Is Taper Attachment worth it?

[gerritv]

I understand, I on the other hand want to use what time I have left to make things And preparing for the time when my fingers don't always do what I tell them.

My simpler life switch was to do software and hw projects only for myself Less traumatic for me as I still get to enjoy those hard earned skills.

I recently completed a Hemingway rotary broach kit. I had been putting it off due to the 0.5mm pitch internal thread that is only 3-4mm long into a blind hole. Short of tiresome hand cranking or setting up to do it in Z reverse (more tooling as I don't have LH type holders), I dialled it into the ELS, fired up the spindle at 600 rpm and watched it happen. A couple of spring passes and done. It sort of makes my lathe into a shaper at times, esp. cutting MT2 tapers. Start it up and walk away. Come back when the noise stops.

But you already know those benefits.

 

[Susquatch]

A technical question for folks.

How do you feel about the difference between a front and a rear anchored cross-slide leadscrew? In both cases, the crank is in the front.

The reason I ask is that my taper attachment relocates the anchor from the front to the rear so that the rear can follow the taper guide way/bar to cut the taper. I wonder if this difference detrimentally or beneficially affects the accuracy and/or rigidity of the cross-slide function? My instincts don't like the rear mount but I can't figure out why.

 

[140mower]

A technical question for folks.

How do you feel about the difference between a front and a rear anchored cross-slide leadscrew? In both cases, the crank is in the front.

The reason I ask is that my taper attachment relocates the anchor from the front to the rear so that the rear can follow the taper guide way/bar to cut the taper. I wonder if this difference detrimentally or beneficially affects the accuracy and/or rigidity of the cross-slide function? My instincts don't like the rear mount but I can't figure out why.

Absolutely no experience and pure speculation on my part, but my thought is that as long as your Gibbs are properly adjusted, it shouldn't make any difference if it's pushing or pulling.
However, I have been proven wrong a minimum of two or more times, and that's just this week.

 

[gerritv]

Other than the bearing mount bracket not inspiring confidence it should be fine? Probably only matters when parting off and pushing it hard. If in doubt, beef that up and get rid of the CI it is likely made of.

 

[jcdammeyer]

A technical question for folks.

How do you feel about the difference between a front and a rear anchored cross-slide leadscrew? In both cases, the crank is in the front.

The reason I ask is that my taper attachment relocates the anchor from the front to the rear so that the rear can follow the taper guide way/bar to cut the taper. I wonder if this difference detrimentally or beneficially affects the accuracy and/or rigidity of the cross-slide function? My instincts don't like the rear mount but I can't figure out why.

My South Bend came like that as stock. I ran into this issue when designing my Electronic Lead Screw. Ideally on a lathe we want to turn towards the headstock to avoid pulling the chuck assembly outwards changing the position of the cut. The problem is that if you are going from small to large diameter in that direction, every time you turn the handle to move the carriage outwards you first have to take out the backlash. Makes for uneven cut. The lathe likes to have things turned towards the headstock and towards the centerline.

By having the cross slide screw move inside the solid telescoping part the taper ways and the carriage ways from a triangle without backlash. I don't think a front anchored leadscrew short of releasing the screw holding the leadscrew nut can be moved that way.

 

[Susquatch]

I don't think a front anchored leadscrew short of releasing the screw holding the leadscrew nut can be moved that way.

I'm not sure I understood all that John. I think maybe it's one of those things you have to describe over a drawing or parts.

I do understand that you think the rear mount system is preferred which is contrary to my instincts. .

 

[jcdammeyer]

I actually went down and pushed on the various parts of my SB while writing that. I'm sure it's confusing if you haven't seen the hardware.

Let me pose a question. Crank your lathe carriage from right to left and by only pushing on the tool post move it inwards as it moves to the left.

Hmmmm. That doesn't work. Darn lead screw threads are locked against the lead scew nut. Only way to move the tool post inwards is by turning the handle. And that's how CNC systems do it. The path of the tool is the hypotenuse of the Carriage Z direction and the cross slide X direction and motors turn the lead screw.

Now think about how we feed with a lead screw. One end of the screw has to be anchored long the axis so the screw itself doesn't move; only turns. Conventional lathes anchor it at the front, it turns with the handle and the nut, which is fastened to the cross slide moves along the screw as it turns and the cross slide moves in and out. You already know this.

But nothing says the screw has to be anchored at the front. Only that it has to stay fixed relative to the carriage so the cross slide can move. If we take the other end of the lead screw and put it in a tube with bearings or bushings at either and and fix it to the carriage turning the lead screw does the same thing. Except the loading is at the other end.

Now what happens if we move that tube? Since the end of the lead screw is locked into it the entire lead screw moves. And since the lead screw is fastened to the cross slide with the nut the cross slide moves.

But wait a second you say... The front ball handle that turns the cross slide lead screw doesn't move in and out and it's fixed to the carriage. What's up with that?

Well imagine it's got a sleeve keyed to a slot in the end of the lead screw. So turn the handle, the sleeve with the key presses on the key which presses on the lead screw slot which turns the screw which moves the carriage.

That slot is just a bit longer than the distance the taper attachment can move that tube at the back.

 

[Susquatch]

Other than the bearing mount bracket not inspiring confidence it should be fine? Probably only matters when parting off and pushing it hard. If in doubt, beef that up and get rid of the CI it is likely made of.

YES! I can definitely beef it up with a machined steel bracket. I can probably beef up the thrust bearing too. Don't like either of those parts anyway!

Now to try and figure out what @jcdammeyer is talking about..... He lost me at "tube".

 

[Susquatch]

I actually went down and pushed on the various parts of my SB while writing that. I'm sure it's confusing if you haven't seen the hardware.

Ya, that's part of the problem.

Let me pose a question. Crank your lathe carriage from right to left and by only pushing on the tool post move it inwards as it moves to the left.

Hmmmm. That doesn't work. Darn lead screw threads are locked against the lead scew nut. Only way to move the tool post inwards is by turning the handle.

Well, actually it does work but only to the limits of the backlash in the screw anchor and the leadscrew nut.

And that's how CNC systems do it.

Ya, a stepper motor turning the screw isn't any different than you or I turning the screw. In both cases, turning the screw pushes the nut which pushes the cross-slide, which pushes the compound, which pushes the toolpost, etc.

The path of the tool is the hypotenuse of the Carriage Z direction and the cross slide X direction and motors turn the lead screw.

You lost me. But is this important? Do you mean the cutter's movement from combined carriage and cross-slide movement? If these are both constant velocities, I can see why you can call it the hypotenuse of those two velocities. But if they are not constant velocities, then it goes to hell in a handbasket. Then again, at any one small interval of time (think calculus) it would still be true.

But still, why is this important?

Now think about how we feed with a lead screw. One end of the screw has to be anchored long the axis so the screw itself doesn't move; only turns.

Yup. I follow that.

Conventional lathes anchor it at the front, it turns with the handle and the nut, which is fastened to the cross slide moves along the screw as it turns and the cross slide moves in and out. You already know this.

Yes, I do.

But nothing says the screw has to be anchored at the front. Only that it has to stay fixed relative to the carriage so the cross slide can move.

Yup, it could actually be anywhere only limited by the fact that the cross slide nut has to be free to move the cross-slide back and forth. So front or rear are the easiest to do.

If we take the other end of the lead screw and put it in a tube with bearings or bushings at either and and fix it to the carriage turning the lead screw does the same thing. Except the loading is at the other end.

Tube? What tube? Where is this tube? What does it look like? Is this threaded? Is it anchored? Does it slide? What is it for? You totally lost me here John.

Now what happens if we move that tube? Since the end of the lead screw is locked into it the entire lead screw moves. And since the lead screw is fastened to the cross slide with the nut the cross slide moves.

But wait a second you say... The front ball handle that turns the cross slide lead screw doesn't move in and out and it's fixed to the carriage. What's up with that?

Well imagine it's got a sleeve keyed to a slot in the end of the lead screw. So turn the handle, the sleeve with the key presses on the key which presses on the lead screw slot which turns the screw which moves the carriage.

That slot is just a bit longer than the distance the taper attachment can move that tube at the back.

All jibberish to me cuz the existence of this fictional tube is blocking the visual constructs of my mind.

HELP!

 

[jcdammeyer]

Ya, that's part of the problem.



Well, actually it does work but only to the limits of the backlash in the screw anchor and the leadscrew nut.



Ya, a stepper motor turning the screw isn't any different than you or I turning the screw. In both cases, turning the screw pushes the nut which pushes the cross-slide, which pushes the compound, which pushes the toolpost, etc.



You lost me. But is this important? Do you mean the cutter's movement from combined carriage and cross-slide movement? If these are both constant velocities, I can see why you can call it the hypotenuse of those two velocities. But if they are not constant velocities, then it goes to hell in a handbasket. Then again, at any one small interval of time (think calculus) it would still be true.

But still, why is this important?



Yup. I follow that.



Yes, I do.




Yup, it could actually be anywhere only limited by the fact that the cross slide nut has to be free to move the cross-slide back and forth. So front or rear are the easiest to do.



Tube? What tube? Where is this tube? What does it look like? Is this threaded? Is it anchored? Does it slide? What is it for? You totally lost me here John.



All jibberish to me cuz the existence of this fictional tube is blocking the visual constructs of my mind.

HELP!

I know you don't like YouTube videos.
here's a video showing the assembly of the taper attachment on a 13" SB.

Thrust bearings installed at 1:38 into the video. Then the tube 'AKA cross feed sleeve' is installed.
At 6:34 he shows how that tube moves the cross feed screw.
And just after that how the front cross feed handle couples onto the cross feed screw.

 

[Susquatch]

I know you don't like YouTube videos.
here's a video showing the assembly of the taper attachment on a 13" SB.

Normally I don't. But that one was excellent. Well prepared. Well spoken. Informative. To the point. No BS. Factual. Not pedantic. No advertising. Just an old man explaining how it all works. Excellent. I wish they were all like that. I would watch a lot more YouTube.

My taper attachment works almost identically, but has no tube like that. Hence all my confusion.

As far as I could tell from the video, the tube acts like a very long leadscrew nut. Mine has a normal split nut that attaches to the bottom of the cross-slide in the normal way.

My taper attachment moves the entire leadscrew in and out as it follows the taper bar, which takes the split nut and cross-slide with it. The hand crank slides in a groove in the lead screw just like that one does.

Your taper bar pushes the tube in and out which moves the leadscrew in and out which moves the cross-slide.

I THINK........ We are on the same page now. Let me know if I missed something.

OK, so how does that affect the precision of a front vs rear cross-slide anchor........

 

[jcdammeyer]

Normally I don't. But that one was excellent. Well prepared. Well spoken. Informative. To the point. No BS. Factual. Not pedantic. No advertising. Just an old man explaining how it all works. Excellent. I wish they were all like that. I would watch a lot more YouTube.

My taper attachment works almost identically, but has no tube like that. Hence all my confusion.

As far as I could tell from the video, the tube acts like a very long leadscrew nut. Mine has a normal split nut that attaches to the bottom of the cross-slide in the normal way..

No. The tube isn't threaded internally. The leadscrew nut is in the conventional place and has a smaller set screw that can be removed to drip oil inside it. The tube moves the entire leadscrew as you describe below.

My taper attachment moves the entire leadscrew in and out as it follows the taper bar, which takes the split nut and cross-slide with it. The hand crank slides in a groove in the lead screw just like that one does.

Your taper bar pushes the tube in and out which moves the leadscrew in and out which moves the cross-slide.

I THINK........ We are on the same page now. Let me know if I missed something.

OK, so how does that affect the precision of a front vs rear cross-slide anchor........

Otherwise not missing anything.

Now as I understand it, because the lead screw thrust bearings are behind the lathe axis, it acts the same as a conventional lathe that has the parting tool mounted upside down and behind the work. So there's no need to have a flat surface behind to mount a tool holder and upside down cutoff tool. On conventional lathes apparently mounting it behind and upside down makes a world of difference. I have no experience there.

Needless to say parting tool tip height is still critical and backlash in either the cross slide or compound slide (I have backlash in both) can make parting off an adventure...

 

[Susquatch]

No. The tube isn't threaded internally. The leadscrew nut is in the conventional place and has a smaller set screw that can be removed to drip oil inside it. The tube moves the entire leadscrew as you describe below.

Ouch. Ok. I accept that. Still, mine has no tube. The leadscrew is moved in and out to follow the taper bar by moving its rear anchor in and out. The rear anchor is a large block and gib on the taper guide. Very similar to yours but without the tube.

Taking another stab at it..... On yours, the block that follows the taper guide bar is pinned to the tube so the tube slides in and out with the block. The rear anchor of the leadscrew is the end of the tube. So the rear anchor ends up moving with the tube which moves with the block.

In my case, the rear anchor is in the block so the tube is not needed.

Otherwise not missing anything.

Now as I understand it, because the lead screw thrust bearings are behind the lathe axis, it acts the same as a conventional lathe that has the parting tool mounted upside down and behind the work. So there's no need to have a flat surface behind to mount a tool holder and upside down cutoff tool. On conventional lathes apparently mounting it behind and upside down makes a world of difference. I have no experience there.

Needless to say parting tool tip height is still critical and backlash in either the cross slide or compound slide (I have backlash in both) can make parting off an adventure...

I am actually VERY familiar with this method. I use it extensively. I can part on the front side in reverse as well as on the rear in forward.

The magic of these methods has nothing to do with rigidity or a solid anchor. In fact it's just the opposite. The magic lies in the fact that the tool can be lifted away from the work instead of digging in. @PeterT did an excellent graphical explanation a while back. I couldn't find it but he presented a really cool way to see the underlying geometry. You will enjoy it if we can ever find it.

On the other hand, I did find the following link to an entire thread on the subject:

Rear mounted parting blade.

I've messed around with a couple of different variations of using a parting blade on my small lathe. I changed out the original 4 way tool post for a quick change tool post on my compound slide and used that for while for parting. I then made a mount for the qctp that eliminated the...

canadianhobbymetalworkers.com

The bottom line is that it isn't the rear mounting that creates the magic. It's the upside down unreacted forces that allow the tool to move that makes it possible. The choice between front and rear is driven by the chuck mounting method - screw on requires a rear mount.

In essence, I don't think that detail helps me decide on the advantages of a front vs a rear anchor.

 

[jcdammeyer]

In essence, I don't think that detail helps me decide on the advantages of a front vs a rear anchor.

My only worry about running the lathe in reverse is the threaded spindle. I think stuff held in the 5C collet wouldn't care. But the 3-Jaw, 4-Jaw and faceplate...

 

[YYCHM]

My only worry about running the lathe in reverse is the threaded spindle. I think stuff held in the 5C collet wouldn't care. But the 3-Jaw, 4-Jaw and faceplate...

9" SM Utilathe Restoration

@140mower Chuck arrived thanks! @Johnwa We might have a winner for you. A Skinner made for South Bend.

canadianhobbymetalworkers.com

Locking Threaded Chucks

Thought I'd revive this topic based on some chatter on @YYCHM's threading tool thread (see what I did there?) The perennial question of how to reverse thread on a lathe with a screw-on chuck. There's this example...

canadianhobbymetalworkers.com

 

[Susquatch]

My only worry about running the lathe in reverse is the threaded spindle. I think stuff held in the 5C collet wouldn't care. But the 3-Jaw, 4-Jaw and faceplate...

No problem. Run it in forward on the backside.

Anyway, my point is that this upside down parting thing doesn't relate to the pros and cons of a front vs back screw anchor.

But the discussion has been good. In an odd way, all this sequence of hardware (this moves that moves this) discussion stuff is probably why my instincts favour the front anchor. I don't think rigidity likes hardware stacks or accumulating backlash.

 

[Susquatch]

The taper attachment repair/rebuild project has begun. Some will be difficult and some will be a clear challenge. One step at a time....

I'm busy stoning out the sliding surface dents right now. I don't believe they are really critical, so I think just stoning the same way as I would a mill bed might be fine. I think......???

It's that or use a small grinding wheel to make a very small dished indent.

I'm leaning toward grinding a very small indent with a die grinder because the two sliding parts are quite large and I think they would just glide over the slight indent but might hangup on a raised surface if I don't get it stoned perfectly.

These are first and second:

 

[Dabbler]

Either way works. You take no harm from the void, and is easier... After grinding you still have to stone to take care of any 'burr'...

 

[YotaBota]

JB Weld to fill the dent? You won't even see the little dents when your done honing.

 

[Susquatch]

And too late I noticed a scoring problem caused by a burr on the Gibb wedge. I'll have to stone that edge.......

But I'm afraid the scoring is there for life........



The fatter mark to the right is just oil. The scoring itself is uniform left to right.