Is Taper Attachment worth it?

[eotrfish]

So how do you drill your stock ends when using it - standard conical center drill or ball end mill profile...? Do you also use a ball support on the headstock end?

I didn't drill the ends. I inserted a press fit brass sacrificial stub into each end and drilled the brass stub. Looking at old drawings it seems that the parts tapered from .465 at the big end to .415 over 10". I found one of the brass inserts and yes - it was drilled with a Radius Centre Drill.

This project was about 25 years ago so details are hazey. I know I had a number of sizes of these radius centre drills so that's likely what I used. I know that I didn't have a ball support for the headstock end so probably just used a Radiuis centre drill at the big end. I made 10 of these parts and they turned out fine.

Radius Centre Drill info from McMaster-Carr. There are other manufacturers of these with somewhat less agressive radii.

Here a couple of KEO Radius Centre Drills and the brass insert. Pardon the plier marks on the brass insert - as I said it was pressed in

 

[Susquatch]

This project was about 25 years ago so details are hazey.

Maybe from your perspective. But from mine, it's brilliant.


I might have been tempted to thread the brass stud and mill flats so it could be easily installed and removed. Correct me if I'm wrong - it's exact position isn't important because it's relative and the taper has to be dialed in regardless.

 

[eotrfish]

Maybe from your perspective. But from mine, it's brilliant.

Brilliant - not really. Necessity is the mother of invention.

The blanks came pre-drilled through. The problem was that the bores were not concentric with the OD. There was lots of extra meat so I used the pressed in centres to turn the OD concentric with the bore. Then I could machine the hex on the right hand end and ream the required bores in each end while the part was still parallel. Then a new set of sacrificial inserts needed to complete the taper. Tedious but it worked well.

 

[Chipper5783]

Uhmm, you could get another lathe, already fitted with a TTA. Com’on how much of an excuse do you need? Problem solved!

 

[Susquatch]

I use a 3/4" one. on the big lathe and a 1/2" one on the little lathe. The big lathe HAS a taper attachment. (!!) The 3/4" one has a 2" throw - which covers most all taper threads possible, including some of the ASME threads used in the oilpatch. A decent offshore BH is about 200$, as oppposed to 500$+ for a TA, and the tricky install.

Hey @Dabbler, I've been thinking about this tooling ball thing ever since the clan all left after Thanksgiving dinner. That got me thinking more about your boring heads.

A question for you. Were the two sizes of boring heads for the two lathes driven by what you had, the tailstock Morse Taper size, some practical limit to the offset that the lathe could handle, or some other factor?

 

[Dabbler]

The little lathe has only a 1.5HP motor, and I had an extra small boring head. My big lathe at 7.5HP can really fling things about, so I felt a larger centre was warranted.Since they are both MT3, it doesn't really matter.

 

[PeterT]

Is the question about why kind of force the boring head will see in offset turning mode on a lathe? If, so, been wondering same myself. The only thing holding the center stub in position on BH from lateral cutting forces of lathe tool on part is those teeny set screws acting on the BH gib strip by friction (or however its configured). Now how does that compare to normal BH mode where the boring bar transfers lateral cutting forces along its dovetail? Its potentially one of those things where we might set the BH offset in the lathe & just focus on speed & feed of cutting the part itself. But the BH is certainly not as locked down as a solid, meaty live/dead center in the TS. I'm sure the answer is go easy until you see how things are progressing.

 

[Dabbler]

Is the question about why kind of force the boring head will see in offset turning mode on a lathe?

Good question. I have always regarded this method as a 'delicate' way to do tapers. So I use HSS tools and take modest DOC. I'm not usually in a hurry anyway... Even so, a BH is a very robust piece of equipment.

To address your concern, the set screw sees almost no load. I use a custom ball that seats using a shoulder on the face of the BH. The set screw is just there to hold it in place during setup. I'd post a pic, but that stuff just got moved to allow me to do a bunch of wiring, and it is deeply buried. the good news is that every week there is slightly more room!

 

[Susquatch]

Is the question about why kind of force the boring head will see in offset turning mode on a lathe? If, so, been wondering same myself.

Yes. I got to thinking about how important it really was to have a tang on the MT to resist any torque on the MT imposed by friction on the ball. That led to thoughts about alignment of the tang and the need for a 2 part boring head so the tang could be clocked. And that led to wondering if the tang was really necessary. And that led to wondering why @Dabbler used 2 different sizes of Boring Heads.

Turns out that had nothing to do with it. I think Dabbler knew that the MT3 has plenty of reserve torque holding especially when you consider the much smaller torque holding of the ball in a cone - even with such a small moment arm. And of course, the reverse torque of the inside hemisphere of the ball. So unless somebody inserts additional concern, I'm prepared to let that one go to my waste heap of stupid ideas. Good thing too, cuz boring heads with integral tangs seem to be very rare beasts.

Right now, my biggest challenge seems to be finding a tooling ball with a shaft big enough to fit my boring head. Most of them seem to be 1/4" which is too small so I might need to make a sleeve - which leads right back to torque on the ball! Sheesh!

 

[Dabbler]

Torsional forces on the ball are insignificant. The only concern is the cantilever created by the boring head. For the offsets in question - under an inch - the boring head can manage quite large forces. But just to be sure, I always make the offset towards the cutting tool, so the cutting forces are partially counteracted by the force pushing directly horizontal towards the centre of rotation.

The force that is not compensated as well is the *upward* force generated by the cutting action. this is trying to twist the boring head upward as a reactionary force of cutting. But Boring heads and MT are designed to handle such rotational forces, so I don't worry about it.

I always cut gently to avoid a host of issues that might arise - such as flex in the work piece, among many,

 

[Susquatch]

I had a really good look at what info I could find on the OEM Taper attachment for my lathe.

It appears to be quite similar to what @thestelster made for his lathe.

The taper way is a simple V block on a center pivot pin. And the follower is a fairly substantial casting with an adjustable gibb. It is only able to cut a 9" long taper and the maximum angle is +/- 5 degrees.

Assuming I'm interpreting the design correctly, I do not have to disconnect the cross-slide nut to switch between modes. Instead the entire cross-slide leade screw, nut, and even the handwheel is replaced so that the cross-slide becomes fully controlled by the v-slide on the taper attachment instead of indexed against the cross-slide crank anchor at the front of the table. By positioning the cross slide at the center pivot, and unlocking the taper follower, the taper becomes zero and everything is normal. Taper mode is achieved by locking the reference bar to the lathe bed.

I think the best way to describe it is to imagine the cross-slide lead screw referenced to the back of the cross slide at the taper bar instead of at the front where the crank is. The leade nut is pulled and pushed from the rear instead of the front.

It's a pretty good design that should be fairly solid.

However, the taper on my grinding wheel arbour is too much for this system, so I'd be cutting it with the compound or an offset tailstock (prolly the boring bar approach) anyway. One less reason to consider it.

Lastly, in measuring the taper on my arbours, I discovered that they are already center relieved so there is nothing to be gained by relieving the center of the taper on a balancing arbour.

 

[PeterT]

I had a brain fart. Lateral cutting force on the part is acting through the ball center & wants to displace the sliding head from the fixed body along the dovetail. But the big thing preventing the sliding head from moving is the adjuster worm gear engagement that connected to sliding head. The set screws are just there to secondarily lock position & prevent worm gear drift. BTW my 1440 TS has no tang socket so it wouldn't do any good if the shank was tanged. I actually have a feeling many lathes don't as well, seems like predominantly friction fit?

 

[a smile]

The East German lathe I sold some time ago has a taper attachment, and it is very convenient to use, but I can only say that for DIYER, who is not a professional taper shaft, the taper rack attachment is really of little effect. Because: 1. Usually there are few opportunities to make taper. 2. There are fewer opportunities to make longer taper shafts. 3. Taper adjustment of taper accessories is very time-consuming. 4. Taper accessories will significantly increase the space width of the machine. 5. Most of DIYER's taper production can be completed by relying on small pallet.

In my opinion, if the taper shaft is not processed in large quantities, please use the small pallet to adjust the taper, and if you have time, please improve the automatic feed function of the small pallet to ensure the uniformity of feed.



Moreover, I am also faced with the problem that the machine tool does not have taper accessories, and I am sure that I will increase the electric feed to the small pallet in the near future.



I have also made the grinding wheel balance shaft used in the surface grinding machine by myself, although it is relatively rough, it is fully competent for the function of static balance of the grinding wheel.

 

[thestelster]

I had a brain fart. Lateral cutting force on the part is acting through the ball center & wants to displace the sliding head from the fixed body along the dovetail. But the big thing preventing the sliding head from moving is the adjuster worm gear engagement that connected to sliding head. The set screws are just there to secondarily lock position & prevent worm gear drift. BTW my 1440 TS has no tang socket so it wouldn't do any good if the shank was tanged. I actually have a feeling many lathes don't as well, seems like predominantly friction fit?

View attachment 38932

"The cutting force when turning is a resultant force that combines tangential, feed and radial force components. These force components can be measured with a three-component force dynamometer. Metalcutting professionals consider Kistler dynamometers the most accurate.

Of the three cutting force components, the tangential force (FZ) is the greatest, the feed force (FY) is less in magnitude and the radial force (FX) is the least in magnitude. As a rule of thumb, the following relationships are used, but it is not a good practice because the results are not as accurate as they could be: FY = 0.50FZ and FX = 0.25FZ."

Calculated forces when turning

Using a new calculation for determining cutting force components and power when turning. All images courtesy Kennametal

www.ctemag.com

 

[Susquatch]

Of the three cutting force components, the tangential force (FZ) is the greatest, the feed force (FY) is less in magnitude and the radial force (FX) is the least in magnitude.

I've never seen a document like this, but it's exactly how I assumed it would be and have tried to describe to others in past debates. I think it's an easy trap to assume that the longitudinal Z-Axis force toward the spindle is the highest, and cutting is toward the spindle. This erroneous assumption is the source of many debates.

Nice to see confirmation like this in an article that can be shared. I've book marked it for future reference. I'm quite sure that debate will be back soon enough.

Might be good to add @PeterT's slow-mo hi magnification video here too.

 

[Susquatch]

I have also made the grinding wheel balance shaft used in the surface grinding machine by myself, although it is relatively rough, it is fully competent for the function of static balance of the grinding wheel.

Good stuff Smile! Very similar to @thestelster 's approach.

And I agree, I don't think the absolute quality of the arbour is really that important for its balancing purpose. I'll order a suitable steel bar and give it a try when harvest is done.

 

[thestelster]

Just a note, that the force labels (X,Y,Z) are inconsistant in the two examples I posted, but the description: tangential, radial, axial are consistent. It's enough to know that the tangential forces represent 2/3rds of the total force; the axial forces are a little less than 1/3rd the total; and the radial force represents the balance.

And in the first article it has real examples and measured numbers, as opposed to theory.

 

[Susquatch]

Just a note, that the force labels (X,Y,Z) are inconsistant in the two examples I posted, but the description: tangential, radial, axial are consistent. It's enough to know that the tangential forces represent 2/3rds of the total force; the axial forces are a little less than 1/3rd the total; and the radial force represents the balance.

And in the first article it has real examples and measured numbers, as opposed to theory.

Didn't notice that. Good stuff Stell!

 

[Susquatch]

Hey @thestelster - I took another boo at your Taper Attachment design and I studied the OEM Taper Attachment design for my lathe. I had hoped I might be able to make my own like you did. But it isn't gunna happen.

The OEM Taper Attachment for my lathe uses a new cross-slide crank and lead screw and leade nut so that all adjustments of the cross-slide are relative to the taper attachment instead of the saddle. I could make much of it, but a new crank ain't gunna happen.

Essentially, the anchor reference for the leadscrew is moved to the back of the lathe instead of the front. This means a new leadscrew, nut, and crank plus all the taper parts. The clear advantage of this is that you don't need to switch the leade nut back and forth between taper mode and regular mode. You either have a taper angle dialed in or you don't. The cross slide doesn't know the difference.

The down side of this design is that it's limited to a 10 degree taper.

That isn't gunna work for the balance arbour which is 3 in 12 or about 14.477 degrees. In fact, the whole idea of offsetting the tailstock, and using a boring head is out the window at 3 in 12. I'll have to do it with the compound.

Btw, what metal did you use to make yours? I don't imagine it needs to be anything special. A 1" bar 12" long will make a 9 inch arbour and nut plus waste. I considered using a takeoff Chrome molly barrel but the hole isn't likely to be well centered for the whole length. I have not seen one yet that didn't have a noticeable bend (arc) in it. So I'll prolly have to buy something.

 

[thestelster]

Hey @thestelster - I took another boo at your Taper Attachment design and I studied the OEM Taper Attachment design for my lathe. I had hoped I might be able to make my own like you did. But it isn't gunna happen.

The OEM Taper Attachment for my lathe uses a new cross-slide crank and lead screw and leade nut so that all adjustments of the cross-slide are relative to the taper attachment instead of the saddle. I could make much of it, but a new crank ain't gunna happen.

Essentially, the anchor reference for the leadscrew is moved to the back of the lathe instead of the front. This means a new leadscrew, nut, and crank plus all the taper parts. The clear advantage of this is that you don't need to switch the leade nut back and forth between taper mode and regular mode. You either have a taper angle dialed in or you don't. The cross slide doesn't know the difference.

The down side of this design is that it's limited to a 10 degree taper.

That isn't gunna work for the balance arbour which is 3 in 12 or about 14.477 degrees. In fact, the whole idea of offsetting the tailstock, and using a boring head is out the window at 3 in 12. I'll have to do it with the compound.

Btw, what metal did you use to make yours? I don't imagine it needs to be anything special. A 1" bar 12" long will make a 9 inch arbour and nut plus waste. I considered using a takeoff Chrome molly barrel but the hole isn't likely to be well centered for the whole length. I have not seen one yet that didn't have a noticeable bend (arc) in it. So I'll prolly have to buy something.

Is there a way for you to decouple the cross-slide screw from its nut easily?

The parts that I made were either CR steel, HR steel, tool steel, aluminium, and angle iron.