New Machine Build- First CNC - Questions

[Jonc80]

I have been reading these forums for a couple of years now and have finally started to build my own CNC router. This will be a small machine, probably only about 1' x 2' cutting area. I will be cutting mostly wood and MDF, although I'd like to be able to cut some aluminum as well.

It will be made from aluminum and MDF. The rails will be 20mm supported rails, I have already ordered these from Glacern Machine Tool. I was looking at a G540 3 axis package from Keling for my electronics, G540 from Gecko, 3x 387oz-in steppers and a 48v power supply. And, I was thinking I would use 1/2-10 5 start acme screws on the x and y axes and a 1/2-10 single start acme screw on the z-axis.

At first I was thinking I would use 1/2-10 single start on all axes but I don't think that would give me the speeds I am hoping for. I might be dreaming for a machine this size but I think I want cut speeds of at least 100 inches per minute and rapid speeds of 200 or so.

So, this is where I am a little bit confused and looking for advice before I order more parts. Should I be able to reliably achieve the speeds I am looking for with the 1/2-10 5 start acme screws and 387 oz-in steppers?

Also, I am attaching a picture of my design so far and if you see anything wrong with it can you let me know. I will probably be attaching the stepper motors to the screws with a timing belt.

Thank you.

[Crevice Reamer]

Hi Jon. Welcome to the Zone!

If you substitute K381s for the K387s, you should have no trouble reaching those speeds.

http://crevicereamer.com/Page_3.html

CR.

[ger21]

Go for at least a 2 start screw on the Z axis.

[Jonc80]

Thank you for pointing out the K381s.

As for 2 start screws on the Z-axis, roton.com says their multiple start screws may backdrive. Would this be an issue or would a 2 start acme screw still be pretty hard to backdrive?

Thanks again,
Jon

[ger21]

If you're concerned about the Z falling, it shouldn't be a problem.

[Jonc80]

I am looking for a suggestions for lubrication on my linear rails and acme screws. The acme screws will have plastic nuts. I am hoping to find a lubricant that will not hold dust and that does not have a strong odor.

My wife is already putting up with me keeping this machine in our apartment, if it ends up smelling like oil inside I'll have to keep it in our storage unit.

Thanks!

[Phife]

Originally Posted by Jonc80 I am looking for a suggestions for lubrication on my linear rails and acme screws. The acme screws will have plastic nuts. I am hoping to find a lubricant that will not hold dust and that does not have a strong odor. My wife is already putting up with me keeping this machine in our apartment, if it ends up smelling like oil inside I'll have to keep it in our storage unit. Thanks!

I have 3/4" lead screws with custom uhmw nuts, I use white lithium grease to keep mine lubed up. Ive tried almost everything and find this works the best for me.

Doesnt smell and lasts a long time, doesnt do much for dust though. I use a dust collector and dont have much of a dust issue.

[ger21]

I use air tool oil on my screws. It doesn't really have any smell at all.

You should be much more worried about dust in your apartment than on your screws.

[hemsworthlad]

Originally Posted by ger21 I use air tool oil on my screws. It doesn't really have any smell at all. You should be much more worried about dust in your apartment than on your screws.

Yeah and he's not talking the flick away with a feather duster type dust eithier.?? . . . more like Extra heavey duty industrial gets in every nook n cranny cant get rid off no matter what type dust. . Lol

Prepare for a b@#*cking.!!

[Jonc80]

Ya, I'm gonna have to take this outside every time I want to use it. That was one of the reasons for making it the size it is, it will fit through the doors. She has been pretty good about this whole thing so far, but I am going to owe her a new vacuum. I don't have a shop vac so I've been sucking up aluminum chips in our house vacuum.

It is starting to look like a cnc machine though!

[Jonc80]

I have my machine up and running, well almost. I don't have my router mounted yet and my wiring desperately needs cleaned up, but everything is moving. I also need to add my limit/home switches still.

However, I do have one issue. My X axis is moving backwards. I checked to make sure I had it wired the same way and that seems to be right. I've searched the forums here and have switched to Mach3 Motor Outputs for the X axis to Dir LowActive. This seems to fix the problem, but I am not sure this is the best way to go about switching the direction. I am not really sure what the difference is with LowActive on or off and I don't want to ruin any of the electronics. I am using a Gecko G540 with steppers from Keling.

While on the topic, what should the settings be for Step LowActive with the G540 be?

I am getting very anxious to start cutting with this thing, I am hoping to get my router mounted this weekend.

Thanks again!

[Hyrum R]

Good work.

If any of your motors are spinning backwards, just go to the homing/limits settings of Mach and reverse it. Took me a while to find that myself, but it's sure easier than rewiring your motors.