Lathe Disaster!

[NickG]

 

Hi all,

The other night I was in the garage ... was not doing any model engineering, can't remember what it was but I ended up messing with the lathe.

The 3 jaw chuck I have is well past it's sell by date so I got a new one from Axminster (I had one for my previous lathe and it was fine for me). Problem is, the current chuck is so tight on the spindle nose I can't budge it.

I had a daft idea that wedging a screw driver between two of the change wheels would lock it sufficiently to undo the chuck, however, I've just mashed one of the gears up!       sometimes I'm so stupid I can't believe it.

The gear is made of some sort of leathery substance, and bolted to a hub. It must be done incase you overload it or something. I thought usually it just had dowels that snap if it's overloaded on the feed shafts. Anyway, my lathe pretty basic now without any screwcutting, feeds or power cross feed!

I need to get another gear made up the same or find a source of gears for harrison L5 lathes. Even more importantly, I still need to get the chuck off! does anyone have any ideas , I've tried putting a spanner on one of the nuts that hold the other gears in place so it was pushing the spanner against the bit of spindle that sticks out of the rear of the headstock however, all this succeeded in doing was tightening the nut too much. I don't want to bend anything either. I'm struggling to think of a way without damaging anything, it's so tight.

Bit of a nightmare this!

Cheers,

Nick

[bogstandard]

Nick,

I think someone else has your problem, go down to the first in the list starting 23 May

http://www.homeworkshop.org.uk/latest.html


Usually you can lock the system up with a gear selection (usually in the low range) and gently tap on the chuck key while it is in one of the tightening holes. Or make yourself an unlocking key out of ply that fits over the chuck jaws.

I don't know which L5 you have, but maybe a root thru on here might give you a bit of help

http://www.lathes.co.uk/harrison/index.html

Or even

http://www.homemodelenginemachinist.com/index.php?topic=1899.0


John

[John Stevenson]

Gotta picture of the broken gear? plus outside diameter and number of teeth ?

[NickG]

Thanks Bogs,

I tried locking it in the lowest back gear but it's so tight it just rotates them! I agree though I think I need to shock it off somehow. Maybe putting it in that lowest gear then locking something in the change wheels, then all the force isn't going through 1 set of gears it's more of a compound effect spreading the load through them all.

John,

I will count teeth and take some pics tonight.

Thanks,

Nick

[bogstandard]

Hi Nick,

On my Atlas, I had an indexing pin that located into the bull gear, and that usually locked it up enough. But do you have a release pin that you pull out when you put the back gears in? If you do, then by leaving the pin in with the back gears in position, effectively locks the gearbox up. But again you will be putting a strain on gears and that is the chance you take.

John

[John Hill]

A method I saw described involved clamping a decent sized piece of wood in the chuck so that when the chuck spindle is turned the wood will hit the ways (or the wall, or the bench etc).

Then, because you want to unscrew the chuck, take hold of the wood and with all your might turn the lathe backwards.  In theory, when the wood hits the ways the chuck will stop and the inertia of the spindle will cause the chuck to unscrew without breaking any gear teeth.

If you do choose a method that involves locking the gear train take up all the slack by putting as much pressure on the gears as you can before striking the blow.

John
The Artful Bodger

[NickG]

Thanks guys, a few methods to try there.

Unlike other lathes I've had though, there is no release pin for the back gear on the Harrison, never really looked into how it works but it's just another set of ratios engaged with a different lever.

Forgot to count the teeth and photo the gear last night. Need to as there's one ending on ebay on Thurs night. Found a couple of places that do change wheels too but not cheap!!!

[websterz]

A method I saw described involved clamping a decent sized piece of wood in the chuck so that when the chuck spindle is turned the wood will hit the ways (or the wall, or the bench etc).

Then, because you want to unscrew the chuck, take hold of the wood and with all your might turn the lathe backwards.  In theory, when the wood hits the ways the chuck will stop and the inertia of the spindle will cause the chuck to unscrew without breaking any gear teeth.

If you do choose a method that involves locking the gear train take up all the slack by putting as much pressure on the gears as you can before striking the blow.

John
The Artful Bodger

4x4 in the chuck...that's the way I was taught to do it. 

[NickG]

Hi all,

The number of teeth on the smashed gear is 50 and have found a place that I can get a 50 tooth for £15 which is great, bizzarely, this place I found on google is 8 miles away from where I work too. Only problem is it's this special 'soft' gear that's bolted to a hub, however, I guess I could use a normal steel one if I make a bush up to suit its arbor.

Here is a pic of the gear. The plain gear is the one it meshes with but is the same size.



Nick

[sbwhart]

Nick is it possible to lock it up with something passed through the spindle bore, a long bolt with a nut one end or something  just trying to get a train of thought going.

Stew

[John Stevenson]

Nick,
Make sure the gear you are getting has the same profile teeth as the original.

Harrisons are usually 14.5 Pressure Angle gears and modern stuff like from HPC is 20.

Very hard to tell just by looking but roll two matching gears together and they should be smooth, get one mis matched and it will be lumpy.

.

[SPiN Racing]

My lathe actually has a couple holes in the shaft for the tool that it didnt come with.

The first time I removed the three jaw I simply stuck the chuck for the 4 jaw's cross handle into one of the holes (snug fit) then put the chuck in the 3 jaw, leaned on it a little and it didnt budge. I then rolled it so the 4 jaw cross handle was just about to hit the metal of the housing, and then lightly, gave it a good yank, speed wise not force. After the 4 jaw chuck hit the housing of the lathe's gears and motor, three or 4 tries into it, the 3 jaw unscrewed.

Often some of the car bolts and things I need to undo are horribly tight. Im ducking Bog's monitor, as well as everyone else who throws them at me... BUT,  if you carefully give a light rap with a hammer to things, in a manner that it wont bend them, or distort things, it might be just that shock to break it free. Impact hammer style. Sharp rap without much force.

[NickG]

Stew,

Have been trying to think of a way myself! Your method might work, the nut would have to be on the chuck end though so it tightened against the spindle as I hold it and try to loosen the chuck! Either that or a left hand thread! Will have to try that route. I have some big lengths of studding.

John, thanks for that, I think with the place being nearby I will just take the two gears with me to see what his are like.

Spin, will have to check for any holes, where abouts were the holes on yours?

Cheers

Nick

[SPiN Racing]

Here is a image of my chuck... you can also see the little arm pieces that keep it from un-screwing in reverse.

[NickG]

Ah, that's handy, there's nothing like that I can see on mine. There is a small hole on the other end but not very deep. It promptly put a right angle bend in the piece of 3/16" silver steel I tried to use! I know, it's only a small dia but this thing is tight!

[bogstandard]

Nick,

The hole you have in your spindle would be fine, except you are using it in slightly the wrong way. By just sticking a 3/16" bar in the hole, it will just bend as the bar is working in tension. But stick a 3/16" bar in the hole in shear, then you have a very strong piece of metal. What I am on about is a C spanner with a 3/16" pin, or something to that effect.

I have done a C-o-C to explain.

Bogs

[NickG]

Bogs,

Thanks for taking the time to do that, I should have thought of this being a mechanical engineer! I now think this is the method that'll work as long as I can make something that will support it nice and solid pushing off the metal stand probably.

Cheers,

Nick

[NickG]

Hi,

Good news, I've got the chuck off the spindle. I had to resort to  but I should have tried this earlier and it would have saved me a change wheel!   

When I originally tried locking it up by putting in lowest back gear, I tried to remove the chuck by wedging a jack handle (big lever) in the chuck jaws and leaning on it. This just turned the gears over so that's when I thought I was at a loss and started wedging things in the, unbeknown to me, soft change gears and broke one!

I was just making a brew before and staring out of the window at which point I decided to go into the garage and give have another quick bash at it (literally)! I put it in the lowest back gear but this time wedged a 10" or so length of what i think is chisel steel (I have a few bits of octaganol steel, I can only assume they are for chisels? ) in the chuck and hit it with the hammer! The small hammer just bounced off but it didn't turn the gears over. So with my heart in my mouth I got the sledge hammer and gave it a few 'taps' with that with the slack taken up and it surrendered!  Just wish I'd done that in the first place   

Anyway, it's off so I suppose I can get on with turning the register on the back plate to fit the new chuck. Need to go and get that new change wheel too and probably turn up some bush for that.

Cheers for all your help and ideas on this one guys.

Nick

[sbwhart]

Well done

Nick you can't beet a bit of good old (carful)  ing

Stew