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machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most.

Tag: soft jaws

Soft Jaws

The bronze gears which I cast yesterday were cut off the tree with small bolt cutters, band saw and hack saw.   Then a belt sander to reduce the daggy bits.

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The gears, and the tree trunk and branches which will be remelted.

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The faces needed to be flattened in the lathe, but how to hold the rather thin, delicate, irregular gears?

Soft jaws.

Soft jaws made of aluminium, and exactly machined to match the external diameter of gear teeth, so there are multiple contact points, and minimal chance of damaging the teeth.  I made these soft jaws ages ago, for just this sort of job.

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The soft jaws are machined to exactly fit the workpiece.

The soft jaws may be used multiple times, machined to shape each time.  Very handy in this situation.

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The larger gears are good.  I silver soldered some extra material on one of them for the shaft, then turned the shaft to size .  But, holding the small pinion gear is more problematic.  I will need to machine a soft jaw with a taper to hold the teeth.  Next session.  I should have anticipated this situation and designed the gear with a shaft to be PLA printed as one piece.

 

 

SOFT JAWS FOR LATHE

I have recently made two sets of soft jaws, and tested them.  One set was successful and the other set was not.  Read on to see what made the difference.

The purpose of soft jaws is that the jaws themselves are turned to the exact size and shape of the workpiece,  and the workpiece should therefore be held perfectly concentrically.  It should be possible to remove the workpiece from the lathe, and to replace it accurately.  It should also be possible to hold very thin disks, which was what I aimed to do in this exercise.

The first set of soft jaws was made for a 200mm 3 jaw chuck.  The aluminium cylinders were bored to fit snugly over the last step of the jaws, and held in position with cap screws.   I cannot remember where the idea originated.

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These soft jaws fit onto existing jaws, and are held in place with cap screws.  Here shown clamped onto a brass cylinder, ready to have the rebates turned.

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Showing the turned rebates in the soft jaws, ready to accept the workpiece.

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The workpiece is a 3mm disk, 38mm diameter.  The rebate is only 0.5mm deep.

The method was successful, allowing the workpiece to be faced, but during a second pass, one of the soft jaws came loose, and the workpiece dropped out.

I suspect that the cap screws did not allow enough purchase on the hardened jaws of the chuck.  Also, the workpiece was positioned beyond the end of the chuck jaws, and it acted as a lever on the soft jaws, working them loose.

I think that this method would work if the workpiece was held closer to the face of the chuck.

The second set of soft jaws was made for an 80mm 3 jaw chuck on my Boxford CNC lathe.

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The aluminium soft jaws are bolted to purchased, non hardened, jaw bases which fit the chuck grooves and have teeth to engage the chuck scroll.  Here shown after turning the rebates ready to accept the workpiece.  The rebates were turned while the jaws were tightened against an appropriately sized cylinder.

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The workpiece held securely.  The face has been skimmed, and the edge bevelled.  The engraving was CNC’d on the mill, earlier.  Subsequent turning produces a very clean, sharply defined engraving.   The workpiece is held in a 1mm rebate.

It can argued that aluminium is not ideal for soft jaws, because it is too soft.   I do intend to make another set of soft jaws from mild steel, for use with steel workpieces, but I will continue using the aluminium soft jaws when machining soft metals such as brass.

And here is another idea which I spotted on you tube.  Not soft jaws, but soft covers.  Click on the arrow to watch the video.