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pntrbl
07-01-2007, 12:30 PM
I realize backplates are usually made out of cast iron, but to make a long story short, I can buy 1018, 4140, or even O1 for just about the same price as a piece of cast iron. Ductile or grey. Somewhere around $30 for a 6"x2" round for any of the above.

It may not matter because as usual I just don't know any better, but I'll be looking to mount a 55lb 10" 4jaw on a 550lb 11" lathe. That chuck's gonna look like a 454 in a Chevy Nova! I'm thinking I better be damn sure I've got a good piece of tough metal attaching it to the machine.

So what would you guys do? .... or .... Would you do it all? :rolleyes:

FWIW, top end on the lathe is 1525 rpm. That could be scary .....

SP

Renegade
07-01-2007, 01:20 PM
Cast iron machines and threads easier than the other materials mentioned,plus it has better vibration dampening qualities.
Nothing wrong with using 1018 it just won't finish as nice as the 4140 or the cast.

Evan
07-01-2007, 01:57 PM
There is nothing magic about a back plate and it isn't going to ring with a chuck hanging on it. Strength isn't an issue. To give some perspective think about the driveshaft in a rear drive front engine vehicle. It may turn at thousands of rpm, transmit hundreds of foot lbs of torque and yet is of such thin material that welding it is difficult. A serviceable back plate can be made from whatever metal is handy and machinable. Once a thickness of about 1/2" is reached in the size you are speaking of the point of diminishing returns is reached and thicker material will not provide a significant benefit.

Willy
07-01-2007, 03:53 PM
I may be missing something here, but I am just wondering how far you can open the jaws on a 10" chuck on 11" lathe without the jaws striking the ways.:eek:

pntrbl
07-01-2007, 07:49 PM
You ain't missing much Willy because the question has come up before. The chuck was/is "available" for use, and being as I don't have a 4 jaw.

Currently my only chuck is an 8" Skinner 3 jaw and I have had occasion to run it with the jaws reversed and extended past the body. My left index and right thumb had some complaints during the 1st session, but I've had the same setup in the chuck several times since then with no foul language being needed.

With jaws reversed the 10" will still accept an 8" dia part on center before the jaws clear the body. My fingers are very happy about this.

A 6" 4 jaw would be ideal for what I'm doing on a daily basis and I've been looking. A decent looking used one went off on E-Bay this morning for $127 plus shipping .... so I'm still looking.

SP

Willy
07-01-2007, 07:59 PM
Hey if ya got it lying around you might as well mount it on the lathe.
As you said with the jaws reversed it will still give a substantial amount of capacity that you otherwise wouldn't have.
Besides it's not doing anybody any good gathering dust on a self.

J.Ramsey
07-01-2007, 08:42 PM
I guess you could make it out of the end of a beer can.
Drive shafts are made of steel or aluminum DOM tube that is easily welded and subjected to different kinds of torque and harmonics,put rims with cleats on a vehicle with a hollow automotive driveshaft and dump the clutch and see what happens, more than likely it will resemble a licorice stick I would guess your not so much interested with the dampening qualities as some people might be by putting a chuck that large on a lathe of that size.

quadrod
07-01-2007, 08:50 PM
ok i have to ask the stupid question, can the chuck back plate be made out of aluminum-aluminymum-alllummminnum, oh you get what i mean.:)

Renegade
07-01-2007, 09:12 PM
If they can be made out the end of a beer can........ why not?

Evan
07-01-2007, 11:32 PM
Aluminum will work fine. 6061, 2024 or 7075 will all do. 2024 and 7075 in a T4 or T6 temper are as strong or stronger than mild steel.

J Tiers
07-01-2007, 11:59 PM
A 6" 4 jaw would be ideal for what I'm doing on a daily basis and I've been looking. A decent looking used one went off on E-Bay this morning for $127 plus shipping .... so I'm still looking.



Well, whatcha want to pay for one?

A 6" 4 jaw plain back chuck will set you back $86 (plus shipping) at Victor Machinery, price from website tonight.

an 8" would be $95.

As I look again, I see that they may not be the Bison I bought for something like that price a while back. (they say to ask for a quote on Bison). But a 4 jaw only needs a few things right about it, compared to a 3 jaw, so it may be OK.

Bound to be better than a pig in a poke ebay monstrosity, though...

And you might as well ask what they want for a Bison brand. I'd guess it to bw worth the difference.

Ain't ANY way I'd pay $127 for a 6" 4 jaw used chuck on ebay. I'd start thinking at $50, maybe. Any more and I'd need to see the thing before I pried open my wallet.

I'm every bit as bad as what John S claims about Alistair....... although I WILL pay for quality if I need to, and I expect quality in proportion to the $$.

pcarpenter
07-02-2007, 04:51 PM
Yeah...the bigger problem than only having 1" of jaw to way clearance is that if you need to work close to the chuck you are talking about top-of-carriage to jaw clearance which may be even smaller or non-existant.

Paul

Evan
07-02-2007, 05:16 PM
Yabut, it should at least hold the same as a smaller chuck. Regardless of the size of the chuck if the jaws are approaching the ways it will hold about the same size work no matter what size body it has.

The main drawback is the weight and reduction in center to center distance. On my SB9 there is no difference between way and carriage clearance.

pcarpenter
07-02-2007, 05:41 PM
I dunno...I have a 6" three jaw and a 7-8ish three jaw and the chuck jaws are both wider and longer on the larger chuck. With smaller parts, this makes no difference. However, there is a diminishing return on chuck size as they do have a larger swing (outside) as you open them up to accomodate the same internal diameter.

I just looked this morning at some lathe damage caused by someone opening a chuck beyond the amount of clearance they had over the cross slide while the chuck was parked with the back side of the jaws straddling the cross slide. They then appear to have tried to start the lathe. as there was a big "whack mark" on the top of the cross slide. It's a good thing that even geared head lathes are actually belt driven (at the motor).

Paul

pntrbl
07-02-2007, 07:43 PM
Well thanx for checking in on the subject guys. I think my Logan's similar to Evan's SB9 in that the section of the carriage that first approaches the headstock is tapered for clearance. Other than my knuckles the first thing I typically have to watch for is the compound/cross slide/etc. getting into the jaws.

I'm gonna be conventional for once in my life and use ductile iron for the plate. I've drilled and tapped cast before but never turned it. Magnet in a bag huh?

JTiers, I watched a used 6" Bison 3 jaw go by at over 2 bills on E-Bay last week. I'll bet it was a nice chuck but new couldn't have been much more. I swear E-Bay's getting harder all the time.

OTOH there's an E-Bay store called Discount Machine with what must be an import that will show up at my front door for just over $70. Dimensionally similar but in fact slightly larger in thickness etc. as the one Victor has at $86 plus shipping. The Discount Machine ad says it's hardened. Got a balance dimple.

If someone could please tell this computer dummy how to post a link to it I'd sure like to put it up for the board's opinion.

SP

Willy
07-02-2007, 09:54 PM
http://cgi.ebay.ca/6-4-JAW-INDEPENDENT-PLAIN-BACK-LATHE-CHUCK-HARDENED_W0QQitemZ330108897577QQihZ014QQcategoryZ2 5292QQcmdZViewItem

Is this it?
After having previously copied the the url from the page you want to link to, go to the reply page and click on the "insert link" icon, then all you have to do is paste it in the url field.
You can check it by previewing the post and clicking on the link.

J Tiers
07-02-2007, 10:55 PM
JTiers, I watched a used 6" Bison 3 jaw go by at over 2 bills on E-Bay last week. I'll bet it was a nice chuck but new couldn't have been much more. I swear E-Bay's getting harder all the time.


That's nutty...... I bought mine for possibly $120 new, several years ago. Good size for a 10" (which swings almost 11").

Used chucks are a crapshoot. Used 4 jaw chucks are a bigger crapshoot.

The 4 jaw is normally a sturdy item, but is also often used to put a part in a deathgrip, so it is not immune to being worn bellmouthed, sprung, whatever.

My original one (came with the lathe) was a big tough 6", huge jaws. Trouble is, it was worn so that each jaw needed different shims, AND one of the adjusting screws had almost completely stripped the jaw threads. It was also a "knucklebuster" with square ended screws sticking out.

Nobody needs to pay $200 for something only to find that out.


Pasting the link is easy, copy the line up at the top of the page that has the site address you want. Then, paste it into the text here, on its own line. Like this:

http://www.lathes.co.uk/page21.html

I copied that while I was at that page of the site itself, and pasted it in here.

Some catalogs will not allow that (deep linking), you can only paste the top page, all the others are shown in a way that cannot be linked to.

Supposedly that pasting internal page links is really poor "net etiquette", but everyone does it. If the page setup at the target site changes it may later go somewhere unusual, but that's the risk.

pntrbl
07-03-2007, 12:24 AM
Yeah, that's the one Willy. That's it! No Canadian dollars on my page and I also had a shipping price. Let's see if I can link it ...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=014&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=330108897577&rd=1&rd=1

Ya know, I've been linking all along but never had enough sense to check the preview.:o

SP

abn
07-03-2007, 04:42 AM
Backing plate costs more than a chuck LOL...



Yeah, that's the one Willy. That's it! No Canadian dollars on my page and I also had a shipping price. Let's see if I can link it ...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=014&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=330108897577&rd=1&rd=1

Ya know, I've been linking all along but never had enough sense to check the preview.:o

SP

pcarpenter
07-03-2007, 12:07 PM
If I'm not mistaken, Discount Machine is Shars. I've bought items from them in the past and have been pleased. The language barrier is difficult sometimes at order time, but they try hard and I get items in stock right away (they are located a few hours away, near Chicago).

The good news is that if you buy from them, you will get a print catalog...which is especially important since thier web site is usually horrible and often completely broken.

Paul

DR
07-03-2007, 01:15 PM
Cast iron would be my last choice of material. Cutting that will make a gawd awful mess of your lathe.

7075 aluminum would be my first choice, except for the price.

Use 1018.

lazlo
07-03-2007, 02:06 PM
Aluminum rings like crazy, which is why it's not used in machine tools.

Gray cast iron has outstanding vibration damping, which is why most machine tools are made from gray cast iron, instead of ductile cast iron or steel, which are stronger.

GRH
07-03-2007, 02:54 PM
Without thing twice definately Cast Iron as a retired machine tool designe
engineer (Cincy Milacron, G & L and DeVlieg ) same reason as lazlo.
C.I. also will not gawl on the spindle and machining is not really that bad, clean all oil off the machine before you start and when finished vac up the dust etc before re-oiling.

Graeme

Willy
07-03-2007, 03:50 PM
I have that same chuck, although I have not used it yet.
For a cheap chuck it doesn't appear that bad, the jaws fit the body of the chuck nice and snug, and the gripping portion of the jaws are square to the face of the chuck. Not having used it I can't say how it will stand up in service, but for that kind of money you can't go to far wrong.
I'm sure we all have more expensive door stops than that.
Having said all that, I can say that I lucked out about a year ago and scored a well used Cushman 4 jaw for fifty dollars that is still a whole lot nicer than the new one, but I'm sure it will be okay when I get around to using it.From what I've seen I sure don't feel bad about it.

By the way I have dealt with Shars/Discount Machine on several occasions as well and what Paul said is true, they do try though. So if you have to communicate with them try e-mail first, thus avoiding the language barrier.

As the others have said cast iron would be my first choice as well, it's not that bad to work with as long as you take some steps before you start in order to keep the dust down. I usually cover everything with paper towels that have been sprayed with WD40 and keep a vacuum cleaner nozzle near the where I'm working...it's usually a non issue. And it does machine very nicely.

Evan
07-03-2007, 04:27 PM
Aluminum rings like crazy, which is why it's not used in machine tools.

Only partly true. In the case of a backplate it won't be able to ring with a chuck bolted to it. In order to ring the material must be free to resonate. As soon as two parts are fastened securely together with no free sections ringing become much less likely, especially if the masses differ significantly. For ringing to occur both pieces would have to share a resonant fundamental frequency or a close harmonic. The real reason for not using aluminum in machine tools is that for the same section aluminum has one third the Young's modulus of steel and about 75% that of gray cast iron. This means that aluminum is more "flexible" under elastic loading and that to achieve the same rigidity thicker sections are required. Any issues with ringing are fairly easy to deal with using correct design. It doesn't usually pose a problem in aircraft where a tendency of a structure to ring could be disastrous.

In the case of a backplate this isn't a problem and the extra material to gain sufficient strength isn't an issue either. Nor is differential linear expansion as the components are radially symmetrical.

lazlo
07-03-2007, 04:51 PM
The real reason for not using aluminum in machine tools is that for the same section aluminum has one third the Young's modulus of steel and about 75% that of gray cast iron. This means that aluminum is more "flexible" under elastic loading

It's not about stiffness (Young' Modulus): cast iron is less rigid than steel. Like Graeme confirmed -- it's about vibration damping/management.

Gray Cast iron damps vibration 25 - 125 times better than steel. Steel, in turn, damps vibration 10 times better than aluminum.
In other words, gray cast iron damps vibration 1200 times better than aluminum:

http://i164.photobucket.com/albums/u15/rtgeorge_album/vibration.gif

If you go to a local DuraBar distributor, they like to demonstrate the superior damping characteristics of gray cast iron by hanging a 1 x 6" bar of steel, aluminum and gray cast iron by strings, and whacking them with a ball peen hammer.

The aluminum vibrates like a tuning fork. The steel rings a lot less. And the gray cast iron just makes a dull thud.

If you've ever switched from a steel to an aluminum frame mountain bike, the aluminum frame is a lot more jarring than the steel frame.
This is also why Harley-Davidson made their knucklehead engines from gray cast iron, instead of ductile cast iron.

This also why toolroom lathes have change gears made from gray cast iron instead of steel -- the cast iron gears absorb the geartrain
vibration and reduce the "phonograph" chatter marks in the work:

http://www.dura-bar.com/downloads/upload/gearBrochure.pdf

Evan
07-03-2007, 05:15 PM
Gray Cast iron damps vibration 25 - 125 times better than steel. Steel, in turn, damps vibration 10 times better than aluminum.
In other words, gray cast iron damps vibration 1200 times better than aluminum:

I don't dispute that. However, the ringing effect can be damped by proper design and a material cannot ring unless it is free to resonate. Ringing is a resonance phenomenon. All it takes to make a bell stop ringing is a small amount of extra mass placed in the right spot or simply picking a shape that has no resonance modes that reinforce (cracked bell for instance). There are many ways to dampen ringing. In the design of my milling machine I used a variety of methods including the use of dimensions for various parts that are different prime numbers, the use of golden sections and the use of multiple layers of material of different masses. By doing this excellent damping can be achieved regardless of the material.

The difference in Young's modulus is much harder to deal with in machinery design as it requires greater bulk to achieve the same rigidity with aluminum. There aren't any shortcuts to achieving a greater modulus of elasticity. This is shown by the fact that all steel alloys have nearly the same modulus.

lazlo
07-03-2007, 05:20 PM
Another pictoral showing the amazing vibration absorbing capabilities of gray cast iron:

http://i164.photobucket.com/albums/u15/rtgeorge_album/vibration2a.gifhttp://i164.photobucket.com/albums/u15/rtgeorge_album/vibration3a.gif

Evan
07-04-2007, 01:01 AM
Two layers of aluminum with an adhesive between is better. The point is that the material must be free to vibrate for it to matter. Even if it is free doesn't mean it will vibrate. Cast iron makes a lousy tuning fork. So does aluminum if the forks are different prime lengths.