Best use of soft jaws in the chuck?

[smfr]

I have a Bison 4-jaw combination chuck that I use most of the time, and I was lucky enough to get a set of soft jaws for it. The soft jaws are unhardened steel, I think, but are pretty tall. I'm wondering how best to put the soft jaws to use.

I was thinking of drilling and tapping two holes in each jaw, so that I can bolt aluminum bits onto each jaw, which can then be machined in-place to hold tricky parts. The Al parts can be easily replaced when damaged or worn.

How do other folks use soft jaws?

 

[n4zou]

When I was working as a Machinist we would bore them out to the exact size of the stock that was to be machined so there would be zero run out. Just place a peace of material back in the chuck behind the soft jaws and clamp down on it. Then just bore them to the desired size. You can also leave some material forming a stop. This was common practice before CNC machines came along.

 

[smfr]

Just to add a bit more, these are marked as "soft jaw blanks". This is what they look like:

 

[Blogwitch]

To me, having soft jaws on an independent jaw chuck is defeating the object of using soft jaws. Which is to have a set of jaws turned perfectly concentric to the lathe spindle, so giving great accuracy of holding the piece part

On the independent, as soon as you touch one jaw to tighten onto the job, you have lost concentricity of the bored jaw set, and you would then have to resort to using a clock to regain concentricity, but you would have much more jaw support for the workpiece.


John

 

[Noitoen]

It looks like a "mixed" independent/fixed jaw chuck to me. Never seen one of those, there seems to be the normal chuck's thread behind the independent jaw adjustment screw. ??? ??? ??? Maybe I'm seeing wrong. :-[

 

[Ken I]

I agree with John - I don't see the point. If you bore them, they are still going to be all over the place after retightening.
O.K. maybe for not marking parts ???

Some three jaws have tapped holes facing forwads at the tips - convenient for screwing in mild steel hex bolts which you can then bore as soft jaws for short parts etc.

Regards,
Ken

 

[Tin Falcon]

This may be a bit of a review because most of these points have been covered.
the advantages of soft jaws.
zero run out.
greater holding power do to increased contact with part.
allows for a positive stop on short parts.
Tin

 

[mocaquita]

Wow, this is the first time I've seen a chuck with a combination scroll and independent jaw adjustment built in! The best of both worlds. A cool alternative to set-tru chucks! Concentricity as close as you can indicate.

There are many reasons to use soft jaws, but many times they are used to hold parts, that because of their shape, would to hard or impossible to hold in regular jaws.

The jaws you have are designed to be machined as desired to fit the part. I assume they are hard to find and/or expensive, so I agree with you in modifying them and topping with aluminum and use that as your machineable soft jaw.

 

[n4zou]

It looks like a "mixed" independent/fixed jaw chuck to me. Never seen one of those, there seems to be the normal chuck's thread behind the independent jaw adjustment screw. ??? ??? ??? Maybe I'm seeing wrong. :-[

If you loosen/tighten jaws 1 and 2 leaving jaws 3 and 4 alone concentricity is maintained. Using a 4 jaw chuck this way will actually maintain it's concentricity better than a 3 jaw chuck. All three jaws are moving on a 3 jaw chuck whereas 2 jaws are moving on a 4 jaw chuck as long as you are only using jaws 1 and 2. A torque wrench is also required.
Using layout die mark jaws 1 and 2 on the chuck.
Before the soft jaws are to be cut use a torque wrench on all 4 jaws setting all to the appropriate torque. At the job shop this torque setting was provided by the shops supervisor. Today the TQM department (Total Quality Management) provides this torque setting. Use your own judgement in your shop. Just make sure you use the exact same torque setting each time and enough pressure to ensure the part(s) to be machined are held properly.
After the jaws are machined jaws 3 and 4 are not to be used, only jaws 1 and 2 are used and are to be set to the same torque setting that was used on all 4 when they were machined.

 

[moconnor]

Hello,

This is a universal or scroll chuck with the capability of adjusting the jaws independently. For example, if you had multiple rectangular parts to bore a hole off center, you could adjust the jaws independently and then use the scroll to open and close the jaws with very good repeatability. A very cool, but expensive chuck.

Regards,
Mike

 

[kvom]

Your idea in the OP seems good to me. I have a 3-jaw chuck with 2-piece jaws that I use exclusively with aluminum outer soft jaws.

 

[smfr]

This is the 5" chuck on http://www.toolmex.com/Products/BrowseResults.aspx?CatID=549, but I got it for $200 on eBay (only 3 bids on the auction). I got the blanks from the same seller for $11. ;D

I don't tend to rely on the repeatability if I open the jaws with the scroll, then clamp down again. But it's useful to loosen the workpiece with just one turn of the key.

It's a little heavy on my Maximat, but it's the one that tends to stay on the machine.

I can see that soft jaws are useful in the 3-jaw to ensure concentricity. I was thinking more along the lines of using soft jaws for awkward work holding. For example, with something like a cylinder cover that I'd otherwise make a fixture to hold, I could just modify the Al soft-jaw tops in place. They would eventually get chewed away with various modifications, at which point I'd just make a new set and screw them on.

 

[smfr]

Well, here's what I ended up doing. I drilled and tapped the blanks for two M8 screws, and made aluminum caps 1/2" thick with 1/2" overhang:



They aren't quite finished yet; I need to trim them to width, make sure they are a snug fit on the jaws, and put a chamfer on the inside corners so I can clamp the jaws down some more:



If I were doing this again, I'd move the inner screw hole out by 1/4" or so to avoid interfering with profiling etc in the center. There's room for another threaded hole between the existing holes if I need one.

Simon

 

[n4zou]

I remember the machinist in the tool room making those for all the lathe chucks and mill vises in the shop. He would keep at least two sets on hand for each chuck and vice in the shop. He would also demand to see the job order requiring the use of soft jaws. Sometimes He would walk out to the machine and check to see if the last set of soft jaws issued to that machine could be reused. Woe be it to you if you could reuse them! I don't know if he was trying to save money or was just being lazy.

 

[kvom]

Rather than cut the back off the soft jaws, I'd suggest leaving them full depth, and countersink the bolts. That way you can use the whole length of the jaws and rebore many more times w/o hitting the bolt heads. You can also hold much larger diameters without extending the ends of the jaws beyond the chuck body.

Trimming the width isn't necessary; the more jaw on the work the better.

 

[Swifty]

If you machine an angle on the sides of the soft jaw that contacts the part, this will allow the jaws to close down even further and you will be able to hold smaller parts.

Paul.

 

[petertha]

Hmm.. now I have to ask a dumb question because I hav enever taken one apart. On chucks like these, can you unscrew the jaw bolts & mount sacrificial bars acting as soft jaw material? Or is it a completely different set-up for soft jaws?

 

[mu38&Bg#]

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[smfr]

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