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How do I remove the chuck backplate on Craftex CX708

1

19shaun79

New Member
Hi All,

I upgraded from a Chinese mini lathe to a bigger Chinese lathe - a Craftex CX708 10x18. I love it!

I am very green. I am learning by practicing and asking questions.

I bought a 6" 4 jaw chuck. It doesn't fit directly on the lathe, so I figured I needed to purchase a new backplate.

How do I get the original backplate off of the lathe??? In the last picture, you can see the piece I am referring to. In the third picture, I am showing the flange that is loose because I removed the three allen bolts that are holding it on.

The first two pictures are of the new chuck and the new backplate I purchased.

Looking at the lathe's manual (which is pretty shoddy), I may have to remove a flange nut on the gear side of the headstock?

Please help,
TIA!

Shaun

cx708 1.jpg
cx708 2.jpg
cx708 3.jpg
cx 708 4.jpg
 
Nobody who has one has chimed in yet.

So, I'll get you started with what I remember. There should be three screws on the back of the backplate that need to be removed. Then soak the interface with penetrating oil overnight. In the morning you can apply gentle heat to the backplate only and then some love taps all the way around with a rubber mallet. It should come off.

The main thing is penetrating oil overnight. That gives guys who actually have your lathe the time to vomit on what I said without doing any harm. Maybe wait with the mallet......
 
19shaun79 said:
How do I get the original backplate off of the lathe??? In the last picture, you can see the piece I am referring to. In the third picture, I am showing the flange that is loose because I removed the three allen bolts that are holding it on.
Click to expand...

I'm not familiar with the lathe but looked up the manual here

Just to clarify, when you say 'original backplate' you mean the highlighted plate on part 49, the spindle, which appears to be fully integrated into the spindle shaft itself?
 

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@PeterT & @David make an excellent point. Definitions Definitions Definitions. What do you mean when you say "Backplate"? The spindle flange on that lathe IS NOT what I would call a backplate. But it's easy to see how someone might call it a backplate. It is not removable without disassembling the lathe. It is part of the spindle itself.

On your 3rd photo, you show what looks like 2 parts. I had first assumed that the part closest to the gearbox was your spindle flange and the outer part was a backplate. My first post described how to separate them. But on closer inspection, the inner part appears to be loose and the outer part appears to be your spindle flange.

Just a wild assed guess, I think that inside part is a cover for the front spindle bearing. It should not be removed.

In other words, I think you have already removed more than you should have.

Please investigate and confirm.

Now, back to back plates. Many guys don't use a true backplate on that lathe. Instead, they machine the back of the chuck to fit the spindle flange directly. Other folks machine a true backplate to go between the chuck and the spindle flange. In my opinion, the chuck itself defines what is needed.

In either case, a tight fit to the spindle flange and/or to the backplate is required in order to ensure good registration and concentricity of the assembled parts. Once tightened in place, they can be difficult to separate - which is the process I described in my first post.

Your spindle flange appears to offer the flexibility of a choice between three or four screw attachments and also appears to have a good registration lip. I'd be inclined to use it as my backplate directly and skip the normal backplate if I could.
 
YotaBota said:
It looks to me like the 4J will mount directly where and how the 3J was mounted.
Click to expand...

Hopefully you are right. He will know when he puts them together. Scaling the photo makes it look like a little machining of the rear face of the chuck where the registration lip engages might be required. This should be a tight interference fit. This is perfectly normal. Then again, it's a four jaw so just a good fit would be ok. You just don't want it to move around or be out of balance. That's why a little machining is usually required.

YotaBota said:
The backing plate you bought looks like a cam lock plate without the pins, totally different mounting hardware
Click to expand...

Very good observation. It looks exactly like a D1-3 or D1-4 backplate without the cam lock pins. Return it if you can or sell it if not.
 
YotaBota said:
looks to me like the 4J will mount directly where and how the 3J was mounted.
Click to expand...
It's a 10 inch lathe so I'd guess it came with a 5 inch 3-jaw. Thus unlikely that the new 6 inch 4-jaw is going to have the same bolt circle.

Might need to make a 6 inch diameter adapter plate?

Craig
 
trlvn said:
It's a 10 inch lathe so I'd guess it came with a 5 inch 3-jaw. Thus unlikely that the new 6 inch 4-jaw is going to have the same bolt circle.

Might need to make a 6 inch diameter adapter plate?

Craig
Click to expand...
I think this is my route.

Or is a 6” too big for the lathe? I have read something about the fps of the chuck spinning and the effect that has on the tooling. Should I return this one and order a 5" 4 jaw chuck?

This 6" 4 jaw chuck was the less expensive option initially, but like all things, it is more expensive and a headache now.

Maybe I'll make an adapter...
 
19shaun79 said:
Or is a 6” too big for the lathe? I have read something about the fps of the chuck spinning and the effect that has on the tooling. Should I return this one and order a 5" 4 jaw chuck?
Click to expand...

Normally, the 4jaw on a given lathe is bigger than the 3 jaw. So if it came with a 5 inch 3 jaw, I'd stick with the 6 inch 4 jaw and make it work.

If the chuck can't be turned to fit the existing spindle flange, then you will need to make an adapter. It's not a big deal.

Once you have the right parts, we can help you get the job done. You will come out of the experience wiser and more confident.
 
CX708 is a newer version of my B2227L. The spindle mounting flange is fixed and can’t be removed. Chucks mount using three or four cap screws.

Easiest solution? Little Machine Shop in California sells chuck adapters in lots of different configurations, so far they’ve been able to adapt every weird setup I’ve done on my B2227L.


Hint: replace the allen-head cap screws for the chuck mount with 8mm studs and make shouldered nuts from 1/2” hex head cap screws. Makes chuck mounting so much easier.

IMG_0348.jpeg
 
There are a few other considerations. The weight of the chuck, not just spinning, but load on the spindle bearings. Not all chucks of a specific size weigh the same. And the new adapter plate will add to that. It may be perfectly fine but bigger may also not be better depending on the lathe. Maybe your manual or lathe specific groups can speak to that (lathe specific) issue. Remember 5" & 6" only refer to the nominal OD of the chuck body. When you grip work, depending on the size of work, the jaws typically extend outward from the body & that must clear your bed ways. Now chucks either have reversible jaws or 2 sets of jaws to accommodate different diameters, so that helps stick-out matters. A lot of these sizes mentioned are kind of 'nominal' but you need to be familiar with the actual swing limits of your machine.

Its best if you can find a plug & play adapter plate if available. Conventional wisdom is you get a machinable blank & turn the lip to fit your chuck back recess & that guarantees concentricity to the chuck or if you have oddball bolt pattern. But as per post #12, it may be unnecessary on these types of spindles & the chuck accessories that are commonly used (I'm really not sure). The idea is if the matching plate is accurate to 0.0005" runout & your 3J chuck is say 0.002" jaw runout, then making the backplate 'zero' runout isn't going to improve the 0.002" of the chuck itself. there are ways of improving on this, but that's another discussion.
 
BB shows a 5" 4jaw ($250) as an accessory so that would be why there are the extra holes in the spindle mount. The BB 5" 4jaw would be a direct replacement for the BB 5" 3jaw.
So the cost of an adaptor or the cost of the direct fit BB chuck,,, decisions decisions decisions.

This is all theory on my part but it sounds good if you read it fast. lol
 
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