Turning a chimney

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Le Corbusier
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Re: Turning a chimney

Postby Le Corbusier » Thu Dec 26, 2019 10:31 am

Thanks Jeremy ... this is fantastic. I hope you don't mind but I have embedded the videos so they are easier to watch in sequence. :thumb

Jeremy Suter wrote:I am Just building a Martin Finney Hall kit at the moment for a friend.

Very surprised to find a bad casting for the chimney which when soldered in place leaned backwards it was just slightly miss cast so decided to turn a new one.
Well Tim as you mentioned to me you would like to watch over my shoulder, I bought a cheap video camera and have done this. Should have bought one with a better lens for close up work. The first shots, the camera is too close but it does show how I set it up.
















Boiler and firebox are not attached to the footplate yet. An excellent kit with every thing but the chimney the safety valve needs the base filing a little before fitting.
Tim Lee

John Palmer
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Re: Turning a chimney

Postby John Palmer » Thu Dec 26, 2019 7:26 pm

Terry Bendall wrote:A very useful video and set of pictures. I was very taken with Jeremy's idea, shown in the video, of the setting up tool held in the chuck to ensure that the bar is set at right angles to the centre line of the lathe before the seating is cut. A very simple idea which I shall adopt.

Learn something new every day. :)

Terry Bendall

Indeed! Truly the content of this thread is mining a rich vein.

Presumably that setting up tool could also form the basis for accurately setting the angle at which the workpiece is mounted in order to cut a tapered seat for a dome or a safety valve bonnet. Possibly not a perfect solution as the objective is to machine a seat that will fit a cone rather than an angled cylinder, but should still mke it easier to get the fitting to sit vertically on a taper boiler.

Is the mandrel fitted into the base of the nascent boiler fitting running in any kind of bearing mounted in the tailstock chuck, or just rubbing gently against that chuck's jaws?

Fascinating to see the flare forming jig in use though I was holding my breath a couple of times in anticipation of seeing a profile milled thumb!

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Fri Dec 27, 2019 1:01 am

Thanks Tim for putting those on here.

John Palmer wrote
Is the mandrel fitted into the base of the nascent boiler fitting running in any kind of bearing mounted in the tailstock chuck, or just rubbing gently against that chuck's jaws?
Fascinating to see the flare forming jig in use though I was holding my breath a couple of times in anticipation of seeing a profile milled thumb!


The rod is only fixed in the base of the work by a force fit and if I have done it correctly which I had, it will need a lot of force to remove it, I cannot pull it out by hand. Anyway I am only running it in the tail stock with a loose fit to make sure it does not whip round while spinning It will hurt if it hits you . As for catching myself on the grind wheel which I have many times over the years it will take your skin off.
Last edited by Jeremy Suter on Sat May 16, 2020 9:10 am, edited 1 time in total.

John Palmer
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Re: Turning a chimney

Postby John Palmer » Fri Dec 27, 2019 1:28 am

Thanks for the clarification, Jeremy; I thought that must be how you had set the job up. Thin rods like that can flail around alarmingly when rotated at speed - on occasion I have to apply a steadying finger and thumb to a long length of stock I am feeding through the spindle, as otherwise it will whip around to such an extent as to distort.

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Re: Turning a chimney

Postby Jeremy Suter » Thu Jul 09, 2020 10:08 pm

More turning

When you need a lot of the same thing.

Today I needed about 60 Gas Lamp Tops for some LYR coaches I am building for a friend.
IMG_5573.JPG

The easiest way to do them is using a form tool.

I made this one this morning from 8mm tool steel steel. I wanted two cutting edges on the top for the flat sections of the lamp top I could have left it flat but I find a dished cutting edge is better on a form tool.
This was done by setting the tool low in the tool post and running a slightly tapered Dremel grinding wheel across the top just grinding two shallow U shapes in the final cutting positions. (Its a well worn one I kept for this sort of job).
IMG_5578.JPG

IMG_5575.JPG

To put the shape in the front, I set the tool high the tool post in the required position and use a slitting disc to do the lips. Its high on the cutting position so that the cutting edge comes an oblique angle and nice and sharp.

The set back section is done with two slitting disc together. Moving the toll backwards forwards against them with the lead screw then moving it in slowly on the cross slide until I have got the required depth. moving it very slowly and carefully so I don't shatter the discs.
IMG_5577.JPG



One thing to note. If using grind wheels in the lathe which is generally a complete NO NO. I don't want to get any grit from the grind wheels landing on the lathe bed.
So I put a piece of damp kitchen towel where the grit might fall so that it sticks to it and keeps it off the bed.

Once the tool is made I set it to the correct height which is just under the centre line about .1mm
This cuts the top.

To do the base I have set a parting tool in the back tool post of the cross slide but it will not part off fully as I need a spigot
to fit it to the coach later, it is also set so that in cuts just below the base of the lamp top
IMG_5568.JPG

Turning the Lamp Top.

Setting a piece of 4mm brass rod in the chuck. My first movement is to cut the top flat this gives me a stating point then pull cross slide out and moving the lead screw in the set distance of 2mm I then send the cross slide back in to a set position which does the first cut.
IMG_5569.JPG

leaving it there for a few seconds until the tool stops cutting then move it in a little further which does the second cut this gives the finished top. I leave the cutter there for a few seconds to allow any bend in the brass to spring back. This position is set at zero as a reference point. At this point I run a file over the base of the lamp top making sure there are no sharp edges before the next step
IMG_5570.JPG

Once the top shape is done the next step is the base
I pull the cross slide out so that the parting tool is up to the other side of the lamp top. then I cut the base by drawing the parting tool across the brass rod producing a flat base with spigot.
IMG_5571.JPG

Again leaving it there to allow any bend in the brass to return to centre.
Once this shape is done I pull the cutters well away and using a piercing saw I almost cut through the base of the spigot then using my fingers I snap of the lamp top off so that i don't loose it. The lathe is still running which is why l make sure there are no sharp edges then the process starts again I do three Lamp tops before having to move the brass rod in the chuck and the closer I get to the chuck the quicker I can do them as there is less bend the nearer I get. doing any more than three at a time will result in the brass snapping on the first attempt. It took about 5 minuets to do three
IMG_5572.JPG

IMG_5574.JPG

IMG_5576.JPG

IMG_5579.JPG

https://www.youtube.com/watch?v=QDT-e4q3bPE
Last edited by Jeremy Suter on Tue Nov 17, 2020 8:24 am, edited 3 times in total.

Terry Bendall
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Re: Turning a chimney

Postby Terry Bendall » Fri Jul 10, 2020 6:51 am

I like the idea of using abrasive cutters in the chuck to make the tool. Not thought of that one before. The paper towel to catch the grit is very sensible. From the pictures it looks like the parting tool is not at 90 degrees to the work which is how I would position it. If my assumption is correct do you have a reason for that please Jeremy?

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Re: Turning a chimney

Postby Jeremy Suter » Fri Jul 10, 2020 12:52 pm

Post by Terry Bendall » Fri Jul 10, 2020 7:51 am

From the pictures it looks like the parting tool is not at 90 degrees to the work which is how I would position it. If my assumption is correct do you have a reason for that please Jeremy?

Thanks for the question Terry
Of course I am not parting off with it only using it as the third stage in cutting the lamp Top.
The parting tool is only set by eye about 91 degrees. So it only cuts with the point on the base on the lamp top I wanted it to end up in a certain position on the rod from the previous cut and make a base of .25mm thick. As always, I sharpened the parting tool just before setting the job. Its also set .7mm above centre line of the work only cutting through about 1.4mm of brass, there should be no deviation when the tool is clamped down properly in the tool post.
IMG_5580.JPG

IMG_5582.JPG

One point.
Don't leave the chuck key in the chuck when not using the lathe or you will forget and switch on send it across the room.
Last edited by Jeremy Suter on Fri Jul 10, 2020 9:32 pm, edited 1 time in total.

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Le Corbusier
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Re: Turning a chimney

Postby Le Corbusier » Fri Jul 10, 2020 1:12 pm

Jeremy, is the tool post which you have for the parting tool something you made up yourself or is it a standard fitting for mounting in this location?

What are the benefits of parting off from the back of the machine rather than using the standard tool post?

Sorry if these are basic questions ;)
Tim Lee

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Re: Turning a chimney

Postby Jeremy Suter » Fri Jul 10, 2020 5:25 pm

Re: Turning a chimney
Post by Le Corbusier » Fri Jul 10, 2020 2:12 pm

Jeremy, is the tool post which you have for the parting tool something you made up yourself or is it a standard fitting for mounting in this location?

What are the benefits of parting off from the back of the machine rather than using the standard tool post?

Hi Tim. To answer your questions.

Having a second tool post is very useful. It allows me to have a second movement with a cutting tool without moving the first one. So when making the lamp tops with a single tool post, I would either have needed another cutting edge on the first tool which would have taken a lot longer to make or move the tool each time to replace with the second cutter. Although it is a quick change Tool Post it only swivels, rather than lifting the cutting unit out and replacing with a second. I use it a lot for this type of work when I need a few items the same it also gives the job more speed.

As for the Tool post. I made it myself about 35 years ago when I bought the lathe. I still have and very occasionally use the original one as it has another lead screw on it for turning at angles.

IMG_5583.JPG


I count myself very lucky. When I was 18 my Grandmother gave me £3000 which I spent on a Lathe, Pantograph Milling Machine and Vertical Mill along with sundry other tools. They have all paid me back with interest. before then I used an old Unimat SL lathe but never liked it. OK for very small stuff but wouldn't use for anything too heavy.
Last edited by Jeremy Suter on Fri Jul 10, 2020 9:34 pm, edited 3 times in total.

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Mike Garwood
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Re: Turning a chimney

Postby Mike Garwood » Fri Jul 10, 2020 8:25 pm

Mesmerising to watch all that. Absolutely brilliant, thank you. Far beyond my reach, but appreciate the skill that goes into that work.

Mike

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Re: Turning a chimney

Postby Terry Bendall » Sun Jul 12, 2020 8:36 am

Le Corbusier wrote:What are the benefits of parting off from the back of the machine rather than using the standard tool post?


One reason for having the parting tool at the rear is that it makes the process easier. Parting off can cause some difficulties with the tool digging into the work when the tool is held in the usual front tool post. Holding the tool in the rear tool post means the the cutting is done as the work piece is turning upwards (think about that :) ) and the risk of digging in is much reduced.

The other reason is that the parting tool in a rear tool post is always available for use without having to rotate the four way tool holder or even worse, having to set it up for the job. You do of course need to have a lathe with a cross slide that is long enough to allow the rear tool post to be permanently in position. A further advantage is that once set up (something that needs a bit of care) no changes are needed unless you use the tool as Jeremy does as he mentions in his reply to my question. Thanks for that Jeremy.

As Jeremy says a four way tool post and rear mounted parting tool reduces the time taken to do a job. On my lathe I usually have tools for turning brass and steel set up permanently which leaves two other positions for other tools which might be needed for a particular job.

Terry Bendall

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Le Corbusier
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Re: Turning a chimney

Postby Le Corbusier » Sun Jul 12, 2020 9:41 am

Terry Bendall wrote: You do of course need to have a lathe with a cross slide that is long enough to allow the rear tool post to be permanently in position.

Terry Bendall


Presumably you could machine up your own extended slide from a suitable piece of steel if the slide which comes with the machine isn't suitable? Or can you buy "universal' longer slides comercially which can be adapted to suite differrent lathes?
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Re: Turning a chimney

Postby Terry Bendall » Mon Jul 13, 2020 1:21 pm

Le Corbusier wrote:Presumably you could machine up your own extended slide from a suitable piece of steel if the slide which comes with the machine isn't suitable?


Given a machine with the capacity to do the job and an operator with the necessary skills, then no reason why not.

Le Corbusier wrote:Or can you buy "universal' longer slides comercially which can be adapted to suite differrent lathes?


I have never seen such a thing, but they may exist.

Terry Bendall

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Re: Turning a chimney

Postby John Palmer » Mon Jul 13, 2020 3:40 pm

More inspirational stuff! I recall that in the golden days of Model Railways Colin Binnie contributed articles that included the use of home-ground form tools. One that particularly sticks in memory involved two pieces of gauge plate cut to an identical profile, then hardened, tempered and mounted as a mirror image at the necessary distance from each other to give the required final diameters of the component. The tool was then pressed against suitable rotating bar stock to generate the profile desired.

For a long time I have wanted a back tool post for my Unimat 3; there are so many occasions when it would be convenient to wind in the cross slide to turn a component then wind out to part it off. However, a big obstacle to this arises from the fact that the motor casing projects past whatever work-holding device you have attached to the spindle, and this leaves you with limited room in which to mount such a tool post in a way that will not bring it into collision with the motor.

To the best of my knowledge Maier never offered any form of extended cross slide, so with the Unimat your only options are to mill your own from scratch or adapt the cross slide supplied. I'm reluctant to start mutilating my cross slide, but think it may be possible to attach a suitable extension carrying a back tool post by means of the existing T slot in the slide. An additional problem that must then be overcome is finding a way of mounting the inverted parting off blade – always assuming you can first obtain blades sufficiently short as to not clash with the motor! Any suggestions as to where such blades might be obtained? I estimate that 2 – 2.5 cm is about the maximum length of back parting off tool that could be accommodated whilst still leaving a reasonable range of diameters in the stock being turned.

Terry Bendall wrote:One reason for having the parting tool at the rear is that it makes the process easier. Parting off can cause some difficulties with the tool digging into the work when the tool is held in the usual front tool post. Holding the tool in the rear tool post means the the cutting is done as the work piece is turning upwards (think about that :) ) and the risk of digging in is much reduced.

Terry, I think I must be missing something here. Surely the cutting geometry is the same as with a front tool post, save that the tool is now inverted? If so, isn't the risk of the tool digging in the same?

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Re: Turning a chimney

Postby David Knight » Mon Jul 13, 2020 5:17 pm

I can think of two advantages for a rear mounted tool post, specifically one dedicated to parting tool use. First: the tool would only have to be adjusted once for cutting height until such time as it needed sharpening thus saving the faff that occurs even with rotating tool posts of getting everything square. Second: time is saved as the parting tool is ready to go all the time thus saving time if one is doing repetitious tasks such as batch production of any given component.

Cheers,

David

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Re: Turning a chimney

Postby davebradwell » Mon Jul 13, 2020 8:56 pm

In my model engineering days I was told an advantage of the rear toolpost was that the cutting force is applied to the bottom half of the headstock bearings which would be less worn and therefore less prone to chatter during this sometimes challenging process when a wide cut is being made. They didn't use them in our super R&D workshop and I noted that Jeremy chose his words carefully as professionals seem to use tools in holders which locate accurately on the machine - I believe such are available for the Unimat - and this is the system I use.

It's all very well having various tools available during a planned sequence such as Jeremy describes but I'd be wary of having additional tools all over the place for casual turning - a fully stocked 4 tool holder can be a fearsome looking beast ready to dig into the hand or chuck and I haven't seen one that indexes to a repeatable location. I get into enough trouble with just one tool to watch and see the rear post as yet another hazard despite its popularity. It was drummed into me that it's a great sin is to machine the machine.

Will finish by acknowledging Jeremy and Terry's far superior machining experience. Perhaps it's my limited skill that makes me very wary of additional hazards and especially because I'm working alone.

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Re: Turning a chimney

Postby Terry Bendall » Tue Jul 14, 2020 7:52 am

John Palmer wrote:Terry, I think I must be missing something here. Surely the cutting geometry is the same as with a front tool post, save that the tool is now inverted? If so, isn't the risk of the tool digging in the same?


I thought someone would ask that question! :) I am not sure of why it works - what I do know is that is does work! Someone who is cleverer that me may have the answer.

John Palmer wrote:Any suggestions as to where such blades might be obtained?


Chronos Ltd sell the proper thin parting tool blades see https://www.chronos.ltd.uk/product/repl ... for-pt000/
The blade is1.5 mm thick x 4.5mm wide x 63 mm long at a cost of £3.83. Other suppliers will have similar things. The alternative is you have a bench grinding machine, or know someone who does is to grind down a standard HSS tool bit. It wil take some time but it can be done. If the pieces of steel is too long. grind a groove in each corner, put the piece you want in a vice and hit the other end with a hammer. Don't aim towards a window! If you want to keep the piece you are hitting hold it in a pair of pliers!

davebradwell wrote:a fully stocked 4 tool holder can be a fearsome looking beast ready to dig into the hand or chuck


Yes it can be and it is the sort of silly thing that can cause trouble. :( Take care is the answer.

Terry Bendall

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James Moorhouse
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Re: Turning a chimney

Postby James Moorhouse » Tue Jul 14, 2020 8:24 am

Terry Bendall wrote:
John Palmer wrote:Terry, I think I must be missing something here. Surely the cutting geometry is the same as with a front tool post, save that the tool is now inverted? If so, isn't the risk of the tool digging in the same?

I thought someone would ask that question! :) I am not sure of why it works - what I do know is that is does work! Someone who is cleverer that me may have the answer.

I'm certainly not cleverer than Terry, but the idea is that when a forward-facing tool is subjected to a downward pressure, it leans forward and digs in to the work, while the resultant upward pressure of a rear-mounted, upside-down tool tends to move the tool back and out of the cut.

Of course, the upside-down tool needn't be mounted to the rear of the work, it could be mounted at the front and the lathe run in reverse, although this isn't a good idea if your chuck is mounted with a right-handed screw!

James

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Re: Turning a chimney

Postby davebradwell » Tue Jul 14, 2020 8:37 am

That finally makes sense after all these years.

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Re: Turning a chimney

Postby John Palmer » Tue Jul 14, 2020 11:51 am

Terry, many thanks for that Chronos link. I feel a purchase coming on, and it's time to dust off the CAD package and work up a little drawing of how I might go about this. Going up a level from Terry's link leads to a range of additional choices, including parting blade holders that look capable of adaptation to the Unimat, though some, regrettably, appear to be currently out of stock.

Very useful tip about using the grinder to create a weakness point at which you can snap an HSS blade. Think it also might be as well to be wearing safety specs when doing this; I've seen hacksaw blades disintegrate into multiple fragments when broken, and with any brittle material I think precautions to protect your eyes are worthwhile when engaging in this kind of exercise.

On the reduced likelihood of digging in point, one thought that crossed my mind was that the force on the conventional 'front mounted' tool-toolpost-slide is acting in compression, whilst in the case of the inverted rear-mounted tool the same force is acting in tension, in that it is trying to lift the tool-post-slide combination upwards and away from the bed. I had rather discounted the possibility that this introduced a degree of 'give' into the setup that militated against digging in, but James' comment is making me think again.

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Re: Turning a chimney

Postby JFS » Tue Jul 14, 2020 4:03 pm

James Moorhouse wrote:I'm certainly not cleverer than Terry, but the idea is that when a forward-facing tool is subjected to a downward pressure, it leans forward and digs in to the work, while the resultant upward pressure of a rear-mounted, upside-down tool tends to move the tool back and out of the cut.


That is also my understanding of why it works - and it certainly does work! Equally, the other point is also valid - setting up a parting tool for centre height and squareness is even more / much more critical than with almost anything else. The last thing you want to do is disturb it once it is set-up. And even just indexing a four-post counts as disturbing it. So setting up a back tool post, then leaving it ready for use is a big time saver.


EDIT:- sorry meant to say - excellent thread this Jeremy - very well done.

Best wishes,

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Re: Turning a chimney

Postby Edward45 » Tue Jul 14, 2020 5:23 pm

Old HSS circular saw blades are a good source for parting off blades. Just chop up the saw blade into strips roughly the right size using a cutting disc in an angle grinder. Finish off to size using the bench grinder.

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John Bateson
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Re: Turning a chimney

Postby John Bateson » Tue Jul 14, 2020 6:08 pm

James Moorhouse wrote:
I'm certainly not cleverer than Terry, but the idea is that when a forward-facing tool is subjected to a downward pressure, it leans forward and digs in to the work, while the resultant upward pressure of a rear-mounted, upside-down tool tends to move the tool back and out of the cut.


OK, now I am really confused so am sticking my neck out here.

If I have a parting tool on the front tool holder set so that it produces a good clean cut and could in a thought experiment move the tool holder around the chuck axis by any number of degrees surely any effect on the cut will be the same in spite of the different angle of the blade with repect to datum and which will maintain the same aspect onto whatever rod is being parted.
Therefore if I move the tool holder through 180 degrees the parting tool will be correctly positioned with respect to the rod and the cutting interference on the rod will always remain the same.
So if the rear parting tool is set correctly in its toolholder it will have exactly the same effect on the rod as if the parting tool was attached to the front tool holder.

Potentially the only difference I can see is that depending on the angle the bearings may experience different amounts of wear for continued use on heavy jobs.

John
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Re: Turning a chimney

Postby grovenor-2685 » Tue Jul 14, 2020 6:18 pm

John, when you turn your toolpost through 180 in your thought it will end up needing a crossslide and bed 180 degrees frohe existing ones to hold it.
However rotating just the tool and fitting it to the same crosslide and bed reverses all the reaction forces in the vertical direction.
ie the anticlockwise reaction force on the tool acts vertically downward on a front toolpost and vertically upward on a rear tool post.
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Re: Turning a chimney

Postby John Palmer » Tue Jul 14, 2020 11:11 pm

For those that can stomach it, 15 pages of discussion on parting off, dig-ins, chatter, load-induced movement of tool/toolpost/crosslide, etc, etc at https://www.model-engineer.co.uk/forums/postings.asp?th=103618&p=1. Some particularly interesting contributions from Cabeng (well I found them interesting) which challenge the argument that the rear mounted tool tends to move out of the cut, suggesting instead that built-up edge on the tool tip is the real villain in the digging-in saga.

And for some impressive footage of parting-off cuts, https://www.youtube.com/watch?v=cLzVQRXysbY is worth a look.


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