# Metal lathe chuck help!



## SBD (2 Jul 2021)

Hi All,

This is sending me round the bend... I have a K11-80 spindle and flange to fit a 3"/80mm 3 jaw chuck but I have a K11-125 3 jaw chuck that I'd like to fit (through hole requirements) there must be an adapter!?

The problem is I haven't got a clue what to search for? An adapter, a flange, an overdrive plate, etc?

Please help 

sbd


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## chaoticbob (2 Jul 2021)

If I've understood your post correctly, the thing you are after is called a back plate, something like this.
Bob.


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## SBD (2 Jul 2021)

Many thanks, yes and no  so I have a 25mm spindle with a 20mm through hole and the 80mm OD backing plate (as per your pic) welded to it for a K11-80mm chuck. I have a K11-125mm chuck so the mounting holes don't line up so in effect I'm looking for an adapter/spacer/sandwich plate with a +20mm hole in the inside, holes for 80mm in the middle and holes for the 125mm around the outside. A0 bit like the spacers used on cars to mount wheels with a different stud pattern/make it look wider.

Hope I'm making sense 

sbd


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## TFrench (2 Jul 2021)

Why is the backplate welded to the spindle? Sounds unusual. Also sounds like its going to be a custom job - you need someone with a dividing head on a milling machine.


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## Inspector (2 Jul 2021)

is a video on making a backing plate adaptor. There are lots of other similar videos. Finding a ready made backing plate may prove difficult. 

Pete


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## SBD (2 Jul 2021)

Thanks both, I can find "adapter backplates" for 3 jaw to 4 jaw of the same diameter but nothing 80mm to 125mm (so far) found a universal that did 80 to 100 but not 125. TBH it's beginning to look like it'll be easier/cheaper to just buy an 80mm chuck and rethink my dimensions...


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## dickm (3 Jul 2021)

TFrench said:


> Why is the backplate welded to the spindle? Sounds unusual. Also sounds like its going to be a custom job - you need someone with a dividing head on a milling machine.


I was wondering why the backplate was welded to the spindle too. What does that spindle then fit into/onto? If, as it sounds, you have a metalworking lathe, then you might be lucky if one of the cogs on the mainshaft happens to have a number of teeth which is a multiple of the number of holes needed in the adaptor plate. You could then cobble up some sort of indexing pin to engage with the cog and mount a Dremel or similar on the cross-slide to drill the necessary holes.
But it would help to have a bit more detial.


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## Rorschach (3 Jul 2021)

What lathe do you have?


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## SBD (3 Jul 2021)

It's in the process of being cobbled together by good old me, yes metal lathe. It's only a headstock as I don't need to turn between centres but the through hole/bore is quite important.
So far I have the spindle and (welded) backplate, the 125mm chuck, barings, motor and speed controller, x/y slides. 
A bed is not required as slide base is fixed in position and I have 180/320mm travel respectively which is enough for what I want. Just the pulley ratio to calculate, steel work to fabricate and throw it all together, its just the 80mm backplate to 125mm chuck that I'm stumped by.


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## Rorschach (3 Jul 2021)

Ok, well I was going to suggest making your own adaptor, but that won't be possible since you don't have the lathe built.


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## SBD (3 Jul 2021)

Plus I'd need a 5" diameter steel billet and an even bigger chuck to hold it


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## dickm (4 Jul 2021)

SBD said:


> Plus I'd need a 5" diameter steel billet and an even bigger chuck to hold it


Not necessarily; rough it out of flat plate of the right thickness, then mount on a faceplate. Which of course you don't have................


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## SBD (4 Jul 2021)

Might have to do something like that, I've got the 80mm faceplate so once it's up and running I'll be able to do it. Probably in a hard grade aluminium. Might get real flash and have a go at anodising it and


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