Smart & Brown Model L lathe help required

[AJAXParticipant @ajax]

I’m having problems with a Smart & Brown Model L lathe lever-operated headstock, specifically the collet-only version that uses dead-length collets 5159.

I purchased the lathe knowing there was an issue with the collet-closing mechanism. The headstock appears to be incomplete and messed around with and I’ve subsequently obtained a nearly identical headstock in the hope to understand how they work and hopefully get at least one of them working correctly.

One headstock has two “hooks” to push (or pull?) the collet-closer tube, and the other headstock lacks these hooks but may have used two dog-point screws to achieve something similar. Curiously, the closer lever is moved to the left in order to push the closer tube to the right and thus press the collet closed. That makes sense but I can identify no part of the mechanism that achieves this reversal of direction and I’m feeling fairly stupid to have drawn a blank on something that I would have assumed obvious.

I have a scanned manual for several different headstock versions and I may have a variant of the PDH headstock. Despite having dismantled and reassembled the collet-closer mechanism many times I am still unable to fathom how it should (and occasionally does!) close the collet. My headstocks do not feature the “obsolete toggle mechanism”.

I’m hoping that someone here has experience with this collet closer mechanism. If so, please let me know and I will try to frame some appropriate questions that will hopefully elicit the information to get this working.

Thank you.

[AJAXParticipant @ajax]

The “hooks” and their respective slots are highlighted.

[AJAXParticipant @ajax]

[AJAXParticipant @ajax]

More photos

 

[DiogenesParticipant @diogenes]

Are you sure the handle swings to the left to close the collet?

..I beg your pardon for questioning but answers don’t seem to be coming thick and fast, and from the section it looks like it should be swung towards the right to push the closer over the taper..?

[AJAXParticipant @ajax]

<p style=”text-align: left;”>Your question is entirely appropriate but I can say with certainty the lever must be moved to the left to close the collet as that’s exactly how it operates when it is working, and currently it is! The erratic behaviour may partly be down to some stickiness in the mechanism or a need for fettling individual parts however that does not explain to me how the mechanism actually works. It has been suggested to me there must be some magic going on somewhere!</p>

[old martParticipant @oldmart]

I would guess that your collet system requires very careful adjustment every time it is used and there is no work diameter difference tolerated without re adjusting. Our model A at the museum uses a simpler collet system not intended for production work like the model L. My only experiance with that style of collet system was with Myford lathes, with the handle at the right hand end.

Do you have any chucks for it? TheL uses the same 1 3/4 x 8W spindle thread size as the model A.

[Julie AnnParticipant @julieann]

On my repetition lathe it is the same; move the lever to the left, away from the headstock, to close the collet. When making production parts it feels natural. Pushing away to close the collet needs more force than pulling to release.

Old mart is correct; the setting is critically dependent upon the work diameter. Even a few thou difference in work diameter can be the difference between loose work and too much force needed to be able to close, and lock, the collet. On my lathe there is a split knurled chuck adjusting nut, on a thread on the spindle, next to the operating lever within the headstock to set the closing force needed.

I would hazard a guess that the fluted aluminium knob on the end of the shaft is an adjustable stop for setting the position of the clamping mechanism to achieve the required force to clamp the work.

Assuming all the parts are there according to the sectional diagram I suspect the mechanism just needs a clean and deburr. Tolerances are quite critical for correct operation. My manual warns against setting the locking mechanism too tightly as the locking levers might get broken.

Julie

[AJAXParticipant @ajax]

I have two complete headstocks. One has a threaded nose to which I could mount a backplate + chuck if required. The other headstock is collet-only for production use. It is a straightforward job to swap the headstocks over, no worse than swapping between horizontal + vertical on my milling machine.

[AJAXParticipant @ajax]

Old Mart, no I don’t have any chuck and backplate made up for it at present but I can easily make one on my other lathe. You are correct about the spindle nose thread.

[AJAXParticipant @ajax]

Thanks for the suggestions everyone. I’ll see how it goes. I can always strip it down yet again if it plays up, but it seems to be working fine again right now.

[old martParticipant @oldmart]

Nice to know that it has started working again. Are you sure that the plain end of the spindle shown in your last photo is not simply screwed onto the 1 3/4 x 8W thread, the diagram of the Mk 2 shows it as removable.

[AJAXParticipant @ajax]

Quite sure. This headstock doesn’t feature the 1.3/4 x 8W thread. But I have another headstock, currently stripped down for refurbishment that does.

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