Thread: Unbranded chain drill

Geoff, I've never used one of these gadgets, so I had to stare at the pics for quite a while to figure out how I think it works. As far as I can see, there appears to be two things that could stop the shaft from advancing when set to auto-feed: either the thread inside the larger cog is stripped or the "idler" cog is turning, which would prevent the large cog driving the shaft. I think it should be obvious which is happening, & you have probably long since checked them out, so I guess I don't have anything useful to offer.....

Cheers

Thanks Ian, on rereading my post it looks like, primarily, I'm asking how to make the tool work properly. I am, but, equally importantly, looking for clues as to the designer or manufacturer of the chuck and/or the chain drill.
Usually, if you can get hold of the original patent description, it gives you all you need to know as to the tool's operation and the drawings will show if something is missing from your example.
Attempting to use the tool, it can be advanced manually which indicates everything is working as it should, it's just not obvious to me how the auto feed operates.
There are a lot of chain drills out there and they are either friction drive as with the frequently found Millers Falls model. (Pic 003) Positive drive, in this case Goodell- Pratt (Pic 006) or manual advance, once again Goodell- Pratt, with this massive two legged model. (Pic 005)
The MF model has a friction clutch plate at the top, as the drill bit cuts into the material being drilled the resistance lowers causing the clutch to forcibly advance the bit. The amount of advance force can be raised by tightening the finger wheel nearest the drive tang.
In the case of the G-P positive drive example, each revolution of the drive causes the pin to turn the little star wheel one leg which advances the toothed wheel by one tooth. From memory there are about 18 teeth on this wheel, meaning the drive has to be cranked 18 times to advance the bit by one thread depth. The manual advance unit is pretty well self explanatory I think.
The chain drill in question doesn't seem to fit easily into any of these categories.
Cheers,
Geoff.

Originally Posted by Boringgeoff

... ..Attempting to use the tool, it can be advanced manually which indicates everything is working as it should, it's just not obvious to me how the auto feed operates.....

Yes, & it's even less obvious when all you've got in the hand is a picture...

Been thinking about it all morning, & trying to nut out how it should work. At first I had it bass-ackwards in my mind's eye, but this is my current 'working hypothesis': With the keyed cog pulled back & only the threaded cog engaging the idler, that's the 'manual feed' position. With the idler spinning freely, the threaded cog can just stay where it is. When the keyed cog is slid forward & both cogs engage the idler cog, the idler effectively locks the two large cogs together, and both are now locked on the main shaft. Now when you turn the main shaft, the threaded cog has to rotate on the main shaft, driving it forward or backwards by the pitch of the screw each turn. For it to work like that, the keyed cog needs to be held up against the threaded one to keep the two interlocked, but it still has to be free to slide as the main shaft is moved in & out by the screw. But I cannot see in the pics if there is anything to prevent the keyed cog from slipping back & disengaging from the idler, which would stop any self-feeding instantly. It might stay put drilling down, bu you would not be able to use it with the chuck facing up unless there is some retaining mechanism.

I've probably still got it bass-ackwards & you've already figured it out.....

Cheers,

Ian, The washer under the knurled nut at the back of the idler cog has a flat machined on one side to allow the keyed cog to slide back and forth under it. (in my first post Pic #003 shows the flat on the washer) In the engaged or disengaged position the washer is turned to flat upwards thus disallowing the cog to accidentally change position. When the keyed cog is disengaged the threaded cog is able to turn on the shaft and move the chuck forward or backward. With the keyed and threaded cogs engaged with each other the keyed cog doesn't allow the threaded cog to turn.
In the trial run in the photo with the two cogs disengaged, I tightened the chain manually and when tight started drilling. The drill is reasonably sharp, bearing and threads clean and oiled and there was no voluntary turn of the cog that I could see.
The idler is on a stepped shaft so the nut cannot over tighten the washer against it, I did temporarily put a small leather washer in there to try to create some friction but it didn't make any difference.
It's back to the shed for another fiddle, maybe bore a solid piece of bar and see what happens.
Cheers,
Geoff.

Ian, thanks for your interest, without which I would still be scratching my head. The short answer to how it works is, the keyed cog and the threaded cog have a different number of teeth. 26 and 27 respectively, which causes the threaded cog to move forward one tooth per revolution.
I clamped a piece of flat bar in the vise and started on it, with a texta mark aligning both cogs and the bearing end of the carrier. After a few turns it was obvious that the bit was being forced forward and when I checked my marks they were out of order.
I'll admit, I had to sit and think for a few minutes, then it finally dawned, count the toothy pegs. Now if you look at the attached photo it is quite obvious there is a disparity but I had put the thinner teeth down to being more worn.

Okay, now who made it?

Cheers,
Geoff.

That's neat, Geoff. It's not quite how I had envisaged it working but roughly, sorta, close - the unequal cogs is the clever bit I couldn't have imagined. I wonder if the bloke what thought it up just had a eureka moment, or did it take months of fiddling & trial & error?

Cheers,

Good question Ian, makes you wonder if any other tools or machinery use that system. Now that we know how it works the next time I encounter a tool with a similar set up I'll have to try to remember to count the teeth.

Cheers,
Geoff.

Just had this Fowler steam rope winder mechanism, from 1862, shown on another forum.
This would predate the chain drill by a few decades and may not be the first use of the idea. Perhaps something like this has been used in clock mechanisms for hundreds of years?
Cheers,
Geoff.

PS, just added a photo of the gear in use on this winch.

Similar problems tend to generate similar solutions. That's why patent attorneys are needed...

When I decided to try adding a screw adjuster to my shoulder & chariot planes, I wanted something more convenient than a simple wedge, and I came up with the idea of a thumbscrew bearing on a brass plug on the wedge: 2 Parts.jpg Ebony infill chariot plane.jpg

I thought it was pretty obvious & wondered why noone else had thought of it, 'til I discovered that of course Tom Norris did, a good 100 years before me.

Cheers,