Information needed Goodell Pratt 5 1/2 B

[RussellT]

I am considering trying to make a pinion. I've never made a gear before but in principle it's doable. Unfortunately mitered bevel gears are the most difficult to cut so I wouldn't hold your breath for a supply of new pinions. It would be very satisfying - but I might try a US forum first.

I'd be happy to measure the springs for you but they're not the originals. The originals were missing so I hunted around in my tin marked "springs" until I found three that looked about right and then I cut them to length. I just looked for springs that would fit the holes in the chuck fairly easily and which would compress from fully open to fully closed.

Please let me know if you still want the measurements.

Russell

 

[RussellT]

Here's a little bit more progress to show. Thanks again Rhyolith for the dimensions. Any inaccuracy in the knob (ferrule is a bit short) I blame on my incompetence.

Russell

 

[Rhyolith]

That looks great! Honestly a bit of ageing on that I would not know that handle was not the original, good job

Any progress with the pinion?

 

[RussellT]

I am shocked to see how long it is since I last reported progress on this. There has been a lot of procrastination going on.

I tried asking on a US forum for the missing pinion with no success and I set up a search on eBay which only found me drills that were in better condition than mine. I read up on gear cutting and mitred bevel gears in particular. All that revealed were that these were not theoretically correct gears.

So having exhausted all avenues of procrastination I decided to try making a pinion. I decided to try making one in plastic first as it would be much quicker to machine and it would be an experiment.

I measured two angles from the drills handwheel. One was the angle the top of the teeth made with the axis of the drill and the other was the angle the bottom of the gaps between the teeth made with the axis. Because of limited space around it I had to make a sort of mini bevel gauge but I ended up with angles of 39 degrees and 28 degrees.

I made a gear blank on the lathe with an angle of 39 degrees and setup the milling machine to cut 20 gaps between the teeth at an angle of 28 degrees using a home made dividing head (another product of procrastination) which used a lathe changewheel to index 20 positions.

At this point I had to confront the main problem that had been putting me off this job. What shape should I make the gaps between the teeth. Best approximation methods for home cutting of bevel gears suggest three cuts for each gap would be needed so I decided to make a cutter the shape of the smallest part of the gap using the other pinion as a model. At this point I realised that the gaps between the teeth are parallel sided and the wider gaps are created by deeper cuts at the larger end of the pinion so only one cut should be needed.

I made a cutter out of silver steel and mounted it to an arbour and cut the teeth so that the gaps between teeth were about the same size as the teeth.

The only remaining difficulty was the diameter which was difficult to measure. It turned out to be too small - but since it's tapered I could make it seem larger by removing material from the small end and much to my delight it actually meshed quite well with the existing gear although it was now too thin.

I made a second one using the same technique but using measurements from the first attempt. This time the teeth seemed to mesh a bit too deeply so I skimmed the top of the teeth in the lathe. It fitted reasonably well and the drill worked.

I have assumed the missing gear was originally made from cast iron as if it were steel it wouldn't have broken so I bought a piece of cast iron and made another gear blank.

I hardened and tempered the home made cutter and tried again on the milling machine.

Then I cut the slots on the back to engage with the dogs on the drill. Can you spot the mistake here?

Then I assembled the drill.

It works. I drilled a few holes using both speeds. Success. I'm really pleased with that.

Russell

 

[AndyT]

Wow, that really is an impressively long journey to put an old tool back in action.

I can see that the slots on the back don't quite match, but if it works, I wouldn't count it as a mistake myself.

Well done!

 

[Andy Kev.]

That looks like excellent work.

One general question: I would imagine that the drill was almost certainly made with all the measurements being imperial. You seem to be having no problems with measuring everything down to tenths of millimetres but I was wondering if it would be more accurate if you measured it imperially e.g. something might be a bang on 1/64" but only an approximate 0.X mm.

Or doesn't it matter at all, as appears to be the case?

 

[MikeG.]

Superb! What an effort. I don't think I've ever seen such an amount of work in restoring an old hand tool. Minor aside: it'd be perhaps be nice to just see the teeth on that pinion rounded over as per the other one.

 

[RussellT]

Thanks Andy, Andy and Kev.

As regards measurements, you're right Andy Kev, it will all be imperial but the only dimension that has actually been crucial is the hole through the new gear, the shaft is 5/16 so that's the size I made the hole. For the outside of the gear it didn't matter much as I was trying to make it fit rather than work to a drawing and my lathe has millimetre feed screws.

MikeG, I thought about rounding the tops of the teeth but the method used to cut these teeth didn't appear to do that originally. Because the small end of the teeth has less depth of cut it would have needed a separate operation to round the tops of the teeth. The teeth on the handwheel clearly have flat tops so it's possible that the ones on the other pinion are rounded through wear in use. I'm not sure about it and in operation it is quite smooth. At the moment I'm inclined to leave it as it is.

AndyT, yes you spotted where I made the mistake. The mistake wasn't that the slots don't match, the mistake was that one was off centre and wouldn't engage, the wide slot was the correction to fix the mistake.

Thanks for the interest and all the help.

Russell

 

[Rhyolith]

Very impressive! You might have said, but is that a dividing head of some sort your using there?

It makes me want to learn to do this too, the number of drills I could have restored if I had spare gears!

It would definitely be worth taking those sharp edges off gently those teeth with a small fine file, sharp edges always a no no with these things.