ACME screw opinion

[SScnc]

Hey guys,

I used 3/8-16 threaded rod on my DIY for moving the gantry, they are each 60" long and one on each side. I used this mainly to just make sure my design works good and it mostly does however, the 3/8" rod is too flexible and of course slow. I have to be cheap on the lead screw selection right now and upgrade later.

My question is, what's the opinion on THESE from McMaster ?

Has anyone else used them ?

Thanks.

[jsheerin]

Try the precision acme rods - I had good luck with those from McMaster.

[arizonavideo]

Originally Posted by jsheerin Try the precision acme rods - I had good luck with those from McMaster.

Roton sell Acme too and they are lower priced, fine screws too I have used them.

For plastic nuts you don't need the hardened screws.

http://www.roton.com/

They sell some of their screws to Mcmasters.

[Aryantes]

I'm currently in the process of building my machine and have had a little bit of experience with lead screws thus far.

I would definitely suggest getting a 5 start lead screw. McMaster sells them.

I bought single start ones and regret it fully. My machine's x-axis is 60 inches long so I probably shouldn't have chosen lead screws as my mechanism in the first place. Didn't read enough before starting.

A single start screw will make you more prone to issues.

This includes...

Screw whipping - if the screw is even slightly bent, the screw will wobble a lot while your axis is moving, creating a bunch of unwanted results.

Every screw has a critical speed where at a certain RPM it will wobble.

The benefit behind a multi start screw, is that the screw will not need to spin as fast to achieve the same speed for your machine.

As a result, your stepper motors don't have to work as hard, therefore spinning at lower RPM, therefore giving you more torque and efficiency.

You give up a bit of resolution/precision with a multi start screw but... depending on what you are milling and the quality of your build, it might be completely irrelevant but make sure you know what your needs are.

I bought single start screws thinking that resolution was my single priority but I didn't foresee these mechanical issues I'm having now. If my machine itself is even slightly flawed, the 1/2000 of an inch resolution I would get form the 1/2-10 single start screw would have been all for naught.

I'll be more than satisfied with the 1/2-10 5-start screw, with a resolution of 1/400 of an inch, before calculating in driver microstepping.

[SScnc]

Originally Posted by arizonavideo Roton sell Acme too and they are lower priced, fine screws too I have used them. For plastic nuts you don't need the hardened screws. http://www.roton.com/ They sell some of their screws to Mcmasters.

Thanks guys, I didn't know Roton would be lower priced, I'll order from them soon.

Aryantes, thanks for all the info, I would like the speed of 5 start but it's a money thing right now, I'll upgrade later.

Thanks again,

Steve

[johnmac]

Aryantes is 100% accurate with his recommendation. If you can't swing the 5 start screws, at least get 2 start. Dumpstercnc.com has anti-backlash nuts, along with other stuff you may need.

John

[SScnc]

Hi Guys,

I changed from 3/8-16 threaded rod to 1/2-13 and my machine is now running decent and I've done a couple of test sign engravings and the quality is really very good. However, as you know, the travel speed is very low and if the IPM is over about 45 it develops some whipping problems. Running at 30 IPM it's very smooth.

So now that I know all my work building this machine is time well spent I'm going to go ahead and upgrade to better screws. I need some advice on which of the following selection is best considering my main use for this machine will be for sign engraving and making edge lit acrylic signs and so the resolution needs to be good enough to produce very good quality engravings.

So based on your previous advice, I'm looking at the following 2 start acme screws. This one and This one I'll also be using the plastic nuts. Which is best for my application ?

Thanks,

Steve

[jsheerin]

Also look at the Mcmaster precision screws in 1/2-10 5 start (2 threads per inch): p/n 99030A704. 6ft for $57.50. Antibacklash nuts from dumpstercnc.com for $22.50. They've worked well for me. I have rapids limited to 200ipm and cut at 125ipm, but I could rapid a bit faster, maybe 250ipm (screws just start to whip with 4' of travel when I'm at one end of the screw). I was cutting an aluminum spanner wrench this weekend and could see the step the cutter made when I offset my toolpath 0.001", so I feel resolution is still fine with these. I'm using the 425oz*in motors from Keling with a G540 controller.

[SScnc]

Thanks jsheerin, that's not much higher than the 2 start I linked to. And the resolution sounds good enough, I appreciate you posting your results using these.

I'll take a look at those now, thanks again.

[jsheerin]

Actually it's twice as fast or more (and thus half the resolution) as the screws you linked to. It will also have less force although it will probably be better than half the force as the efficiency changes with the pitch of the threads. The price is about half as much as the Rotons per foot and the nuts are about the same price.

[Highlander01]

So, with the upgraded screws, what did you do for end machining of screws? ex. roton does not do end machining from what I can see on there web page.

[jsheerin]

I didn't do any end machining. File a flat for a set screw in your coupler. Get a 1/2" coupler for the screw and whatever size you motor needs (mine were 1/4" shafts, I believe). Get some lock collars to put on the screw to support your thrust bearings. You only need to do machining if you want to get fancy with your thrust bearings.