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Free hobbing - a rogue method for spur gears

Robint

New member
I am posting this thread topic to see if there is any interest in this obscure practice.
The very mention of the subject seems to rattle cages and bring out some very thin skinned machinists like I was talking heresy

To summarise
Its a method of cutting gears without the complexity and cost of a manual dividing head and formed milling cutter or even worse a head geared to a mill spindle and using a hob cutter

Let me say up front that I have the greatest respect for the science of gear technology and its practitioners. Its a very complex subject and has some highly skilled manufacturers who hold much of the expertise that is well beyond the home hobbyist

What I propose for discussion and experimentation will in many ways tear up the rule book and start from scratch

This method has been used to make wrom gears and this is a well documented procedure with ample vids on YT. I dont propose to elaborate on the area save to say that making spur gears is no more than an extension of the method (which has got some bad press in the past mainly IMHO due to faulty implementation of the technique)

I have been experimenting in this area and have produced some encouraging results - even successes. I will offer to post pix and vids of my work and invite others to try the technique and report

Up front
This is a Cheap Charlie method that can knock out gears in minutes
These gears - at this stage wont be to accepted DP/Mod standards (yet) but they will make quasi involute forms and can be assembled into a meshing train that seems to work
At present the method only produces Mod 1(ish) 30PA pieces and is only suitable for light duty low power xmission on non ferrous mtls
These might suit a model maker or experimentalist. The wheels are likely only to work amongst themselves but that may not be an issues - for example making a set of change gears for an old lathe

I think the method can be extended to perform reliably to meet des criteria eg No of teeth, and predictable Pcd but it needs skill and experience

I welcome the participation of open minded machinists but I wont be producing reams of explanatory words as the convolutions of the subject will be one big turn off, put a picture is worth...............
and even better get your hands on when much will become clear

for me very much work in hand and I believe there are others on this board who have been down this path


Hope this doesnt start a forest fire

Robin (no affiliation to Batman)
 

jariou

Member
Hey Robin,

I am quite familiar with the method to create worm wheels with, say, just a tap and perhaps a series of gnashes on the blank to get started.

I can see how to extend this to spur gears theoretically. I am curious to see your approach and the results you have been getting so far.

Jacques

Sent from my SM-G998U1 using Tapatalk
 

Robint

New member
some pix

Some of my earlier work, often paused waiting for parts
20210927_123226.jpg
An experiment with a single tooth cutter made from a 22mm spring washer

I had ideas of making a variable pitch tool, but it would involve some tricky design and I needed to produce more tangible results to a skeptical host of viewers who said

You cant do that its Against State Law

so that is shelved just now - the tool only cost a few dollars and a few hours
20210927_123836.jpg

Note that the gear is slightly helical cos I didnt tilt the work piece ca 2 deg in the vice
tool 9-10-21.jpg

a tool made from M24 bolt. the slots are too wide and I am making a better on from bottom picm24gear.jpg

OD 45mm
Calc teeth 47 as predicted
Pcd 43.7
CP 2.91
Mod 0.93
DP 27.39

tool 9-10-21.jpg

I knocked out an aluminium gear to squash the naysayers

More improvements due

Robin Reliant:nono:

ps note than in all cases the blank freely rotates on the mandrel, driven by the hob
 

52 Ford

Active member
I wouldn't call it a rogue method, exactly … more like when you forget to clamp the parts down on the worktable.
I think a rogue method would be holding the parts down with your hands while you make a cut.

Sent from my SAMSUNG-SM-G891A using Tapatalk
 

DDoug

Active member
I am posting this thread topic to see if there is any interest in this obscure practice.
The very mention of the subject seems to rattle cages and bring out some very thin skinned machinists like I was talking heresy

To summarise
Its a method of cutting gears without the complexity and cost of a manual dividing head and formed milling cutter or even worse a head geared to a mill spindle and using a hob cutter

Let me say up front that I have the greatest respect for the science of gear technology and its practitioners. Its a very complex subject and has some highly skilled manufacturers who hold much of the expertise that is well beyond the home hobbyist

What I propose for discussion and experimentation will in many ways tear up the rule book and start from scratch

This method has been used to make wrom gears and this is a well documented procedure with ample vids on YT. I dont propose to elaborate on the area save to say that making spur gears is no more than an extension of the method (which has got some bad press in the past mainly IMHO due to faulty implementation of the technique)

I have been experimenting in this area and have produced some encouraging results - even successes. I will offer to post pix and vids of my work and invite others to try the technique and report

Up front
This is a Cheap Charlie method that can knock out gears in minutes
These gears - at this stage wont be to accepted DP/Mod standards (yet) but they will make quasi involute forms and can be assembled into a meshing train that seems to work
At present the method only produces Mod 1(ish) 30PA pieces and is only suitable for light duty low power xmission on non ferrous mtls
These might suit a model maker or experimentalist. The wheels are likely only to work amongst themselves but that may not be an issues - for example making a set of change gears for an old lathe

I think the method can be extended to perform reliably to meet des criteria eg No of teeth, and predictable Pcd but it needs skill and experience

I welcome the participation of open minded machinists but I wont be producing reams of explanatory words as the convolutions of the subject will be one big turn off, put a picture is worth...............
and even better get your hands on when much will become clear

for me very much work in hand and I believe there are others on this board who have been down this path


Hope this doesnt start a forest fire

Robin (no affiliation to Batman)

First post and your lecturing ?
 

Robint

New member
Q
First post and your lecturing ?
UQ

Thats unfair and a snide comment - surely not worthy of your gravitas

and I hope this is not going to be the flavour of how this board conducts itself

My opening statement follows College convention in that the researcher sets out his pitch/aims/limitations and its supporting background

I'll leave others to form their own opinions

Please play nicely

Robin
 

pavt

New member
There you go again, doug. Perhaps he grew up and was educated somewhere besides here. He is kind of a cocky bugger though. After watching the start at HSM I predict it will go south here before too long.

By all means, check out the most recent posts/current discussion over there. I think the discussion here will be more interesting though. Especially if Zahnrad Kopf decides to participate.
 

implmex

Active member
Hi Robint:
The reason why you get pushback from all the professional machinists is because this is the most cumbersome way to get the crappiest gear shapes possible.
If I have a gear to make I have lots of better options that will cost me less and produce a far better gear.

I could:
1) Buy a gear cutter and index a blank on the dividing head.
2) Build a rack cutter and fake the Sunderland process with a rotary table.
3) Wire EDM cut the gear
4) Contract a gear maker and order what I need.
5) Go to the Boston Gear catalogue and get the closest match.
6 Build a little gear hobbing contraption for the lathe or mill.
7) 3D print the gear in plastic or metal.
8) Hand file the gear from a layout against a single tooth hardened template.
9) Investment cast the gear from a pattern.
And on and on.

Although some of these methods will produce a pretty crappy gear too, none of them will be as awful as a free hobbed gear.
If you wish to discuss just what makes them so awful, there is a long list, but you really need some basic gear knowledge for the conversation to mean anything to you.

So this is a method attractive only to a beginner hobbyist who does not need to work to a high standard to make his project go, and can spend as much time as he wants fucking around to get not very much as a result.

Yeah it sounds harsh, but that's the reality, so that's why the contemptuous pushback on this forum.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 

TGTool

Active member
OBTW I am not selling or pushing anything here - not a drop of snake oil in sight - just physically probing whats possible rather than armchair speculation

I invite the adventurous manual machinists to join in this pursuit and share results

Robin the brave

Not entirely true. He's pushing the idea that he's the one to make a huge splash in gear production, one that no one else has done. The reward is lots of attaboys on the forums.

I'd make just a couple points. First, that someone with their own shop and time can do anything they want. He's doing what he wants and that's great, but it doesn't require a salute from the industry.

And second, from an industrial perspective, if it had enormous merit it would have already taken over. Why buy expensive machines and spend time chasing precision if you don't have to? Ideas and processes that provide an advantage take over. It's been than way from time immemorial. Spears take over from rocks, bows and arrows take over from spears, firearms take over from bows and arrows. Over time people recognize advantageous ideas and adopt them. And where has free hobbing been all this time?
 

GregSY

New member
I think the point is...you show up with a hard-on from the moment you walk in the door. Are you looking for intercourse, or a fight?

It looks to my eyes that you gears are Third World quality. Yes, they are gears but they look like gears that will work poorly and wear out fast.

As for the 'stick shift' crowd...there seems to be an uprising taking place. A swelling of pride, if you will, amongst people who proclaim they can drive a stick! No automatics for them! They all share one common attribute that I can't help notice when I ride in a car with them....they suck at driving a stick. Yes, they are moving the car down the road so they are driving it....but their clutching sucks, they shift too soon or too late, and they suck at driving the rest of the car, too. I know about 3 people who can actually drive a car, stick or auto.
 

pavt

New member
I know about 3 people who can actually drive a car, stick or auto.

:D and then there are those of us who grew up driving both semis and farm tractors, as well as cars and bikes. I still do the semis, being that I work in a semi repair shop. So, gears are kinda "interesting".
 

DDoug

Active member
:D and then there are those of us who grew up driving both semis and farm tractors, as well as cars and bikes. I still do the semis, being that I work in a semi repair shop. So, gears are kinda "interesting".

Double clutch, and some times, no clutch......
 

pavt

New member
Double clutch, and some times, no clutch......

Most of the OTR drivers I know don't bother with the clutch. The 13 and 18 wheelers (Eaton gearboxes) arent' synchronized and it allows them to do it. My pickup uses the Aisin-Warner 5-speed, synchro, so there is no possibility to "float" the gears, you must use the clutch.
 

DDoug

Active member
Most of the OTR drivers I know don't bother with the clutch. The 13 and 18 wheelers (Eaton gearboxes) arent' synchronized and it allows them to do it. My pickup uses the Aisin-Warner 5-speed, synchro, so there is no possibility to "float" the gears, you must use the clutch.

I had no problem-o with my Dodge 2500, you've got to match the speeds.
 








 
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