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View Full Version : Steel, cast iron, weld up ??



steve herman
01-03-2017, 04:48 PM
Bought a plane back 3 jaw chuck for my Logan 10 lathe and wondering the best way to make a back plate for it.

Steve

Mcgyver
01-03-2017, 04:55 PM
Bought a plane back 3 jaw chuck for my Logan 10 lathe and wondering the best way to make a back plate for it.

Steve

i don't know what spindle that lathe is, but CI would be my recommendation. You can buy un-machined blanks or machined blanks; threaded or cam locks

J Tiers
01-03-2017, 06:15 PM
It will have a 1 1/2-8 threaded spindle.

CI or steel, either works. I like CI also, but you CAN make it of whatever. Probably aluminum is a bad idea........

The blanks usually come with the spigot section cast-in. I'd not try to weld-up the thing.

What is your starting point? Do you have a faceplate? Do you have another chuck? Procedure would be different depending.

flylo
01-03-2017, 06:18 PM
It's a screw on chuck & back plates should be available. What size is it the chuck?

BCRider
01-03-2017, 06:37 PM
If you would need to buy some material anyway then I'd vote for either a pre-threaded or blank cast iron option.

On the other hand material on hand always trumps having to buy something else. If you have some 1/2" or thicker plate and a slug of steel large enough for the threaded collar then why not weld and turn? But to get the best and most stable joint I'd suggest boring out a hole in the plate and turn a shoulder to match on the slug. Then weld inside and out with suitable fairly aggresive "V"'s to allow for good deep welds that don't end up being mostly turned away when you clean up the outsides.

As far as machining goes steel is going to be far tougher to turn than CI. And for that reason alone I'd lean to a cast iron blank or pre-threaded option. Myself I prefer a blank as I like to fit the threads to the little test stub I made up that matches my spindle thread within a small amount as measured with both the 3 wire method and for OD. Plus my test stub has a registration diameter and shoulder that again matches the spindle so I can test fit for that as well. And for all these reasons I much prefer to bore and turn my own threads for something like this.



Sadly the Harbor Freight just down the road in Albany does not seem to have threaded or blank cast backing plates. If you can't find a local source then it seems like Grizzly up north in Bellingham is your next best bet.

brian Rupnow
01-03-2017, 08:15 PM
I wouldn't advise welding it. That being said, if you did weld something up, you would certainly want to have it stress relieved. If you don't have it stress relieved, the internal stresses which are a result of welding will gradually relieve themselves and in doing so critical surfaces will gradually move as the stresses release. Not a happy thing on a chuck or chuck backplate.

BCRider
01-03-2017, 08:40 PM
I'd forgot about welding stresses. That's an excellent point.

I suppose some of the concern could be avoided by seriously pre-heating the parts. But all in all it starts to sound like finding a CI threaded or basic blank is the way to go.

steve herman
01-04-2017, 03:30 AM
I'm aware of the cast iron blanks available but I would like to make it from scratch. There is a large salvage yard close by to find material so I'll start there.

I want to experience the full build.

I have a larger lathe ( 16 inch) to build it on and a mill.

If I were to weld it up according to BCRider could I stress relieve it by tossing in my large wood stove that I use to heat my shop and if so how long?

Steve

J Tiers
01-04-2017, 09:22 AM
There is no LAW that says it has to have a big spigot sticking out the back. Just enough to give any required clearance, plus a bit to establish a clean surface and have the chuck clear the spindle nose is all that is needed. And the less spigot, potentially the less stick-out of the chuck.

So a thickish piece of steel or CI would work fine. Total as thick as the spindle nose is long, plus enough for cleanup and establishing surfaces. One of mine has a "spigot" about that sticks out only about 3mm from the back surface.

wdtom44
01-04-2017, 10:15 AM
If you have a "hub" large enough in dia. to allow a circle of socket head capscrews you could screw a plate to the hub and not worry about welding distortion. The plate could still distort when you surface it after it is on. The plate could be a light press fit onto the end of a step turned on the end of the hub.

1-800miner
01-04-2017, 10:40 AM
I have welded many. Throw it in the kitchen oven and let it sit there for six months. Wife thinks I am stupid but it is easy stress relieving.
Of course you need six months lead time.
Now that I have a 16" lathe, she might put her foot down.
Hmm. Maybe I should find an oven for the shop. I could bake cookies!

bob308
01-04-2017, 10:40 AM
maybe I am missing something but there is nothing wrong with making a weldment. if you know how to weld that is . I have made many weldments for things far more critical then a back plate. if want to stress relive it just put in a fire for about an hour then let cool slow in a bucket of samdor ash.

J Tiers
01-04-2017, 11:10 AM
maybe I am missing something but there is nothing wrong with making a weldment. if you know how to weld that is . I have made many weldments for things far more critical then a back plate. if want to stress relive it just put in a fire for about an hour then let cool slow in a bucket of samdor ash.

Nothing wrong, but the diameter of the spigot is such that you probably will not V-out and weld the entire contact surface. So it is not as much of "one piece" as if it WERE one piece. Can affect vibration, etc.. Depends on how much V-out is done, if any.

A backplate is best as a single solid unit. Welded or cast, both are melted and allowed to cool. But more material holds the solid cast parts (spigot and plate) together, so the springiness of the "assembly" is different for cast vs just welded around the outside.

lakeside53
01-04-2017, 11:14 AM
and.. cast iron is easier on the spindle mount.

BCRider
01-04-2017, 08:31 PM
.....If I were to weld it up according to BCRider could I stress relieve it by tossing in my large wood stove that I use to heat my shop and if so how long?

Steve

I'd go a little farther than that. I'd preheat them in the stove to get them up somewhere around frying pan hot and weld them while hot. Then dump the whole thing in the stove again after and just let it all heat up and cool slowly as the stove dies down. By next morning it'll be well relieved. Sitting in the stove on the ash with the embers below and above should provide a pretty good slow cooling.

JTeirs' suggestion of a single thick heavy slug of steel is a great idea too. It would result in a LOT of excess weight though. And depending on how heavy the chuck is already it may prove to be more weight than you want for that size of chuck. But there's no doubt at all that it would be a functional back plate.

Doozer
01-04-2017, 09:17 PM
Once when I had an Atlas lathe,
and I got a 6 jaw Buck chuck from the dumpster
I made a 1-1/2"-8 spigot and bored the existing
backing plate that the chuck had to accept the
spigot, then Tig welded it in with 309L filler, and
it has been fine for many years of use. It is about
a 3/16" bead of weld, not overly much. I believe
many of you are overthinking this. It seems like
a lot of good theory had been posted, but there
seems like also lack of experience with all this,
as the recommendations seem overly obsessed
with stress relief and warping and the confidence
level seems low. I have even made threaded
back plates out of 6061 aluminum, and they last
just fine in all the use I have given them. I am all
for good theory, but I am more for what works well.


-Doozer

mattthemuppet
01-04-2017, 10:28 PM
I made a back plate for a 4 jaw out of 1in thick steel plate, works fine. Did one out of 3/4in plate for my first lathe, but I didn't keep it long enough to test, I imagine it works fine. Unless it's a monster lathe, I imagine it would be easier just to turn it from round if you can't find one new. It's not rocket science.

J Tiers
01-04-2017, 11:44 PM
....

JTeirs' suggestion of a single thick heavy slug of steel is a great idea too. It would result in a LOT of excess weight though. And depending on how heavy the chuck is already it may prove to be more weight than you want for that size of chuck. But there's no doubt at all that it would be a functional back plate.

It depends a lot on the chuck diameter, and how much you taper the backplate toward the OD. Not all that weight is "excess".

I have seen pics of old SB machines with backplates that look as if they are barely thick enough to have the threads.... they look to be about 0.187 thick all over, and have the big chuck sticking WAAAAYYYYY out on that slim adapter. They look very bouncy and limber.

What I am suggesting is a "slug" that ends up as thick in the middle as the spindle nose is long, but tapers to the OD, and has a small spigot of maybe 0.125 turned in it at the spindle shoulder. I would suggest that it is LESS heavy than a big cast plate with a spigot on it.

The chuck would end up against the plate surface just a little past the end of the spindle nose. About the minimum material you can possibly have, but all of it is where it counts.

steve herman
01-05-2017, 01:22 AM
It's a screw on chuck & back plates should be available. What size is it the chuck?

The chuck is a 6" 3 jaw an there is full clearance behind the spindle threads. i.e. the back of the back plate could be flush.

I could make it out of a round 1 1/2 " thick

Not able to get to the salvage yard, closed due to snow.

Steve

Doozer
01-05-2017, 11:19 AM
I'm aware of the cast iron blanks available but I would like to make it from scratch...

I want to experience the full build...


Steve


Steve, you are awesome !!!

--Doozer

lakeside53
01-05-2017, 12:55 PM
Whole experience? Well heck, quit cheating. Go dig up some iron ore, smelt it, cast in a mold and go from there! ;)

steve herman
01-05-2017, 02:01 PM
Whole experience? Well heck, quit cheating. Go dig up some iron ore, smelt it, cast in a mold and go from there! ;)

Not quite that whole.

Steve

LARRYR
01-05-2017, 04:41 PM
most of the discount supply houses sell blanks and threaded backplates. your logan is probably a 1 1/2 -8 or 2 1/4 -8. if i were ambitious and wanted to make my own i would try to find a piece of 12l if possible. but you will probably pay as much for this as a commercial blank. you will need to make a plug gage to match your spindle nose. make it with a base, that way you can use it mount a chuck to your rotary table. the down side to machining a commercial blank is that its probably going to be cast iron and its going to make a real mess. but hey this is what we do for fun right?

Peter.
01-05-2017, 04:45 PM
Bought a plane back 3 jaw chuck for my Logan 10 lathe and wondering the best way to make a back plate for it.

Steve

You could make your backplate from a cast iron bar bell weight, they have a 1" hole. I've made a couple and once you're through the crust pretty easy to machine. Stick it in a 4-jaw or faceplate, turn the register, bore and thread, then mount it on your spindle and machine the OD and chuck mounting face.