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Turning long slender arbors

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Nigel Watts24/05/2019 16:06:31
26 forum posts

I am turning some clock arbors in silver steel. The steel is tough so I am finding it easier to do in my Myford ML10 than in my Cowells. I have a reasonable set of collets for the Myford - most 1/32" increments - so holding the work at the headstock end is OK (except that the Cowells watchmaker collets are all metric, so switching over is awkward). The problem comes with the tailstock as all my centres are far too large and I can't get the cutting tool close enough to the end.

The Myford tailstock is 2MT and hollow all the way through so I am thinking that some 2MT collets plus a homemade drawbar might be the answer (I can't use the Myford collets because they only work with the headstock adapter). I could then turn some smaller centres (male, female, 1/2 centre etc) in 4mm or thereabouts silver steel before hardening them and holding them in the collets. Does this sound sensible?

John Wilding, in his book on clock wheel and pinion cutting has some rather more sophisticated adapters which allow a watchmaker's collet to be held in a rotating bronze component within a Morse taper adapter, but this sounds a bit too advanced for me!

JasonB24/05/2019 16:13:18
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What tool are you using I can happily ctr drill and turn down to a 3/32" shaft and use a MT3 revolving ctr.

Nigel Watts24/05/2019 16:17:57
26 forum posts

My Myford tools are a bit clunky - about 3/8" square. Now you mention it I guess there is no reason why I shouldn't use one with a much narrower tip.

JasonB24/05/2019 19:10:50
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YYes that's the basic Idea. I tend to use a 10mm shank 55 degree insert tool which leaves a 5 degree clearance to the live ctr.

close cut1.jpg

You can also grind up some HSS to a similar shape. Also you don't need such a large section tool though depending on your toolpost it may clash with the tailstock Ctr unless you have a lot of tool sticking out in which case one of the Dickson extended tool holders comes in handy

close cut 2.jpg

Nigel Watts26/05/2019 07:30:55
26 forum posts

Thanks for this. The photos are especially helpful. I have some HSS blanks and will try grinding one to the shape in the second picture. I don't have a Dickson style toolpost but my 4-way quick change one should work I think.

Being able to fit small centres into collets in the tailstock seems to be a watchmakers' thing and I think it might still be useful, for example for finishing very small diameter pivots.

roy entwistle26/05/2019 09:19:12
983 forum posts

You can get half centres for turning right up to the centre.

Roy

Nigel Watts26/05/2019 09:27:26
26 forum posts

I have a 2 MT half centre but the ground down part still leaves too much of a cone at the end to get my current tool in for the very small diameters. I might try grinding the flat down a bit.

Clive Foster26/05/2019 10:01:09
1736 forum posts
52 photos

Make an extended carrier for a small tool bit. Either a simple U slotted bar with small hex socket grub screws to hold a suitably small piece of square tool steel or bore a steel bar to take a round tool bit boring bar style albeit pointing out the end rather than sideways. Broken centre drills and small milling cutters make excellent round toolbits. Bit short when it comes to grinding but shaping them in the holder works just fine and gives you plenty to hold. Nice heatsink so they don't burn your fingers so fast too.

Arrange things so the toolbit angles up a little, Armstrong holder style, to give simple fine adjustment of tip height by sliding the bit in and out. Need to get it just so on this small work.

You may well find that making the bit holder wider so the tool is actually off to the side of the four way block gives more room around the tailstock and centre. No issues with stiffness as this is a light cut job. Plenty of room to make the holder far too strong, especially if cantilevered out the side.

I'd long considered making some U channel holders for small tool bits but it always seemed too much trouble . Then I lucked into a couple or four in a "can you use this rubbish" bonus box given to me by a non machining friend. First time I used one convinced me that not making some when I first thought one would be nice was, ahem, exceedingly stupid. Some round bit holders in there too but for larger sizes.

Clive

SillyOldDuffer26/05/2019 10:06:55
4396 forum posts
956 photos

As the job has caused trouble on a Cowells and an ML10, both of which are up to cutting Silver Steel, I wonder if the problem is entirely due to choice of knives? Old-timers ground a huge variety of shapes and sizes to get the job done, and carbide inserts are even more diverse. I still get into trouble through not changing cutter to suit the job. (Perhaps I should order a quick change tool-post). Bother getting big tools into tight spaces, not getting enough reach from a small tool, trying to finish with a roughing tool, and wasting time while a baby insert eats it's way through a lot of metal. Etc.

Grinding HSS is an acquired skill, and it seems not everyone is good at it, blush! Partly for that reason I use carbide most of the time. To get the necessary range of cutting options I have holders in 6, 10 and 12mm for round, triangular, square and sharp inserts. (Not in every size!) Although I own a good selection, I still occasionally find myself grinding HSS.

Jason pictured two cutters shaped to tackle the problem. My preference would be the sharp carbide insert because I have one and it's easy. Second choice would be to grind HSS to shape. Although lots of chaps will tell you grinding is easy, it would take cack-handed me a while to get a satisfactory cutting profile on Jason's HSS example. Try it and see. You might be a natural, but don't despair if sharpening HSS takes more practice than you were expecting. Sparey's 'The Amateur's Lathe' is helpful.

Unless a clockmaker knows different I wouldn't put collets in a tail-stock and then make centres to fit them. I'd buy a set of live centres to fit the ML10. If necessary centres can be made to fit that.

Dave

roy entwistle26/05/2019 10:45:14
983 forum posts

I have a tailstock for my watchmakers lathe ( make unknown ) that has in internal taper like the headstock to take collets.

Roy

speelwerk26/05/2019 11:25:07
320 forum posts
1 photos

When diameters get small it can be handier to make a male centre on the arbor end. A female centre in the tailstock is quickly made with a piece of brass in a drillchuck and centredrill held in the headstock chuck/collet. Niko.

arbor.jpg

Martin Hamilton 126/05/2019 11:29:59
97 forum posts

For getting a good finish even on silver steel in small lathes get yourself some of the aluminium carbide inserts that Jason show in his 1st picture. These inserts are fantastic on small lathes, they are unbelievably sharp so watch your hands on them. They work great on aluminium, brass & steel. Both tool holders & inserts are available from online sellers very cheaply & are good quality considering the low prices from the right sellers. I use nothing but these now on my little Sherline lathe & get a close to a ground finish even on steel.

Bizibilder26/05/2019 12:05:40
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56 forum posts
7 photos

You say you have Myford collets in Imperial and Cowells in Metric? You should be OK to turn clock arbours with them - Just hold the embryo arbour in the collet of choice and machine one end, turn the arbour round and machine the other end. Collets should hold the arbour with little or no run-out. There is no need for a tailstock centre for this work or to work between centres. I'm not saying you shouldn't work between centres, just that it is not essential. For final filing and burnishing you may find making a Jacot tool will help (Google will find info for you).

If you want to do some "bulk removal" of metal on an arbour - say to make an integral pinion - you can get most of the waste removed using the three-jaw and then change over to collets to finish off.

For pivots the finish you get from the late tool and the exact pivot size is not that important as pivots are always finished and burnished with a pivot file (which are expensive but essential!).

In clockmaking the hole for a pivot is always broached out to fit the pivot - you do not need to know the exact size - just drill the hole slightly undersize and broach to fit. Broaches make a tapered hole so that you only get a tiny "ring of contact" with the arbour to minimise friction. This can take a bit of practice to get right but is quite easy to do. John Wildings books do give more detail of how to do it.

It makes no difference if your arbours are metric or imperial - just use the appropriate collets and make all the parts to fit each other. If the design calls for 1/8" you can use 3mm (or 4mm) just as easily - or buy some blue pivot steel of the appropriate size and use that - it is not available in all sizes so you often have to compromise. Always use the "next size up" to avoid making things too flimsy - the loads on clock arbours can be quite high especially on arbours close to the weight or spring.

As for tooling HSS will work perfectly well and home made silver steel cutters also work.  Nothing wrong with carbides and inserted tool bits  - its just that they are not necessary.  It seems they have a reputation for solving your turning problems.  They don't.  A sharp tool presented to the work at the correct angle and at centre height will cut and give a good finish.

Edited By Bizibilder on 26/05/2019 12:08:55

Edited By Bizibilder on 26/05/2019 12:12:01

Howard Lewis26/05/2019 12:15:36
2035 forum posts
2 photos

If the arbors are long and slim, you could make up a Roller Box, as used on Capstan or Turret lathes.

Rollers Leading locate on the round raw material, with the cutting tool just behind, (3mm or s less).

Rollers Trailing locate on the newly turned diameter. For this, to set up the box, you need to turn a short diameter close up to the chuck. Once set, you can than extend the raw material, (which does not have be round ).

Recently, I made up a Reversible Roller Box, which can be used in either configuration, but so far remains unused!

The rollers are small ball races. Having a Micrometer barrel available, that is used to control tool advance.

Howard

Nigel Watts26/05/2019 17:12:46
26 forum posts

Lots of fantastic tips and ideas - thank you.

My current project is the restoration of a once rather complicated London made bracket clock dating from around 1710. About half the mechanism, including the quarter repeat, the alarm and the original verge escapement, is either missing or altered. I have used Fusion 360 to model the missing mechanism and have now started the process of making the components. Here is an example drawing I have produced from the Fusion software. The dimensions are rather spuriously accurate.

Putting bits back into an existing clock involves a slightly different process from making a new one in that the pivot holes in the plate are the givens rather than the dimensions and modules of the wheels and arbors.

For the wheels i am using cast yellow brass to get the right colour but for the arbors I am using silver steel. Originally they would have used hand forged shear steel but this is not available as far as I am aware.

Once the pinions have been cut on the solid arbors I need to taper the arbors from the middle towards the ends, which I would like to do with a graver if I can master the technique.  The tapering is a characteristic of the style of the time the clock was made and will also allow me to fit the brass wheel collets by riveting rather than having to use solder,

 

Edited By Nigel Watts on 26/05/2019 17:17:08

Edited By Nigel Watts on 26/05/2019 17:18:11

Edited By Nigel Watts on 26/05/2019 17:18:43

Edited By Nigel Watts on 26/05/2019 17:19:16

SillyOldDuffer26/05/2019 20:35:41
4396 forum posts
956 photos

Posted by Nigel Watts on 26/05/2019 17:12:46:

...

For the wheels i am using cast yellow brass to get the right colour but for the arbors I am using silver steel. Originally they would have used hand forged shear steel but this is not available as far as I am aware.

...

Fascinating job Nigel. Always good to see old machines restored sympathetically.

I've seen something close to Shear Steel being made on a couple of TV documentaries where they demonstrated how historic steel was made. There are people in the UK and US who know how. The furnace could be built in a back garden but there's a fair bit of skill needed. The iron is made as pure as possible and then the slag is beaten out of it. TV makes the next stage look quick, but my 1875 source quotes an iron bar 7/16" thick taking 9 hours to convert, and mentions the importance of the carburising heat being kept uniform throughout, not easy. Once the raw steel is available purifying is done by repeated folding and hammering - an enormous amount of forge welding, ideally repeated twice to make best quality 'Double Shear Steel'.

Although very expensive to make my 1875 book isn't enthusiastic about the result: 'Steel so produced cannot be said to be perfect' and 'During the last few years the manufacture of this steel has been limited, mechanics preferring a soft cast steel, which is much superior...'

The amount of time, effort and skill that went into making the original clock is amazing. I reckon the 1710 maker would have killed to get his hands on your cheap but lovely Silver Steel!

Dave

Nigel Watts27/05/2019 20:02:26
26 forum posts

Ground a tool along the lines in the photo. Its working very nicely!

old mart27/05/2019 21:59:45
182 forum posts
15 photos

Have you thought of getting a straight shank ER16 collet (1-10mm) that has collets in 1/2mm increments to use in a normal 3 or 4 jaw lathe chuck. The absence of a draw bar would be an advantage, as you could slide the work in and out.

Nigel Watts07/06/2019 09:27:48
26 forum posts

I have just finished making a drawbar for the tailstock of my ML10, with a 3/8* Whitworth thread on one end to engage with the 2MT collet, into which I will be able to fit some watchmakers' runners. The thread was much more difficult to cut and fit than I expected and the result is a bit rough, but works. I used the back gear (for only the second time ever) and a very slow speed to minimise the risk of the tool crashing into the larger diameter part. My V tool was a little less than 60 degrees, i.e. about the correct 55 degrees, but I hadn't appreciated the need to shape the teeth with a curve at the top and bottom, so it took a long time until it engaged (in the end I skimmed a bit off the diameter to blunt the peaks).

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