In comparison to my last post, this is something you SHOULD look at, if you actually use the compound slide to move exact amounts. I just plunge when threading (rather than the 30 degree method), and use it to cut tapers where the length is fairly irrelevant, so I've never realised this before. It's probably been discussed before, I guess.

I wanted to face 0.2mm off an existing part on the AL335 last week, so I thought I'd use the compound to make it easier to dial in the small amount, given the carriage handwheel is graduated in 0.5mm divisions, and I'm not sure that they're actually accurate anyway, as I've tried to dial in a specific amount off that handwheel before and got some odd result. It'd be nice to blame the single set of graduations that bend the laws of physics to be both 0.02" and 0.5mm at the same time, but from memory it was out more than that. I usually just use verniers to measure the part as I go anyway, as the length between shoulders usually doesn't matter for what I do, and I also have a mount to set up a dial indicator to measure carriage travel if I want.

In this case, I wasn't 100% sure on the exact amount I needed to take off anyway, given I was measuring it with feeler guages and thumbnails, so I figured I'd just use the finer resolution of the compound to be able to dial in really fine cuts and check the fit. Dialed in 0.2mm on the compound, and scratched my head. Just didn't look right. Fiddled around a bit, and decided, well, surely it must be right, must just be the nose radius on the insert playing tricks on my eye. Made the cut, and what do you know, took twice as much off as I wanted. Eh? Backed the carriage off, flushed up the front edge of the compound slide to the lower part, zeroed the dial, wound on 1.25mm, and measured it with a ruler. 2.54mm travel. Okay, I thought, it's just the old diameter/radius deal, dialed in 0.1mm on the compound, and faced the mating shoulder, job done. Didn't think anymore about it until I got out of the shower last night, and went hang on, WHAT THE F.....

Upon inspection today (Easy since the compound is still stripped on the bench), the screw for the compound is 10 tpi. Thus, every turn of the compound moves the slide 1/10 of an inch, 0.1 inches - which is exactly whats marked on the compound dial on the imperial side. So far, so good. The metric side, however, is marked as one full turn being 1.27mm - where it SHOULD be 2.54mm. Unfortunately on my machine, the ink has rubbed off the little plate that tells you how much each division is supposed to be (probably would have helped me realise earlier), but upon checking the photos on H&F website, each graduation is supposed to be 0.02mm. The way the graduations are on my handwheel, every second major line is marked as an increase of 10. It SHOULD be, either every major line marked as 10, or every second major line marked as 20.

Having looked at the photos on H&F websites, this applies to both the AL335 and AL336, but it wouldn't surprise me if this was a common thing on most variants of the CQ6230. I have a vague recollection a few people have had weird struggles with threading using the 30 degree methods in the past, and this might have something to do with it.

Attached a photo straight off H&F website to hopefully help visualise what I mean, if you look at the 70 thou mark on the imperial scale, you'll see that the metric scale shows about 0.9mm, which is only 35 thou. It SHOULD be 180. Now I'm considering turning the numbers off the metric side, and remarking them, cause I KNOW I'll forget that with the amount I use the compound...

*EDIT* Aaaand, I just realised the tailstock handwheel has the same issue, not that I've ever used it - but something to keep in mind.
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