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Tuesday, January 4, 2011

Pros & cons of the SIEG C4 lathe

I have had the SIEG C4 lathe for a couple of weeks now and although I haven't had the opportunity to turn anything to chips with it yet, I have seen quite many good and not so good things in it while disassembling, cleaning and assembling. My comparison level is basically the older C2 lathe and the "real" lathes that I use at work (TOS and one huge chinese machine).

  • Weight is a nice 94 kg and comes from the bed casting mostly. This is a good thing to have, except I would list it as a con when I have to lift it to the workbench or move it around. The size of the lathe in terms of travels didn't increase that much from the SIEG C2 lathe, but the weight really jumped from the 37 kg mark, so this really is a big jump from SIEG.
  • The 1000 W brushless motor really provides tremendous torque versus the C2 lathes 250 W DC motor that had brushes.
  • LCD dislay for RPM reading
  • Leadscrew cover keeps the chips out of the screw and also protects fingers, as the screw has a keylot along its lenghth and it has quite sharp edges.
  • Leadscrew bearing blocks and the apron both have hardened pins to lock them in certain place and this helps keeping things in proper alignment. More points from using pins that have a threaded hole to help yanking them out if needed.
  • Tailstock has a lever operated locking mechanism, very fast to use especially when drilling deeper holes than the quill movement is.
  • All metal change gears are nice and have precise holes that allow smooth sliding fit to the axle ends when installing, unlike the C2 plastic gears that had an undersized hole in them.
  • Metal gears in the headstock transfer more power than plastic ones and will also handle more loading conditions without chipping a tooth.
  • Oiling ports everywhere: Apron, carriage, tailstock, spindle, gearbox axles, leadscrew bearings, cross slide, headstock etc.
  • Split nuts in the compound and cross slide movements provide a mean to adjust the backlash to a minimum. In basic turning operations the backlash doesn't have any effect on anything and in some instances it is a nice feature to have.
  • Carriage handwheel has a graduated collar that measures 0.5 mm between lines. Very good update from the C2 that had no kind of way to get Z-axis measurements.
  • Carriage handwheel can be disengaged by pulling so that it won't rotate while power feeding.
  • Cross feed helps hands if turning larger diameter parts.
  • Feeding directions are logical in the sense that when the Z-axis feed is towards the headstock, the cross feed is towards the center of the part.
  • The changing of gears is easy due to the B/C gear arm that is very quick and easy to adjust.
  • Total indicated runout of the spindle MT3 bore is 0.005 mm or less
  • Total indicated runout of the chuck index is 0.005 mm or less
  • Total indicated runout of the spindle face is 0.01 mm or less
  • The tailstock ram accepts full size #2 Morse taper tools unlike the C2 lathe that required the tang to be cut off to utilize the full movement of the ram.

  • Spindle and leadscrew relative rotation directions are fixed. There is no change lever like the C2 had, but then again, how many times that was needed? Personally I never used it.
  • Cross feed speed is sssslooowww compared to the longitudal feed at the same change gear setting. Basically if the longitudal feed is 0.1 mm per revolution, the cross feed is only about 0.032 mm.
  • The change gear cover box doesn't come off unless the electrical cabinets panel with the small fan is removed first, as the panel screw heads will be in the way. And removing the little screws is dificult because the gearbox cover is in the way.
  • There was either sand mixed with heavy oil/lube or some sort of course lapping compound in the headstock gears that was causing huge noise and was a possible wear inducer.
  • Almost every electrical wire is either blue or black inside the machine. Not good when trying to figure out where some wire went, but at least some wires had labels on them.
  • The beeper is plain annoying. Beep when you turn the machine on, beep when you push the buttons. A jumper on the PCB for disabling it would have been a nice feature.
  • The safety interlock in the chuck guard is not logically done: If you don't push the microswitch (like remove the whole shield), the machine runs fine. But when you push the switch, the machine shuts off.
  • The tailstock can bump in to the gib screws of the cross slide. This could be prevented by installing a small screw in front of the tailstock.
  • Painting has been done for a half-assembled machine, as there is painted socket head cap screws, some not painted, some parts painted that should not be (like the carriage gib "paws") and the paint also flakes off easily from the cast iron surfaces.
  • Carriage gibs don't have counteracting screws or locking nuts for good adjustment.
  • The cross feed dial is reading radius and not diameter as would be useful.
  • The cross feed dial numbers don't correlate to any "real" values, they are just for counting.

All things considered with the relatively low price of 1100 EUR that I paid for this is a very good investment and the SIEG quality has gone up since the C2 lathe. Personally I can suggest this C4 lathe to others and say that I very much like it.


  1. Nice Blog! Well most of your content and image is original and informative. /many thanks for sharing this, cheers.

    Shop Electronics

  2. The cross feed dial numbers don't correlate to any "real" values, they are just for counting. - are they not graduated at 0.5mm per revolution?

  3. editor, the cross feed dial has 50 small lines on it, meaning 0.02 mm per line (radius) as the screw is with a 1 mm pitch. But the numbers that are engraved (like 10, 20, 30, 40) doesn't mean anything, they are not measurements, they are just for counting.

    For example, I want to have a 1.4 mm depth of cut and I have the cross feed dial at zero mark. I turn one full revolution to get 1 mm and then the 0.4 mm is...well, umm..have to calculate: 0.4 / 0.02 = 20, so I have to turn the crank so 20.

    Now you can see that the number 20 that is on the graduated wheel doesn't mean anything, as it should read "0.4" on it (or actually, 0.8 if reading in diameter as I'm used to).

    Hope this cleared :)

  4. Thanks for that -must admit have same problem with my cheap Chinese mill. Not quite sure why they cannot just mark the dials correctly? Have I missed something?

  5. editor, have to say that I don't have a clue as to why they do it that way. I'm about to rip the handwheels off, take some measurements and make new ones with proper dials that will read diamter for the cross slide and millimeters for the carriage :)

  6. Hi Jaakko, thanks for the great blog! You mentioned between "cons" that "Spindle and leadscrew relative rotation directions are fixed." Probably you had also figured out the solution since than, however you may check my blog here about that issue.

  7. Hi Gabor

    Thanks for that piece of information, very informative! Hadn't even thought of that, as it is very rare or never that I do left hand threads.

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  9. Hey, I have a Sieg C4 lathe too! Thanks for sharing your experiences.

    How much play is there in your spindle gears? I've noticed mine has gotten worse after 2mo of use -- it makes a tapping sound when rotating the chuck right-n-left.

  10. Curtis, thank you for your comment! :)

    There is a slight play in the spindle gears and seems to be quite normal. A small play doesn't do any harm other than it is annoying. Did you clean the gears from the obvious lapping compound that I talked about in the "cons" of the article? I'm pretty sure it is what wears them out fast if left in place.

    At work I have a TOS lathe that is older than me and has a huge play in the gearset and it works just fine. Means that it has worn out much but still works fine albeit makes that clacking sound if making interrupted cuts.

  11. Jaakko,

    Thanks for the response. Being a relatively new lathe owner, I wasn't sure what to expect. I realized that there would be a breaking-in period with my equipment, so I guess I'm being a bit paranoid. Your experience and input is reassuring.

    Yes, I did clean the gears completely and lubricate them. The tapping sound is a good reminder to keep doing so.

    Without a threading dial and, as the instructions state, leaving the half-nut engaged throughout the threading process, I thought the play in the spindle gears would adversely affect the accuracy of the threads if the chuck rotated slightly before the lead screw engaged to push the compound back into position. (Obviously, I haven't started threading yet).

    On a related note to your original post, some of the CONs I've encountered:

    - The shaft that goes through switch gears C & B can be tricky to tighten properly and might be slightly under sized. I've learned the hard way and sheared off the stud by not realizing that I was tightening the nut and lock washer against the threaded shaft that goes through the adjustable arm and into the square-slotted nut (make sure to hold the shaft in place with the small wrench and tighten against the counter force).

    - Related to the above, the user manual that came with my lathe (bought in US) is a blurry photo copy, is incomplete, and has poor schematics of the parts. This makes ordering replacement parts difficult. Luckily I was able to find other Sieg resellers (Grizzly) that had complete PDFs of the manual online.

    Thanks again and looking forward to see what modifications you find useful.

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  13. Is it possible that the "40" represents thousandths of an inch?

    1mm = ~0.040inch (0.03937...inch to be exact).

    What's the parallel feed's divisions?