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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: TTFN
19/07/2019 14:46:08

Good grief, I'm stunned by the responses. I thought i may get a few "that's a shame" and a couple of "thank gawd for that" replies, but not the flood that has happened. What can I say, other than thank you, very much appreciated. It's really good to know that people find my posts helpful.

Truth be told I'd be really sad to leave the forum permanently. Over the next few weeks I have a fair bit of paid for work to do and I have some family care commitments. So I plan to step back for a few weeks, and then I'll be back, like it or lump it.

It would be iniquitous to pick up on only one of the responses, but I'm going to do it anyway. A special thanks to MartinM for reminding me of the project we did together way back in 1975 at SETC (Student Engineers Training Centre) at RAE Farnborough. I've still got copies of my original reports and sure enough the report I produced with Martin was in my handwriting. It is correct that we failed to achieve a working 100MHz amplifier, although I think the logic for the counter itself worked. Of the three projects i did at SETC only the mechanical one worked; may be that should have told me something. smile

Once again, thank you for the supportive replies.


18/07/2019 15:11:12

A few days ago there was a thread (now closed) started about abuse and intolerance within posts. Rather ironically there were a couple of derogatory posts made, one of which was directly aimed at me, apparently because I use, and talk about, ex-industrial machinery rather than "hobby" machines. I suppose I should at least be grateful that I wasn't excoriated for having a CNC mill.

I understand that the offending post has been removed, but I can't be doing with the attitudes expressed. Consequently I have decided to leave the forum. Time will tell whether my absence is temporary or permanent. If it does turn out to be permanent I will not be deleting albums and asking for my account to be deleted as that will mess up many posts in which other people have posted in good faith.

In the short term at least I will be reading and responding to PMs.


PS: The title of this thread is an appropriate acronym, although I'm not old enough to have experienced its birth first hand in WW2.

Thread: moore and wright internal micrometer
18/07/2019 14:24:52

Further investigation shows that the end with the spanner flats is screwed in, and is a very tight fit:


On "calibration" against an external micrometer and gauge blocks the internal micrometer reads about 1 thou under with the end screwed fully home, So it can be adjusted to be exact.


However, I do nor believe that to be the correct means of calibration. The knurled ring is definitely screwed onto the plain shaft that fits into the micrometer thimble. I expect that shaft to also be screwed into the extension rod, so the knurled ring can be used to set calibration. However, the knurled ring is very tight, and I don't feel like fudging an extension piece just to prove a point.

As new M&W are claiming an accuracy of 0.0001", I find it difficult to believe that they are machining extension rods to that accuracy as a matter of course in production. Much easier, and cheaper, to machine to a looser tolerance and calibrate.


Thread: What Did You Do Today 2019
18/07/2019 11:49:08

Nigel: Thanks for that, no doubt you're correct. In the only picture I have of fullsize frost spikes they're so rusty it's impossible to tell how they were manufactured. You're also correct about quantities, I've made 36 and that's only for one engine.

It's not clear how the frost spikes and anchor bolts were held in place. A straight tapered key wouldn't fit properly if perpendicular to the axle due to the curvature of the wheel rim, and if parallel to the axle there wouldn't be room to fit it. In the picture referred to there is a partially hidden tapered key; so that's what I've gone for. It's designed, a 1:1 card model made to check the fit, and the next step is to make one from metal strip. which arrived yesterday..


18/07/2019 10:09:07

The spikes are resting on two lengths of nominally 1/8" keysteel, held in place with double-sided tape. Keysteel is normally a few thou over nominal size so gives just enough clearance as the stock material was 5/8" and the machined shank is 3/8".

The spikes were hand held during broaching. Once pressure was applied the down force kept everything in place. The biggest problem I had was maintaining the broach vertical. The relatively small diameter of the shank meant that at best only two teeth were engaged at a time. Sometimes the broach went straight through with ease, other times it jammed. A jam simply required the broach to be twisted slightly back towards vertical and then it went as normal.

Not ideal, but I suspect the original spikes and rectangular holes would have been made by the blacksmith, so at least I'm better than that.


17/07/2019 22:21:25

I have now finished forming the rectangular slots in the anchor bolts and frost spikes for my traction engines. To summarise the sequence:


Three holes drilled and then the slot milled to size with a slotdrill, both on the CNC mill. Finally the square ends were done with a keyway broach, thinned on the surface grinder to be a snug fit, using an arbor press, with a drill and shims as required:



Thread: moore and wright internal micrometer
17/07/2019 21:58:52

On my Moore & Wright 2" to 12" internal micrometer I'm pretty sure the additional rods are adjustable:


The shortest rod (bottom left) doesn't appear to be adjustable. In that case I assume the micrometer head is adjusted. I think all the other rods are adjustable. Looking at the shortest of the other rods (top left) there are spanner flats on the left hand end and the knurled nut at the right is a separate item, and can therefore be loosened. I don't know what the exact method of adjustment would be, but no doubt it would be clear once the knurled nut is loose.


Edited By Andrew Johnston on 17/07/2019 22:00:54

Thread: Further Adventures with the Sieg KX3 & KX1
16/07/2019 10:22:14
Posted by JasonB on 15/07/2019 07:39:17:

Yes, having done a couple the manual way it is certainly quicker, whether it is a satisfying is debatable and certainly not so high on the willy waving scale.

I'd argue that it's more satisfying and higher up on the willy waving scale. After all in order to produce the part one needs to create the design and be able to use 3D CAD. Then one needs to create the G-code and cutting schemes which requires a proper understanding of speeds and feeds versus depth and width of cut. Fixtures also need to be created that allow the part to be machined without getting in the way of the cutter or chuck.


Thread: Aircraft radio scanner
16/07/2019 10:15:31
Posted by RMA on 16/07/2019 09:46:03:

Yes, if we don't know what you're on about Neil, you're an editor and communication is your business. You've failed if your audience doesn't understand you. However, why is this post on a model engineering forum? I have an aircraft scanner but not that interested in how it works, but I saw the title and clicked on it. Surely there's a more appropriate forum.

It's impossible to write for every level of audience, some a priori state of knowledge has to be assumed. As it happens I know what all the acronyms mean, as it was radio that got me interested enough in electronics to pursue it professionally. But if I'm interested but don't understand I'll either do an online search or ask for clarification - it's called curiosity.

While this is nominally a model engineering forum it covers a far wider range of interests and techniques than a man in his shed building a steam loco, and long may it continue.


Thread: A few newbie questions, sorry
16/07/2019 10:00:13

1. Traditionally an endmill would not be able to plunge vertically, but is designed to cut on the side. A slot dril normally has two flutes, and on the end one edge goes to the centre, so the cutter can be plunged straight down. For reasons of cutting geometry a 2 flute slot drill should cut a more accurate width on a slot than a multi-flute end mill. The distinctions are somewhat muddied now as 3 and 4 flute centre cutting endmills are very common.

2. I suspect it's simply what individual manufacturers specify rather than some fundamental difference between 3 and 4 jaw chucks.

3. Don't know; as someone has "helpfully" pointed out recently I don't have a Myford lathe. smile


Thread: Worm and Wheel manufacture
14/07/2019 20:36:10

If I were to do a rough calculation I'd work out the diameter of the pitch circle, add the addendum and a bit more to account for the curved nature of the worm wheel. And then watch the tap cut the number of teeth it wants to, irrespective. The worm wheel illustrated was for a "speed" control on a Pickering governor, so the number of teeth was unimportant. I simply decided what OD I wanted to give the appropriate centre to centre distance and then cut steadily deeper until the teeth on the outer edges were fully formed. The precise centre to centre distance of each worm and wheel set was measured on the job rather than relying on the theory. I suspect that gashing the worm wheel first would help, but it's not something I've tried.

However, for the steering gear worms and worm wheels in the other pictures the worm wheel was gashed beforehand using a convenient involute gear cutter and the dividing head, plus swivelling the table on the mill to the appropriate helix angle, like this:

worm wheel gashing.jpg

In this case the number of teeth was important as there was no latitude for adjusting positions on the job, so gashing was essential. When free hobbing the worm wheel the dividing head plays no part, it's simply a convenient way of holding the arbor on which the worm wheel freely rotates.


Thread: Aircraft radio scanner
14/07/2019 20:18:28

In the UK it is definitely illegal to transmit on VHF aviation frequencies without a licence, with two exceptions. One, there are a number of frequencies set aside purely for gliding and a private glider pilot does not need a licence to operate on these frequencies. Two, if operating under the instruction of the licence holder, ie, a student pilot. From a practical viewpoint most ATC units say they would much rather glider pilots contact them, even if technically illegal. When I was getting my power licence I also did a course and took the exam to get radio operators licence, which is for life. The radios themselves also need to be licenced. So I pay £15 every 3 years to Ofcom for the handheld transceiver I use in my glider.


Thread: Worm and Wheel manufacture
13/07/2019 18:22:29

If you use a standard V-thread it's easy enough to screwcut the worm and use a commercial tap in the lathe to make the worm wheel:

hobbing worm wheel me.jpg

A spiral flute tap helps, but isn't essential.

Alternatively if you can screwcut an Acme worm then you can also make a hob for free hobbing the worm wheel, although you will need to gash the worm wheel first. Here's a home made hob cutting a worm wheel:

worm wheel hobbing.jpg

And the final worms and worm wheels:

worms and worm gears.jpg


Thread: Electric Cars
11/07/2019 23:07:47
Posted by Barnaby Wilde on 11/07/2019 21:08:52

but you are still a long ways from the actual reason.............................

Not something I'm going to lose any sleep over though; there are things that matter and those that don't. smile


11/07/2019 20:48:51

EVs are quiet, so the people you run over don't even hear you coming. The cost of insurance isn't particularly tied to write off value. It's much more to do with potential costs if you injure people and they require lifetime care. And you can just as easily do that in a £100 banger as a £300k supercar.


11/07/2019 17:30:15
Posted by Russell Eberhardt on 11/07/2019 16:05:27:

Diesel vs petrol: Diesel cars are more efficient and produce less CO2. Older diesel cars produce a lot of particulates and NOx which give rise to poor air quality in cities however current models complying with euro 6.2 standards produce much less.

Oddly we had a meeting today at a gas sensor company for whom we're designing an updated PCB and signal processing for their NDIR CO2 sensor. They also sell optical particulate sensors, often used for air quality monitoring. At lunch one of the scientists was saying just that, modern diesel engines are less polluting than petrol for some gases and especially for particulates.

Whatever we do there'll be some "expert" or government "adviser" thinking up a new pollution source or new target to hit. Even if we all walked people will be worrying about particulates from shoe soles. The only permanent solution to pollution is to get rid of everybody. Then at least there'll be nobody to worry about cows farting. smile


Thread: My new lathe a Warco 918
11/07/2019 17:20:06
Posted by Ron Laden on 11/07/2019 07:49:14:

How do you guys approach spindle taper rollers

At an angle; I find a couple of beers beforehand helps with getting the optimum angle. smile

My lathe uses Gamet super precision opposed roller bearings. The manual says nothing about lubrication, and there are no oil points for the bearings. The geared headstock is filled with an ISO68 hydraulic oil, which splash lubricates the spindle gears. I assume the same oil must also lubricate the spindle bearings. The manual gives the spindle torque needed for correct preload and how to measure it, and then strongly advises against even thinking about it. I've never touched the bearings in the last 20 odd years.


Thread: Milling a T slot - am I doing it right?
08/07/2019 13:42:18
Posted by John Hinkley on 08/07/2019 12:16:02:

For further info - the Mill is a Warco VMC - so reasonably substantial with a 1½ HP 3-phase motor/VFD combination fitted by me.

That might be the problem. First, you should be able to get the VFD to show the nominal output frequency which would give a fair estimate of motor speed, given the number of poles in the motor. If the speed of the motor has simply been reduced by reducing the frequency, and any belt or gear drive not changed, then you may well have a lot less than 1.5hp at the tool. If anything I'd reduce spindle speed a bit and stay with the feedrate. Provided of course that you're getting full power at the tool.


08/07/2019 11:13:10

This is a theoretical answer; while I've got a fair selection of T-slot cutters I've never had the need to use one yet. Feeds and speeds seem reasonable, albeit quite a low chip load. I've got two comments. One, I suspect there's a fair amount of flex in the tool spindle; not good as the cutting edge is long and forces will be hgh. Second, as an estimate I reckon the cutter is removing about 1.2 cubic inches of material per minute. I don't know what mill or drive arrangement is being used, but that removal rate will require comfortably over 1hp at the tool.

Another couple of thoughts. If the material is cold drawn BMS has it gone slightly banana shaped due to the initial machining, thus causing the T-slot cutter to jam? It's normal to cut the initial slot slightly deeper than the T-slot so that the T-slot cutter only cuts on the sides and doesn't rub on the bottom. I can't see if that is the case here.


Thread: In need of a steel ring 132mm dia
07/07/2019 12:34:53
Posted by not done it yet on 07/07/2019 12:16:28:

As in a 5mm washer? I think a piece of 6mm plate, as a starting point, would suffice for that.

That's the way I read it, and I'd also start with 6mm plate, but I already have some in stock, left over from the traction engine hornplates. A sketch, or confirmation that I haven't gone off at a tangent, from the OP would be good.


Edited By Andrew Johnston on 07/07/2019 12:35:18

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