Smart and Brown Sabel

OK if the wheel is made of steel. That is good as it means that if you can find a good skilled welder get him to rebuild the tooth making sure the rebuild is ‘chunky’, if necessary almost fill the gap left by the broken tooth. I would then skim the wheel in the lathe to clean it up. Next make up a template by clamping a piece of bright mild steel coated with marking blue (or copper sulphate dissolved in vinegar). Clamp it to the wheel and with a sharp scribe follow closely the teeth. Now saw and file up the profiles.

If your gear wheel is hardened an alternative is to copy the teeth as ‘positives’ by clamping two thin scraps of gauge plate and filling up exact copies of the teeth. As I approach the thing I am copying a use finer and finer files. When finished harden the gauge plates and use them as filing guides.

As a young lad I have done this sort of thing, many times in a pair of waders refitting wooden teeth to the great wheels at t’mills.

Ah! you did not say it was the small headstock wheel that was the problem. Can you tell us more about this wheel? What is its DP (Diameteral Pitch) being a US machine it will probably be Inch standard. Count the number of teeth and measure its diameter divide no of teeth by diameter and round the answer up to the nearest whole number –because you have measured over the ‘Addendum’-. The D.P. will be a whole number. Example suppose the wheel has 40 teeth and measures 2.625 inches then the calculated DP would be 15.24 so round up to the nearest whole number which is 16 and there you are.  Actually you can visti HPC Gears web-site and look ar their on-line catalogue this gives you the Overall Diameter (and the PCD)

I would have a very close look at the whole assembly. I have a feeling that unless the wheel concerned is larger than the nearest pulley it will have had to be made separately. Can you post a picture of the assembly? Can you tell us also how wide the thing is.

Actually cutting wooden gear teeth by hand is not difficult you just have to have some razor sharp long chisels, one or two nice sharp gouges –for roughing- a good template which spans a few teeth and patience –Dad paid me 6d an hour to do them.- I think he charged 5/- per hour for the job.

Edited By Richard Parsons on 08/02/2011 16:42:28

Edited By Terryd on 08/02/2011 17:01:50

Richard

(No of teeth +2) X Mod=OD - but work in mm

Keith

Philip - Yes it was machined on the common shaft and is integral with the pulleys. It was either cut with a gear ‘shaper’ or by a ‘rack’ planning process, the details do not matter. The gear is i think 16D.P.

Looking at your pictures and thinking about how I would mass produce the thing I am fairly certain that the whole pulley assembly is a casting made in ‘Spherical Cast Iron’. The fracture displays many of the characteristics of a fracture in cast iron. I have seen quite a few of this type of fracture mainly on agricultural machinery. The surface finish also shows a similar type of finish to that found on spherical cast.

From the photos and a bit of (trickery) I think you have only about 3/8” to play with. This will limit your options as cast iron does not like being under tension. That would rule out the ‘Special screw’ or ‘peg’ methods of fixing the problem. If you want to see an example of this visit the Submarine Museum in Gosport where you will see an example of a repair made at the bottom of the ‘great dampness’ to a helical cut bevel gear. By gosh the 'Tiffies' must have been good to do that by hand! If you cannot get a spare then I think you have only two options, flog the lathe and let someone else make the repair, or repair it yourself. If you choose the latter case then I am afraid only leaves you with, I think, two alternatives methods which could be used to make a repair, one of which will defiantly need access to a lathe.

This first method is to buy a suitable 16D.P. 40 toothed wheel and machine away its centre.. Then machine away the old damaged gog down to a good ‘shrink fit’. When SWAMBO is not looking heat the gear you have trepanned out to about 200-250°C in the kitchen oven and slip it onto the pulley assembly. When it has cooled, to hold the thing in place, I would drill 3 or 4 say 2BA tapping sized (or similar) holes into the gear and pulley assembly exactly on the join between the two parts, tap them and insert suitable socket heads grub screws with a little thread-lock for added security. These act as both keys and retainers. You will need to check the hole up the middle as you may need to ream it if the added gear wheel has compressed the pulley assembly.

The second method is to have a welder build up a new tooth stub. Then by careful filing, clean everything up. File the new tooth to length and then profile it using a template and fitter’s blue for the final fitting. (You can pinch SWAMBO’s lipstick for this process but it is not as good) and in my experiance causes ructions if you are caught). It will mean refitting the assembly several (or many) times checking the fit with fitter’s blue. Filing or scraping down the high places until the thing runs nicely. Laborious job but very satisfying when completed.

I hope others can find other alternative methods, but part of the problem is that spherical cast contains graphite which precludes the use of modern adhesives and does not braze very well.

Any way Good luck as it looks a nice machine