[PurduePete]

I designed this using IronCAD 2011. I plan to use this for my CNC. Was wondering if you guys thought it might work?



The flat washers are not flat, they are beveled and designed to act as springs and fully compress under a load of 260lbs. I feel they would make a good spring action that is both effective and small. Just looking for input from the community that has actually built a machine to see if this will work. I can include a picture of my machine design thus far if it would help.

[Dragonfly]

Maybe I don't get the idea but IMO you need 2 nuts with spring tension between them.

[OCNC]

That's not going to work. You need two nuts with the spring pressure between them as Dragonfly already points out. I think the Belleville washers at 260lbs are too stiff. I had success lightly compressing an O-ring between the two nuts to give the pressure. Also the 10 TPI screw is going to give you low feed rates using typical stepper/driver combinations. Generally, 2-4 TPI puts you into a better feed speed range.

Chris

[PurduePete]

Yeah I got to thinking about after I put it up and figured two nuts rather than two washers. An oring is a good idea. You had a plate similar to mine to keep the nuts from moving?

As for the threaded rod. I'm not really that worried about feed rate. This is my first machine. It is not professionally designed. It's my learning process. If it takes an hour to mill a PCB I'll be happy it did. My second machine will be a prototyping machine to make models from plastic. This might even be capable once it is done.

I am close to finalizing the backlash nut, next is the coupling of the drive motor and thread.


PurduePete

Sent from my iPhone

[PurduePete]

Sorry, double post somehow. I am hoping to keep the size of the anti backlash but low profile. My z axis needs to be small. The design is a moving gantry. I think ive thought it out well. Moving gantry can have bad effects but it's a learning process right

If you guys have pictures I'd appreciate it.

[OCNC]

Yeah I got to thinking about after I put it up and figured two nuts rather than two washers. An oring is a good idea. You had a plate similar to mine to keep the nuts from moving?

Replace your nut with two nuts and an o-ring on a piece of the acme threaded rod. Run the nuts into each other by hand until you get the condition of no backlash. Close off the ends of the box that contains the assembly and then set the assembly on a piece of poly sheet or waxed paper and fill the space with epoxy to encapsulate the nuts. When cured you should be good to go. You might want to change out the bolts for some threaded rod to give you four opposing studs after everything has cured.

Chris

[PurduePete]

This is what a MIT student used for his. His machine is what I am modeling mine from with other pieces from a few of the other machines from "Machines that Make" project MIT did.

I believe it will work. He was able to use threaded brass rod but at $30 a foot I will be using plain steel if I can find nothing. When he made his project it was only $6.57, that was 2009.



If the nut used a nylon washer to prevent it from backing off I do not think it would work. But with it being one of the heavy duty deformed nuts I do believe that this design will create enough pressure to prevent backlash. This is the design that I will probably end up using if I can find some threaded brass rod. Steel is too hard to make this work.

Now let me know what you think of this design, the first one was stupid. I've since made three more that I believe would work. The other two are under here. The second is self correcting and the most expensive


The oring is only if the two blocks are compressed continuously.

[OCNC]

They all look like they'll work but seem overly complex to me. You can get an anti backlash nut from dumpstercnc for ~$20. Don't be buying brass rod at $30. a foot in the struggle to make a nut.

Chris

[rowbare]

Using an o-ring, while it will take up backlash when testing with an indicator, will likely not do anything for you when you are cutting. The spring tension has to be greater than the cutting force otherwise the spring will compress. i.e. if your axis generates 100 lbs of thrust, the springs holding the nuts apart need to be at least 100 lbs. In practice your cutting thrust will be less than maximum. If your springs are only say 20 lbs, light cuts will likely be ok but heavy cuts will show backlash effects.

bob

[OCNC]

Using an o-ring, while it will take up backlash when testing with an indicator, will likely not do anything for you when you are cutting. The spring tension has to be greater than the cutting force otherwise the spring will compress. i.e. if your axis generates 100 lbs of thrust, the springs holding the nuts apart need to be at least 100 lbs. In practice your cutting thrust will be less than maximum. If your springs are only say 20 lbs, light cuts will likely be ok but heavy cuts will show backlash effects.

bob

This is a tiny machine he is making. He probably won't have 5lbs of thrust. The o-ring will easily work.

Chris

[PurduePete]

He is right, this is a pcb mill. Cutting forces will be minimal. I may end up buying one but the whole point of this for me is to make as much of it as possible. I will probably end up putting this in my portfolio to take with me to jobs. Going to use it too but mostly the experience is what I want.

The PCB mill will eventually morph into a larger machine for aluminum but for now I want to mill plastic and circuit boards. By morph I mean I will take what I learned not use the machine and change it, won't be big enough. Only want a 4"x6" cutting area, maybe even 4"x4".

[OCNC]

....I may end up buying one but the whole point of this for me is to make as much of it as possible.

Just to be clear, I'm not trying to discourage you from making your own components. There is a lot that can be learned from it and I do it all the time myself often misspending along the way.

Chris

[ger21]

I made a Delrin AB Nut with an O-ring for my router similar to this. After I realized how much effort it was, I bought the rest of the nuts I needed from DumpsterCNC.

[rowbare]

This is a tiny machine he is making. He probably won't have 5lbs of thrust. The o-ring will easily work.

DOH! I hadn't keyed in on that...

This might be another option: Making Acetal leadscrew nuts the easy way

Since the nut is molded to the screw, backlash should be minimal. If using a high quality screw, the travel should be quite smooth.

bob

[PurduePete]

Thanks rowbare, I think I'll use that method. I'll look around this weekend for that type of plastic. Thanks for the help guys.


PurduePete

Sent from my iPhone