Member postings for PropPete

Thanks Gary, that's very useful.

Nice setup, Gary. Are your motors original? If so, did you have to do anything to them to suit the VFDs output?

Mine's a stone-age tacho, not optical

I realised I would need 2 VFDs, and probably 2 remote control boxes. Getting expensive! What make are your VFDs? I looked at Mitsubishi from Newton Tesla as I've had a good experience with them.

I like the note about stopping the feed before the cutter. You wouldn't make that mistake very often before it was seared into your brain

Yes, I've no idea how converters could do that. I kept checking the 4 pole Centec motor speed because I didn't believe it. I checked the tacho against a single phase synchronous motor, whose unloaded speed is rated at 3000rpm, give or take a bit of slippage.

Coincidentally, I was looking at the prices of VFDs when your post popped up. I have one on my lathe and am pretty happy with it. I've had to forego the heaviest of cuts though!

Thanks Dave, I'll take a look at that, though I believe the Yahoo site is now no longer accessible? Thinking about it, I probably do over-grease the machine, so I'll try to curb my enthusiasm in future.

It is a 3 phase motor, driven by a Motorun converter, Duncan. I hate to think what it would sound like if it was single phase!

However, today I measured motor and spindle speeds for the first time after 15 years of owning the machine - just shows what an amateur I am!

The motor runs at 1510 rpm, which is nearly 8% faster than it would with a 50Hz supply. The energy companies are required to hold a tolerance of +/-1%, so the difference will be down to the phase converter.

Surprisingly, the spindle speeds are 25% higher than the published figures! Clearly, a previous owner has modified the pulley diameters. I'd like a lower bottom speed, so I will probably change the motor pulley some time. I suspect these higher speeds help explain why it is so difficult to achieve the max speeds when the machine is cold.

Thanks 'not done it yet'.

I replaced the power feed motor switch, which cured the problem of it cutting out due to 'overload'. The original switch was well past retirement age!

The labyrinth seal is a series of grooves rather than a scroll, so I don't think there is any pumping action. I do reverse the drive direction from time to time - I seem to have acquired a few LH reamers over the years, and sometimes it's more convenient for access for a slitting saw. I didn't change the quill seal, so was somewhat surprised and delighted that no oil seemed to be sprayed over my clothes. It's early days, and some oil might be working its way out, so I'll keep an eye on it. If the problems come back, I might introduce breathers in the enclosed spaces just to see what happens.

Fortunately, I've no need for riser blocks because the stuff I work with is relatively small (so far!). I do have a portable crane I could have used, but it's in another garage 100 yards away, and I would have to clear a lot of stuff out of the workshop to get it in position. I don't think I'll be manually heaving the head about again - anno domini is taking its toll on the muscles and joints, I fear!

I have never used the Centec in horizontal mode, even though it came with a formidable set of cutters. I can't think of a job I've done which would warrant the change over. Vertical milling might be slower at times, but I'm usually in no hurry (or not adventurous!).

With the motor in the metal pedestal, I suspect a lot of the noise is caused by resonance. The belt tensioner is a bit of a bodge, and uses the drip tray as the reaction point, metal to metal. For years, I've been meaning to try a rubber mounting on the belt tensioner, and some sound dampening material on the panels to see if they reduce the noise but, as usual, I 've not done it yet.

Thanks to all those that gave advice. Risking a hernia, I removed the VH, cleaned out the old grease and other crud as best I could without a total strip-down, re-greased the pulley spindle bearings, and remounted it. After a bit of warming up at low speed, I could get all 6 speeds, though the highest speed was only stable if I changed the 3 phase static converter from 1/2 - 1 hp to 1 - 2 hp. I suspect that things will be easier in warmer weather.

Interestingly, there is a labyrinth seal for the rear pulley shaft taper bearing. They are obviously not perfect seals but are good enough for thick grease, plus they have the advantage of venting air from enclosed spaces. That bearing and the seal were pretty choked with grease before I cleaned up, so I wonder if air pressure as things warmed up was the reason why grease was sprayed out over the rear pulley, and why I had to dodge a few drops of oil spraying out from the quill seal. Since I remounted the VH, there's been no leakage of grease or oil from either of those regions.

Running at the highest speeds reminded me that, although a delight of a machine to use, the Centec is not the quietest one I've come across!

I left the workshop heater on to warm things up this morning, then tried a few things.

The motor is definitely rated at 0.75hp, so the m/c is probably underpowered. I'll look out for an affordable 1hp motor.

I guess the problem of not running at max speed is down to the low power motor, but I know it was running ok early last year. This afternoon I warmed things up by running at a lower speed for 10 mins or so. After that, it ran happily at the 5th speed (it couldn't from cold), but just rumbled away as before when I tried the 6th speed.

I use an ISO 68 lubricating oil, which I believe is an approximate equivalent to the recommended Shell Mex CY2. Pretty thick stuff, though it has the advantage of reducing leakage from the bottom seal of the VH.

A lot of grease sprays from the VH pulley shaft rear bearing, and spreads all over the pulley. I'm guessing the rear seal has gone, so I think I'll strip down the head, give it a good clean and replace that seal. I've not investigated the arrangement, but I'm assuming the shaft runs in taper roller bearings with separate seals, and not in deep groove sealed ball bearings?

It would make sense to replace the vertical spindle seal at the same time since it seems to be a bit of a weakness with this VH. Has anyone replaced this? If so, what type and size is it, please?

Thanks. I'll check the motor hp when I feel like getting on my knees and burying my head inside the base again. A previous owner has replaced the motor, and may have used a lower power one.

I checked the oil, which I always do without using the dipstick (never discovered the art of using it without getting oil all over it!), and it was a little low but good enough. I ran it for a few minutes at low speed, then tried a high speed. It sounded promising but still didn't get up to speed. I'll investigate further when the weather warms up.

My Centec 2B doesn't work for the highest 2 speeds. The 3ph 0.75hp motor, powered by a static phase converter, turns over slowly, but I've not left it on long enough to see if it eventually overcomes the resistance. I've had the mill for10 years and it doesn't get used much. I know it's cold and the old grease might have turned to the consistency of pitch, but I think it might be time to strip, clean and rebuild the Mk III vertical head while I'm looking at other causes. Has anyone any tips and tricks for servicing the vertical head?

Pete

Thanks Emgee

There seem to be many tricks that model engineers use which are unknown to relative beginners like me! I should have realised that a hemisphere is perfectly adequate to control crankshaft endfloat in such a lightly loaded engine, but, as an ex-designer of full size stuff, I seem to have some difficulty in making that leap of faith!

Pete

I noticed from EW's drawings that the crankcase central web and the attached crankshaft bearing cap are different widths, and from the width of the crankshaft journal, it looks as if the web is too thin. I didn't notice this until I had made the crankcase! Because of this, I think the pilot hole for the bearing was thrown off-centre, and I'm having some difficulty with line boring it. Has anyone else noticed this? Are there any drawing errors that have been spotted by others? Only 499 more components to make!

Pete

Thanks RAB

I eventually measured the currents on each phase and was rather taken aback by how different they were. Benn scratching my head ever since.

I hadn't considered the low voltage relay, and I guess there must be one because the table motor switches off a few seconds after I switch off the main motor. Reminder to myself - stick my head in the casing and sketch out the circuit!

Pete

I use a static phase inverter to power both motors of my Centec 2b. The motor for the power-driven table is 0.125hp, 1350rpm, FL amps per terminal 0.28A. I believe the existing starter switch for this motor is faulty because after a few minutes use, even with light cutting, the overload protection triggers, though I’m pretty sure the current is not reaching anywhere near full load. Any ideas how I can check this, or what replacement starter I can buy?