as to which modelling tool was used. Very nice work.


10-03-2003, 02:34 PM
The modeling was done in Rhino 3, it is a very good surface modeler that isnt to expensive. It doesnt have all the goodies that ProE or some of the other high end engineering packages have but it will model anything. I used Penguin to render the model; its a non-photorealistic rendering plug-in.

I havent used the slides for this application before. They are aluminum with UHMW-PE bearing pads. Im not concerned about a small amount of friction. With a machine this light a little firmness should reduce the vibration.

Im using rack and spur gears only because the people I have talked to who have it on the X and Y axis are happy with it. I couldnt fine a clean way to use it on the Z. The parts are easy to find and reasonable. My goal is to have a 18x18x5 machine making chips for under $1000.00.

The frame in this case is 2 steel, but you could use aluminum, or pipe, or I even considered 3 PVC pipe filled with concrete. You just need something solid to bolt the extrusion to.

Gary :D

10-03-2003, 04:45 PM

The extrusion in the model is 1515. I started with the lighter stuff but you get the best price if you buy at least 12'. Then I made the machine bigger to use up the stock. The beams for the table span 33" so I went with the heavy stuff.

Gary :D

10-03-2003, 09:00 PM
duluthboat how did you do the extrusions in Rhino. Did you import in a dxf or did you do everything in solids?


10-03-2003, 09:41 PM
I imported a 2D .dxf profile and extruded it. You can get the files at, http://www.reidtool.com/store/store/download.asp the 8020 stuff is in the power category. I got slides from there too.

Gary :D

10-06-2003, 03:28 PM
Good out of the box thinking.
What kind of bearings will you be using on the axis?

10-06-2003, 07:57 PM
I'm working out the details now. I'll update as I get more.

Gary :D

10-21-2003, 10:57 AM
I have been busy with many things but think I have a better plan for the table drive. This is a much simpler way to keep the gear meshed with the rack.

Gary :D

10-21-2003, 11:39 AM
A thought; If the table motion has a heavy resistive load, and the spring is not strong enough, the pinnions will ramp out of the rack and free spin. Otherwise, I really like the simplicity. I especially like the length of the stepper mount plate, allowing for adjusting the stepper to tension the belt. I might widen the central piviot to stiffen it up a bit?

Tim T

10-21-2003, 11:50 AM
The spring tension would take some tinkering but I think it could be worked out. The pivot base needs beefing up and Ill work on it as I explore this idea.

Thanks for your response.
Gary :D

10-21-2003, 04:04 PM

I like your construction. I would consider building something like yours. Is it a welded steel construction? If so...

Then how do you manage to maintain an exact vertical on both "gantry verticals".

When i try to weld such a construction, i start out with short delicate welds to keep it all together. Then when i finish the complete welding job, the whole structure would start bending and twisting.

I would never succeed in maintaining a "perfect" vertical / parallels. I tried this on my home-made Telescope. I failed and so had to construct it with nuts and bolts so that it wouldn't distort.

Just how did / will you do it?

Nice design though, i love it, i eat steel for breakfast :D


10-21-2003, 05:35 PM
With welded steel contruction, you need to either shim things like linear rails and such or machine it flat after welding it.


10-21-2003, 06:05 PM
That is also my thinking Eric, build a nice frame and shim the extrusion as you mount it to square things up.

Gary :D

PS Mr Ed your avatar cracks me up more than mine. ;)

10-28-2003, 10:09 PM
I beefed up the pivot block, and added some detail.

Gary :D

01-04-2004, 09:56 AM

Any progress with your design? I noticed the thread has been inactive.

I live in Nothern MN, Hibbing to exact, and am thrilled to see other with my intrests in the area.

I have just recently become interested in CNC. I just happened to stumble upon this site, and my interest spiked.

I would love to see you progress, and I am interested on how those 8020 slides are working.


01-04-2004, 01:19 PM

Im also glad to see someone else in the area is into DIY, NC machines. The design I posted is a concept, I left it to ferment for a while. The idea was to design a quality bench top 3 axis machine that would require little or no custom parts. This is still the goal, but other interests and a lack of ideas has slowed me down. I currently have a 4X8 MTC machine in my garage; I have it mostly complete except for the electronics. Work has stalled on this as I ponder modifications. Any ideas you have about the concept machine would be appreciated. I also would be glad to help you with anything I can. My e-mail is in profile.

Gary :D

01-23-2004, 04:08 PM
Hey Duluth,

I grew up in Duluth, went to Central high school in '81'

what is really bizarre is that I have a design that I am working on that is really close to yours.

whats your name.

Eric Z

01-23-2004, 04:50 PM
Where have you found rack and pinion inexpensively? You could build a very simple jig for the welding just by using pieces of 4 by 4 lumber attatched to a stout piece of plywood. Weld slowly skipping around for heat distribution. I'd like to see you build it, or anybody for that reason. Are the slides for the 8020 homemade or something they make? What is an MTC?

01-23-2004, 05:21 PM
The slides are from 8020 also. You can get them, the extrusion, the rack and gears, and much more from Reid Tool Supply Co. I likely will build one someday, but if anyone else wants to I will help them where I can.

Eric, I sent a PM

Gary :D

01-23-2004, 05:23 PM
The slides are from 8020 also. You can get them, the extrusion, the rack and gears, and much more from Reid Tool Supply Co. I likely will build one someday, but if anyone else wants to I will help them where I can.
MTC= Machine Tool Camp

Eric, I sent a PM

Gary :D

01-23-2004, 06:31 PM
Here is my gantry, that I will bolt the 8020 to.

I will try to post a pic of my design.


just tried to post pic. too big.

01-23-2004, 06:48 PM
Originally posted by duluthboat
I beefed up the pivot block, and added some detail.

Gary :D

The overhanging shafts in your drawing may flex alot under load. you'll need big shafts or support at the ends in addition to the center.

01-23-2004, 07:06 PM
It's .375 dia. and only bridges 2.75", I don't believe it will have much flex. If it is a problem, going to .5"dia. should take of it.

Gary :D

01-24-2004, 11:25 PM

playing with solidworks

hopefully this will upload


01-25-2004, 06:49 AM
Hello Duluth,

Speaking just to the z axis part of your machine...

I'd affix the gold part to the y slide, and let the 8020 rail BE the z slide. Move the motor around to the "back" side, and it will take care of a few things. First, the pulley size will no longer be an issue. Next, the weight of the motor will offset the weight of the spindle tool (router?), and hep prevent "torqu-ing" of the gantry and y axis. Third, the t slot in the extrusion now is available to mount things to...


P.S. I think your table rack and pinion is going to give you problems; Get some support out near where the rack meets the pinion. In other words, use two angle brackets near the outer edges to support TWO arms, and use TWO springs, also near the ends...

But if it were me, I'd just use a screw and nut for all axes.

01-25-2004, 06:58 AM
Hello again,

A few more thoughts. Spread your table support rails as wide as possible. This will improve your ability to shim th etable into precision, and will help in other ways too. Using the dual pinion mount plates; put the stepper on one, with the belt reduction toward the OUTSIDE of the machine--means towards the rack. Use spherical bearings in the bearing blocks and be sure the crossshaft is a large enough diameter to prevent inaccuracy by it's torque-ing from one end to the other.

These mods should make things much stiffer than what you have drawn so far, IMO. And the table drive will be easier to make as well...


01-25-2004, 10:48 AM
Nice rails, but thats a lot of machining.

I have a lead screw drive option for the table. Im still thinking about the Z.

Gary :D

01-25-2004, 02:05 PM
It would be alot of machining, unless you know someone that would water jet them for you for free.

I lucked out, a friend of a friend water jetting them. I got all my aluminum and jetting done for $100


01-25-2004, 04:40 PM
Looks good but I have two words of caution.

I used a similar spring pivot design on a gear train to eliminate the backlash on a design. The concept was recommended by a tech guy at WM berg. The only problem was that the spring can add a lot of friction and resistance to the system which may mean that you will have to upsize your motor.

Teh 8020 concept you have is interesting as well. I made a microscope stand with that same slide and extrusion layout. I noticed that the delrin on the silde needed a little WD40 to slide nice. I was using the 8020 bought slide I am not sure if you were planning on making custom ones or not.

Any how I just thought this would help. I think your design is creative and I hope to see pictures as you are building.

Have fun.

01-25-2004, 05:34 PM
updated bridge

01-25-2004, 09:12 PM
Here is how I designed the z axis using 8020. used 2- "6825" linear bearing for the Y, and I used 2- "6860 " UNI-Bearings for the Z. using the 1530 for Z also.

Like Ballendo said, you can mount the motor on the other side of the bridge, and figure out the pulley system, which I havent done yet.
I should have almost 36" of travel across my bridge, my gantry should travel 60" and the Z Im going to shoot for 6". thats why I made it so beefy, and also why I took out the weight on the gantry.


01-25-2004, 09:43 PM
IMHO, you should make the gantry heavy as possible. My Z axis travel is 12 inches vertical with an X movement of 24 inches. With the Z axis extended, the last thing I want is lightweight. Too much deflection if you dont beef it up.

01-25-2004, 10:13 PM
after reading your post, I looked at this. I think that the pieces that have all the circles cut out should be on the other edge of of the gantry, so that it will take the flex out of the cross members where the linear bearings are mounted.

hard to discribe.

I will fix it.

Im not an engineer, but I think that how rigid you make it, makes the difference in strength, not just weight. for example, which will flex more. a 2x4 on edge or a 2x4 on the flats. same weight, just stronger on edge.


01-26-2004, 08:42 AM
fixed brace for bridge.