Question on Aluminum Plate

[robrmcc]

Hi All:

I am planning out/designing a CNC router based on supported rails and ball screws and have a couple of questions.

1) I am making some pieces (gantry supports, Z axis parts) from 1/2 inch aluminum and was thinking I would just use 1/2" aluminum flats because they are inexpensive. Am I going to run into a problem with the finish on these, are they just not flat enough? Specs say 2 thou over 12" I think which seems close enough for this job but I am not sure.

2) I was planning to bolt my rails to misumi extrusions. I have seen that done other places. I did read a comment however that said these extrusions are not flat enough and bolting directly to them can cause issues. Has anyone had this experience? Misumi does provide some extrusions with milled faces, is this necessary?

3) I am planning out a design that uses toothed pulleys with drive belts for a couple of reasons. I am turning the motors back parallel with the ball screws to get them out of the way and reduce the footprint of the machine, and I may want to play around with the ratio of the pulleys to get more accuracy or higher transit rates. Question is about backlash. DOes this arrangement introduce any backlash into the system? I have certainly seen it used elsewhere so I assume not, but am not sure.

Thanks as usual.

Rob McC

[Phife]

Hi Rob,

1) Im using 1/2" aluminum, generally its probably flat enough for no critical parts, but I would consider getting your aluminum from Misumi, they do 6 side machining on the plates for a reasonable price.

2) Im bolting the SBR20 supported rails directly to the Misumi 6 series extrusion. While the extrusion may not be perfectly flat, its probably good enough for most uses and the SBR rails can handle slight misalignment better than the Linear rail type which are much more rigid.

3)Many professional systems use belt to connect the motor to either the screw or pinion. They work well, you should have no issues if you plan it well and allow for adjustment and proper tensioning of the belt.

Im using AT5 belts and pulleys, also from misumi, they seems very well suited for this type of application.

Good luck!

[louieatienza]

If you need flat aluminum plate look for mic-6 cast plate on ebay. Machines nicely, leaves a good surface, and is ground flat. Regular aluminum plate is extruded, and can have internal stresses. Like Phife mentioned, for non-critical areas should be fine, but I wouldn't reference or indicate off extruded plate, unless you face mill it...

Where you run into issues is with profile rail. Even a 30 series rail will move. Usually they are pushed up against a reference edge to keep them perfectly straight. the edge of the t-slots in the extrusion are canted at an angle, and that can cause problems with smaller profile rail. I have it mocked up this way on my currrent build, but will have the face milled once all the parts are done.

You can choose belts that have almost no stretch. Many machines are built this way (look at DataCut machine for example). Also acts as adampler pf sorts between motor and screw.

[robrmcc]

The mic-6 looks like it should work and not too expensive.

I found the aluminum plate from Misumi quite expensive but I might have been using their price tool wrong.

I did find that Misumi will mill the surfaces of the extrusions I am planning on using (series 6) so I will likely have that done for the extrusions I am mounting the rails on. It is quite reasonable price for the service.

Thanks for the feedback. This is a great site.

Rob McC

[Phife]

The mic-6 looks like it should work and not too expensive.

I found the aluminum plate from Misumi quite expensive but I might have been using their price tool wrong.

I did find that Misumi will mill the surfaces of the extrusions I am planning on using (series 6) so I will likely have that done for the extrusions I am mounting the rails on. It is quite reasonable price for the service.

Thanks for the feedback. This is a great site.

Rob McC

Ya, the price can be a scary.. But you have to remember that they are machining all 6 sides for you. MIC6 only makes it so you dont have to surface both sides. You will have to machine the other edges. If you go with Misumi You wont have to pay a machine shop, or spend the time yourself if you have the tools to make sure all the plates are flat, square and the right length/width. In my research its quite a bit cheaper to have misumi machine the plates than it would be to pay a machine shop to do it.

[robrmcc]

I can see if you are paying a machine shop Misumi might be comparable Fortunately I have a small mill that I think I can do most of my own machining on. I am not sure I can do the surfacing of the flat sides, but maybe I should look into that too. Althought the Mic-6 stuff seems to have some promise.

Thanks again.

Rob McC