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Assembly question
« on: March 12, 2011, 11:55:30 AM »
Hi all,

Yet another question !

The main assembly of my machine was bought from Ebay, new but unused and unassembled with no instructions. I managed to find a couple of diagrams of it (each diagram is slightly different) and managed put it together however Im at a loss as to how the threaded drive is supposed to be supported at the opposite end to the motor.
I have attatched a photo showing how I have assembled it. The locking nuts and collet each side of the bearing at the motor end are obvious, but the locking nuts at the other end (lose at the moment) dont seem to serve any purpose but Im sure they must somehow help support the end of the threaded bar. The brass coloured thing has a bearing inside, the 2 nuts will just about fit into it.
The "best" diagram I found is here
Im sure this will be obvious to someone !

Thanks

Calv

Larger pic here


Re: Assembly question
« Reply #1 on: March 12, 2011, 01:56:41 PM »
There is usually a nut on each sid of whichever bearing you are using as the thrust bearing for the screw.
Apply a slight preload to the bearing with these 2 nuts, then jam/lock them in position with the other 2 possibly.
Russ
Re: Assembly question
« Reply #2 on: March 12, 2011, 02:10:40 PM »
Like this. I can't open the diagram you posted the link to.
Just guessing,
Russ
 :)
Re: Assembly question
« Reply #3 on: March 12, 2011, 03:02:58 PM »
Hi,

Thanks for the reply.

The motor end I have done as per your diagram apart from using a collar with a locking grub screw on one side (as per the "instructions"). That side has a bearing that goes in each side of the white plastic end plate, each side of the plastic is counterbored so the bearing goes in just enough so that the outer edge is flush (ish) with the plastic. The bearings appear to be ball races and do not seem to be tapered  (hope not anyway or they could be in the wrong way!)
The other end is different (no idea why). There is a single bearing inside the brass coloured "tube", this brass thing is firmly attached to the plastic end plate, one side is flush with the plate, the other isnt as can be seen on the pics below.
Not sure why the link wont work, I have copied the diagram and it is also shown below (the quality is poor - as is the original, made worse be reducing the size but the original is very poor too !)

Thanks

Calv

Oh, by the way, are my image sizes ok ?

Full size here for what its worth




Bigger pic  here



Bigger pic  here

Re: Assembly question
« Reply #4 on: March 12, 2011, 03:23:17 PM »
The print pretty clearly shows 3 ball bearings, 1 in place of the bronze bushing you have.
Are all 3 axis this way?
I would not use any nuts at the bronze end of the screw.
The only reason I see for using the nuts at that end would be to keep the flanged ball bearing from coming out if it were there.
If it were mine, I believe I'd carefully preload the 2 bearings near the motor using the 4 nuts as mentioned earlier instead of the collar with the grub screw.
Maybe the design has changed and eliminated the single ball bearing ? ? ? ?
Good luck,
Russ
Re: Assembly question
« Reply #5 on: March 12, 2011, 03:57:51 PM »
All 3 axis are the same, 3 endplates with the bronze things, and 3 of the others. As you say, maybe the design changed and was possibly documented in any instructions that were originally supplied. I did think a collar and grub screw was a bad idea, especially on a threaded rod. All 3 axis do move very smoothly (took some doing), but I'll take your advice and reassemble using pairs of locking nuts rather than the collars. I was concerned that I was missing something with the nuts at the other end but seems Im not.
Do I need to be concerned about play between the bearing and the threaded rod ath the bronze unsupported end? there isnt a lot, probably < .5mm movement between the rod and the  bearing. Im assuming that if anything then the threaded rod will eventually wear rather than the bearing, but other than act as a guide/support this end doesnt do anything so it wont affect the movement?

Thanks

Calv
Re: Assembly question
« Reply #6 on: March 12, 2011, 04:16:31 PM »
I'd but a dab of grease on it, or whatever lube you will use on the screw and nut.
Two small delrin, nylon or uhmwpe sleeves pressed into that bronze bushing would be great but it shouldnt give you any probs for quite some tim as it is.
Re: Assembly question
« Reply #7 on: March 12, 2011, 04:40:01 PM »
Many thanks, Im probably being a little over concerned but its years and years since I did any engineering of any kind (even forgot you are supposed to preload bearings until you mentioned it!) and I would rather be over concerned than just put it all together any which way and end up with more problems. I appreciate it isnt the finest machine in the world but I think it will serve its purpose as a starter DIY project. I was going to go the MDF route until I came accross the frame on Ebay, and whilst a bit small, it should hopefully work well enough for pcb's and learning CNC, and may well be used to make parts for my next one which will be a bit bigger.

Thanks again

Calv