Is this normal?

[magicniner]

4 Jaw INDEPENDENT chucks give better precision than 3 jaw chucks because each jaw is adjusted INDEPENDENTLY.
What you have is a 4 jaw scroll chuck with nothing to give you better precision than a 3 jaw scroll chuck.
You can get scroll chucks to meet your expectations but expect to spend a lot of money, more than you expect!

[A_Camera]

Yes, I understand the independent chuck jaws can give good precision because each jaw can be adjusted individually, that's obvious. But it also means a lot of extra time before the work piece starts spinning. Anyway, it looks like that I could get MUCH bigger and better precision by just cleaning the surfaces.

[A_Camera]

Now I am back. I was a bit busy so I could not answer. Anyway, I don't know what happened, why replying was not possible earlier.

I didn't want to pull it apart before I was through the discussions with the seller, but now we made an agreement so I am good to go on. Basically, the seller admitted that the MT2 live center is not normal and we agreed on my proposal refund which basically covers the purchase of a new live center. He could not ship one from EU, and I did not want him to ship from China, which is why we agreed on refund so I can buy from someone else. For the chuck play, he basically said that that's normal, "you get what you pay for", which I understand very well also, even though I was hoping for something better and it is actually outside his own specifications.Anyway, with the refund I paid 250 USD for the 4-jaw 100mm 4-th axis and the MT2 tailstock with the damaged center pin, which I think is still usable, unless I really need the very sharp pinpoint edge. I think that's a good price.

What I did so far to improve the situation is that I removed the chuck and the pulley and cleaned up everything. I reassembled the pulley and also moved the stepper pulley out a bit. After this it's a bit better, there is not as much play in the pulley as before, but of course, the chuck is the important part.

Before reassembling the chuck, I made some measurements on the chuck plate, and that shows no real problem as far as I can judge, so that's good. The thing I noticed was that it was very hard to remove the chuck, and the reason for that is because the chuck plate inner flange (I don't know if that's the proper name of it) is I think a bit too large in diameter, so the chuck is VERY tightly fitted on that flange, I think it is too tight because there is ZERO possibility to adjust the chuck. I will see if I will try to do something about that later, but for now I don't have time, so I just reassembled the chuck after cleaning the surfaces and made some new measurements. To my surprise, the play is now half of what it was before, so it is definitely within the specifications, which means that I am satisfied for now.

So for now, I am OK with this as it is, I will test it ot for some real work also before I try to fix anything more. Perhaps one thing I will do is that I remove the chuck once again and try to clean that flange with some very fine sand paper, maybe some grit or something else will be removed by doing this which might improve it even more. I feel that before staring to grind anything I will need to learn some more about using the 4-th axis. I don't want to destroy it or make it worse, after all, a slow start with a less then perfect chuck is better than a destroyed and useless one.

[Kitwn]

This link is to a video by Dan Gelbert who started from nothing and built up a whole business based on high precision machining. In this video he demonstrates a scratch-built lathe accurate to one micron, including details of the chuck. This is only one of many videos by Dan. Fascinating stuff for geeks like us.

Kit

https://www.youtube.com/watch?v=sFrVdoOhu1Q&t=40s

[A_Camera]

This link is to a video by Dan Gelbert who started from nothing and built up a whole business based on high precision machining. In this video he demonstrates a scratch-built lathe accurate to one micron, including details of the chuck. This is only one of many videos by Dan. Fascinating stuff for geeks like us.

Kit

https://www.youtube.com/watch?v=sFrVdoOhu1Q&t=40s

Thank you for the link. It's really interesting to watch, too bad it ended so suddenly. I wish there was a part two and three also...

He said it's "very easy" to make a machine like that, though I think that's overestimating most of the humanity, because even though I regard myself as very capable of doing many things, I doubt I could make one which is as good as his machine. Anyway, it was a joy to watch that. I love the idea of air bearings also and his demonstration of it. I also love how quiet that machine runs, but I suppose that's largely one benefit of the air bearings as well.

Back to the topic, yes his chuck is special, like the rest of the machine. The idea of moving pins in the chuck jaw is good, but again, requires very high precision, so in the end, I think traditional chucks are better for the "average Joe" most of us are.

[cropwell]

A 4 jaw chuck allows you to hold square stock. An independant 4 jaw allows you to do offset milling, but is a PITA to set up every time if you don't need it.

[A_Camera]

A 4 jaw chuck allows you to hold square stock. An independant 4 jaw allows you to do offset milling, but is a PITA to set up every time if you don't need it.

Yes. That's why I was only interested in the self centering type. Individually adjustable chucks are very good when really needed, but I figured that an independent 4 jaw is a real PITA most of the time because every time you swap a work piece you must recenter it, so in the end you might not get better accuracy in general due to lack of patience, even if on occasions you can get 100% accuracy after spending a lot of effort on centering. I don't think I will buy a 4-jaw chuck with independent jaws, but will however buy a 3-jaw chuck later on since that is more suitable for some work.

[Muzzer]

Another option is multisize collet chucks. https://www.ebay.co.uk/b/burnerd-collet/bn_7024823313

Still quite a few around and a set will cover a wide range of sizes with very good runout. There are several types but mine (EC?) go up to 38mm with no gaps. You might get a chuck for £200 and a set of collets for a similar price if you keep your eyes open.