Colchester student lathe

[Nick AndrewsParticipant @nickandrews96758]

Hi ,I have just acquired a Colchester student lathe,i saw it working and was all good from a dealer but since finally getting it all wired up it won’t run in high speed ,it runs in low speed ,in high the chuck wants to rotate ,but the best way to describe the noise is that it grunts,there is the occassional grunt in low speed on start up but every now and then .i am running it from a 3 kw rotary converter ,the lathe motor is two speed 1.5 /3.0 up,anyone had this and what can be done,regards nick

[Nick AndrewsParticipant @nickandrews96758]

Will not run in high speed

[John RuddParticipant @johnrudd16576]

If the lathe was ok at the suppliers running from a 3 ph supply and you are now trying to run it from an rc unit, sounds like an issue with your converter?

Any noises from that when the lathe starts?

Are you running the lathe in high speed from a stopped condition?

Edited By John Rudd on 26/09/2017 08:26:11

[Nick AndrewsParticipant @nickandrews96758]

Yes been trying to run from a stopped position ,rc makes no noise when starting up but the lamp on the lathe does dull as it accelerates, in high speed the chuck wants to rotate but sort of grunts ,a couple of times it did actually reach full speed

[Neil WyattModerator @neilwyatt]

Is it a two speed motor?

I have heard they won't run properly off a static converter, you need a rotary one.

Neil.

[Nick AndrewsParticipant @nickandrews96758]

Yes it’s a two speed motor 1.5/3.0 hp and I have a 3 kw rotary converter, thought I was doing everything correct

[Clive FosterParticipant @clivefoster55965]

Rotary converter is almost certainly too small. The high speed setting of these two speed motors is notoriously demanding on start up current and many of the standard rotary converters aren't up to the job despite theoretically having enough power capability. If its new talk to the supplier. They ought to be able to supply an extra boost set of capacitors with automatic switching which might give it enough kick to get going.

Quick and dirty option is to add a free running pilot motor. 3 HP should do. With the pilot running there should be enough "generating" capacity to supply the start load on the motor to get things moving. Cut the extra pilot out as soon as the lathe motor comes up to speed. Besides acting as a third phase generator and rotary transformer the pilot motor on a rotary converter also acts as a spinning mass energy store. When the load motor comes on some of the rotational energy gets converted into generated power. If there is ever next "Help sort my converter" time I'd be tempted to try flywheel.

In my view commercial rotary converters are usually undersized in the rotary department. Usually the motor rating is less than the actual converter rating. Old line advice is that it should be bigger. When I converted a 3 KW MotorRun static converter to rotary I put a 5 HP pilot on it. Worked very well even on two speed motors. Brute force has its moments. I'm somewhat skeptical of the claims for "more sophisticated" rotary converters with so called load matching capacitor switching to more exactly match the motor demand and specially wound rotary elements instead of standard motors. My limited experience suggest that although they work OK in less demanding applications they can't handle the tough jobs. More to go wrong too.

Clive.

Edited By Clive Foster on 26/09/2017 23:43:32

[ScrumpyParticipant @scrumpy]

I have the same problem but I've come to except the following Low speeds full range High speed not the top speed but I can live with that as its a good machine

[Stuart BridgerParticipant @stuartbridger82290]

Slightly different scenario, when I first got my Chipmaster, which is VFD powered with the original variator and motor. It wouldn't run at full 3,000 RPM. It was drawing too much current. Following an oil change and a gentle run in with gradually increasing the speed. It will now run at top whack, provided it is warmed up first. Not that I really need 3000 RPM!

[larry PhelanParticipant @larryphelan54019]

For what it,s worth,

I had a similar problem with a static converter which would run my lathe,mill,bandsaw,1.5 hp motors each,but would not even start my planer or spindle moulder 4hp motors each.

Enter a 10hp rotary converter, end of story !

I recon your converter is just too small,size matters !

[Nick AndrewsParticipant @nickandrews96758]

Hi ,thanks for all the advise,I decided to speak to the manufacturer of the rotary converter as I bought it from new(converter king)as it happened he is from Birmingham and was is Bournemouth today (I live in Portsmouth)and offered to come round and introduce himself and see what was what ,initially he thought it would be a case of adding a few capacitors ,but it wasn't and spent the next 90 mins checking everything out ,a very knowledgeable man,but cut a long story short he had a 4 kv rotary converter in the boot as a back up plan and suggested we should try it out,hey presto all my troubles gone ,he had added two hours to his travelling time along with the time he spent with me and only charged me the difference in the price of the two .Clives post was pretty much spot on .Can not praise Alan's services enough at converter king and well worth a call if you need advice,nick

[HopperParticipant @hopper]

Great to hear that old fashioned customer service like that still exists. Happy latheing.

[Author]

Posts