Turning a chimney

Jeremy Suter
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Turning a chimney

Postby Jeremy Suter » Tue Apr 16, 2019 4:18 pm

I picked up a small job of turning a CR Dunallastair 440 Chimney .
54473 Elgin29.5.58.jpg

So Starting with the Flycutting I have set the Vertical slide in the lathe.
IMG_4819.JPG

Setting the height or the centre line
IMG_4811.JPG

Making sure its set to a right angle to the cutter the Flycutter is a home made effort if 12mm Bar an a 2.5mm broken drill ground to shape for the cutter.
IMG_4815.JPG

Fly cutting.
IMG_4817.JPG

Checking its right with a disc cut to the right diameter as I have not got the smokenbox to test against.
IMG_4816.JPG

Now with the
base flycut the bar is placed in the lathe and a 3mm hole drilled in base the reamed out with a 1/8th reamer by turning the chuck by hand so that the reamer stays tight.
IMG_4821.JPG

with a tight fit 1/8th hole a 1/8th inch rod is pushed in and is a very tight fit.
IMG_4822.JPG

The Rod Is removed while the bar is turned to just over the largest diameter needed.
IMG_4823.JPG

Now the Basic shape is marked.
IMG_4825.JPG

The basic Shape is turned and then parted off.
IMG_4826.JPG

Once parted off I fitted it to a 1/8th inch rod and mounted to the flair jig.
IMG_4827.JPG

In the Chuck I now use a 5mm Diamond Ball Grinder and offer up the chimney. Turning the chimney round and cutting the flair to shape.
IMG_4829.JPG

Now cut off and slotted into a 1/8th Collet for the Boley lathe
Attachments
IMG_4830.JPG
Last edited by Jeremy Suter on Fri Apr 19, 2019 6:44 am, edited 1 time in total.

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Will L
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Re: Turning a chimney

Postby Will L » Tue Apr 16, 2019 6:50 pm

Excellent post as always Jeremy.

While I'm not a lathe user, I thought i understood fly cutting but the flair jig was a new one on me. Very clever. I think I see how it works but a bit more detail on how you use it would be interesting. For instance, presumably you need several passes moving the flange follower on the jig progressively closer to the cutter.

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Tue Apr 16, 2019 7:21 pm

Hi Will
The Flair Jig is another home made tool.
It is clamped to the back post on the cross slide where the parting tool is usually held. The chimney or dome of safety valve is fitted/Soldered to a 1/8th steel rod slotted into the jig and then the base runs against the runner which is in brass so it does not cut the base when rotating. It is held there by the spring at the back. I slowly turn the brass wheel at the back holding the object being machined to keep it steady as the 1/8 rod will actually bend if too much cut is taken off at a time no more than 5 thou on each turn. Slowly with the cross slide I bring the ball grinder closer to the cutting area and work my way down it. It took about 10 mins to form the shape.
The Chimney still needs fine filling and polishing which is done as the finishing stage when the chimney has its measurements checked at the moment everything is slightly too large as its easy to take a little off rather than put it back on again.

JFS
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Re: Turning a chimney

Postby JFS » Tue Apr 16, 2019 10:08 pm

Jeremy Suter wrote:The Flair Jig is another home made tool.


Hmm - rather brilliant. One of those things which is blindingly obvious once you have seen it - but I have never seen mention of one before!

Many thanks for the tip Jeremy!

Best Wishes,

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Wed Apr 17, 2019 7:50 am

Now moving it over to the Boley Watchmakers Lathe.
I love this lathe as it has a foot peddle switch so it only runs when I am ready to cut, and I can use the big magnifier on it.
IMG_4831.JPG

Now drilling the top with a 4mm drill I have already put in 2mm pilot hole in and will go down about 5mm.
IMG_4833.JPG

Now shaping the top lip.
IMG_4834.JPG

When shaped I now drill out with a .5mm drill and go as far as I dare about 6.5mm.
IMG_4835.JPG

Before I finish I check the measurements and with a Fine File I take any extra off before Polishing with 1200 Emery Paper and a Glass Brush.
IMG_4837.JPG

Lastly I clean up the inside with a coarse grade then fine grade of emery paper
IMG_4836.JPG

Total time taken about 3 hours on this one with staged pictures.

Philip Hall
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Re: Turning a chimney

Postby Philip Hall » Wed Apr 17, 2019 9:58 am

Jeremy,

It looks as though you are shaping the top lip with a round nosed tool moved in and out and around as necessary, finishing off with a fine file?

I don’t have a watchmakers lathe, nor collets of any accuracy, but I have some home made brass collets which I could use. I renew these from time to time as a job comes up. My very old Unimat SL has a Sherline chuck which is amazingly accurate but possibly not quite accurate enough (1 thou runout).

Philip

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Wed Apr 17, 2019 11:19 am

Hi Philip
I used to have the Unimat SL with milling attachment. Excellent machine and have done chimneys and domes on it. It did have a self centring chuck but even with that it did spin about 2thou off centre as most self centring chucks do. Its always best to use Collets they are usually expensive but the centring should be dead accurate. You can also remove the collet without removing the chimney from the mount, which I prefer.
As for the Round Nose Cutter it does have a .5mm radius on the tip but cuts very nicely and the top lip of the chimney is radiused so when drawing the cutter back and moving it down the chimney it produces a cleaner finish I then go in with a sharp pointed cutter to do the top and any other 90 degree angles. I should have Photgraphed this bit.
IMG_4857.JPG

The work is always finished off with a file before polishing with fine grit emery paper I tend to use the small Square, Three Square and Round files before polishing with fine grades of Emery paper.

Philip Hall
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Re: Turning a chimney

Postby Philip Hall » Wed Apr 17, 2019 12:23 pm

Jeremy,

I did purchase some Swiss collets for the SL some time ago but only one of them turned out to be remotely accurate! Hence I usually make my own from brass bar, turned and drilled to size and then split after marking for the chuck jaws. I have to make new ones from time to time but it seems to work. The problem with the SL is the 12mm threaded headstock spindle, no one seems to make collets for that now, apart from the ones I purchased which were rather dud!

I do have a round nosed tool so now I understand how you did it will have another go at a chimney soon. Many thanks.

Philip

John Palmer
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Re: Turning a chimney

Postby John Palmer » Wed Apr 17, 2019 2:02 pm

First class treatment of this technique for machining a flare. It was also the subject of a 1995 article by Geoff Helliwell in MRJ 79, but Jeremy's photograph-rich exposition makes an excellent complement and suggests an alternative mounting arrangement for the jig.

Geoff comments upon the importance of arranging to fly cut precisely on the centre line of the bar from which the chimney/dome etc is to be generated, as otherwise the finished item will be offset from the flared base. As an alternative to the scriber shown in Jeremy's third picture for setting the centre height of the workpiece, it should be possible to use a centre mounted in the spindle nose for the same purpose.

For those lacking the very useful vertical slide Jeremy has available, it may be possible to mount the workpiece in the tool holder of a quick change toolpost (of the type where the tool height is screw-adjusted). Unfortunately the depth of the tool holder is liable to restrict the size of the bar that can be securely clamped - in my case, using the quick change tool holder designed for a Unimat 3, the maximum size bar that could be clamped firmly is no more than about 9mm diameter, making it unsuitable for a dome of larger diameter over its flared base.

Enigma
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Re: Turning a chimney

Postby Enigma » Wed Apr 17, 2019 7:14 pm

Thanks to Terry Bendall's excellent lathe tutorial class I am the proud owner of a fly-cutter and also have all the parts to make a Geoff Helliwell version of the flare turner. How long it will be before this actually gets made is another matter! I have a 'commission' to make a pair of domes for a Barclay Fireless loco, a relatively simple job but fine as a 'starter for 10'.

Excellent post Jeremy, many thanks, I am sure I will be returning to read it again.

And again and again etc...................... :thumb

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Wed Apr 17, 2019 7:44 pm

Hi John
It was getting a set of engraving balls with a Dremel drill kit that made me think of using them to producing the flair I just needed to hold the work steady and rotate it.
The Vertical slide is one of the best tools I bought for the lathe. I had to make it fit the cross slide but that was only drilling an extra hole and tapping it.
Before I bought it I used to use a Machine Vice mounted on the Cross Slide but as it was lower than the Flycutter I hade to put the bar in at an angle and work out how far I needed to go in to get the curve in the centre.

Hi Phil
Its a shame you have had such trouble with the Swiss collets the word Swiss usually you think of high quality tools.

Terry Bendall
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Re: Turning a chimney

Postby Terry Bendall » Wed Apr 17, 2019 8:42 pm

JFS wrote:Hmm - rather brilliant. One of those things which is blindingly obvious once you have seen it


It is, and an idea that is new to me. Learn something new everyday. :)

Philip Hall wrote:I did purchase some Swiss collets for the SL some time ago but only one of them turned out to be remotely accurate


This may be a fault with the collets but it may be the collet holder. I bought a holder and some collets for my Cowells lathe and found that because the holder had been made on another lathe, it was inaccurate on my machine. The seating for the actual collet must be "true" or concentric. My lathe has a top or compound slide that can be set at an angle so what I did was to set this at the correct angle and then take a skim off the seating. Since then everything has been fine. With a nice sharp tool set exactly at centre height I have been able to hold 1mm diameter rod and reduce it to 0.5mm quite successfully.

Philip Hall wrote: The problem with the SL is the 12mm threaded headstock spindle, no one seems to make collets for that now


It is probably an M12 fine thread and it is possible to buy taps that size, or for those who are really clever, to screwcut an internal thread on the lathe. One way is to find someone with a larger lathe - something the size of a Myford ML7 or similar to do this part of the job and then rough machine it. If the final machining is done on the lathe on which the holder is to be used then it will always be accurate. That of course sound easy but is a bit more difficult to do in practice.

Terry Bendall

Philip Hall
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Re: Turning a chimney

Postby Philip Hall » Wed Apr 17, 2019 10:13 pm

Jeremy, yes I thought the collets should be OK but was disappointed! I did have the chance recently of a watchmakers lathe but it was beyond my pocket...

Terry, I will have to have a look sometime to see if I can improve things. However, one collet is true but others are not, which points to the actual collet rather than the holder.

Thanks for the useful guidance.

Philip

billbedford
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Re: Turning a chimney

Postby billbedford » Thu Apr 18, 2019 9:01 am

Very clever, but using the ball mill will give the wrong shape to the flare.

Deeley Chimney.jpg


Note the difference in radius of the flare on the two views. While having a constant flare radius would not be too noticeable on modern locos with large boilers, it will stick out like a sore thumb on older, small boilered ones.
Bill Bedford
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Dave Holt
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Re: Turning a chimney

Postby Dave Holt » Thu Apr 18, 2019 2:16 pm

Presumably, one could use the ball cutter to remove the bulk of the material and then use a smaller cutter, file, or burr to create the smaller radius and blend in to the larger? Still looks a lot easier than trying to do it all by hand.
Dave.

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Thu Apr 18, 2019 8:33 pm

Post by billbedford » Thu Apr 18, 2019 10:01 am
Very clever, but using the ball mill will give the wrong shape to the flare.


Thanks Bill for pointing that out .
I only put the basic shape in the chimney in the big lathe all the detail is done in the Boley.

You will notice in the picture that the finish is rather rough round the base and I do say that the measurements are over size till the fine finishing later on. This method is about doing lower flair neatly and quickly. Anybody who has filed the sides knows its a pain to do and time consuming. In fact it only took about 15 minutes to get the flair to where I wanted it.
It is far easier to take the excess metal off at the top with a round file and smooth round to the base as of coarse its a transition curve, than take the large amount of metal off the sides and work up.

IMG_4830.JPG

It is cleaned up in the Boley lathe with a file. A Small D file and a 2mm round file is used first to get the flair to match the base then a 1.5mm round file finishes the top then cleaned up with emery paper to finish. I do have some 1mm round files but there getting shorter.

Here's some I did earlier in fact nearly 30 years ago now a bit battered now but still loved. and since then around 300 others in various scales.
IMG_4871.JPG

Terry Bendall
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Re: Turning a chimney

Postby Terry Bendall » Sat Apr 20, 2019 5:59 pm

Philip Hall wrote: However, one collet is true but others are not, which points to the actual collet rather than the holder.


Sounds like it Philip in which case I would ask for a refund or an exchange from some that are true.

Jeremy Suter wrote:and since then around 300 others in various scales


Which sounds like a pretty good recommendation for the method! :D

Terry Bendall

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John Bateson
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Re: Turning a chimney

Postby John Bateson » Fri Apr 26, 2019 9:31 am

I thought I might take some space and show how I do things, end result is supposed to be the same though I must defer to Jeremy's skills when considering the end results.
I have been known to make a few domes and chimneys over the past few years and following a lead-in from Terry Bendall way back in 2011 the following became my approach.
Rather than use a sharpened drill bit held in a piece of bar and held in place by a nut/screw etc, since I found it hard to get what I thought to be an accurate curve and it is very difficult to measure from the centre to the outside cutting point. So I purchased a set of these...
Fly Cutting Tool.JPG

Since some of the domes and chimneys were way beyond my tool holder capability I asked a lathe forum for advice and was told I should have got a bigger lathe. Not helpful but I ended up with the dumbbell arrangement shown. The centre bar is 8 mm which sits nicely in my tool holder and is held firmly in place. The ends are cut to the diameter of the target chimney or dome. The length of the ends is such that it just meets the fly cutter i.e. about 32 mm in my case.
Dumbbell.JPG

The dumbell is drilled at each end by 5 mm for domes and 4.5 mm for chimneys.
Fly Cutter and Dumbbell.JPG
and the main drawing is
Dome.png
Dome.png (19.75 KiB) Viewed 1629 times


Now comes the problem of making sure that the fly cut is accurately centered, top to bottom and left to right. I use a mirror tile behind the cross slide! Taking very gentle cuts it is possible to see the effect in the mirror and adjust the tool holder correctly. The picture show a part where the initial cut is offset quite badly. Not quite the Swindon version of optical alignment but it works for me.
Mirror Tile.JPG


Once the cut is complete simply turn the tool part around and cut the other end then part off both to the appropriate height.

Completed Blank.JPG

With a spigot inserted this is easily turned in the lathe

A spigot with a very tight fit is then added and the final shape apart from the flares is cut using various tools, lathe, file, wet and dry etc.
Part with Spigot.JPG
I have sets of etched templates for each chimney and use these to determine the shape above the flare. Short lengths of brass tube of the right diameter (with a 5 mm hole cut out if doing this after the spigot has been fitted) can be used to test the accuracy of the fly cutting.

I was given some round cutting tools some years ago, very high quality steel not the diamond version, but these were for bone rather than brass and I was not successful with them. So I do the flare in the old fashioned way, which is time consuming and incredibly boring but keeps me out of the house. Needle files, coarse wet and dry and then fine wet and dry. For ages.
Finishing is done back in the lathe. After some inital polishing simply by using Brasso/Duraglit I get out my trusty Dremel with a polishing bit and finish off with that on the flares and the main body. If both lathe and Dremel are turning at the same time and loaded up with Brasso a good finish can be achieved. The target is that a reflection of my face in the part is recognisable and does not look like a horror picture! The downside of that is the Brasso goes absolutely everywhere...

It should be noted that the spigot for the dome is now part of the finished dome - which is why an accurate fit is needed. For the chimneys the spigot will be tapped out using a box spanner over the spigot, so that the edges of the flares are not impacted.
Slaving away still on GCR stuff ...
Avoiding the soaps ...
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John Palmer
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Re: Turning a chimney

Postby John Palmer » Fri Apr 26, 2019 6:03 pm

John Bateson wrote:... it is very difficult to measure from the centre to the outside cutting point.

If the position of the tool can be adjusted in its holder, a setting gauge gapped to the radius to be cut plus half the diameter of the holder could be used for this purpose, as per this sketch:
Fly cutter setting gauge.jpg
This assumes, of course, that the axis of the reference surface on the tool holder is concentric with the axis of its shank. The gauge can be a throwaway item made from any convenient scrap sheet.
John Bateson wrote:Since some of the domes and chimneys were way beyond my tool holder capability I asked a lathe forum for advice and was told I should have got a bigger lathe. Not helpful but I ended up with the dumbbell arrangement shown.

I think you need to find a more enterprising lathe forum; much of my enjoyment in using a machine tool comes from finding novel ways to exploit its capabilities. Your solution of reducing your bar stock to a dumbbell so that it can be clamped in your toolpost is just such an exploit. :thumb

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John Bateson
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Re: Turning a chimney

Postby John Bateson » Sat Apr 27, 2019 3:32 pm

John,
Thanks for that - its now on the list!
John
Slaving away still on GCR stuff ...
Avoiding the soaps ...
http://www.greatcentralmodels.co.uk

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Sun Dec 01, 2019 10:35 pm

Moving on from the Chimney.

I have just been asked to turn a couple of Domes.
One for the SECR L class 440
img20191201_20532369.jpg

The other for the GCR LNER O4/7 with Flat top.
img20191201_20534430.jpg

Although in 7mm scale I use the same method as in 4mm.
Starting on the L class first with a block of solid Brass at 22mm diameter it will not fit in my Vertical Slide so I have mounted a Machine Vice direct to the Cross Slide.
IMG_5280.JPG

The block has been packed with steel blocks so that the bar sits central to the fly cutter. Like the chimney this is the first part cut once cut I check the radius with a plastic wheel to make sure the curve is cut too the correct size (I forgot to photograph this at the time).
IMG_5318.JPG

With the base cut its then mounted in the lathe chuck and turned to slightly larger than the base diameter and a ball cutter is used to put a pop mark in the centre of the base before being drilled with a 3mm drill.
IMG_5284.JPG

IMG_5285.JPG

I drill in 8mm. Then using a 1/8th reamer I hand wind the reamer into the hole so that it makes a tight 1/8th hole, I will fit the Rod in later.
IMG_5287.JPG

The next step is to mark for cutting the shape of the dome, all over sized for now.
IMG_5288.JPG

IMG_5290.JPG

Using the V shape cutter I have turned the middle section of the dome then the top ready to be parted off.
IMG_5292.JPG

IMG_5294.JPG

Before parting off I add the rod using the tail post to keep it straight. This is a push fit and very tight I have not fixed with anything although sometimes I solder them in place. which I had to do on the next one for the O4.
IMG_5295.JPG

Parted off and mounted in my flair cutter.
IMG_5296.JPG

IMG_5297.JPG

In 7mm this took a good hour to run through cutting approx 5mm deep on the sides.
Mounting it in the Boley lathe to finish the flair.
IMG_5299.JPG

IMG_5300.JPG

Using a selection of files round and half round to finish using the small diameter ones on the top part.
IMG_5306.JPG

Using small a round file on the top flair is much easier than trying to do the side part.
IMG_5301.JPG

IMG_5302.JPG

Once the base shape is done I move onto the middle section.
This dome is slightly tapered so have moved it onto the BTM lathe which shows the angle on the tool post at 2 degrees.
IMG_5327.JPG

IMG_5305.JPG

At this point I have checked the measurements and smoothed off the base.
IMG_5308.JPG

Now the top
It would be nice if they were plain ball shaped but most aren't they tend to change from one radius to a second through a transition curve and I always assume they have a pip on the top as its easy to remove it rather than add one later.
IMG_5310.JPG

One way to do this is dodging it. Which is pulling the cutter out with one hand while winding it in with the other, easy on the big lathe but will jam the work on these small watchmakers lathes and the belt will carry on, which doesn't do thm any good. So I tend to start off with a bastard file to take the corner off then dodge to smooth it.
IMG_5309.JPG

A selection of big flat files for the top along with a radius cutter.
IMG_5316.JPG

This is the radius cutter a 6mm on ine end and an 8mm on the other made from a piece of steel bar and case hardened.
IMG_5312.JPG

IMG_5313.JPG

The files get the basic shape and the radius cutter finds the correct radius when its flush with the dome. For the start and finish as this dome starts tight and gets shallow over the top.
IMG_5314.JPG

IMG_5315.JPG

Using a tool resting post the 8mm for the top part and the 6mm for the side before smoothing with emery paper.
IMG_5320.JPG

The last job is to put the pip on the top. This is done with the plain cutter run in .6mm and and then pulled out slightly dodging to get a very shallow curve before smoothing with 1200 emery paper.
IMG_5328.JPG

The O4 dome is done exactly the same way although I started with 1 inch brass bar, it has a 6 degree taper on it and I used a 4.5mm radius cutter.
IMG_5329.JPG
IMG_5330.JPG
IMG_5334.JPG
IMG_5335.JPG
Last edited by Jeremy Suter on Mon Dec 02, 2019 8:53 am, edited 1 time in total.

Terry Bendall
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Re: Turning a chimney

Postby Terry Bendall » Mon Dec 02, 2019 7:58 am

Jeremy has given a very full description of how to make chimneys and domes which I am sure will be very useful. Forming the base of the dome using the ball ended cutter is a very useful dodge which bis new to me but is saves a lot of filing.

A small word or warning however on using files in the lathe. They do the job but it is always advisable to fit them with a handle. On a small lathe such as those shown, there is probably not sufficient power to cause injury if the file gets caught in the lathe chuck, but on a larger machine this is always a possibility, even with needle files. Using a collet chuck as shown makes things safer since there are fewer things to catch the file on.

Terry Bendall

Jeremy Suter
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Re: Turning a chimney

Postby Jeremy Suter » Mon Dec 02, 2019 8:26 am

A small word or warning however on using files in the lathe. They do the job but it is always advisable to fit them with a handle. On a small lathe such as those shown, there is probably not sufficient power to cause injury if the file gets caught in the lathe chuck, but on a larger machine this is always a possibility, even with needle files. Using a collet chuck as shown makes things safer since there are fewer things to catch the file on.


Thank's Terry.
A very good piece of advice I learned the hard way may years ago and got a small file embedded in the palm of my hand when it hit the chuck, luckily I could just pull it out with not much damage. Since then I always use a file on a lathe like this, so I can see where I'm cutting. and there is always a magnifying glass between my face and the work
IMG_5336.JPG

The finished domes.
IMG_5337.JPG


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