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26-04-2013 #21Flip 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
Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answerLast edited by Ross77; 26-04-2013 at 06:00 PM.
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26-04-2013 #22Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer
Last edited by Swarfing; 26-04-2013 at 06:19 PM.
If the nagging gets really bad......Get a bigger shed:naughty:
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26-04-2013 #23
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
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26-04-2013 #24
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 ;-)
If the nagging gets really bad......Get a bigger shed:naughty:
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26-04-2013 #25
Its good to know that I'm heading in the right direction, and I am happy with the progress so far.
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27-04-2013 #26
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.
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.
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27-04-2013 #27
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.
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27-04-2013 #28Having 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.If the nagging gets really bad......Get a bigger shed:naughty:
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27-04-2013 #29Sorry 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,
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......
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27-04-2013 #30Yes but it would need a link arm or bar to connect back to the bearings hence lever arm.If the nagging gets really bad......Get a bigger shed:naughty:
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