A Challenge – How Would You Machine This Part?

[Anonymous]

There definitely appears to have been some confusion here. It was never my intention to make castings from patterns; indeed I hadn’t even thought of castings until it was mentioned by Jason.It’s an interesting thought though! Jason is also quite correct in stating that I am machining in aluminium simply to check the G-code and learn about stepover values versus surface finish. At some point even I stop thinking and do some experiments. Aluminium is cheap and readily available (here I apologise to Richard P) whereas I will have to order cast iron specially, and the real crown wheels are actually castings with other features attached.

 

It was never my intention to suggest that all this effort was needed to make gears for a traction engine differential. That is why the purpose of the gears wasn’t mentioned in the original post. In fact the post was originally intended to be a gentle nudge to the ‘no CNC’ protagonists. May be it is fortunate that it has morphed into something else.

 

My horizontal mill was a snap decision buy, on offer from a model engineering tool dealer (not normally noted for cheap prices) at a knock down price. I assume they’d got a job lot from a college, and, since it is a larger machine than might normally be found in a home workshop, they just wanted to move them on. It cost more to have it delivered than the mill itself cost. So far I haven’t even managed to get the motor to change note, let alone struggle. I’ve cut all the pinion gears for the traction engines on it, 6DP in EN8 and 5DP in cast iron, in one pass, with not even a cough from the motor.

 

Interesting pictures posted by Jason. The bevel pinions must have been CNC’d, difficult to see how else it could have been done given that the teeth are effectively pockets. It looks like the stepover used was radial rather axial. I chose axial, as then at least the machining marks are parallel to the line of contact. Wow, it must have taken ages to machine the holes for pinions by handraulic means. I wonder how the pockets for the pinions were done, doesn’t look machined, but too clean for flame cut, laser or water jet maybe?

 

Ah, now JohnS has opened another whole can of worms. I was only thinking earlier this evening, while weeding one of the fruit bush areas in the garden, about the steering worm and wheel for the traction engine. I have seen a worm, machined by CNC, at my supplier, and frankly it looked a little rough, I could do better! But I may well end up machining the worm (two start) by manual means. But what about the worm wheel. My supplier, in common with others I expect, simply uses a helical spur gear. Perfectly adequate for the job of course. But, being obtuse, I wondered if I could machine a proper worm wheel. I have the kit to do it, if I had the necessary hob. The question then becomes could I machine a suitable hob, with relief, on the CNC mill?

 

Watch this space.

 

Regards,

 

Andrew

[mgjParticipant @mgj]

Rarely have I had the privilege of reading so much twaddle about over-engineering a component for an unstressed rustic device.

 

And as for blinkers- thank you but I have done my share with cogs. Real ones for racing engines, and tank turret fire control systems.

 

And on that note may I bid you all a very fond farewell

[John Stevenson 1Participant @johnstevenson1]

Posted by mgj on 06/06/2011 22:52:57:

Rarely have I had the privilege of reading so much twaddle about over-engineering a component for an unstressed rustic device.

 

And as for blinkers- thank you but I have done my share with cogs. Real ones for racing engines, and tank turret fire control systems.

 

And on that note may I bid you all a very fond farewell

 

 

The prams and teddy post is still open…………

 

John S.

[JasonBModerator @jasonb]

Posted by Andrew Johnston on 06/06/2011 22:40:54:. Wow, it must have taken ages to machine the holes for pinions by handraulic means. I wonder how the pockets for the pinions were done, doesn’t look machined, but too clean for flame cut, laser or water jet maybe?

 

 

 

Thats a HAND ratchet drill NOT hydralic and the blank was flame cut. The faces where the pinions touch were later cleaned up with a slotter.

 

Well I won’t abandon this thread as John has said the methods suit any bevel gear so onday when I need something like that I will know whats required.

 

John has some pics on another forum of cutting helical gears on his CNC maybe he will post them if you ask nicely.

 

 

[Anonymous]

That’s why I said handraulic, not hydraulic, precisely because it is a hand ratchet.

 

Regards,

 

Andrew

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Jason, I presume the flame cutting was done on a programable profiling machine, if they were done by freehand, the bloke that did them would have a very steady hand.

 

The ratchet drill is something many people may not be aware of these days, I’ve seen a very old one but never used one. They were common at one time for site work, before magnetic drills became popular and affordable.

 

Regards Nick.

[John Stevenson 1Participant @johnstevenson1]

As Jason has said I do have some pictures of cutting helical gears, some are also on you tube.

 

This is an interesting one

 

Spiral bevel video

 

Unfortunately not a good video as regards showing what it can do. The program Cut3D cuts in raster passes and you get a choice of doing a clean-up pass at 90 degrees to the first and that is what this is doing.

 

This is the reason it doesn’t look to be cutting, it is, but only small clean-up cuts in places.

I should have videoed it on the first pass but never thought to get the camera.

Another problem is the step over, because this was the first time and I had no idea who it was going to turn out I increased the step over between cuts to save time at the expense of quality.

 

However as a concept operation I thought it came out well, the gear in question is about 2 1/2″ diameter and cut with a 2mm ball nosed mill, cutting time was around two hours, programming time was about 20 minutes from a CAD model from SPI gears site on the web.

 

At the moment there is no way to cut one of these in the homeworkshop. The Shay gears cut by the Japanese guy are not true spiral bevels but offset bevels, a different animal. As I say just a concept to prove what can be done.

 

This is another one.

 

Gearotic cutting a helical gear

 

Just using a standard 3mm 3 flute end mill / slot drill, no special cutters.

Watch at about 2:00 into the video after it has blocked the tooth shape out. It then proceeds to move over in the Y and rotate the gear to do a shaving pass, basically mimicking a Sunderland gear planer that shave the involute shape on in a series of very small steps.

 

John S.

Edited By John Stevenson on 07/06/2011 09:31:37

[Anthony KnightsParticipant @anthonyknights16741]

According to Mr Stepenson all you need to do is create an image in a suitable computer program, send this to your CNC machine, and it will churn it out for you. How interesting. I really love sitting in front of a computer screen. I suppose the next technological advance, will be to have a robot which assembles all the bits which your CNC machine makes. You can then spend even longer on the computer making assembly drawings.

The ultimate techological advance will of course be the Virtual Engineering Workshop.

Put on the suit and helmet, choose all the machinery you would love to own but can’t afford and away you go. Four years to make a model traction engine? With this program you can make one in the morning and drive it in the afternoon.

Before anyone else say it, I’ve probably watched “The Matrix” too many times.

[Steve WithnellParticipant @stevewithnell34426]

Funny thing, 3 of us trekked around Harrogate looking for (real) engineer’s files. We found 1 with at least 6 good teeth for a £1. So there ain’t much appetite for manual effort! Ended up going to J&L mail order. So probably too many articles in MEW that need a file too!

[Anonymous]

So, for my 400th post on this forum, I am proud to present another load of grossly over-engineered twaddle.

 

After a bit of a delay, partly due to work and partly due to toolpath issues, I’ve finally finished machining the prototype crown bevel gear. In one sense this is more complex than the pinion, in that the radius at the bottom of the tooth requires a 2mm cutter, but clearly it wouldn’t be sensible to use that for roughing out. In the end I roughed out with a 4mm cutter, did a quick clean-up pass with a 3mm cutter and finished with a 2mm cutter. On the other hand the crown wheel is simpler than the pinion, in that it does not require the use of the 4th axis.

 

The crown wheel blank:

 

After roughing out:

 

And the finished gears:

 

The gears mesh together extremely well; better than one might have thought looking at the finish. All I need to do now is make the real gears in cast iron.

 

Regards,

 

Andrew

 

PS: If you think this is over-engineered, you ain’t seen nuffink yet, wait till I get onto the steering gear.

[Steve WithnellParticipant @stevewithnell34426]

Hi Andrew, how did you get rid of the machining marks on the crown wheel, that it was a graphic at first!

 

Since this is all done for pleasure and recreation, not sure why over-engineering is a problem Unless it causes it to be too heavy or too expensive of course. I’d have gone broke years ago if I needed to make a living off the models I make

 

Steve

[blisterParticipant @blister]

Posted by Anthony Knights on 08/06/2011 18:46:11:

According to Mr Stepenson all you need to do is create an image in a suitable computer program, send this to your CNC machine, and it will churn it out for you. How interesting. I really love sitting in front of a computer screen. I suppose the next technological advance, will be to have a robot which assembles all the bits which your CNC machine makes. You can then spend even longer on the computer making assembly drawings.

The ultimate techological advance will of course be the Virtual Engineering Workshop.

Put on the suit and helmet, choose all the machinery you would love to own but can’t afford and away you go. Four years to make a model traction engine? With this program you can make one in the morning and drive it in the afternoon.

Before anyone else say it, I’ve probably watched “The Matrix” too many times.

 

 

Well said Anthony,

I don’t think those comments are from watching ‘The Matrix’ too many times but from seeing what a CNC can do. The way engineering is going at the moment, the greatest skill required in the future will be song selection on your Ipod and the safe insertion of earphones into your ears while you watch the relevant machines ‘pump’ out a model for you. I can only imagine the sense of fulfillment in a job well done when we go down that path. I guess I am a bit ‘Old School’ but can remember scoffing at the older machinists when I was an apprentice who would try to impress on me that the only way to machine with any skill was by using internal and external calipers. Funny thing is I use calipers at work for demonstration purposes to show people “How it used to be done”. I guess in the not too distant future someone will be demonstrating machining without using a CNC

 

Yours

( in anticipation of a tirade of vehement harangue from the CNCers)

Phil

[John Stevenson 1Participant @johnstevenson1]

Posted by Anthony Knights on 08/06/2011 18:46:11:

According to Mr Stepenson all you need to do is create an image in a suitable computer program, send this to your CNC machine, and it will churn it out for you. How interesting. I really love sitting in front of a computer screen. I suppose the next technological advance, will be to have a robot which assembles all the bits which your CNC machine makes. You can then spend even longer on the computer making assembly drawings.

The ultimate techological advance will of course be the Virtual Engineering Workshop.

Put on the suit and helmet, choose all the machinery you would love to own but can’t afford and away you go. Four years to make a model traction engine? With this program you can make one in the morning and drive it in the afternoon.

Before anyone else say it, I’ve probably watched “The Matrix” too many times.

 

 

No not really you have to take it all into context on what you are doing. Whilst I’m a big believer in that CNC has a place in the home workshop it’s not at the expense of all CNC

 

This week I have done 24 three HP electric motor conversions where the shaft has to be turned down and the keyway deepened plus making 24 steel conversion plates up out of 10mm thick laser blanks and guess what ? All done on manual machines you will find in the average larger workshop.

 

Now if I had just one of these to do.

 

 

Can you just imagine what tooling and jigs would be needed for a job like this ?

 

Six speed gearbox selector drums for racing motorcycles BTW, and less than 3 hours work.

 

John S.

 

 

Edited By John Stevenson on 18/06/2011 21:19:39

[blisterParticipant @blister]

Hi John,

are you saying that if you ‘did’ just have one to do like most of us ‘Model Engineers’ as opposed to ‘Production Engineers, you would not bother, or would it be a challenge to figure out the best possible way to get the job done, ‘one off ‘ as we quite often have to. The point being that excercising the mind to achieve success is better than “dumbing down” and letting the machine think for us.

 

ps I don’t believe you own at least (according to the photograph) 11 racing motorcycles or is that ‘paid work’ as opposed to a hobby.

 

Kindest regards,

Phil

[John Stevenson 1Participant @johnstevenson1]

Phil.

 

I think it all depends on how you look at the finished job. The closest I came to doing something like the above but manually was when I was racing and wanted some oil pump plungers for the old Pilgrim pumps.

These had one cam track on them that caused the plunger to oscillate backwards and forwards as it was driven.

 

Being very much pre CNC I scratched my head and came up with a swash plate follower that was literally a large disk welded on an angle to a shaft, a follower dog then pushed the new plunder over in a very crude 4th axis whilst I milled the groove.

 

For me even though it worked I resented the time taken to achieve this as my main interest was getting the bike running again, not how to get it running again. If I had have had access to CNC at this point in time I would have used it in a heartbeat as for me it was all about the reward, not the journey.

 

I don’t regard it as dumbing down, in fact on those cams in the picture there is far more work in making sure all the dogs are in the correct point and space in time than actually doing the job. Some of the engagement dogs miss by 10 thou whilst shifting.

 

Although paid, I do regard it as a hobby as it’s not my normal line of work and I find these sort of jobs interesting and only take them on if interested.

There are some very lucrative jobs in the vintage movement if you can spot them, especially where the owners have more money than sense.

 

John S.

[Anonymous]

Phil: You won’t get any rude comments from me; if you don’t want to use CNC that’s fine by me.

 

Steve: The comment on over-engineering was a gentle nudge at an earlier respondent, who threw his teddy out of the pram, turned the pram over, and then stomped off.

 

I didn’t want to overfill the post with pictures, so it might have looked a bit misleading. The gear teeth were roughed out with a 4mm ball nose cutter, as shown. That was followed by a quick pass with a 3mm ball nose cutter to clean out the small end, and then a final pass with fine stepover with a 2mm ball nose cutter. The final gears as shown are straight off the machine tool, apart from a little deburring of the tooth ends where I machined the tapers on a (manual) lathe.

 

The comment on the steering gear is a project in hand. The drawings I have are completely inadequate. They only say that the worm is two start, 0.5″ pitch and give the OD and a lead angle. The worm wheel simply says 22 teeth and gives an OD. The supplier I get my castings from uses a helical spur gear for the worm wheel, which is of course perfectly adequate, if not prototypical. But I got to thinking (dangerous I know), could I make a proper hob and consequently make a proper worm wheel. Like everybody else I’ve made worm wheels using a tap as a hob, but I’ve never made one using a ‘proper’ hob. Once I’ve checked my maths and tidied up the 3D models I’ll start another thread.

 

Regards,

 

Andrew

[Steve WithnellParticipant @stevewithnell34426]

Posted by Andrew Johnston on 19/06/2011 19:20:30:

 

I didn’t want to overfill the post with pictures, so it might have looked a bit misleading. The gear teeth were roughed out with a 4mm ball nose cutter, as shown. That was followed by a quick pass with a 3mm ball nose cutter to clean out the small end, and then a final pass with fine stepover with a 2mm ball nose cutter. The final gears as shown are straight off the machine tool, apart from a little deburring of the tooth ends where I machined the tapers on a (manual) lathe.

 

snipped>

 

Looks very impressive Andrew …I really must get organised and have a run at CNC milling, my current project cries out for it.

 

Steve

 

 

[blisterParticipant @blister]

Posted by Andrew Johnston on 19/06/2011 19:20:30:

Phil: You won’t get any rude comments from me; if you don’t want to use CNC that’s fine by me.

 

Andrew,

I can’t for the life of me find where I wrote that I don’t want to use CNC’s. It’s odd because I find them fascinating and shall continue to harrass my boss to get us one. In the meantime I will continue to learn as much as I can about them.

You may have missed my point.

 

Regards,

Phil

[blisterParticipant @blister]

Hi John (Stevenson)

Thanks for the excellent response. I had never looked at it like that before. You now have me considering a small CNC for my home workshop to the point where it almost shot straight to the ‘Must Purchase’ list. It did make it to the ‘When I get the money’ List though

 

Regards,

Phil

[Anonymous]

Finally, after delays and interruptions due to having to work for a living, the complete set of bevel gears has been finished in cast iron.

 

Due to problems with the drawings, I threw away the castings for the bevel gears and machined them from cast iron bar. The spur gears were part of the original casting. The only thing left to do is cut a keyway in one of the bevel gears. It’s a bit of bottom clenching job swinging the ram round on the Bridgeport, so I’ll do it in one big session when I have other items ready that need keyways.

 

Regards,

 

Andrew

[KWILParticipant @kwil]

 

Andrew,

 

Sample fully hobbed wormwheel for your enjoyment, material PB, 3.5″ dia or thereabouts. Must confess I provided the blank and a friend used his hobbing machine!

 

K

 

 

 

 

[SpringbokParticipant @springbok]

A friend from Japan sent me this Email

 

Legarding what you are looking at

I can make thousands of these items velly cheaply and incluse a fully operatonal manual.

 

toung in cheek

 

smile it could get worse she indoors could ask you to do some work in the house………

[Anonymous]

KWIL: Looks a lovely job; I just hope my worm and worm wheel look as good. I don’t have a hobbing machine, so will be relying on gashing and then free hobbing. But I must finish the differentials first.

 

Springbok: I hardly think ‘er indoors is likely to ask me to do something in the house, when the kitchen looks like this!

 

 

Andrew

[Phil PParticipant @philp]

That is absolutely disgusting and not very hygenic at all.

 

I really cannot believe some people and the things they do.

 

Do you not realise that having plantpots on your worktop is not a good idea.

 

Phil

[blowlampParticipant @blowlamp]

Agreed Phil.

 

Look at the ridiculous way that food resides on the worktop, whilst precious metal has to make do with the floor.

 

A classic case of mistaken priorities – I’m genuinely shocked

 

 

Martin.

Edited By blowlamp on 26/09/2011 13:53:31

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