1.7*0.74*0.4m Mill / Router building...

[Jonathan]

Success!

I made the mount for the angled bearing thingy on the Y-axis. I'm not using springs/belville washers at the moment since I don't have any...yet. Currently it's just a few bolts pushing the bearing onto the screw at the right angle, but it seems fine!

So about an hour ago I clamped the motor mount and just the bearing for the Y screw at the motor end onto the gantry using G-clamps and mole-grips :whistling:

Motor is half stepping, 42T pulley on motor and 28T on the 2mm pitch screw. Currently I can just get 3600mm/min rapid feed but I'm sure it'll be more if I use a smaller than 28T pulley and mount the bearing on the floating end of the screw. Still a respectable amount though I think?

Anyway....backlash: 0.006mm :exclaim:
I spend about an hour checking that figure so I'm pretty confident it's right. I was using a 0.0001" indicator and the reading averaged 0.25 thou.

I think I'll settle for that :rofl:

[Jonathan]

Got the motor and bearings fixed down properly on both ends of the Y screw now.

Been experimenting with the pulleys. With 42:13 I could get 6000mm/min, but that's above the critical speed of the screw as calculated by Irving's spreadsheet, and yes it started whipping at that. So I tried 28:13 and got 4800mm/min (maybe 5000), which seemed pretty smooth. Acceleration currently 800.
I don't think I'll use the 42:13, Irving what do you think would be best if you don't mind working it out? I've got plenty more pulleys to experiment with. The motors are the 3N.m ones from Zapp moving an 18kg Z-axis.

I know it's a balance between high rapid feed and having sufficient torque for cutting, but it's difficult to work out where this point is since there's so many variables!

I measured the backlash again, and got 0.01mm this time...

I'm not sure wether to tension the screw or not. It wouldn't be too difficult to tap a hole in the end and use that to tension it with a thrust bearing, but is it going to make much difference if I stick with less than the current critical speed?

[irving2008]

Jonathan,

I'd try the empirical approach.. decide on your required rapid speed. Setup for that. Then put a rope and pulley on the router so that movement of y lifts a weight... add some weight (stones in a bucket or something), about 4 - 5kg and see how fast it'll go without losing steps (use a DTI to measure that it returns to the same point after moves). I'd start with the 28:13 ratio as this gives a nice rapids at 4800-ish and see what you can manage with load... 3000 would be OK, 4000 would be good... then turn accel down a little and speed up... you'll soon find the sweet spot... plot a chart (speed along bottom, accel up side) and you'll get a line for a given weight... change the weight, different line. That way you can tune it for different materials as you'll know what its capabilities are.

[Jonathan]

Irving,

Thanks for those instructions - I'll do that at some point when I've got the whole router together. Thought I'd done my last physics practical :lol:

Some photos...

'Nut' I may well add springs/Belleville washers.

[Kenneth Paine]

Irving2008,

There's a big thread regarding this idea on CNCZone... seems some have used it successfully and theres a commercial offering based on the idea.

Would you be so kind so as to post the link to this thread? I am unable to find it.

Many thanks,

Kenneth

[Jonathan]

Irving2008,



Would you be so kind so as to post the link to this thread? I am unable to find it.

Many thanks,

Kenneth

Here it is...

http://www.cnczone.com/forums/showth...=13593&page=26

I can't find the link to the shorter thread where the method I use is dicussed, but it's linked off that thread somewhere!

I may use the method discussed in the above link for the Z axis as I'm running out of space.

[Kenneth Paine]

Lee, thanks for letting me know.

Jonathan, thanks for the link. Fascinating!

Kenneth.

[Jonathan]

Been at university recently so have not had much chance for router building. I came back on a couple of weekends and made a few bits - stepper motor mounts for X-axis and bearing mounts also for X-axis. I decided to scrap the latter and buy two SBR25-2000mm rails, which have now arrived. No customs charges either

Also had a change of plan with the Z axis. I couldn't get the drive mechanism I've used on the Y-axis to fit at all easily, so I decided to go for the easy option and bought a RM1605 ballscrew at the same time as the above bearings. I got back for Christmas holidays on Friday and on friday/saturday CNC milled the bearing mounts and ballnut mount for Z. One angular contact bearing at the stepper end of the ballscrew, and a normal bearing on the other end.

Somewhat randomly I picked a 42T pulley for the stepper and 22T for the ballscrew, so effectively the pitch is now 9.545 mm. PM752 driver with 3Nm motor as with the other axis and I'm getting 10,000mm/min :exclaim: with 1000 acceleration. That means only 2.5 seconds to travel the whole 400mm Z axis. I might try some other pulleys/ratios but that can wait until I've done the X-axis and found which of the pulleys I have is most optimal...
Backlash on Z is negligible. I've not measured it with the more accurate DTI yet, but the 0.01mm resolution DTI moves just over one division if I move the motor back and fourth one quarter-step (0.012mm)...To be expected really since the mass of the Z axis itself should eliminate the backlash.


All that's left now is to mount the spindle/router, mount the X-axis linear bearings and do some wiring. If I had the metal to mount the bearings I'd probably be 'making chips' by tomorrow morning. Can't wait

I'll add some photos soon.

[Lee Roberts]

Kenneth,

Irving is going to be absent for the next 3 weeks as he is on a trip to the states.

Lee

[blackburn mark]

10,000mm/min

holy sh** jonathan !! i guess thats what you pay the extra for... my best X axis rapid is 1500mm/min

Question: do i need to keep my axis rapid speeds the same as my Y will run at 2000mm/min ?