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Member postings for Macolm

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

Thread: How can you check that DVLA field of vision machine is OK.
26/04/2021 15:44:44

The design of varifocal lenses is always a compromise between the desired gradation of optical power, and the inevitable distortions that result. The latter are the reason for the "swimming" effects, which for those lucky enough are completely corrected in the brain, and which for a minority are never tolerated. Designs have improved greatly over the years, but often minimised distortion results in perceived peripheral soft focus.

Most of the more expensive makes give some form of money back guarantee on the lenses, though mounting costs will probably not be covered.

Thread: Home Made Rear Toolpost Issue
04/04/2021 21:53:25

Carbide needs to be kept in compression. Setting the tip slightly high (in a front toolpost) helps ensures this, even if there is a dig in; if the tip is low, there is a good chance the cutting edge will be pulled off.

Thread: Tyre Guage DRO - capacitance issues?
03/04/2021 15:19:08

I doubt if earthing the lighting will make much difference. This sort of susceptibility is common with high impedance logic circuits. If the capacitive scale is like most others, the positive of its battery is already connected to the metalwork of the scale. What is happening here is that the “operator” is an aerial receiving radiation from the lighting. The capacitance between his finger and a susceptible point in the scale circuitry is sufficient to induce a big enough "signal" to cause malfunction. If he “earths” himself to the mill metalwork, the unwanted signal is bypassed and its magnitude much reduced.


I doubt if it would matter whether the mill is earthed or not. There is plenty of signal path at the relevant frequencies to the mains wiring via stray capacitances.


Prevention would need an earthed screen, probably impractical in this case.


Edited By Macolm on 03/04/2021 15:20:22

Edited By Macolm on 03/04/2021 15:23:47

Thread: Removing a J2 arbor from a drill chuck
27/03/2021 14:20:28

I should have mentioned, if the arbour has a drawbar thread, a "slide hammer" technique will work with screwed rod, a nut and a sliding weight. Someone recently reported success with this technique. A sufficiently robust drawbar would also do, but many just have a hex sleeve retained by a small pin rather than an integral bolt head.

Treated with care, keyless chucks are excellent to use. Do not attempt to drill or hammer in the centre recess. The actuation thread occupies the central core.

27/03/2021 12:44:23

Not difficult if you follow the Albrecht instructions. The main problem is to undo the two halves of the main body. Well fitting half clamps to hold it in the vice and a chain wrench is best, but other means to grip it can be Jubilee clips or exhaust clamps, Protect the chuck with thin aluminium sheet. Dismantle over a tray!

Once dismantled, there is through access to knock out the arbour.

Edited By Macolm on 27/03/2021 12:47:53

Edited By Macolm on 27/03/2021 12:48:35

Thread: Broken Electric motor Junction box
21/03/2021 21:50:35

If the box was a standard single electrical box, Toolstation have good quality metal boxes complete with lid. It looks as if the board might mount on the long screws without the live connections shorting.

See Product code: 15062 - Axiom Metal Clad Blank Plate 1 Gang + Back Box

There are also similar boxes in other sizes. The website is frustrating though, and not everything they stock is necessarily displayed, but may be found with different search text.

Thread: Pictures in posts and font sizes.
18/03/2021 21:40:31

If using Windows, for managing and processing images, Faststone Image Viewer is free, very easy to use, versatile and powerful. Navigation is similar to Windows Explorer, but double clicking an image brings it up in full screen. Then hover the cursor at an edge, and editing menus appear. To convert to jpg (or whatever) just use “Save as” to select saved image type.

Advanced features include batch processing and renaming, and very straightforward tools to move (sort) images to one of several folders.

There are a number of similar free image applications, but of these, I find Faststone the easiest and most comprehensive to use.

Thread: Motor control board
09/03/2021 22:37:37

Agreed that the brush resistance is (necessarily) very low. However, the brushes inevitably short circuit the commutator segments as they bridge them, though there should be very little back emf between them at the point of commutation. Choice of brush material is thus a compromise between the series resistance introduced in the main current path, and the losses due to any residual circulating short circuit current (which higher brush resistance would reduce).

If the motor were rewound for, say, half the supply voltage, the current would double for the same power, and the back emf, per above, would half. Thus the optimal brush material resistance would need to be four times less for the losses to remain the same.

09/03/2021 17:11:02

Perhaps I should have made it clearer – “The choice of brush material resistivity is mainly a function of the supply voltage”. To make it clearer yet, it is down to how it affects allowable current density in the brushes, so for similar size motors, the current will increase as the supply voltage decreases. This is why battery tools will usually have copper loaded graphite brushes, whereas small mains universal motors will use straight carbon/graphite.

In practice, choice of best brush composition is much more complicated. There is plenty on the Internet about this, but mostly oriented towards large machines rather than typical diy motors. If cutting down brushes to a smaller size, selecting them with the same supply voltage is a way to reduce the risk of problems.

09/03/2021 10:30:35

The brush material resistivity is mainly a function of the supply voltage. A brush bridges two commutator segments so partially shorting the relevant winding, but theoretically at the commutation point there should be no coupled flux. However nothing is perfect.

I suspect the “AC or DC" question was really “mains or battery”. Certainly, some heavy portable tools like angle grinders have different brushes for 240v and 110v versions.

Thread: Help needed, can't release cast iron wheel
06/03/2021 22:15:27

I note the cast iron wheel appears to have a groove at the front, probably for a dedicated puller. The aluminium may just have the same feature. This feature was sometimes used to allow removal of tight fitting car engine and suspension parts.

To use it, you would need to make up a split puller which is turned up to fit the groove dimensions, then sawn in two axially so that it can actually be fitted over. You also need a close fitting sleeve to go over to retain it. It is usual to make the split sleeve also have the detail repeated to fit a threaded bush for the extraction bolt.

A puller like this is able to apply much more force that the universal type, and with little risk of causing damage, but is quite a lot of work to make.

Thread: Changing a drill-chuck adapter
28/02/2021 14:36:46

If the chuck is a copy of Albrecht etc, the main knurled sleeve is in two parts with a thread between the tightening knurling, and the remainder. As supplied, it is not only invisible, but also very tight. However, if you make up hardwood or aluminium half shells to allow firm damage free gripping, it can be unscrewed.

Dismantling is then straight forward (but don’t loose balls), and there is through access to drive out the arbour.

Thread: Warco GH 18 Milling Machine
22/02/2021 21:07:44

It is quite possible to design a two phase inverter (VFD) to run a "single phase” induction motor (ie with main and start winding). Indeed, Maplin did sell such a thing briefly some years ago. The phase angle of the second output would simulate the capacitor(s) phase shift, and the effective voltage would probably also need to be reduced.

However, while there might be merit in being able to make an already installed motor into variable speed, there would seem to be little merit in this configuration in a new machine since the disadvantages of the single phase motor would remain.

Thread: Jacobs Chuck
02/02/2021 22:14:26

I would be inclined to try a somewhat nasty fudge to restore the necessary interference between the split ring and the outer ring. Find some 2 thou (or thereby) brass shim and make packing pieces to insert in the splits. Brass would be more able to conform to the irregular split line and bed to a uniform spacing, and if necessary, anneal it.

Putting 2 thou in both splits would result in circa 1.3 thou increase in diameter, so quite a tight interference. You would probably need to glue the slivers of shim in place for assembly, but once pressed together it would be solid.

Thread: Colchester MK1 Bantam
27/12/2020 16:10:57

Belatedly, I came across the spacer piece I made to eject short MT parts on my Bantam. It slides across the slot, then the smaller section is offered against the offending item, and the normal ejection made with the handwheel. Make it a close fit, very similar to photo. While anything that fills the gap might assist ejection, it may get wedged and be very difficult to recover, particularly if ejection fails.


It was made from an offcut, and turned between centres.

Thread: thunderbird update
14/12/2020 22:16:12

My version also 78.5.1. I have just checked file location of my address book (which I changed long ago on to a second drive that is reguarly backed up to an off line store). There is indeed abook.mab.bak file, not very recently accessed. The active address book is in a file abook.sqlite, and I checked it is indeed the active file.

So indeed, the format may have changed, but if so this has been transparent to me. Perhaps it was done in the background, and the process failed on your computer. Thunderbird and such like are very prone to make a new (empty) file if unable to access the "right" one.

02/12/2020 22:12:21

Check the Thunderbird website. I think sometimes the program creates a new profile, but the files are still there and there is a procedure to reinstate things. Hope for the best, but even then still very annoying.

Thread: Best way to remember Mill movements when turning hand wheels
17/09/2020 14:25:22

My first lathe has a mix of feed directions, and no, I never had confidence which. The solution was to inscribe arrows beside the hand wheels as follows;-


Thread: varifocals
31/08/2020 22:02:51

Lens manufacturing technology has advanced to the point that any practicable optical design can be produced. Different lens maker have their own methods to blend the “infinity” distance zone to the reading patch at the bottom, but it is always a trade-off of distortion against optical aberrations. That said, the best varifocals work very well for most people.


If you are comfortable with ordinary varifocals and have a proactive optician (and sufficient money!), you can do what I have done and have an extra workshop pair. It seems best to choose the same lens type as your main pair. You choose a closer maximum distance, but keep the reading focus the same. I find one meter focal distance (to replace infinity) best for me, which means one dioptre more. The benefit is that the progression is more gradual, and all of the range is useful.


For example, suppose your prescription is +2 dioptres for distance and +5 for reading (addition is +3), then the workshop glasses would be +3 for “distance” and still +5 reading. The lenses do need to be set up to converge correctly. Some makers produce such specialist lenses, but these might have a different “feel" from your main glasses.



Edited By Macolm on 31/08/2020 22:04:48

Thread: Coping with voltage spikes
16/08/2020 21:40:15

Quite so, but he has had limited success with that.

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