Author Topic: Broken lathe (Read 17020 times)

John Rudd · « **on:** March 22, 2012, 06:20:06 PM »

While busy machining parts for my single cylinder engine, I've discovered that the bearing/shaft support for the crosslide spindle has broken....

Looks like the cheap chinese alloy has finally given way...and fractured

I wondered why the handle appeared sloppy.....

So, looks like it will be out of action for a while until I can effect a repair...

New parts required...

Oh bother....

If it where electrics/electronics it wouldnt be soooo bad, but mechanicalthingumbybobs....is a different ball game...

Rob.Wilson · « **Reply #1 on:** March 22, 2012, 06:22:38 PM »

Bummer John

Hope you get it sorted soon ,,,,,,,,was hoping to see your engine build

Rob

John Stevenson · « **Reply #2 on:** March 22, 2012, 06:26:00 PM »

Get Wilson to make you a new one - he's not doing anything................................

Rob.Wilson · « **Reply #3 on:** March 22, 2012, 06:30:35 PM »

Quote from: John Stevenson on March 22, 2012, 06:26:00 PM

Get Wilson to make you a new one - he's not doing anything................................

you right there John he is doing nowt ,,,,,,,,,,,, bust me back

,,,,,,,,,,,,, you had that voodoo doll out

Rob

Stilldrillin · « **Reply #4 on:** March 23, 2012, 04:38:28 AM »

What lathe is it John?

Hope your back's soon sorted Rob.

David D

John Rudd · « **Reply #5 on:** March 23, 2012, 05:13:10 AM »

It's my Chester 9*20 that has the broken cross slide lead screw bracket...I'm on with a new one.

I'll take a photo later of whats bust and how the new one is progressing...Shame I couldnt cast a new one out of aluminium

Would have been much easier to work with than this steel I have

Rob,
Hope your back gets better soon... :thumbup:I know that sort of pain all too well

John Rudd · « **Reply #6 on:** March 23, 2012, 06:06:37 AM »

Some snaps of the broken bits....

Although not apparent here's the broken bearing support....

Here are the parts....

Think I might get a new one out of this...its 2-1/2" in diameter

A little while later after some heavy sawing and cutting....We're on the way..

Fergus OMore · « **Reply #7 on:** March 23, 2012, 01:48:08 PM »

Why didn't you give Miss Warren at Warco a buzz? I was stuck for a pulley for a 9120 which Axminster wouldn't supply and she put one in the post- for free.

That, in this day, is what I call service.

Cheers

Norm

Aestus57 · « **Reply #8 on:** March 23, 2012, 02:44:49 PM »

Now I know I'm a bit slow to work these things out but how are you managing to fix your broken lathe ON your broken lathe ????

Regards

Peter

John Rudd · « **Reply #9 on:** March 23, 2012, 02:52:50 PM »

Norm ,
The orignal piece was made form cheap Chinese alloy...Why would I replace it with the same?
The new one will be made from steel with bushes and lube points for the spindle...

Peter, I can still use the lathe although this is not ideal....and the big piece of metal is too big for my Sieg...

Fergus OMore · « **Reply #10 on:** March 23, 2012, 03:23:37 PM »

I was merely getting the lathe back to working order by a cheap replacement so that you could make a better, more substantial replacement.
Digressing slightly, I had a 9180 which is one with a Myford type spindle but I fitted a steel subtable which took my bits that I had made for the Myford. Never liked the 918 tee slots which ran the 'other way'.

Good luck, it's still quite a nice lathe once you can drop the speed below 130 rpm.
Norm

Rob.Wilson · « **Reply #11 on:** March 23, 2012, 03:33:42 PM »

Hi John

Looks like you have the repair well in hand

Cheers lads ,,,,,,,,,,, my back is on the mend ,,,,,,,, well it wont keep me out the shop this weekend

Rob

John Rudd · « **Reply #12 on:** March 26, 2012, 01:24:17 PM »

Spent most of the weekend trying to effect a repair...

Boy this steel bar I have is hard to turn...

especially with a dodgy lead screw support...

Finally got it down to dimensioned size only to find the holes I had drilled were out....

So plan B....Err there is no plan B...

I priced up a piece of suitably sized aluminium bar from my fav supplier....What!!!! £24 inc delivery..

So a quick call to Chester tools and I had a copy of the manual to refer to...
I'm now waiting for them to give me a price of a spare so I can get the lathe back up and running to make a proper one from more steel bar...

I'm not going to get this fixed fast...I'm off on me hols come Saturday so it will have to wait until I get back..

Stay tuned for more developments.......

John Rudd · « **Reply #13 on:** April 11, 2012, 03:41:21 PM »

Despite best efforts to get this sorted, I've now managed to shear the leadscrew.........

After making a new leadscrew support with bronze bushes in it, I stripped the whole of the cross slide down to clean it up and get rid of all of the swarf that has accumulated...

On re-assembly, things seemed a little tight..Fine just needs a little fettling...Oops...what was that?
First thoughts were the Woodruff key had sheared...Not so ...ahhh maybe the leadsrcew nut has stripped....Not so...

After stripping everything off again, the leadscrew has sheared!!!!! Oh bu88er...

I'm going to call Warco and see if they have stock of parts for their 918 lathe....Chester got back to me but wanted £15 for a new bracket as it is called...no stock and its probably made from the same shitty alloy...
I'll post some piccies when I've calmed down a bit...grrrrrrr

loply · « **Reply #14 on:** April 11, 2012, 03:58:58 PM »

The leadscrew sheared, as in physically broke into two bits? Or do you mean stripped the threads on the leadscrew?

What was tight that caused this?

Fergus OMore · « **Reply #15 on:** April 11, 2012, 04:21:18 PM »

My memory suggests that your leadscrew is a lot thicker than the average Myford one.

Anyway, why don't you use a bit of studding from someone like Screwfix until you get mended?

Cheers

N

John Rudd · « **Reply #16 on:** April 11, 2012, 04:37:27 PM »

Guys,
The leadscrew has broken into two pieces..........
I'm not sure what the underlying cause of any tightspots that exist...Obviously I need to remedy this before rebuilding.......

Cant use a piece of studding because the leadscrew has a left hand thread...I would need to make a new leadscrew nut to match..

The leadscrew is 8mm with a 1.25 pitch

Fergus OMore · « **Reply #17 on:** April 11, 2012, 04:48:35 PM »

Quite a lot of tools are designed with only studding.
My Stent has 3/8th BSF and a nut was tapped.

In fact, it is rather more accurate than some people's lathe's . 3/8th BSF is 20 TPI which is-- rather convenient. A 50 tooth gear to make thous divisions.

You have looked at Steve Bedair's 9x20 web site, haven't you?

I'll get me coat

John Rudd · « **Reply #18 on:** April 11, 2012, 05:19:50 PM »

Quote from: Fergus OMore on April 11, 2012, 04:48:35 PM

You have looked at Steve Bedair's 9x20 web site, haven't you?

On many occasions.....

I've even implemented some of his mods and made his ball turner.......

Fergus OMore · « **Reply #19 on:** April 11, 2012, 06:35:56 PM »

Quote from: John Rudd on April 11, 2012, 04:37:27 PM

Guys,
The leadscrew has broken into two pieces..........
I'm not sure what the underlying cause of any tightspots that exist...Obviously I need to remedy this before rebuilding.......

Cant use a piece of studding because the leadscrew has a left hand thread...I would need to make a new leadscrew nut to match..

The leadscrew is 8mm with a 1.25 pitch

Instead of using the existing feed screw nut, you thread the body of the saddle- not the slide.

The studding is also 8mm 1.25mm pitch.

John Stevenson · « **Reply #20 on:** April 11, 2012, 07:10:08 PM »

John,
Is it standard metric thread but left hand or trapezoidal ?
i.e. vee thread or acme type, the reason I ask is I keep M8 x 1.25 in LH taps and dies.

Care to throw a drawing together ? and I'll make you one and post it down.

John Rudd · « **Reply #21 on:** April 12, 2012, 03:23:50 AM »

John,

Problem for me is that it isnt just a straight forward thread cutting excercise,

the lead screw has a Woodruff key slot cut into it...and I dont have a suitable cutter..

Very generous offer...I'll put pencil to paper and post up the details later...

Fergus OMore · « **Reply #22 on:** April 12, 2012, 03:34:27 AM »

John R,
What has the leadscrew got to do with a 'broken feedscrew bracket and feed screw?'

The leadscrew has a slot, the feed screws haven't.

If I have got confused somewhere in this, please accept my apologies.

Norman

andyf · « **Reply #23 on:** April 12, 2012, 03:57:24 AM »

M8 seems a bit slender for a cross slide feedscrew, John, particularly when it will be used in compression unless you are boring a hole or facing from the middle outwards. Even 7x mini-lathes use M10x1, which has 75% more the cross-sectional area on its core diameter.

If a replacement is to be made and space permits, I'd seriously consider an M10 replacement screw and a nut to go with it, with 1mm pitch for one turn=1mm, and a 50 division dial.

Did you bolt your new bracket on firmly before fitting the cross slide? If so, that might be the cause of the screw breaking. If there was any axial misalignment between the nut and the bushing in the bracket, the screw would flex slightly at first to accommodate this, but as the nut got near to the bracket, the strain may have become intolerable. Better to leave the bracket a bit loose until the cross slide has been wound back as far as it will come towards you, so the bracket can float into the right position, then tighten up the fixing bolts.

Andy

John Rudd · « **Reply #24 on:** April 12, 2012, 04:08:23 AM »

Quote from: Fergus OMore on April 12, 2012, 03:34:27 AM

John R,
What has the leadscrew got to do with a 'broken feedscrew bracket and feed screw?'

The leadscrew has a slot, the feed screws haven't.

If I have got confused somewhere in this, please accept my apologies.

Norman

Leadscrew/feedscrew whatever...its the screwed rod that has a handwheel on the end of it to make the crosslide traverse a work piece when facing...

The handwheel is keyed to the screw with a Woodruff key, the half moon shaped thing....

Andy,

On reflection, I did find that the hand wheel turned a little easier as the crosslide moved to the far side of the lathe bed..Maybe there was a bit of misalignment...

When I get around to re-assembling all of this, I'll take my time and double check everything before giving everything a final nip up....

Fergus OMore · « **Reply #25 on:** April 12, 2012, 05:04:58 AM »

Deleted- Sorry

John Rudd · « **Reply #26 on:** April 12, 2012, 06:46:40 AM »

Norman,

The four gib screws are fine as is the gib strip....

My theory is that there may have been a slight misalignment with the bush and feedscrew nut...Although I did slacken the nut to allow the whole assembly to align itself.......

andyf · « **Reply #27 on:** April 12, 2012, 08:45:28 AM »

Quote from: John Rudd on April 12, 2012, 06:46:40 AM

My theory is that there may have been a slight misalignment with the bush and feedscrew nut...Although I did slacken the nut to allow the whole assembly to align itself.......

John, I think that's a likely theory.

Looking at the Grizzly's online parts list for their G4000 (same lathe, I think), there's a spigot on top of the nut. On my (completely different) lathe, that spigot fits into a recess under the cross slide. If yours is the same, loosening the fixing bolt would allow the nut to swivel, but not to move from side to side as it would need to do in order to line itself up with the bushing in the feedscrew bracket if there was axial misalignment.

When you have made or acquired a new feedscrew, it might be an idea to make the bolt holes in the bracket a bit oversize, to give the bracket a bit of wriggle room.

Andy

John Rudd · « **Reply #28 on:** April 12, 2012, 08:50:54 AM »

Quote

When you have made or acquired a new feedscrew, it might be an idea to make the bolt holes in the bracket a bit oversize, to give the bracket a bit of wriggle room.

Andy

Andy, The holes I made are already over size....but obviously not big enough

John Rudd · « **Reply #29 on:** April 15, 2012, 09:44:48 AM »

Here's the offending leadscrew.......

Here's the new one........

and its new key, I milled a 3mm slot into the shaft with an endmill as I didnt have a Woodruff keyway cutter..needs must again...

finaly the new leadscrew bearing support........

I apologise for the apalling qaulity of the photos...Im useless when it comes to close up shots or its the camera..

Stilldrillin · « **Reply #30 on:** April 15, 2012, 10:34:20 AM »

John.
Yes, the old feedscrew's definitely broken!

Not bad pics. But, definitely the camera's fault.

Suggest you don't fit the screws, until the crosslide has been wound all the way out.
The holes may need elongating, rather than oversizing.......

David D

Bluechip · « **Reply #31 on:** April 15, 2012, 10:58:35 AM »

Quote from: Stilldrillin on April 15, 2012, 10:34:20 AM

John.
Yes, the old feedscrew's definitely broken!

Either that or it's spatially discontinuous ...

Can't really see from here ..

Check it with a meter. If it's more than 10Meg, it's open circuit .. for sure ...

BC

John Rudd · « **Reply #32 on:** April 15, 2012, 12:59:18 PM »

Well after a good scrub and swarf removal session, I'm happy to say we're back together again...

A good dreasing and oiling of mating surfaces/faces and the machine is as good as new or even better...I do recall the crosslide action has always been stiff but its a lot better now, I can turn the handwheel with one hand

Just as an aside, the new lead screw I made from Silver Steel, boy it was hard to cut

The new bearing support from a lump of steel I had, but I bushed it with some Phos Bronze reamed to take the lead screw. The shoulder on the lead screw just where is broke, I've added a PB thrust washer, instead of having steel on steel everywhere... Were my choices of materials good or bad?

Thanks to all who have contributed and a special mention to JS for his offer of making a new leadscrew...Shame I'd already ordered taps and dies before seeing his comments...Never mind, I have lh M8 taps and dies for the future should I need them..

loply · « **Reply #33 on:** April 15, 2012, 02:42:35 PM »

Quote from: John Rudd on April 15, 2012, 12:59:18 PM

I've added a PB thrust washer, instead of having steel on steel everywhere...

Forgive my ignorance here, but when you say you added "a" thrust washer, you mean you added only one? And do you mean a proper ball bearing thrust bearing?

I made a similar set up myself for my Chinese mini lathe, but I firmly concluded that it was required to use two thrust bearings in order to absorb the thrust of going both inwards and outwards whilst not having a steel-on-steel interaction somewhere. Otherwise you're surely just clamping the screw between one thrust bearing and a piece of solid steel somewhere?

I've seen several people make similar things using only one bearing though, and wonder what I missed

Stilldrillin · « **Reply #34 on:** April 16, 2012, 01:15:01 AM »

John.

I, for one, am very pleased you got the good result you were hoping for.......

Well done !

David D

lordedmond · « **Reply #35 on:** April 16, 2012, 02:53:06 AM »

John

IMHO that silver steel feed screw unless you have a very good surface finish will wear the nut quickly

Stuart

John Rudd · « **Reply #36 on:** April 16, 2012, 06:32:38 AM »

Stuart,

My selection of Silver Steel was based on Steve Bedair's use of drill rod when he made his new lead screw for his 9*20..

Ok he also made a new nut from Brass.

I'm happy to run with the crappy alloy until needs must...

News:

Author Topic: Broken lathe (Read 17020 times)

Rob.Wilson

Rob.Wilson

Rob.Wilson

lordedmond