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Member postings for Chris Hembry

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

Thread: Inverters and stop switches
07/11/2019 21:24:57
Posted by old mart on 07/11/2019 21:11:20:

How would an EStop work between the inverter and the motor, there are three wires to disconnect.

Which is why I specified a three phase EStop so all three wires are broken together. Or use a contactor, with a 24V coil fed from the inverter control circuit to give another protection level.

Of course you are free to do what you want on your machinery, but I prefer an EStop to actually guarantee to make a machine safe rather than just in theory.

This stems from an instance when a machine had a dangerous but rare tendency to start on it's own because the inverter picked up a stray signal from the spindle encoder when the chuck was moved by hand. I lived with it for a short while, but there was no way I was going to let anyone else anywhere near it !

07/11/2019 20:13:03
Posted by not done it yet on 07/11/2019 19:32:04:

It’s a mill, so the motor can be braked as hard as one can manage. No such thing as an emergency stop for “normal running”. Emergency, by definition is not normal, but there are different degrees of emergency!

If one wishes to disconnect the motor between it and the inverter, one requires a much larger inverter than the motor power - to avoid inverter damage. Much larger.

There is a STOP for normal use, and EStop for emergency use, hopefully never ! One uses the inverter to brake, the other doesn't, just in case it is the inverter at fault.

You don't need a larger inverter than you would have specified anyway since you are not looking to ever have to use the EStop. As said above I'd rather buy a new inverter than lose an arm !


07/11/2019 18:51:13

I seem to be in a minority here, but I would always recommend the EStop being between the inverter and the motor.

The EStop is your last line of defence should you be stuck in the machine...the last thing you care about is whether it damages the inverter !

It is true that the inverter CAN be made to stop the machine more quickly than just disconnecting the motor, but what if the inverter itself is at fault ? And what if the only person able to operate the EStop does not know how it is wired ? The only thing that matters is that it MUST make the machine safe.

There must be no stop switches on the Input side of an inverter except to electrically isolate it for maintenance. As others have said, the inverter will continue to run until the DC bus has dropped low enough for the inverter to trip out.

So, what to do ? - Fit a normal Stop button that operates the control circuit on the inverter (programmed to stop at whatever speed you wish). This is for NORMAL operation and should not have the big red mushroom head. Fit a three phase, normally closed, latching EStop switch with the mushroom head between the inverter and the motor. You could use a control contactor instead, and have that energised only when ALL safety devices have been proved to be in place (this is the usual method on machinery).

Regards, Chris

Thread: Tom Senior vertical guards
10/10/2019 19:24:45

A bit expensive, but we use this type on our Senior mills at school :

Must be other ones around for less. They mount directly onto the tee slot at each end of the table and can rotate right around that axis.

Thread: Myford workshop Manual
29/03/2019 20:32:01

There never was one, only document was an sales/operating manual covering the ML1-4 lathes. Download available from several sources.

Thread: How much do Colchester spares cost ?
02/10/2018 10:14:42

It all depends on the model that the company uses for spares pricing. Some companies will heavily discount the original product in order to generate sales, and then attempt to recoup that with the cost of spares. Large machinery producers regularly use this technique, think combines, tractors, trains and lathes !

Bear in mind that when the lathes are originally produced, a number of parts that are deemed to be consumable will be stocked as spares. These may well be reasonably priced. However, not all parts will be kept in stock, so you will be charged a one-off or small batch price for the component to be manufactured for you, if they even offer to supply parts for obsolete models

Thread: Small twin cylinder compressor pump identification.
28/09/2018 21:46:50

Can't help with identification, but I also have a set of castings for this compressor. Only difference seems to be that mine has a 4 spoke fan/pulley. Had the parts a long time but think they were a one-time student project.

Thread: How to big gear to small gear with a 1:1 ratio? Capstan lathes
27/03/2018 20:18:28

Simples : It's not a 1:1 ratio. While the turret rotates 1 position at a time, the stops can rotate either 5 or 7 positions making the gearing much simpler

Thread: Holes drilled in side of Warco Super Major column?.
28/11/2017 13:00:25

Hi Martin,

An odd place to fit a DRO arm, but not about a one-shot oiler system ?

Either way I doubt it would cause any issues.

Regards, Chris

Thread: Warco T210 change wheels.
27/11/2017 13:27:09

Don't worry Peter, already in contact with Bill over the missing parts. Drawings done previously for a previous customer who didn't get the full set of spares with his machine.

Regards, Chris

26/11/2017 21:25:20

Hi Bill,

To add to what Peter has written, it may be worth adding that the friction drive involves using two parts to replace a pair of gears. If you are missing gears, it is likely you are also missing these components. As a fellow 220 owner, I'm sure we can come up with a solution as you will be unlikely to get any help from Warco.

You should have the threading chart on an aluminium plate attached to the inside of the changewheel cover. The manual gives a straight copy of that.

Z is a common designation for number of teeth used in Germany, Bulgaria etc.

Regards Chris

Thread: Chester or Warco.
20/11/2017 21:36:35

I have a Chester Super issues with accuracy or finish. Also have a Warco lathe....the famed aftersales service has never materialised as all emails have been ignored. Just my experience !

Thread: best inserts
01/04/2017 22:11:05

I've tried several different sources of inserts and have to say that in future I'll stick to named manufacturers. Those supplied by third parties without naming the manufacturer MAY be ok, but there is no guarantee that they always will be since they are free to change supplier at any point. I'll stick to using Sandvik and Korloy for production work.

Thread: New member
26/02/2017 17:23:45

Welcome Carl, also a couple of air rifles here and another ML4 in the queue for a rebuild. Not quite sure which direction to take it yet, might yet be CNC.

Thread: Warco GH universal milling machine dismantling advice
14/02/2017 14:28:25

No problem Mark. By choosing a gear head mill, you've already solved the torque issues that the 20vs will suffer from. The normal drilling capacity of these machines is 45mm with 1hp, and I can say that it manages this in steel all day if you want it to.

I'm sure Chester would fit a 3 axis DRO for you if you asked.

Personally, I can only see the powered spindle downfeed being really useful on boring head jobs, whereas the head elevation is used on nearly every tool change. To have both would be a nice feature, but I would not have spindle in place of head.

14/02/2017 10:11:40

+1 for the Chester SuperLux as the better version of the same machine. I have had one for 5 years + and 1HP is more than adequate for this size of machine. You'll also get the stand and DRO thrown in. Power downfeed on spindle sounds interesting, but not as handy as the Chester's powered head elevation. You will want to move the head rather more than just the spindle, and winding the handle is a chore.

Thread: Warco vs Chester
20/01/2017 10:29:33

Warco vs Chester

Many years ago I bought a 220 lathe new from Warco with most of the accessories. Made sense at the time as it offered Myford capacity at a fraction of the cost. Over the years, the topslide feednut has worn out, so I emailed Warco regarding the availability of spares. Not just once, but about 5 times over the space of 4 years (at the time I had the use of other lathes, so not urgent). Not one single reply to any email, not even the expected 'sorry, but we don't carry spares for this machine any more'.

When the time came to expand and buy a mill, I compared the pricing from Warco and Chester, and went for the Chester Super Lux. Machine turned up exactly as specified, when expected and was positioned in the workshop in 10 mins by the truck driver. This was 5 years ago, and no fault has been found so far, even so much as the tram was within limits straight out of the box. This machine has not been used lightly either, for about 6 months it was being used for 8 hours a day.

I'd still look at the pricing from both companies in future, but those are my experiences.

Thread: Sealing BSP fittings
18/01/2017 12:13:03

PTFE Tape was banned on railway air brake systems due to the fact that loose strands could easily block small orifices. Loctite 572 was preferred alternative. Other cheaper alternatives available for less demanding applications - try Tru-Loc range

Thread: "Tang" on the end of a male Morse taper?
07/01/2017 12:34:37
Posted by Andrew Tinsley on 07/01/2017 12:05:34:

Your capstan unit has the axis of rotation of the toolholding disc at right angles to the lathe axis. Mine is at approx. 45 degrees to the lathe axis, just like a dedicated capstan lathe.This explains the difference, I hope!

Not really, a production capstan lathe has the capstan pivoted vertically at 90 degrees. The bores are finish machined once fitted on the lathe to guarantee absolute axiality. If your capstan attachment is putting the tools out of alignment with the tailstock, it is at fault.

Regards, Chris

Thread: Dickson T1 tool holder
17/12/2016 18:58:49

A genuine Dickson post should have a second hole through the post fitted with a close fitting dowel post mating into a hole in the topslide. This, combined with close-fitting centre stud bushes should prevent turning enough for manual lathes. Since I'm using CNC, I can't allow any turning whatsoever, so I've fitted a piece of square bar to the topslide as an extra backstop against the tool more problems so far.

The Imperial info came direct from Bison as I was needing a pair of new cam bolts. The spares currently supplied nearly fitted, but just needed a skim off the diameter to be able to fit into the toolpost holes. The hex size is also different from original.

Edited By Chris Hembry on 17/12/2016 19:01:41

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