Calculating wheel sizes from centres?

[Peter BellParticipant @peterbell11509]

Just spent most of the morning working on the CB Reeves gravity clock. I am using ballraces in housings which fit into recesses in the plates to support the arbours.

Marked out the housing centres out using my depthing tool with the appropriate wheel and pinion and pocketed the frames accordingly.However when I tried it all together the arbours are too close together and I get a tight meshing, just about 12th but enough to ba a pain

So what I am doing to depth the wheels it is not working!

Rather than move the bearing housings think it may be easier to make new wheels working the wheel blank diameter out using the centres between the arbour's and then size the wheel accordingly–I can cut the wheels on the cnc mill.

Does anyone else work backwards like this?

The wheels are 0.6m, pinion 12t and I am using Thorntons cutters.

Peter

[Peter BellParticipant @peterbell11509]

[John HaineParticipant @johnhaine32865]

If you’re thinking of re_cutting anyway, why not run them in with a fine abrasive? Might just work and save some time.

[Russell EberhardtParticipant @russelleberhardt48058]

Or set them up for cutting again and run the cutter in by a thou ro two?

Another posibility would be to fit bushes and recut the recesses.

Russell.

[David Clark 13Participant @davidclark13]

Hi There

Could you recut one wheel only?

regards David

[Peter BellParticipant @peterbell11509]

Thanks for the advice.

I thought about using an abrasive but could be a bit messy and suspect it would pobably alter the tooth form. Dont want to rebush the holes and try again as I may have the same problem and it seems a shame to ignore the pockets I have now.

Think I will recalculate the wheel blank dia (or will get my son to do it!) from the arbour centres and turn the existing wheel down. We should be able to get it back on the mill and use the existing teeth to set it up and then re cut it to suit. We stll have the g code saved so my expert should be able to "tweak" it in a bit.

Thanks Peter

[Les Jones 1Participant @lesjones1]

Hi Peter,

I assume that now you have reached this stage you solved the problem of the thin tooth on the gear wheel. What was the solution to that problem ?

Les.

[Peter BellParticipant @peterbell11509]

Hi Les,

No never solved it really and suspected something moved but gave up and have now got the 4th axis working on the Seig KX3 mill so cut some more wheels on there—seems to have overcome the problem—yes I know its cheating but I want to crack on!

Peter

[Les Jones 1Participant @lesjones1]

Hi Peter,

I don't consider it cheating. It's just making the best use of the equipmet you have available.

Les.

[speelwerkParticipant @speelwerk]

Clock and watch makers in the 19th century used an "arondeer machine" (rounding up tool) to make the wheels fit. With it you can remove material from the teeth using the teeth itself as a guide. You can still find them on eBay and in auctions but you must have a good selection of the special cutters needed since these are no longer available, it is a very simple but useful machine.

[Harold Hall 1Participant @haroldhall1]

I am not conversant with the Reeves clock Peter but assume the wheels are of a comparable size to those in most others clocks made in the home workshop, In this case, it is unlikely that you will want to reduce the diameter of the pinion which will have very little effect on the eventual centres of the pinion and wheel.

Why then are you considering making a new wheel, I would suggest the following.

Set the existing wheel up as you originally did and align the cutter with the gap between two teeth. With that done, set the cutter a little deeper, say 0.05mm and re-cut all the spaces. You will end up with the same size spaces but very slightly narrower teeth. This will be exactly the same as you will get if you make a new wheel.

You may need to set the wheel up on the lathe to reduce the diameter by 0.1mm if re-cutting the teeth as above does not achieve this, perhaps though, it would be worth doing first.

Unless I am missing something, I think it is worth a try, nothing to be lost.

Incidentally, I am in the process of making a clock and it has two wheels, both with 96 teeth, but one on a smaller diameter than the other. This is to give clearance to the next arbour, indicating that the theoretical diameter, number of teeth and cutter mod size combination, is not rigidly adhered to in clock making.

Harold

[Peter BellParticipant @peterbell11509]

Hello Harold,

Thanks for your comments, that is what I intend doing, its got to worth a try setting up to recut slightly deeper with as you say nothing to lose., at least its too big!

This is the first clock I have made using ball races and its giving me lots of new experiences which is good but its making it difficult to fiddle things like pivot holes which is why I asked if anyone works backwards and decides the final wheel dia after the arbours have been planted

Since my last post I have discovered my simple depthing tool made years ago as described by John Wilding is no longer flat which has led to the error so I have at least found something.

I have now remember that I have repaired clocks with what apeared to be identical wheels on tooth count until they were measured so it looks like sizing of wheels is more common than what I realised

Peter

[BazyleParticipant @bazyle]

Have you tested with blue to see which bit is binding ie top, root , or width?

You could skim a little off the top with impunity and the bottom of a cycloidal wheel tooth is often square so can be cleared witha  narrow file quicker than setting up a cutting rig.

Edited By Bazyle on 22/03/2012 12:00:49

[Russell EberhardtParticipant @russelleberhardt48058]

Since my last post I have discovered my simple depthing tool made years ago as described by John Wilding is no longer flat which has led to the error so I have at least found something.Peter

Yes, I found the same problem. The slightest bow in the base makes a significant error.

You shouldn't need to turn the wheels down as there is plenty of cearance at the root of the pinions. Just go a bit deeper with the cutter.

Russell.

[Author]

Posts