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turning a 120 degree valve spindle point

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Tony Martyr19/02/2010 15:29:29
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My steam regulator design calls for the seat of the valve stem to be a point of 120 degrees included angle. I can't remember having to do this before on a Myford and because the top slide only swivels to 45 degrees (90 degree included angle which would probably work as well) either I am missing an obvious answer or I have to be inventive.
How is a 120 degree point machined on a Myford 7?
Tony
David Clark 119/02/2010 16:03:51
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Hi There
Turn the tool upside down and machine to 30 degrees cutting the back of the job.
regards David
 
Tony Martyr19/02/2010 16:07:55
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David
I just knew the answer would be embarrassingly simple!!
I blame the heavy ingestion of soldering fumes this morning on the dulling of my senses.
Thanks
Tony
JasonB19/02/2010 16:24:21
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Won't that give a 60deg included angle, the topslide needs rotating to 60deg whichever direction you turn the work and if it only goes to 45 each way it cant be done that easily.
 
Jason
Jeff Dayman19/02/2010 16:34:41
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If the angled face is short, just take a lathe tool with a straight face and angle it in the toolholder  to 60 deg off the lathe axis, and cut straight across the lathe Y axis to make the valve conical face. You can set the angle of the tool face with a protractor or 60 deg setsquare if you have one.
 
JGD
 
PS I made a sketch and posted it in photo album "120 deg spindle cutting"

Edited By Jeff Dayman on 19/02/2010 16:47:00

mgj19/02/2010 17:42:21
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You probably have a gauge - its called metric/Unified screwcutting gauge - to grind the tool accurately if you don't have such a tool already.
 
The tool is called a standard metric or unified screwcutting tool, and you use one side of it as a chamfer tool. 
 
1/2 x 60 =30. Yes.  and 2x30 off one end will give solid angle of ....  wait for it...  wait for it 120deg.
 
Come on team - we seem to be losing the wood for the trees. ..  or making a very simple thing complicated.
 
No one is going to offset anything.
 
(Wise to make a d bit at exactly the same time and setting in Silver steel. Harden and temper and use to form the the seat. Few seconds with Brasso or any other fine lapping material and you should be away.

Edited By meyrick griffith-jones on 19/02/2010 17:44:31

Edited By meyrick griffith-jones on 19/02/2010 17:45:16

Edited By meyrick griffith-jones on 19/02/2010 17:49:18

David Clark 119/02/2010 18:16:06
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Hi There
I meant 30 degree from straight in.
I am sure you can get that on a Myford.
You might have to take one of the bolts out or clamp the outside of the top slide from another tee nut but I am sure it can be done.
regard David
NEIL SMITH 119/02/2010 19:12:15
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Remove the compound rest spigot and clamp the comp. rest towards the back of the cross slide so that the handle is in fresh air,set the angle with a protractor or the 30 deg. blade from an adjustable square.The clamps are just two plain pieces,the front one is longer than the back,using the appropriate tee slots.
mgj19/02/2010 20:07:22
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Course you can David. Its just the mirror image of the screwcutting position. . Slacken, lift over the dial wheel, and set 30. So the topslide looks fairly across the lathe, and you are cutting towards the tailstock - ish. But that will probably run out of space - see below. So actually one will have to set up 180deg around from there with the handle in the middle of the lathe and cut across and towards the headstock. on the 30 deg line. As Jason indicated. NOT the 60 deg line.
 
Some may be thinking 60. 60 deg off centre is what you LEAVE. 30 deg is what you cut off or it was last time a 120deg solid angle appeared on a drawing. So no-one has to turn a topslide round to 60 deg - only to 30 (off the x axis).
 
If you cut on the 60 deg line you'll take 120 deg OFF, leaving a 60deg solid or included angle. 
 
However this rod is what .375 dia tops - .188 radius probably in stainless, so you don't want a lot of protrusion in front of the chuck or fixed steady if that's what was used.
 
Its a 5 second chamfer job.
 
More likely on a smallish loco which Tony is making its roundabout 3/16 dia or about 90thou on radius. Even less do you want much protrusion. It takes longer to mount the QC holder with a screwcutting tool mounted, and turn on the coolant than it does to apply the chamfer, and there is absolutely no cause to disturb a carefully parallel (set by clock) aligned topslide..

Edited By meyrick griffith-jones on 19/02/2010 20:10:49

Tony Martyr22/02/2010 17:37:27
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The answer was a variant of David's first reply
By winding the topside right back it is possible to turn it to near 60 degs and still have over an inch of useful traverse when the lathe is run in reverse and the cut is taken from the back of the work.
I also managed to silver solder the boiler stays on the inside of the firebox today - a job that is quite impossible, with my kit, unless the whole boiler, tube and firebox external, is lagged with fire blanket. When I followed the idea of hanging the tube section through a hole in the base of the brazing hearth all the heat went out through the same hole!!
My motto for today is 'If I ever had the time or money or energy to build another loco I now know how to do it'
Tony
mgj22/02/2010 18:59:38
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Glad it worked for you Tony. I have a similar job to do this week. I bought a blowdown valve which does not have a captive core and got a "compulsory" for it on the boiler test. So I shall have to replace it with one of the right type before the steam test. .
 
It will have a 120deg tip, because that's optimum. Being decayed imperial, I don't have the required 60 deg threading tool (mine being 55deg ground for Whit/ BSF) so thats no good.
 
But I do have a 120 deg countersink. 
 
And a boring bar holder of the right diameter. 

Edited By meyrick griffith-jones on 22/02/2010 19:01:03

Tony Martyr22/02/2010 19:24:16
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Meyrick
I am puzzled by the fact that you can buy a blow-down valve that does not comply with the requirements of a boiler test. I was intending to buy mine from Blackgates or similar and had assumed that they consisted of a ball held shut by a screwed 'ball holder'.
Is this the design you are having to follow?
Tony
Nigel McBurney 122/02/2010 19:30:43
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hi   Meyrick   why do you need a top slide set up with a clock,parallel turning should come off the saddle not the top slide.
mgj22/02/2010 20:38:11
1017 forum posts
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Tony - blow down valves. Yes - so am I, (surprised!) and a bit peeved!  I don't know how long the rules have been in, but if it passed with the old type, then I understand it can continue with the old type. (I believe). Anyway, I suspect it's become important to specify "captive core". Looking at them most of the handwheel valves are- you can see the nut, that hold the core captive. But some are not.
 
The type I'll make will just be a standard needle type valve into a seat, but it will have a flange on the central rod, with a nut going over the od. That should do it. I may get exotic with the seat - I have some Delrin doing not very much so I might make a replaceable seat. Be a pleasant bit of designing over the lunch break, and a nice bit of turning and silver soldering, so I'm quite looking forward to it in a way.
 
Your ball held in a ball holder is a good idea too, but I think the needle valve arrangement is more conventional. If it doesn't work too well, I'll do a ball job. Thank you for the idea.
 
 
Nigel. On the Myford the whole topslide has been replaced with a topslide which is tenoned into one of the tee slots and is set exactly parallel.(The Radford design) On tht 1337 the topslide is set exactly square with a clock.  The reason is that setting to length for a shoulder, I can set short upto a depth stop, do all my machining, and hen advance the tool last few thou (2-3) and wind out to take out any toolmarks on the shoulder, without upsetting any bearing seat on the shaft. 
 
Its just a way of working that suits me because I can set lengths very accurately using the feedscrew  handwheel and then topslide on the Myford. (you can't do that trick with an ordinary Myford topslide, because it fouls the tailstock  The Radford design is offset.
 
 
On the 1337 the DRO will add or subtract Z0 and Z1 automatically, which makes it very easy. Just bring it up on the apron handwheel, and finish setting length with the topslide (on what is quite a chunky apron/saddle) and get a combined reading in one window.
Nigel McBurney 118/03/2010 19:57:31
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hi had an idea,if you have a swivelling vertical slde,mount it on the cross slide table facing operator,set slide to required angle  ,mount tool by clamping it to v/slide table.then feed downwards toward lathe centre lineI just tried it on my super seven before I wrote these notes,alternatively perhaps on the seven  the top slide could be clamped vertically to a suitabe angle plate mounted on the cross slide  the slide set to the required angle in the other plane and again the slide fed downwards, basically this follows the arrangements on some auto lathes where the all the tool slides feed radially.  I think the angular faces of valves and seatings are better turned with single point tool rather than formed with a wider tool.

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