Modding a fixed steady

I want to work on the end of a length ( around 400mm) of 3.5" round steel bar. Trouble is the fixed steady supplied with the lathe won't accommodate more than 57mm despite having an aperture of 100mm:

The reason the fingers won't retract further should be apparent from this pic of another steady from the same manufacturer:

If the fingers are long enough to meet in the centre and have enough meat to engage with the bore in the casting, they can't retract fully.

The eagle eyed among you might have noticed that the bores in the casting for the two 'bottom' fingers in the second pic are longer than in the first - that's true and those fingers do indeed retract almost fully - but the top one is the same as in the first pic, so that doesn't help much. Maybe they redesigned the casting at at some point and I got a new bottom part with an old top?

Anyway, apart from this particular problem the steadies have always been a PITA to use. The bores in the castings are poorly machined - they are mostly either sloppy or too tight. The grubscrews running in the finger keyways which do double duty in preventing the fingers from rotating and locking them are impossible to set to give smooth adjustment even on the fingers where the fit is OK. It's a horror story!

So to the question. Can anyone see a way of modifying the steadies to remedy these deficiencies? I'm wondering about sleeving the bores and remaking the fingers with a better way of adjusting them, but that's about as far as I've got so far.

Any comments welcome*.

Robin

*Except throw away your lathe and buy British. It's a fairly recent Far Eastern version of the 12x36 GH design and there's a lot right about it for the money.

Edited By Robin Graham on 01/07/2019 01:35:30

What's stopping the fingers from sliding all the way out? That grub screw on the outer diameter of the steady? If so, remove the grub screw and use just the one in the middle? Maybe put a third grub screw in between the two existing ones to clamp the finger?. You'd have to lose the screwed adjustment, but just set the fingers in position manually and then lock up the grub screws, similar to the way a Myford steady works with its slotted fingers.

Or make shorter fingers. You could probably get away with just a flat down the side instead of that slot for the grub screws to locate in.

Or tap a thread down the bores of the three holes and make threaded fingers like this one:

That puppy is rock solid. Much much more so than the standard puny Myford item. Make the tips from hard bronze so they don't wear flats on there.

Edited By Hopper on 01/07/2019 04:56:46

Just use them without the screw adjuster and the small grub screw that the adjuster is retained by.

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Seems an expedient solution for an occasional job

That said: There is obviously an underlying quality problem, so; in the longer term, a full redesign/rebuild would seem appropriate.

MichaelG.

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[quote]

The bores in the castings are poorly machined - they are mostly either sloppy or too tight. The grubscrews running in the finger keyways which do double duty in preventing the fingers from rotating and locking them are impossible to set to give smooth adjustment even on the fingers where the fit is OK. It's a horror story!

[/quote]

Then you are relying purely on the grub screw in the finger groove to stop them moving.

In the original design, the lower grubscrew acting in the groove (the one with the locknut on it) is purely for rotational location purposes. It should be dog-pointed and a good fit in the groove. A nylon tip might be a good idea so a little axial friction can be applied to the fingers but this screw should never be used for locking. The reason for rotational fixity is so the bronze tips can have line contact with the work rather than point contact.

Right now, the axial thrust of the fingers goes into the threaded adjuster and is resisted only by the top grubscrew in its groove. This is the worst part of the design. If you are to reengineer it, some kind of bronze thrust washer here to resist the axial force is needed. This then lets you use the upper grub screw (or replace with knurled screw for toolless use) for locking purposes, just stopping the threaded bit from rotating loose due to vibration.

Ream out the bores to the nearest size of ground MS or silver steel bar, make two sets of fingers (one same length as standard, one shorter so full capacity is possible) with keyways to fit dog point grubscrews (may need to fettle the grubscrews as well for concentricity of dog and constant diameter).

What you have is a good starting point that just needs a little easy tweaking.

Not quite what the manual says, if you don't lock them in place they could work loose.

Make a short bronze tip for the few times you need maximum capacity or make one that screws in and can be variable length. Rebore and sleeve the casting if you want to use the existing fingers or make new fingers. If the single grub screw retaining the finger is considered inadequate make another one on the other side. The finger control screw could be remade with less meat on the screw side of the groove and a longer thread. The body could be extended at the top boss which is perhaps the easiest but most risky in modifying the casting.

Make a second set of shorter fingers (by 22mm) with new adjusters of appropriate length so that the full range could be used, but needing selection of parts? No more hassle, then, than storing and changing inside or outside chuck jaws.

While at it, make the necessary modifications first (so replacing the existing fingers with new ones that fit the improved bores). You would then at least have a steady which worked reasonably over the whole range possible.

Or cut the existing fingers down shorter to accommodate large diameter jobs, and make some longer bronze extensions to fit in the ends for smaller jobs.

Three simple "L" shaped brackets drilled one end to be held using a screw in the outer grubscrew threaded holes and the short leg of the L long enough to engage in the adjusters slot will move them all out further so you can use them when turning large diameters and no need to alter fingers or adjusters. If you want to improve play then just sleeve the holes and have clearance holes in the sleeves for the inner and outer screws.

Alternative would be a top hat sleeve with a second screw hole further out that the adjuster grub screw could be moved to when doing large work and just use the existing grub screw position for smaller work

Hoppers idea is likely good but sleeves into the bores would likely prevent those long fingers retracting sufficiently.

But plenty of options to modify a piece of poorly designed junk into a more useful bit of kit. Good fixed steadies are not a cheap item. Urine poor ones are just that. At least this poorly designed steady looks like it is a robust item.

That is very similar to the fixed steady I bought to use on the Smart & Brown model A. A base was made to fit the bed of the lathe. The reason I bought it was that original ones cost an arm and a leg. The shortcomings were exactly the same and I shortened the original fingers to allow 100mm stock if required. I also made a set of fingers with sealed ball races to span 14-80mm. It is certainly sturdy enough to be useful. With the use of a mill, making the fingers is easy.

If the original fingers are shortened, they will not reach smaller diameter stock, unless an extension is made for them.

Thanks all for replies - lots of useful suggestions.

JasonB - I confess that your first idea of just letting the fingers poke out without the constraint of the top collar hadn't occurred to me. Wood and trees I guess. I had a quick go and could probably make it work for this job, but it's frustrating because whichever combination of steady/fingers I choose, there's always at least one finger which binds and has to be 'adjusted' with a mallet.

There come a point (for me at least) when I have to decide whether to go for a lash-up to get the job done or take a step back and fix the problem. Increasingly I find I'm going for the latter. Obviously the point is to get to the finished part, but I actually enjoy machining (I don't do this to make money!) - it's the setting up which bores/frustrates me. So anything that reduces setting up time is good!

As I have two steadies there may be possibilities for cutting down the screws to make one for big stuff and one for smaller. I'm not too worried about the fingers winding down to zero as I can get <= 37mm through the spindle. I'd still have the problems of what seems to be a poor design badly implemented though.

I like the look of Hopper's screw-in fingers, that would be a relatively easy mod and rock solid is good enough for me. I'm not sure about threading the (possibly crappy) cast iron though, so might want to sleeve. The current fingers are 18mm diameter - do you reckon sleeving down to 12mm screws would be OK? Or 14?

Robin.