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Member postings for Andrew Tinsley

Here is a list of all the postings Andrew Tinsley has made in our forums. Click on a thread name to jump to the thread.

Thread: A question about traction.
29/10/2021 09:53:29

The statement "the smaller diameter wheels give higher traction" should read, "higher tractive effort". A somewhat sloppy mistake.

The basics mean that smaller wheels have lower gearing and hence can start a higher mass train from rest. It has nothing to do with friction between the rails and wheels. Any such effect is of a miniscule second order.

Andrew.

P.S. All bets are off if the wheels slip on the rails!

Edited By Andrew Tinsley on 29/10/2021 09:54:35

Thread: Holbrook lathe on Ebay
28/10/2021 16:55:31

Hi Tony,

If you look at the original post, you will see that I surmised it might be badge engineered product.

Andrew.

28/10/2021 13:54:20

Thanks Bikepete,

Your link explains everything. So it was an early 80's design by a Holbrook gent (who was working for Herbert). That explains the non Holbrook appearance.

It was manufactured in India, so was in fact an imported lathe.

Andrew.

28/10/2021 13:38:08

I know that the lathe is styled as a 10B, but from Lathes UK site, there doesn't appear to be such an animal. The styling of the lathe is nothing like any Holbrook lathe I have come across.

So come on you Holbrook experts, have you any information on the Holbrook 10B? I suspect that it is a rebadged import lathe, looks far too modern to be a genuine Holbrook design. But happy to be proved wrong.

Andrew.

28/10/2021 12:35:59

Currently, there is a combined item on Ebay entitled "Lathe and milling machine". The lathe appears to be a Holbrook, at least that is what is emblazoned on the front! It appears to be a very modern lathe, quite unlike any Holbrook that I have seen. Lathes UK doesn't list it, so I am at a loss. Could it be a badge engineered import? It looks too good for that!

Anyone know what it is?

Andrew.

Thread: Load reactors for VFDs
17/10/2021 22:31:48

Thanks everyone, especially Mark , Andrew and Robert. I think Robert has hit the nail on the head, three simple inductors, non optimised, is going to be the simplest solution . It would certainly get rid of most of the Fourier HF.

I am sure that I was over thinking this one. It will only cost me time and will be better than running the motor direct from the VFD. Roberts suggestion of an earthed brush on the shaft is a good solution to the leakage current via the bearings. Although the very occasional use that the drill will get, probably doesn't even warrant the mod.

It has been an interesting experience saving this old warhorse, I still can't get over the size and weight of the drill compared to modern designs. If the motor does eventually expire, I will get it rewound to modern standards.

Thanks everyone, I am certainly more well informed on the topic than when I started.

Andrew.

17/10/2021 15:56:52

I forgot to mention that I have been running the drill on a Siemens inverter. Total running time is probably about an hour, so despite peoples worries that it may be a bag of nails, the motor has behaved with no problem. I have to say that it must be the coolest running motor I have come across. Must be the huge thermal mass of the beast.

If a load reactor will keep the pwm, square wave, Fourier harmonics in check, then it will be a worthwhile precaution, especially as it will cost very little to construct.

Andrew.

17/10/2021 15:39:35

Dave,

The first thing I do with any motor is to megger the separate windings to earth using a 1000 volts DC and incidentally each winding to each other. That is before I even try to run them.

Your warnings of all that can go wrong are precisely the reason that I was looking at load reactors.

I too tried calculating values of capacitance and inductance and although my results are adrift from yours, I doubt that some of my basic assumptions are correct.. As you suggest , some measurements on the motor are really needed to have much confidence in the calculations!

There is little to be done about the earth leakage via the bearings. I have changed them for new in any case as the motor is 2800 rpm. For the little use it will get, I doubt if this will be a real problem, rather more a theoretical one..

The cost of the inductances are well nigh zero. I have a large amount of various diameter copper wire and stacks of iron E and I section for the cores. The only expense would probably be for the capacitors and I may well have some that would do the job.

Unlike you, I am not too bothered about old motors, as long as they are well earthed then about the only real danger is destroying the rectifiers in the VFD. This isn't the end of the world either,as surprisingly I have found that a lot of the branded VFDs rectifier units are available and replaceable. I have already done this on a couple of blown VFDs that were given to me and one that expired on me!

Thanks for your comments,

Andrew.

Edited By Andrew Tinsley on 17/10/2021 15:42:45

17/10/2021 10:51:41

Thanks for your input John, The motor is from the pre war period. It drives an Alfred Herbert high speed drill which I have restored. I am finally getting round to sorting out the drive for the motor.

For what it is worth, the motor plate says Alfred Herbert Ltd, 1/3 HP, 400/440 volts, 3 phase 50 cycles. The motor type is an SA 53. I have dug out the star point and is now wired in delta.

As one would expect from an 85 year old motor, it is massive. I need to retain the motor because the top end plate is a large casting which has an extension that is part of the sliding belt tensioning system and so the motor is unique to the drill.

I do not want to butcher the drill by fitting a new motor. I am looking on the drill as a museum piece, which can be used in anger on the odd occasion. Its early use was in the manufacture of Merlin magnetos in a Leicester shadow factory. The drill has an air ministry plate and also a BTH brass plate (BTH ran the factory for the Air Ministry)

If and when the motor fails, I shall get the motor rewound to modern standards of insulation. but obviously I hope to put off the day when it fails.

Andrew.

17/10/2021 10:25:58

Thanks Andrew,

You have confirmed what I thought and remember reading re load inductors. As you rightly say they are an expensive item. although I don't see why they are so expensive.

I am just finishing off the mechanics of a coil winder , so I can wind my own. Anyone any suggestions as to how to calculate the required inductance? Most load reactors laminations are like those usually seen on 3 phase transformers. Is there any reason not to use a lamination stack for each of the 3 inductors. I ask simply because I have a large supply of such laminations.

Andrew.

16/10/2021 21:42:12

I have several VFDs I can use, Siemens, Fuji, Telemecanique and Hyundai. I can check on what each manual has to say about load reactors.

Having looked at VFD voltage outputs on a scope, they are anything but sinusoidal and I am sure that driving a very old 3 phase motor from such a source will be putting more stress on it than using genuine 3 phase supply.

I seem to have read somewhere that a load reactor will produce a much more sinusoidal output, which I suspect will be much kinder to the motor. Not sure if this is true or a figment of my imagination!

The motor will only be operated at 50 Hz.

Andrew.

 

Edited By Andrew Tinsley on 16/10/2021 21:44:49

16/10/2021 14:19:10

I am interested in using a load reactor between a VFD and a very old 3 phase motor.

I understand that a load reactor will reduce the nasty spikes that would normally get to the motor. Not sure if I have this correct?

The motor is a special to some very old kit. I could get it rewound to modern standards or use a load reactor to reduce the stress on the motor. The existing VFD powers the motor without any problems but I suspect that will not last long!

I also suspect that line reactors are probably as expensive as a rewind. Anyone got experiences they would like to share?

Andrew.

Thread: Chester 920 cross slide & Backlash
15/10/2021 10:46:01

I renovated a Chester 920 and it really does need a fair bit of work to get a decent lathe . It wasn't so much worn parts, but a poor design, Quite a few bits needed upgrading over standard, before it became a pleasant machine to use. Upgrading the cross slide leadscrew and nut to 12 mm was one of the things plus using a bearing to control the end float. The standard nut and 8mm leadscrew isn't really up to the job.

Andrew.

Thread: Valve seat cutters?
15/10/2021 10:34:35

Hello and thanks for all the helpful information. It seems that the power of advertising is greater than I expected.

I had a phone call from a model engineering "friend" this morning. He had read my post and realised he was the guilty person who had borrowed my Sykes Pickavant cutters. They will be returned tomorrow.

A special thanks to noel Shelley who offered me the loan of his kit to do the job om my MGB stage 2 head.

Thanks again everyone,

Andrew.

Thread: Bench grinder
14/10/2021 21:43:00

It could be the start capacitor that has gone faulty or the run switch is stuck in the run position and hence the motor is struggling to start.

Unless you have a capacitance meter and can check the start capacitor, I would simply change it out for a new one. If that doesn't cure it take the end plate off the motor and check the centrifugal switch isn't stuck.

If you are tight fisted, like me, check the switch first, you might save the cost of a start capacitor, at the expense of some disassembly work!

Andrew.

Thread: Chester 920 cross slide & Backlash
14/10/2021 21:30:10

As far as I know, Chester are the only people in the UK to still offer the 920. Usually they have no spares stock and need to order from China. Prices are reasonable but the postal costs are very steep. The quality of the spares isn't brilliant in my limited experience.

Grizzly in the US are usually much better on stock and prices, but the cost of postage and customs  to the UK is even worse than the Chester quoted prices from China. The quality is not brilliant either.

Much better to take the bull by the horns and re engineer the cross slide drive. If you are not up to it, then find someone that can do the awkward bits for you, otherwise you will just have to put up with the backlash as it is, bodging the nut isn't a good solution. It would appear that someone has already done the bodge and the nut is now even more worn.

Andrew

Edited By Andrew Tinsley on 14/10/2021 21:34:30

Edited By Andrew Tinsley on 14/10/2021 21:46:02

Thread: Valve seat cutters?
14/10/2021 19:13:54

Hello Noel,

I am in Rutland.

Andrew.

Thread: Hermes. A Company in Total Confusion!
14/10/2021 19:09:59

Just had a delivery which had taken just 24 hours to get here. Amazing service. People are quick to moan when things go wrong, but don't often praise when it is due.

Andrew.

Thread: Chester 920 cross slide & Backlash
14/10/2021 19:06:30

The "leadscrew" for want of a better word and the captive nut are really a bit undersized. Most people would replace with a larger diameter cross slide screw and a new machined nut, in say bronze. Doing this mod also allows you to increase the range of the cross slide.

Look on line for "Tricking out the 920 lathe". This will give the details as will some other sites (920 lathe forum for one). The trick of partially sawing through the nut and then using grub screws to enlarge the gap, is at best a bodge and it won't be long before you are back to square one, with lots of backlash.

Andrew.

Thread: Valve seat cutters?
14/10/2021 13:57:44

Hello Chris,

I am firmly convinced that SP cutters have legs. Are the diamond coated cutters specifically for valve seats ? Sounds a good idea providing the cutters are not an arm and leg.

Andrew.

Edited By Andrew Tinsley on 14/10/2021 13:58:09

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