New vs Old Chuck Dimensions

Hi all,
I've been wondering about why newer chucks and backing plates universally seem to be so much thicker than older ones. I bought a 4-jaw chuck, supposedly direct mounting, which actually showed up with a 7/8" thick backing plate already bolted to it. Given the pretty sizable depth of the chuck itself (about 3" or so) and the large shoulder on the threaded portion of the backing plate, the chuck uses up 5+ inches of bed. Looking at older chucks, it seems they were all much "thinner", and if not direct mounting, the backing plate was a smaller diameter disc with not all that much mass. Why the change? Is the newer practice because the setup is that much more rigid? I own cheapo chucks, if I bought higher quality chucks would they be as bulky and "oversize" in this dimension? Even looking at pictures of large old lathes, great big chucks seem very narrow proportionally to the ones I have. I've been thinking of removing the 4-jaw from its backing plate and remachining the backing plate to reduce its size. This would gain me a little bed space (not much, granted) and reduce the weight of the thing a little. It seems an awful heavy weight cantilevered way out from the spindle nose. What gives? i have been using it like this for a couple of years, with no apparent ill effects, but it really bugs me, and recently created difficulty in turning a relatively long piece because of the loss of available bed (if I'm explaining that well enough to get my point across).

A similar issue is the coarseness of the threads on the jaw adjusting screws in my 4-jaw chuck. This makes centering a workpiece very difficult because the tiniest rotation of the jaw screw has a large affect on the work. Do higher quality chucks have finer threads on these screws making them easier to adjust?

Eric

Eric, I dunno if more expensive chucks would be thinner or not, probably depends on the manufacturer. Better chucks would certainly have a smoother screw action. It certainly wouldn't hurt to thin down your back plate a little. Threaded spindles usually require a clean up cut to true up the chuck anyway. I also have a cheap 4 jaw but the screws are pretty smooth. Luck of the draw, I guess. Disassembly & a careful de-burring of the parts might improve things a lot. Hope this helps, Ed

It does seem like the new chucks these days are much larger than their older counterparts. I fitted a new import 6" 3-jaw on my SB9 last year, and it is much bigger, thicker, heavier, etc than for example than the older 4-jaw that is original to the lathe. I think it has become the style to make chucks with larger jaws. My neighbor fitted a 3" 3-jaw to replace a old worn one, and the diameters are the same, but it is almost twice as long. These import chucks seem to be fair quality, and I can't figure how they can make a 6" 3-jaw with harden and ground jaws for $60, and it is still holding within .003 a year later. The other trend seems to have been to move away from chucks with the threads cut right in them, now all chucks seem to need a back plate, making them much longer and heavier. The one benefit of my new longer chuck is that is puts my carriage farther down the bed, somewhat out of the worn spot. Greyson

Old 4-jaw


New 3-jaw

Yep, that's exactly what I mean, Greyson. I agree, the one side benefit is that the work is then almost out of the worn spot on the bed. But jeez, there's so much wasted travel! I think I might remove the chuck from the backing plate and "shrink" the backing plate. There's enough room in the threaded spigot to trim that down a fair amount and If I reduce the thickness of the backing plate that will seriously reduce the mass of the thing.

Ed, it's no so much that the screws are difficult to turn, just that the threads are so coarse that trying to dial work in to less than .001 is exceptionally tedious because the tiniest adjustment makes for a big movement in the jaw. Guess that's just te nature of the beast.

Eric

I recently fit a new Bison 3-jaw to my 10k. I followed Paula's lead (see stickies above) and machined away as much of the new back plate as possible to minimize the additional mass and to minimize the over-hung length. I think it's far worse to have the over-hang than the "benefit" of being on less worn ways. I made at least half of the new plate into chips. Very happy with the result.

John.

Personally, I have wondered this for a while. You might try posting this in the "General" category. If you won't, maybe I will

There is not a manufacturer difference with this phenomenon, in my experience. I have intentionally sought out older Buck brand chucks for this exact reason. The way older Adjust-Tru 3 and 6 jaws are almost half the weight and 2/3rds the depth or more---look at the 1434 and 1462 models. These are from before Buck even began the "AT" designations on their chucks. The same is true for Pratt Burnerd. Old 4-jaws (mostly made for the Myford lathes in 4") are only 1" thick and weigh 3.5 lbs.

The only chuck manufacturer I know of that offers quality slim designs today is Maprox (Feinmechanik Zürich, Kranzspannfutter, Markiergeräte, Maschinenbau Zürich, Messmaschinen, quick-action chucks). Their "ZF" style chucks are wonderfully designed in this respect. The bore is kept large in relation to overall diameter, and the jaw width is what it should be. A 3ZF 110mm (~4-3/8") diameter chuck weighs less than 4.5 lbs and is just under 1-1/4" thick. Unfortunately, the retail price of $1395 basically eliminates it from anyone's toolbox.

I am surprised this question didn't find more responses. It is a very valid concern, IMHO, and a point worth mentioning.

Arthur,

I completely agree with you. And those Swiss chucks sure are nice...but at that price, it won't happen.

Here is the link to that thread I mentioned that Paula wrote on machining a back plate. It's a great read.

Link-->> http://www.practicalmachinist.com/vb/south-bend-lathes/machining-chuck-adapter-130129/

Hey, about those older thinner Buck chucks, can you please give us a little more information on them? How old are they, what model numbers? are they on Ebay? Can you post some pictures of yours?

John.

John,
I don't know how exactly how old they are, but I have a Buck catalog which lists back to the original "AT" models. They are not in it. They also predate the numbers Buck list for outdated chucks that correspond to new mounting plates. One of mine was bought as NOS. It included an inspection certificate dated 3-26-94.

All are 4" chucks. I realize this may be marginally too small for a 9 or 10" SB, but I am using a Schaublin 102 with 8" swing and 5C spindle. I have to go back to the old Buck models because they do not make a 4" chuck today. Also of note when looking at the pictures, these are all Adjust-Tru chucks. There is only one pinion to turn the scroll. All other screws are for precision centering and not for closing/opening the jaws. So even if they look like a "normal" new chuck, you must remember to compare to a new chuck with centering screws, which is always a deeper body.

Buck 1434, 3-jaw. 4lbs 10oz, 1.720" thick (body, not including jaws)
Buck 1462, 6-jaw. 4lbs 6oz*, 1.720" thick (*the thru-bore was enlarged to 1.25")
Pratt Burnerd Int. 1520-11001, 4-jaw independent. 3lbs 8oz, 1.130" thick

...and the Pratt pictures. One reason I like the lower weight and smallest chuck for the job is that I use 5C mounting plates. The idea being, I can turn on the lathe and move the whole chuck to a second operation without re-truing the work.

I must note on the Pratt Burnerd Int. 4-jaw that it was not produced as anything other than a self-proclaimed "light-duty" chuck. The jaws have a very thin arch which reaches down to engage the adjusting screw. I have had issues with them cracking here. The design is similar to an old "Craftsman" model 4" 4-jaw which I have never tried. I doubt if they would hold up much better. Still, regardless of that issue, this is my most-used chuck. When I get the new (old) Buck 4-jaw I will have to report back. http://www.practicalmachinist.com/v...e-wanted/buck-4-4-jaw-chuck-w-adaptor-200391/

As for the Maprox chucks, they really are just super-precise, grown-up versions of the Sherline chuck. (It goes without saying that Maprox has made chucks longer than Sherline, of course) I would buy a 4" or 5" Sherline chuck in a heartbeat if they made one. Sherline 3-Jaw Chucks The 3.1", however, is a bit too small and/or the lack of thru-bore ruins its use mostly for me.

Thank you Arthur.

The 3-jaw Buck in picture #1 and #2 is beautiful! Is that the NOS one?

Do these old Bucks have the model number marked on the chuck? I ask so I would know if I found one on Ebay. There is one on Ebay right now but it does not seem to be an adjust-tru.

Do you know if Buck made a 6" version of the low profile model?

Congrats on getting the one form GDL264

Thanks again, John.

These are all the same as I posted:
4" Buck Chuck 3 Jaw Chuck 1434 T900 U.S.Made, Nice - eBay (item 120540425760 end time Mar-14-10 18:01:52 PDT)
Buck Adjustru Chuck, 4", 3 Jaw, 1 3/8-8 U-449-5-A - eBay (item 380213804958 end time Apr-08-10 14:21:27 PDT)
ELLIS DIVIDING HEAD W/BUCK ADJUST TRU 4" - eBay (item 130374039795 end time Mar-19-10 12:10:08 PDT)

I have to admit they are not that hard to come by. There's just about always one of them on eBay or found through used dealers. Remember, though, these are all 4" chucks. I don't know which size you prefer or need. Yeah---the 3-jaw is my NOS one. Also note, my NOS came with both sets of jaws. Be aware of which jaws you buy when you buy used. They almost never come with both sets.

You may be mistaking the listing you mentioned earlier as not Adjust-Tru because there is only one pinion. So if it is not rotated to show it, you mistake the rear centering screws for the pinion screw (Notice the hex vs. square socket cap) And yes, the model number is clearly stamped on the front face of the chuck.

Sorry, one last note. You mention a 6" chuck. It seems to me that between 5" and 6" is an unusually large sequential leap in size and weight.

I checked with the current Buck catalog online, and was able to find the appropriate vintage models to mine in 6" size: Model 3634 is the 3-jaw and Model 3662 is the 6-jaw.
Buck 6" 3 JAW SELF CENTERING LATHE CHUCK - eBay (item 190323145431 end time Mar-18-10 12:17:45 PDT)
6 in. Buck Adjust-Tru 3-Jaw Chuck - eBay (item 330395389286 end time Mar-15-10 12:00:49 PDT)
6" 6-Jaw buck lathe chuck adjustable body - eBay (item 120532676085 end time Mar-20-10 06:13:31 PDT)
Those are mostly crazy on price---especially the last one!!--- but you can see them at least.

Also found in the catalog, Buck does still make 4". Who knew?! But compare the specs: 2.36" deep and 9lbs for the solid, 6-jaw 4" model. That makes the new model double the weight and 37% more deep.

Thank you Arthur. I'll keep my eye out.

John.

Just an update on this discussion. I recently came across this: Arc Euro Trade - Lathe Chucks If you scroll down, you will see a new line of "slim body" chucks made by Zither, an Indian company. I know nothing of the quality of these chucks, but the spec's are great. Price is okay too.

From what I have seen of old and new chucks, the old chucks were designed for one particular spindle nose and proportioned for that spindle size, such as 1 1/2-8 or 2 1/4-8. They also were built a bit lighter than the current chucks, perhaps because the expected cutting force was less (no carbides, ceramics or hard metal turning).
My 24" Logan came with an old worn-out 3 jaw chuck that was half the depth of the Bison I replaced it with. The backplate of the oldie contained the pinions, and the front plate was only about 1/2" thick, just enough for the rather shallow jaw slots.
Having said all that, I think the main reason is economic. The old chuck style required a separate, complex, integral backplate for each spindle nose. With the modern chuck you make one chuck and hang a relatively simple adapter on the back. Less part numbers to stock = better turns = more money.

toolingjim (Just a guy who likes to build stuff)

I avoid the long chuck assemblies like the plague. More leverage on the spindle, more deflection, chatter, and a loss of usable capacity. I have seen a perfectly serviceable lathe become a horrible chattermatic by simple replacing a compact chuck with a long plate-chuck assembly. Keep shopping, it’s worth the effort.
Is the chuck bore big enough to remachine the back plate, flip and fit it so that the threads are inside the chuck?
Good luck, Mike