[clarnibass]

Hi

I was reading about small lathes for months and only now found this website
I'm a musical instrument repairer. English is not my first language and I'm not an expert with lathes (i.e. the terms and names of the parts) so I hope you can bear with me...

I had a Sherline lathe (long bed model) for years and wanted to change mainly to get more space for parts and instruments. I changed to a Sieg SC3 (400mm between centers) a few weeks ago and I'm not completely happy with it... I worked for over 30 hours making the head, tail, carriage, slides, etc. as aligned and as accurate as I could. I even replaced the bearings with high quality angular contact bearings. I solved some other issues (e.g. chips getting into the carriage gears). After all of this I'm still not sure the lathe is good enough...

The short version is that I'm considering replacing the Sieg lathe.
Some of the main problems I had so far were when parting, turning finish and the entire setup going whacky (I'll explain). I'm wodnering if any of that is a result of the lathe or me...

I was working on a 35mm diameter aluminium tube (pretty thick walls), making shaker (the musical instrument) as an experiment for the new lathe. It was sticking out about 12cm. I haven't worked on a large part like this on the Sherline but it was close sometimes and I did work on 45mm diameter plastic (obviously not the same but still...).

When turning, if I used power feed I got poor finish. Even for cuts approx 0.05mm (0.1mm off the diameter). If I used approx the same speed feed but manually I got significantly better finish, but not great. If I did a very small cut (let's say 0.025mm) with power feed, then if I reversed the turning and power feed directions, instead of a spring cut I got the entire to make noises and jam. This happened if the first (forward) cut was a spring cut.

I was trying to part off 35mm aluminium rod and this was extremely difficuly. I had to do it super slow and it still was noisy and chattery, far more than I thought it would be. I haven't worked on aluminium on the Sherline so maybe the size and the material were the reason and my expectations are unrealistic?

I really tried to adjust the lathe far beyond what I read about in all the mini-lathe websites, etc. so if even more adjusting is needed I'm losing my patiance... It is definitely not so stable because even if I press the head a bit I can hear the tool noise changing, which means it is cutting more/less depending on the direction I press.

So I found some other lathes that I'm considering. Kilppfeld, Wabeco and Proxxon, or any used similar lathe. I'm very limited in space and haven't found any used lathes that would fit. I just can't do anything about it, it's either a lathe that fits or no lathe (or in this case, keeping the Sieg). Also consider that I'm using the lathe at most once or twice a week for a little bit. Sometimes it's a month that I don't use it at all. It's not a lathe that works all the time and not one of my most important tools... but I'm tired of cheap and bad tools...

I eliminated the Klippfeld because the smallest one is too big and it's not sold here anyway.
I probably eliminated the Wabeco because the larger model is far too big and the smaller model is only 35cm between centers which is really borderline. It's really annoying to have one or two cms missing when you need them... and I often mount approx 26cm in a chuck and a live center... these are clarinet sections and one of the main reason I bought a new lathe.

That leaves the Proxxon. So... should I expect the Proxxon to be significantly better than the Sieg and not require all of ridiculous adjustments?
The two main problems I'm not sure abotu the Proxxon are changing belts to change speed and the power feed. The Sieg is variable speed and has a handle to to engage the power feed gear. The latter isn't critica, it's just much quieter when it's not engaged.
If I understand, on the Proxxon it is necessary to open the case to change belt for speed and also for engaging or disengaging the power feed gear, right? How annoying is that in comparison? Can I expect a Proxxon to not have the problems I mentioned I have with the Sieg?

If the Proxxon was truely accurate out of the box and had a variable speed motor I would probably go and buy one right now... but now I'm not sure what to do...

Help...?

Thank you

[hanermo]

Please dont take thus the wrong way ... but ..
I think your problem is
1. lack of skill and experience,
2. far too small a lathe, for *what you did and *how you did it

1. 12 cm overhang, on 35 mm diameter alu, is very prone to chatter and vibration
A 0.1 mm cut on this will not work well, in general

2. Because there is a lot of moment-arm on a tiny lathe like this, the problem is greatly magnified

The 0.1 cut would work on my 12" *industrial lathe, but would not work on my tiny 7x lathe, at all.
It would be ok, but not great, on my big lathe, that is about 20 times more rigid.

If you support the workpiece with a tailstock, the setup will be 100x (honestly, the 100x is engineering, not an opinion) more rigid, and will likely work.
3. Use half the depth of cut, 0.05 mm, to 0.03 mm, to finish with.
4. Use a new CCMT insert.
The above would work, on the small lathe.
I am not saying something else may not work. I am saying that the above will definitely work.

In general, you are trying to never cut more than 1-1.5 diameters from the workpiece D.
Thus, for 35 mm D stock, the max overhang is == 50-60 mm.
After that, you *need* to use a steady rest or TS support.

In my opinion, none of the options mentioned would be significantly better.

Basically, look at adding about 4x the mass, == 150 kg, in the lathe.
Heavy is not = big, it can have the same size.

I made a big, 150 kg, rigid bed for my 7x lathe.
It was a total success, and improved it 200%.
BUT..
It was a waste of time and money. I should have started with an 8x lathe, instead.
Making a good rigid bed cost about 250€ in cash, and 200 work hours.

I then went on to a 12x24 lathe, almost the same size in foorprint, its only under 10 cm large on all edges, than the 7x (total 20 cm more room).

[clarnibass]

Thank you. That is more or less what I was hoping to hear. Regardless of that, I can also feel/see how the Sieg is cheap and not made so well (had a few major issues to fix, such as incorrect angle threaded hole in the bed, causing the lead screw to bind), so I don't like it... but if I can "solve" the problems without changing a lathe that is best.

I'm sure I lack experience. Machining is such a small part of what I do overall and I'm pretty much self taught with the Sherline. 80cm length (or width actually) and 30cm depth are the absolutely maximum foot print I have for the lathe. First I'll try to secure the lathe better to the table and see if that makes a difference.

By the way, the parting of the 35mm diameter aluminium was very close to the chuck (approx 10mm) and even when it got to half the diameter and less it kept having the same problems.

I understand what you are saying about the 35mm long tube, but I don't see how a spring cut forward will then cause all hell to break loose (is the correct expression in English?) when I just do a backward spring cut after? It refused to move and I started seeing chunks and scratches on the piece, the tool digging into it, etc. The finishing cut wasn't even 0.03-0.05mm. It was under 0.015mm and even a spring cut... and still problems.

Thanks again