So driving in to work this morning with “My mind on my OX and my OX on my mind” 
I’ve been cutting crazy amounts of aluminum and can identify the weak points in doing so. I have made a few iterations to the OX plates from havering the NEMA 23s sit flush with the plate to adding two more rows of wheels across the top of the X gantry to distribute weight better. The goal is to strengthen the power in the X direction and reduce deflection if more weight is added or the length extended. The motor will do it but I have skipped a tooth in the X on more than one occasion.
So this morning I had a thought, see what you guys think. If I remade the X gantry plate to utilize two 8mm ACME blocks held on the horizontal plane and used a 1000mm long ACME screw in the horizontal plane and mounted an additional Nema 23 on either the left or right Y gantry plate with a coupler, seems I could lighten the X gantry and make a system that could not skip or miss a step. This would also considerably lighten the X carriage making it more feasible to extend the X without deflection or add a huge spindle like Alex has. It would require drilling holes in the ACME blocks where there are none currently. Just a thought.
Let me try to understand better. Are you suggesting we add another acme screw threaded rod along the x axis to 1) bear some of the weights on the current beams 2) Add extra torque to the x axis movement via another nema 23 motor?
I wonder if simply adding a smooth rod and a pillow block would alleviate enough weight and lower the friction coefficient enough that adding a second motor on the x axis would not be necessary.
Hey @Dat_Chu , I’m thinking of getting rid of the belt drive on the X axis and going to the lead screw.
The accuracy of the ACME tr8*8 is good enough for printing, should be acceptable for CNC as well.
So the NEMA 23 that currently resides on the rear x axis plate would be removed and placed on one of the side plates. A coupler could be used the rotational motion of the motor to the lead screw in the same fashion the Z currently works.
The only thing that would be on the X axis would be the small Z gantry, spindle, ACME block, and wheels.
This should reduce the weight of the X gantry considerably. With reduced weight, one could extend the length of the gantry or add a larger spindle.
Sounds good to me.
I am intrigued by this idea. My only concern is that lead screws tend to whip at longer lengths. At 1000mm it might be okay but that is probably pushing it, especially for an 8mm lead screw. I have a machine with a 1/2" x 48" long acme lead screw and I get whip on that. A little whip is tolerable, and my guess is a lead screw would probably be fine. Yet. I think the best way to go is rack and pinion. It is really not that much more expensive than a good multi start lead screw, but it would require redesigning the X axis plates. Here is one I have been eyeballing: http://www.mcmaster.com/#racks-and-pinions/=v46cyu
@Wes_Hansen I think this may be the best add yet! I will look a little deeper into this, hopefully later today.
Main reason I wanted to go lead screw though was to get weight off the X axis. With rack and pinion the motor would still have to be on the X right? I know you have some good experience in this realm.
That is a good point. The steppers would probably have to stay on the X. Also, the system would have to support the added weight of the rack itself (surprisingly heavy). However, I think a rack and pinion setup will easily handle the extra weight.
It is my understanding rack and pinion is 2-3 times more efficient than a lead screw. Typically rack and pinion is 85-95% efficient while lead screws are 30-50% efficient. If you add an anti-backlash nut figure on being closer to 30% efficient. In my experience, on the X and Y you will definitely want an anti-backlash nut because you don’t have the assistance of gravity to minimize backlash. I think the rack and pinion system will be able to handle the added weight because of this significant advantage in efficiency.
Also, with a rack and pinion system it is pretty simple to setup a gear reduction. This allows you to take full advantage of the usable torque range of the stepper motors. Whereas with a direct drive lead screw you lose most of the stepper’s torque at higher rpm’s. You could try doing a gear reduction with a lead screw but with their poor efficiency it might take a pretty large stepper.
I really think rack and pinion is the way to go. It will require redesigning the X axis plates but I think it is worth it. I’ve never run a belt system before but I am skeptical. I am working on a design to incorporate the rack on the OX. I think it will actually be a pretty simple mod. I am borrowing heavily from http://cncrouterparts.com. I think they have an excellent design. I ordered the rack and spur gears from McMaster, they have a pretty good selection. I will post my progress once I get started on it…
I should add that I am biased in favor of rack and pinion. I have been researching a way to integrate rack and pinion in the OX for the past week and I ordered two racks and spur gears yesterday. So be warned my mind is already made up on this subject. A lead screw setup might be fine too. I don’t want to discourage anybody who understands the pros and cons of both from going that route.
Wonderful add, I am excited to see your build!