Z-Axis design and advice

[Mad Professor]

Good day all.

I am now starting to look at moving away from my DIY Built MDF & Plywood CNC Router/Mill.
It has been ok for small job's, and my pcb's, but I now want to move on to slighty bigger jobs, and also would like to start milling things like alu.

I have been looking on web sites, google, etc, at how other pepole have made there own z-axis.

Here is what I have come up with so far.



If you wish to view my design I have the SolidWorks files here: Click Me <1.2Mb.

I am not very good with SolidWorks, but I get there in the end, so the files might be some what messy.

I am looking to have it made from 20mm thick alu.
Will be using a TR16x4 leadscrew.

Any advice you can give me is grate.

Thanks for your time.

Best Regards.

[wiatroda]

If that was me, I would try to use supported rails- you will gain extra stiffness and increase on travel (because you won't need support blocks anymore) . Otherwise looks OK

[JunkieHobbo]

I am newbie at this CNC design/build area but most of the advice that I have seen has been along the lines of "Use Supported Rail".

Currently working on a Project aswell and from my investigation, Profile Rails are the way to go, then again I could me wrong.

HTH

[wiatroda]

It is beneficial for additional rigidity to add extra mounting screws between joining screws of rail and supporting part- in middle, between two screws at the back of the rail

[JAZZCNC]

If you have to use the unsupported rail then yes it's ok and just about the only way you can do it.!! . . . BUT it will struggle with Ali.!

If you can use supported rail then you would be best advised to change things around.! Put the rails on the front plate and the bearings on the rear plate.

This will give you maximum strength because the rail supports the front plate but more so because the distance from cutter to bearings is proportional to the Z axis extension. Less extension more support.
The way you have it now the distance from the bearings to the cutter tip is always the same no matter the Z axis extension and therefore the amount the front plate can or will flex is always the same.
When cutting hard materials like Ali this extension is very impotant to finish quality.!

Edit: On reflection if you have to use the unsupported you could still swap the rails/bearings and gain by reducing the extension. There will be slight strength gain to the front plate because you'd have to put braces top and bottom to clamp the round rails which will help slightly but you will always have the negative of unsupported rails potential to bend and flex.!! . . . . Hence why supported is better.!

[JAZZCNC]

Profile Rails are the way to go, then again I could me wrong.HTH

Your not wrong they are far superior it's just the price becomes prohibitive to most DIY users.!!

[Mad Professor]

Thanks for your feedback.

So what you are saying is that my design is no good, and will not be upto the job.

I was hoping to reuse the unsupported rails, and bearing blocks that I already have.

What sized supported rails would you recommend?

Thanks for your time.

[Jonathan]

What sized supported rails would you recommend?

Might get away with 16mm, but I'd say minimum 20mm rails.

As it is the design will be much better than what you have made from plywood, but it has the potential to be significantly better with the changes already mentioned. Though it would be nice to use profile rails I don't think it's worth the money for this size machine as you will still be able to cut aluminium perfectly well with SBR20 rails on Z (as I do), just not quite as fast as with profile rails.

[JAZZCNC]

Thanks for your feedback.

So what you are saying is that my design is no good, and will not be upto the job.

I was hoping to reuse the unsupported rails, and bearing blocks that I already have.

What sized supported rails would you recommend?

Thanks for your time.

Not saying it's no good but it's not the best it could be and with a few changes could be made stronger.

Supported rail is far better.!. . BUT. . If you have them then just change the design so the rails are on the front plate and bearings on the rear.

You won't gain the extra support to front plate supported rails give but to be honest this is minor and secondery to the gain from less cutter flex thru the proposional extension not acting like constant length spring board which is what your design allows. The 20mm plate will be strong anyway so IMO with these changes you'll be ok.

If you do go with supported then 16 or 20mm will be fine.

[JAZZCNC]

Ermmm I've just down loaded your drawing and can see that your using 12mm round rail.!! . . . This would concern me and would seriously consider selling and upgrading to supported rail.

It's a lot of work and expensive aluminium to potentially waste and I'm confident to say it will significantly reduce your depths and feed rate in aluminium..:sad:

So times it's less painfull and expensive to cut your loss's and start a fresh.! . . . If you have a fully working Z axis now why not sell it complete to someone who doesn't need the strength or abilty to cut harder materials. Then treat your self to supported rails and ballscrew from china.? . . . Think you'll be surprised how cheap you can build a great Z axis for with supported rails and ballscrews.!!