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gld
05-29-2008, 09:25 PM
All or most backplates in catalogs are cast iron.

What is the reason for this???

I've been given a 5 inch dia. by 14 inch long piece shaft...would like to make a couple backplates...don't know what steel is ,but it is machinable.

Any reason not too use this???

franco
05-29-2008, 09:48 PM
Steel back plates should be OK. I have two which I made from 25 mm plate years ago which have been quite satisfactory.

franco

J. R. Williams
05-29-2008, 09:55 PM
gary
Cast iron --- Easy to cast to near size, easy machining, stable and low cost when compared to a steel casting or cut off bar stock.

JRW

garyphansen
05-29-2008, 10:47 PM
Another advantage to cast iron is if you cross thread the chuck it will mess up the back plate and not the lathe. However, steel will work. I made them out of AL. Gary P. Hansen

b2u44
05-29-2008, 11:08 PM
Cast iron usually has better damping characteristics than steel. For a backplate, steel should be okay.

JRouche
05-30-2008, 01:58 AM
Cost comes to mind, like most items produced, cost.. JR

oldtiffie
05-30-2008, 08:03 AM
The OP has not said nor has anybody else asked if the back-plate is screwed for the spindle nose thread or is flanged to bolt onto a flanged spindle?

The reason I ask is that if the spindle nose is screwed it will most likely need a screwed back-plate.

If the spindle is flanged - as many modern 5" lathes are - then it is possible - provided that the bolting/screwing/fastening holes on the machine flange and the back of the chuck are matched - that the chuck can be direct-bolted to the machine flange.

If that is the case, no adaptor plate is needed.

JCHannum
05-30-2008, 08:17 AM
The spindle nose has nothing to do with whether a back plate is required or not. The chuck design is the deciding factor. A plain back chuck will require a back plate.

Cast iron is usually used for the reasons cited, but steel is good if it is available at a reasonable cost.

derekm
05-30-2008, 08:49 AM
tony over at Lathes.co.uk has this to say (http://www.lathes.co.uk/latheparts/page7.html)on his website
" At all costs avoid steel backplates; they can bruise or otherwise damage the spindle nose and, if they become stuck, will be much more difficult to remove".

Seems to make sense to me

Derek

oldtiffie
05-30-2008, 09:22 AM
The spindle nose has nothing to do with whether a back plate is required or not. The chuck design is the deciding factor. A plain back chuck will require a back plate.

Cast iron is usually used for the reasons cited, but steel is good if it is available at a reasonable cost.

Perhaps it is in everybody else's shop Jim.

But in mine the 3-jaw chuck bolts and fits straight onto the spindle flange in my shop:
http://i200.photobucket.com/albums/aa294/oldtiffie/Part_off1.jpg

The 4-jaw chuck has an adaptor between the chuck and the spindle flange. It works well enough and I've never thought it necessary to machine the back of the chuck and/or insert new M8 (3) studs into the back of the chuck to suit the spindle flange.

My ER-32 adaptor has an integral flange which bolts directly onto my lather spindle flange:
http://i200.photobucket.com/albums/aa294/oldtiffie/AirSmith03.jpg

As does my face-plate:
http://i200.photobucket.com/albums/aa294/oldtiffie/AirSmith08.jpg

The adapters available from Littlemachineshop.com are at:
http://littlemachineshop.com/products/product_view.php?ProductID=2347&category=

http://littlemachineshop.com/products/product_view.php?ProductID=2358&category=

The flange configuration to which these adapters are made to suit is standard on many Chinese lathes.

JCHannum
05-30-2008, 11:18 AM
While some of the smaller Chicom lathes may use a flanged mount that will accept a chuck directly, the majority of mounts, L series, threaded, D1, A and the European mounts will require a separate mounting plate.

This is a typical plain back chuck;

http://members.aol.com/jchannum/pbc

One would be hard presssed to mount this style without a suitable backplate.

As pointed out on Tony's website, cast iron can be more forgiving, especially in the case of a threaded mount, but if care is taken and mounting surfaces are cleaned when mounting, steel is acceptable.

oldtiffie
05-30-2008, 11:48 AM
While some of the smaller Chicom lathes may use a flanged mount that will accept a chuck directly, the majority of mounts, L series, threaded, D1, A and the European mounts will require a separate mounting plate.

This is a typical plain back chuck;

http://members.aol.com/jchannum/pbc

One would be hard presssed to mount this style without a suitable backplate.

As pointed out on Tony's website, cast iron can be more forgiving, especially in the case of a threaded mount, but if care is taken and mounting surfaces are cleaned when mounting, steel is acceptable.

Points well made Jim - and well-taken.

Irrespective of the method of mounting/adapting, there is a problem that many may not be aware of or just ignore.

That is that many 3-jawed chucks, when new, have a "spec"-ed total indicated run-out (TIR) of anywhere between 0.002" and 0.004" (or more?) when a machined surface is turned on a lathe and the new chuck is gripped with its own jaws on that true-turned surface (actual run-out is half of the TIR).

If the chuck-to-mounting/adaptor-plate and mounting/adaptor plate are a dead-neat fit, then all things being equal when the chuck is mounted on the lathe (with the previously turned surface still gripped in the chuck) the TIR of the surface will equal the TIR of the chuck as previously.

For that reason I leave 2 to 4 "thou" "clearance" between the adaptor plate and the chuck if the adaptor and spindle nose are screwed or between the adaptor plate and the flange are flanged. I just lightly "nip" the fastening bolts/screws, put a pre-machined cylinder (about the size I want to turn) in the chuck, check the TIR and if OK, just "snug" the bolts/screws. If TIR is "out" too much, I just "tap" the chuck (with a phosphour-bronnze "dolly" that I've had for years) until the TIR is "in" and then "snug-up", re-check, and if OK - no more to be done.

This is a very quick effective, no-cost "tap-true" method, that in my shop (all light work) is as good as any other method of "true" adjustment.

Same applies to my 3MT/ER-32 collet adaptor in the lathe spindle.

It is just as effective as a set-up in a 4-jaw chuck, but its better for repetitive works as it "stays put".