Messages

11

FAQs / Re: Assembly question

« 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

12

FAQs / Re: Assembly question

« 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

13

FAQs / Re: Home/Limit switches - triggering limit when homing and where is zero

« on: March 12, 2011, 03:05:32 PM »

Thanks, the debounce interval sorted the false triggering. I also had one of the axis direction set wrong but it seems to be sort of ok now, just trying to sort the motor tuning and get it to move the right amount.

14

FAQs / Re: Assembly question

« 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

15

FAQs / 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

16

FAQs / Home/Limit switches - triggering limit when homing and where is zero

« on: March 12, 2011, 11:21:21 AM »

Hi all,

Project is making slow but sure progress. 3 axis moving table machine.

 I have fitted temporary limit/home switches- X,Y,Z have their own home switch made from optical sensors from old printers, the home switches are also configured as limit switches. The other ends of each axis have a mechanical switch, these are connected in series to one input. Wiring is a mess as you can see but will obviously be sorted once I figure everything out and get it working properly. Motor couplings etc are also temporary !

Couple of questions here, my X and Y home/limit switches seem to work fine, but the Z switch pretty much always triggers a limit before it triggers a home. I'll try to explain - I press REF ALL HOME and Z moves up as per the first photo, but then more often than not, instead of stopping and setting Z to zero as the other axis do, it triggers a limit and therefore makes me do a reset and jog away. This happens 99% of the time, on occasion it will actually set the home position without setting off the limit warning. What I did as a temporary measure to get the machine sort of zeroed was to set the switch to just a home switch rather than a limit switch.
I noticed that each time I homed, the actual position was slightly different - only fractions - Im presuming this is down to the accuracy of my machine. What I think may be happening is that when the Z axis has homed, it isnt moving back away from the switch quite enough, is there anywhere I can alter how much it moves back off the switch once home has been found? Also is there a way to home an individual axis rather than having to do all 3 at once?

My next question is also regarding switches, but more to do with positioning. I am getting very confused with setting up the home position. I have been through quite a few tutorials/giodes etc but Im still lost. I have taken a couple of pics which will hopefully explain things better than I can in words.

I have indicated on the bottom two photos where my switches are. The pic without the table top removed to show the switches is taken from the end of the Y axis, the other from the front of the machine.
Hopefully Im right in my X,Y zero position, but no matter what I try in the configuration I cant get it to move to the rigth place, for eg if I put G0X10Y20 I would expect the machine to move to roughly where it is on the pic (i.e. the table towards the front of the machine by 10, and to the left by 20 therefore "moving" the tool to 10,20 in relation to my 0,0 position). It does move, but I cant for the life of me get it to move the right way ! Im sure this has to be something simple in the settings, can anyone offer any advice?

Thanks

Calv


Z axis home/limit switch Bigger Pic




Table coordinates Bigger Pic




Switch layout Bigger Pic

17

FAQs / Re: Grounding question

« on: March 04, 2011, 06:30:57 PM »

Thanks,

Ive made some modifications and its now all ready to go into the case, I cant do anymore now though as I need to cut out the back panel for the DB25 connector and its a bit late to be out with the dremel so I'll carry on in the morning.

Thanks again,

Calv

18

FAQs / Re: power supply capacitors

« on: March 04, 2011, 06:27:46 PM »

Hi,

I assumed so but was suprised at the size of them. Are they all that big at that rating ? I presume 50V ones will be smaller but I couldnt find any at a decent price.

Thanks

Calv

19

FAQs / power supply capacitors

« on: March 04, 2011, 06:52:44 AM »

Hi all,

Working on my power supply, using the transformer and bridge rectifier from an old audio amp (Im also going to use the case to house the supply and my driver boards etc)

I have identifed the windings and got myself 5V DC regulated using a 7805 regulator with the standard couple of capacitors (from 9V windings on the transformer) and also 36V (from 25 VAC windings).
The 36V goes through a bridge rectifier, with a smoothing capacitor which was temporarily 4700uF 50V, this wokred fine in a test driving a motor. I read up and calculated the capacitor value for my system which came to about 17000uF. The nearest I could source without paying the earth was 2 x 10000uF 100V capacitors (new) from ebay. My idea was to parallel these giving me 20000uF. They arrived, and are MASSIVE ! They measure about 4 1/2 inches high by 2 1/2 inches accross. Have I got the right ones? I wasnt expecting anything this big. The spec of them is:

10000uF -10 +50 %
100VDC
MAx ripple 14.9A at 100Hz @ 85C
55/085/56 (not sure what these numbers mean)

Here is a pic of one. Can anyone please tell me if these are ok to use ?

Thanks

Calv

 

20

FAQs / Grounding question

« on: March 04, 2011, 06:34:06 AM »

Hi all,

Putting together my DIY machine and am just working on the power supply. I have built 3 driver modules - 1 per motor, and a BOB. I have just had a concerning thought whilst planning the mounting of the PSU and other boards.

My BOB is a simple affair, basically a pcb with a DB25 connector on which routes the port pins to screw terminals with LED indicators. The screw terminals from the pins connect via cables to the driver modules. I used screw terminals rather than plugs/sockets at the moment as it is obviously easier to change wiring if need be. Once Im 100% happy I will probably change the terminals for molex connectors or similar.

I have 2 power supplies at the moment, a 5V to supply the logic, and a 32V, both standard mains power supplies that come with most low voltage appliances - black box that plugs into with a cable and typical DC socket on the end. My new supply (hacked from an old audio amp) now gives out 5V regulated using an LM7805 and 36V.


The parallel port pins 18-25 are also connected to the db25 outer metal casing, which is of course then connected to the PC ground when plugged in, and therefore also connected to my mains earth. I have connected the grounds of both supplies and my BOB, and it all works fine.

Is this correct so far? should the pc ground/earth be connected to my 5V/32V ground? My new power supply will obviously be earthed, and at the moment will be sharing the common ground too, i.e. everything that is  0V will be connected, and also connected to mains earth. Should they all be connected like this or should I seperate the mains earth and DC grounds?

Hope that makes sense !


TIA

Calv