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6th March 2019, 04:15 PM #16SENIOR MEMBER
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6th March 2019, 04:18 PM #17
That's a pretty good price, considering it is a one-off. I'm guessing that Enzo is a tad curious about it himself.
I hadn't given any thought to the bearing slipping out under load; the Loctite is a good thought. Probably a good idea for the threaded section too, unless you devise a lock-washer or drill tap for a grub screw.
Tony_A makes a good point, anything turned that way will have to be thick enough to not twist until both ends are up to speed... and then be turned down to size in one sitting.
- Andy Mc
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6th March 2019, 06:20 PM #18SENIOR MEMBER
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6th March 2019, 06:58 PM #19
Yes, Ted, I did consider the Mcjing offering. As you point out, theirs is a v. good price, but after contacting them they couldn't assure me that the thread adpator component would stay in place with the way I plan to use it. And, I didn't think I had the necessary skills to retro-engineer it myself. Some others on the forum may be more confident in doing so.
Stay sharp and stay safe!
Neil
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6th March 2019, 07:21 PM #20
Yes, I was prepared for it to be a lot more. Interestingly, one of the earlier sellers that I listed in my first post has since got back to me after saying their unit had no drawbar thread to ask me a few questions. They are now considering adding a drawbar thread to theirs in the next production run.
Without it getting very complicated with an engineering solution and pushing the price way up, the Loctite fix will be good if it does hold up under reasonable tension. But, I'm glad Enzo is going to be doing it. If I were to attempt it I'm sure the bearings would be all glued together tight!
I expect that a variable speed lathe that can be slowly dialed up and down could be essential for long fine spindles. As Colin points out, long fine spindles will be at greatest risk when they are at their thinnest cross section near their completion and during the wind down. This is one of the reasons I was originally looking at the small 50mm chucks which have a lot less mass than a standard 100mm scroll chuck. I also considered Jacobs chucks with less mass again, but they also have a restricted gripping range.Stay sharp and stay safe!
Neil
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6th March 2019, 07:50 PM #21
Hi Neil, not too sure how It is held together , pressed together I would imagine,
I don, t think it would pull apart if thats what you mean , why do you need a thread for a draw bar , surely a chuck tightened correctly and just a 1/4turn backwards on the tailstock would give enough "pull" for your experiment ?Cheers smiife
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6th March 2019, 11:32 PM #22
You could well be right, Smiife.
I'm just cautious about such matters. If I'm going to play about with a lump of metal spinning at 2k rpm, or more, I'd like to be confident that it is going to stay put in the tailstock. I'm getting too long in the tooth to lose any of them.... : - )
Sent from my ZTE T84 using TapatalkStay sharp and stay safe!
Neil
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7th March 2019, 11:18 AM #23GOLD MEMBER
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Neil
I just checked this morning and my Mcjing transfer mandril already has a small recess in the end of the morse taper and can be held in a 120 chuck with longnose jaws with the morse taper pointing to the tailstock .Drilling and tapping a hole should be a breeze .
I look forward to hearing the results if you get it set up . I had also thought about spindle turning with a "tension" system .
Ted
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7th March 2019, 11:44 AM #24
I think you'll be surprised at how much tension you may need to pull out even a tiny deviation.
It's the classic "tension a cable to pull out sag" problem, except using centripetal forces rather than G in the equation. The straighter the "cable" the more tension is required to remove the same sag amount, quickly approaching infinite tension needed. On paper, anyway.
Of course, it's possible that on the scale we're talking about here the deviation can be brought into "acceptable" limits... I hope so, my fingers are crossed and I'll be quite content to be proven wrong.
('Tis good to see someone actually testing it out; that's what makes the difference between a practical engineer and a University lecturer in the engineering dept. )
- Andy Mc
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7th March 2019, 12:42 PM #25GOLD MEMBER
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Another thing to consider is that a thin piece under tension will try to resonate. This may result in chatter or worst the tool digging in and destroying the piece.
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7th March 2019, 06:12 PM #26SENIOR MEMBER
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7th March 2019, 07:00 PM #27
Ted, thanks for that information on how the McJing device can be readily held in a woodturning chuck with long nose jaws. Also, that the end of its Morse Taper already has a centre recess hole into which to start the drilling. Any thoughts on how to keep the MT from rotating in the live centre while drilling? My earlier thinking when I thought I might have to do this was that enough masking tape wound around the two components would probably be sufficient if the drilling went up in small incremental sizes.
Interesting that you have also thought about some sort of tension holding system. I can understand why woodturning developed as it did between centres, coming as it from origins like pole lathe turning, but I'm surprised that there has not been any development of tension holding systems between centres since the introduction of clamping style chucks for woodturners, which we have had now for many decades.
There is theoretical support for the benefits of a tension system over compression, but almost no published experimental results, and no off-the-shelf workable system that I could find. The best article on the topic that I could find was Dennis Gooding's:
You will need to be logged on to that forum to see his tables and images. His experimental results showed that a spindle under tension is more rigid and can be turned to a smaller diameter over more length, but the apparatus he use to achieve tension was not a workable solution outside of the experiment.
I could try to replicate Dennis Gooding's results with his setup, but I though it would be more useful to try to find a workable setup that others can readily adopt if it proves to be worth it in terms of cost and greater turning satisfaction.
As always, at least try to......Stay sharp and stay safe!
Neil
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7th March 2019, 07:04 PM #28
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7th March 2019, 07:33 PM #29
In Dennis Golding's experiment he got up to 55 pounds of tension to get his result. This is why I think a drawbar will be a necessary component of a workable solution.
Right, as can be seen in any suspension bridge!
Me too, but if it proves to be a dumb idea then I'm also happy to put it too bed...Stay sharp and stay safe!
Neil
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7th March 2019, 07:47 PM #30
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