Agreed.
Sounds like a cheaper solution to try before getting a whole new chuck.
I had no problem with the spindle thread, unlike the face plate that came with the 9x20. I could not get it on the spindle. The vendor sent a replacement which they swore fitted OK on one of their spindles. Same problem. I had to re-thread both plates and it was not a subtle process of a few thou. I had to take a fair bit off.
Michael Koblic, Campbell River, BC
Barely...There are much better chucks for woodworking.
They have two versions - one which needs inserts and one which is threaded 1"-8.
Oddly enough I do it because of advice I received on this very group from someone about two years ago :-)
Michael Koblic, Campbell River, BC
This sort of thing?
Jim Wilkins mentioned pie jaws.
A quick flit through Google turned up more questions than answers:
1) Pie jaws are available only for chucks with 2-part jaws, right? 2) The reason for soft jaws is ease of machining to fit the part? 3) What is the minimum size of the step that will hold a 3/16" part securely (in aluminum)? 4) Should one be able to get pie jaws that will hold larger OD than the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck is just too small to hold the 4.5" piece on the outside (hence the 4-jaw use).Michael Koblic, Campbell River, BC
I believe your eccentricity is due to one edge of the ring being lifted up, you then get an angular section of a cylinder instead of a circle, an ellipse in other words. Has been a kink written up in old machinists' books to bore elliptical holes.
What you list as workflow wouldn't be my choice if I wanted concentric inside and outside. I'd start with flat stock, roughing out a blank on the 4x6 first. If your flat stock is that much out or you need machined surfaces, face off both sides first. Precision ground stock isn't that expensive, saves facing and possible "wedgies". With the blank still stuck in the chuck, bore your hole to whatever limit you care to. Make up a mandrel for between centers to fit your hole, I'd make up one with a shoulder and a retaining sleeve. Now finish off the outside to size. If you're doing multiples, make your mandrel long enough to put a bunch on and finish them all at the same time.
It always bugs me when somebody reverses the process. It's always much easier to get a precision hole bored and finished FIRST, then reference everything from that. You get much better results from putting a part on a mandrel between centers than trying to indicate a part in a chuck. Concentricity is pretty much guaranteed that way.
I've not seen any metal lathe supplied with such a flimsy 4 jaw chuck, even the 7x has a better chuck than that. Didn't cost as much, either. Reminds me of some of the faceplate add-ons I saw in The Model Engineer ads circa 1899 for treadle lathes. I wouldn't trust it on a wood lathe, either.
Stan
Generally, yes, but creativity can provide a way to use soft jaws that are inserted on hard jaws. Not the best of all worlds, but a solution to a difficult problem.
Correct, but there are more reasons that just that. For one, if you are running volumes of parts, they offer the ability to remove and replace parts on a continuing basis without losing registration with tooling. They are also capable of holding concentricity and parallelism to a half thou, or less. That often isn't close enough for critical work, but is within acceptable guidelines for the vast majority of work one will encounter. Not to detract from acceptable standards, but a half thou is virtually nothing. The human eye can't discern .003" runout---so it's very good in the scheme of things.
Hard to say, but you can hold a part with 1/16" of surface, assuming you don't crowd the cut. The nice thing with soft jaws is you can hold the part as deep as you wish, leaving only the amount of material showing that might require an edge break. For a 3/16" thick part, I'd feel very comfortable holding it by 1/8", and taking the cuts that may be required. Remember, that part is held captive---it can't do anything but come out--so it's very stable, even with modest chucking pressure. With pie jaws, you can get down on the part quite nicely without fear of distortion, although it is possible to bow the part outward in the center from excessive chuck pressure.
The big problem you'd have with soft jaws is that small chucks normally do not have what I call master jaws---those two piece jaws that make it all possible. If you do have them, you can design a soft jaw that will hold the maximum swing of your machine---all without trouble. That's the beauty of soft jaws. They can be built to conform to your needs, so long as they don't exceed the capacity of the machine on which they're used. A good example is a set I made to turn some 4" aluminum tubing. Fairly heavy wall at about 1/2", but the pieces were more than a foot long. Made 8" long jaws, installed a stiffener to prevent the ends from springing and ran the job with no issues.
Hope some of this helps.
Harold
I just uploaded a photo of mine:
This shows the standard mounting geometry for top jaws:
You could mill the mortice and tenon in the back of the jaw blanks. The radial mortice is about 1/4" deep so I'd look for at least 3/4" thick stock.
If your initial jaw depth isn't enough to hold the work you just turn the recess deeper. As long as the bit pushes the work against the chuck you don't need much. Just don't forget and make a cut towards the right.
jsw
It is a thought, however, to get a 0.007" error on 4.5" that way (without any flexion) the disk would have to be tilted over 3 degrees. Even I would have seen that :-)
I am still voting for the "lay chips" pattern :-)
Roger Shoaf suggested something essentially identical. I can see the benefit of doing the ID first even using pre-fabricated blanks as I do. I am still confused as to the benefit of a mandrel vs. 3-jaw chuck.
I am not sure why the need to indicate if the piece is clamped inside the hole by the 3-jaw self-centering chuck. Concentricity within
0.003" is fine for this application.Which I guess is the reason they throw it in with the lathe. It is of comparable quality to their face-plates and the stand the lathe comes with for that matter. Not to mention the work one has to do on the lathe itself.
Michael Koblic, Campbell River, BC
Hm. I am not sure I am *that* creative...
Would steel jaws not do the same?
Good enough for me.
OK
My Taig 3-jaw has two-component jaws. I have turned the aluminum ones to suit a similar job on a much smaller scale. I do not think I have seen 4" 3-jaw scroll chucks with two-component jaws at the usual vendors. I have not looked elsewhere.
Very much so.
Michael Koblic, Campbell River, BC
Am I looking at pie jaws which have been made but not finished to any particular work piece?
Won't the master jaws move *out* to give you more range? Am I missing something?
I had a look through the site and a couple of others. I see no two-component jaws available for anything smaller than a 5" 3-jaw chuck. So I guess the two immediate questions are:
1) In the overall scheme of things is a 5" 3-jaw chuck with master jaws and a suitable back plate a better investment than a good quality 4-jaw independent chuck (with a back plate)? 2) Is a 5" scroll chuck too big for a 9x20? I do not mean the swing but the weight, inertia, load on the headstock spindle etc.I take it you are talking about a cut along the z-axis? I guess that would occur if I was backing the boring bar out of the ID...
A thought occurred to me: Say one wants to turn something close to the swing of the 9x20 (actually 8.75") - say 8" disk. If I get pie jaws that just clear the bed (8.5") would a rim of only 1/4" be enough to hold such a piece? Just thinking ahead to the next project...
Michael Koblic, Campbell River, BC
I didn't see any smaller than 5" with separate top jaws.
FYI in case you trip over one used as a doorstop, 2 jaw chucks adapt well to custom top jaws. At their simplest a left+right hand screw operates the two jaws, but having made a 4 jaw out of a slotted rotary table faceplate I think making a chuck is too much trouble.
jsw
[ ... ]
There actually is a small 3-jaw scroll-back chuck with two-piece jaws. Not quite as nice as the larger ones, but satisfactory for a lot of things. This chuck comes with the Taig (or Peatol in the UK) lathe.
This web page shows everything about it except the mating surface of the master and top jaws.
And on *this* page:
Scroll down to part number 1050 (the chuck with un-machined jaws).
Scroll a little further (to 1051) and you will see a second set of jaws.
And yet a bit farther (to 1052) and you will see jaws which make a good pie jaw setup. (Extruded aluminum for those).
The one disadvantage of all of these is that they only have a single groove milled the length of the underside of the top jaws, which keeps it from twisting -- but does not form truly precise repeatability of grip. The bigger ones have a second groove at right angles to the first on one part, and a matching projection on the other part to set the radial spacing as well.
The total diameter of the chuck is 3-1/4", with a 3/4-16 thread for screwing onto the spindle.
So -- the question is whether this is large enough for your needs. The prices are certainly reasonable.
Oh -- in item # 1060, they have a 4-jaw universal (scroll-back) chuck. That is new to me.
If you back up to 1030 (the 4-jaw independent chuck) -- I've taken one of these and modified it to mount on a different lathe (The Emco-Maier Compact-5/CNC) with a very different mounting system.
Enjoy, DoN.
Yes -- if you can machine them. One-piece jaws are often hardened and ground to finish dimensions, so you can't turn them to achieve the accuracy you need. But two-piece jaws often have the top jaws a mild steel (actually probably more often than aluminum for the bigger ones).
For that matter -- that is also how the master jaws for two-piece jaws are made -- hardened and ground, so the wear is concentrated on the replaceable jaw parts.
[ ... ]
Have you seen the pie jaw blanks for the Taig? I just posted pointers to a web site which offers them.
The question is whether you could adapt the Taig 3-jaw to your larger machine. (Or whether you could put a riser block in the Taig and use the 3-jaw with the pie jaws for your workpiece size.
Good Luck, DoN.
That's more than enough material to hold a piece, even if the jaws are made of aluminum. Key to success is not having an overly long piece, which can be levered from the chuck, or to take excessive cuts, which may do the same thing. Also, there's nothing preventing you from running a live center with a plate on the item being held. That keeps it from pulling out of the chuck under adverse conditions. You'd put the center drilled plate against the part, then start the machine. Back off the live center ever so slightly, so the plate can find natural center as the part rotates. Assuming you have machined a proper pocket for the part to be turned, it holds the part securely against the back of the pocket. Only enough torque on the handle of the chuck needed to drive the part, with no fear of the part coming out.
If the part must be faced, you'd have to use good judgment as to how hard to tighten the chuck. It's all just a matter of having a little experience. You get a feel for these things pretty quickly.
If you do explore soft jaws, make sure you understand how they should be applied. If you don't follow the simple rules, they don't work worth a damn. No better than hard jaws in most cases.
Harold
snip-
I trust you mean steel jaws that can be machined, not the factory hard jaws.
Yes, they can do the same, and may well be made of steel. Some of my soft jaws are. Because you preload the jaws before they're machined, and because you machine an identical profile in reverse, the parts are nested such that they are oriented properly. No worry about perpendicularity, and rarely a concern of more than a half thou eccentricity. They can be even closer, depending on several conditions. The point is, even a rather worthless universal three jaw can yield surprising precision when soft jaws are applied.
If you're interested in reading a document I prepared years ago, pertaining to the use of soft jaws, please ask and I'll provide a link. Not promoting myself here, just trying to share what I learned in my years of using soft jaws.
Harold
It's pretty simple. Any time you can avoid using a mandrel, you're likely better off. That would be especially true when attemting to turn what is, essentially, a large, thin washer. Chatter is an ongoing problem, as is driving the part without slippage. By preparing the OD of the part first, easily accomplished by pressing the part against a plug, using a plate with a live center. Once the OD is machined, the part can then be chucked in soft jaws and faced, bored and reversed with no issues. Best of all, chucking the OD pretty much eliminates chatter, especially if the part nests on a proper cavity. Soft jaws solve all the problems of holding large diameter thin pieces.
Harold
Yes.
I am very much interested.
Michael Koblic, Campbell River, BC
It's boring and ID on such piece that had me worried.
[...]Michael Koblic, Campbell River, BC
You said it! The piece I described certainly does that. I have got rid of the chatter by putting a spacer behind it.
I see your point, too. OTOH you gotta love the diversity of opinions on this group :-)
Michael Koblic, Campbell River, BC
snip-
Here's the link.
Should you attempt to register, do provide the reasons you'd like access to the board. Marty approves all registrations.
Good luck! I think you'll find the thread very enlightening.
Harold
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