Another Westbury Seal 15cc

[petertha]

I tried this on my 16 tooth gears with 1.57mm rods but the calculator wouldn't accept M0.8.

The calculation seems broken for me too. If I enter module 1.5 it calculates correctly. But any smaller module it complains Module must be between 1.5  which corresponds to the greyed (suggested?) module range.   Well that blows. What can I say, it worked for a different tooth count M0.8 gear for me a few months ago. Maybe they are now limiting calculations to gears they sell?

[petertha]

I just did a quick AI search & let it grind out the calculated answer attached using your pin diameter. But I am going to step through the calculation & write an Excel sheet because it will be useful tool for me too. Looks like it involves an iteration/convergence but I've dealt with that before.

[petertha]

I think I have a functioning spreadsheet but I want to do some more checking. One thing arose in the algorithm steps: the min/max/optimal pin diameter is basically a function of Module. AI is suggesting these sizing factors. Your selected pin diameter is on the high side. MOW also varies by even or odd teeth count, but that is factored into using slightly different equations towards the end.

[doubletop]

Yesterday I made two blanks for the 32 tooth camshaft gear. Two blanks, one for the engine and one for Murphy. I attached them to an arbor with Loctite 680, which has a 24hr cure time so not a lot could be done until today



Both were successful

I then need to extract one steel pinion and one bronze idler from the two bars of 16 tooth gears I made the other day

A bit of fettleing and a zap in the sand blaster to tidy up any sharp edges I now have a set of gears 



I am quite happy with the result as making gears was all new to me a few pages back in this post. But now, mostly,  I've got my head around it.

I have this 'thing' about gears that goes back to my Meccano days when I got the gear set. They transformed my Meccano for me. When I was 16 I started to do A level Tech Drawing and I remember doing gear design and a level of understanding that entailed a lot of principles. I was trying to remind myself of the level of knowledge I had back then. Fast forward 60 years and you don't really need to know it. What I have picked up in the last few days is more than sufficient for my needs. And if I don't know something I do know where to ask.

(actually I have a similar issue with transistors, I also learnt how they worked nearly 60 years ago. These days you rarely have to go to that level of detail, they just do their thing)

Pete

[doubletop]

I think I have a functioning spreadsheet but I want to do some more checking. One thing arose in the algorithm steps: the min/max/optimal pin diameter is basically a function of Module. AI is suggesting these sizing factors. Your selected pin diameter is on the high side. MOW also varies by even or odd teeth count, but that is factored into using slightly different equations towards the end.

Peter

Really?

The crank pinion with 1.57mm measuring pins

Pete

[Charles Lamont]

You may want to bear in mind that the idler does not have to have 20 teeth. If you use 19 or 21, say, you get a 'hunting' tooth - each tooth of the idler meshes with all those on the other gears instead of the same one all the time, which should even out the running-in and wear.

[petertha]

Peter Really? The crank pinion with 1.57mm measuring pins

I think you are OK. I'm just regurgitating what AI is suggesting for actual cutting. The recommended pin diameter seems to +/- go around with other MOW tools I've come across, because they are determining it occurring on pitch diameter circle. But laying it out in CAD is not quite the same because you are generating a fresh involute based on actual PD & not necessarily applying tooth corrections. Now certain CAD programs, i think Fusion 360, do generate functional tooth forms, but I cant speak with authority here.

But we ultimately have to make them in the shop. These numbered cutters (form cutters), are optimized to make a good compromise gear tooth within their specified tooth count range. By compromise my understanding is they are 'closer to' a true involute at the lower tooth count of their specified range, thereafter they deviate progressively more. This makes sense because DOC is a function of module yet the pitch circle is growing with higher tooth counts. Something has to give. Also, they supposedly factor some amount of tip clearance into the form, so (AI is suggesting) a large pin diameter could be entering this tooth area vs the primary involute area & get measurement tricked. These pin diameter suggestions are primarily a function of module but secondarily a function of the typical 20-deg pressure angle of module gears. So not to be applied to 14.5 deg tooth forms & vise-versa. Too small a pin diameter can get tricked by the root fillet form baked into the cutter & also influenced by the the involute being less curved compared to closer to PD.
Model engineers seem to have many, many successful models using these cutters so they must be OK.

Well, I'm still testing but I might have a functioning tool

[doubletop]

You may want to bear in mind that the idler does not have to have 20 teeth. If you use 19 or 21, say, you get a 'hunting' tooth - each tooth of the idler meshes with all those on the other gears instead of the same one all the time, which should even out the running-in and wear.

Charles

Yes I did look at that. I am doing 16/32 teeth in mod 0.8 which comes out just about the same size as 20/40 in dp40. I was going to do the idler in 17 teeth but that was to big and fouled the casing. Then 14 teeth puts the centre too close to the main bearing. So I did the idler as 16 teeth

Pete

[doubletop]

"Model engineers seem to have many, many successful models using these cutters so they must be OK."

Well, I'm still testing but I might have a functioning tool

Exactly; we use what we have available and make it work for us. We are not production shops so are not necessarily looking for repeatability, just functionality.

Pete

[Vixen]

You may want to bear in mind that the idler does not have to have 20 teeth. If you use 19 or 21, say, you get a 'hunting' tooth - each tooth of the idler meshes with all those on the other gears instead of the same one all the time, which should even out the running-in and wear.

Charles

Yes I did look at that. I am doing 16/32 teeth in mod 0.8 which comes out just about the same size as 20/40 in dp40. I was going to do the idler in 17 teeth but that was to big and fouled the casing. Then 14 teeth puts the centre too close to the main bearing. So I did the idler as 16 teeth

Pete

Pete,
I did 20/40 in dp40 with a 20t idler.
Here is a photo of the 20t idler held in the correct position with Milliput epoxy putty to drill for the bearing shaft. I did not trust the 'calculated' position. Worked well and the mesh was spot on without backlash. Jason has a slightly different way of doing the same thing. I believe it was much safer to do it our way and get it right first time, than the risk of the theoretical centres being out by a few thou.



Cheers   

Mike

[Laurentic]

Interested in your technique re the Milliput epoxy putty Mike. 

Was it a case of, hold the gear in place, whack the putty on, mark the position for the shaft and then whip the putty off before it had set, for if once set surely removing that putty would have been a nightmare?  Love the lateral - sideways - thinking, using the putty for that purpose but.

Chris

[Vixen]

Hello Chris.

Don't clean all the oil and grease off the parts, especially the gears. The epoxy putty, when cured, does not grip that well to oily metal, but well enough to align the cutter with the gear centre. Afterwards the epoxy putty breaks off fairly easily. Acetone (or cellulose thinners) removes any stubborn bits.

Mike

[doubletop]

Pete,
I did 20/40 in dp40 with a 20t idler.
Here is a photo of the 20t idler held in the correct position with Milliput epoxy putty to drill for the bearing shaft. I did not trust the 'calculated' position. Worked well and the mesh was spot on without backlash. Jason has a slightly different way of doing the same thing. I believe it was much safer to do it our way and get it right first time, than the risk of the theoretical centres being out by a few thou.



Cheers   

Mike

Mike

I will keep this in mind.

As well as CNC I have separate DROs on my mill. My plan would be to set the engine up vertically with the crankshaft and camshaft in place with their gears. Take a reference from the crankshaft center and then put an arbor in the chuck with the idler on the end and offer it up to the crankshaft and camshaft gears. Then have a little sweep-stake with myself how far out the actual idler location is compared to my drawing.

That's the plan, reality may be a tad different.

Pete

[Jasonb]

having the gear "live" also allows for any eccentricity that may have crept in when cutting the gears as you can set them up so there are no tight spots when rotated.

Here is a good example of theory vs actual on one I'm building at the moment. These gears were cut by a commercial gear cutting firm and Georotic tells me the ctrs should be 22.2592mm but they ran fine at 22.14mm which is where I bored the bracket for the vertical cam shaft gear. They are MOD1 but equal PCD 10:20T

[doubletop]

having the gear "live" also allows for any eccentricity that may have crept in when cutting the gears as you can set them up so there are no tight spots when rotated.

Here is a good example of theory vs actual on one I'm building at the moment. These gears were cut by a commercial gear cutting firm and Georotic tells me the ctrs should be 22.2592mm but they ran fine at 22.14mm which is where I bored the bracket for the vertical cam shaft gear. They are MOD1 but equal PCD 10:20T