what are the proper procedures for boring soft jaws?
do you bore the jaws to the exact dimensions of what you
are turning, or do you make them slightly over size?
how do you measure the size of the hole you are boring?
thanks in advance for any replies
Be careful taking Harold's word on things. He's pretty long in the tooth
and maybe getting senile.
Seriously, I read the article and would only give Harold grief over one
thing, his preference of steel. He did give me a positive response when
I suggested 7075 for soft jaws, so maybe there is some hope for the
To add some emphasis to the sizing of your jaws when boring, *if* you
don't get the bore to exact size of your parts, miss the size under, not
over. If undersize you will get 6 contact points, the edges of each jaw.
If oversize you only get 3, and those are a crappy 3.
I owe you an email, H. Maybe later tonight, still quite busy.
You tell the old hippie (Michael) that he can't weld new tops on his 7075
jaws, so they aren't as good as steel ones, if for no other reason, that
one. It's a lot of work to make a set of soft jaws, so why not make them
from steel so you can recycle the base pieces by welding on a new top piece
when they've been used up? I think I may have mentioned that in my long,
dragged out post. Damned hippie. It's a hard enough job being a Grampa
without having to constantly correct you!
Just like a flaky old hippie, always running late.
If Michael had my years (oh! so many!) of experience, he'd know that boring
soft jaws slightly undersized is not a great idea. When you grip your
nicely finished parts with the sharp six corners of the jaws, your finished
parts get marred. While they grip better, such as for roughing, I'd
personally err on the side of too large, if for no other reason, the jaws
don't damage your finished parts when you turn them over to do the second
finishing operation. If you miss by only a thou or so, it doesn't really
make a great deal of difference. The lesson to learn is to use a spider,
discussed in my original post, so you can readjust the jaws slightly and
re-bore them, achieving the desired size and not taking off much in the
process. The spider is a wonderful tool, be sure to make one.
In truth, you don't want the jaws either too big or too small. When you're
doing fine work, boring the jaws to the desired diameter is critical to
success. If you go either above or below targeted size, you'll often
introduce concentricity problems because the scroll on chucks isn't
necessarily dead true. When you hold size, not only on the jaws, but on the
parts you intend to chuck, you end up using the same place on the scroll
from part to part, which gives you the best chance of holding concentricity.
Good luck with your soft jaws. Best holding device going for lathe work!
(Looking forward to the email, M, but don't lose sleep, get the work out
I'll stick with Aluminum, you did a bunch more turning than I ever will. You are
correct about sizing the bore, I spaced back to the 60s and did not mention the
roughing aspect. But I don't understand the comment about marking the parts, I
have seen none of those on my parts for so long I have forgotten how they get
there. Finish looks the same all around. Dang arm is sore from patting my
shoulder. Back to making chips.
BTW, heard the one about the pot and kettle? Hippie indeed.
The really sneaky trick is to chuck up an slightly undersized innie (a slug),
make a ring, drill and tap the jaws, chuck the work again lightly, attach the
ring with screws very tightly, knock out the work, reset the pressure, and bore
with the pressure, direction, and diameter the same as they'll be for the work.
Did I get that right?
For an innie, the ID of the ring clears the unfinished work OD. For an outie,
the OD of the ring clears the ID of the work.
Just remember, finish the jaws with the direction and pressure the same as for
the work, and finish them to a close fit, maybe even size-to-size, with the
surface they will grip. This is just not useful for doing a one-off. There's
too much time invested.
Doug Goncz (at aol dot com)
Replikon Research, Seven Corners, VA
1200+ original posts at:
What you stated is correct, but so is your statement correct about the
procedure of the ring being too labor intensive to be used for a one-off
application. Properly used, soft jaws can economically be used for a
one-off, you just have to use better (read that faster) procedures.
There are no benefits using your system aside from boring jaws for holding
parts by the interior. Using a spider to set the jaws for external
gripping is extremely fast and allows for miniscule adjustments of the jaws
so very little of the jaw needs to be machined in order to get them running
properly. There is nothing to make, you just grab the spider and adjust it
for the job at hand.
Using a ring with tapped holes in the face of jaws doesn't permit fine
adjustment. If you over cut the jaws, there is no way you can make a minor
adjustment so you can re-bore to proper size. I would not recommend that
procedure for anything but internal gripping, and even then you'd likely
have to make the ring to fit the job, otherwise you'd have to remove a lot
of jaw material as you went from one size bore to another.
I have no magic bullet for internal gripping. I've done it, but have used a
ring of proper diameter to load the jaws. Sadly, I haven't come up with a
device of sorts to replace the ring.
I thought I just might ask from someone that knows, and that sounds
like you. I've asked my buddies in the tool & die, and they have
never seen/heard of one. A couple of years back, I E-bid on a
circular thingy that the seller had no knowledge of it (a la Babin?).
Turns out I didn't either! I thought I might make a quick centering
device mounted to the outboard end of the lathe spindle, for holding
longish stuff through the spindle. Anyway, for 10 bucks plus shipping
(I was the only bidder) I got something bigger than I expected, and
too big for THAT job.
It is a ring with three scroll driven spoke "jaws". I don't have it
to hand, but it may be about 1" or so thick, has an OD of about 10",
an ID of about 8" or less, and the "ID" ends of the jaws have a
knurled boss (1/2" Diameter??) perpendicular to jaw motion. It's got
a nicely chemically blackened "gun barrel" finish, and made by "ROYAL"
So, I tossed it under the bench for a future-as-yet-to-be-determined
project. Then later I saw something that made me realize it might be
for either truing chuck jaws, or lo and behold, the "bosses" mentioned
are a perfect fit for the mounting holes in the soft jaws of the chuck
on my 15" Colchester. So maybe it is that "spider" you and Doug
An now (finally) my question. No way I want this thing turning at
normal turning speeds. The only way of applying pressure to tighten
it in place is the hand operated scroll, ie no "chuck key". It
would make shrapnel look like kleenex if it came loose. But I would
think that turning it at less than the turning speed for the eventual
workpiece wouldn't be right either. Can you enlighten me as to it's
exact use? I have maybe 10 sets of soft-jaws available, but I've
never used any of them.
Take care. Always enjoy your posts.
If I'm following your description (good chance I'm not, so send me a pic on
the side if you'd like, which would make it easier for me to suggest if I'm
right), the adjustment that is made by hand would be strictly for adjusting
the position of the restraint, which would be the fine tuning of the spider
I mentioned. That function permits the location of jaws for optimum
machining, i.e., locating the jaws for minimum stock removal. The
pressure of holding the device in place would than be applied by the chuck
wrench, via the chuck, as the jaws are tightened against the spider. At
this point, one would run the chuck at the proper speed for machining. The
spider is unlikely to move easily, and it is not receiving any cutting
What you have may be this device!
The advantage of your device over the one I use is that yours will work for
chucking in either direction, inside holding or outside holding. If it's
what I think it is, I'd give my interest in hell for one like it for my
Graziano. Turning chuck jaws for internal holding is much more difficult
(labor intensive) without a device such as yours.
If you haven't used soft jaws yet, I think you're going to be pleasantly
surprised when you first do. They are truly the magic bullet for holding
most anything in chucks. There's no way I could get by without them, even
for one-off's. Regardless of the time it takes to prepare a chuck to hold
a specific item, soft jaws still are usually the best choice. The very idea
that you machine them to the same diameter permits tighter chucking without
distortion, and the smooth jaws don't mark your part(s). So many
advantages with soft jaws, so few with hardened jaws.
Thanks, Brian. I've enjoyed sharing what little I know. I was given
special attention when I struggled, by one person that saved my job when my
probationary period was not successful. I feel I owe a debt for this
wonderful person's gift, and I try to repay it by helping others. Funny
thing is, some of them don't much like hearing it! Ah well! Others do,
and they make it all worth while.
It's always a pleasure to read your posts, too, Brian. Love your upbeat,
I think you should just give up on the outlock and just send it to me. I
think it would go real nice with my 16" Pratt & Whitney lathe. By the way I
have run outlocks at 2500 RPM and I have had no trouble at all with them.
J&L calls them "True Jaws for power chucks". Look in the number 73
catalog on page 1088. Item number QDR-75230J. We have always called them