[4]

Bull Nose Live Center

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Ray,
A couple questions.
Why didn't you turn the MT first and do your boring with the piece held in the H.S. MT?
Also, would it be "better" to grind your 30° point after completion? I wouldn't know how you'd hold the MT though unless you did it in the H.S.
These questions are mute though as yours turned out perfect but curious to your answer.
Excellent question!

If I cut the taper early on, I would not want to risk doing that many boring and facing operations on a piece only held in the spindle with a Morse adapter. The headstock has a native MT5 taper so, a MT5 to MT3 adapter would be needed. That arrangement works fine to hold a dead center but, it would not hold a workpiece -especially if any kind of side pressure is applied. I can almost guarantee that would have a very bad outcome.

Immediately after the part was heat treated, it was cut the entire length and the big and small outer diameters were made perfectly straight and concentric. If the taper were cut early on, I would limit the options for holding the piece and also reduce (by over 50%) my ability to indicate the part over it's whole length. You can never indicate a part in one place and assume the entire length spins true. Since the small diameter was under 1-1/16", a 5C collet chuck was the natural choice to hold it. I'll add to that and mention that my 5C collet chuck is as close to perfect as is humanly possible.

The take-away here is that you can only use the headstock taper to spin between centers whereby the tailstock pressure keeps the part held firmly. If the tailstock pressure is compromised, the two interfaces in the headstock (headstock itself and the adapter) will give way. That's almost a foregone conclusion.

Good questions...

Ray
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
Okay thanks.
I guess I thought as long as you are not taking big DOC cuts it would be okay to turn in the MT HS. Thanks for clearing that up. I won't try that.
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Okay thanks.
I guess I thought as long as you are not taking big DOC cuts it would be okay to turn in the MT HS. Thanks for clearing that up. I won't try that.
Best not to try that. A part held solely in the headstock taper could go flying -for sure.

Ray
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
Ray,
I'd like to make one of these but I can't see the dimensions.
Could you post them again maybe in a different format?
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Ray,
I'd like to make one of these but I can't see the dimensions.
Could you post them again maybe in a different format?
Certainly... Later this evening, I'll post something in a better format. Keep in mind, that economically, you're better-off purchasing one. I did this just to see if I could pull it off and went into this fully aware that it might not turn-out successfully.

Ray
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Here you go... These are not classic mechanical draftings but rather, 2D profile parametric diagrams used to create the CAD images. Everything is fully specified to laborious degree. The format is PDF. Just open the file but do not activate the 3D image rendering and you should be able to see all the dimensions and values.

Regards

Ray
 

Attachments

Downunder Bob

H-M Supporter - Sustaining Member
Staff member
H-M Platinum Supporter ($50)
Joined
May 16, 2016
Messages
1,220
Best way to heat bearings is put them in a container with suitable bearing oil and heat it slowly with a thermostat control, (borrow your wife's electric frypan, When she's not looking). Your deep freezer is also a handy way to chill the shaft.
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
Best not to try that. A part held solely in the headstock taper could go flying -for sure.

Ray
What do you think about this little do-dad? Good idea, no?
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
What do you think about this little do-dad? Good idea, no?
Sure that works... He is making a spindle-side dead center with a built-in drive leg. I've done similar things by taking a piece of shop-drops, tapping a hole in it then, putting it in the 3 jaw and cut a point on it. Once that is done, I can insert a bolt in the threaded hole to serve as the drive leg. It's a one-time use thing but, works fine when I don't feel like mounting the dedicated drive plate.

I've also been known to tack weld a bent shaft to the workpiece then, mount it in one of the older chucks. The bent leg gets driven by one of the chuck jaws.

There's a million ways to skin that cat...

Ray
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
So the MT would hold fine? Any concern about heavy cutting?
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
So the MT would hold fine? Any concern about heavy cutting?
As long as the workpiece is being supported by the live (or dead) center in the tailstock and there is sufficient pressure from the tailstock ram to hold the piece securely then, yes that MT shaft will stay put in the spindle.

The point is, a stand-alone MT device stuffed into the mouth of a spindle will not stay put by itself. It needs some kind of force to hold it in place. That force can come from the tailstock or, as one person suggested, a drawbar thru the spindle can hold it. Personally, I've never seen a setup where a drawbar holds a taper piece in the headstock but, sure, it's possible.

Ray
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
First things first, lets talk about turning a shaft. Boring a hole is pretty much the same thing (but in reverse).

1.310 - 1.1250 = 0.1850 (EDIT: I had a typo here and changed 1.1255 to 1.1250).

On my machine, when I dial-in 30 thou, it reduces the diameter by 60 thou (some lathes are calibrated for diameter reduction and not tool position). Since .1850 / 0.60 is 3.0833 we know I must take 3 passes at 30 thou and an oddball pass at 2.5 thou (.0833 x .06 / 2 is 0.0025).

Here’s the rub… What you dial in and how much comes off are two different things most of the time. Unless there is a gross F&S error or tool alignment issue, it will almost always take off less than what you desire. First, just go ahead, dial in the 2.5 and remove it. An amount that small should come off with no problem.

Ray C.
Ray, I think you meant 0.06 not 0.60.
What if you miss your .0025 and end up taking say .002 off. Do you just start from there or?
My machine was taking more off than less so my percent number was over 100.
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Ray, I think you meant 0.06 not 0.60.
What if you miss your .0025 and end up taking say .002 off. Do you just start from there or?
My machine was taking more off than less so my percent number was over 100.
If you under shoot by a small amount, emery cloth or if necessary a good file followed by emery cloth.

You will likely get more than 100% if you dial-in and increase from your last dial setting vs, scratching-off and re-establishing your next starting point.

For example. Take your first cut and dial is on 0.015. When you take your next cut, you just add the new amount to your old 0.015 and go directly to say 0.030. In this case, you might take off more than 0.015.

In contrast:

Take your first cut and the dial is on 0.015. When you go to take your next cut, you back the tool out then move in until you see a faint scratch (this is called scratching off). The scratch off happens at say, 0.012 so for your second cut of 0.015, you turn the dial to 0.027. You will never get more than 100% this way.

The technique works either way and you have to solve for a ratio either way.

Ray
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
That's exactly what I was doing. Okay. I'll try again perhaps tomorrow.
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
That's exactly what I was doing. Okay. I'll try again perhaps tomorrow.
Carbide? HSS? Are you below center? Is the piece supported properly? If you're scratching off, followed by a dial-in, the amount removed should never be more than twice the dial in assuming your crossfeed indicates distance and not diameter reduction. (The crossfeed dial on some lathes is calibrated to show diameter reduction).

If for some reason, you very lightly scratch off and the overall diameter is reduced by more than 2x the dial-in amount, something else is going wrong.

E.g. if you dial in 30 thou, your part should theoretically be reduced by 60 thou. In reality, it will be reduced by say 55 thou.

So, you dialed in 30 and effectively got 27.5. Lets say you need to reduce the diameter by 58 thou on the next cut. Here's what you do:

To reduce dia by 58 thou, you theoretically need to dial-in 58/2 = 29 thou. In reality, you need to dial-in a little more than the theoretical amount.

27.5/30 = 29/X. Solve for X: 31.636 (which I would round to 31.6).

Go to your lathe, crank the dial until it just barely scratches, move the tool away then dial in 31.6 thou. That should do it.


Ray
 

ddickey

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 21, 2016
Messages
2,275
Oh, I was meaning that I was taking a cut and returning then feeding in another .03" on the dial rather than re-establishing my next start point That explains why I was getting a positive removal rate.
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Oh, I was meaning that I was taking a cut and returning then feeding in another .03" on the dial rather than re-establishing my next start point That explains why I was getting a positive removal rate.
Ahhh, ok. Either way, it works. This is nothing more than linear extrapolation. As long as you don't try to extrapolate beyond about 10% of your previous data points, the system works quite well.

FWIW, when I'm doing a critical cut and the two or three cuts before it, I do a scratch-off. For bulk removal, I just stack the cuts from the last value.

Ray
 

Ray C

Platinum
Staff member
Registered
Joined
Nov 16, 2012
Messages
5,215
Quick status report here... The Bullnose Live Center was used for the first time today and it performed perfectly. It was a fun project executed only to see if I could pull it off. LOL: If I had to do it all over again, I'd pry a couple hundred out of my wallet and buy one. But... this one does the job nicely and now I'll see how long it holds up.



IMG_20180211_152157.jpg

Later

Ray
 
[5] [7]
Top