manual lathe machine

[uzobethel]

plz am doing a project on an old lathe machine.the machine has its contactor bad i want to knw the consequences of running the connection straight that is by-passing the contactor

 

[canadianhorsepower]

plz am doing a project on an old lathe machine.the machine has its contactor bad i want to knw the consequences of running the connection straight that is by-passing the contactor

It would be a bad idea
contactor are high current relay they take the beating when
you start your lathe, that's what they're made for:fan:

plugging it direct would cause severe arcing when plugging and unplugging the cable

 

[n4zou]

Another reason not to do that is the inability to shut it off in an emergency. You could get your clothing hung up in the lead screw or feed shaft and be unable to shut it off before serious injury occurs.

 

[Swifty]

Exactly as Luc said, if no contactor, you would have high current running through your on / off switch causing all sorts of problems.

Paul.

 

[ornithorhynchus]

Contactors are the quintessential item of
the electrical circuit, especially when switching
high current loads frequently.

Imagine yourself trying to switch a light switch,
slow in the electrical sense, which cause an arc to
flow between to silver contacts. This arc slowly
burns out the contacts, thus overtime you need to
replace the light switch.

Now, the contactor, it's requirement is to switch a
high load in say .002 of a second, thus stopping the
arc flash which in turn reduces the load on the switching
gear, wiring, msb and transformer.

Think before you take out. If you need to replace then
replace with same.
(from your electrician)

 

[chrsbrbnk]

Threre's a number of surplus shops both on the internet and probable in your town that have surplus contactors like for $10 or so well worth installing

 

[Hopper]

Although, the 1hp motor on my lathe has been wired directly with a plug and relies on the switch on the wall outlet for stop and start. Been running like that for at least 40 years.

 

[va4ngo]

Hooper, you need to reach the wall to switch off? I recommend you read incident and accident reports for what you do. Not good engineering or work safe practice.
Phil
Melbourne Australia

 

[canadianhorsepower]

Although, the 1hp motor on my lathe has been wired directly with a plug and relies on the switch on the wall outlet for stop and start. Been running like that for at least 40 years.

I also know people that have been playing Russian Roulette and were lucky
but one day

it could be worst ask your insurance company how do they feel about this:hDe:

 

[gus]

Manual isolators are not designed to handle the high making/breaking current when switching on or off motors. I witnessed flash-over severely scorching a mate's face.He lost his eyebrows and some hair. Lucky for him he had glasses and eyes not burned. I did warned him about bypassing the faulty contactor to test spin 10hp 415/3/50 Squirrel Cage Induction Motor.

Most low power mini lathes have no motor starters. I have no idea on the border-line above which a motor starter is mandatory. Our desk fan/stand fan/ceiling fan have no starters.

 

[Tin Falcon]

Most low power mini lathes have no motor starters. I have no idea on the border-line above which a motor starter is mandatory. Our desk fan/stand fan/ceiling fan have no starters.

True from what I have seen this applies to fractional horsepower motors.
The larges motor I have dealt with was a 1 hp dc motor and the circuit was set up to start the motor and minimum rpm and then speed up after the initial start up.
I think the lesson here is if the OEM installed a contator do not bypass it. If it is faulty replace it with a direct replacement or suitable substitute. If you are not qualified to determine suitable or not qualified to replace hire someone who is.

Tin

 

[chrsbrbnk]

this is really not rocket science Look at the full load amperage on the motor, as a rough guess your starting switch or contactor needs to be at least 2x the amperage at the correct voltage , dc current may derate the switch slightly. Doing this decently also might allow you to have a reverse switch position on controls. The relay approach also allow you to have the machine be depowered when there's power interruption and the like, preventing accidental activation. it also allows for low voltage controls, may pay off in damp conditions and also allow for a nice big emergency off button, may save a life or limb. So if your motor is above say 1 hp think about going a relay starter approach and if under 1hp get serious and put a decent switch on it. an old toolmaker with all his fingers and thumbs... Chris

 

[gus]

True from what I have seen this applies to fractional horsepower motors.
The larges motor I have dealt with was a 1 hp dc motor and the circuit was set up to start the motor and minimum rpm and then speed up after the initial start up.
I think the lesson here is if the OEM installed a contator do not bypass it. If it is faulty replace it with a direct replacement or suitable substitute. If you are not qualified to determine suitable or not qualified to replace hire someone who is.

Tin

Hi Tin,

Good advice.

 

[gus]

this is really not rocket science Look at the full load amperage on the motor, as a rough guess your starting switch or contactor needs to be at least 2x the amperage at the correct voltage , dc current may derate the switch slightly. Doing this decently also might allow you to have a reverse switch position on controls. The relay approach also allow you to have the machine be depowered when there's power interruption and the like, preventing accidental activation. it also allows for low voltage controls, may pay off in damp conditions and also allow for a nice big emergency off button, may save a life or limb. So if your motor is above say 1 hp think about going a relay starter approach and if under 1hp get serious and put a decent switch on it. an old toolmaker with all his fingers and thumbs... Chris

Hi Chris,
Good advice. Still having all ten fingers is good indication,you took personal
safety seriously. Though I still ten fingers now at 70, the left thumb does not bend well due to wearing cotton thread globes while drill many 1/4 holes and globe got grabbed by swarf and drill.

 

[chrsbrbnk]

yea I was going to leave the bit about beginning arthritis out. there's few enough people in the occupation or hobby

 

[Hopper]

Hooper, you need to reach the wall to switch off? I recommend you read incident and accident reports for what you do. Not good engineering or work safe practice.
Phil
Melbourne Australia

No. The switch is at the end of the lathe, not behind it.
I keep my chuck keys and tool post wrenches etc on a board behind the lathe so no room for a switch there.

 

[Engineeringtech]

About 4 years ago, I noticed arcing in the contactor box mounted on the side of our Bridgeport mill. I opened up the box, and found that all the wiring insulation was dried and cracked. It was a tangled mess too. I wired the three phase directly to the three phase switch on the side of the head of the machine. I've switched the machine on 10 - 20 times a day for the past 4 years, and have noticed no problem. Lathes tend to have bigger motors though, and maybe that would be an issue. One thing I know is that having a long cord, introduces a small amount of resistance, which reduces the inrush current. I suppose the inductive arc you get when you switch off the motor is a bigger issue. Probably some varistors might help there...

8/26

I should say, that just because we got away with wiring the power direct to our motor start switch, bypassing the contactor box, that you should be very wary about doing this. Motor contactors are designed to switch high currents, and resist electrical arcing. We may have long term issues with the switch on our Bridgeport head. The pictures show the switch on the side of the head, and a contactor SIMILAR to the one we removed. The one we removed did not have start and stop buttons. It only had a reset button.

 

[canadianhorsepower]

plz am doing a project on an old lathe machine.the machine has its contactor bad i want to knw the consequences of running the connection straight that is by-passing the contactor

can you send me a picture of your contactor
I might have one here, that I can ship to you

cheers