Many thanks to everyone for your replies.

I think the blade is almost certainly the problem, as Jason and others with experience of these things clearly sensed.

I took off the blade used in the video, located the weld seam and emeried it as smooth as I could get it, even though it was pretty smooth to begin with.

After refitting I expected at least some improvement, but there was none; it still jerked downwards disconcertingly. [In the video the jerking and clunking is more noticeable in the last half].

Fortunately, Aldi supply two blades with this saw [M42-grade steel, so perhaps a bit better than bargain bucket territory in their material at least?]. I fitted the second blade. There is a slight detectable deviation downwards once per rev., but this is much less than with the first blade, and there is no audible clunk.

As for cut quality, I've uploaded a couple of photos of steel bar showing the difference between cutting with the bar flat and cutting with it standing on edge, as initially. Lying it flat produces an obviously better cut.

There are still two minor issues. The picture of the brass bar [in the first image and 3/8" x 2", I think] shows the first: the two short patches near each end of the bar. I can't detect any difference in surface height with my finger at these points, so I'm not too concerned by it, but does anyone have a suggestion as to why these markings have occurred? There is nothing on the surface of the bar either side to explain their existence, and further cuts produced exactly the same result. The bar was cut lying flat.

The second issue is that now I have shimmed the vice on one side with washers [around 1.25 mm thick], the plastic guard on the inner side of the saw slightly fouls the angled side of the vice at the bottom of the cut. I can probably resolve this fairly easily, but why the clearance between the edge of the vice and the body of the saw has to be so small I don't know.

John Baron, there are no missing teeth.

John Haine, if you click on the second link in my opening post you should find my post about the Femi on that page.

Ady, the user manual shows the blade tension lever pointing almost vertically downwards when the blade is tightened according to the instructions ["to the stop"]. Are you saying it would be OK to use the saw with the lever backed off part way? I will back it off when not in use.

Martin, yes, the third one is top right.

I suspect my problem is a combination of the first blade having a marginally too thick weld area and one pair of guide bearings [before and still] being marginally too close together.

If I can loosen off the screw going through one of the bearings that are too tight, will this allow me to retighten the screw with a bit more clearance? I ask because I can't really get to the bearing screws with the saw mounted on the pivot arm, and after the trouble I had mounting it in the first place [having to do the work practically one-handed] removing and remounting it isn't something I look forward to with relish.

Thanks for the further replies.

Robin, disturbing to hear about your Axminster saw – puts my problem in perspective.

I'd got Tuffsaws earmarked even before the present saw arrived.

Sadly, at the moment, I'm getting the following message on all pages of their website:

"Due to experiencing higher than usual levels of orders, the website is currently offline while we catch up but will be back up shortly.

Please check back later or email us at sales@tuffsaws.co.uk"