Member postings for Andrew Johnston

Geometrically rolling work in a V-block does not give an accurate measure of out of roundness. it measures height from two tangential support points. Professionally out of roundness measurement is done by rotating the work, or the stylus, on an ultra precision bearing.

Andrew

None at all, just clamped them down as normal. I'll have a look tomorrow and see if I can dig out some pictures.

Andrew

First thought is I wouldn't done it that way. To second previous comments I'd have machined both sides equally first and then drilled and tapped the holes.

Rectangular gauge plate is only ground on the wider sides. The narrow sides are left as sawn, so there may be some stress from the sawing. However, I suspect technique and/or material may be the problem. Where was the gauge plate sourced?

When I made the slidebars for my traction engines i machined 20mm x 10mm gauge plate down to 3/4" x 10mm. I took approximately 0.5 mm off each narrow side. The slidebars are 8.5" long. They are on the engines so I can't measure them against a surface plate. But with a rule held along the machined edge i can't get a 1 thou feeler in. So it should be possible to do what is required without distortion.

To save, I'd clean up the narrow edges to remove the bowing. Not much to remove so I'd draw file rather than try and machine. How much bow is acceptable?

Andrew

Edited By Andrew Johnston on 27/11/2022 20:48:45

How do you know that the Arduino Clock Cycle is accurate and stable? A quartz crystal probably won't vary enough to give the results seen. But they do drift, usually 50 to 100ppm at the lower cost end. Stability is also dependent on the quality of the oscillator. Presumably there is softare between the crystal oscillator and the measurement being made?

Andrew

Dryness fraction is not easy to measure. If the steam is reasonably dry the normal method is to use a throttling calorimeter. This only works if the steam becomes superheated after throttling. For wetter steam one can combine a seperating and a throttling calorimeter. I doubt that all model boilers are the similar, so quoting one figure is most likely an estimate.

Andrew

Depends on the accuracy needed. I use anything from a ruler, to the 1/2 function, to a co-axial indicator. For accurate work I use a Haimer Centro, works on spigots and holes:

Andrew

I designed and built my own bending rolls to form the rims, and the plan had been to add a couple of grooves to roll flat bar the 'wrong' way for the T-rings:

For reasons I can't remember I decided against this and bought laser cut quadrants for the T-rings. These quadrants were then arc welded together to form rings. Once rolled the rims were arc welded, and then the T-rings welded in place. I used a fixture to ensure that the T-rings were welded in the correct place, completed T-ring in the background:

The T-rings were an easy push fit in the front rims after welding so my calculations were correct. On the back wheels I had to remove about 15 thou from the rings as I had forgotten that the hot rolled steel used for the rear rims is not accurately sized.

It was a lot of work welding the quadrants together, and the laser cut quadrants were not cheap, so in retrospect it might have been easier to roll the rings as initially planned.

Andrew

I have asked a mod to delete the offending post.

Andrew

The final drive gears can be cut horizontally:

Why do the wheels need to be machined? The hubs for my front and rear wheels were machined on the lathe, but the rims, T-rings and, during assembly, the wheels never went near a lathe. Front wheels:

Rear wheel:

Andrew

Mine are unbranded, but are bought from professional electronics suppliers. The last few came from Mouser. They are fine for hand soldering down to 0402 and, at a pinch, 0201.

Andrew

I don't bother with flycutting flat surfaces for the reasons given above. I find that milling cutters give flatter, and better finished, surfaces:

I only use flycutting when I need a large curved surface:

In the above the DOC was 40 thou and feed was 8 thou per rev. The flycutter is homemade with a HSS toolbit.

Andrew

I've never bought anything from Warco. With an attitude like that I never will.

Andrew

Personally I no longer buy from Tracy Tools. I got so frustrated with the last set of taps and die that I widlarised them:

Andrew

I've bought a lot of tooling from Drill Service over the years and have been pretty happy with the quality. Although, to be fair, I haven't bought many dies as I don't use them that often. In the picture FEW is the French Engineering Works which, despite the name, is in South Africa. I have quite a number of their taps and have no complaints. The die from TWT is by the Taps and Dies company in North Yorkshire. I have no experience of them. I'd be surprised if Drill Service sold poor quality as they supply to the commercial sector.

Andrew

It doubles the time needed on the pick and place machine, every fraction of a cent counts.

Andrew

Could be caused by wear in the machine and/or inaccurate setting of the tool and topslide angle. With threading inserts I don't mess about with settinjg the topslide at an angle. I just plunge straight in so the insert is cutting on both sides.

Andrew

If it makes you feel better I've been there, done that, too.

Andrew

I don't think the original schematic is representative. Fairy lights implies a number of LEDs. It seems unlikely that each LED is drawing 270mA. Conversely if each LED is taking 10mA or so, then each 2R7 series resistor will only drop a few tens of millivolts.

Presumably we are talking a consumer product here, so it seems unlikely the manufacturer would waste time and money adding a resistor to each LED when one will do.

Andrew

Where does it say that each LED has it's own series resistor?

Andrew

The series resistor creates a crude current source. The larger the voltage drop across the resistor compared to the voltage across the LED the closer the arrangement is to an ideal current source.

Andrew