Machining soft jaws

[Peter Cook 6Participant @petercook6]

[Peter Cook 6Participant @petercook6]

My 3 jaw chuck (Taig) has reversible machinable aluminium jaws. So far I have only trued up the centres, however I now need to machine some steps in the jaws to get hold of larger items.

I seem to have three options.

One is to bore them from the inside, which produces concave inner faces If I clamp the centre down on something fairly large before cutting, the concave faces will be fairly shallow. This is how they are trued in the first place.

Reverse them and machine from the outside to produce convex faces on the steps.

Or try and mount them in the mill (either as a set, or mount the vice on the rotary table?) and cut flat faces on the steps.

I don't think I could get all three located accurately enough on the mill to get the precision needed. I am inclined to go for reversing the jaws and producing convex faces as that seems likely to give me more consistent contact surfaces (theoretically tangential) at different openings, but I thought I would ask first.

[JasonBModerator @jasonb]

Turn in situe and that way there are going to be totally true, doing them the opposite way round or in a mill will be unlikely to give cconcentric running.

I would suggest you just bore for the job in hand rather than make a set a random steps that way you get full contact so no marks to the surfac eor if holding something like a gear with odd number of teeth the grip is spread over several teeth on each jaw. Also just make the cut shallow then it will allow thin work to be held with something to register the back against so it does not wobble.

Edited By JasonB on 11/05/2021 13:02:37

[Martin KyteParticipant @martinkyte99762]

Thats not the idea with soft jaws. They are soft so you can machine them true for fixed diameters not so they will not mark the part.

The idea with soft jaws is to machine to fit the size of the part you wish to hold. So for example if you wanted to hold a thin 1 inch disk truly concentric hold a small bar right inside the jaws (sub flush) and tighten. Bore the tops of the jaws 1" dia a little under the tickness of your part. When you release the jaws you will be able to hold your disc true to it's circumference and as it is back against the recess in the jaws with no wobble. As the chuck has not been removed from the lathe and the recess was bored at that diameter everything will be spot on for as many discs as you need to machine but only for that diameter.. You need to do this each time for different diameters and shapes of part.

regards Martin

PS Jason beat me to it.

Edited By Martin Kyte on 11/05/2021 13:09:25

[Paul LousickParticipant @paullousick59116]

Soft jaws are normally machined in situ on the lathe to give a precise fit and centre for a prticular job as shown in this Youtube video **LINK**

Paul

[DiogenesIIParticipant @diogenesii]

..Yes, what these men just said..

Some further discussion & drawings here including new tops for 'used-up' soft jaws;

Harold Hall Using Soft Jaws in the 3 Jaw Chuck

[Peter Cook 6Participant @petercook6]

Thanks for the inputs – something to think through.

The core problem is that the Taig 3 jaw doesn't come with "normal" jaws. It only has aluminium replaceable jaw faces. which can be reversed on the steel bases.

As it stands the maximum diameter it holds is about 40mm. I don't use it often as most work I do fits in the ER Collets that the headstock holds. Occasionally I would like to hold something a bit bigger. I do have a four jaw independent with steel stepped jaws that I use when required, but was thinking about modifying the existing jaws to in effect give me a quick "normal" 3 jaw.

I have considered a Sherline 3 jaw, but Mill Hill don't stock the ER thread (1042) version, and when you factor in shipping costs the cost delivered to the UK is horrendous. Dean Williams has made steel tops for the Taig 3 jaw, and that is probably the final route I will take. Looking harder both the Sherline and Dean's version have convex faces – so If I go that route, that is the way I will go.

Thanks again for the inputs.

[old martParticipant @oldmart]

Firstly, you need to eye up the way to machine the jaws removing the least ammount of metal. They should be clamped in the direction that they will hold the job to take out any slop or backlash. I have dozens of soft jaws, and even when they are close to worn out, there is the possibility of turning the stumps into master base jaws with bolt on tops.

[HOWARDTParticipant @howardt]

Grip a diameter in the jaws while machining, this will ensure that the jaws don’t rattle about and are forced to the correct side of the scroll wether for inside or outside holding.

[Nigel McBurney 1Participant @nigelmcburney1]

The photo is good it shows what the Taig chuck is all about, I would suggest making some more sets of 3 jaws in alloy or mild steel.they could be kept in numbered sets drilled s they could be attached to the lower steel jaws and for position accuracy a locating dowel could be used provided the lower steel jaw can be drilled and reamed.So two sets could be made with similar jaws to conventional 3 jaw chuck and another kept in hand as spareThe usual soft jaw use is for holding a part or a batch of parts very accurately,also good for holding thin washers,and despite the comments above, they can be used to prevent damage to the workpiece,for instance on a larger chuck ,a workpiece with a fine thread and larger than an available collet can be held safely and accurately in soft jaws. Industrialy it was quite usual to see soft jaws with special jaws welded on, EG like pieces of steel tube which had a large area of grip to hold thin tubular workpieces.

[Peter Cook 6Participant @petercook6]

Posted by Nigel McBurney 1 on 11/05/2021 14:49:17:

The photo is good it shows what the Taig chuck is all about, I would suggest making some more sets of 3 jaws in alloy or mild steel.they could be kept in numbered sets drilled s they could be attached to the lower steel jaws and for position accuracy a locating dowel could be used provided the lower steel jaw can be drilled and reamed.So two sets could be made with similar jaws to conventional 3 jaw chuck and another kept in hand as spare

That is the base plan. I do have a spare set of soft jaws which I plan to keep for use as "soft jaws", and will probably one day (when my round tuit arrives) make a set of steel jaws. This was the first step to machine a set of jaws like a conventional chuck. Hence the question.

The comments have raised another "interesting" thought. Some time ago I came across a thread on 3D printed soft vice jaws. 3D Printed CNC soft jaws for work holding | Model Engineer (model-engineer.co.uk). I wonder if …

Thanks for all the input. Always enlightening.

[Rod RenshawParticipant @rodrenshaw28584]

Howard T makes a good point about gripping a stub of something round in the back of the soft jaws while machining them to fit a job.

However if the job is a ring, and the jaws will grip it by pressing outwards on the inside of the job, then for the task of machining the jaws to fit the work, the round stub needs to be replaced by a ring. The ring goes around the outside of the set of soft jaws so that the jaws will be pressed outwards ( to take up any slack in the scroll) rather than inwards. I hope this is clear, it does make sense when you think about it.

The idea of keeping lots of numbered sets of soft jaws works very well. Soft jaws are essentially sacrificial items but the more sets you have the more likely you are to have a set which is nearly right. And the less you have to machine off to get a fit for a new job, so they last a long time.

Rod

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