I just ordered a few 1/2-10 (3') Acme for $5 each from them! Seems like a bunch of their other Acme threads are discounted. Anyways just passing the info hopefully will help someone
Yeah, you get what you pay for. I think enough people have proven that 1/2-8 2 start up to 1/2-10 5 start is the way to go. With the same motors people were using with 1/2-10 acme, you can get up to 5-10 times better performance. Sure, it costs more, but most people that start with 1/2-10 end up changing the screws down the road when they realize that they'd like to go much faster. And changing the screws is the cheapest, easiest way to do that.
Now if you're building a small machine and don't need speed, then those $5 screws might work well for you.
Mach3 2010 Screenset
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
I bought three of the six foot 1/2-10 acme from use-enco when they were on sale for $7 each. All of them were straight, and two of them were reasonably smooth, but one of them was rough at the tops of the thread corners. These are roll formed and are not the precision grade that MSC sells. (MSC has the roll formed rods also) I was able to knock off the rough edges with 400 grit wet/dry sand paper and some cutting oil.
As long as the rods are smooth and straight they should work ok for you if you use anti-backlash nuts. Rough threads will quickly wear out the delrin nuts.
I looked at the MSC online catalog earlier today and the six foot precision 1/2-10 5 start rods are $94 each now. I sure wish I had bought them last year when I ordered the 1/2-10 1 start I have now. To upgrade at this point I have to buy much more expensive rods and four new anti-backlash nuts. I agree with ger21 (if you can afford it) buy the 5 start precision if you think you want to run any kind of speed at all. These rods will only go up in price. If the three foot rods are long enough for you the upgrade price won't be quite so bad.
Ah ok. I'm not too worried about speed at this moment since it's my 1st machine (well 2nd really), and will be using dumpsterCNC's backlash nuts with the Acme. I can upgrade to a 2? start later, but for the meantime these would be an improvement to my current allthread setup at least.
What's the downside of the 2 start, etc? Just loose a little precision... but I guess since alot of people use them the loss of precision is worth the trade off. I thought a 5 start would be too much and most people use a 2 start?
It depends on which motors you are using.
The ~300 oz/in size steppers can use the 2 start rods effectively since they don't run out of torque at the higher shaft speeds as will the Xylotex 425 oz/in steppers that I have. I can make use of the 5 start rods (with some loss of precision) because these effectively reduce the shaft speed for the same rate of travel down into the region where my steppers have the most torque. For my uses I'm more interested in repeatability than absolute accuracy. If my parts are all the same, but off a little in dimension, I'll make corrections in the CAD drawing to account for the error in the acme rod.
If your table size is under 24" travel in x and y axes then waiting for it to move four to eight feet won't be an issue either. All of this cnc design stuff is related to table size, level of precision, and what you want to do with it, not what we want you to do with it. I do wish I had not cheaped out on my first build though, and that was my point. Now I'll end up paying for two sets of rods and ABNs to get what I originally wanted. The best alternative is to build a second machine and "do it right".
If you are happy with the speeds you are getting then buying more expensive rods and ABNs is not such an issue for you.
cool, thanks for the help. I forgot alot of the machines here are as big as an acre, so understand now why a 5 start would be practical with those machines