Need Help!- Some Simple Questions

[RockBoy]

I'm looking at some acme rods here: McMaster-Carr

Do these have a machined end?

And I've heard people on here before talk about 1 start 5 start etc. what does "x start" mean??

Also I remember seeing some site on here before which sold high quality nuts for this thread, but i can't remember the name?

Thanks

[jjacstcy]

No machined ends, a normal rod has 1 start meaning 1 continuous thread for the length of the rod. 5 start for example has 5 separate threads that run parallel to each other down the whole length of the rod. I ordered my nuts from dumpstercnc.

[CarveOne]

Originally Posted by RockBoy I'm looking at some acme rods here: McMaster-Carr Do these have a machined end? And I've heard people on here before talk about 1 start 5 start etc. what does "x start" mean?? Also I remember seeing some site on here before which sold high quality nuts for this thread, but i can't remember the name? Thanks

I didn't look at the link, but usually they come without machined ends.

The number of starts refers to how many grooves are cut into the rod. One start has a single groove spiraling around the rod. If you grind a regular bolt square on the end you will see it clearly.

A five start screw will have five individual grooves spiraling around the rod and the grooves will all be equally spaced from each other. There are 2 starts and 8 starts available also.

One start screws will be too slow to have much of a cutting speed. They are low cost though. 2 start and 5 start screws are what I would recommend even at the higher cost. I use 5 start screws now after trying one start screws on my first machine with poor results.

DumpsterCNC and CncRouterParts both have anti-backlash nuts for Acme rods and couplers or adapters to use the rods without having to machine the ends.

CarveOne

[louieatienza]

No, they come in 3 and 6 foot lengths, with no machined ends.

Some screws have multiple threads or 'starts.' This has an affect on how much the leadnut travels when the screw turns.

I believe in McMaster Carr's site they use different ways to explain the same thing.

For example they have 1/2" 8, 8 start. They also call this an 8:1 ratio (8 starts, 1TPI effective), or a lead of 1" (meaning 1" travel per turn). A 1/2" 8, 4-start would have a ratio of 2:1, or a lead of 1/2". And so on...

If you look at Roton's site, they describe their screws by pitch. They don't have 1/2" 8, 8 start but they do have 7/16" 8, 8 start. But they describe it as 7/16" x 1", the first being the major diameter, and the second being the lead. Then if you click on the item the description will tell you the number of leads.

Generally the higher amount of starts, the faster the movement, and vice versa.

Edit: the 1/2" 8, 4 start is actually 4:1 ratio as listed on their site. They have a 1/2" 8, 2 start which is the 2:1 ratio...

A lot of guys here use the anti backlash leadnuts from dumpstercnc.com

[RockBoy]

Thanks for that. Do you think the precision rod is good enough or should I go the ultra smooth?

Also any tips on where is should buy the bearings for fixing the rod?

[CarveOne]

Originally Posted by RockBoy Thanks for that. Do you think the precision rod is good enough or should I go the ultra smooth? Also any tips on where is should buy the bearings for fixing the rod?

The smoother the finish, the longer the Delrin nuts will last. Depends on the cost differential as to which one I would choose. My 5 start screws are the precision grade and are plenty smooth.

My bearings came from VXB.com

CarveOne

[DonFrambach]

Originally Posted by RockBoy Thanks for that. Do you think the precision rod is good enough or should I go the ultra smooth? Also any tips on where is should buy the bearings for fixing the rod?

I believe that McMaster-Carr's ultra smooth leadscrews do not have standard ACME threads and must be used with their ultra-smooth nuts. That may not be a problem for you but I found that using ACME nuts from CNCRouterParts.com convenient. CNCRouterParts

For my router, I used the design and bearings from CNCRouterParts.com for fixing the leadscrew. Very easy to install (no need to machine the leadscrew) and seem to work just fine. CNCRouterParts