turning long small diameters

[Speedy Builder5Participant @speedybuilder5]

Farm Boy again.  Making the valves.  3/8 dia valve head with 1/8″ dia x 1.4″ long stem in stainless.

Lathe:- Boxford 9″ dia

I have some stainless which turns OK but trying to turn the long stem as the workpiece flexes is giving unacceptable run out.  Do you step turn say 1/2″ to diameter plus 0.001″ then turn the next 1/2″ until required length, then burnish with emery cloth?

I think 1/8″ is too small for travelling steady.

Ideas please.

Bob

[JasonBModerator @jasonb]

I just use a BS 0 ctr drill and put a very small hole in the end so I can turn valve stems between ctrs. Never had a problem with them not sealing. Use 303 stainless

[IanTParticipant @iant]

In the past I’ve drilled a small bushing held in my tailstock drill chuck to the materials diameter and used that to support the material…a form of between centres turning.  I also have a tool-holder with a ‘guide’ that can be drilled to the (un-machined) diameter of the piece and where the cut happens as the metal is fed through. Can’t recall ever using it though. Seemed useful when I purchased it!  🙂

IanT

[Speedy Builder5Participant @speedybuilder5]

Thanks for the ideas gents.

Bob

[DalboyParticipant @dalboy]

I turned mine a little at a time they seem OK. Or you could do as Andrew Whale did and make it in two parts

See THIS

[bernard towersParticipant @bernardtowers37738]

small dia turning tool, easy to make

[duncan webster 1Participant @duncanwebster1]

Here’s one

I’ve also seen one with a brass block with a vee cut in the end so you can adjust it to different diameters. Basically it is a turning tool with a built in travelling steady. As others say, you go from full diameter to finished in one cut.

Hemingway do a kit as well, which looks a bit easier

[duncan webster 1Participant @duncanwebster1]

<p style=”text-align: left;”>It probably will struggle going from 3/8 to 1/8, stick to Jason advice</p>

[David SeniorParticipant @davidsenior29320]

A couple of techniques worth considering:-

One is to turn it down in 1 pass. Might work if you can set a very fine feed. Many years ago I saw the technique demonstrated at a Model Engineering exhibition – I think it was on the Myford stand with a 254 lathe. The principle is that you have the stiffness of the starting diameter, rather than the more slender interim diameters. It’s a bit buttock-clenching at first! Maybe worth testing with a very short standout from the chuck first to see whether the cut works.

An alternative to the tailstock live centre is a tailstock revolving chuck. This will need a sacrificial extra length to be cut off afterwards, but in theory it will restrict the bending of the thin section better than a centre.

[Nigel BennettParticipant @nigelbennett69913]

+1 for IanT’s use of a bush in the tailstock chuck. If you’re turning slender diameters, using a centre can impose significant buckling loads on the workpiece – and it’s likely to get hotter as the cut proceeds if you aren’t using flood coolant. A bush gives exactly what’s needed – radial support. Some lubricant on it is a Good Plan, too.

[JasonBModerator @jasonb]

I’ve not found bowing to be a problem due to either excess pressure or expansion, I don’t have flood coolant but will just add a dab of neat cutting oil. Seems to have worked for about 20 pairs of 4-stroke model valves and plenty of other items too.

If you are worried about heat expanding the metal and making the work bow it is easy enough to slacken the tailstock lock and adjust between cuts. I might do that on a longer part like a tapered column where the expansion of a longer item would be greater than something short like your valves.

[Speedy Builder5Participant @speedybuilder5]

Mission accomplished, I followed Jason’s advice by turning up to a centre.

 

[Speedy Builder5]

On Speedy Builder5 Said:

Mission accomplished, I followed Jason’s advice by turning up to a centre.

 

Good job did you remember to make one a little longer than the other

[Speedy Builder5Participant @speedybuilder5]

Yep, 0.10″ – need to machine the ports in from the sides of the cylinder head without bogging it all up!

As to the cylinder head, I went for M4 cap head screws and as the top screws came mightily close to the screws which hold the Water Hopper, placed them 40degrees either side of the vertical (instead of 45), and made pockets in the head such that the head of cap screws are sunk level. I that makes sense.

Bob

[Bo’sunParticipant @bosun58570]

It might be worth having a look at Joe Pieczynski’s channel.  It’s the sort of thing he’s likely to have a technique for.

[bernard towersParticipant @bernardtowers37738]

This is using the simple tool from Hemingway. 0.250 down to 0.0625, the tool is dcgt tip

[egaParticipant @ega]

bernard towers:

Is that a cross slide lock that is seen in the bottom right of your second photo?

Presumably, the tool tray is “just visiting” ie not a permanent fixture?

[bernard towersParticipant @bernardtowers37738]

blimey your observant yes its a crosslide lock, block of steel with two holes vertically and two custom bolts to replace the myford items and a threaded hole horizontal to the fixing bolts with a socket grub screw and brass pad, verypositive as its on the plain dovetail side not the adjusting screw side. The bits and bobs tray is in MEW somewhere and yes its a slide in slide out item.

[bernard towers]

On bernard towers Said:

… its a crosslide lock…

Thank you for elaborating that. I can see that it is more positive than the alternative and probably more accessible depending upon the position of the topslide. Not an obvious option for me as I have a full length wiper between saddle and cross slide where your lock sits.

Another candidate for this position is the ingenious click stop described by the late T D Walshaw.

[bernard towersParticipant @bernardtowers37738]

My son has the TDW version on his trileva, when I can get to him I will post a photo as it doesn’t seem to be avail on the net.

[old martParticipant @oldmart]

I have a revolving centre with interchangeable ends. Some are made with female cones in them.

Another way to make that valve would be from two pieces of metal, the shank being ground silver steel. The valve head could be riveted in place.

[bernard towersParticipant @bernardtowers37738]

Is this what you are looking for ega.?

[egaParticipant @ega]

bernard towers:

That is indeed a version of TDW’s screwcutting depth stop as described in WPS 28.

Your son seems to have taken good care of the bed on his Trileva. I wanted one rather badly before my Super Seven came along but having since added a VFD I suppose I shall now manage without!

I noted the neat ball handle lock on the topslide.

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