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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: 24v dc motor powering a drill press
23/03/2019 09:03:50

I'd agree wholeheartedly with MikeP. The machine runs at the sort of speeds I use for drilling anyway. It doesn't seem sensible to replace the motor with one running at a significantly higher speed.


Edited By Andrew Johnston on 23/03/2019 09:04:14

Thread: What Did You Do Today 2019
22/03/2019 20:39:45
Posted by Mike Poole on 19/03/2019 21:28:16:

It might be worth swinging the Kurt round so the cutting force is against the fixed jaw, it looks as though the vice is big enough to clamp the job endways to still cut in one pass.

Indeed it is; the vice will take 8.5" between the jaws. Although given the ends were sawn I wonder if the work might have tilted over instead? Clearly I've still got a lot to learn about man-sized milling on a horizontal. On the high speed range the motor power is 5hp. The spindle is driven by a gearbox so at 100rpm that's a lot of torque. I suspect 'orrid things might happen before the spindle stalls. Thus far I haven't got the motor to sound like it's even working. embarrassed


Thread: KX1 CNC Mill Clearance Offer
22/03/2019 20:32:42
Posted by SillyOldDuffer on 22/03/2019 13:53:10:

My list of H&S infringements includes not owning a Fire Extinguisher...

Tut-tut, if you're not careful you might end an XoD. sad

By my workshop door I've got a small fire extinguisher, a professional eyewash kit and first aid kit.


Thread: Making split bronze bearings [ silver soldering ]
22/03/2019 12:55:12
Posted by JA on 22/03/2019 12:31:32:

My attempts at using solder and glues failed so I made a proper fixture to hold the halves.

Same for me; the solder joint either gave way when machining, or the bearings required a serious amount of heat to melt the solder - not easy. Depending upon the bearing I made a simple jig:

Crankshaft Bearings

Or made a jig plus the actual bearing housing:

boring crankshaft bearings.jpg


Thread: KX1 CNC Mill Clearance Offer
22/03/2019 12:48:00

This is the stand I made for my CNC mill from 50x50 ERW steel tube, complete with coolant tank and fitting for a pump:

tormach stand me.jpg

I even did a calculation to check the buckling load of the uprights.


Thread: A Simple Protective Coating For Steel, Indoors
22/03/2019 09:53:47

We used lanolin to protect, and lubricate, the steel control cables in aircraft. i don't remember it having a solvent, I think we just heated it gently until it went runny.


Thread: Milling curves
22/03/2019 09:45:53

Personally I regard filing buttons as disposable. I make them from low carbon steel and never harden them; it's only a few minutes work. My procedure is to hacksaw away as much as possible. Then use a coarse file to get within a few thou of the buttons, without actually touching them. The a finer file to remove material until the file just touches the buttons. Finally a smooth file to finish the profile and then draw file after removing the buttons. The little ends on these connecting rods were done using filing buttons:



Thread: What Did You Do Today 2019
19/03/2019 20:49:16

I've set the radius of the press tool to 10", whereas the radius of the wheel is 11.75". I used CAD to determine the radius as it means the strakes will be curved 2 thou or so too much at the outer edges. I hope that means they'll be a nice fit on the outer edges. The rivets may pull the parts together as well. The strakes are 1/4" thick and to match the wheel radius only need to move about 20 thou at the edges, so I suspect that springback would be a real problem, especially forming cold. That's why I think I'll need to form hot. But I'll experiment once I've finished the tooling.


Thread: KX1 CNC Mill Clearance Offer
19/03/2019 20:40:39

So far I've used all three milling machines (two manual and one CNC) to make my press tooling for forming my traction engine rear wheel strakes. Oh, and the manual lathe as well.

I use CNC for a variety of reasons:

Parts I design myself where time is money and if I can use CNC to profile or pocket strange shapes i don't need to make multiple parts and then fabricate

Multiple parts where I'm too idle to use the manual mill - like the spokes for my traction engine wheels - and not just the outline but a zig-zag hole pattern for the rivets as per full size, which would be a real pain to do manually, even with a DRO

Onesies and twosies like the wing valves for my traction engine water pump or the internal spokes on my hollow pistons that would be very time consuming to do manually

Parts that are impossible to make on manual machines - like proper bevel gears

For me the parts are the important thing, not the machining. So I'll use whatever mix of machines gets me the part quickest, and that includes CNC milling.


Thread: What Did You Do Today 2019
19/03/2019 20:23:24

More progress on the press tooling. The parts were machined to length on the vertical mill, and the curved surface on the press tool base machined on the CNC mill:

machining press tool base.jpg

The CAM was set to leave a scallop height of 0.05mm. That's probably ok as it is, but a few minutes with a fine file will knock off the peaks. The finish feels better than it looks:

press tool base.jpg

It's most likely that I will be forming the strakes hot so whatever the finish it isn't going to look pristine by the time I've finished.

I also made a threaded spigot to hold the moveable part of the press tool in the flypress. The thread chosen was 3/4" BSW at 10tpi, screwcut at 180rpm with a full form profile insert:

press tool spigot.jpg

Back to work tomorrow, so the press tooling is now on hold. crying 2


Thread: KX1 CNC Mill Clearance Offer
19/03/2019 14:01:39
Posted by SillyOldDuffer on 19/03/2019 11:54:42:

I can see why CNC might not be welcome in Model Engineer, but surely it has a place in Model Engineering Workshop? As the latter focuses on tools and techniques it should be covering modern as well as established techniques.

Carbide inserts, 3D-printing, CNC, CAD, SVG, microcontrollers, DRO, VFD, Superglue, Stepper Motors, Metric, PPE, Brushless, Diamonds, bring it on!

Agreed, although personally I'd leave politics out of it.


PPE = Philosophy, Politics & Economics - an almost obligatory Oxford degree for wannabe prime ministers.

19/03/2019 11:12:56
Posted by Neil Wyatt on 18/03/2019 20:09:03:

Seriously, CNC articles don't need to be a series - Joe Noci's shaper was a good example, although I did want it to have another page or two, so we gave it the cover instead. There have been others, but not as many as I would have expected.

Never considered a series, just one off articles. A CNC article may be longer because it might be discussing a complex part that cannot be made with standard manual machines. So as background there may be some design theory, 3D CAD and CAM.

Reading the forum it is clear there is a definite anti-CNC undertone. So I expected the magazines to minimise CNC exposure. It is interesting to contrast with some US based forums where everybody is pretty positive about CNC, whether they use it or not.

Andrew (Pot stirrer extraordinaire)

Thread: What Did You Do Today 2019
18/03/2019 20:57:05

After many months of fighting bullders, kitchen designers and kitchen fitters I'm on the home leg of getting my new kitchen done and dusted. The main downside is that I've been banned from putting the traction engines back into the new kitchen.

On the plus side I've had some "me" time this afternoon (and also tomorrow) so I've been able to restart on the traction engines. I've started to make some press tooling so that I can form the rear wheel strakes to the correct shape. The first operation is to clean and square up some lengths of hot rolled steel. I thought this would be a good chance to try some of the slab mills I bought ages ago on Fleabay. First operation is to clean up the narrow surfaces:


The HSS cutter is 4" diameter and 4" long. Cutting parameters were 88rpm, 160mm/min feedrate (with 20 teeth about 3.6 thou per tooth), width of cut just over 1.5" and depth of cut 0.1". A bit of vibration but nothing serious. The fuzzy grey area behind the cutter is steam. I tried doubling the depth of cut but the cutter pulled the work out of the vice. embarrassed It didn't break the cutter, it just carried on like nowt had happened but with a much bigger DOC. Clearly I'm pussyfooting about with feeds and DOCs, but I also need to get serious about clamping the work down before I up the ante.

Once the sides were cleaned up I started on the wider sides:


Same spindle speeds and feeds with a WOC of 2.5" and DOC of 0.02". I've only got about 40thou to play with in terms of bringing the work to thickness.

Clearly I've still got a lot to learn about using man size cutters. I don't think I'm ever going to manage to stall the horizontal mill, unlike the Bridgeport.


Thread: KX1 CNC Mill Clearance Offer
18/03/2019 19:19:47
Posted by Neil Wyatt on 18/03/2019 19:01:08:

As for the magazines, they follow the interests of the readers and the authors - I am always surprised that we get relatively little CNC oriented content.

I have had articles published that include CNC machining. But given the current requirements for shortish articles, especially for beginners, I'd rather assumed that CNC was off the table?


Edited By Andrew Johnston on 18/03/2019 19:20:16

Thread: Precision division plates
18/03/2019 15:32:51
Posted by AdrianR on 18/03/2019 15:09:44:

It uses a Hirth coupling. It was cut not using any bevel so only the outer edge makes contact.

In #54 Scribe a line there is further discussion about setting the correct angle to cut teeth that mesh properly.

Err, in which case it wasn't a Hirth coupling but simply a radial spline. By definition a Hirth coupling uses tapered teeth that mate over the full length. The scribe a Line in #54 describes the mathematics to make a Hirth coupling.


Thread: HY Series (Huanyang) VFDs, setting maximum speed?
17/03/2019 16:07:14
Posted by Niels Abildgaard on 17/03/2019 14:00:07:

Programme step 009 sets a voltage and 006 a frequenzy.

Thanks, that helps. The normal volts/hertz curve below base speed (at 50Hz) is often a 1/f curve. But of course that can be tweaked, as set by the parameters. The parameters can also be used at very low frequencies where winding resistance has a disproportionate effect and the 1/f curve is no longer adequate to maintain current.

With regards to interference issues my take would be as follows. I'd agree that the VFD itself is unlikely to be affected. On the input side the lower power and/or cheaper VFDs do not have power factor correction on the input, just a rectifier and capacitor bank. So the current draw is very non-linear, creating current harmonics in the mains network. That's not good. An (COTS) external filter is needed to reduce harmonics below the regulated limits. On the output side the cables will definitely be producing radiated interference, as the signals are PWM with reasonably fast edges. The radiation can be greatly reduced by shielding the cables. Filtering is generally a bad idea on the output. Whether the shielding should be grounded at one end, or both ends, is controversial, so I'll keep my own councel on that. wink 2

If by VHF one means FM radio then I think a long or medium wave (AM) radio would be better to detect radiated emissions. An FM receiver normally has a limiter before the discriminator to ensure that any residual amplitude variations do not affect the output of the discriminator. One of the claimed advantages of FM is that it has high immunity to impulse (ampiitude modulation) noise.


Thread: Workshop insurance
17/03/2019 13:45:03
Posted by JohnF on 17/03/2019 12:42:18:

I have just renewed our house insurance this month and changed to a different company due to rising cost of the previous outfit.............

After changing insurance company every year (household and car) I started putting all the details back into the current insurers website, getting a cheaper price. Then I called and insisted they matched the price, which they do. I did the same with household and car insurance for my mum a few months ago.

When I renewed my own insurance last month I did the above and got the standard 20% or so off the car insurance. But the household insurance online quote was more expensive, instead of the 40% or so I normally get off - very odd. I also got an email reminder for my aircraft insurance, with a long spiel about how the number of insurers had declined, equals more expensive insurance. But the quote was comfortably less than last year! Even odder.


17/03/2019 13:37:38
Posted by Tony Pratt 1 on 17/03/2019 12:09:47: compare sites won't cut it.

I don't use comparison sites; they're worse than useless, and some cases plain dishonest. Every time I look they select energy deals that are worse than I've already got. Or give me a price for a hotel that is above what I get simply by ringing the hotel to book.


17/03/2019 12:03:53

I'd be very wary about relying on normal home insurance to cover workshops, built-in or otherwise. My double garage is attached to the house and is linked into the alarm, but it still isn't covered. Way back my home insurance only covered £2k in garages to cover the sort of thing most people have like lawnmowers and DIY power tools. When I asked about cover for other items like a lathe and mill all I got was a silence, and then a no we don't cover. In other words they had no idea what they were and it's easiest to say no.

I have a friend on another forum who confidently told me that his detached, but brick built, garage and workshop was covered by his holdhold insurance up to £30k. A couple of years later he sheepishly told me his wife had made some comment when renewing, and the insurance company had said nothing was covered, and never had been.

My workshop machines, tooling, part built engines and materials are covered by Walter Midgeley. They're by no means cheap, but they seem to be only player in town. A couple of years back when I thought about changing I couldn't find anyone else other than a few one man and his dog brokers who all led back to WM..


Thread: HY Series (Huanyang) VFDs, setting maximum speed?
17/03/2019 11:38:34

I'm not familiar with the PD009 parameter. But I suspect the issue is as follows. In a basic model of an induction motor torque is proportional to winding current. So the only way to increase torque at low speed is to increase current. This can be direct or indirect. A direct parameter simply controls the current at a higher level. Indirect means that the parameter controls the applied voltage, over and above what is needed to supply the motor rated current. Higher voltage means a higher current.

So far so good, but higher current means more I squared R heating so the motor will run hotter. I expect that's the issue regarding the warning. Too much over-current and you may overheat the motor in short order.


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