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Member postings for Jon Freeman 2

Here is a list of all the postings Jon Freeman 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Petrol Gen for 7 1/4 locomotive
18/09/2019 18:07:25

Hi Andy,

As Neil suggests, take a look at the series currently running in M.E. (I’m the author). You’ve had some good guidance above, but a few quick points :

Super capacitors – really ain’t that ‘super’ once you look a little deeper. Take a look at time specs. They don’t like being charged/discharged too quickly. If you spend £120 to buy 6 pcs 3000F 2.7V super-caps, once wired in series the capacitance is 3000F/6 = 500F. If charged to, say, 12V, how much useful energy have you stored?

Energy E = ½ C V^2 = 500 * 12 * 12 / 2 joule = 36kJ, or 0.01kWh. Not going to get you far! Spend the money instead, maybe, on a 12V 100AH traction battery, storing 1.2kWh, a safely usable 0.6kWh.

As for power sources, a standard mains voltage gen feeding a VFD driving small three phase induction motors ought to work well but I’d be a little wary of the voltages involved. For safer, lower voltage systems, a 4 stroke petrol engine driving a permanent magnet generator or vehicle alternator are good starting points. I use a large brushless motor as a 3-phase permanent magnet generator, but with this type the output voltage varies with engine revs (not a problem with the electronics I use). Using small 4 stroke engines to drive vehicle alternators – seems like a simple idea that ought to work well, but many a model engineer has fallen into a bit of a hole here by not appreciating that for any given output, alternator input torque rises as revs fall. So easy to design a system good mainly for stalling engines! There are ways around this, some better than others, and this is a project I’m currently working on.

A good place to start is to decide how much output power you want – what load do you hope to pull up what gradient at what speed, what acceleration, and with what losses, then do the arithmetic. Choose a 4 stroke capable of delivering twice this. Then if you want any further advice, contact me ‘jon at jons-workshop dot com’.

Thread: Facing off on Sherline
24/08/2019 14:34:10

I would face this with far less of it protruding from the chuck. Angles look about ok

Thread: 3 phase - radio puzzle
30/07/2019 11:05:07

Depending on your location relative to the fm transmitter your reception could be very variable even at different points around your property (multipath reception). Devon wasn't designed for good fm reception, the terrain is too lumpy (same problem just up the road in W Somerset!). As for MW, I don't have the info to hand but the MW transmitter is probably relatively flea-powered.

Your installation looks good, IMO is a good pedigree piece of kit, I'm not inclined to think there's anything wrong. All VFDs will produce interference, reduced but not eliminated by built in filters. It's quite likely your kit is all 'in spec' but your BBC signals are weak at your location.

Try a different station perhaps.

30/07/2019 10:46:04

Is this Radio Devon on medium wave or fm showing the problem?

Thread: What mills have you had
22/07/2019 11:49:52

1980s - Hobbymat Yellow Peril - dreadful mistake.

2000s - Chinese Bridgport clone from Chester with Newall DRO - use this often, good machine, will see me out

2010 or thereabouts Sieg KX3 CNC - produced some useful and interesting work with this but very little used now (for so many jobs not quite enough Y travel).

Thread: What lathes have you had?
22/07/2019 11:39:12

Bought a Myford ML7 new while still at school - up at 4.am every day doing several paper-rounds to pay for it.

Carried this around for over 40 years, then bought a 'Chester Challenger', the idea was to carry on doing small stuff on the Myford. After a year or so it was apparent the Challenger was being used for all jobs of all sizes, sold Myford.

Thread: Why are CNC lathes more expensive than a CNC Mill
22/07/2019 10:38:05

There's one good reason for CNC lathes being more complex, therefore potentially more expensive, than milling machines - screw cutting.

Cutting screw threads requires accurate synchronisation of spindle speed to the speed of in particular Z axis movement. This adds cost of a rotary encoder on the spindle - not a huge cost in itself perhaps (£74 from zappautomation.co.uk), but this needs to output three signals - an index pulse to identify one 'home' spindle angle, plus a pair (e.g. step and direction) enabling the controller to keep track of the angle of the spindle at any instant. This should have many pulses per revolution, otherwise the controller can not be made aware of any spindle speed change at any point through the cutting pass. Software and digital electronics to keep all this sweet is non-trivial. LinuxCNC does a pretty good job, Mach3 not.

The only way around this would be to use a hugely more expensive servo motor driving the spindle, in the hope of maintaining constant spindle speed with minimal angular error, while cutting.

Thread: Using a lathe
30/06/2019 12:08:53

Back in my school days a few of us used to be allowed to spend lunch hours unsupervised in the metal work shop. The teacher thought we were sensible enough, we got to make some useful stuff and no harm came to anyone. He was taking a big risk I think for the small reward (a few of our cigs) he got, but he wanted to encourage us.

I sometimes now have junior club members invite themselves to my workshop. I welcome them and hope to encourage a new generation of model engineers, but for my own protection as much as theirs, I make it an absolute rule they will be accompanied by a responsible adult (parent, grandparent) the whole time. If using the lathe, mill, or any powered kit they will be under my constant supervision. I'm more relaxed leaving them to it with hand tools and bench work. Cuts and scrapes - hard to avoid completely learning workshop skills

Thread: Hello (again) from Somerset
04/06/2019 13:51:07

Thanks Neil,

Now I have wi-fi that reaches the workshop I'm more likely to post.

03/06/2019 14:02:03

Hi all,

I have posted here a few times a fair while ago, can't access previous login so started afresh today.

I'm into building locomotives, started a Springbok a few years ago but got sidetracked into electrics and particularly brushless motors.

Currently working on the problem of how to make a good match between small petrol engines and vehicle alternators - I know of many a good engineer who've found this a tricky issue.

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