backgear

[David CarruthersParticipant @davidcarruthers68650]

Hi from the scottish borders, I am a first time poster. I am hoping one of the members could help me out i am trying to find out the diameter of the backgear wheels of a ew stringer lathe i know they are 20tooth and 48 tooth but little else, any help would be greatly appreciated David .

[David CarruthersParticipant @davidcarruthers68650]

[DC31kParticipant @dc31k]

Is one of those gears doing the driving and the other being driven?

If so, measure the centreline distance of the shafts upon which they sit (when the backger is engaged). That number and the 68 total teeth in the train (or 34 teeth in the gap between shafts) will allow you to calculate pitch circle diameters

[Howard LewisParticipant @howardlewis46836]

Have you looked at the pages on the EW Stringer lathe on Lathes UK website?

There may be a reference to the DP and Pressure angle of the Back Gears, and the Changewheels, on there..

Maybe somone on here will be able to provide this information. that you need.

,You need to know the Diametral Pitch of the gears, since it affects the Outside Diameter of the gear.

Presumably, the gear centres are already fixed by the journals for the Back Gear Shaft.

So you need to count the teeth on on one of the gears that will mesh with the Back Gear assembly, and measure the O D of that gear.

Ivam Law's book, on Gears ( Gears and Gear Cutting ) gives the formuka

(Tooth Count + 2 ) / DP = O D,

Thus a 20 DP gear with 20T will be 1.10" OD.

To complicate matters, for the gears to mesh correctly, they need to be the same Pressure Angle

You will not be able to measure it easily!.

Being an older lathe, my guess would be 14.5 degrees

You should not mesh a more modern 20 degree PA gear nwithn a 14.5. Will cause noise and wear.

HTH

Howard

[Ady1Participant @ady1]

There is a strong probability that your backgears are a mirror image of the gears you already have on the EW spindle, but the opposite way round of course

Edited By Ady1 on 18/05/2023 09:36:22

[noel shelleyParticipant @noelshelley55608]

Hi David, Firstly welcome to the forum, you have tapped into large font of knowledge here ! Howard has answered your question by giving the way to calculate the size using the other gears. It will probably be DP and whole and even number so 16 or 20 DP are likely candidates, so 48+2/16 = 3.125OD ! Good luck. Noel.

[michael pottsParticipant @michaelpotts88182]

David.

The EW lathe uses 16 DP gears. These are relatively coarse and fine feed is not possible. Many years ago someone, J Constable, designed a fine feed. I have the article in an old Model Engineer.

Almost certainly the pressure angle of the gears is 14.5 degrees. Most gears available now are 20 degrees. Going back to gear diameters, the 48 tooth wheel should be 3.125" diameter, the 24 tooth wheel should be 1.625" diameter. I assume that both are on the lathe mandrel, and you do not have the back gear fitting.

Howard Lewis gave a lot of information in his post. If you have further questions come back and ask. Someone will have the answer.

You have a very good lathe, solidly made and easily adjustable. It does use Whitworth and BSF threads, so you would need to become familiar with these. If you need taps and dies to either make or repair them, then Tracy Tools in Devon are probably your best bet.

Finally, could you tell us a bit more about your lathe. What do you have with it, chucks and accessories, but also any other bits and pieces that came with it. It will make any advice you get more relevant.

Regards. Mike Potts.

[Nigel Graham 2Participant @nigelgraham2]

Good thing my own EW lathe is in the hall, only a few steps from the computer!

A quick play with change-wheels shows the back-gear pairs are indeed of the same DP as the change-wheels.

Measuring the 40T change-wheel with a rule across the pitch-circle by eye gives 16DP,

By that DP value, and the formula Howard quotes, we have 42/16 = 2.625" OD verified by vernier-caliper.

Using the counts you give, our Outside Diameters are of:

– 20T: (22/16) = 1.375" (not 1.10)

– 48T: (50/16) = 3.125"

Calculated.

Verified by measuring the actual machine.

I do not know the Pressure Angle and as Howard also points out, gears of differing pressure-angles should not be combined. If you are asking in order to replace missing or damaged gears, unless you can determine the pressure-angle it would be best replace to both in the affected pair – which may mean all four.

.

DC3K – well, yes! This is a back-gear so two driver-driven pairs. You can determine the gear dimensions as you say if the shafts are directly accessible, but the two shafts are too well hidden on this lathe for easy and accurate measuring.

[michael pottsParticipant @michaelpotts88182]

David.

I got the tooth count on one wheel wrong. I read 20 tooth and then wrote 24 down. Apologies.

I you have not come across this internet item, you may find it useful. It is 'model engineering norge'. Written by someone in Norway he deals with the EW lathe in some detail much of it nowhere else. They are worth reading.

Regards. Mike Potts.

[Howard LewisParticipant @howardlewis46836]

NG2

The 1.10" iwas stated as being for a 20 DP gear.

16 DP gears will be larger for the same tooth count.

Changewheels will probably increment in fives. EW owners, such as NG2, will be able to detail what they have, and dimensions, (Bore, thickness etc )

Howard.

[David CarruthersParticipant @davidcarruthers68650]

Hello, Thanks for all your answers, I have read about the ew on uk lathes and engineering norge i got the teeth numbers from his article by counting them on a photo in it, the lathe itself came with a small four jaw chuck,the motor and a really wellmade countershaft frame with all the correct sized picador pulleys on it . There was also a q-change tool post with some tools . I also have a very nice little flexispeed meteor 11 thoug it has not got its motor or countershaft with it then there is a early drummond bros lathe which i traded for some old landrover wheels, getting back to the ew i should have said that it does not have the drive gear on the spindle shaft either, all this should keep me busy and away from the jobs my missus has got lined up for me now that ive retired . David ps my nickname is crockett, once again thankyou for the info.

[Nigel Graham 2Participant @nigelgraham2]

Sorry Howard, I mis-read it as 20 teeth!

'

Yes, the standard change-wheels are 20 to 65 X 5 teeth; and can be set in a 2-stage train.

NB: ,What the change-wheels will not do, and were never intended to do, is provide a power feed.

They are for cutting screw-threads only but will give a wide range. Though two that defy it are 1/4" and 3/8" BSP, which are of 19TPI.

The change-wheel disc sizes are 5/16" thick and 5/8" bore, with a small hole in the face to engage a pin in the driving-collar or adjacent wheel.

Using an 'Excel' spreadsheet I have even managed to calculate them for several metric threads with an acceptable pitch error within 10 turns – often enough for small studs, though probably best part-cut and finished with a die or chaser.

For small threads it is often easier to use a die completely, in a sliding-body type tailstock die-holder, but the tailstock taper alone won't have much gripping power against the torque transmitted back through the die-holder unless that is given some extra restraint. Taps can be used with a manual tap-holder and a sprung tap-guide – with the power safely off of course.

Since these lathes have permanently-engaged full-nuts it is better to carry out screw-cutting manually, by a mandrel hand-wheel. Withdraw the tool at the end of cut, wind the saddle back several turns past the work and come back. This should mean the tool will always meet the thread properly, unless the lead-screw and nut are very badly worn.

'

By "drive gear" do you mean one of the back-gears or the spindle pinion on the outboard end to drive the change-wheels? The latter happens to be the 20T one on mine at the moment, but can be changed for one of the others in the set if necessary.

It is retained on the spindle by a collar on the outside of it, grub-screwed to the flat, and with an 1/8" dia pin to engage the hole in the gear.

–

You don't mention it but if you have the boring-table with the lathe I would advise making quite long T-nuts with protection against winding through, as the slot flanges are quite thin and delicate.

[Howard LewisParticipant @howardlewis46836]

If the changewheels will withstand screwcutting bforces, presumably they could be set up to cut a very fime thread, and use that for a longitudinal power feed. (Although you might be looking for a 250 t[i thread set up! )

Some time ago, I did this on a Myford ML4. 20:60 / 20:65 / 20:60 to get a feed of about 0.004" per rev.

Howard

[Nigel Graham 2Participant @nigelgraham2]

You can't do that with the existing EW Lathe machine because it accommodates only a two-stage reduction.

The most it will give as standard is 0.016" / revolution = a very useful 62.4TPI.

It would need a new banjo making to add the extra step.

[michael pottsParticipant @michaelpotts88182]

You would need a new leadscrew as well, as it will run in the wrong direction with only one extra step. J J Constable tackled this problem in a Model Engineer article in volume 111, # 2790 dated 11/11/54. Essentially he added two extra steps in the screw cutting gear drive, very neatly done, but the explanation was not quite so clear. It took me some time to work out how it operated.

Regards. Mike Potts.

[Nigel Graham 2Participant @nigelgraham2]

Really?

I've never heard of having to swap the leadscrew to cut any thread, whether a right-hand one needing a 3-step gearing, or to cut a left-hand thread from 1 and 2 step gear-trains.

The reversal is normally by a tumbler-gear between the spindle pinion and the first stud wheel.

'

If your lathe can take only a one or two stage change-wheel set anyway, then the problem does not arise:

1 Step: Spindle Clockwise (looking on end of spindle) – Idler (anticlockwise) -Leadscrew (clockwise)

2 Step: same but the idler is replaced by two wheels keyed together, and the leadscrew wheel is moved outwards to meet the 2nd middle wheel.

.

On the EW with its standard change-wheels, that will cope with most BSF, BSW, Brass (26tpi) and ME (32 and 40tpi), and most of the smaller-pitch UN series. It won't manage 1/4" and 3/8" BSP threads, at 19tpi, with its standard wheels.

If you want to cut metric threads you can get close to some of the common ISO-M ones with the standard wheels, over short lengths of thread. Otherwise you'd need include a 63T or perhaps 42T wheel if you can obtain or make one of proper form. (The EW won't have room for a 127T wheel but 63 and 42 give close approximations based on 63 X 2 and 42 X 3 each = 126.)

The least accurate ISO-M thread it can cut is M8 X 1.25mm, giving an accumulated error of 0.32mm short on 10 turns. (30T spindle, 40+35 stud pair, 65 lead-screw).

.

NB: Don't try to cut threads approaching or exceeding the lead-screw's own 1/8" lead. It is unfair to most lathes, usually needs operating it manually from a leadscrew hand-wheel; and is certainly cruel to a small machine like the EW.

.

3 Step (.e.g Myford and most lathes with change-wheels and 8 or 4 TPI leadscrew): then by tracing the rotations along the wheel chart rows shows where you use the tumbler reverse.

To emulate that on an EW Stringer lathe would not be easy but since you'd need make a 2-stud banjo anyway, that could be designed to take a reversing wheel.

I think this is more or less how the Drummond B-type lathe reverses its leadscrew. It has no built-in tumbler, as on the Myford 7, but its headstock has a pair of slotted lugs, like ears, to take the reverser pinion stud.

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