[duluthboat]

This is a prototype for a 5” Z axis. The parts are motor, timing pulleys, ½” 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

[wjbzone]

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?

Bill

[High Seas]

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

[HomeCNC]

That is a similar idea I used on my Z axis conversion for my Drill/mill.

[anoel]

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.

[duluthboat]

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 18”x18” 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 hasn’t got much response. For me it is as much an exercise in 3D modeling as it is tool design.

Gary

[HuFlungDung]

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.

[duluthboat]

HFD,

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

Thank you

Gary

[duluthboat]

Might as well show you the rest. I haven’t given much thought to motors or controls yet.

[duluthboat]

From down under.

Gary

[duluthboat]

And one more.

Gary

[jimini]

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.

[thielert]

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.


Tim

[ehiebert]

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.


Thanks,
Eldon.

[duluthboat]

The modeling was done in Rhino 3, it is a very good surface modeler that isn’t to expensive. It doesn’t 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; it’s a non-photorealistic rendering plug-in.

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

I’m 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 couldn’t 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

[duluthboat]

Tim,

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

[turmite]

duluthboat how did you do the extrusions in Rhino. Did you import in a dxf or did you do everything in solids?

turmite

[duluthboat]

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

[Mr.Chips]

Good out of the box thinking.
What kind of bearings will you be using on the axis?
Thanks

[duluthboat]

I'm working out the details now. I'll update as I get more.

Gary