rmac wrote: ↑Wed Jan 05, 2022 7:13 pm
Are lathe chucks standardized enough that it's common to buy soft jaw blanks rather than make them? If so, how do you know which jaws to get? I don't think my chuck says much more on it than "Made in Poland".
The chuck you need to have for this is one where the jaws are two pieces, a top and and a master. Only the top is soft.
There are several systems, but the most prevalent are American standard tongue and groove and serrated (usually goes by the brand name Kittagawa). The serrated ones seem to be used more on power chucks.
If you measure the hole distance, the width and the size of the key, you will find a match in any lathe chuck catalog.
There are options on the size of the jaws for a given chuck.
If you are going to machine them to hold work that goes thru, you want a lot of material at the end so that you can get a lot of machining operations out of them.
If you are going to put part in the face of the jaws (think holding a train wheel in a recess cut in the face of the jaws) you might want deeper ones.
There are even pie shaped jaws that are great for holding thin round parts.
rmac wrote: ↑Wed Jan 05, 2022 7:13 pm
Aside from the time savings, is there any reason to buy the soft jaws rather than make them?
I made a set for my lathe, and it was an interesting exercise, but the reason I did it was that they were too expensive to buy.
Now you can get them cheap from usshoptools.com .
You can also buy them on ebay.
rmac wrote: ↑Wed Jan 05, 2022 7:13 pm
If you're only planning to run a few parts, is there any reason to use steel for the soft jaws rather than aluminum?
I made mine out of aluminum and I haven't found a reason why they would not work. I do have a pile of steel ones. I suppose most of it is the time to machine them
rmac wrote: ↑Wed Jan 05, 2022 7:13 pm
When you're machining the jaws to hold a specific part (after they're installed), it seems like you'd need to preload the chuck in order to keep everything stable. I guess you just put something behind the soft jaws so the master jaws clamp down on it. Correct?
You can take a nut, drill and thread on three of the sides (alternating) and install socket head cap screws. Hold that with your finger and stick it far enough in the jaws that the screw heads will contact the master jaws and clamp the jaws down. That will give you your preload. Note that you should set the screws to preload the chuck just slightly smaller than the finish size you need so you don't need to machine a half inch off your soft jaws.
You can get one of these to hold the jaws:
They are a couple hundred, but you might find one on ebay for less.
The bee's knees is one of these:
- TL_JawBoringRing[1].jpg (9.25 KiB) Viewed 7058 times
You set the chuck to just undersize, install this in the holes, crank it to where the pins are tight in the holes and then tighten the chuck jaws. The original is the Revellica Outlock and they are almost a grand. US Shop tools sells these ones for about half that.
rmac wrote: ↑Wed Jan 05, 2022 7:13 pm
Another thing I read recently (nothing to do with soft jaws) was that you should always use the same socket on a scroll chuck to do your final tightening. That didn't make any sense to me. If that's not just a myth, what's the reasoning behind it?
If you have three pinions, you will find thru experimentation, that one of them is more accurate and more consistent. Mark that one with a dab of paint and use it. Check it every once in a while, because as it wears, another one might end up better.
Steve