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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: Source of Machined Nuts
17/05/2019 19:29:05

Plenty of suppliers for machined BA and small metric nuts but not so for BSF. I've been caught by a supplier advertising machined BA nuts sending cold formed BSF nuts. I wanted the old style thicker nuts, so I made my own, 1/4" BSF full and lock and 5/16" BSF full:

nuts_me.jpg

Andrew

Thread: DC Treadmill Motor
17/05/2019 16:20:56

In addition 48V is a standard industrial distribution voltage within automation cabinets and the like, as well as for power over Ethernet units. The problem with 60V is that it is at the SELV voltage, so regulations get rather more onerous.

Andrew

Thread: What Did You Do Today 2019
17/05/2019 14:55:40
Posted by Ron Laden on 15/05/2019 13:31:28:
............from starting how long has it taken you to get to this stage.

I'm embarrassed to say about 10 years. But in my defence I'd note the following:

  • I'm building two engines, so everything in the picture is doubled
  • There are quite a few parts made but not yet installed, like hollow pistons, eccentrics and brake handles
  • All the parts exist in 3D CAD for several reasons; some imperial materials are no longer available, I've made a number of design changes for increased authenticity, I've redesigned a lot of items as the original drawings are poor and riddled with errors
  • I have an out of control garden
  • I've got sailplanes and aeroplanes to fly
  • Until recently I've been working full time

That's probably enough excuses to disguise my indolence. smile

Andrew

Thread: Work Holding For CNC Milling
15/05/2019 20:56:44
Posted by John Pace on 15/05/2019 20:39:26:

In the original article the subject matter was the production of a pair of
shears to make some dummy cover tapes for a model aircraft.

Miniature pinking shears?

Andrew

Thread: Ever have one of those days..?
15/05/2019 10:24:21

It's a rare workshop day when I don't make a mistake. Likewise it's a rare day at the gliding club when I don't get a rollocking for something or other!

Andrew

Thread: Work Holding For CNC Milling
14/05/2019 16:23:40

What's the problem? According to the experts all you need to do is press the button marked 'GO'! smile

How would I do it, assuming rotational symmetry? For a start I wouldn't split the big end at this stage, and I'd leave the material over length. I'd drill and/or ream the little end. I'd also drill a hole in the big end, but of a size and in a position that will disappear when the big end is opened out. I'd set the work co-ordinates to zero in X & Y on the little end bush. Then mount the work with bolts and washers in the little and big ends. If one is particular about accuracy you could bush the little end or provide a tapped spigot. Machine the profile (except the outer end of the big end, so to speak) and then relieve and flute one side. Turn over and relieve and flute t'other side. I'd clean up the outer edge of the big end, and drill and start the tap, for the big end bolts while the stock is still rectangular; makes life easier.

Once all that's done I'd split the big end, clean up as required and bore the big end hole.

Andrew

Thread: Parkson M1250 Beast
14/05/2019 15:17:41

Depends if the electrics/electronics work and you have a 3-phase supply. If neither then bin the lot and take note of Muzzer. If yes to both I'd be inclined to play before stripping out.

Andrew

Edited By Andrew Johnston on 14/05/2019 15:18:13

Thread: Shipping to USA
14/05/2019 15:13:37

I've done it the other way round, importing a new mill from the US. I used ACC Shipping in Gravesend:

**LINK**

Going t'other way may be different but the following points may be useful:

I don't think ACC do pallets and boxes

Normally the supplier needs to provide a description and nominal value - ACC can say what they need

They will pick up from the supplier, ie, you, and take it to the docks.

A small item will be LCL (less than a container load) so ACC will combine it with other items to minimise cost by ensuring that the container is full

They organise the ship

Into the UK they looked after all the customs forms, duties and VAT - I then paid them

They organised shipping from the UK port to me - don't know if they do the same overseas

Best thing is to give them a call; I found them pretty helpful to a novice.

Andrew

Thread: Cutting steel to size
13/05/2019 11:09:07
Posted by Speedy Builder5 on 13/05/2019 06:37:24:

So what do you use for flat plate?

For material up to the thickness mentioned I use a power guillotine. thumbs up

Andrew

Thread: Cylinder mounting.
12/05/2019 23:07:17
Posted by not done it yet on 12/05/2019 22:07:06:

Same as on agri tractors - at least the old ones?

Errr, I think so? Burrell called them anchors, which is something of a misnomer as they're designed to get you out of a sticky situation rather than keep you in it.

Andrew

Thread: What Did You Do Today 2019
12/05/2019 21:51:52
Posted by Boiler Bri on 10/05/2019 17:41:43:

Im jealous Andrew. My wheels have been clamped to slab of 1” aluminium for months awaiting riveting. When i made my first set i was in my 30’s. Swinging a 3lb hammer was not a problem, you ached and got better. Now in my 60’s i have to pluck up courage to do over 100 1/4” rivets.

You're a better man than me; I couldn't even close a 3/16" rivet with a hammer. Well, not strictly true. I can hammer the rivet end flat with a hammer, as I'm doing at the moment with the strakes. But no way could I form the domed head with a hammer. I got so far, but couldn't force the head that last little bit. So I resorted to the flypress. Much less drama and less chance of hammer blows in the wrong place, followed by naughty words.

Andrew

Thread: Cylinder mounting.
12/05/2019 19:15:57
Posted by DMB on 12/05/2019 15:24:51:

It seems like I'm not the only one not understanding "Carrot bolts". Come on, spill the beans!

Wot Jason said.

If there's trouble with vegetables I'd better not mention traction engine spuds! smile

Andrew

Thread: Which thread for T nuts
12/05/2019 19:11:33
Posted by Nick Hulme on 12/05/2019 17:12:38:

If used correctly the threads should be acting purely in tension...................

The bolt might be in tension but the threads themselves will be in shear. For many materials the shear strength is greater than the tensile strength. That's why a bolt shank will break before stripping the thread.

Andrew

Thread: Cylinder mounting.
12/05/2019 14:40:51

Many full size engines have the cylinder fixing holes drilled right through the boiler shell. The only difference being the holes are not tapped; carrot bolts are used instead of studs.

Andrew

Thread: Taper attachment
12/05/2019 13:14:40

A further variation concerns the cross slide feed. On smaller, cheaper, lathes the cross slide screw is disconnected and the slide driven by the taper attachment. Feed is put on using the top slide set parallel, or close to parallel, to the cross slide. On larger, mostly industrial lathes, the cross slide screw is telescopic so feed can be applied with the cross slide handle as normal while still allowing the cross slide to move in sympathy with the taper attachment.

Apparently the taper attachment for my lathe (Harrison M300) is of the latter type. I don't have a taper attachment; if one came up at an advantageous price I'd buy it, but I'm not desperate to buy at any price. If I need to cut long taper I use the hydraulic copy unit. if the taper really needs to be accurate I'll use the cylindrical grinder. The swivel table on the cylindrical grinder is marked in degrees.

Andrew

Thread: What Did You Do Today 2019
10/05/2019 14:52:23

Over the recent Bank holiday weekend I assembled enough of one engine to have it sitting on it's own wheels:

engine.jpg

After I'd recovered my jaw from where it hit the floor my reaction was bleep bleep that's seriously BIG! Where on earth am I going to put the second engine? It's just as well I moved the parts out of the kitchen, the assembled engine won't go through the door. Fortunately I got the specification for the front door correct when it was replaced a few years back, there's an inch or two of clearance.

Andrew

Thread: Larger VFD/Motors
10/05/2019 14:45:19

Posted by SillyOldDuffer on 10/05/2019 14:12:01:

The disadvantage of the current transformer method is it might not have the frequency response needed to catch spikes and it can't give accurate current measurements without me doing some sort of calibration.

Current sensors are fairly good straight out of the box. You need a burden resistor on the secondary, usually tens or hundreds of ohms. The secondary has many turns, often 1000, and the primary one turn, ie, a wire through the hole in the middle. The manufacturer wil often give a formula for the voltage across a given resistor for a given primary current.

However, there's a caveat. Last year at work we had a need to measure a three phase supply, so we used three cheap, made in China, current transformers. The client complained about non-linearity at low currents. The transformers were rated at 20A and sure enough at less than 200mA or so they went non-linear. A lot of effort went into measuring the effect and correcting same in software. Then we bought exactly the same part (same company name and part number) but made in India. They were linear down to the limits of our measurements, a few milliamps. Go figure!

Andrew

10/05/2019 11:47:45

If I recall correctly differential probes have been discussed before, quite possibly wih SoD. This is what I use:

differential_probe.jpg

It's not isolated and doesn't need to be. However, it's not really the best probe for the measurement specified as it uses an input divide ratio of 100:1 or 1000:1. That's fine if you're measuring mains size voltages, but not helpful if one is trying to measure small voltages riding on a large common-mode voltage.

Andrew

Thread: Form Tool Sharpening
10/05/2019 11:42:39

For free form shapes I hand grind, possibly against a template, and finish with diamond hones. If the profile is important I'll machine it and finish with diamond hones.

Andrew

Thread: Oil, lubricating the lathe
10/05/2019 11:39:43

Oh dear, I use an ISO68 hydraulic oil in the geared headstock of my lathe; although that is as recommended by the manufacturer. I use an ISO68 slideway oil on the slideways, feedscrews and change gears. The change gears are totally enclosed so they're not going to get dusty. The quickchange gearbox uses an ISO220 straight oil.

It's interesting to note that the ISO68 slideway oil doesn't work too well on my repetition lathe; too much drag makes the slides difficult to operate. All by hand lever of course. Instead I use an ISO32 hydraulic oil.

Andrew

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