Author Topic: Set-Over Centre (Read 86779 times)

Fergus OMore · « **Reply #50 on:** March 04, 2012, 03:39:17 PM »

Ah, yes but. You have to be a bit careful with debunking the theory.

So you are attempting to to revert to plane geometry- or back to Euclid.

To be honest, it's all an academic exercise in machining. Of course, this has a certain relevance but Ian Bradley was merely 'fooling about'. It was the Beginners Lathe thing in ME which is not to be taken too seriously.

Fergus OMore · « **Reply #51 on:** March 04, 2012, 04:30:13 PM »

Spririt levels, perhaps -- and females with balls

Miner · « **Reply #52 on:** March 04, 2012, 04:46:31 PM »

LOL, Norman knows quite well I know exactly what he means. He's referring to George Thomas's writings where having the correct support while using an off set center idealy needs what are called Bell Center Drills that will drill a radiused center hole and also a hardened ball at the tailstock end. This gives you the best contact and support possible while your part is offset from the lathes center line.

Apologys Wong, We seem to have gone a bit off topic on your thread.

Pete

Fergus OMore · « **Reply #53 on:** March 04, 2012, 05:08:30 PM »

Hmm?? My top slide has a removable parallel dowel that automatically locks and gives No 2 Morse Taper. Plain simple Plane Geometry and the setting is unaffected by the length of the material and all sorts of circus perfomances.

Bung a peg in, and with nothing up my sleeve, one has a beautiful taper shank just for the turning.

The authority-- Martin Cleeve ( Hart)- not George Thomas.

wongster · « **Reply #54 on:** March 04, 2012, 06:45:03 PM »

Hi Pete, no OT at all. All within the scope of turning taper. I did some reading online and saw the bell centre drill used to create the radius-ed centre hole. Though someone else in that forum mentioned about using a ball (balls? where did the other one goes...) on the centre, a pic was shown without one in use. I don't think I'm capable to whip up a ball end type of dead or alive centre at this moment. Would the 120 degree centre hole from the bell centre drill suffice?

To keep the set-over centre on plane, I would be doing what Ralph did - leave the side of the Base square so that squaring it up would be much simpler.

Will these work?

Miner · « **Reply #55 on:** March 04, 2012, 07:19:36 PM »

Hi Wong,
Your right, And I didn't go far enough with my explanation. Your work piece would have a bell type centers drilled in it at each end. And then a ball type center is used at both the headstock and tailstock ends. You then just use a standard lathe dog to provide the drive.

Finding a hardened ball for the headstock isn't tough. You'd just buy what are commanly referred to as Tooling Balls. You would want the unthreaded or plain shank ones.

Using one at the tailstock end? And especialy as a ball end live center? That's a tough one. And for building something like you are right now? You'd need to design and incorperate the proper bearings in right from the start. None of it's impossible, Just quite difficult to do. Due to the slideing action on the ball as the part rotates. Even a hardened tooling ball will wear over time. So designing a simple system to replace that live ball center would be another high priority. Even that $450.00 Royal offset capable center in 1982 didn't have that set up, Or at least that I know of.

I can think of at least one way to do it. But it would take at a minimum a tool post grinder.

Pete

wongster · « **Reply #56 on:** March 04, 2012, 09:51:27 PM »

this is starting to be beyond my capability at this point. And I was thinking that if I can successfully complete building according to plan, I can start making taper...

I saw from some sites that sell live and dead centres some different tips. If I can find one with ball end for head and tailstock, will that work?

Regards,
Wong.

Miner · « **Reply #57 on:** March 04, 2012, 10:01:15 PM »

Wong,
No problem, Yours will work just fine as designed. We just ended up moving towards the "ultimate" tool defination. Maybe a future project for you to keep in mind. I'm not all that sure I could do a proper 100% job on a tool of that type. It might be fun to try though. I do know there's members here that would have no problems making one.

Pete

wongster · « **Reply #58 on:** March 04, 2012, 11:57:34 PM »

Thanks Pete. I'm sure we've folks here that have the ability.

Xldevil · « **Reply #59 on:** March 05, 2012, 03:01:23 AM »

Hello.
I'm using no ball center with my soc. and my first attempt to make anMT 2 looks good to me.I've adjusted the soc. by the use of a dial indicator and the fomular given here at the bottom of this page:
http://www.digitalproducts.de/Kegeldrehen.php
You only have to fill out the form and it will show you how much you have to offset your tailstock.It even shows you,if the offset is too much to be safely turned between centers.
http://digitalproducts.aklein.org/formeln/Berechnen.html
Unfortunately the page is German,but math is international.
Nevertheless,a little translation:
D wanted biggest taper dia.
d wanted smallest taper dia.
L given length of taper
Lwgiven length of workpiece
VR needed offset of the tailstock
VR max maximum safe offset of tailstock
Cheers,Ralph

Xldevil · « **Reply #60 on:** March 05, 2012, 03:01:59 AM »

mistake,sorry

wongster · « **Reply #61 on:** March 05, 2012, 03:12:08 AM »

Thanks Ralph.

Btw, the bear in your avatar is cute.

Regards,
Wong

Xldevil · « **Reply #62 on:** March 05, 2012, 03:21:15 AM »

Quote from: wongster on March 05, 2012, 03:12:08 AM

Thanks Ralph.

Btw, the bear in your avatar is cute.

Regards,
Wong

Hi,Wong.
That guy is called flat Eric.
He has been popular in Levis commercials.

#Cheers,Ralph

andyf · « **Reply #63 on:** March 05, 2012, 08:34:25 AM »

He's always getting in the way round my shop

Andy

wongster · « **Reply #64 on:** March 05, 2012, 09:05:00 AM »

Cool...

and Andy, what is flat eric sitting on the lathe with the swarf and everything?!

This chap didn't appear in any ads here. The last Levi ads I ever seen on TV was so long ago...

andyf · « **Reply #65 on:** March 05, 2012, 12:26:02 PM »

I only took him on to sweep up the swarf, Wong, but he's too idle to do it.

Andy

Fergus OMore · « **Reply #66 on:** March 05, 2012, 02:28:54 PM »

Pete( Miner) and I have been having our usual cross Pond banter about this. The first point is that my original reply from this AM seemed to disappear. There were 4 other posts- and all far less valuable.

The first point to consider is that it is almost impossible to produce a taper in hardened steel- with what you possess.You can produce 'soft centres' and I don't mean 'chocolates' but if you want points which will stand the hurly burly at the tailstock end, you need to re-think. You might have to resort to making a centre in soft metal and drill it and add a hss or perhaps carbide round insert. Again, you are going to be pushed to make a hard half centre which, despite all the shenanighans about rotating centres is going to be accurate to a much higher degree.
Having said that, you can make rotating centres with caged ball races but you will need to get friend Sparey's Amateurs Lathe book or similar!
If you are going to simply interspace a ball bearing between the fixed and rotating bits, you'll be wasting your time.

So let's move on. Pete and I came to the conclusion that the Hemingwaykits thing is the least practical of the alternatives. What are the alternatives? Ideally, the common or garden boring head- be it bought out or home made will create better morse tapers that the one mentioned. Again, the boring head will go on to produce ball handles!

However the taper be it soft or otherwise, is not going to be anyway as accurate as one which is produced on a regular taper turning attachment fitted to a lathe-- or better still, on a grinder. Does anyone really think that a kit containing a ready made Morse taper shank was done on a model maker's lathe on ' something or other'?

Pete and I got on to 'real' taper turnings. I had said that a 5 inch sine could be squeezed onto a lathe- if any sort of accuracy was required.
Recall that our Mr Morse adopted the taper to hold a cutting tool with accuracy and not causing murder and mayhem like the wheels of Queen Boudicca's chariot.

Ten inches is better(

) but Pete had a yearning to fit a Sherline long lathe bed to the bed of his bigger lathe. I sort of gulped at the idea- which is sounder than one thinks. I simply countered with the comment about my little home made Stent tool and cutter grinder by saying that the working table is - well, 10" and it swivels and is able to swivel not only in degrees but will not 1.49107 or 1.42871 or 1.43069 or 1.43770 or even 1.48759 degrees for half angles. These are the quoted figures. I can just about manage the one and
half degrees on a good night with a following wind

This, despite all the Jazz, is what morse tapers is all about.

wongster · « **Reply #67 on:** March 10, 2012, 04:15:43 AM »

I only had a short time to play before my scheduled weekend duty. Started on the side job making the washer for the drawbar to hold the ER32 collet chuck in the 3MT spindle. I removed the lathe chuck and put on the ER32 collet chuck to determine the length required for the M12 drawbar.

A piece of steel rod inserted to roughly mark the length from the back of the collet chuck to the edge of the spindle end. It measures around 125mm.

Picked up these while packing lunch yesterday. 3 lengths each of M12 bolts and socket head cap screw of 150mm, 180mm, and 200mm.

Of the six pieces of M12 bolts & cap screws, only the two 150mm fit nicely with an allowance sufficient to add in a washer of sort. Of the 2, I like the socket head better as it is smaller in diameter and allow the gear box door to close properly. Also, I don't think I'll have sufficient room to use a spanner to loosen the bolt should the hex head is used (unless a thick washer is made to extend the drawbar out of the gear box bore. But that would mean I have to leave the gear box door open when the chuck is in use).

The hex head in use to determine which length works best. Can't use the socket head ones as their head is smaller than the spindle bore. I decided on the 150mm length as it allows a washer to be used with sufficient threads engaged.

The gear removed to properly measure the ID and OD of the spindle end to make the washer. ID is 20.45mm and OD 24mm.

1" diameter steel stock is all I have for this job.

A section of about 40mm in length cut in the bandsaw.

The uneven end was first faced.

Reducing the diameter to match OD of the spindle end. My target size for the washer is 24.5mm.

A short section was then turned down to 20.44mm for a loose fit in the spindle bore.

I've to stop here as I need to prepare to go to work. What's left is the drilling and boring of the 12mm hole and part it off. Hope to finish it tonight and move on to work on the rest of the parts for the Set-over Centre. One thing I read about but don't understand how it works. Instead of tapping the drawbar hard to break the taper's grip, you turn another nut to squeeze the drawbar out. Anyone can explain how this work and what do I need to do to include that.

Hope to do more work tonight.

Regards,
Wong

wongster · « **Reply #68 on:** March 20, 2012, 07:40:32 PM »

I've not been updating my progress here as I was rather caught up with my day job. The work continued last Saturday for a couple of hours and Sunday for another hour or 2.

The drawbar washer was completed and the collet chuck was put into use. The bore at the gear box cover was widened due to its misalignment to the spindle end. Now I can remove the drawbar without having to open the door.

The washer on the spindle through the bore of the gear box. You can see the misalignment here which require the widening of the bore so that removing the washer can be done without opening the gear box.

The ER32 Collet Chuck mounted.

The drawbar which is basically an M12 socket head screw/bolt.

The silver steel chucked up and turned to accept 5/16 BSF.

Adding a little chamfer.

Using the die holder I made for my Sherline lathe with the tailstock live centre pushing against the 3/4-16" tapped hole meant for the 0MT to 3/4-16 adapter. Turning it is so tough with those little SHCS.

Swapping it with the die handle I bought. One handle was bearing against the bed way while I turned the collet chuck with its wrench.

The tailstock removed so that I can finish threading without the carriage in the way.

Testing the fit. The part test was supposed to be the Slide but since both the Base and Slide have the same tapped hole, it doesn't matter as long as it fits one of them.

The part was cut off to length with some allowance for cleaning up.

The partially completed 1/2 centre was removed from the chuck. See the gap between the 2 parts? I chased the threads with the die flipped over but realised that both sides have taper on them to help start threading...

Next was to make an arbor with a threaded hole to mount this for the turning of the 60-degree cone. I found a piece of steel that was actually a tap guide I made when I first started.

Finish was rather bad when I attempt to true up the part though it is not required but to remove the rust.

I was told by a reader of my blog that this was due to tearing and not cutting. His post: "...problem of the rough finish it appears to be tearing, not cutting. Check the tool for a good sharp well honed cutting edge and that the geometry is correct for the metal you are cutting. I can't see just how the tool is shaped, make sure you have enough back rake to make it shear off the metal not scrape and tear."

I didn't have the problem when facing it. I'll try again to see if I can solve that.

DaveH · « **Reply #69 on:** March 20, 2012, 08:01:38 PM »

Wong,

You are doing a great job, nicely posted and great pics

That finish I agree looks like "tearing" I am suprised you didn't hear it as well. Also check the cutter is not chipped and it is still on the centre line.

A great job Wong

DaveH

Fergus OMore · « **Reply #70 on:** March 21, 2012, 04:16:41 AM »

As the late and and lamented George Thomas would remark 'It does look as if it has been gnawed by rats'

At this point, you have two obvious faults. The first is that your collet chuck is NOT designed to accept a larger diameter than that specified to accept and secondly, it is not supported.

Somehow, the chamfer tool is wrong as it is one for brass and I wonder what the rest of the set up is.

If you think about it carefully, you are using a split collet and the whole thing is able to rock about 'like a pea on a drum'

Others may disagree but that is their prerogative.

Fergus OMore · « **Reply #71 on:** March 21, 2012, 06:59:01 AM »

I occasionally look at the postings on 'Homeshop Machinist'. There is an interesting discussion on taper turning in the General section.

Some of these posters are quite expert with wide experiences. No further comment from me on what was written. However, it is worth more than a cursory look.

DaveH · « **Reply #72 on:** March 21, 2012, 08:18:39 AM »

Norman.

The early and quick DaveH replies; the collet is an ER collet designed to hold machine tools like end mills in a ridgid and precise repeatable manner.

Provided it is tightened correctly on a nice round surface it should not be a major cause of problems.

DaveH

Fergus OMore · « **Reply #73 on:** March 21, 2012, 08:58:28 AM »

However there is a dreaded overhang of metal far in excess of the collet diameter.

Quite simply, he should change to his three jaw chuck and keep the collets for what they are intended for- the right size.

The work should be then supported, prior to putting a proper lathe tool to work.

I remain adamant, sorry!

wongster · « **Reply #74 on:** March 21, 2012, 09:07:32 AM »

Thank you guys for you comments and encouragement. I just finished a long day at work.

Norman, I was under the impression that the ER series of collets provide repeatability rigidity within its limit when used for workholding in the lathe. That's why I bought it. What would be the right size?

Anyway, I did swap in the 3 jaw chuck on Sunday night for a quick session. A fresh piece of silver steel was used. Same finish. I'll try to angle the tool differently in my next session. The HSS tool is still rather sharp.

On the "chamfering tool", it is but a Proxxon roughing tool placed at an angle.

Regards,
Wong

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Author Topic: Set-Over Centre (Read 86779 times)