Member postings for John Haine

Hello Michael, welcome to the forum. Would be great to see some photos especially of the Webra (and/or a link to the video).

Given that the Taplin is a British product of the 50s/60s IIRC, it may well use BA sizes. From my days messing around with British diesels in model aircraft (PAW19D, ME10 etc) I think they used BA sizes.

Each small division round the large scale is 0.01 mm as is printed across the dial. So that's 0.15mm TIR which isn't bad though not wonderful.

Totally unacceptable. Return it and get a refund. 0.15mm would be just about ok.

I can't immediately recall the thread on the stud, but when I converted my S7 to non-topslide I just bought a corresponding HTS hex head bolt from my favourite supplier.

I took the topslide off because it's flimsy and I wanted to make sure the QCTP worked repeatably, so there's a dowel pin in the hole at the bottom left of the block to stop it deflecting (which was one of the issues with the original slide. I haven't missed the slide at all but I do use CNC so there's nothing it would do for me.

I have a S7 but can't see any need for a set of engineering drawings. The main dimensions of interest are for interfacing accessories, usually to the spindle nose or carriage, and they can be measured in a trice. Likewise individual parts. Interesting that everyone leaped into the debate about dimensions and threads without answering the initial question!

Mind you, I suspect that Myford might like an accurate and detailed CAD model!  I wonder what state the "original" drawings are in?

Edited By John Haine on 16/09/2023 10:36:15

Well it could be for a specific amplitude as always for circular deviation, but the aim of compensation is to make the rate independent of amplitude.

https://www.libreoffice.org/download/download-libreoffice/

**LINK**

Very easy to install just like any other app.

Andrew pointed out a small error, my formula

(+a^2/16)/13 = a^2/208

should have been...

(+a^2/16)/11 = a^2/176

Clearly though this is for specific physical parameters and could be larger or smaller depending.

Edited By John Haine on 13/09/2023 10:53:43

Sorry to keep saying the same thing but why not just add 2 steppers or servos to your lathe plus a spindle sensor and use a standard CNC controller? All the "thread to a shoulder" stuff plus a wide range of threads all comes for free.

Indeed, that's the one. Maybe one can shape the corners of the polepiece to prevent this?

If I may, just to close this topic off, I did mention earlier that it is known that the cycloid does not make a compound pendulum isochronous (and in fact there is no curve that can do that). My friend Andrew Millington (who is a real mathematician) has looked at this and come up with an approximation for the circular deviation of a compound pendulum moving in a cycloid, and also checked this against Woodward's analysis. This would apply to David's magnetically suspended pendulum as well as a pendulum with cycloidal cheeks. There are two factors to consider. One is the distance from the suspension point to the CoG of the whole pendulum, which is "r". The other is the "radius of gyration" which is a measure of the pendulum's "compoundness", which is "k".If the amplitude of swing is "a" radians, then the fractional change in clock rate is:

k^2.a^2 / [16(r^2 + k^2)]

If the pendulum is "simple" then k = 0, so the rate change is zero.

Suppose we want a 1metre pendulum. The bob weight can't be too large because it has to be supported by the magnet. So let's suppose it was 1kg. The "shoe" which has the circular face and contains the magnet needs steel polepieces and the magnet has to be strong and probably quite heavy. For the sake of argument suppose the whole shoe weighs 100g. Assume the rod is say carbon fibre and effectively weightless. Given the length of the rod and the weights you can calculate the position of the CoG and the value of k. Putting them in the formula and calculating gives a fractional change in rate of:

(+a^2/16)/13

For a normal circular pendulum the standard expression for CD is:

-a^2/16.

So while the CD is significantly less than for a conventional pendulum it isn't zero and can't be made zero. I think your suggestion and the experiments you did were very ingenious, but the fact that one does lose the "ideal" anisochnonicity (is that a word?) combined with the practical difficulties you've highlighted make this approach of theoretical interest only.

I'm not sure I see that Dave. Why wouldn't the arrangement I sketched work?

Two things to add to Duncan's excellent description.

If you want to plot two Y variables against one X, put them in adjacent columns to the right. You can add column titles (say "time, amplitude, period" at the top of each column and select the titles as you select the columns.

If you choose the line option in the insert/... command it will plot a line through your points.

I think they are prolate trochoids, according to Philip Woodward.

Just emailed to you, Joe.

This is my previous thread on the opto precision issue.

**LINK**

I wrote a longer article for HSN which I could share if of interest.

I have done this and posted the results here somewhere.

Duncan, you're quite right, it's Minimag. The SPC1 or SPC3 (or is that no longer made?).

**LINK**

The SPC1 has a cored coil which makes it unsuitable for clocks but the SPC3 is un-cored. But for this application cored might be fine. Adjustment would probably be either changing drive voltage (1.5 - 4.5Vdc) or just proximity to magnet.

Robin that's cool - how did you make the bearings please? I'm quite tempted.

There's a way to drive pendulums with a magnet on the end that interacts with a coil. The coil is connected in a simple transistor circuit which, when the pendulum swings past the coil in either direction, is triggered to pass a current through the coil which repels the pendulum to keep it swinging. For an example see:

**LINK**

...but there are loads of links on the web. I've used the principle in a clock but using an Arduino instead of a transistor.

**LINK**

I think that 4QD of loco speed control fame used to sell a self-contained unit to do this.

Two alternatives. One is a games controller - I use a Microsoft one with Mach3 and have done for years, it's wireless and has joysticks. For GRBL there is Grbl Controller which is an Android app that links using Bluetooth. Neither speak Linux but both might be adapted?

I think the killer to cycloidal approaches is the fact that all real pendulums are compound to some extent, as the bobs aren't point masses, rods have mass, whatever the pendulum uses to support the top of the rod has mass, and there could be things like weight trays and so on fitted on the rod. As Mike alludes to, there is no path the CG of a compound pendulum can follow which will make it isochronous. What the error might be for the magnetic configuration being discussed here I'm trying to ascertain.

I first came across the term "isochronous" probably in 1972 when I was working on digital data transmission at the PO Research labs in my first job, so it has been around a long time.