I recommend using drill rod and a shaft coupler, rather than running the ACME directly through the bearing, as mentioned on the parts page of my site. However, if your machine is already set up without the drill rod, just use something to fill the threads. A thick epoxy or caulk can work -- people have even used spackle. You can also wrap a thin piece of tape around the screw. The thrust washers have extra clearance (I think they're 0.515", so there's extra room).
Ahren
www.cncrouterparts.com
I use the drill rod and the shaft coupler as well in all my designs. It is more components, but well worth it. Filling the threads seems to have turned out well for many people though. The single start screws are more prone to this problem than the 5 start screws.
Nate
I used 5 start screws with no drill rod. I didn't even fill in the screws and everything is working great for me. Probably have around 120 hours of time on the machine so far. It works great. I am very happy I went with this design. Here is an image of my latest project. I just these box out of 2x6x12 chuck of oak. I love my CNC machine!
Ahren, any updates on the rack and pinion system? I've been contemplating making a laser cutter and think this might be a good match. No rush since I have too many projects as it is, but I'm going to keep an eye on how that turns out.
I used 5 start as well with no drill rod. The drill rod never seemed like the best approach to me. Instead of supporting the lead screw between two bearings, now you're supporting it with a bearing and a drill rod / coupling supported by a bearing. But the drill rod can rotate angularly (tilt) in the bearing some small amount, so you are depending on the shaft coupling to be rigid. For common usage I imagine it is stiff enough, but it just didn't seem like the ideal scenario to me. Also, if it did tilt, you'd potentially be putting a higher radial load on your stepper motor's bearings and on your lead nut. And when the alternate approach is also cheaper it was a no-brainer for me. I suppose if I had single start screws I might reconsider. Also, I'm coming from the perspective of having 70" long screws which makes me leary of thing like that but I imagine it'd be less of an issue for a smaller machine.
It is not always that cut and dry cost wise. For instance, with the router plans I released, the x and the y screws come out 1" shy of the 72" size that leadscrews come in. If I did not use drill rod in the design, I wouldn't be able to fit both axis on 1 6' screw. It's a matter of convenience, and in this case it actually lowers the cost of kits because there is no waste. Also, on a cost note, it's only a few more dollars per axis. The cost is close enough where you won't notice it.Originally Posted by jsheerin
I still worry about the needle thrust bearings getting caught in the screws. The Single Start screws are very prone to it, as Ahren and I have had a few reports of it happening already.
I am also going to have to disagree about the rigidity problems when use the bearing. The drill rod from MSC is always a couple of thou oversized which results in having to press it into the bearing. It is a tight fit with no rotational tilt. The shaft coupler is also rigid enough to correct this problem. I have not had any problems with this method which is w.
I would also say that 1/2-10 screws are too small for a 70" long span and you should either switch to a larger screw size or another drive system.
Nate
Howdy all,
Looks like a lively discussion over drill rod -- I'll say there are good points from both sides. I'll second Nate's assertion that with a rigid coupler, accuracy is not an issue. However, the system is designed to work either way. You can always add the drill rod (or a dowel pin) later if you decide you need it, and the beauty of putting everything in the t-slots of the extrusion is that you can make adjustments for this kind of change fairly easily. For real budget systems, I can see saving the cost of the coupler and drill rod. I'll leave it at that!
As for the R&P, I'm making progress. I've got the reduction prototyped, and am close to getting the mounting parts done. Should be around next weekend when I can do a full system test. I'll post some pictures tonight if someone reminds me.
Ahren
www.cncrouterparts.com
All,
A quick update on the rack and pinion system. I should have prototypes by next week if all goes well. Unfortunately, I'm trying to remodel my house at the same time as I'm developing this system, which makes for some tough discussions with the wife. It helps my side of the discussion when I get more orders (hint hint...
Here's a couple shots of the pinion gear+48 tooth timing belt pulley assembly. It's mounted on a common 1/2" shaft with a cross drilled pin. It's really rugged, and I think should hold up well to the abuse of a dusty cnc environment.
I've got my shop test rig set up with a new G540, and am awaiting some of Keling's NEMA 23 motors for testing purposes. This should be a popular combo if it works as well as I hope.
Ahren
www.cncrouterparts.com
Parts Bundles for the FLA100-00 Router Kit are available for purchase here
Also, I now offer the option to tap the mounting holes for linear carriages for 3/8-16 screws. This is useful for mounting carriages to the Z-Axis Plate.
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