How to change gears in C4 lathe

I have to admit that this new change gear system SIEG has done is just wonderful, as the change can be done in a minute and easily without any modifications nor hard to reach places.

First open the small socket head cap screw from the front to get the gear cover open. Inside you'll find the regular arrangement of gears. In this picture I have the new gears ready and the BC-gear pairs mounting axle dismounted and all the necessary tools to make the change.


Put the sleeve with the key on the axle, then the small washer and thread the T-nut on the axle a little. Slide the T-nut behind the geartrain holding arm and the washer on the front side. Snug up the axle with fingers.


Slide the B gear on the sleeve and then the C gear after it. Now move the axle so that the C/D pair engages properly and tighten the axle with a 7 mm wrench. If the A/B pair gets in the way or is not engaging, open up the socket head cap screw in the lower end of the arm, located just behind the D gear and turn the arm down a little. When you have C/D engagement correct, move the arm to engage A/B properly and tighten the arms screw.

As a last operation drop the cutout washer on the axle and thread the locking nut in place. Even fingertight is enough, but I'll usually snug it up a little bit with a wrench to be sure it doesn't open up under vibration.

This is so easy and fast to do than on the older C2 lathe that I could change the gears just for the fun of it! :)

Test chips with the C4 lathe

Two words: Eye protection. Really, this thing makes chips fast and not just bogging sounds like the old C2 lathe I had. Here is a nice comparison photo of the old C2 lathe that I had and the new C4 lathe that I now have, both mounted on the same table in both pictures. Have to find a place or build a stand for the drill press, as it is a good thing to have when the mill is reserved.



I whipped up a quick test to see how much better this new C4 lathe is compared to the C2 that I previously owned. I found a piece of steel scrap from my material box that measured about 60 mm in diameter. The only tool that I had ready for this test was an old but sharp HSS turning tool measuring 7.5 x 7.5 mm, so I had to shim it up 2.5 mm to get to about center height.

I used an RPM of 150 which means about 28 m/min surface speed. The recommended speed for HSS in steel is about 25-30 and with coolant, but I did this test dry. I touched the workpiece and dialed a depth of cut of 1 mm and engaged longitudal feed. The feed was 0.15 mm per revolution, so something between a roughing and finishing cut.

As the tool came to contact with the steel bar I could hear a small bogging sound in the RPM but at the same instance the motor grunted more power and chips started to fly around. Hot blue chips on to the table, the floor, over me and that was the point I withdrew the cross slide and cut off the feed. Just..wow! On the old C2 lathe steel would have been a problem and basically anything with a 60 mm diameter, but this machine barely noticed that there was something in the way of the cutting tool.

The other test I conducted was a drilling test to see how big drill bit can be used safely in to solid steel workpiece. The tailstock has a #2 Morse taper and biggest drill I know for that size is 24 mm in diameter, so I used that size drill bit. The tailstock ram is better than in the old C2 lathe as it can hold a Morse taper with the tang in place. But there is no slot in the end of the ram for the tang to go in to, so there is a risk that a little bit loose tool can turn in the taper.

I set the RPM to 350 to provide about 28 m/min cutting speed and I had no pilot hole in the test piece. The tailstock tended to come loose from the lever lock but when I kept it in place the drill went in nicely and the machine power was more than adequate to drill the hole.

After drilling I noticed that the tailstock ram was a little bit stiff and revealed that the small M6 grub screw that acted as a "key" was a little bit bent. No wonder under that load, but have to put a new screw in there.

I can't wait to get my new Multifix Aa type quick change tool post and to modify the DNMG carbide insert holder to a 12 x 12 mm size, as it originally is 20 x 20 mm. I already milled and surface ground the height to about 11.90 mm, but the width is still to be done. The turning insert holder cost me 68 EUR plus 36 EUR for 10 pieces of DNMG 110404 inserts. This holder I bought from the German eBay seller cd-tools.

Frank J. Hoose Jr. at mini-lathe.com did also a nice review of this C4 lathe which you might find interesting.

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).

Pros

• 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.
  

Cons

• 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.