Help with lead screws (ACME vs UNC)

[PotvinGuitars]

I'm just finishing up a Model D build and I have some questions about lead screws.

The table is 4' x 3' (working area of ~ 3' x 2'), so I have 4' and 3' lead screws. I used 1/4-20 threaded rod, and while jogging, I noticed that even at 10-12 inches per minute the 4' rods whip like skipping ropes!

My first question is, will a 1/2" rod eliminate the skipping rope on a 4' span?

Assuming I solve the skipping rope issue, I'd like to crank out more than 10 ipm. I've heard legend of similar sized D models getting 20-25 ipm which would be great. Would switching to 1/2-10 ACME lead screws improve my ipm dramatically?

Lastly, if ACME screws are the answer, are the screws with more than one start more accurate? Greater resolution? or is single start all I need?

Thanks,
Mike

[ger21]

My 60" 1/2-8 2 start whips a lot over 100ipm, but I can still run it reliably at 150ipm. My 40" Y axis whips a small amount when the nut is to one side, but not enough to cause any problems at 180ipm.

My Z axis is 1/2-10 single start, and I get 55ipm. These speeds are using a Xylotex at 24V.

You really should be using 1/2-8 or 1/2-10 acme 2 start. It's at least twice as efficient as all thread, so you'll lost a lot more power due to inefficiency.

[PotvinGuitars]

Thanks Gerry. What's the advantage of 2 start over single? I can source single start locally so I'm wondering if I should go to the effort of Internet ordering 2 start from the US (I live in Canada )

Mike

[ger21]

It's more efficient, and will usually double your speed.

[PotvinGuitars]

Originally Posted by ger21 It's more efficient, and will usually double your speed.

Ah yes, I see. Two start halves the turns /inch. Thanks!

[aslatte2]

While all this is true, what would be the difference between "ACME 1/2-10 2 start" and "ACME 1/2-5 1 start"

[ger21]

I've never seen 1/2-5 single start, but my guess is the 2 start would be more efficient.