Hi, does anyone have any experience in gear cutting on a milling machine or lathe?
Me and another guy from work are starting a machine shop night class in a few weeks, he's got a steam locomotive to be doing and i need things to make really.
I know gear cutting is unbelievably complex so it would take ages to learn this but would it be possible to make my own gearbox for my rally car? Choose the exact ratios i want, make the gears straight cut.
I have started reading about gear cutting and its a very large field, Cyclodic curves, Hypocyclodic, PCDs.
I could sort of have this project in the back of my mind after years of practice i might begin to make it.
The lecturer said he can make absolutley anything on the machines, i think he was just boasting. So if things are to complicated for me to make, he'll make them.
What do you guys recon? The machine shop is amazing, every machine you could ever think of, plus they do heat treatment and tempering and things there.
So, I know it is possible cause anything is possible, but just how difficult and complex is it? and whats the difference between doing it in a lathe or a milling machine?
Im in the process of looking for a milling machine and maybe lathe for my workshop at home so I will be able to practice and play about a LOT. Im not going to just go to the course for 1 term, im going there for years and years to get as good as I can. Everything I do, i want to be the best.
The gearbox project wont get under way for many years probably, because there's no point in starting if my skills aren't good enough

Thanks for your time and patience.

We have this thread going http://www.cnczone.com/forums/showthread.php?t=23867 and yes depending on form you can cut a gear on a mill

is that gear cutting with cnc i take it.
what aspect of gear cutting is so difficult then? i have been told that most engineers avoid it because of its difficulty.
from my very small knowledge about the subject, it seems to me that most of the work is in the designing of the gears and obtaining the right cutter. Such as deciding your cycloid and hypocycloid curves.
In that sortware, i see blocks for entering stress angles or whatever, how are these found then?
Im 21 and a head mechanic in a fairly large workshop and regularly service and re-build car gearboxes, but this time i want to make my own gearbox using the original box casing and bearing housings but changing the design of the gear type from helical to straight cut for less transmission losses and changing the ratios to suit different evens and my engine torque curve.
Any help will be appreciated.
P.S I have a book on order "Manual Gearbox desgin" which might help me a little.
Thanks a lot

Making gears in the traditional way using a dividing table is a piece of cake, using gear cutters. These gears are limited usable, because they have evolving errors. So for better gears you go for hobbing, where the gear is made, like it is contact with another gear. But car transmissions use different gears. All the different set of gears must have the same pitch (centre to centre distance). They must also have prime numbers of tooth, to avoid the same tooth constantly meeting the same tooth of his partner. Then they use techniques of tooth bottom strength heightening, where they enlarge the pitch circle. This is advise and expertise land. After this comes case hardening. Same land.

Conclusion:
For industrial use: Make your own, only in emergency, if not for sale and preferrably not above 1000rpm.(noise).
For automotive: outsource.

You live between open gearboxes, start measuring gears and see how it's done.

Hi Owain. Who publishes the book 'Maual Gearbox Design' ? Also if you could look at the thread in post no.2 above and give me any advice on attaching the drive shaft to the gear from your experience it would be much appreciated. There won't be any housing around the gear. Thanks.

Why are the teeth made using a dividing head and a cutter so different to other methods then? Is there a way of cutting the gears like this then modifying them to have some properties of the other processes?
They are gonna need to cope with around 150nm and about 8000rpm!
I take it making them straight cut gears will make then A BIT easier to cut than helical plus they wont have to cope with side thrust.
I have been advised by a guy to use N39 to cut the gears from by a historic car builder, any comment on this material?

With the dividing method you use a set of 8 cutters for the range of tooth between approx 15 tooth and straight, somewhere around 135 tooth. They are approximations. The hobbing method uses the a mill with the "straight profile" and is geared to the gear to make. The profile of the gear is in this way automatically corrected. You would see, feel and hear immediately the difference of this two methods.
For "sport" appliances straight is the normal choice, more noise, no side pressure. Keep also in mind, that you will have to broach the internal splines and make the intricate connecting lips on the gears. The lips have an angle to keep the gear "in gear" and radiuses on the bottom that with high power, scratches and unoptimal hardening can come of.

You seem to know your stuff about gear cutting.
So do you recon the hobbing method will be doable in the machine shop they have at the engineering college im going to? Its a well equipped shop.
So say i want a 5 speed box, i will need 10 gears plus an idler for reverse. Will i require 11 different cutters for this then?
I know what broaching is but how difficult is this to do? I guess all the gears can have all the same splines on them so id only broach them all the same then?
What dissadvantages would i see from making the gears from a dividing head and cutter over the other? I dont really care about noise from the box anyway, the 4 throttle bodies i have sucking away make quite a bit of noise already.
Thanks a lot

Well, you need a hobbing machine. They are certainly more rare than lathes and mills.
The thing I worry about is the elevated pitch circle. Once I had to outsource primary transmissions for racing motorcycles. I had everything sorted out, according to industrial standards. The manufacturer, who was experienced in this (and also in hardening) told me, that standard sizing, for the small gear, would make the teeth to vulnerable. The correction for low tooth gear weakens the base. An extreme example is the ancient roll dryer, used for drying clothes. The design (roll dryer) allowed only for four extreme corrected and vulnerable teeth. When you see one, look at this detail.

So he designed within the dimensions his own pitch circles and hobbed the special gears with a standard hobber. These gears never broke down and a championship proved he was right. Knowing this, and putting your caliper here and yonder, you see this is widespread. Transmission gears are high-stressed components.

Ah i see what a hobber is now, looks like a torture instrument.
Can you use the hobbing bit in a lathe or mill and use a dividing head or is that being stupid? Im sorry in rubbish at this right now as i have no experience.
I dont see that being a consideration really with gear sizes, they all seem to be of a fair size, cant remember diameter of smallest gear right now. So you're saying smaller gears tend to be weaker because of the smaller number of teeth or smaller diameter? Because the teeth can still be same pitch cant they?
Sorry, what do you mean by elevated pitch circle? Do you mean Pitch circle diameter? sorry again :(

I'd say google a little on "Module" or "Modula", read up a catalogue of industrial gears, find out how a hobbing machine works, reread what I've written and come back next week. It doesn't sink in just on one saturday night. :cheers:

module or modula in conjunction with what then? Modula the programming language?
Sorry, thanks.lol

One good turn deserves another so heres a site that you will probably find useful Owain. :) Unfortunately most of the stuff is for sale not free, but theres a couple of relevant links on the site such as the second link below.

http://www.drgears.com/

http://www.geartechnology.com/

Hi there,

I have done a fair amount of gear cutting at home using a dividing head and involute cutters. Most of the gears I have made are lightly stressed, so high-tech alloys and heat treatment haven't been necessary.

As fkaCarel mentioned, I would think that hobbing (or some kind of 'true' generating method) would be needed for what you want. I have no experience with car gearboxes, but I would think that designing/generating the teeth would only be half the struggle over. I would imagine that the material used, along with the heat treatment would be quite critical.

Regards
Warren

Here is a fine example of base-width versus number of tooth. Both gears are hobbed at the same factory according to the same industrial specs and the same modula. Yet you see that the tooth of the smaller gear are more corrected, leading to a smaller/weaker base.

This is going off the subject a little bit but I made this toothed pulley for a supercharger last week end and discovered the following: The manufacuter's information for the toothed belt stated the pitch as being 12.7mm. I calculated the diameter of the pulley to the closest number of teeth to fit the material I had. I milled out the teeth using a dividing head and discovered the pulley diameter I calculated was too big. I believe the reason for this is because the belt has a very strong braid inside it that forms the strength of the belt. The rest of the rubber surrounding the braid is "there for the ride" you may say. If the belt is running in a straight line it's eask but if you bend the belt around a curved surface, you have to take into consideration the compression or expansion of the rubber around the center line of the braid (which remains constant). To cut a long story short, the correct pulley radius is from the center of the pulley to the center of the braid minus the distance from the center of the braid to the carrying part of the toothed belt. Clear as Mud!!! Hope this didn't confuse anyone. :confused: Here are some Pix to have a look at.......

Yea here are the pix......

Chich, which type of machine is shown cutting the gear in the first photo? Thanks.

If the heat treatment required is going to be very specialised then i will send the gears away and get them treated by someone who can do it.
I dont mind forking out for expensive metals as long as i dont waste it by starting to make the gears when im not ready and stupid things like that.

Sorry but i cant see the differences in the gears you refer to :(
My eye isnt trained like yours :(

Do you see any harm in having a go at this project when i think ill be ready and sort of make the gearbox, try it out, then strip down, re-asses things and maybe change the plans a bit then try again. This is how a lot of things are developed isnt it?

Maybe give someone like Quaife, TranX or hewland a call and ask them if they would be willing to give me a bit of advice. Probably wont share their secrets with me.

Chich, you could have looked it up in the catalog. Biggest H(12.7): 40tooth, Pitch circle diameter: 161.70mm. Difference Pitch circle(neutral line)-outer diameter: 1.37mm
If I counted correctly, you made a 47 tooth pulley.
((47 * 161.7) / 40) - 1.37 = 188.6275 mm. Right?

Owain, your week is not over yet. So I give you some homework. I will keep it simple. You have a transmission. 1 gear is 20 tooth. the other gear is 30 tooth. The module is 1. What is the centre (of axle) to centre distance? Let please nobody else in their enthousiasm cry out:"I know, it's X". And Owain: no cheating, the answer and the way you came to the answer. We all had to start that way.

And I have to add to all this: If you make something which is mobile and can harm bystanders or yourself, such as what you want to do (and our handy Flying Irishman) you can come in deep, deep trouble. If evidence proves that you have done this through louzy design, ignorance or whatever, everybody, and your insurance company first, will put the blame on you.
You have no clutch to disengage a blocked gearbox.

And I have to add to all this: If you make something which is mobile and can harm bystanders or yourself, such as what you want to do (and our handy Flying Irishman) you can come in deep, deep trouble. If evidence proves that you have done this through louzy design, ignorance or whatever, everybody, and your insurance company first, will put the blame on you.
You have no clutch to disengage a blocked gearbox.

I have been following this thread and this was also going through my mind. What you are aiming for is possible; it must be because it has been done in the past but then there was a lot less regulation and assignment of liability.

Another aspect is that it can be tedious and expensive. When a single part fails in a gearbox sometimes you simply finish up with a lot of fragments spread along the road; how do you identify the primary failure?

I don't want to discourage you but go into this with your eyes and mind wide open.

ok, here's my go.

m = ((centre to centre) * 2) / total no of teeth

therefore

1 = 2(centre to centre) / (30+20)

1 = 2(centre to centre / 50
*50
50 = 2(centre to centre)
/2
50/2 = centre to centre

25mm?????

Your answer is correct, but the module is not in the equasion. So now 22 teeth / 35 teeth, module 1.5. The 5 questionmarks are a little bit a giveaway of casinostyle calculations. :D

1.5 = 2(centre to centre) / total no of teeth

1.5 = 2(centre to centre) / (22+35)

1.5 = 2(centre to centre) / 57
*57
(1.5*57) = 2(centre to centre)

85.5 = 2(centre to centre)
/2
85.5/2 = (centre to centre)

42.75 = centre to centre

42.75mm centre to centre

What ever do you mean casino style calculations, module was in the previous calculation, i just substituted it with 1 because that's what you said it was.

I was going to do a PhD in Pure Mathematics at university but decided not.

And I have to add to all this: If you make something which is mobile and can harm bystanders or yourself, such as what you want to do (and our handy Flying Irishman) you can come in deep, deep trouble. If evidence proves that you have done this through louzy design, ignorance or whatever, everybody, and your insurance company first, will put the blame on you.

I promise I'll be careful. I live a few miles from the Curragh plains, largest area of open grassland in western europe, so I'll find a nice empty spot before trying anything. Also, I'd like to keep all my bones in one piece and attached at the correct points. ;)

Please keep posting the 'homework', although I never intended to do a Phd in maths, I'm struggling through them. :)

Originally I was going to be a vet, but at that age euthanesia scared me off. So here we are now, doing number games on an obscure website.
And you are spot on, without question marks!

How do you derive the numbers, for normal industrial gears? Gears are specified in number of tooth and the module. The number of tooth * module gives the pitch circle diameter. So at the pitch circle diameter the tooth are Pi * module spaced. The outer diameter is (number of tooth + 2) * module. Outer diameter of 20 tooth, module 2 = 22 * 2 = 44mm.
A gear drives the other gear via the radius, so for calculation of torque and force applied on tooth, you look at the radius instead of diameter.
So I learned for centre to centre is:
(Gear1 / 2) * module + (Gear2 / 2) * module
With the example:
11 * 1.5 + 17.5 * 1.5 = 16.5 + 26.25 = 42.75
Now there are a number of modules, just out of my catalogue:
0.5, 1 , 1.25, 1.5 ,2, 2.5, 3, 4, 5 and 6.
So if you dive into your dismantled gearboxes, measure tooth, outer diameters and center distances, you get a grip on what is going on in this wonderfull world of transmission gears. I did this afternoon some reverse engineering on the forementioned gears, and it is better and not conforming. You have to understand the underlying fundamentals, before you can start engineering.

I really like these questions actually. Do you have SLIGHTLY more complex ones for me now?
You are absolutely right in your ideas actually.
With the gearbox ill be making, the centre to centre distance will be constant for all the gears involved because ill probably be using the standard input and layshafts. Only thing that will be changing is the number of teeth on gears really. So basically, the module will be different on each gear then?
Also, how is the shape of the tooth choosen then? I see things such as pressure angle which might contribute to the design? Does the size of the gear to be cut decide on your cycloid and hypocycloid, or do these stay the same for different gears in the same powertrain?
I like your way of making me work for the information because you dont lean anything by just getting all the answers. You should go in to teaching.

Yes this forum is obscure, it's a bunch of masochists.
When and if you start counting your gear pairs, you will see that the number of tooth added per pair, is up and about equal over the sets of pairs. An example from a mill:
22/26
27/21
34/14
They all add up to 48. You will also see the prime numbers shining through, although not fundamental enough. the first and thirth set must be divided by 2, before prime, the second by 3. The use of prime numbers is important for long duration use, I think Schumacher and Ferrari can live easily with a lifecycle of 500km, so they would not have any trouble with a 24/24 gear.

All these gears can be made with one hobber. Metric gears have a pressureangle of 20 degrees, so the toothdesign is "machined".
So if the left gear numbers of the mentioned mill are driven at 1000rpm, which rpm's can I generate with these sets?

26/22 = 1181rpm
21/27 = 777rpm
14/34 = 411rpm

then to calculate power or torque its

power = (torque * rpm)/5252

Also in regard to the prime numbers. Is the dividing factor to get the prime number important? Say you have to divide by 2 to get the prime number, does it mean the same teeth mesh every 2 revolutions and if you had to divide by 3 to get the prime number then the same teeth mesh every 3 revolutions? So diving by 3 gives slightly longer life than having to divide by 2? Or is that not a rule? thanks

I disagree with your rounding off, I come at 1182, 778 and 412.
With the prime number you approach the gears mathematical.
26/22 = 13/11
21/27 = 7/9
14/34 = 7/17
For power and torque, I would have to dive into my books.
Same tooth meeting is the product,= 143, 63, 119 revolutions. So higher division before prime, gives worse numbers.
Let's assume a distribution for a camshaft with 40/80. The 1/2 is a must, we are not inventing new engines. they divide down to 1/2. 2*1 = every second revolution the small gear tooth meets the same tooth on the big gear. So from this viewpoint a pushrod engine qualifies for a morse chain, because it disqualifies for even wear. It is not the law, but you have to know this, just to know when you're compromising.
To synchronize our calculators: a 17/41 drive, driving a 23/43?

Chich, which type of machine is shown cutting the gear in the first photo? Thanks.

diarmaid,
The machine I use is a Hafco Metal Master HM-52. Its a cheap version of a bridgeport mill. I got it from http://www.hareandforbes.com.au Extremly good value for money. Very rigid. It has a verticle spindle and a horizontal spindle with quiet belt drives on both spindles. I am about to convert it to CNC and will shortly be adding a thread on the project. I also have a Hafco Metal Master AL-340A Lathe.

sorry, yes you are right with the rounding off, i didnt pay attention.

sorry, what would you like to know about the ratios you've given?

if its revolutions till same teeth mesh then:

17*41 = 697revolutions

23*43 = 989revolutions

so they appear to be pretty good in terms of wear.So really you're looking for the highest possible prime number of teeth, but most often this isnt available really is it? If your stuck with a fixed pitch circle diameter and you're stuck with the gear ratios you have choosen.

What do you guys think of this milling machine for me to buy for practicing at home? I cant justify the space require for a huge machine at the moment because i dont know how serious ill get about it.

http://www.chesteruk.net/store/champion_mill.htm

it looks like a good machine and its fairly inexpensive as well.

what do you think? thanks

sorry, what would you like to know about the ratios you've given?
Gear ratio & output rpm if input rpm = 1000.
And the prime numbers are not the law, you have to be aware of them. A typical motorcycle (6-speed) racing gearbox can be described as: max rpm in first gear is half topspeed, difference in gear ratio is the smallest between 5 & 6 (powerband) and grows every time you go to a lower gear. This is of course an universal and not circuit specific box. To make the gearbox not to big the ratios are spread between slightly larger on incoming shaft (upspeeding) and slightly larger (reducing) on outcoming shaft. These are (the) parameters. And then you have to choose a fair module, there is an idiot operating it (and hopefully lots of power). With these data you can design a virtual gearbox with let's say center to center 47mm module 2?

And Chich, would you be so kind to check post #20?

Owain: I looked at your proposed mill, for gear cutting in steel it lacks rigidity. Chich's machine wins. A module cutter is at least 50mm (just measured) and that's what is going to pain. chatter.

I calculate it as being 221rpm output

You have 2 gear reductions going on there.

One thing that worries me is, how do i come about deciding the shape of the teeth? Or is there software that will do this for me? And the pressure angle on the teeth?

I didnt think of that machine for cutting my gears really, i mean as a machine at home to play about with and get some experience.
I guess ill do the gear cutting on the machines in the college. So i should be able to cut the gears with a module on a milling machine then? I dont have to use a hobbing thingy?

One thing that worries me is, how do i come about deciding the shape of the teeth? Or is there software that will do this for me? And the pressure angle on the teeth?
I explained this in post #30, last alinea.
And if I calculate ((17 * 23) / (41 * 43)) * 1000, I get 221.78, which rounds to 222rpm. It seems everybody knows how to do this, when it's about money. (chair)

Sorry. So all metric gears have a 20degree pressure angle, but what about the shape of the tooth then? Or are they all sort of standard.

Yes again you are right with the rounding off, i did the calculations without a calculator so i rounded them off to (0.414 * 0.534) *1000.

What do you mean everyone can do it when its about money?

I have learned quite a bit from you about gears. Do I have to learn how to use CAD software for designing the gears even though ill be cutting them by hand or what? Are gears easily designd with CAD, they're just round disks with teeth on them arent they.

I think i have to remember that they're just disks turning on a shaft, because you can get carried away with all the design i believe.

What type of meshing have you used for some of the gearboxes you've made? The current gearbox has synchromesh but i might consider something else such as dog engagement?

What type of meshing have you used for some of the gearboxes you've made?
That's the difference between you and me. I had to build complete engines & frames. I researched which modern gearbox fullfilled my needs and designed it in. A gearbox is that specialised that it will let you lose the greater picture. I did today some calculations on this problem. Making transmission gears, according to specifications, deliver and sleep well. 1-3 years. Designing, stress analysis and endurance tests etc and sleep well. 3-5 years. Both numbers after finishing mandatory pre-schooling. This is good hearted advice: at the moment you have a plethora of questions, but you can't comprehend and associate the answers. It will come. Visit trade shows, you will find the hobbing machine there. Take your time. You don't have to prove anything, it is not necessary your final goal, it is your goal for today. Make a pro/con, do/don't list. And I don't want to change position from teacher (which I am not) to preacher (which I certainly am not)
Take care.

Owain, do some googling and reading up on gears & design - there is LOTS out there. I agree with fka that you quest for knowledge (which is great to see) is taking you so far past where your're at, the answer's won't mean much. designing and building a synchro mesh 8k rpm tranny and not really having the basics down is like wanting to build the Taj Mahal but not being able to hammer a nail without bending it over. I believe in think big - maybe you could build the Taj Mahal, but there's a few interim steps.

at the end of this thread
http://www.cnczone.com/forums/showthread.php?mode=hybrid&t=9800
is a link to site describing a very simple way to make a simple spur gear with low cost equipment, doesn't need a form cutter but is not hobbing either. you will need a much beefier mill though, avoid round column if you can. Short of buying a hobber, you really need a universal mill (3000 lb beast) to be able to hob and hence get better gears than simple profile cutters will provide. study the involute form and why generation is superior to profile approximation will become clear

Thanks a lot for your advice and experiences.
I will do a lot of research on gears as im doing other pieces trying to learn my skills on the different machines.
I'll let you know how things are going.
Again, thanks a lot.

Chich, you could have looked it up in the catalog. Biggest H(12.7): 40tooth, Pitch circle diameter: 161.70mm. Difference Pitch circle(neutral line)-outer diameter: 1.37mm
If I counted correctly, you made a 47 tooth pulley.
((47 * 161.7) / 40) - 1.37 = 188.6275 mm. Right?

fkaCarel,
Sorry for not replying. When you refer to "the catalog" where did you find this information? I went to the belt manufacturer's web site and read a data sheet on the belt but it didn't give me pulley details like PCD as you have supplied me. This is the first grooved pulley I have ever done so any help in this area will be great.

Thanks,
Chich

If you go to www.maedler.de you will see, they also have a supplier in Australia. Ask them for a catalogue or maybe you can find this on their website. All these numbers from almost every existing timing belt, you can easily grab out of the catalogue. I just wanted to verify if you came to the same number by trial and error. The calculation can serve other people, I used it myself, but one must also have happy customers.

fkaCarel,
Yes you are correct. The pulley is 47 teeth at 12.7mm pitch. It's finish diameter is 188.6mm.
((47 * 161.7) / 40) - 1.37 = 188.6275 mm.

I just made a smaller one today and will put the grooves on it tomorrow. It is an 18 tooth. I took the size straight of a chart. I also made a stub shaft so I can hold it in my dividing head without the cutter hitting the chuck.


Chich.

Module or modula = metric version of pitch

Pitch = how many teeth there are per circumferential inch measured along the pitch circle.

The higher the pitch, the thinner the tooth and vice versa.

The higher the pitch, the more teeth are simultaneous contant with each other, and vice versa.

If you use shoe size as a reverence, you can't put a size 10 foot into a size 6 shoe. Thus, you can NOT match a 12 pitch gear with that having either 10 or 14 pitch. This does not take into consideration pressure angle, helix and other fine points of gearing.

Literally, there have been VOLUMES written about gearing. A beginner's guide to the understanding gearing can be found in:

Machine Design by M.F. Spotts

IT goes into gearing and the basics of lots of other machine design terms/concepts.

Home cut gears are genearally adequate for low speed and/or low power applications. However, when you start putting serious power thru the gear train, fits/finish/materials become MUCH more critical. What might be tolearable in a gear train that lumbers along, could result in the gears trying to EAT each other at the speeds you've mentioned.

Keep in mind that gears are also trying to force each other appart at an amount that is proportional to the pressure angle as well as the power being transmitted. Hence, you also have to take the case and shafting into consideration when you design a gear train.

I'd suggest doing a LOT more homework into the understanding of gear and gearbox design. especially, before you even THINK about cutting metal on gear blanks or try to make a gear box.

The Spotts book would serve you well as a gear understanding primer.

I have finished the small pulley. As per chart information, an 18 tooth puley is almost the smallest I can go for the "H" series belt and still achieve a reasonable life from the belt and pulleys. Once I drilled and tapped the holes in the arbor I bolted the pulley blank to it then dialed it up in the mill. Since my dividing head is 40:1 I went 2 full revolutions and 4 holes on an 18 hole sector plate. (2 4/18). Here are some more pictures.

Chich

Here a funny one. It started like this: I have a machine which uses 1" wide XL belts. These are special cuts, thus expensive and they did'nt last that long. So at the end I replaced it with two 3/8" belts XL side by side. Never had to replace them, so there must be also an quality difference.

Knowing this, and noticing in the catalog that MXL belts have the same diameter/width power transfer, you could make a reasonable power transmission in a limited space with more tooth on the pulley. As an MXL has the same pressure angle as an module gear, I could even use a gear cutter for these.

On the photo a 4-belt, one belt removed, in the background a hobbed timing belt bar, which are available at timing belt suppliers. But I see hobbing for timing belts not as necessary as it is for gears. With this approach and a casino like program to play with belt lengths and number of tooth I am able to replace gears. And this does'nt off course apply to automotive gearboxes.

Would the SIEG Super X3 mill be rigid enough for cutting gears?

I suppose it depends on the size and thickness of the gears your cutting.....?

http://www.syil.cn/

Here a funny one. It started like this: I have a machine which uses 1" wide XL belts. These are special cuts, thus expensive and they did'nt last that long. So at the end I replaced it with two 3/8" belts XL side by side. Never had to replace them, so there must be also an quality difference......


Did you monitor operating temperatures? Two narrow belts would probably run at a lower temperature than one wide; the surface to volume ratio thing in action once more.

Bit difficult to monitor the temperatures, with a damaged original one. It's just typical that a replacement with a reduced width of 25% last longer, as in till today. A two belt replacement, directly available, costs up and about 3 Euro, instead of the original +/- 15 Euro, so I am more careless too. The pair is 12 years old now, while an original lasted 5.
As a timing belt has a spiral cord it tends to move to one side according to direction, so they are cosy side by side, closing the extra cooling area. The sidewall of an XL belt in only 1mm, so there is only a slight increase in cooling area.
I know there are quality issues with timing belts. I read here that Uniroyal invented the timing belt in 1946. At a certain moment production was licensed, patents freed, with quality issues as a logic consequence.
But honour to honour, these are Pirelli's.

nice work guys