Beginner with a lathe turning issue, what to look for?

[RaisedByWolves]

I don't bother retracting and haven't noticed a problem related to the cutter or being able to hit my target OD's. At least, none that can be attributed to this particular thing (there are others, 99.9% due to moix ). This is on a not-so-rigid mini lathe, perhaps it's different for larger, more rigid machines?

I can take it or leave it.

Its more about finish as far as I'm concerned, cutting is cutting.

 

[SouthernChap]

Is it a C

It may make a difference because if it was a conversion vs. factory CNC then it may have some idiosyncrasies that need to be considered.
But for what it's worth, programming a tool withdrawal will almost always produce a better finish and may help tool life.

I'm assuming that it's one of the actual Boxford CNC models that were popular in schools or technical colleges. They pop up on the used market pretty often here in the UK.

 

[xbartx]

I'm assuming that it's one of the actual Boxford CNC models that were popular in schools or technical colleges. They pop up on the used market pretty often here in the UK.

Yes, it is a Boxford TLC 160 and was being offered at a garage sale for $100.
I'm running it now using a Centroid Acorn board and their CNC12 software.

 

[homebrewed]

I can take it or leave it.

Its more about finish as far as I'm concerned, cutting is cutting.

I've noticed that I often get a better finish on otherwise problematic steel alloys if I don't retract. It probably is due to the much lighter cut.

 

[RaisedByWolves]

I've noticed that I often get a better finish on otherwise problematic steel alloys if I don't retract. It probably is due to the much lighter cut.

I was taught not to retract in certain situations as the machine may not repeat and you will be stuck fighting/guessing/struggling to hit your final dimension.

If your part is tapered so much this is causing you tool wear or other problems I would be looking at setup issues and tooling selection or tool bit angles.

Each machine or job may like something slightly different.

 

[RaisedByWolves]

I’m a total beginner here and working on an older Boxford CNC lathe.
The issue I’m seeing is when taking a cut running the lathe in the -Z axis, it will also take a skim cut if I run it backwards +Z without moving the X axis.
The stock I have mounted in the chuck is 1” and sticks out of the chuck 1 1/2”
The lathe has ball screws and even so if I’m not moving the X axis it seems like this is not normal.

What do I look for as a possible cause.
Do you need anymore info from me that might help diagnose the issue.
-Brad

Back to this.

After looking at your pics, what is the orientation of your tool bit when turning.

If it’s top down you may have worn ball screws/lead screws.

On one hand I’m jealous of the deal you got, otoh, guesstimating over the machines operation there’s a lot I don’t like about it.

Just an opinion.

 

[xbartx]

Back to this.

After looking at your pics, what is the orientation of your tool bit when turning.

If it’s top down you may have worn ball screws/lead screws.

Yes, the tooling is top down. I did go through everything I could think of to tighten up any possible slop.
The cross slide was a bit loose and I tightened the gibs up and think it is better.

 

[RaisedByWolves]

Yes, the tooling is top down. I did go through everything I could think of to tighten up any possible slop.
The cross slide was a bit loose and I tightened the gibs up and think it is better.

Is there any kind of lock on the carriage you could lightly lock to add some drag?

With the top down nature of this I wouldn't be surprised if gravity is playing a part in the tool back dragging a bit.

 

[xbartx]

Is there any kind of lock on the carriage you could lightly lock to add some drag?

With the top down nature of this I wouldn't be surprised if gravity is playing a part in the tool back dragging a bit.

There is no lock on the carriage. Being a CNC stepper driven axis wouldn't the stepper motor hold the carriage?

 

[RaisedByWolves]

There is no lock on the carriage. Being a CNC stepper driven axis wouldn't the stepper motor hold the carriage?

Yes, until things get worn.

Any way you could put an indicator on the carriage and look for deflection during the cut?

You could always measure, but tool deflection vs part deflection then comes into play.