Wadkin AGS fine fence adjust dimensions help

[KT_NorCal]

Don't be too impressed, that was after a soak in a dilute solution of citric acid for 5 or so hours and then a light going over with a very soft wire brush. Looked like this before.... The saw sat in a warehouse unused since the mid 1980s and had a uniform coat of what we call "barn rust" over here in the States... Citric acid works really well cleaning that type of rust off alloy steels. Essentially just wipes off after a few hours in a very dilute solution.

 

[J-G]

...I know there was a lot of a very detailed discussion about proper ratios for gears at whatnot, but to my eye these look straight cut.

Yes they will be 'straight' sided, you are dealing with the 'Rack'. Only the 'Gear' will have involute curve sides.

Getting a photo looking directly across the rack would be most useful - probably with a sheet of white paper as the background - and if the background were 'lit' and the foreground not that might work. Oh yes, using the Zoom facility would also help.

You've done a great job up to now KT - thanks.

 

[KT_NorCal]

Here are the best I can come up with. Hope it helps. Was just in the middle of cleaning up the fence rails and re-mounting them to the saw so opportune timing..
KT

 

[KT_NorCal]

Part deux

 

[KT_NorCal]

Part Trois.

 

[deema]

Thanks KT, really appreciate it.
The citric acid certainly cleaned it up beautifully.

I think that the slots are actually involuted form, I might be wrong but both looking at them thanks to your brilliant photos, and also from my reading I’m sure they are rather than just straight slots.

A rack is evidently a cog of infinite diameter, and as such has the same tooth form as the cog it mates with to work properly......if I’ve understood it correctly!

 

[KT_NorCal]

The close ups show the rack does have a rounding of the edges at the very top. It's also clear that each slot in the rack was cut in a two part process. I think if you just follow the profile of the knob as shown in the pictures it would be fine. The "sprocket" part engages the rack with basically zero lash, so even if you were off by a bit I don't think it would matter much. It also looks like there was a hard nickel plating added to the knob from the beginning.

 

[J-G]

I think that the slots are actually involuted form, I might be wrong but both looking at them thanks to your brilliant photos, and also from my reading I’m sure they are rather than just straight slots.

A rack is evidently a cog of infinite diameter, and as such has the same tooth form as the cog it mates with to work properly......if I’ve understood it correctly!

Regrettably the later is not the case -- (understood it correctly) -- to 'work properly' as you put it, the rack MUST have straight sides. It's how an involute curve is formed.

You have made one very significant statement of truth though -- 'a cog of infinite diameter' -- by definition that of course IS a straight line.

I've now done some further drawings based upon measurements taken from Photo 21 where I can see a very clear delineation of the rack top flat, along with the width of the space at top and bottom of the teeth.

This drawing :

shows the rack shape assuming either of the PAs and either of the Dedendum ratios likely to be used by Wadkin.

As I'm typing this I see that KT has made further comment which is pertinent. Yes it has been produced using a two pass (at least) process.

The dimensions shown with a Purple line are derived from the photograph and all others are as a result of knowing the PA, DP etc. the right hand drawing assumes that the Dedendum is calculated using 1.4 / DP and that makes the Addendum 0.032147 whereas the theoretical value is 0.03125 --- within <3% error - from many assumptions and measuring a photo, I have a reasonable confidence in making the assumption that the gear is a 14½º PA.

 

[deema]

JG you are amazing! I really really appreciate you taking the time to do the analysis. Thank you soooo much.

Would it be possible to repost the diagram spilt into two photos to hopefully allow it to be bigger so that the text is readable?

Clearly I need to study more! Just as you think you might be getting a glimmer of understanding you find out how little you know!

If you could, I’d appreciate knowing why a rack has straight sides and a cog has an involute tooth form. I’ve tried to find an explanation in the small number of books I’ve been leant (thank you Sideways) and by google.......but I keep getting stuck on a rack being a cog of infinite diameter so, at what diameter does the tooth form change?

 

[Myfordman]

Just click on the drawing and it will open up fully readable size.

 

[deema]

Thanks I can now see the diagram, got it.
I’ve also worked out why a rack has straight sides. A good walk with the dogs and The light bulb came on!........it also explains why there are different gear cutters for different numbers of teeth.......

 

[J-G]

Thanks I can now see the diagram, got it.
I’ve also worked out why a rack has straight sides. A good walk with the dogs and The light bulb came on!........it also explains why there are different gear cutters for different numbers of teeth.......

Hooray!!

Sometimes it does take a 'Lightbulb' moment but I could also have been more explicit earlier. I'm always a little cautious when discussing technical details on any forum where the participants are very knowledgable and it takes some time for me to find the correct level

I think the key is to explain how an involute curve is generated.

An Involute is a mathematical curve where the radius is constantly increasing based on a 'Base Circle' . To quickly draw one you could take a pencil and attach a length of string to and wrap that around a jar or other round container. Place that on a sheet of paper on a flat surface. With the 'jar' held firm, keep the string taught and gradually unwind the string from the jar marking the paper as you go.

The line that you draw is an involute curve with a base circle equal to the diameter of the jar. More accurately, I generate it in a CorelDRAW! drawing marking off 1º increments and calculating the tangential radius for each. Plotting the points and then drawing a line between each.

Here are some drawings I've created :

The diameter of the Base Circle depends upon the PA and that affects where the Pitch Circle sits relative to it. In the case of a 14T - 32DP - 14½ºPA gear the Base Circle is 0.424", Pitch Circle Dia. = 0.438", OD = 0.5. The Root Diameter will depend upon decisions taken by the manufacturer regarding the amount of relief they want (1.4 or 1.25 / DP) -- or even some other 'in house' decision.

The whole point about using an involute curve is to maximise the power transmission and minimise back-lash. Where neither of these parameters are paramount, then other forms are used - such as Cycloidal as in clock mechanisms.

Hobs, rather than the set of cutters ( 1 - 8 ), used to cut involute gears are straight sided so that they 'generate' the involute curve. You only need one Hob to cut a gear with any number of teeth (within reason) for any DP or MOD. I have MOD 0.3, 0.4, 0.5, 0.7 at 20ºPA and 20 & 40 DP - 14½º PA. That's just 6 tools. If I were to use 'gear cutters' I would need at least 48 tools to cover the same range.

Hobs are also made with involute sides to make 'splined' shafts - which of course then have straight sides!

 

[deema]

Again, thank you so much JG for taking the time to explain how the gear form works. Your explanation is very clear (to me) and I do really appreciate the time it takes to sketch it out and detail how it all works.

I’m now waiting for a gear cutter! The one I’d found is now out of stock! There seems to have been a run on this particular gear cutter as everyone is OOS #-o

 

[J-G]

Again, thank you so much PT (JG) for taking the time to explain how the gear form works. Your explanation is very clear (to me) and I do really appreciate the time it takes to sketch it out and detail how it all works.

I should have mentioned Ivan R. Law's book - Gears and Gear Cutting (Workshop Practice) - before now as a very good initial read. I have a copy somewhere but couldn't (can't!!) find it when I pointed you to W.O.Davis' tome.

At £6.95 on Amazon it has to be a no brain decision

 

[deema]

Thanks JG, I will look to buy it. Appreciate the pointer.
I’ve now corrected my Billy Do in all posts. Sooo sorry to have got that wrong. I should have noticed autocorrect changing the initials.......

 

[J-G]

Again, thank you so much JG for taking the time to explain how the gear form works. Your explanation is very clear (to me) and I do really appreciate the time it takes to sketch it out and detail how it all works.

I’m now waiting for a gear cutter! The one I’d found is now out of stock! There seems to have been a run on this particular gear cutter as everyone is OOS #-o

I've been keeping an eye on the RDG Tools Listing for 32DP Nº7 cutters and see tonight that they now have 10 in stock.

 

[deema]

Thanks, I’ve put my order in.......shouldn’t be long before I’m having a go at making the micro adjust (hammer)

 

[deema]

Thanks for the help and advise I received which enabled me to make a new fine adjuster. I’m happy to say it works perfectly.

I’ve no idea why the image doesn’t show the right way around, tried to fix it but don’t seem able to do

 

[J-G]

That looks like a good job Deema.

I initially wondered why the work was so far out of the chuck. I can't see, but have to assume that the 'Free' end was supported by a tailstock centre.

 

[deema]

Good question, the work needed to be so far out to allow the cutter to make a full pass and not hit the chuck.
Your right, the other end was supported by a tail stock.