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Member postings for Andy Stopford

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

Thread: Strange effect when turning
24/05/2021 21:13:43

This can happen if the chuck is worn so that it's gripping more tightly at the base of the jaws, allowing the workpiece to flex away from what's effectively line contact at the gripping point.

Thread: Kennedy Hexacut Model 90
21/05/2021 21:43:19

Sorry, Adrian R, I hadn't noticed your pm. Set up with the face you're trying to machine parallel to the mill table (packed up with 1-2-3 blocks in my case), there is just enough clearance to end-mill the worn faces flat.

One side is quite easy to set up, the other harder because of the shape of the pivot block - I had to hang this over the end of the table:

sam_0380.jpg

It would be easier with slimmer clamps than these - I must get around to making some sometime.

Thread: Laser Cutting Guide for Femi NG120ABS bandsaw
21/05/2021 21:31:11

Yes, the Hexacut* I think. It lives in the dark under the bench, so the laser would definitely make it easier to set up.

*funny how many posts there've been about these recently.

Thread: Kennedy Hexacut Model 90
21/05/2021 21:26:44

See my album for milling Hexacut 60 guides - it's a bit of a fiddle setting them up, especially on a small mill, but easier than making a complete new arm assembly. The ideal would be just replacing the hexagonal bars, but its hard to see how they're fixed to the pivot block - as Dave Wooton suggests above, they may be cast into it.

Thread: Laser Cutting Guide for Femi NG120ABS bandsaw
20/05/2021 19:22:33

Aha, a use for the £1.99 laser pointer bought, for some unknown reason, from ebay a while back.

The question is, should I fit it to the bandsaw, or the Hexacut?

Thread: Manson Engines ????
15/05/2021 14:29:21

Looks an interesting idea, though I would think the thermal efficiency would be very low:

http://techref.massmind.org/techref/member/rat_ring/Manson.html

animation here:

http://manson-ericsson-hae.blogspot.com/p/ma.html

Thread: Painting staircase spindles
13/05/2021 13:26:16

The only water-based gloss I've found that gives a comparable finish to oil-based is Albany:

https://www.brewers.co.uk/product/AA0142001J

I did an Edwardian-ish staircase with it recently, no problem at all (apart from the awful tedium - you need something good on the radio).

if I have a painting job I always insist on using Albany now - absolutely no horrible stinky oil-based allowed. And as for lead paint - yes, great, let's spend an hour stirring the wretched stuff and as an added bonus, poison ourselves!

By the way, it's reputed that water-based paints won't yellow in dim light the way oil-based does.

Thread: Kennedy Hacksaw Dashpot Oil
02/05/2021 17:00:52

Glad you've got it working well, Chris.

I was using mine this morning, and watching it, the idea that the forward cutting stroke makes the blade lift on the return stroke doesn't seem to hold water - the reverse if anything. I know that I tried the blade both ways, and it worked better forward, but that might have been when the machine was in its original worn state. I shall have to experiment with reversing the blade again.

I remember reading a warning not to leave these unattended because if it jams and the belt slips, the heat generated will ruin the belt, and they are not cheap.

01/05/2021 21:32:23

Yes, it has the switch, but no evidence that it ever had the rods to flip it

01/05/2021 20:16:35
Posted by Chris V on 01/05/2021 17:41:06:

Thanks Andy, Interesting to hear and see others issues with these!

No certainly not fast, but a darn sight less effort than using a hand saw! I have a vertical wood bandsaw for my brass which works fine but way too fast for steel.

I had obviously missed that about blade direction, I will change it tomorrow.

Chris.

Yes, it might take over an hour to get through a 50mm stainless bar, but then so would I!

Dave, mine has clamps at both ends, no blade holder pin - maybe they added that later - mine is an early one, it has the Hoover motor, and no auto cut-off (something else which would be quite easy to add).

Oh by the way, I use an 18 TPI blade (again a Kennedy recommendation). Definitely desirable for aluminium, 24 might be better for steel, but I generally just use the 18 for everything.

01/05/2021 17:22:16

I use EP90 in mine and it seems to work OK.

The motor is pretty gutless and will stall quite easily. The feed is supposed to be assisted by a spring pulling the arm downwards - mine has the wrong spring. It is far too powerful and will cause the motor to stall/belt to slip on steel, though it just about manages aluminium, so I have disconnected it. The weight of the arm is good enough for it to work, though at some stage I intend to add a sliding weight, as on bigger power hacksaws.

The blade is supposed to cut on the push stroke, Kennedy were explicit about this in their instructions. I think the idea is that the geometry of the arm and crank is such that it tends to lift the blade on the return stroke. The dashpot then lowers the blade gently back into the cut.

Mine had highly visible wear on the guide arms, and the bearing holes in the connecting rod were badly worn, so it made a lot of noise and tended to be prone to jamming as the bow racked around in the guides.

I bored out the holes in the con-rod and fitted bronze bushes and new pins.

I removed the worn areas on the guide bars with this rather precarious-looking setup:

sam_0380.jpg

sam_0386.jpg

The retaining bar that runs along the top was badly worn, so I replaced it with a piece of hexagonal brass:

sam_0444.jpg

I scraped the bars to ensure that they had a decent bearing area, and adjusted the fit of the brass bar with a couple of beer can shims. The bow was surprisingly free from wear and I left that as is, with just a light scraping to help it bed in with the newly refinished guide bars.

The dashpot boot was perished beyond usability, so I made a mould out of aluminium (couldn't be bothered to try to get the 3d printer to work for this task) and cast a new boot in 2-pack silicone rubber (it feels rather repellent when oily, but it does the job).

The saw works well now - it's not particularly fast, but it's quite accurate, and it gets there in the end. Sometime I'll replace the flat belt drive, which is prone to slipping. Maybe.

Thread: Gas Fitting
11/04/2021 21:06:50

I've never been able to get a definitive answer on this; every source seems to be different, but most are somewhere around the information in Michael's link, i.e. you can temporarily disconnect a bayonet fitting, and then re-connect the same cooker. You can't leave it disconnected (reasonable enough because you can't be sure the fitting doesn't have a slow leak without checking for same). How long 'temporary' is, is not specified.

This has always been a problem in the Removal industry - some firms will cheerfully disconnect the cooker, others won't. For the firm I work with, I've now specified that we shouldn't touch them.

Thread: Replacing a Canon printer with a Brother Laser?
10/04/2021 19:55:42
Posted by Peter Greene on 10/04/2021 17:35:02:

On the subject of Laser Colour Printers, I checked these out when the low price ones first came out and it seemed that they were OK for documents but not good for phtographs etc. So I went the inkjet route.

That was quite some years ago now though and I haven't really looked at them since. So how good are the current crop of lower-priced colour laser printers at handling graphics images ... particularly photographs?

Unfortunately the process seems to be intrinsically inferior to inkjet - the colours are muddier, and the tonal range is limited. It might help to experiment with different types and grades of paper.

09/04/2021 20:17:59

I have a Brother HL-3150CDW colour laser printer and I'd certainly recommend it. It works well, is quite robustly made (it would be OK for light business use), and you can refill the toner cartridges:

https://www.urefilltoner.co.uk/

After printing 1071 A4 pages (assorted monochrome text, colour images, etc), it has 20% of the colour toners remaining and I've refilled the black toner once (fairly recently). As the above website explains, you can get some extra mileage out of them just by resetting the cartridge - I haven't done that with the colour ones yet, with the black one, I added some toner while the cartridge was out of the machine to be reset.

There's an easy-to-use Linux driver installer on the Brother website - don't try to do it the hard way (says the voice of experience).

Thread: Any advice on how to cut/file a 45 degree chamfer on a 1mm steel sheet to EXACTLY 45 degrees?
23/03/2021 20:05:23

1 mm is very thin. Even if your 45 degree angle is absolutely perfect, you're going to have problems ensuring that the parts remain flat enough to obtain a <0.1mm gap all the way along the edge.

Given lack of space, equipment, etc., I'd make a simple jig out of MDF, flat-topped, with a piece of steel plate screwed to it, and an angled support at 315 degrees to it to clamp the part to. Use appropriate fences and dowels (through previously drilled holes in the part, as per your drawing) to register the part so that the edge to be chamfered is just above the steel plate.

Then file the chamfer level with the plate. You can let the file contact the plate to guide it. It will last long enough for the purpose.

chamfer_jig.jpg

Add fences, stiffening webs, etc. Draw filing is probably the way to go.

Thread: RH vs LH threads
15/03/2021 12:14:40

Zen and the Art of Motorcycle Maintenance?

Too much Zen, and not enough motorcycle maintenance, I thought when I read it as a teenager.

And he completely blew it for me when he's doing an oil-change and just lets the old oil run out onto the ground.

Quality, Robert, quality.

Thread: Design of boilers
05/03/2021 10:00:12

Go on, build one!

Thread: water level sensor
05/03/2021 09:34:05
Posted by duncan webster on 04/03/2021 21:58:33:

I quite like Noel's capacitance idea, but it's beyond my electronic expertise. Are we talking relaxation oscillator and phase locked loop chip? If so I've just bought some of those for another project, but I can't find them either!

Here's a fairly simple device for capacitive sensing, using a 555 timer and an ATMega 328 microcontroller (as in an Arduino). The schematic, MaquinaSafetyLevel.sch, is in the PCB folder, and is a KiCAD file.

https://github.com/andystopford/SCRAM

It works in the opposite sense to what you want, i.e.it switches on if the water is above a pre-determined level (to power a heater element).

The level probe is a commercially available one intended for espresso machines, though it seems to be just a stainless steel rod, with all but the last 10mm or so sheathed with acetal or something similar.

In main.ino, at line 10, I've commented it as voltage, however I think the values are arbitrary - it certainly doesn't carry 600 volts (I hope). These values were determined experimentally, and take a while to settle down; I'm not sure why, but I had to change them several times in the first few weeks of operation. They always drifted towards the 'safe' condition though, with shutdown occurring even when there was water in the boiler.

Thread: Design of boilers
04/03/2021 20:15:21
Posted by Nigel Graham 2 on 03/03/2021 23:09:22:

Thank-you. yes, I did discover the sorts of fields in which matrices are used, including graphics programming; but only much later. The course taught only their internal manipulations, no definitions, no purposes, no examples.

...

I think computers like matrices because they suit the physical nature of the circuits.

Indeed. When I was suffering O-level maths in the seventies, there was no hint of any practical application for matrices, or anything else; pointlessness was regarded as a virtue - hence the fetishizing of Latin, that most useless of subjects (academic linguists are free to differ).

The reason that matrices are used in CGI is that a common construct in computer programming is the array, and a matrix is, essentially, an array, and can be manipulated using simple rules.

Human-friendly controls in the program's user interface essentially manipulate vectors which conceptually aren't as easy to represent in the computer's world. It has to convert them into lower level arrays to actually work on them.

To comment on the thread, from which we've drifted, I think its interesting to consider whether boiler design can be improved, even if the practical answer is that there's no point/it's as good as it gets already, or whatever.

03/03/2021 21:12:47
Posted by Nigel Graham 2 on 03/03/2021 11:06:17:

Taking a GCSE Mathematics evening-class course over 20 years ago as a refresher for work reasons, I was baffled by the one topic new to school maths, hence to me: Matrices - taught as a pure abstraction linked to nothing else. I sought help from one of the scientists at work. Surprisingly, despite her PhD in Very Hard Sums, she could not explain the basic information I needed, so I was still baffled. She did though tell her work involved gigantic simultaneous-equation blocks soluble only by matrices; so I now knew their use - Finite Element Analysis (of vibrations, in her field). I realised the computer just made the arithmetic feasible. Though using a bought-in programme, she still needed to understand FE Analysis and extremely advanced mathematics.

As for the Matrix... It know the sort that is the clay in what used to be called "Boulder Clay"!

Matrices are much used in 3D computer graphics - a single 4x4 matrix can contain all the information necessary to Translate, Rotate and Scale an object, itself defined by it's transform matrix - how they do this is very non-intuitive, but computers seem to like it.

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