PDA

View Full Version : Machining spiral bevel gears



mike4
12-15-2012, 09:30 PM
Not wantingto derail the other thread on making hypoid gears , I would like to find information on setting up a manual milling machine to produce gears for various applications from time to time .
The material used will vary with the application and speeds of the area the gears are used in , heat treatment will be carried out if /as required. The final product is to replace parts which are extremely over priced or no longer in production .

All sensible suggestions will be appreciated , and to put it simply I want to drive the indexer off the table to cut gears , the gear train required and how to calculate what gears to use for a specific gear is all that I want .Something like the setup here https://www.youtube.com/watch?v=8aUQM-VtElo
Michael

mechanicalmagic
12-15-2012, 09:55 PM
I believe you need a "Universal" mill, where the X axis can be set at an angle to the Y axis. At least it was needed in 1967 when I cut my last helix.
DJ

Mcgyver
12-15-2012, 10:17 PM
what is going on in that video? grinding or out of control hacks running a milling cutter 50x too fast? :eek:


You cannot make a proper bevel gear on a mill. Guys make pretty good approximations by jogging it over (profile is different from inside to outside) and thats ok for say a model, but depending on your intented application its not a proper bevel gear and may not perform.

Their set up is what you'd do for helical milling. They are not going to get a proper bevel gear profile - again it may be adequate for a model or emergency.

These gears are being cut with a profile cutters. That does not require a universal mill, but you'll note how the spindle is perpendicular to the helix. You need the universal when using a hob, not sure that would work or not...I've only ever seen bevel gear 'approximations done with form cutter. You do need a differential dividing head and gear train to the table as shown

mike4
12-15-2012, 10:31 PM
I have the universal mill , also have the dividing head , what I want is the gear train to table as in the video , which is what I said originally .
What is happening in the video is of no concern of mine I was using it to get a picture of the gear train thats all.

What is so wrong with attempting to make something a different way .

If I want to continue to pay exorbitant "manufacturers prices) then I wouldnt bother asking how to set up a machine to at least experiment. , its a case of nothong ventured nothing gained.

I am also over the attitude that many have of "unless it is made on a specific machine its no good or not accurate ", what ever happened to "lets give it a try " or "lets git er done"
I am not singling out any individual with the above comment, just a little tired of the "that wont work" type of comments .
Michael

Mcgyver
12-16-2012, 12:12 AM
take lots of pics

mike4
12-16-2012, 12:30 AM
So far I have only found heavily edited text from several older instruction manuals , not a lot of help but the idea is good and persistence should pay off , wheres Tiffie when you really need his research ?????
Pictures shouldnt be a problem just getting the geat train up amd running seems to be the difficult bit .

Michael

RussZHC
12-16-2012, 01:07 AM
Way outa my league but my copy of Machinery's Handbook does have one page of sort of generic explanations with a formula at the end where the lead of helix to be cut divided by the lead of machine = product of the driven gears divided by product of driving gears.
That is followed by ten pages of change gears for different leads, a couple more pages of lead of helix for a given angle, page of ratios for determining helix angles (there are formulas along the way if the number is not included in tables).
If you don't have a copy, I know there are some online.

Edit to add: I Googled "spiral gears on a milling machine", first page there is a PowerPoint file by "machiningbymorley..." that more or less duplicates the pages in Machinerys

...way outa my league, the math gets real funky esp as they start discussing things like subtle changes if the shafts supporting the gears are not at right angles or parallel to one another etc.

pipeclay
12-16-2012, 01:24 AM
Do you allready have a selection of change gears,do you know the lead of your machine when using the dividing head.

mike4
12-16-2012, 01:39 AM
Purchasing or makinh the change gears isnt the problem its how to connect them to the dividing head , the lead of the machine is also known , it is frustrating that I am only able to readily obtain information which forces me to use CNC , not happening for this project .
I would like to put some of the rapidly dissapearing old ways into practice ,yes the machining may take time ,could have some innacuracy (which can be fixed), but is the way I want to do the work , just to show that it can be done without cnc..
If I wanted to use a cnc machine it wouldnt have the same feeling of satsfaction when the gears are conpleted .Just another lump of metal and a program in a pc. Big deal.
Michael

pipeclay
12-16-2012, 01:58 AM
Do you mean the order on the bracket or how you are going to attach to the leadscrew and dividing head shaft.

mike4
12-16-2012, 02:07 AM
The bracket and connections to leadscrew and dividing head drive.
I you can steer me in the direction of that info it would be greatly appreciated.As I said earlier it seems to have been edited out of most of the sites that I have come across so far.
Michael

pipeclay
12-16-2012, 02:32 AM
Once you have calculated the change gears required to get your helix mount your driver on the screw and the follower on the worm shaft,the other gears that you have calculated to fit on the stud,banjo can really mesh with either as this will not effect the final ratio.

The only other thing you may need is an idler if correct rotation has to be considered.

willmac
12-16-2012, 07:12 AM
Mike -

If you can tell us what universal mill you have, plus the type of universal dividing head and any existing bits you might have to drive it (banjo, gearbox housing etc) we should be able to sort out what else you might need. You will still need to work out the gear ratios you need, which unless you have the full original gear set might require some extra gears. Ideally you should have the manual for your universal dividing head which will contain sets of tables which show how to set it up for any particular lead. If you don't have the manual, you might be able to find one online, or failing that I think John Stevensons wife's company 'marypoppinsbag' had a DVD collection for sale which covered a lot of the popular universal dividing heads. If you are missing some parts, such as banjos, then you should be able to make one out of steel plate that will work OK. In this case somebody will probably have one and can give you a photo to work from.

At the end of this, what Mcgyver has said remains true and you cannot cut any kind of correct spiral bevel gear by standard spiral milling. You can make a rough ordinary bevel gear with an ordinary dividing head which you can correct by hand to some extent. You can also take multiple cuts at different settings to approximate a correct bevel gear. None of these methods are are really satisfactory for anything but lower speeds. It would be a shame to invest time and maybe money and be disappointed. If you do want to investigate this approach for straight bevel gears then a couple of books should help:

Brown and Sharpe 'Practical Treatise on Gearing' - This is an old book which you may need to hunt for, but it covers a lot of the gear cutting methods from a long time back, including how to cut bevel gears by using the 'set-over' method. This doesn't give you a theoretically correct tooth form, but it is better than nothing. The book also covers filing teeth for correction. I bought my copy from an Amazon second hand shop a while ago so suggest you start there. The book also has photos of various setups using a universal dividing head which might be useful.

Lindsay Publications, Colvin and Stanley, 'Gear Cutting Practice' - This is also an old book, but was available in modern reprints. This dates from 1937 but covers a wider range of processes than the Brown and Sharpe book, It also has a section on cutting bevel gears. This is a really useful book.

More modern books are available of course, but they tend to cover gear cutting processes that are actually used in production, which for bevel, spiral bevel and hypoid gears means special purpose machinery, so not really useful for your project.

Hope that helps.

oil mac
12-16-2012, 07:44 AM
what is going on in that video? grinding or out of control hacks running a milling cutter 50x too fast? :eek:


You cannot make a proper bevel gear on a mill. Guys make pretty good approximations by jogging it over (profile is different from inside to outside) and thats ok for say a model, but depending on your intented application its not a proper bevel gear and may not perform.

Their set up is what you'd do for helical milling. They are not going to get a proper bevel gear profile - again it may be adequate for a model or emergency.

These gears are being cut with involute profile cutters. That does not require a universal mill, but you'll note how the spindle is perpendicular to the helix. You need the universal when using a hob, not sure that would work or not...I've only ever seen bevel gear 'approximations done with an involute cutter. You do need a differential dividing head and gear train to the table as shown

McGyver like you i am baffled as to how the poor cutter is standing up to that abuse &also what is it doing to the spindle in the poor old mill, Some of the stunts i see on you tube worry me as to any thought being given to safety, Should that cutter shatter at that speed it could be lethal

kitno455
12-16-2012, 08:21 AM
starts on page 332 of this book: http://archive.org/details/treatiseonmillin00cincrich

allan

mike4
12-16-2012, 05:13 PM
Thanks for all of the replies at least now I can start to draw the support banjo for the gears and check if I have the correct change gears.
As to the correct shape of the teeth that can be adjusted by either grinding or filing before any heat treatment , the gears which I have had made previously seem to have been done in cnc equipment and it took about a week for some to run correctly even with so called "matched ' sets.

The part which I wish to fabricate is currently priced at $380 US plus freight and a lead time of three months .
I have to buy five to get that price ,(something like a rip off,or discouragement) so there is a bit of an incentive to make my own .

So off searching for copies of the books which the various posters have suggested.

Michael

.RC.
12-30-2012, 07:16 AM
Before you get too far advanced Mike, you cannot cut spiral bevels gears that will actually work correctly on a milling machine using a form cutter..

Have a read through here which explains why it cannot be done with any accuracy on plain milling machine

http://www.practicalmachinist.com/vb/general/spiral-bevel-249664/

Heap of videos showing spiral bevels being done on CNC milling machines though as they can coordinate the necessary movements to do the job...