Sieg lathe motor conversion

[76dave]

If you look at the last photo in my original post, you will see that the lathe controls are on a pendant, with a cable which connects to the inverter. This is located on the bench at the tailstock end of the lathe, so well out of the way. Before investing in the 3 phase inverter system, I had the original motor fail. (shorted windings on the armature). Bought a replacement motor (about 100 beer tokens) and fitted it. A few weeks later the control board died. (probably damaged by the motor failure). Rather than pay for replacement board, which are notoriously unreliable anyway, I decided to splash out on a full 3 phase inverter system. I selected a half horse power motor (about 320 watts), which was as near as I could get to the original 250 watt motor.
The lathe is actually raised up to a comfortable working height, by mounting it on two pieces of thick walled 80mm square tubing. This also enabled me to fit a home made coolant system underneath. I fitted a longer tube at the headstock end and made and fitted a 10mm plate to take the motor (see photo) The whole mod was done for reliability as I was fed up with unreliable ,expensive Chinese crap.

 

[Steamchick]

Good stuff. Well thought through. I like the idea of the controls on the pendant - I missed that. Are the 2 square section steel supports joined other than by the lathe? All the components joined together make a much stiffer support that helps keep the lathe true (I know the problems of weak supports because my lathe is poorly supported!).
I think you will enjoy your new motor?
K2 ☺

 

[Nikhil Bhale]

Nikhil, FYI: recently I was cutting threads on some brass and bronze fittings - really easy to machine, but reached the limit for the lathe.

HI,
The last time I run my lathe was about 1 month back. I made a backplate for my new 5" 4 jaw self centering chuck. The lathe was cutting the steel plate quite easily. DOC was about .3mm and rpm 200 if I remember correctly. Now after reading your post I have to plan and fix the lathe to something stiff. It is only fixed to the chip tray it came with originally and is kept on top of a 30mm thick stone slab table top.

Regards
Nikhil

 

[Steamchick]

Hi Nikhil, Good idea. It is what I should have done many years ago - before I joined this site and learned about things I didn't learn at school, or during my apprenticeship (because the machines were already installed and set-up).
There are "proper people" on this website who can advise and help better than I can, so when you want to ask I suggest you raise a new thread?
I may know some stuff, but not all, and not all that is "best practice".
K2

 

[Steamchick]

Hi Nikhil, I have a larger lathe, that very crudely, I can stop the motor with a wrench using less than the torque I apply to car wheel nuts (80ftlbs).
But doing some very approximate modelling of the stiffness (actually deflection under load calcs.) of the lathe bed versus 2 in square and 3 in square steel tube, I conclude that the lathe bed (cast iron, from China, is only about as stiff as the 2in. square tube. So to get a GOOD stiffer base I need at least a 3in square steel tube (rectangular) welded frame bolted securely to the feet of the lathe bed. This should halve the deflection of the tool when cutting at the further part of the lathe, approx 20 inches (0.5m) along from the headstock.
I guess you have a smaller lathe, less torque? Shorter bed? slimmer and therefore the bed is not as stiff?
But if you can bolt it securely, or clamp it to the stone slab, then that will make a big difference.
You can do some checks. Use a torque wrench on a bolt fitted into the chuck, to measure the stall torque from the motor. - Don't power the motor stalled for more than a couple of seconds! A quick "ON and OFF" is all I do... with controller at lowest speed. Then apply this torque (using your super muscles!) to the chuck while holding the lathe on the table at the furthest setting of the tailstock. You will probably "feel" the twist as it lifts a foot off the surface? - BUT you need to be able to lock the mainshaft (safely) somehow.
You can of course do some sums, or look-up the motor's torque details and do the sums on the gear (pulley) ration to the mainshaft to see what torque you can get at the chuck...

Enjoy!
K2

 

[ajoeiam]

Hi Nikhil, Good idea. It is what I should have done many years ago - before I joined this site and learned about things I didn't learn at school, or during my apprenticeship (because the machines were already installed and set-up).
There are "proper people" on this website who can advise and help better than I can, so when you want to ask I suggest you raise a new thread?
I may know some stuff, but not all, and not all that is "best practice".
K2

It would seem that the number of people "who know how to set up things" is shrinking.
Ditto for me - - - when you're learning or working - - - machines are already set up - - - - setup - - - I think - - seems to be a different kind of art form.
(Hmmmmm - - - wondering - - - - anyone on here that has a background in machine setup and installation?)

 

[Nikhil Bhale]

It would seem that the number of people "who know how to set up things" is shrinking.

Hi,
We recently got a new lathe installed on the oil rig where I work. The shipyard people just made a base of heavy angle plates and bolted the lathe to it. No checking of anything was done.
Lathe was purchased only to fulfill some commercial requirements and to put a checkmark on some checklist. The lathe will be used once in a blue moon and that too for non precision work. We don't have a trained machinist to work on the lathe. All our lathe jobs are done shore side at a proper workshop.

Regards
Nikhil

 

[Steamchick]

Heavy angle plates welded to an oil rig sounds stiff enough to me, apart from the induced twisting distortion when they tighten down the last mounting bolt with heavy hands on the spanners to pull the last gap closed... "What? It must be shimmed? It'll do for what we want!"

K2

 

[ajoeiam]

Hi,
We recently got a new lathe installed on the oil rig where I work. The shipyard people just made a base of heavy angle plates and bolted the lathe to it. No checking of anything was done.
Lathe was purchased only to fulfill some commercial requirements and to put a checkmark on some checklist. The lathe will be used once in a blue moon and that too for non precision work. We don't have a trained machinist to work on the lathe. All our lathe jobs are done shore side at a proper workshop.

Regards
Nikhil

A precision level doesn't cost that much - - - - too bad.
After a while bolted down hard and not level the bed will develop a nice warp!
Precision - - - if there's enough stress - - - well it might even do some other funky things.

Maybe you could offer to cross train or what ever its called so that you could also run the workshop equipment.
(If you're comfortable running a 8" x 14" lather you can certainly run a 18" x 40" one - - - its not that different. )

 

[william_b_noble]

Hi,
We recently got a new lathe installed on the oil rig where I work. The shipyard people just made a base of heavy angle plates and bolted the lathe to it. No checking of anything was done.
Lathe was purchased only to fulfill some commercial requirements and to put a checkmark on some checklist. The lathe will be used once in a blue moon and that too for non precision work. We don't have a trained machinist to work on the lathe. All our lathe jobs are done shore side at a proper workshop.

Regards
Nikhil

I think what is shrinking is the number of people who imagine that the manual might tell them anything is striking. And the number of people who can read, understand, and follow instructions is shrinking to zero

 

[Nikhil Bhale]

After a while bolted down hard and not level the bed will develop a nice warp!

Hi,

A ship or Rigs deck plating are never rigid. There is always some flexing, bending or twisting going on depending on sea condition or loading condition. The engines and propeller shaft are supported by additional strengthening frames to minimize this. Additionally there are always some vibrations transmitted throughout the structure. So unless the lathe support are very rigid it will develop some warp. Or the lathe may be supported on some stiff spring to reduce this, I have no idea.
Maybe someone who has worked on ships where lathe is used extensively can shed some light on it. Some ex navy machinist maybe

Regards
Nikhil.