K2 Review, KT-3925

[carlnpa]

Pictures of machine, limit switch, router in mount, 1/2in Mic6 plate

[tauscnc]

Hey carlnpa,

I love that aluminum top! Wow. How did they finish that, looks like one HUGE flycutter The router also has a real cool look to it. Nice setup. How is the double nut setup working out? I am should have most of my setup done this weekend and will also take some pics.

Nice.

taus

[ckirchen]

Taus,

I can't tell for sure from your pictures, but the link for the ballnut you gave is not an anti-backlash nut. If that's what's on your machine, the only benefits you'll see are smoother motion and higher efficiency. To eliminate backlash, you'll need to use preloaded ballnuts (like the ones on carlnpa's machine).

I'm a strong believer that cleaning the ballscrews/ballnuts is the only way to go. When cycling my machine by hand after initial assembly, the X ballnut jammed on the ballscrew. When I cleaned it, I found, along with the grit and dirt, a couple ~1/8" steel chips. I promptly cleaned the other two axes. It was a good thing the machine wasn't under power--I hate to think what would have happened...

Otherwise, your and carlnpa's machines look great. I can't believe you guys got them together so fast. One of those K2 kits sure beats building a machine from the ground up. And it doesn't sound like they're much more expensive.

Chris Kirchen

[carlnpa]

Taus - one huge flycutter, that plate is flat, feels very smooth but you can see the cut pattern. Factory spec 0.005 flatness on the plate. It weighs maybe 60+ lbs but is real stiff and reduces the deflection that was giving me problems, it also seems to make the whole machine real stable. The new ballnut has zero backlash, I was running accuracy numbers again today to check cutting accuracy, will have to check again but it looks like less than 0.002 on 5.0 in cuts in y, 0.001 in x axis. The y axis maybe a ballscrew issue. The ballscrew tolerance numbers are +-0.004 in/ft. The x axis numbers have been real good but I may yet replace with another preloaded ballnut.

[ballendo]

Chris,

Total agreement about cleaning the lower cost ballscrews and ballnuts (rolled thread types).

Also want to add that a single body(single circuit) ballnut CAN be an anti-backlash type. There are two common methods used: oversized balls, and "preloading" the grooves in the nut body itself that the balls run in. (When preloaded grooves are used the ballnut may be a multi-circuit type, and still "look like a single body nut.)

There is a third methos used with single circuit ballnuts, but I've only ever seen it used by Techno-Isel. This uses a clamping-down-across-the-body technique which is similar to the method used with pillow block thomson style linear ball bushings. Seems to work okay, according to Techno-Isel owners.

Ballendo

P.S. I think it's more than "probable" that most low end ballnuts and screws, regardless of distributor --like so many other motion products these days-- are being sourced in China. I know that a supplier I use for motor couplings is sending me Chinese stuff. The related point is that we need to run a reamer in these before use, and replace the "cheese" steel 4-40x3/8 socket head capscrews with decent Domestic screws. (Had problems witrh slippage until we did.) I too have seen those "1/8 pieces" when doing this. The Chinese parts do not seem to be finished well, and the de-burring is incomplete at best!

Ballendo


[QUOTE=ckirchen]Taus,

I can't tell for sure from your pictures, but the link for the ballnut you gave is not an anti-backlash nut. If that's what's on your machine, the only benefits you'll see are smoother motion and higher efficiency. To eliminate backlash, you'll need to use preloaded ballnuts (like the ones on carlnpa's machine).

I'm a strong believer that cleaning the ballscrews/ballnuts is the only way to go. When cycling my machine by hand after initial assembly, the X ballnut jammed on the ballscrew. When I cleaned it, I found, along with the grit and dirt, a couple ~1/8" steel chips. I promptly cleaned the other two axes. It was a good thing the machine wasn't under power--I hate to think what would have happened...

[ballendo]

[QUOTE=tauscnc]Hey carlnpa,

I love that aluminum top! Wow. How did they finish that, looks like one HUGE flycutter

Taus,

A fly cutter can't give the required flatness and surface finish...

Mic 6 alum plate is blanchard ground. A blanchard grinder is like a HUGE floor polisher that you see being used to polish the floors in supermarkets sometimes. One large grinding wheel, which cuts on its face.

Blanchard grinding is the typical process used for flattening large metal plates, like those on machine table tops--like a table saw.

Here's a link to an explanation about how mic-6 plate is mfd. (It didn't mention the grinding specifically, so I added that here.)

P.S. I use 5/8 mic-6 plate for my "expensive" PCB mill CNC machines; because it has the best flatness spce of the thicknesses around 1/2". (IOW, a 5/8 mic 6 plate will arive flatter than a 1/2 or 3/4 mic 6 plate.)

Ballendo

Helps to add the link<G>

http://www.designnews.com/article/CA270744.html

[tauscnc]

Hey ckirchen,

The link I sent is the link we found while talking with Nook. I don't think this is a preloaded ballnut. Just a single one.

Can you guys please explain to me the cleaning process in some detail.

For example, if I use scotchbrite pade or #0000 steel wool should I hold it again the screw as I have something turn it...should I do this 50 times, etc. For the ballnut what should I do? I can put paper towel into it and get it clean but after that I have no way to "clean" the hole edges etc. Also, since there is no wiper on them aren't they just going to get jammed with saw dust etc. quickly?

Any ideas are welcome.

Thanks!
taus

[tauscnc]

I added some more pics to my website and a movie !

http://cuttingedgecnc.com/cncrouter.htm

taus

[ckirchen]

Hey Taus,

You should definitely use wipers. You never know what is going to end up on the ballscrew (chips, sawdust, or otherwise). I run wipers on all three axes, even though two of them are hidden by steel. The ones that the manufacturer sells are good, so are rolling your own (http://bellsouthpwp.net/A/r/Arts_home_page/cnc/) or using hot glue (post #19 in http://www.cnczone.com/forums/showthread.php?t=7180).

To clean the ballscrews, chuck one end in a hand drill. If you can't use a drill, connect the drive to the screw. Run the drill/drive slowly and allow the towel/scotchbrite to move back and forth as guided by the threads. Also, don't overdo the scotchbrite. All you want to do is take off any hard-to-remove grit. You don't want to remove the oxide and make the screw silver. When you're done, you should have a clean dark brown surface. Put some 3-in-1 oil on a towel and apply it by running the drill/drive again.

Like you said, it's a little more difficult to clean the ballnuts, because you have to reach all the inside corners. I used degreaser with a couple different sizes of pipe brushes (from Walmart). Then, blast them out with air (I don't have a compressor, so I use a can of compressed air). Do it over a white towel, so you can see if any dirt comes out with the air. Repeat the degreaser if necessary. Finally, oil/grease the bodies as soon as you're done to ward off any chance of surface rust.

Chris Kirchen

[tauscnc]

Hey guys,

I was just playing around testing the "enclosure" I have almost finished and the Y axis stopped! I checked and the Gecko seems just fine. So I opened the motor (I did not pull it out of the casing...have already leaned that and found 3 wires were yanked off! Man, I lucked out on this one. I have put it all back together and it works find. Wheeee... All is well.



I also found that the ballscrew on the Y axis runs very free if it is not fully tightened down. So I did some more investigating and found the mount must not be perfectly 90 degrees. I put a "plastic paper" shim at the bottom and the Y-axis is MUCH SMOOTHER!!!! I am not kidding, it has LOST a lot of its gritty feeling, sound, etc. I can even push on the Y axis and it will "run" through the ballscrews (w/ belt off).



I think I will now have to check the X-axis. If I recall, I noted the mount had to be pushed down a little for it to slide over the crossbrace. I can now jog the Y-Axis a full speed with out any problems.



taus

[cbass]

Taus, Its looking very nice.

Sounds like you're well on your way to fine tuning your machine.

One question about this...

Originally Posted by tauscnc I also found that the ballscrew on the Y axis runs very free if it is not fully tightened down. So I did some more investigating and found the mount must not be perfectly 90 degrees. taus

I'm assuming that you want the axis to move through the screws when they are pushed. This is without the screws being connected to the motors, correct? When the motors are hookedup, they'll create resistance, which is why the z axis won't just drop when the machine is turned off.

Am I on the right track?

Carlo

[JavaDog]

Originally Posted by tauscnc taus

Hey, is that the Kobalt workbench from Lowes??