Thread: 3 Axis CNC router
Thanks Guys, Chai has given me a quote including 50mm extra machining - wanted to be on the safe side in case the design changes!
He seems pretty reasonable, I wanted to go with "proper" linear rails but when you can get change from £30 for a 1500mm long SBR20....
I think another thumbs up for Chai is in order...
Last edited by JoeHarris; 31-07-2012 at 12:15 PM.
I know you have all seen these bits and pieces a 1000 times before, but I'm excited so heres a picture of what arrived yesterday from china.
The BK/BF Support blocks seem a nice snug fit - any techniques for getting them on (and off!) - I don't want to set about them with a rubber mallet just yet. Also does anyone have any thoughts on lubricating ballnuts? how often and what to use...?
Last edited by JoeHarris; 31-07-2012 at 12:18 PM.
The BK/BF can be a tight fit so a light flick round the shaft with some fine emery is some times required. They can be pulled on/off with even pressure but some times you will need to give them a very very light tap evenly on either side with rubber mallet.
Thing to watch out for is the rubber bearing seal rubbing on the screw causing binding when butted up to the little spacer. Some times you'll need to either add another spacer or push the seal in further, just be careful not to push in so far it rubs on the bearings.
Also don't tighten the nut like nut and bolt just nip it up enough to take the play out then lock with grub screws. If you over tighten you'll cause binding and wear the bearings quickly. After a week or so running then re-check for any settle movement.
The ball-screws I just use light way oil pumped into the nuts every so often. You don't need much for every day use and it should just leave a very light film on the screw after running up & down it's length. If the screw is dripping or blatherd then thats too much.!! Every now and again I'll pump loads of oil thru the nut to flush any crap out.
The Following User Says Thank You to JAZZCNC For This Useful Post:
Further to my previous post I have some questions:
1) to drive the two ball screws on the x axis I am using a belt driven by one stepper and driver. I am doing this because of fear of missed steps. If I use digital drivers (not closed loop) does this issue go away?
2) if I stick with the belt drive arrangement shown does it matter where the motor is placed in the belt loop. I have shown it off to one side currently, I had it in the middle previously? I figure it shouldn't make a difference? Probably need to add in another idler though.
3) the four sides of the base of the machine is comprised of two aluminium plates fixed to the ends of two aluminium profiles. These sit onto a series of aluminium box sections. I have no cross bracing in this frame. Would it be prudent to add some in??
I intend to build the timber table next so I have a base to work up from - any comment would be greatly appreciated before it is too late!!
Some of the digital drivers have a stall-detect feature which changes an output on the driver if the motor stalls. You can connect this to the e-stop so that the machine stops moving to prevent any damage should only one of two motors stall. However I don't think this feature alone is that big an advantage since if you're stepper motors are stalling, even just occasionally, then there is something wrong with the system - either you are trying to get too high acceleration/speed from the motors or there's a mechanical fault. If there's something causing the motors to stall then one should find the problem, not compensate with a safety feature.
Once you have tuned the motors properly they will not miss steps or stall. Plenty of people, myself included, use two stepper motors on their X-axis with standard drivers and do not have problems.
Thanks guys. For the bracing - some 20x6mm thick aluminium flat bar arranged in a big X across the base should do it ?
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