Brass and I forgot to add that it needs to be ACME threads, can you still do that?

Is the brass nut round on OD? And how big?

Rudi wrote:

Acme is not a problem, length of thread is. Straight thru or blind hole?

The length is a long as I can get it so I have extra material to work with and the threads are strait through

DC wrote:

Is the brass nut round on OD? And how big?

It really doesn't mater because I have the ability to modify it after I get it.  All I ned is a chunk of brass with the threaded hole in the middle.

Rudi wrote:

Whatcha building?

OKAY here is my crazy story
 
I have been improving my 3-in-1 Harbor freight lathe.  I replaced all the spindle bearings, two taper and one ball, I upgraded the chuck from a 4" to a 5", I modified it to except a quick change tool post, I cleaned up some high spots on the gibs, and I installed a treadmill motor so I can adjust speed from 100RPM all the way up to 1800RPM with the turn of a dial.  The next thing on my list of upgrades was to remove the backlash from the lead screws.  I have .015" on the X and .010" on the Z.  Being a cheep unit there is no adjustment to remove the backlash so I decided to build my own adjuster with a second set of leadscrew nuts.  Seams simple enough but has become way more complicated. I took a bunch of measurements on my leadscrews and then spent hours searching the Internet but couldn't find replacement lead screw nuts for my mill/lathe. The lathe is a harbor freight Central Machinery 46199.  Everything about the machine is metric except the dials so I assumed the lead screws were also metric.  Z measured 20MM with a 2.5mm pitch and Y measured 16MM with a 2.5mm pitch. I couldn't find anything close. All the T16 and T20 trapezoidal nuts I have found are all 4mm pitch. 2.5mm pitch works out to 10 threads per inch so on the off chance the lead screws are actually in inch I measured again. The X in inches would 5/8"-10 but for the Z I am getting .79-10 and there is nothing close to that.  the answer, the longitudinal lead screw is both metric AND inch. Hear me out on this, The last time I measured I took a 3/4"-10 tap (not ACME) and laid it in the threads of the both screws and it lined up perfectly, so the thread is absolutely 10 TPI. The problem is being a "metric" machine the threads were cut into metric round stock. Not a problem on the X axis because 16mm is the same as 5/8" The Z axis was cut from 20mm bar stock so it is .030" bigger than 3/4". I can only assume the manufacturer cut 10 threads per inch on these screws because the same screw was used on another lathe with a threading gearbox.  My solution for the X axis is simple I have ordered an ACME 5/8"-10 LH tap and will use it to make the bushing I need. The Z axis is more complicated. I could not find a reasonably priced 3/4"-10 LH ACME tap so I was forced to order a pre-made 3/4"-10 LH brass nut. I am now faced with 6 choices: 1. I can take the correct nut to a local machine shop and have them cut the threads .015" deeper. 2.  I can see if I can find a friend that can hook me up with what I need (why I made this post).  3. I can make an ACME blade and turn both the chuck and lead screw BY HAND to cut the threads deeper myself.  I will need to turn both by hand as my lathe is 100% manual and has no threading gearbox. 4. I make a single cut through one side of the nut so it can expand.  Would work if the nut was steel but I worry about the brass bing to brittle. 5.  I split the nut down the middle into two halves and clamshell it over the leadscrew. Only being .030" undersized I think I will have enough tooth engagement to make the lash adjustment. 5.  I modify the tip on my metric/inch lead screw to use it as a "tap" and then tap/ream out the 3/4"-10 nut to 20mm-10TPI.   Because the 3/4" nut is only .030" under I am leaning toward the last two options but obviously exploring getting the correct nut made.  Thoughts on what might work best? I am open to any other ideas as well. Thanks

 

I may have chosen a cheap DRO over tackling backlash!

LOL- Happy to help. 
A DRO is a fantastic upgrade.

Certain thread topics, like this one, make me realize I know nothing. Dang brainiacs.

 

McMaster Carr

I should have picked this up from your first post, at 20 mm od it seems you do have a metric screw. Have you thought of recutting the threads to acme specs.
With .030 thou difference it just might clean up to the inch diameter.

If you do decide to go down the Digital Read Out path there are a ton of Chinese options.  On my old machine I put a Shooting Star DRO (made in Canada). They are inexpensive but don’t use glass scales.  They use some sort it rotary encoder that isn’t quite as accurate.  Overall it suited me well and the DRO takes backlash out of the equation.

Daze wrote:

Bentworker wrote:

If you do decide to go down the Digital Read Out path there are a ton of Chinese options. On my old machine I put a Shooting Star DRO (made in Canada). They are inexpensive but don’t use glass scales. They use some sort it rotary encoder that isn’t quite as accurate. Overall it suited me well and the DRO takes backlash out of the equation.

I googled them and they are about $700.  I was able to get a 3 axis display and 3 slides on eBay for about $220

 
Even though Shooting Star is in Canada they are too pricey for me I can get a 3 axis set up AliExpress  for half the eBay amount

Rudi wrote:

I should have picked this up from your first post, at 20 mm od it seems you do have a metric screw. Have you thought of recutting the threads to acme specs.
With .030 thou difference it just might clean up to the inch diameter.

 
Would he have excessive play/backlash with the other components that ride on the jackscrew if he turned it down to SAE?

Nos681 wrote:

Rudi wrote:

I should have picked this up from your first post, at 20 mm od it seems you do have a metric screw. Have you thought of recutting the threads to acme specs.
With .030 thou difference it just might clean up to the inch diameter.

 
Would he have excessive play/backlash with the other components that ride on the jackscrew if he turned it down to SAE?

If I had it turned down to 3/4" I would also need to replace the nuts with 3/4 otherwise yes I would have excessive play.  

If I wanted to make it 3/4 (and I almost went this way because it would probably yield the best result)  I think I would purchase a piece of 3/4" ACME rod with the correct threads already on it, then I would machine it to replace my current leadscrew.  Tough part is (and why I decided against it) I would need to fully disassemble my current leadscrew and bushings, take every possible measurement I could think of, put it all back together, and then do all the machining with only my measurements as reference.  If I had a second lathe it wouldn't be an issue but making a replacement part for the machine you need to use to make the part is challenging to say the least.  After mulling it back and forth that is why I opted to ream out the replacement nut and go with the metric/standard mess I have.