Really basic lathe question

[TorontoBuilder]

The other shaft is strictly for power feed if I understand things correctly.
On really big lathes there will be a third which I think controls the spindle engagement.
Abom79 has one like the latter.

My brother's has three rods too

 

[Former Member]

My Logan had only a lead screw which drove both carriage (feed and threading) and cross slide depending how you activated it.

My BB CX707 has a lead screw for threading only, a drive rod (no thread on it) to move the carriage or cross slide and finally a power shaft for on/off, the does not rotate more than about 90 degrees to turn the lathe on or off with a lever at the carriage (this took a little getting used to but now that I am I love it and understand its importance). This final feature is more something that started on large lathes and is migrating towards the small lathes.

 

[VicHobbyGuy]

did yours come with the gears to get proper pf speeds ? or did you just use the highest tpi gear setup it came with ?

What's "proper"? Standard PF on a 7X mini lathe with a 16TPI leadscrew is .0039"/rev. (20T-80T-20T-80T gear train) Gears to reduce that to about .0026"/rev are readily available. Since the standard gears are plastic, 3D printed versions work well.

 

[VicHobbyGuy]

Didn't your lead screw have a keyway slot for PF?

7x lathes don't have a keyway along the length of the leadscrew.
I thought the keyway in my Logan 210 leadscrew was just for driving the cross-feed.

 

[Susquatch]

*Edit* -On most lathes- the half nut does not run the carriage feed on a single shaft lathe, the carriage power is taken from the keyway slot in the lead screw,

I don't know about "most".

My newer lathe is the 3 shaft design and also has a gear rack that runs the length of the bed.

My old lathe is not a mini lathe by any stretch of the imagination. I'd guess it's bed is 6ft long. It is just old. It has only one shaft and no rack. The one shaft has no keyway slot. Power Feed is done with the half nut. The half nut is sloppy as hell but it has not changed since I got it. I did some amazing work on that old girl. She taught me most of what I know.

I don't think this is an either or situation. I think they come in all kinds somewhat loosely depending on vintage, cost and size.

I have not been with enough different lathes to know how most are built. I like em all!

 

[Former Member]

I don't know about "most".

My newer lathe is the 3 shaft design and also has a gear rack that runs the length of the bed.

My old lathe is not a mini lathe by any stretch of the imagination. I'd guess it's bed is 6ft long. It is just old. It has only one shaft and no rack. The one shaft has no keyway slot. Power Feed is done with the half nut. The half nut is sloppy as hell but it has not changed since I got it. I did some amazing work on that old girl. She taught me most of what I know.

I don't think this is an either or situation. I think they come in all kinds somewhat loosely depending on vintage, cost and size.

I have not been with enough different lathes to know how most are built. I like em all!

Both the Logan and CX707 have a gear rack running on the top side.

I think the big difference is long term accuracy and wear on the lead screw assemble (split nut included). I believe the single lead system creates more wear as the split nut does all functions.

With the multi-shaft system the rack takes the wear for feed and lead screw for threading. While wear on the rack is one of those things for regular feeds doesn't make an issue, a worn lead screw/split nut effects the thread as this what determines the accuracy.

Again thing age/size of machine and intended market.

As the machines scale down in size it becomes a head stock and carriage limitation on how much mechanicals can be installed along with cost.

ie: Would pay $5800 for a 13x36 or $5800 for a 10x22 (with the 3 rod system) or $3400 for a 10x22 without. The cost difference between last two is the mechanics as while cast iron does add some cost is a small portion vs the extra hardware and time to set up.

 

[slow-poke]

Thanks for all the great explanations, my lathe has the key slot, but it's only used to drive the cross slide. When engaging the half-nut for longtitudial travel and in between threads I tend to keep pressure on the lever while waiting for it to drop in, it seems it would be wise to be more patient and less ham-fisted to minimize half-nut wear.

How long does a half-nut typically last on a hobby type machine like a CX706?

I'm wondering if I should order one while they are available, because if in all likelihood I will need to change it a few years from now the cost will probably be double or triple what it is now. If it is more likely to last 10 years then perhaps wait?

 

[Mcgyver]

How long does a half-nut typically last on a hobby type machine like a CX706?

Kept clean and lubricated, close to forever? Keep in mind that wear on the nut has no affect on accuracy, its uneven wear on the leadscrew that creates lead error. i.e. as the cut moves from a worn to unworn section of the leadscrew. Some leadscrews, like on my DSG are reversible so if it ever becomes so worn its a issue, you swap it around and have qn unused thread flank, at least in the TS ->HS direction

 

[Susquatch]

I'm wondering if I should order one while they are available, because if in all likelihood I will need to change it a few years from now the cost will probably be double or triple what it is now. If it is more likely to last 10 years then perhaps wait?

Assuming that your lathe still works, you can always make one. But if I were you I'd buy one just in case cuz that would basically guarantee that you never need it......

 

[Former Member]

Like @Mcgyver said, don't get overly worried about life span, properly maintained even in light industrial use, these system last (think how many used ones are out there). My Logan had seen serious use well before I got it and I know I added some as well, no issues.

The new owner is using it and loves the machine (he gave it a little TLC when he set it up).

The only worrisome wear issue comes from true heavy industrial use (or serious abuse in any setting) at which point you have other factors to consider.

And if you wear it out in 10 years, you'll likely be looking for a better lathe to meet you requirements as they likely have expanded beyond your current needs.

 

[RobinHood]

…. my lathe has the key slot, but it's only used to drive the cross slide.

Are you sure about that?

From the manual for a CX706, it appears that both longitudinal Z-axis (carriage) & traverse X-axis (cross slide) would use the key slot in the lead screw. It is just a matter if you push the feed lever in and up (cross feed) or pull it out and down (longitudinal feed).

 

[Larry_C9]

phaxtris It was the Craftex B2229 that I sold to a member here and that is what led me to this forum.

 

[DPittman]

I'm wondering if I should order one while they are available, because if in all likelihood I will need to change it a few years from now the cost will probably be double or triple what it is now.

I ordered one from Busy Bee for my 10x22 lathe for the same reasons you mentioned. I think stripping the half nut out might be more likely than wearing it out but I'm not sure. I figured I was going to have my little lathe for a long long time so having a component on hand like the half nut was "insurance" I was ok with.

 

[slow-poke]

Are you sure about that?

From the manual for a CX706, it appears that both longitudinal Z-axis (carriage) & traverse X-axis (cross slide) would use the key slot in the lead screw. It is just a matter if you push the feed lever in and up (cross feed) or pull it out and down (longitudinal feed).

You are correct. I did not appreciate that the actual drive source changes based on the in out position of that lever. I incorrectly assumed it was just a gear ratio change. I will stop using the half nut for anything but thread cutting.

Thanks for bringing this to my attention.

 

[RobinHood]

No worries.

I have a similar set-up on my Standard Modern 1120 for feed direction selection. It does have a separate feed shaft though. The SM 1340 even had one more shaft ( lead screw, feed rod, and spindle control ), but also used the “in and up / out and down” motion on the feed selector. So quite familiar with said operation.

Many lathes are just copying that mechanism. Don’t know who used it first…

PS: Colchester Master 2500 offers a fourth shaft: a 6 position “revolver” carriage stop. It allows you to preselect 6 different stopping points which, when engaged, will trip the automatic feed and stop the carriage. Would be great for production work of the same part.