Thread: It's begun....
Thanks for all the welding advice chaps, that should give me enough to go on.
@Wilfy - no video yet, as I'm going through the usual pain of 11th hour moving hurdles at the moment, so the gantry is off the machine and ready to shift to its new home. Of course I will need to get new home up and running once I land there (I have a task list that is several pages long, but luckily the CNC machine is quite high up, as it needs to be cutting MDF for a custom desk for my office along with other stuff (Sketchup pic attached).
I will get some video of it though once I have the second ballscrew on.
i know the moving pain too well.. last house we were in was our longest stay since we've been together an that was 3 years, we lived in 3 houses previously and just moved again 6 months ago.
oh and forgive me for being stupid or blind.. or both.. but what is the cutting area?
Cutting area is currently ~770x280x110mm, so quite small compared to many machines, although once in the new workshop I'll be making a few changes to increase the area if needed:
1. I am going to make the side support extrusions removable so if I need larger pieces I can index them and cut in sections (for wood/MDF though) just need to think about how to mount them without the need to remove the x-axis rails each time I want to switch function....
2. If I bolt the machine to the steel framed workbench and its rigid enough I should be able to "drop" the bed down to increase my Z axis (a 4th axis may require this dependant on the diameter of work piece and size of 4th axis I need or get).
A while ago i was looking at mig welders and gas. BOC were doing a deal through the gas supplies head office (0161)930 6822. I think it was half size argon at a decent price and the deal was called "volkszone" years rent £35 plus fill up £25. Worth a ring?
Seems like years since I last posted (it has almost been ;) ).
Thought I'd give an update on progress, as I've finally managed to get near to the CNC machine on a long dependency chain not least of which meant rendering the workshop and infiltrating the entire property with structured cabling and updating the entire electrical layout in both the main house and my barn (some may recall a house move in January).
The machine is now assembled to where it was when I moved and in its new home and I am about to retrofit the second ballscrew on the X Axis (I've had the parts for over 6 months....or at least most of them as I find I need a bore reducer for one of the pulleys to fit it to the back of the stepper motor (8mm to 6.35mm). Also need to drill out and thread some grub/set screw holes to the pulleys, which I'm a little nervous about as they'll be 4.2mm through a fair chunk of steel.
Sharper eyes may notice the new gantry mounts are fitted and also I have Oldham couplers all round in place of the spiral cut ali versions the ballscrews came with and to help with that here are two photos of one half of the workshop and the machine itself. Now I'm getting on top of the property, rather than vice versa, I should have more updates and also a vid or two when things are moving again.
Oh and I've already got plans to build a second machine, which I hoping to build a kitchen with, as I've decided I'm very fed up buying stuff designed to a price rather than a spec ;)
i have a question about your gantry, your Y axis rail are quite far apart but the X axis bearing blocks look quite close together.
does the height of your gantry make a negative effect on your machine? i'm thinking the tallness would make it like a big leaver?
Thanks for commenting.
I'm by no means an expert, so I'll defer to one of the J's on this, but my reasoning was that when the cutter is moving through material in the X-Axis (either towards or away from the camera in that shot), then the leverage force would be at the cutter opposite to direction of travel.
The fulcrum point would therefore be at the lower Y axis bearing and would be trying to deflect the upper bearing mounting point (or the top of the gantry). As the distance between the lower bearing and the cutter tip is going to be considerably shorter than the distance between the lower and upper bearing point (the other side of the fulcrum), then the deflection should be minimal/reduced.
Of course the forces may cause the gantry mounting brackets to flex, but I have yet to see any by leaning into the gantry at the top - I wish the same could be said for the yaw in the gantry, due to only having one X-axis ballscrew however, but this is to be shortly remedied :)
At least that's the theory ;-)
A bit of an update and hopefully if I can work it out a vid to follow:
Its fun to be back on the learning curve and earlier in the week I retrofitted my second X Axis ballscrew. The ballscrew itself was not much of an issue, but I had some "fun" getting the pulley onto the back of the stepper motor and not wobbling about.
Anyway after doing that it was obvious I have some slack in my drive belt, which needs taking up so just for testing purposes I found something "suitable" to take some of the slack out it (see pic). I then ran a few full speed jogs around the table and all seemed well, but there's a few things I need to do:
1. Add some support to the 2nd ballscrew where it extends to the same length as the stepper motor (there's some flex in there when the axis changes direction) - a suitable bearing has been ordered.
2. Add a proper 3rd pulley to provide belt tension rather than the hasty affair you can see in the pic, although I'm not sure how much play should be in the belt - parts ordered anyway
After that I decided to push my luck, being an impatient bugger, and run a short job "cutting air", just to see how it goes. That ran OK from start to finish, which was nice although you'll hear that the belt (or maybe ballscrew alignment) is out if I can get the vid posted. The job is a 3D roughing operation from Cut3D that took ~15 minutes and I also ran the other "side" of it, which also completed OK (~15 minutes).
Flush with success I loaded up a longer job (50+ minutes) and ran that. Again all was well for 20 minutes or so, but I noticed that heat was building up in the X Axis stepper motor. Then all of a sudden during a longish X Axis run (@1200 mm/min) the stepper made what can only be described as a "graunching" sound, like it had met sudden resistance and I hit the feedhold and then the estop. After that I checked that the x axis could be moved by hand (as the motors were no longer "holding position" in the e-stop state) and it could.
I'm assuming therefore that my gantry hadn't crabbed and bound up due to the ballscrews getting out of sync, but I could be wrong as hitting the estop could have "relaxed" the binding. Also I noticed that the stepper motor was hot to the touch i.e. hot radiator temps, but I'm not sure what behaviour an over heating stepper usually exhibits and whether the stepper (3Nm SY60 Nema 23) is maybe not man enough to drive 2 ballscrews?
Anyway once I get the other parts I'll tidy up the belt and pulley arrangement and then work out next steps, which I guess might mean getting and then trying to fit a larger stepper on that axis (the other two axis motors were cold/barely warm)? Perhaps Nema 34?
And hopefully here's the video:
Last edited by Washout; 30-08-2013 at 09:30 PM.
What voltage are you running those steppers at.?
How are motors wired, Series or parallel.?
Regards heat then steppers do get Hot can you hold your hand on them for a minute without burning you.? If so then they'll be fine. They can take much higher heat and still work ok it just shortens there life.! . . They would have to be very very hot to lockup.
Your problem will almost certainly be coming from that belt setup causing misalignment and binding. Being honest now your always going to struggle with that long extension like that on ball-screw without some proper sturdy support or holding fixture. Even then it will need to be aligned spot on.
I'd seriously look at running 2 motors . . or . . Dumping the existing motor bracket then have 2 pulleys on one screw with belt on one across to other with shorter belt on other pulley to motor. This way you could apply some gearing and keep the Nema 23 which should do this job ok provided you have decent amount of volts.
That size machine with 2 x 3Nm motors running decent volts even with 5mm pitch screws should be running easily 6mtr/min at minimum.
I built a very similar machine with probably heavier gantry for Michael Marino running 5mm pitch screws with 2 x 3nm motors on AM882 drives with approx 70Vdc and I'm pretty sure he's had it up in the dizzy heights of 16-17mtr/min when pushing for it's limits.!! . . . Sure he's regularly running it around 8-9mtr/min with high acceleration.!!
IMO dump that belt setup you have now it's a serious bottle neck.!! . . . .Use belts by all means but needs to be better setup than that.!!
Last edited by JAZZCNC; 31-08-2013 at 12:57 AM.
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