Help with AB Nut mounting please

[slickrick]

While designing my CNC, I'm trying to figure out how I am going to mount the AB nuts.

I'm thinking about buying 3/8" ACME rod through Grainger (get a discount through my work), and and 3/8" ACME Anti-Backlash Leadnuts from dumpsterCNC.

Can anyone give me an idea on how to securely mount these?

Thanks,
Rick

[CarveOne]

Simple right angle brackets work well enough for the smaller machines but you can get as elaborate as you want to with any size machine. You can drill and tap the delrin AB nuts for screws or use through-holes. Make the bracket that the AB nuts are mounted on adjustable by putting slotted holes where they have mounting screws.

CarveOne

[slickrick]

Awesome....thanks for the pics. That also gave me ideas for the limit switches too.

Rick

[CarveOne]

Part of the round flange can be band sawed off if you don't go too close to the Acme threaded hole. I needed to do this for clearance purposes on all four of the ABNs on my machine. In the photo showing the limit switch you can see where the round ABN flange looks like a "D" shape.

The ramps are made of a single piece of aluminum angle that is cut to form the ramps and also provides a tab to mount the ramps to the ABN angle bracket. The lowest point of the ramps can pass by the limit switch(es) without damaging the limit switch. These short lever snap action roller switches came from Arturo at CNC4PC.com. They are mounted to small squares of 1/16" aluminum sheet. The squares have a pivot hole and a slotted hole to allow for adjustments. Easy stuff to make at home with a hacksaw, drill, and file.

CarveOne

[slickrick]

Yeah I noticed that the nuts were cut to fit. I didn't notice how you made the ramps though, very clever.

Do you have any pictures of the ends of the screw and how you made that connection?

I have some ideas on what I might do, but haven't gotten to that point in my design yet. I've been leaving some of this stuff for the end, but it's getting to that point.

Rick

[slickrick]

Another question I have on Anti Backlash nuts;

Is it better to just have one on the leadscrew, or can I have two that will spread out the thrust to move the axis?

I would normally think that two would be better, but in this application, I'd rather hear from you guys?

Would having two create too much friction that would counteract the advantage I might get by having that many?

Added Picture.

[CarveOne]

Although that looks like a better way to do it, I would not do it because of the added drag on the smaller machines and the steppers commonly used on them. The springs on the ABNs like mine (DumpsterCNC) are loading the threads pretty snugly. Two of them would tend to cause more problems with missed steps.

If you want to try it, just design your ABN mounts for two ABNs and then remove one later if your steppers can't drive them reliably. The ABNs don't last forever and you will already have spares on hand.

If you make the dual nut mounting plate you will need to make the mounting screws of one of the ABNs adjustable so that it will align with the acme threads properly. Just slot the holes enough to match the ABNs when screwed onto the threaded rod.

CarveOne

[CarveOne]

Do you have any pictures of the ends of the screw and how you made that connection?

Rick

In my CarveOne's Solsylva 25x37 build log I used 1/2" acme rods. I used 1/2" acme nuts to hold everything together. I could have turned the ends to 5/16" in the lathe but decided to leave the ends square and order the correct bearings. Turning the ends didn't look stout enough to suit me. More photos are in there.

CarveOne

[slickrick]

Thanks, I'm checking out your build thread as I get time.

I'm also rethinking the size of the ACME rod I may use. I am not sure that I like the 3/8" size I have been planning. I may up it to 1/2" for the one I am designing.

What have you guys seen as far as the difference between 3/8" and 1/2"? I'm thinking it may give me less whip over the length.
My cutting surface is 36" in the X (overall length 38), 26" in the Y (overall 34) and the Z is pretty short at only about 6" of travel.

Putting larger dia rod in there should help but how much between 3/8 and 1/2 is it going to help.

[CarveOne]

slickrick,

With cheap 1/2" 1 start acme rods from Enco and DumpsterCNC anti-backlash nuts on my machine now, I think my first upgrades will be to change the Xylotex controller to the new Gecko G540 controller when it is available (May 2008), then change to 1/2" 5 start acme. It then may run fast enough for minor whipping to appear. A friend has a steel box tube frame CNC router with 1/2" acme rods and servos that can run at 300 ipm. That thing can really show some violent x axis whipping. He is currently changing the x axis to 1" lead screws but he didn't say if it was acme rods or ball screws.

I have run mine at 60 ipm and get some stalling in one direction but never see any lead screw whipping.

You will not regret using acme rods instead of threaded rod from Lowes or Home Depot. I paid $7 plus shipping for acme rods from Enco versus $11 each for 1/2" threaded rods from Lowes. The 1/2" acme nuts are more expensive than threaded nuts though, and the ABNs were much more expensive than threaded couplers. I don't regret following the advice of other build logs to use the acme rods. I still have the threaded rods, couplers, and nuts that I didn't use after seeing how poorly the threads are made. They will be saved for some other home project.

CarveOne

[slickrick]

Thanks CarveOne, I have decided to use 1/2" rod. Checking the Enco site you mentioned, they have it pretty cheap. maybe you guys could tell me what the difference is between the two rods on the link below. Besides the price...hehe
http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2

Is the price difference because of one being Alloy Steel and the other Oil Finish Steel?
If so.....which is better for our application?

And if the Oil Finish is Ok to use...then I'll buy some of that.

As far as my steppers.....I haven't decided what size to use yet. I still haven't figured out how to size them. Looking around, I am thinking Nema 23's but not sure of the size.

I'll be using a craftsman router initially and will be cutting .050 aluminum minimum.

[CarveOne]

slickrick,

The link you posted goes to flat steel stock.

This link goes to the Keystone brand acme threaded rod catalog page:

http://www.use-enco.com/CGI/INPDFF?P...MITEM=319-7392

Enco 408-0220 (low carbon steel) was on sale when I bought mine. One of the three rods I received had some rough edges on the threads but some polishing with 400 grit wet or dry sandpaper cleaned it up. The rods were straight and were shipped taped together in a cardboard tube. The alloy steel rods should be a higher grade finish and a somewhat harder material than the low carbon steel rods.

Most of the under 4'x4' cnc router designs use NEMA 23 ~300 oz/in steppers or 425 oz/in steppers. The Nema 34 steppers can be used if you make the appropriate mounting plates for them. Read up on the differences in torque vs speed for each type of stepper. More torque usually means at lower speeds. But not always.

CarveOne