Member postings for Andyf

I'm not sure that's quite right; chloroform is CHCl₃ (carbon, hydrogen and chlorine). "Ethers" are a class of straightforward hydrocarbons (just carbon, hydrogen and oxygen). The one which was once used as an anaesthetic is diethyl ether, CH₃CH₂-O-CH₂CH₃ , but I don't know if this is the particular ether my pal used to weld Perspex for me. I doubt if you can buy it at the local chemist now; long gone are the days when you could buy the ingredients for gunpowder at the local Boots.

Andy

Oo-er, John. I hope it works. As a (long non-practising) radio ham, digital electrickery scares me to death! I'm better with cogwheels.

All the festive best to you and everyone else on the forum.

Andy

Thank you, kind sir!

Nothing at all wrong with your idea, but a combined gear/dial down at leadscrew level might strain my poor old eyes. Lifting the dial up an inch helps them a bit.

Andy

John, I needed to make an pretty accurate metric LH tap for a one-off purpose, and that started me off on some pretty boring and repetitive maths to see if I could do better metric threads than those on the chart supplied with the lathe, using two sets of compounded gears between the spindle and leadscrew gears, rather than one set plus an idler. There are programs around to help with the calculations, but I couldn't find any which dealt with two compounded pairs rather than one. Then I found that many theoretically good combinations wouldn't work because gears would foul one another, or the overall length of the gear set was too long to fit on the banjo. It was irksome trying each combination to see if it would work, and (if not) whether rearranging the order of the drivers and drivens would help. In the end, I devised an Excel spreadsheet containing the relevant dimensions which, when I entered each theoretical gear set, would test the six possible arrangements of it and tell me if any of them would work in practice.

Anyway, my 1mm pitch threads now have an error of about 1mm in 100 metres.

Maybe I should get a life...

Andy

My granite chopping board (I forget where it came from) wasn't acceptably flat, so I went to a local supplier of made-to-order granite worktops, and asked if I could buy an offcut like a sink cutout to use as a surface plate. They took me to the skip, and let me help myself for nothing. I got two likely looking bits, and sliding my DTI around on its stand shows no more than half a thou deviation anywhere, which is good enough for my purposes.

Andy

Hi Johan,

Yes, the imperial threads you cut with your metric leadscrew will be almost, but not quite, correct. But using the chart supplied with my imperial lathe for (almost) metric threads, the error was often around 0.5%. Another page on ny website shows how I used the gears supplied with my lathe to get much closer metric threads, when I need more accuracy. Of course, the error figures rely on my Chinese leadscrew being accurate!.

The only way you can get them exactly right is to use a 127T gear (but a threading dial still won't work).

Have a nice warm Christmas in South Africa, and spare a thought for us in the UK, where the rain is so heavy that serious flood warnings have been issued!

Andy.

Though your lathe will cut both metric and imperial threads, it has a metric leadscrew, so a threading dial will only work for metric threads.

I made a crude threading dial for an imperial lathe, shown here:

As you will see, the leadscrew is used as a worm to drive a gear, which turns the dial. For imperial leadscrews, a single gear is all that is needed , with the same number of teeth as the threads per inch of the leadscrew, or a multiple of that TPI. Thus, for my 12 TPI leadscrew, I made a gear with 24 teeth. If that dial only had one mark, I could engage the half nuts each time that mark came round, because the leadscrew would have turned 24 times, moving my carriage 2” along. If it had two marks, I could make quicker progress by engaging each time either of those marks came round and the carriage had moved 1”, because imperial threads are all expressed as the number of threads in one inch.

Life is more difficult with metric threads. Unlike imperial ones, there is no conveniently small distance into which all metric pitches will fit. If you have a gear with 15 teeth and a single mark on it, the carriage will move 30mm for one full turn of the leadscrew. The 11 standard metric pitches you might want to cut are 0.5, 0.6, 0.7, 0.8, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5 and 3mm. Only 0.5, 0.6, 1.0, 1.25, 1.5, 2.0, 2.5 and 3mm pitches will divide exactly into 30mm. That leaves 0.7, 0.8 and 1.75 mm pitches; those will divide into 28mm, so a gear with 14 teeth will cover them (and would also cover 0.5, 0.8, 1.0 and 2mm pitches).

So, you will need both a 15T and a 14T gear if you want to cover all the 11 metric pitches mentioned earlier. The thread dial indicator could have interchangeable gears, or both gears could be permanently mounted on a single shaft which could be moved along to bring either of them into mesh with the leadscrew. Indeed, as the entire indicator will can be made so it can easily be attached to and removed from the apron (see my web page), it might be easiest to make two separate indicators, one with a 15T gear and the other with a 14T gear. Of course, you might decide that you could easily use dies to cut 0.7 and 0.8mm pitches, and that you wouldn't want to cut 1.75mm (as used on M12 coarse) very often, so your needs could be met with a single 15T gear.

As to the number of marks on the dial, two examples might help:

1. Imagine using a dial with a 15T gear to cut a 3.0mm pitch. The dial goes round once as the carriage moves 30mm, and 3.0 divides into 30. But it also divides into 15, so you could have two marks on the dial, and engage the half-nuts when either came round.

2. If you were cutting a 0.5mm pitch with your 15T dial, 30mm/0.5mm = 60, so you could put 60 marks round the dial and engage the half nuts on any of them.

But too many marks can be very confusing, and I have four around my dial. That means that for the finer threads, I may have to wait longer than necessasy for a mark to come round, but in reality little time is wasted.

Going back to my first remark, the reason you will not be able to use a dial to cut imperial threads is that none of their pitches will divide exactly into a conveniently small number of millimetres.

I hope this helps!

Andy.

Edited By Andyf on 23/12/2012 18:18:51

To extend your digression: not a new phenomenon. My 1951 Jowett Javelin had a purple light to tell you that the wipers were switched on, in case you were in the habit of driving without looking through the windscreen.

Andy

By coincidence, I've just been messing with the 40T mini-lathe gear I use as an idler to reverse my leadscrew. It looks like this pic . The central "boss" is 18mm diameter, so there's not much meat to cut into, and it would be hard to match the curve round the bottoms of the four "keyways" shown in John S's last pic.

It might be easier to make 8mm gear spindles, to match the simple keyed bushes which suit minilathe gears, though that wouldn't help at all when it comes to fitting any of the various gears on the end of the leadscrew.

Andy.

Edited By Andyf on 19/12/2012 00:09:22

If, as is quite common on smallish Chinese lathes, the change gears are Mod 1, then it might (depending on the bore of the gears, or rather the bore of the keyed bushes which fit in them and run on the spindles on the gear quadrant) to use the readily available and cheap acetal gears from a minilathe. I think those gears are 12mm bore, and the bushes are 8mm bore.

James, examine the gear you have. If its outside diameter (across tooth tips) gear in millimetres is equal to (or just a bit less than) N + 2, where N is the the number of teeth, then it is a Module 1 gear. Of course, if the spindles are missing from the quadrant so you have to make your own, you could make them 8mm diameter.

The gears for the drive to the milling head drive may be to a different, probably larger, module, but places like HPC or even Technobots may be able to help.

Andy

"Au secours!" might be a useful French phrase to shout in that situation, Jason, as well as "Help!". Or you could split the diff between the languages and use Mayday.

I stopped learning French when I was 13. Now, I spend three or four weeks a year over there, so some of it has come back. Nouns galore, but too few verbs to string them together into a sentence, so I can bravely ask for something in a shop and then get completely flummoxed when asked what size or colour I want. My German and Spanish are similar - just enough to make a fool of myself.

Andy

Douglas,

Jason gave me his home address so I could send a cheque. Without being too specific, a hundred miles or so further south and he'd have to speak French.

Andy

This is the reasonably comprehensive German list I mentioned earlier on. It displays a lot of boxes saying "Web page can't be found" but that seems to be because adverts have gone missing. 24 and 25 BA are listed, though.

Andy

Bear, bhere's an even better German website, but I don't have it bookmarked. Maybe someone else knows the one I mean.

Apologies for dragging this into the cyber world, Merlin. I appreciate that you probably want a book you can keep in the workshop.

Andy

The Zeus handbook is pretty good. That said, I usually refer to my inherited 1941 Machinery's handbook, because it's much easier to find, and nothing regarding screw threads or drill sizes seems to have changed much.

If I can't find either, I usually try Maryland Metrics for threads and tap drill sizes.

Andy

Hi Dean,

You might be right about the cast iron, but the base of my dial indicator stand seems to be CI and displays no magnetism when its internal magnets are swirched to "off". Nor do any CI machine parts after the stand is detached from them.

But Brian's laminations sound ideal, and are sure to work.

Andy

I should think so, Dean.After all, laminations work well in transformers. Wouldn't cost much to try it out, if you have a scrap transformer or some strapping lying around.

You mentioned soft iron, but if rigidity wouldn't be a problem, you could try cast iron.

Andy

My first thought was that you might dismantle a scrap transformer and use the laminations, but it would need to be a substantial one to provide strips 200mm long.

Less destructively, the metal strapping used around crates etc might work; I have just tried stroking a piece with a magnet, and it didn't want to pick up any swarf afterwards. If you have any, you could try the same test.

In either case, you would have to glue (epoxy or similar) the layers together to build up the thickness required, or maybe use brass, copper or aluminium rivets.

Andy

Martin, I use about 15 or 20% for anodising, so adding your acid to the same volume of water (add acid to water, NOT water to acid) would get you there.

I have had perfectly acceptable results using the acid from dead car batteries given to me by a local garage, added to the same vol of water, but that's difficult now that most car batteries are sealed.

Andy

Hi Robert,

I had a similar problem in finding a 3-jaw scroll chuck to fit my Perris (now the Cowells) lathe with an obsolete 1/2" x 20 UNF spindle nose. I picked up a cheap 2.5" 3-jaw with an M14x1 thread, bored the hole out and rethreaded it M17(ish) x1, made up a bush with a matching thread, and then bored/threaded the bush to the desired 1/2" x 20 UNF. Full story here. The same technique could be used to bore out and bush a 4-jaw, though it does require access to another lathe with screwcutting facilities.

A backplate would be simpler, at the expense of a little of the chuck to tailstock distance. I was unable to use one, because the bolts attaching it to the 3-jaw might have fouled the internal scroll. That wouldn't be a problem with the solid body of an independent 4-jaw.

Andy