A vfd for my lathe

[Carl Wilson]

Friend Alan got in touch with me yesterday about his M250 vfd conversion. He is making great progress.

Alan told me that his motor mounting plate had two of the holes filed to slots. He opined that this had been done by the original owner, to square the motor up as the rubber mounts sagged.

Mine has been filed in exactly the same way, and I assumed this had been done by Harrison on the build, especially given the rough and ready flat bars they'd made for the rubber mounts.

I'm now wondering if there was a Harrison approved mod to do this as the rubber mounts sagged - doesn't seem likely. Either it was done in the factory originally or two different owners did the same mod to compensate for the stretching of the rubber mounts. My lathe was owned by a school before I bought it, so it's possible they could have done it.

Motor will be going on this afternoon.

 

[Carl Wilson]

The new motor is fitted to the mounting plate and back on the lathe. The drive pulley doesn't foul on anything and the line up of the motor and headstock gearbox pulley was OK first time.

Belt tensioned up and running nicely.

I'm going to have to get some longer plastic convoluted tubing, or do something else to protect the motor cables ad they pass into the cabinet. The old one is now too short. Perhaps I'll just heat shrink the full length.

Think I might just rotate the box around on the motor by 90 degrees clockwise. That should give me the extra length. The outside of the box can be rotated independently of the connections.

Measurement confirms that the splash guard has more than enough clearance to accommodate the fan cowling on the new motor.

 

[Seadog]

Nicely done. I think you should learn how to post photos though

 

[Carl Wilson]

Yes maybe just a few too many! Not so much learn how to post them as learn how to remove them. Having said that, they are all slightly different. You see, but you do not observe...

 

[Pete.]

Looks like a lot of duplicates to me.

Anyway, use cable ties to keep the conduit away from moving parts.

 

[Seadog]

Not so much learn how to post them as learn how to remove them. Having said that, they are all slightly different.

Get the cursor to the right of the image nd hit the 'Delete' key. There are duplicates though

 

[Carl Wilson]

Anyway. It's not a case of needing cable ties to keep the conduit clear of moving parts. The conduit is too short to reach the gland where the cable passes through into the cabinet, because I've orientated the junction box wrongly. Turning it round 90 degrees will give me enough length to reach.

Like I said.

 

[Pete.]

Like I said.

You didn't say that, actually, but it did seem obvious when looking at the pics.

 

[Carl Wilson]

Well, never mind. We got there in the end.

 

[Carl Wilson]

Trial run today with temporary set up. Everything worked well. This is the machine running with the headstock gearbox in the lowest ratio.

Using the headstock gear ratios will give greater versatility. That way even if the spindle is going at a crawl, the motor can still be running relatively quickly to get good cooling flow from the fan.

 

[Pete.]

Trial run today with temporary set up. Everything worked well. This is the machine running with the headstock gearbox in the lowest ratio.

Using the headstock gear ratios will give greater versatility. That way even if the spindle is going at a crawl, the motor can still be running relatively quickly to get good cooling flow from the fan.

That's the highest ratio you have selected there (B1) not the lowest. Sounds very tight too I would check your end cluster gearing for appropriate backlash if I were you - it sounds like you don't have any.

You should take great care not to spin a chuck up to such a high RPM like that with nothing in the jaws. If the scroll un-winds it can throw a jaw out and at even quite low speed it can mess up your day pretty badly. At the speed you just had it running it'll fire a jaw straight through a plasterboard wall.

 

[MCKDAVID]

City Electrical Factors in Elgin, used to stock Kopex - flexible conduit.. presume they still do. While you're there measure up the belts and get a couple of new vee belts, they used to stock them too.. will run a lot smoother than link belt.

 

[Carl Wilson]

Thanks for the advice regarding the plastic conduit. I did find some in screw fix but I will try CEF as they might be cheaper. I'd always intended to replace the belts. A job long overdue, even when the machine was single phase.

I checked and adjusted the change wheels yesterday after I ran everything up. Quieter now. Regarding the ratio that is the way I've always termed it and comes from my training. Lowest ratio giving lowest reduction. Also numerically lower. Hence the term lowest.

I've heard the horror story of the exploding chuck but in 30 years I've neither seen nor heard of it happening. I think that's a bit like the story of the piece of optical fibre that will work it's way to your heart and kill you.

That was not the cue for a hundred exploding chuck anecdotes.

 

[MCKDAVID]

might not be cheaper for material, but no postage etc. I'd call them first and ask, it's years ago since I was up that way, so they might have changed supplier, but it's bog standard stuff for sparks so if not kopex they'll have an equivalent for sure.
aye I'm not the fan of linked belt that a lot of folks are, yes it has its uses, avoiding removing bearings shafts etc. However it's noisy, constant adjustment / stretches like a bstard until it settles and takes a set etc... handy to keep and use in a pinch, but I'll always go for v belt as a long term option.

 

[Carl Wilson]

I worked for many years in the aircraft industry. Regardless of what it says on the gear lever, the position with a 4 on it is the lowest ratio. 1:1 being lower than 5:1 or whatever it is. The numbers on the lever or terms like 4th gear etc have nothing to do with the numerical ratio.

I agree with the comments about linked belts. I'd always meant to replace them at some point but just never got round to it. Now seems like the right time!

Looking at where I'm going to position the inverter I'm probably not going to use the same routing for the cables as before. Ideally I want the unit to be inside the cabinet, my lathe is one of the 250's with a door at the front over the alcove. So I'm going to put the inverter in there out of the way.

The shortest and least circuitous route will be to go straight through the back of the cabinet with the motor cables. So I probably won't use the conduit. Not really any chance of the cables getting oil or coolant on them where they'll be, should be well out of harms way.

 

[Carl Wilson]

Ok I see what you are saying! I was thinking of the highest reduction versus lowest reduction.

I just adjusted the change wheels again and the whole drive train is even quieter now. The noise of the belts is now the most noticeable thing but that's not too bad. However I will be replacing them.

 

[Carl Wilson]

Indeed. I was looking down the wrong end of the telescope. Not for the first or last time!

 

[Pete.]

I've heard the horror story of the exploding chuck but in 30 years I've neither seen nor heard of it happening. I think that's a bit like the story of the piece of optical fibre that will work it's way to your heart and kill you.

That was not the cue for a hundred exploding chuck anecdotes.

No-one mentioned exploding chuck. I said that the scroll can unwind releasing the chuck jaws. It can and does happen, you should never spin up a chuck to high rpm with the jaws loose.

 

[Carl Wilson]

The tachometer arrived today. It looks like a nicely made unit. There are a lot of these around.

I'm going to be driving this with the 24 volt supply from the vfd. I will put a 7812 regulator in line with it to meet the supply requirements.

I am going to set the unit up with a battery drill or similar to test it.

Interestingly the unit seems to have a comms port on the back of the pcb, like a lot of Chinese made measuring instruments have.

By the way, apologies for the light reflection in the pictures.

 

[Carl Wilson]

Fitted the new belts this morning. They are SPZ825's.

Running at 750 ish rpm here. Is it quieter? Perhaps.