4x8 router 8020 and all the fixins

[crocky]

Originally Posted by coop2005 The bearings i am using are Hiwin HG 25mm linear bearings. The bearings are moving linearly along the rails which is boggling my mind. I realized it was a racking problem after noticing that the motion of the bearings on either sides was in opposing directions. I cant imagine what is possibly moving to give this gantry such a twist, i need to spend some more time with the dial indicator figuring this out. I remember coming across a thread that you mentioned about fixing this with wire and pulleys but I couldnt find it yesterday, thanks for the input.

Splint has used wires and pulleys like that, do a search on splint and see if you can find his build log

[LeeWay]

Here is a link to the racking cable thread.
http://www.cnczone.com/forums/showthread.php?t=51485

A single screw is notorious for racking on this type machine. I was able to eliminate it on mine, but it is smaller, narrower and has a steel frame.
I was able to load or preload the sides of the gantry to the frame to take out any possibility of rack. I looked at your frame and I don't think that would be doable on your's without adding some bracing between the Z railsand then adjusting screws on the gantry.

That may work, but may be around the same cost as adding another driver, screw and motor once you consider the time and materials involved. Then it may not work perfectly because of the machines size.

The cable thing may be your best bet and might work pretty well considering the size of machine. It would certainly be the cheapest easiest thing to try.

Looking good so far though.

[coop2005]

its been a while since i posted as i moved and wasnt able to access my machine, i have made some progress in the last week and things are getting close to finished. Here are some updated pics. I am putting together the table and making some dampers for the steppers right now, im looking at about 300 ipm rapids.

[coop2005]

here is some updated pics with the table attached and some cable tracks on the x and y. The table is 5/8" MDF with a grid of 3" strips of mdf on the underside for support. I am going to beef up the frame by welding on some cross members, it does some wobbling when the gantry stops and starts.

[coop2005]

Here is a quick video showing the rotating nut in action. Kinda shaky i am no James Cameron. There is about .001" difference when it returns after 20" of travel after the first run, after that i can go back and forth 10 times and no see a difference on the dial.

YouTube- Rotating Nut CNC.MPG

YouTube- Rotating Nut CNC.MPG

[coop2005]

Made a new video of the first cuts.
I upgraded my 1Ghz cpu to a 2.5 ghz and went from barely 100 ipm at 25khz pulse rate in Mach3 to a easy 400 ipm at 60khz pulse rate. anyone having trouble with stepper performance don't be to quick to blame it on resonance or power supply or any thing other than the cpu speed. I was getting lost steps, motors locking up during a g00 command and just just bad noisy perfromace from my steppers, i built a damper and it seemed to help; however, after upgrading my computer the performance was so much better. I took the damper off as i don't need it at all now.
just my 2 cents

YouTube- First Test Cuts.MPG

YouTube- First Test Cuts.MPG