Let The Fun Begain, New build on the Table.

[Ross77]

Flip the 'Y' axis (top to bottom) arrangement over and add another plate to the back to mount the ballnut and you will always have a nice clean screw

where's the fun in clean? yes you can do that but moves the ball screw away from the Z carriage and reduces rigidity and can lead to racking or binding of the bearings the extra distance can mean the alignment would be a mare as well.

Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer

[Swarfing]

Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer

There you go great minds think alike. The distance is minimal and would not make any noticeable difference. As for binding then you need to make allowances in the bolt holes so that you have adjustment

[Ross77]

Hi Paul
yeah I agree that it probably wont affect the performance to much but without going through all the calcs and then changing/ widening bearing spacing to compensate then it is best left as it is. remember this is being built with a pillar drill so ease of fabrication and also dimensional tolerance is less than parts made on a mil or cnc.

the binding is as a result of the lever arm of the system. the original set up was Bearing-Ballscrew-Load so the ballscrew can control the load directly. moving the ball screw back results in Ballscrew-Bearing-Load so the ball screw has to work through the bearing to contol the load and vice versa, the load is transmitted through the bearings before the ballscrew can control it. Under sudden loads this can cause the system to rotate around the bearing and as open linear bearings have clearance they could bind or cause premature wear.

Again it can be designed out but I think it will be easier to just clean the ball screw

[Swarfing]

Sorry Ross in this instance i would have to disagree. Swapping it over as i said would result in the ballnut being roughly in the same position, as the plate showing on the 'Z' could be set further back still. For this type of build it will work absolutely fine. Have a look around the forum with such a design and ask how they are getting on ;-)

[Bush Flyer]

Its good to know that I'm heading in the right direction, and I am happy with the progress so far.

[Jonathan]

Moving the ballscrew, whilst not disastrous, hardly gains anything. All you're gaining is some protection for the ballscrew from swarf and there are plenty of other ways to do that - for example adding seals or bellows. So even if the difference to the overall machine due to the loss in rigidity is small, you're doing this to correct a problem which is also very small since it's clear that swarf on the ballscrew is also only a small problem. I recall Jazz saying he'd worn out his ballscrews from letting the swarf pile up on them over a few years, but I've not come across anyone else who has had a ballscrew (or nut) fail for that reason.

For this type of build it will work absolutely fine. Have a look around the forum with such a design and ask how they are getting on ;-)

Having the ballscrew on the back on my machine has crippled the stiffness of my Y-axis and although the distance is greater, that shows how the effect can be significant.

[Bush Flyer]

When I am finished with a tools I am probably OCD about keeping tools clean and put back ready for the next time, It's the same when building a new RC model before finishing for the day I will tidy up and put all tools back where they come ready for the next time, and I have always been like that so keeping the ball screw clean will not be a problem.

[Swarfing]

Having the ballscrew on the back on my machine has crippled the stiffness of my Y-axis and although the distance is greater, that shows how the effect can be significant.

Correct Jonathan yours was a huge distance from centre hence your issue. Switching would save a lot of hassle having to sort extras like seals and way covers etc. My suggestion was a sound one but the choice is yours of course. BF your design is a good one i would like to point out and will work great without the changes so well done. Building these things is a costly venture and you spent the time listening and looking at what works already. Mine is no way near as good as what you have so you should be in a good place.

[Ross77]

Sorry Ross in this instance i would have to disagree

No need to apologise, the more opinions Mike gets the better.

Swapping it over as i said would result in the ballnut being roughly in the same position,

Yes but it would need a link arm or bar to connect back to the bearings hence lever arm. It just seems odd to me that people use ball screws to rid of backlash to 0.01mm and then mount them in systems that deflect more than that.

I still agree with Jonathan and don't see why you would risk compromising machine ridigity just to keep a ball screw clean, that's what guards are for

Any way i think this point has been laboured enough and mikes happy to keep his tool clean......

[Swarfing]

Yes but it would need a link arm or bar to connect back to the bearings hence lever arm.

Mmmm! not sure what you mean here? If you are making a box to encompass the supporting rail then you are actually increasing rigidity. The bearings will be supported both sides of the fence so to speak so can not for the life of me see how it is worse? the ballnut will still be roughly in centre and mounted on the backplate. I really don't see what there is not to understand here.