Cutting Gears

[Carl Wilson 4Participant @carlwilson4]

Hello Ladies and Gents,

I have decided to have a go at making some gears. I've wanted to master this for some time, and I have a Harrison M250 that has a full set of metric change wheels, but is lacking the ones to machine imperial threads. I sense a project coming on…

Right. So I have a Chester Eagle 30 Mill/Drill. Made in Taiwan I know but she's a fair old beast. I also have rotary table, indexing plates and so on. So I can cope with that side of things. Material wise I was looking at Delrin or black acetal, or something similar as the change wheels are fairly lightly loaded.

I imagine it is a case of mount blank, mount cutter, bring the two together, depth tooth (possibly using a fixed stop on the table's travel?) then index, depth next tooth and so on and so forth.

And here it all gets a little hazy…the detail in between those steps is where I'm vague. I would appreciate a bit of advice or information on things like set up, what is the best way to mount the blank, will I need to make an arbour of some type supported by the tailstock, or can I turn a portion of the blank down and use this to hold it? Any pearls of wisdom you care to throw before this particular swine will be greatly appreciated.

Many thanks,

Carl.

[Carl Wilson 4Participant @carlwilson4]

Advice required please

[Billy MillsParticipant @billymills]

That's a bookload of info Carl, so you might be better off looking at "Gears and Gear Cutting" by Ivan Law from the Workshop Practice series. You can also see some gear cutting on you tube.

Billy.

[Anonymous]

Like Billy says the basics can be found in books. The book mentioned by Ivan Law is a good start, especially for spur gears.

When gear cutting I normally make a simple arbor to mount the blank. For small gears, say less than 4" diameter, I normally use a screw in the end to expand the arbor and hold the gear. For larger gears I tend to make ends with 'proper' clamping arrangements. When setting the cutter I use a length of gauge plate to 'touch off' the side of the gear cutter against a convenient point, often the OD of the gear blank. Then I move the milling machine table by half the OD of the gear, plus half the width of cutter, plus the thickness of the gauge plate. The cutter should then be centred over the gear. I then 'touch off' the cutter on the top of the gear blank and move the knee of the mill an amount equal to the calculated depth of the 'tooth'. Then it's just a case of cut, index, and repeat as needed.

I normally do a trial run, no cutting, to make sure I've got the indexing right. I cut full depth in one pass, although that may depend upon the rigidity of the setup. Here's a 12" OD 6DP gear being cut:

I normally use tailstock support, as it increases rigidity. The green clamp is belt and braces to stop the gear slipping on the arbor. The cutting forces should be symmetric, but you never know………

Gear cutting isn't difficult, and the maths is pretty simple, so I can't see you having any problems.

Regards,

Andrew

[Carl Wilson 4Participant @carlwilson4]

Hello Billy,

Thanks a lot for the advice. I might have known there'd be a Workshop Practice series about it. I will get that. I also have Chapman's books on workshop practice…and my training, which seems like the lifetime ago that it was.

Any advice or little tips and tricks I'd still be greatly pleased to hear. I am sure I will have further questions…When I did my engineering training in the Royal Air Force they told us "If you don't know what to do, do something, then measure it…" I have always found that sound advice. I find if you set off, even if it is in the wrong direction that will point you to the right one. So I will learn by doing and with the culminated wisdom of you kind Ladies and Gents.

Thanks again Billy,

Carl.

[Carl Wilson 4Participant @carlwilson4]

Hello Andrew,

Thank you for your excellent advice and the picture, which tells a thousand words. That is most definitely a gear you have got there my friend. The process you described is what I have had in my head so far, so it is nice to hear it vocalised. I am glad to hear that it is usual to cut the full depth in one pass. Obviously my machine does not have the rigidity or power of yours, and I reckon I'd get a poor finish if I did that in Delrin, but it is good to know.

Your words of wisdom re set up, workholding and clamping are just what I'm looking for. It is all the little tricks that make the job so much easier. These are the types of things that in our society are being lost. And it is a tragedy because we are the Nation who industrialised the world; we make things, it is who we are. I am determined to hoover up all these skills. In fact I seem to be becoming something of a collector of them.

I will keep you updated on my gear making attempts.

Carl.

[Anonymous]

I would think that you'll have no problem cutting a Delrin gear for a M250 full depth in one go. I have a Harrison M300, and some of the intermediate gears are plastic, Tufnol I think, rather than Delrin.

Another useful book on gear design is 'Gear Design Simplified' by Jones and Ryffel, ISBN 0-8311-1159-3. This book deals with the design of gears, not manufacture. Here's a picture of more gears, and some arbors, which may give you some ideas:

After a lot of faffing about adjusting cut depths, I found that the gear verniers are a bit of a waste of time. Just cut to the calculated depth and the gears should mesh without a problem. The only caveat is make sure you know what depth the cutter is designed to use. For gears designed using diametric pitch the total depth is normally 2.157/P, where P is the diametric pitch. However, some gears, with low numbers of teeth or fine pitch, may use 2.25/P. The cutting depth is sometimes marked on the cutter.

Andrew

[Carl Wilson 4Participant @carlwilson4]

Hello Andrew,

Thank you for taking the time again to post on this subject and for the photograph, plenty of food for thought there!

I was in two minds about wether it would be advisable to take the full depth of the gear tooth in one bite out of the delrin, so thanks for the affirmation. I thought to use delrin as it would be less strain on the machine and less trouble if I make a mistake, which is quite likely! By the same token, using delrin means I will end up with a serviceable end product, once I get it right that is.

Some of the change wheels on my M250 are tufnol and I may opt for that, I will see. Thanks also for the book recommendation, I have several books on machine design and gearing but I'll certainly look it out. Fascinating reading your comments on depthing the teeth, I am looking forward to having a go.

As you have a Harrison M300 I wonder if you are a member of the Yahoo Harrison Lathe Group? It is a useful little thing, I have had several leads on various bits and pieces from it.

One final thing. I had a problem with the torque limiting clutch on the powershaft of my M250, and I also had to source and replace the 240-110V control transformer, and I wrote both of these activities up on my blog. You may find the articles of interest. The blog is mainly concerned with my attempts to build a liquid fuel rocket engine. You can find it here:- http://www.britishreactionresearch.blogspot.com

Many thanks again,

Carl.

[Carl Wilson 4Participant @carlwilson4]

Update:- Ivan law's book is on the way.

Carl.

[Carl Wilson 4Participant @carlwilson4]

Hello Ladies and Gentlemen,

Further to my researches into gear manufacture, and to be more specific, making some imperial change gears for my Harrison M250. The Harrison change gears have a female spline as their driving feature, and I have learned from a source on the Yahoo Harrison Lathe Group that such a spline can be made using a keyway broach. This makes sense to me, but I'm wondering, does anyone have any experience in the use of keyway broaches? If so can you give me some pointers? I understand they are used in conjunction with an Arbor press. I hear this is better than using a hydraulic press as there is more feel.

Any advice gratefully received. Many thanks,

Carl.

[steamdaveParticipant @steamdave]

Posted by Carl Wilson 4 on 27/07/2013 21:52:34:

Hello Ladies and Gentlemen,

Further to my researches into gear manufacture, and to be more specific, making some imperial change gears for my Harrison M250. The Harrison change gears have a female spline as their driving feature, and I have learned from a source on the Yahoo Harrison Lathe Group that such a spline can be made using a keyway broach. This makes sense to me, but I'm wondering, does anyone have any experience in the use of keyway broaches? If so can you give me some pointers? I understand they are used in conjunction with an Arbor press. I hear this is better than using a hydraulic press as there is more feel.

Any advice gratefully received. Many thanks,

Carl.

Or you can make a simple keyway slotter to mount in the toolpost.

http://www.hemingwaykits.com/acatalog/Keyway_Slotting_Attachment.html shows a stand-alone item for a Myford lathe, but the basic idea can be adapted to fit your toolpost.

Dave
The Emerald Isle

[Tony RayParticipant @tonyray65007]

Carl,

I can recommend the Ivan Law book having used the info within to cut 18 DP gears for a Boxford.

I made an arbour to hold the blanks – turning a section of the blank to make a shaft would waste a lot of material especially in the larger sizes – an 84T 1.5 MOD wheel is approx. 130m in dia. These are better made out of sheet material.

I too have an M250 and have looked at this very issue (yes I'm on the Yahoo group)

On the subject of material I really would not use delrin; Tufnol or aluminium will prove to be far more durable and these are readily available in sheet form. I have cut gears in both using my SX3 mill without difficulty.

Whilst it is possible to make single point cutters using the method in the book ( and I have for another application) I opted for buying Brown & Sharpe cutters but you will need more than one to cover the 30 – 92 Tooth range of the imperial conversion set.

As you already know the standard of fit of the 6 spline is very high. Keyway broaching 6 splines getting them to within 2 thou will be a challenge – you will have to find a way of ensuring the bush and broach are accurately indexed. If it were me I would build a slotting device. I looked at the Hemmingway kit but thought that it was a bit on the small side for cutting that many keyways in e.g. steel. Something based on a lathe tailstock casting might be more robust.

My conclusions were that if I could find a reliable method of cutting the splines I would opt for buying ready-made gears wherever possible. They are available in Hostaform -acetal (yes that's Delrin) and steel and the typical stock thicknesses can be reduced. This is one of the cheapest sources:

**LINK**

An alternative idea I had to the spline issue is to make up a splined inner bush that could be moved from one gear to another to cut down on the number to be cut. I also think that it might just be possible to 3D print the spline as an insert and bond that into the centre of a premade gear, or to resin cast them from a master spline

You probably also know that the splined section of the shafts on the M250 are bushes held in place with shear pins. If you removed the bushes you could replace them with simple keywayed bushes and then your gears could have one simple keyway.

It has to be said that however elegant the 6 spline arrangement is overkill in this application.

In the end I was offered an imperial conversion set. I swallowed hard & parted with the required sum but I think I would recover the cost if I ever wanted to sell them. Interestingly like Andrew some of my original gears are Tufnol but the conversion set is all steel.

Do also post your progress in the Yahoo forum as it will be of interest – these 6 spline gears sets are rare and getting them made is costly.

Tony

[DMBParticipant @dmb]

Hi Tony,
Re your remark about original Tufnol gears being superceded by steel ones. I once had a lot of trouble with Myfords original ali motor pulley – just could not fit tightly and in the end obtained a new one which was in Iron and no more trouble. I guess thats another example of original spec. being uprated.
John.

[Anonymous]

Carl: I was a bit boggled by your blog on swirl chambers. I used to work for a scientific consultancy that specialised in acoustics, vibration and CFD, so I've picked up a bit of knowledge, but not at your blog level. I'm not a member of the Yahoo Harrison group; probably because I would have needed to register with Yahoo.

I think that Harrison used Tufnol gears to minimise noise. It seems to work, the noise from my lathe is dominated by the headstock gears. I've not had any trouble with the Tufnol gears.

I'm not familiar with the M250, but on my M300 I can cut imperial and metric threads without removing and replacing gears. My lathe is imperial, so I assume that the metric pitches must be an approximation, as there is no 127 tooth gear in the train. I bought the additional gear needed to cut Module and DP 'threads' on Ebay.

I need to cut some internal and external splines for the crankshaft and gears on my traction engines. For the external splines I plan to use the dividing head and horizontal mill, in conjunction with a spline cutter that I have designed, and will make from gauge plate. This is the 3D model of the cutter, for scale the central hole is 1" diameter:

For the internal splines I plan to use the rotary table and slotting head on my vertical mill. I will make the cutter from 3/8" square HSS by milling and grinding to get the precise shape.

It's just a question of finding the time!

Regards,

Andrew

[BaldricParticipant @baldric]

I have seen this way of doing internal splines and should produce good results.
http://modelengineeringworkshop.co.uk/broaching-splines.php

[jacques maurelParticipant @jacquesmaurel42310]

For cutting short threads, with no new gear, go to: **LINK**

regards.

J Maurel

[Carl Wilson 4Participant @carlwilson4]

Hello all,

A lot of very interesting and illuminating information. Thank you very much to all. Firstly, let me state clearly that when I mentioned and Arbor press I of course meant Arbour press…

Tony:- re material, I have some 6mm aluminium plate that would serve to make the gear blanks from. I thought to use a plastic as it would be easier going, but I am more confident in using aluminium after what you said. Tufnol I can get easily also. I realise that I could buy the gears I require but I think that making them would be a good little exercise. I am going to go with getting a set of Brown and Sharp cutters, RDG do them and I can bear the outlay. My experience in obtaining Harrison Spares leads me to believe that the Brown and Sharp cutters will likely be a snip compared to a set of imperial change gears…Regarding the splines, I had thought about making a single splined bush and using it interchangeably. 3D printing might be an option; I have a friend who just 3D printed a 1/4 scale Merlin engine propshaft, so he could help. I think though that solving the engineering problem of making the spline and then actually doing it is an exercise I need to go through. One idea I had for making the splines was to mill them with a slot drill on a rotary table. I reason that it will not matter too much about the slots having a semi-circular end portion. I will post on the Harrison Group site as I progress.

Andrew:- Many thanks for your kind comments regarding my blog. My experiments in swirl are intended to produce an efficient fuel injector for my projected rocket engine. I studied various texts and then attempted to put the theory into practice. I do not have complex measuring gear for analysing sprays that Universities have access to, but my military engineering training taught me the value of a common sense approach and careful observation. I have also learned that the method of atomisation I'm using, namely swirling the liquid fuel and then shearing it with a co-flowing gas, is also used in oil fired loco boilers where swirled fuel oil is atomised by co-flowing steam.

On the M250, there is a screw cutting box, but it is neccesary to use change wheels on the input to this to obtain a series of pitch ranges. I imagine this was one way of keeping the cost of the machine lower for schools and colleges. Thank you for the information regarding spline cutting. I'm going to look into the vertical slotting head idea though my initial thoughts are it'll be a non starter on my Chester Mill/Drill. Your spline cutter looks very interesting and I am in awe of your skill. I am trying to build up a better machining capability whilst at the same time produce something worthwhile, thereby killing two birds with the one stone. And I sympathise with you on finding the time!

Best wishes all,

Carl.

[Carl Wilson 4Participant @carlwilson4]

Update:- Have purchased a set of Brown and Sharpe type mod 1.5 cutters and an arbour to mount them on from RDG. I'm starting to lean towards milling the slots for the splines with a slot drill.

[Carl Wilson 4Participant @carlwilson4]

Update:- I am back in the UK and my Brown and Sharpe type cutters have arrived:-

As I write this the cutters are sitting in a bath of white spirit to remove the packing grease. My next task is going to be to make an arbour to mount these on. Then I can get on with cutting some gears.

Carl.

[Author]

Posts