Can anyone explain or post a photo of these two areas. I'm planning my CNC router and would like to know exactly what is needed for these areas. I'm plan on using standard threaded rod but later on want to upgrad the machine to acme rod. what do I need to do this??

Thanks

That area is just the mounting points for your leadscrew. Different people will have different things there, just depends on how you want to put it together. Some will have the motor directly coupled on one end and the other end free floating, some will add a bearing to the non-motor end to help support the rod, and some will add bearings to both sides to be able to tension the rod.

The plans should be very detailed as to the way JGRO designed it. I say go ahead and build it as is, then you will better understand what is going on there and what you may or may not want to do to improve on that when you switch to acme.

Does anyone have any photos that show this ?? I think photos will better help me to visualize what is going on.

Thanks

That area is just the mounting points for your leadscrew. Different people will have different things there, just depends on how you want to put it together. Some will have the motor directly coupled on one end and the other end free floating, some will add a bearing to the non-motor end to help support the rod, and some will add bearings to both sides to be able to tension the rod.

The plans should be very detailed as to the way JGRO designed it. I say go ahead and build it as is, then you will better understand what is going on there and what you may or may not want to do to improve on that when you switch to acme.

Here's what I did:

For the shaft coupling I had the 1/2-10 acme screw end turned down to 1/4 and used fuel line tubing. For the thrust bearing, I'm using Joe's idea of an adjustment block holding a 1/2 ID bearing with a acme nut on either side. This gives me plenty of adjustment for screw alignment.

Dave

with some motor standoffs that would be nice to do on both sides :D only downside would be you couldn't tension the rod very much.

Here's what I did:

For the shaft coupling I had the 1/2-10 acme screw end turned down to 1/4 and used fuel line tubing. For the thrust bearing, I'm using Joe's idea of an adjustment block holding a 1/2 ID bearing with a acme nut on either side. This gives me plenty of adjustment for screw alignment.

Dave

How does that work in the first photo? I'm thinking that the nuts will also turn since the acme thread turned and it would want to pull the nuts toward the direction that the stepper motor is turning. Like the gantry is moved when the X axis stepper turns. Or am I missing something?? I apologize for being so thick headed:(

The nuts do turn with the acme rod but no pulling can occur since the nuts are touching the inner bearing hub and simply spin with it, as the outer bearing hub is held still.
If you are still having trouble get a bearing a short piece of allthread and two nuts.
Assemble with the two nuts on the outside and the bearing in the middle ensuring that the nuts only touch the inner bearing hub. Use small washers next to the bearings if the nuts are too large.
Hold the outer hub still as in the picture,it should become clearer now.

jason

I'm giong to try that and get my mind working:) what about turning the end and using a flange bearing that holds the acme rod sandwiched between the stepper. This will just rotate freely correct, and will not go anywhere as the end is turned down??

I appreciate you guys walking me through this!!

I built a JGRO and had a time with lead screw whip. I then built a second machine and really studied the problem. Two things that I learned were the maximum screw speed and the screw mounting.

Maximum speed: Look at the second chart here (http://www.nookind.com/acme/acmecharts.cfm) called ACME INCH CRITICAL SPEED. It is the law. You can not go faster that this. Look up your lead screw tpi on the right, and your length on the bottom. Follow the curve to see the max speed (no matter how strong your motors are). Notice that there are 4 rows of length at the bottom, the reason for this is called End Fixity. This is explained in a hyperlink at the top of this chart as A,B,C,and D.

Screw Mounting (End Fixity): If you use the simple rubber hose you are in category A or at best B. The screw can really flop around, but heh, it works for a lot of people, and it is better to get going than to keep trying to decide what to do next. Later, if you want to do it more correctly and pick up some speed, change to Fixity C, try the way I did it here (http://www.cnczone.com/forums/showpost.php?p=102831&postcount=294) and detailed in my build log. It will also save the bearings in your motors.

Steve

I just received some 2 hole flange bearings that are from igus. They have a 1/4 inch hole and I wanted to turn down my acme screw ends to fit these bearings. WIll this work? I plan to use one on each end to fully support both ends. Here is a link to what I have Its the EFOI-04 model

http://www.igus.com/igubal/sizepresent.asp?p=EFOI

what size acme? 1/2"? i would not turn it down more than one standard size because of weakining it.

what size acme? 1/2"? i would not turn it down more than one standard size because of weakining it.

Yes I have 1/2-10 acme rod. I want to machine it down to 1/4 inch becuase the steppers are taht size and I have the bearings that I aksed about in the last thread.

What is the benefit of pre-tensioning the lead screws?? Is this absolutely necessary??

thanks

Almost no particular detail is absolutely necessary. The more details you attend to the better your machine will perform.

Pretensioning the leadscrew will further the benefits of supporting it at both ends of the frame - improved accuracy and repeatability, and reduced shaft whip allowing higher speed.