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Author Topic: Broken lathe  (Read 17021 times)

Offline John Rudd

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Broken lathe
« 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.... :Doh:

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

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

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

New parts required... :scratch:

Oh bother.... :doh:

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

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Re: Broken lathe
« 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  :dremel:


Rob
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Offline John Stevenson

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Re: Broken lathe
« Reply #2 on: March 22, 2012, 06:26:00 PM »
Get Wilson to make you a new one - he's not doing anything................................ :poke:
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John Stevenson

Rob.Wilson

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Re: Broken lathe
« 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................................ :poke:

 :lol: :lol: :lol: :lol:  you right there John  he is doing nowt ,,,,,,,,,,,, bust me back  :( ,,,,,,,,,,,,, you had that voodoo doll out  :poke:


Rob 
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Offline Stilldrillin

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Re: Broken lathe
« Reply #4 on: March 23, 2012, 04:38:28 AM »
What lathe is it John?


Hope your back's soon sorted Rob.

David D
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Offline John Rudd

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Re: Broken lathe
« 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 :scratch: Would have been much easier to work with than this steel I have  :hammer: :hammer:

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

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Re: Broken lathe
« 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 :dremel:



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


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Offline Fergus OMore

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Re: Broken lathe
« 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
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Offline Aestus57

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Re: Broken lathe
« 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 ????
 :scratch:

Regards

Peter
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Offline John Rudd

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Re: Broken lathe
« 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...
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Offline Fergus OMore

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Re: Broken lathe
« 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
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Rob.Wilson

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Re: Broken lathe
« Reply #11 on: March 23, 2012, 03:33:42 PM »
Hi John


Looks like you have the repair well in hand  :thumbup:

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

Rob
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Offline John Rudd

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Re: Broken lathe
« Reply #12 on: March 26, 2012, 01:24:17 PM »
 :update:
Spent most of the weekend trying to effect a repair... :dremel:

Boy this steel bar I have is hard to turn... :coffee:   especially with a dodgy lead screw support...

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

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


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

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.......
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Offline John Rudd

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Re: Broken lathe
« 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......... :doh:

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
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Offline loply

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Re: Broken lathe
« 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?
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Offline Fergus OMore

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Re: Broken lathe
« 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
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Offline John Rudd

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Re: Broken lathe
« 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
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Offline Fergus OMore

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Re: Broken lathe
« 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 :bang:
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Offline John Rudd

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Re: Broken lathe
« 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..... :coffee:

I've even implemented some of his mods and made his ball turner....... :dremel:
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Offline Fergus OMore

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Re: Broken lathe
« 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.

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Offline John Stevenson

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Re: Broken lathe
« 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.
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Offline John Rudd

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Re: Broken lathe
« 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,  :dremel:  the lead screw has a Woodruff key slot cut into it...and I dont have a suitable cutter.. :doh:

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

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Offline Fergus OMore

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Re: Broken lathe
« 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
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Offline andyf

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Re: Broken lathe
« 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
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Offline John Rudd

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Re: Broken lathe
« 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.... :thumbup:

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.... :ddb:
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