Member postings for Andyf

Sorry; forgot to add the LINK to GadgetBuilder's site.

Andy

Geir, I think my lathe is a smaller version of yours. To adjust the free play on the cross slide feedscrew, I just tighten up the Nyloc-type nut which holds the handle on, to close up any gap between the rear face of the dial collar and the front face of the bracket behind it. If yours is the same, it's a very easy adjustment to make.

Lining up the headstock so that the spindle is parallel with the ways is rather more complicated. If your lathe is a bigger version of mine, the headstock will have two Vee grooves on its underside, which locate it on the same prisms on the top of the bed which locate the saddle and tailstock. I think re-aligning the headstock would mean shimming or scraping those Vee grooves, reassembling, taking a test cut, disassembling to try different shims or do more scraping, re-assembling, and so on. The procedure is described, but with only one Vee groove to deal with, on GadgetBuilder's website, here. He relies on "Rollie's Dad's Method" to check alignment, but that is not foolproof. For example, it can't distinguish between a badly aligned headstock and a warped bed.

For the sake of 0.01mm over 100mm, I wouldn't bother in case things were made worse!

I hesitate to suggest it, but as your spindle seems to point ever so slightly to your side of the tailstock, you might try a light tap with a soft hammer on the front of the headstock, at the pulley/changewheels end.

Andy

Lloyd, I reckon that for simple "hold things together / nut and bolt purposes" it's OK if you are within about 1%. For example, over 6 turns, the cumulative error on your 12.1266 TPI thread will only be be about 0.005".

It looks as though you could get pretty close to 1.0, 1.5, 2.0, 3.0 and 4.0mm pitches, though the last one is coarser than the leadscrew so the gearing would be against you (but you could always turn the tables by handcranking the leadscrew so that it drives the spindle via the gears). You have nothing near enough to 1.25mm (as on M8 coarse) or 1.75mm (M12 coarse). Among the inch threads, only 12 and 20 TPI seem to have tolerably close versions in your table.

Andy.

So did my Dad, until he went bald and didn't need it any more

Andy

Lloyd, I haven't worked through all your reasoning, but you last calculation for a 1mm (actually 25.46 TPI) pitch is certainly correct. So is the earlier one where (without a compound gear) you arrive at 20 TPI.

It is a very longwinded business to work out what gears you need to use to get a particular thread pitch. Programs like Nthreadp are only really helpful when you have a pile of gearwheels and want to know if they can be set up to cut a particular pitch. They don't help much at all when you only have a few odd-sized gears and want to know which extra ones might usefully be bought to cut standard pitches, or close approximations to standard pitches. As you said earlier, 3 is the magic number where inch threads measured in TPI are concerned. The 3 derives from the 24 teeth on the first driver divided by by the 8 TPI of your leadscrew, and means that for inch threads you need a set of gears where the tooth count increases by three, like the one I suggested. As an aside,if you had a 40T gear on your spindle, you would need a set in increments of five (40 ÷ 8 = 5).

However, help may be at hand. If you load the seven gears I suggested (24 to 42T in increments of three), plus another 24T to represent the one on your spindle, and also a 63T, and then try to find combinations for the standard metric pitches of 0.8, 1, 1.25, 1.5, 1.75, 2, 2.5 and 3mm (those being the metric coarse pitches for M5 up to M27) you will find various combinations offered with 24T as one of the drivers, and all within 1% error.

So, I suggest eight gears: 24T to 42T in increments of three, plus a 63T. If you want to get at the finer TPI pitches, you will also need a compound pair with one having twice as many teeth as the other.

Two last points:

It doesn't matter in which order the gears are assembled, as long as the ones specified as drivers are drivers and those specified as drivens are drivens. From your point of view, this means that where a compounded pair is needed (driven by your 24T spindle gear, and driving another gear on your leadscrew), it doesn't matter which of the drivens forms part of the compounded pair and which goes on the leadscrew. Swapping them can help when it comes to the practicalities of assembling the geartrain on your banjo (aka gear quadrant).

Gaps can be filled in with idlers, but bear in mind the reversing effect of each additional idler you add. Of course, this is of no consequence if your lathe has a tumbler reverse, which you can set so the leadscrew rotates in the direction you want.

My brain cell has got tired with all these sums, so I'm going for a pint.

Andy

If you can accurately measure the distance your lathe carriage travels, and are confident that your top slde dovetail is parallel to the slide's rear edge, maybe you could try this,:

Set up the topslide at roughly the right angle, and bring the plunger of an indicator which is fixed to the lathe bed to bear on the far side of the top slide. The indicator must be both at right angles to the lathe bed and parallel to the bed in the horizontal (i.e. flat). Trim the top slide angle until the indicator shows a deflection of 36.07 units when the carriage is moved 100 units. The units might be millimetres. If you work in inches, try something in proportion like 1.443" over 4".The greater the distance over which you measure, the more accurate the result.

Note: this assumes that the included angle of your taper is 2 x 19° 50' = 39° 40', which sounds a bit steep. If the included angle is 19° 50', you will want to set your topslide to half that which is 9° 55", and the figures then become 17.48mms over 100mms, or 0.699" over 4", or any other pro rta figures.

Do check my maths carefully; I was always a bit of a duffer at trig, and find aids like this calculator useful, though it needs decimal parts of a degree rather than minutes, and setting to more than the default 3 significant figures.

Andy

David, when I looked at it after David Clark put me right, I opted to show automatic bids and it is apparent that the current top bidder is/was using them.

The auction hasn't closed yet, but I'm not giving a direct link because some readers might pile in, and I may bid myself!

Andy

Thanks for the explanation, David. When I get it to show automatic bids, it is obvious that there were auto bids from _***b between each of the ones which mystified me.

Andy

It's bid histories like the one below (copied from an item currently on offer) which I find odd. Why has a***p been bidding against himself to take the price up from £50 to £104? And, indeed, why was his £104 accepted as a valid bid when -***b had offered £106 about an hour before?

Andy

Member Id: _ ***b £106.00 09 Feb 13 14:42:06 GMT

Member Id: a***p £104.00 09-Feb-13 15:37:02 GMT

Member Id: a***p £100.00 09-Feb-13 15:36:48 GMT

Member Id: a***p £55.00 09-Feb-13 15:36:28 GMT

Member Id: a***p £50.00 07-Feb-13 22:32:32 GMT

Member Id: e***r £30.00 07-Feb-13 15:41:30 GMT

Starting price £29.99 06-Feb-13 20:01:08 GMT

I think that's for mini-lathes with a 75mm (approx) spindle flange, Jason. Not sure where you'd find one for a 125mm flange (or, more pertinently, the right register diameter to go on such a flange). Arc Euro do one for 100mm and another for 150mm (both for ER32s), but none for 125mm.

They are handy; I have a 100mm one for ER25, and as Stuart says it's useful for holding long stock up to 16mm dia. which needs to pass through the spindle.

Not too hard to roll your own, I suppose, though that would turn a lot of metal into swarf unless fabricated from a large dia. disc and a smaller dia. nosepiece.

Andy

Jack, I think everyone else will probably have realised that was a mipsrint for "manual rotation"

Andy

Hi Lloyd,

The TPIs and metric pitches shown in your table are correct, but (apart from the first, which is close to 1.5mm as used on M10 coarse) don't correspond to any normal standard threads.

The full formula linking changewheels, leadscrew pitch and the thread which will be cut as a result is Drivers/Drivens = Leadscrew TPI / TPI that will be cut.

“Drivers” is the tooth count of the driving gears, and if more than one then their tooth counts multiplied together.

“Drivens” has a corresponding meaning in relation to the driven gears.

Idler gears are ignored.

To work out what threads can be cut by the gears you have, the formula can be rearranged as:

TPI that will be cut = Leadscrew TPI x Drivens / Drivers. Your Leadscrew TPI is 8, so if you only have one driver (the 24T on the spindle) and one driven (on the leadscrew), this can be simplified to: TPI that will be cut = 8 x Driven / 24 which simplifies further to Driven/3. This is reflected in your table.

If you include a compound gear in the train, so there are two drivers (24T and Driver2) and two drivens (Driven1 and Driven2), then:

TPI that will be cut = 8 x Driven1 x Driven2 / 24 x Driver2, which simplifies to

TPI that will be cut = Driven1 x Driven2 / 3 x Driver2.

"So if i had my 24t on the spindle turning 52t/32t compounded, and had the 46t on the leadscrew I’d get 25.46tpi and 0.99mm?"

That has a 24T driver, a 52T Driven1, a 32T Driver2 and a 46T Driven2. Using the formula in italics, TPI that will be cut = 52 x 46 / 3 x 32. I make that 24.92TPI or 1.02mm pitch. If the length of thread engagement is fairly short, that would be a practical substitute for 1mm pitch unless you were making something needing more accuracy, like a feedscrew.

Andy

That will be a tight fit, Stuart. only about 630mm or 2'1" to spare, and the shelves to fit in at the tailstock end. Might they prevent you sliding the tailstock off?.

If the shed wall at the headstock end isn't on a boundary, I'd be templed to fit a sort of windowless oriel bay in it at the headstock end, to get a bit more space and so gears can be set up on wet days as well as on fine ones. Maybe with a little trapdoor so that really long stock can be passed through the headstock to the exterior, though a support would be needed to stop it flailing round.

Andy

Wish I had a back gear. Not so much for turning large diameters, but more for screwcutting without the need for quick reactions as the tool approaches the end of the thread. My other lathe - a little Perris (now the Cowells) - has a back gear, but I have no changewheels for it, apart from those for fine feed.

Andy

I have one of its baby brothers. sold by Warco as the WM180 and by other retailers (eg Amadeal and Chester) under other names. They are made by Weiss Machinery in China, and are almost identical to the range sold in Germany under the "Optimum" name. I think the factory producing the Optimum machines may be under German management.

The overall design of mine looks very similar to the WM250. My gear/pulley cover was originally held on by a couple of knurled nuts, but I found that inconvenient and hinged it at the back. I did find myself going in there fairly often, both to fit changewheels and to switch one of the drivebelts between pulleys. The 50 to 2500 rpm variable speed on mine isn't continuous. Rather, it is in two bands of 50 to 1250 or 100 to 2500 rpm, and the drivebelt has to be shifted to get from one band to the other. That was a fiddly and tedious job, because to slacken/tighten the belt an Allen screw on the back of the lathe had to be accessed by feel. I have modified that to make life a bit easier.

As mentioned above, mine is a smaller version, and the WM250 may differ from it in relation to the way the gear cover is retained and the drivebelt. It looks as though it has a tumbler reverse and a knob offering a choice of fine feeds, so is obviously a more sophisticated machine than mine. The ideal thing would be to hold off until you have seen one, at Warco in Chiddingford Surrey (they used to have models on display at Newton Tesla's place in Warrington, but I don't know if it's still there or whether there is a WM250 on display), at Amadeal in Leytonstone or at Chester Tools in both Hawarden near Chester and in Burntwood Staffs.

Andy

I always thought it stood for the Ready, Steady, GO! Brigade

Andy

G1 B**

Lloyd,

First, to cut threads less than ¼” in diameter, it is probably easier to use a die than to cut them on your lathe, though the lathe can be a great help in ensuring a die-cut thread is true, if the stock is held in the chuck and the die in a tailstock dieholder. Annual rotation is probably in order, unless your slowest speed under power is very slow – 60 RPM or so is OK.

Looking at threads between ¼” and 1” in diameter, all Whitworth, BSF, Unified Coarse (UNC) and Unified Fine (UNC) threads will be covered if you can cater for 28, 26, 24, 22, 20, 18, 16, 14, 13, 12, 11, 10, 9 and 8 threads per inch ("TPI". Note that the first, second … seventh threads in that list have double the TPI of the eighth, ninth …. fourteenth.

There is a formula which works out the gears required to cut threads of the required TPI on a lathe with a given leadscrew TPI. I believe your leadscrew is 8 TPI. If your driver gear (the one on the spindle) is 24T, that formula can be simplified. Just multiply the TPI you want to cut by 3 to get the number of teeth needed on your driven gear, which is the one you need to put on the leadscrew.

So, looking at the second seven TPIs listed in the second paragraph above, the driven gear to go on your leadscrew is 24T for 8TPI, 27T for 9TPI, 30T for 10TPI, 33T for 11TPI, 36T for 12TPI, 39T for 13TPI and 42T for 14TPI (none of which you have; your 24T is already on your spindle). You will need to bridge the gap between the 24T on the spindle and whatever is on the leadscrew with one or more idler gears of any convenient size. As long as there are no compound gears in the train, the idlers (which will include those on a tumbler reverse, if you have one) have no effect on the overall gear ratio, which is determined only by the first and last gears in the train. A compound gear comprises two gears on the same shaft which are fastened together so they revolve as one. One of the two is driven by the gear above it in the train, and the other drives the one below it.

But a compound gear will be useful to get at the first seven TPIs in the list. If in place of the idler (or one of the idlers) you compound two gears together, one of which has twice the tooth count of the other, and use the larger one as a driven gear and the smaller as a driver. Then, you will get twice the TPI out of whatever gear is on your leadscrew. That will give you the first seven in the list.

I have assumed that the bore of the 24T on your spindle is such that you can’t change it for any of the other gears; if you can, then further, more complicated calculations might produce the right ratios from fewer gears.

As to metric threads, the only way to get these exact is to use a compounded pair and a 127T gear somewhere in the train. But given the rather odd tooth counts of your present set, you may be able to produce “near enough” metric threads for practical purposes.

Finally (at last!) : before investing in gears meant for a Boxford or South Bend, check that their bores match your spindles, or be prepared to make new spindles to fit them.

Andy

Lloyd, if you load up and save your gearset (including the 24T on the spindle) into Nthreadp, and then specify the threads you might want to cut, you can look through "driver gears" for a combination which uses 24T as one of the drivers. Don't forget to click "Load gearset" each time you start the program.

However, I've tried setting up the gearset as 24, 28, 32, 32, 46, 47 and 52T and it there are very few inch threads those gears will produce exactly. You need a better set of gears!

Andy

Thanks, Michael. I stand corrected; didn't realise there were two Czech companies with similar names.

Andy

TOS Kurim is now a subsidiary of the Alta Group in the Czech Republic, along with Skoda Machine Tools (not Skoda cars, which is owned by VAG) and other companies . See the caption on the photo here. You may need to click on the flag at the top right for a translation.

TOS certainly seems to make machinery and tooling, though it is always possible that some work is outsourced to manufacturers in other countries.

Andy