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Member postings for Andrew Johnston

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

Thread: Taking Leave
21/09/2020 11:55:37

Thanks for the encouraging replies. I've also had some PMs and a couple of 'phone calls, in one of which I was smacked round the head and told to stop being an idiot. embarrassed

The plan is now to take a break and concentrate on the paid for work that is finally coming in. After that, like it or lump it, I'll be back. I will still be reading, and responding to, PMs. The timing may be slow though, as for reasons never explained I no longer get an email to say I have a PM waiting.

I'm not entirely abandoning the traction engines and other engineering. There are three main tasks upcoming:

1. Collect the set of wheels from the rubber tyre company and get the second engine on it's wheels.

2. Re-design the safety valves to be pop types.

3. Understand the maths and see if I can create a 3D CAD model of a spiral bevel gear. If I can model it then I will be able to 3D print and/or machine it.

Andrew

16/09/2020 22:53:48

Following an unfortunate post in a recent electronics thread that was misconstrued I got excoriated. That has been the trigger, if not the root cause, of me deciding to take leave from the forum.

One thing the current panic has done is make people re-assess what they're doing and it's worth. I'm spending way too much time on forums and not enough time actually doing things. smile

On a more practical note after nine months of enforced idleness I've now got some work flowing in. So that takes absolute priority.

I understand that deleting my albums would remove the pictures from posts. So, for the time being, the albums will stay.

Andrew

Thread: Marking out blueing or pens?
16/09/2020 22:28:21

There are two basic products. Engineers blue in a tin is a sticky paste used to identify high points when scraping. For instance if one wants to scrape a surface flat against a reference (surface plate) the work is smeared with a thin layer of engineers blue. The work is then pushed across the reference surface. The points where the blue has been rubbed away are high points and need to be scraped. Then repeat as required. The watery blue liquid in a bottle is for marking out. It's painted or wiped on where it dries and leaves a thin blue sheen. Scribed line then show up more clearly.

Andrew

Thread: capacitance in long cables
11/09/2020 20:33:25
Posted by Joseph Noci 1 on 11/09/2020 14:32:42:

Not really fair.........

Nothing personal intended and I apologise. If I've understood Duncan's follow on post correctly there never was a signal problem, so nothing to solve.

I'm happy to hold my hand up and say it's all my fault. Some years ago, after a disagreement on this forum about the Fast Fourier Transform, I resolved to never get involved with electronics threads. Stupidly I broke that rule. I must stick to my own rules.

Andrew

11/09/2020 14:40:01
Posted by duncan webster on 11/09/2020 14:21:09:

The last 2 have blown on board regulators, which led me to look into the supply voltage requirements. Nano and Uno quote up to 20v, mini quotes 12v. We supply 13.8 via a diode, so 13.2.

Ok, so the Arduino has changed - makes sense. Simplest solution is to stick two or three more diodes in the supply line. If interference on the 5V line hasn't been a problem I wouldn't worry about trying to fix it unless it has been proved to be such.

Andrew

Edited By Andrew Johnston on 11/09/2020 14:45:55

11/09/2020 14:07:24

If I've understood correctly the system has been working fine for two years, but has suddenly had a number of failures? This is put down to the applied supply voltage. Has the system been run from a different supply, or flat batteries, over the last two years? If not, then why would the same supply voltage suddenly cause failures? Has anything else changed? Sticking Zeners/capacitors in without understanding the issue is a job creation scheme for monkeys. smile

Andrew

Thread: Steel stock for newbie ???
11/09/2020 11:02:43

For small sizes of steel, below 1-1/2" diameter, I buy standard 10ft lengths from commercial suppliers. Likewise I buy the standard 20ft lengths of hot rolled steel. For hot rolled it is cheaper to buy the full length than a shorter length. I also buy full 1m x 2m sheets of steel. After a number of years I've built up a good stock of steel, such that I don't need to buy much now. I mark the steel before storing, on rounds I stamp the EN number on the end.

I don't use aluminium on my traction engines, other than for fixtures. I have bought a lot of aluminium section and plate for work. Section is bought in standard 20ft lengths and plate cut to size from commercial suppliers.

Silver steel and gauge plate comes from Coventry Grinders, usually in 500mm lengths.

Cast iron, bronze and brass come from M-Machine (cut to the length I need) or Macc Models nearest standard size. I normally add a bit for fumbles. So if things go right I build up a small stock. Plastics come from a local supplier (EDP Plastics) in Cambridge.

I rarely buy material from Ebay. Usually only when it's mega expensive elsewhere, such as tungsten alloy, or I just need something for making a fixture and don't care about the machinability or finish, Such as this lump to make a former for the engine chimneys:

chimney_former_blank.jpg

Andrew

Thread: Scaling back forum activity
11/09/2020 10:42:13
Posted by not done it yet on 11/09/2020 10:18:52:

There will be a few ripples - but they will soon subside.............

Consider what happens to still water; it goes stagnant and everything in it dies.

Andrew

Thread: Strength of Beams
10/09/2020 16:04:30

Despite calling it strength I think SoD means stiffness. If all beams are the same length and weigh the same then they must have the same cross sectional area. The deflection of the beam shown by SoD is inversely proportional to the moment of inertia. So it's simply a case of comparing moments of inertia for constant area to find the stiffest shape. All the information needed is in Machinery's Handbook.

Andrew

Thread: COVENTRY DIE HEADS
10/09/2020 10:01:15

The RH & LH gauges are marked for 20mm, 3/4", 1", 2-1/2" FT and 3-1/2" FT dies. The numbers run from 50 to 145 on both gauges. I also have a RH gauge for 1-1/4" dies where the numbers run from 70 to 145. A die marked 77 is pretty close (±1) on both RH gauges. So I surmise that the numbers are linear across the complete range of dies, at least in the sizes we are likely to use. The height at 120, measured with gauge blocks, is 0.359".

I measured the angle on two gauges with a clinometer. I got 2°55" and 2°52". I'd agree that the markings appear to be 1/16" apart, as measured with a rule.

Andrew

Thread: Scaling back forum activity
09/09/2020 19:38:27

Oh dear, that's a shame and a loss of valued insight. Sorry to see you wind down, although I understand the reasons. Good luck with the other ventures.

Andrew

Thread: COVENTRY DIE HEADS
09/09/2020 15:09:35

As far as I'm aware the angle stays the same, as it controls the transition from cutting to guiding. I don't know the value of the angle.

I have LH and RH height gauges for 3/4" and 1" dies. Height gauges vary; I've got one for 1/4" and one for 1/2" but the values overlap slightly. So presumably one or the other would also do for 5/16" and 3/8" dieheads. In theory it should be fairly easy to make a height gauge. One just needs the angle, the spacing of the ticks and one reference point from a known good die.

I don't know when the new grinding fixtures came in; I'd hazard a guess in the 1960s. They're not in my Ed 22 version of the handbook.

Andrew

Thread: Harrison 300 Swarf Shield
07/09/2020 12:24:57
Posted by Len Morris 2 on 07/09/2020 12:10:52:

Not sure what they are for as I have nothing to bolt into them.

On my M300 the rear pads hold a beveled pattern bar for a hydraulic copying unit:

pattern bar.jpg

The front pads carry a trip bar for an Ainjest high speed threading unit:

capstan.jpg

The Ainjest unit is bolted on the right hand side of the saddle and the rectangular trip bar runs the full length of the bed below the electrical actuator rod.

Andrew

Thread: New Moderators
06/09/2020 20:24:48
Posted by ChrisH on 05/09/2020 21:42:12:

I have long maintained that no real engineer worth his weight can spell correctly through a whole phrase, let alone a whole sentence.

So that's where I've been going wrong. sad

I take the time to read what I've written before posting and try and correct spelling errors and grammar. So I must be a lousy engineer. Of course Chris is confused; engineering and model making are not the same thing at all. A good engineer might be good model maker and vice versa, but one doesn't automatically infer the other.

Andrew

Thread: How to move a Colchester Student ?
05/09/2020 11:03:39
Posted by SillyOldDuffer on 05/09/2020 09:25:08

I guess lifting a lathe with a heavy stand suspended underneath is likely to twist the bed or worse!

My Harrison M300 (1500lbs) is bolted to the manufacturers sheet metal stand. I understand that the lathes were shimmed to the stand during assembly. So it is an all round bad idea to separate the lathe and stand. The manual recommends slinging using either an eyebolt in the M16 thread in the bed cross member or with a sling around each end of the drip tray, so lifting on the stand rather than lathe itself.

Andrew

04/09/2020 21:05:04

Using an engine crane is a right royal PITA. It doesn't generally have enough reach to place the machine where you want it on the trailer and the legs and trailer wheels or rear stands always seem to clash. If at all possible roll the machine on and off the trailer. I use lengths of 2" steel bar as rollers.

Andrew

04/09/2020 17:20:24

If by a car trailer you mean one designed for moving a car forget it. You need a two, or ideally four, wheel trailer with a solid floor and ideally a rear ramp. Once the machine is loaded and the balance is right, ~50lbs downforce on the hitch, then block the base of the machine in all directions. And I mean blocks, don't rely on straps. Perfection would be to mount the machine on large cross baulks of timber before loading as that will also help to stop it tipping during loading anf unloading. Once on the trailer and blocked then add straps at angles to prevent any fore and aft or side to side movement. While you may not expect to do an emergency stop, you don't want the machine sitting alongside you in the car if you have to.

This is how I moved a cylindrical grinder over 100 miles. I was cautious and limited myself to around 50mph on the M25:

Grinder

The straps have been removed along with the tie for the counter-balance weight. A better trailer was this one, moving a repetition lathe, only 15 miles but it's still securely fixed. For ease of loading the lathe is actually sitting on a pallet truck, but everything is still blocked and tied:

back_home_sized.jpg

Note the stands at the rear of the trailer, very useful when loading/unloading. Make sure you tow with a sensible car, ideally at least 1.5 tonnes kerb weight. It's no fun when the trailer takes charge of the car. sad

Andrew

Thread: VFD for M300
04/09/2020 15:52:26

We're talking two completely different cases. When driving the M300 we're comparing driving a motor in star at 415V with driving the motor in delta at 240V. In this case the power output, and torque, remains constant.

In a star-delta starter the applied voltage does not change. The motor is designed to run in delta. Direct off line startup currents would be very large. So the motor is started in star (with the fixed applied voltage) so phase currents and start up currents will be lower. The currents, and hence torque, in star are about a third of the values when the motor is running in delta. So when the applied voltage doesn't change the power output, and torque, are different in star and delta. They're both higher in delta.

Andrew

Thread: modifiying a right hand toolholder to universal?
03/09/2020 21:34:23
Posted by Neil Wyatt on 03/09/2020 21:13:19:

....................such as the outer diameter of large discs

LH boring bar works fine and has the appropriate reach:

flywheel_rim.jpg

Andrew

Thread: VFD for M300
03/09/2020 19:25:23
Posted by Alistair Robertson 1 on 03/09/2020 16:27:35:

The VFD supplier said in the paperwork that there would be a reduction in torque when running in "delta"

I don't understand why they would say that? The frequency doesn't change, so neither does the speed. Given that the plate I showed indicates that the output power stays the same then the torque must also stay constant.

Remember that the phase currents in delta are higher than in star. So if the current limit in the VFD wasn't increased that may explain why the motor didn't start properly in delta. The start currents will also be proportionally higher so may be the VFD was going into current limit? A longer ramp time may ameliorate that.

Andrew

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