Smithy lead screws/nuts

[mac1911]

Hi Everyone,
I have the smithy Midas 1220 LTD, and have been going through those brass half nuts "on the regular". From conversations with Smithy over the years of owning this tool, they've always made this part from brass, and consider it a wear part, as they don't want the screw to experience wear.

Now Smithy just discontinued the line completely and has no back stock in these.

So the lead screw is NOT anything standard. It's a 20mm with a 10TPI pitch. It's not an ACME screw and won't fit that profile. The trapezoid angle of an ACME screw is 30deg, and this is more like 20deg.

If anyone's interested, I have a CAD model and am 3D printing one in bronze/steel right now. Once it's tested working I'll be happy to make the file available to all takers.

I would love a copy of the file when it’s finalized .

I’m a little ignorant when it comes to CAD. When you finalize your file, would you be able to show the pitch dimensions. I don’t want to get too off subject here. I know there are sections about CAA.

How hard is it to alter the file if you would want to make that part complete like a nut and then have it print three-quarter acme 10th thread per inch could it do that.

 

[Extra Fox]

Total printed was about $150 shipped in bronze steel. I honestly jumped the gun to get the tool up and running at the expense of cost. I can do a good bit to cut that down by skeletonizing it, or even just printing a ‘thread pad’ that screws onto the existing brass after some milling.

Showing the dimensions can be done, but I’m still making sure what I have is a good fit. Thanks, Smithy for using an oddball thread. It’s NOT acme. I can easily change the thread profile/pitch/type etc, model as a complete nut. Right now it’s being modeled as a custom helical cut since it’s such an oddball thing. Normally you’d basically tell the CAD system the pitch and type, select the cylindrical surface, and press go.

Printing a nut that’s already available (like 3/4-10 acme) isn’t going to be cost effective. You can do it, but with a quick search online I’m seeing them in steel for under $10, and brass mounts and sleeve nuts in the $40 range.

 

[mac1911]

Total printed was about $150 shipped in bronze steel. I honestly jumped the gun to get the tool up and running at the expense of cost. I can do a good bit to cut that down by skeletonizing it, or even just printing a ‘thread pad’ that screws onto the existing brass after some milling.

Showing the dimensions can be done, but I’m still making sure what I have is a good fit. Thanks, Smithy for using an oddball thread. It’s NOT acme. I can easily change the thread profile/pitch/type etc, model as a complete nut. Right now it’s being modeled as a custom helical cut since it’s such an oddball thing. Normally you’d basically tell the CAD system the pitch and type, select the cylindrical surface, and press go.

Printing a nut that’s already available (like 3/4-10 acme) isn’t going to be cost effective. You can do it, but with a quick search online I’m seeing them in steel for under $10, and brass mounts and sleeve nuts in the $40 range.

What I have into my smithy I still could not replace it with anything much better. Im only about $700 into the machine $350 or so into some tooling.
Made everything for the lathe so far.

 

[Extra Fox]

I hear that. Switching main machines like a lathe... I have so much tooling and jigs and processes built up around it. I suppose a fair % of it would be workable on another lathe, but it's always enough that repairs are worthwhile.

 

[Extra Fox]

So a sad update for anyone who happens to still be interested. I have gone through several iterations with really good measurements, and I just can't get this dialed in. Not sure if it's a limitation of the laser sintering process, or my own abilities.

Either way, I've heeded the writing on the wall, and bought a Grizzly G4003 lathe to replace it.

 

[mac1911]

So a sad update for anyone who happens to still be interested. I have gone through several iterations with really good measurements, and I just can't get this dialed in. Not sure if it's a limitation of the laser sintering process, or my own abilities.

Either way, I've heeded the writing on the wall, and bought a Grizzly G4003 lathe to replace it.

I know your tooling up for a new lathe…but
What if you where to print a complete nut rather than the half. Touch on the small side.

Then turn one end of the lead screw into a “tap”
We do this often at work on cars to salvage a stripped hole we dont have a tap for. Badically slot the screw like a tap , its not going to cut new threads but will clean up whats there.

So with this approach you could put the finishing cut to the plastic nut. ?
A new lathe is not going to be in my budget anytime soon , heck I cant even get the monies together to get a 3/4-10 acme lead screw and nut< even still im left with yet another project redesigning the half lead screw nut assembly to 3/4-10?

 

[Extra Fox]

The half nut being anything softer than brass is a no-go. It literally drives the bed across the ways.

As for the sintered steel/brass 3d printed material, that stuff is shockingly hard to machine. Tapping it is way harder than it should be. My theory is that because it’s made of steel chunks in a softer brass medium, when the cutting edge hits a steel particle, it’s easier to compact it into the brass than cut it, almost regardless of how sharp the tool is. Same for lapping and other cutting methods. It will (and did when I actually tried your screw cutting method) chew up the steel thread before it formed.

 

[Spottswood3]

Total printed was about $150 shipped in bronze steel. I honestly jumped the gun to get the tool up and running at the expense of cost. I can do a good bit to cut that down by skeletonizing it, or even just printing a ‘thread pad’ that screws onto the existing brass after some milling.

Showing the dimensions can be done, but I’m still making sure what I have is a good fit. Thanks, Smithy for using an oddball thread. It’s NOT acme. I can easily change the thread profile/pitch/type etc, model as a complete nut. Right now it’s being modeled as a custom helical cut since it’s such an oddball thing. Normally you’d basically tell the CAD system the pitch and type, select the cylindrical surface, and press go.

Printing a nut that’s already available (like 3/4-10 acme) isn’t going to be cost effective. You can do it, but with a quick search online I’m seeing them in steel for under $10, and brass mounts and sleeve nuts in the $40 range.

I have run into the same problem with the brass half nut for my Smith 3 in 1 machine. I found a source for a 3/4" x 10 TPI LH ACME tap and was planning to make one but after seeing the various posts, I don't think it would work. Did the 3-D printed half nut work and if so, where can I purchase one. I don't think I have enough experience to try to grind a threading tool to the profile necessary or to try to cut threads with it.

 

[David2011]

For future reference, McMaster carries 5/8-10 LH Acme threaded rod in mild, stainless and 4140 steels. Taps are readily available as well.

Just in the last few days I repaired my Victor 13x40 cross slide screw. The dimensions were much like the Smithy. The screw was about .605” OD and 8 tpi. It wasn’t a whole number metric size and .020” under the Imperial diameter. I bought 3 feet of the 5/8-8 LH Acme rod, a matching tap and a piece of bronze and fixed it myself by splicing the Acme rod onto a shop built hand wheel end.

 

[Spottswood3]

For future reference, McMaster carries 5/8-10 LH Acme threaded rod in mild, stainless and 4140 steels. Taps are readily available as well.

Just in the last few days I repaired my Victor 13x40 cross slide screw. The dimensions were much like the Smithy. The screw was about .605” OD and 8 tpi. It wasn’t a whole number metric size and .020” under the Imperial diameter. I bought 3 feet of the 5/8-8 LH Acme rod, a matching tap and a piece of bronze and fixed it myself by splicing the Acme rod onto a shop built hand wheel end.

Thanks for the info. I thought about doing the same thing with my Smithy, but wanted to explore all the "easier" options first.