I want to DIY.. some questions please!

[Lee Roberts]

Now it's not quite a perfect fit because the top of the nut is slightly ~0.5mm) taller than the top of the bracket housing. So one could either fit a thin sheet on top of the bracket, or trim the top off the nut if you can figure out how to do it.

You could use shimming steel to do this, a bench grinder can also be used to take the nut down a little.

Thanks Lee! Four of the six screw holes can be used, so I thought that is enough. I also considered putting a bit of lock-tight around the nut before inserting it.

Humm are you sure?, the top two holes look as though they would pass through the mounting holes for the SMA unit, the middle two dont look like they would have much material for a thread because of the bore in the unit?

As Jonathan said you may need to jig the nut about to get it concentric to the screw, all sounds a little to "make do" for me when a little creativity is all that is needed. Our right honorable gentleman Jonathan could properly fix you up with some custom mounts for a reasonable price.

Somthing to think about also is machine maintenance in the future, maybe unlikly but what if a ball gets jammed or stuck in the nut and you need to take it apart....smash it out with a hammer ?!?!? Obserred, how dare you



.Me

[Jonathan]

You could use shimming steel to do this, a bench grinder can also be used to take the nut down a little.

I'd be very wary of grinding a ballnut since any dust from grinding in the ballnut is a recipy for disaster. You could try and cover it up but I don't think its worthe the risk.

CAN NOT STRESS ENOUGH. . . . . .DONT DO IT. . . . ABSOLUTLY DONT DO IT.

+1

When I said earlier that 16mm rail would be fine 'if done right' I was assuming supported rails. You'll be much better off getting some SBR20 (supported) rails.

The 6mm single flute cutters are brilliant...get lots! Although they are much better than most at plunging you shouldn't need to plunge - use spiral toolpaths or ramping. Router cutters with a 1/2Q shank are much much stronger than the 1/4" ones, so well worth the extra.

Very nice mounts. If I use your super rotating ballnut systems on the Y and X then I only need a nut-bracket for the Z right?

Yes... but how long is the Y-axis screw going to be? It's a bit sledgehammer to crack a nut using a rotating nut on the gantry, althought it would work well.

[Lee Roberts]

Hi Tenson,

I see your cnc endeavours are coming along nicely!

I have toyed about a little with ball nut mounts myself using the "off the shelf" components, what I found with using the SMA units is the mounting holes for the Nut. If memory serves me right only two of the fixing holes could be used.

Your drive nut is properly one of if not the most critical part of an axis, personally I wouldn’t be happy with such a fixing, however I have seen machine’s up and running and only using the same two fixing points. I am guilty of being a perfectionist though with a little OCD topping to add to the flavour :)

In the end I decided to design my own drive nut mounts, I wasn’t able to machine them myself but another member on the forum was able to and did a great job for me. The price wasn’t a lot however they did stress that clamping was an issue due to the shape/design.

I have attached the finished picks for you to view, if you want the part details I am happy to post them for you.

.Me

[Tenson]

Thanks Lee! Four of the six screw holes can be used, so I thought that is enough. I also considered putting a bit of lock-tight around the nut before inserting it. Not too much, since it should come out again with a whack.

P.S. your mounts look like a super-charger!

[Jonathan]

Thanks Lee! Four of the six screw holes can be used, so I thought that is enough. I also considered putting a bit of lock-tight around the nut before inserting it. Not too much, since it should come out again with a whack.

I wouldn't put lock-tight round it. You'll need a bit of room for adjustment when you first fix everything together to ensure the nut can be set precisely concentric to the screw.

I've made a few ballnut mounts for myself and these for people on the forum:
\

I hope you're not intending to use those unsupported rails on this machine?

[Tenson]

I wouldn't put lock-tight round it. You'll need a bit of room for adjustment when you first fix everything together to ensure the nut can be set precisely concentric to the screw.

Do the mounts usually have much room to move? This fits absolutely perfectly and tightly so no room to move at all, although it could rotate a little.

I've made a few ballnut mounts for myself and these for people on the forum:

*Pictures*

I hope you're not intending to use those unsupported rails on this machine?

Very nice mounts. If I use your super rotating ballnut systems on the Y and X then I only need a nut-bracket for the Z right?

The unsupported rails are for the 25cm Z axis.

[JAZZCNC]

The unsupported rails are for the 25cm Z axis.

CAN NOT STRESS ENOUGH. . . . . .DONT DO IT. . . . ABSOLUTLY DONT DO IT.

You will regret using unsupported rail and even more so on the Z Axis.!!

[Shinobiwan]

CAN NOT STRESS ENOUGH. . . . . .DONT DO IT. . . . ABSOLUTLY DONT DO IT.

You will regret using unsupported rail and even more so on the Z Axis.!!

Simon, I'd really listen to this advice. I know you think you know what your letting yourself into here but honestly, you have no idea. I mean that in the nicest way possible.

I had to have my Z-axis rebuilt because it was using unsupported rails and was shit. About +/-1mm of flex at the bit and that means you'll get a crap finish even in MDF with anything like a decent DOC and feedrate. Your parts will be undersized, oversized and generally a mess. And you can forget it if your thinking of aluminium. Plus your using a heavy spindle with heavy 16mm alu plate. That's a bunch of weight right there before you've even got to the cutting forces.

Do your self a massive favour, ditch it and go with supported round rail. It'll add nothing to build complexity and hardly anything to the price. Cannot stress enough how shit round rail is, it should be banned on anything calling itself a decent CNC router.

Listen to the knowledgeable folks on here and save yourself from a world of pain, you'll get you a much better finish, more accurate parts and will let you move up to harder materials like alu, Corian and so on.

I'm trying to stress this because I fell in to the same trap your about to and its costs me a lot of money to put it right. Do it right the first time.

[Jonathan]

The main advantage with profile rails is that they are preloaded. This means there is negative clearance between the bearings and the rail, so there will not be any play. It also makes any deflection linear and crucially, with rails with 4 rows of balls which are the type you should get, the load ratings are equal in all directions. Conversely supported round rails have little if any preload and the load rating varies significantly depending on the direction the force is applied since the open side of the bearing clearly offers less support. Ideally we would mount supported rails so they 'oppose each other' on Z, however as you say it's quite difficult to accomplish rigidly without a somewhat radical gantry design. Hence most people mount them both the same way round. If I measure the deflection when a force is applied to my Z-axis parallel to X the reading varies quite a bit, due to the uneven load rating.
However this is of course all relative - compared to unsupported rails the deflection is tiny. You wont regret using supported or profile rails on the Z-axis - ultimately depends on what you can afford.

[Tenson]

Is there a big advantage in build quality terms using profile rails for the Z-Axis rather than supported round rail?

I must admit I can't see an easy way to use supported rail so that the bearings oppose each other on the Z axis. I have seen Jazz used HiWin rails facing out, not opposing, so is this only okay with profile rail?