53 tooth gear

Ian, Neil: I admit it, I'm being an idiot. I agree that the relative accuracy does not change as the gear gets proportionately larger. I'm not quite sure what I was trying to say!

As far as machining my final drive gears go, I did the sums as follows. The gears are 5DP, 72 teeth with an OD of 14.8". My dividing head has a quoted maximum error of 1 min 30 sec. I'm making an assumption that my industrial 12" rotary table is similar. I make that a maximum error of about 3 thou on the circumference of a 14.8" disc. So the tooth width could be 3 thou wider, or narrower, than theory. The rule for cutting deeper for one gear of a pair, with 20°PA, is backlash times 1.46. So that means I need to cut about 4-5 thou deeper than normal.

Neil: I am intrigued as to how you measured the maximum error on your rotary table?

Regards,

Andrew

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So will there be a difference if you cut the gear in daylight, at night with a florescent light or under under the bed covers with a torch.

Wouldn't want to get it wrong you know.

John S.

Hi John, just listen to a bit of rock-n-roll while your doing it and you should be OK.

Regards Nick.

HI Andrew,

I didn't measure it, I made the rash assumption my home-cut worm and wheel are accurate, and then calculated the theoretical error for being half of one division out.

All the gears I have made to date using this method of divising with Ivan Law's book beside me seem to work fine.

13T pinion with splined insert

My gear cutting setup, using home made rotary table/dividing head:

A pair of bevel gears made using the above equipment:

A 63-tooth metric changewheel for my mini lathe:

Regards

Neil

Neil: Thanks, I was wondering. I'm not sure how one would independently measure the position of the table, versus the dial reading. May be a test indicator on a bar on the table? If the angular changes are small enough I guess one can ignore the arc versus straight line errors.

The gears look fantastic; are the bevels parallel depth? How did you cut the splines on the pinion? I need to cut some splines for the gears that slide on the crankshaft for my traction engines. I'm prevaricating, which means I'm not sure how to go about it! The only thing is, I think the pinion shown has more than 13 teeth, surely not a dividing error!?

Regards,

Andrew

I make it 17T, the other one must be the 13T. Ian S C

Andrew I cut the four splines on the Fowler by planing with the lathe but at 3/16" wide its as much as I would want to do that way.

If you make a plug for the bore of the gear with the required number of keyways in it, just like a broaching bush but with more than one slot. You can then broach the first keyway, locate the plug with a bit of key steel and then run the broach down the next keyway etc

Edited By JasonB on 18/11/2012 13:39:15

Jason: Thanks for the insights. I'll rephrase the question. I have a slotting head on the back of the Bridgeport, which is fine with a 1/4" wide keyway in cast iron. My prevarication is due to wondering how it is going to cope with a 5/16" wide spline in EN24T? And more to the point, if it cannot cope, will it simply stall, or will I end up badgering it?

Regards,

Andrew

Never tried a slotting head so can't comment on the Badgering. What about taking teh majority out in two goes with a smaller cutter and just finishing to width with the 5/16"

Have you not got an EDM machine tucked away somewhere in that garage? might be lurking in a dark corner.

J

Edited By JasonB on 18/11/2012 17:56:25

Edited By JasonB on 18/11/2012 17:58:15

... or buy something like this - **LINK** and use it to lash up a simple indent type indexer.

I cut my splines using my version of Stan Bray's slotting tool in the Workshop Practice Book.

The pinions are constant-depth, again using the Ivan Law method. It works on really small gears. This is the smaller of a speed up pair for the governor of a stationary engine:

Neil

Neil: Thanks for the information on the gears. I'll have to read up on the parallel deptth method, as I need to make some small bevel gears for the governors on my traction engines.

I could take out the splines in a series of steps, but I'd still like to finish with a full width cut. I want the outer edge of each spline groove to be circular so as to exactly match the crankshaft, rather than square. I guess I'll have to suck it and see.

Regards,

Andrew

PS: Sadly I don't have an EDM machine lurking in the garage, at least not yet.

Edited By Andrew Johnston on 18/11/2012 21:07:41

Good question Andrew - how do you turn accurate splines and ensure the gear is a close fit on the shaft?

This is how I did it (and I had to have a good look at the gearbox to find out!) The gearbox is for a 1/4 scale Forson Model F tractor, that has never got beyond the gearbox, some patterns and a lot of dreaming and drawing.

I turned the gear blanks so that each has a decent boss (needed for the shifter to engage with in any case). with the boss outwards and bored right though at the diameter of the inside of the splines. I bored the boss (but not the gear (the gears are 1/4" thick, the bosses either 1/4" or 5/16" (I didn't check) over size to be a light force fit for bronze bushes made to be a close sliding fit on the gearshaft.

I parted off the gears and mounted them on a mandrel to cut the gears.

reversed them and cut the splines so that the grooves were a wider diameter than the shaft, but still smaller than the outside of the bush.

Finally, I inserted the bushes so they butted up against the splines. The gears now slide freely aliong the shaft using the bush as a guide on the original outside diameter of the PGMS shaft. The splines only act to stop rotation.

I also bushed the other gears which slide but do not have splines.

Internal gears (which act as dog clutches as other gears slide into them) were not cut as proper gears, just milled-out semicircular notches.

The layshafts run in ball races but all the gears just have PB bushes except the input and output gears which run in ball races and have.internal races for the ends of the layshafts. Layout and dimensions are as near the original as I could get, aside that I think the original may use a stub-tooth form.

Neil

Edited By Stub Mandrel on 20/11/2012 10:41:01