Cutting gear rumors

[Stepside]

Here are the results: Basicly it depends upon the size of the project, the machines available, if it is for profit or enjoyment as well as the quality required.

So I used my "home built" dividing head/indexer, my ProLight CNC vertical mill and a new made in China" involute wheel cutter. I hand wrote the code to cut the teeth. The first time I conventional milled the gear in one cut. The results were usable but nothing special. The second time I climb milled the gear and used 3 cutter passes. he results were much better.
My next step was to use thread wires to check the gear for size. The gears were within .0005 of computed diameter.
Then I drilled and reamed two dowel pin holes in a plate the correct center distance for the two different gears. I pressed the pins in the plate and installed the gears and they ran great.
The gears had a reamed bore that fit the pins.
So my conclusion would be that the numbers work out and how you get there depends upon what you have in your shop and what the gears need to do.
Thanks for all the input.
Pete

[vincemulhollon]

Some say that you must cut them in a single pass, giving no reason besides "thats how I was taught".

No one's mentioned it yet, but lets be honest here, if you're using a manual rotab, everyone screws up X percent of the time, doesn't matter if X is disturbingly large or impressively small, if you make 2 cuts you'll by definition make twice as much scrap as a one cut machinist, or if you make 3 cuts you'll make 3 times as much scrap... Also when you really screw up and destroy a cutter (sometimes arbor!) making 3 cuts per gear means you only make 1/3 as many gears, per destroyed cutter. Finally the labor cost of gear cutting is going to be directly proportional to the number of cuts.

Its a financial thing from a job shop, not an inherent technical issue. If you're mr super-machinist and never mess up, then technically one cut will cause less wear and less strange shaped profile wear, very much in theory, but the "destruction" and labor time effects swamp the wear argument unless your cutters are like 4 digits each and your labor is one digit/hr etc.

[mc_n_g]

Absolutely no harm Mcgyver. I did not take it that way. My wife is more angry at me than anyone on these boards.
If I was doing something long term I would recommend anyone buy a correct involute cutter (if available) and use better materials than I used.
I was happily surprised by the delrin. It cut cleaner than I thought it would.
I never used this method before and I think it is very handy for the homeshop.
I was worried about trying the Dean Williams method of making the cutter( he was not the first but has a fantastic website on the method) .
http://www.deansphotographica.com/ma...ultipoint.html
I was worried the cutter was going to end up too thick and take out too much leaving the tooth too thin.
I think the excentric cutting to get relief is fantastic. The pictures are great and really shows how to do it.

[Mcgyver]

depending upon the diametric pitch and the number of teeth I can see nothing wrong with this method for simple home use.
[/URL]

absolutely, i hope my post wasn't taken as casting aspersions, just explaining the difference. I've used it and it works well.

[lane]

For what you are doing you can easily cut 24 DP in one pass. As for as all said . They are right . But in machine work their is no have to do it this way method. What ever works for you. its your machines and your project .So I say get er Done what ever it takes right are wrong. One thing I have learned over the many years of doing this is what works for you may not work for some one else and vice adverser. To each his own way.

[Bill Pace]

While on the subject of "hobs", heres a link to my post on making up a worm and gear for my Sheldon lathe a while back. (please overlook the fact that I failed to put "hob" with the quotation marks, I am aware that it is not a 'real' hob) As mc_n_g noted this method is not for long term use, my "hob" cutter was pretty shot by the time we were through. Sure saved the Sheldon though, the apron was non-functioning otherwise.

http://bbs.homeshopmachinist.net/thr...-Sheldon-lathe

Since that was done, I have had the lathe under operation for some time now and feeds and threading modes on the apron is working great.

[Wirecutter]

Listen to the machine and just watch the cut . Don`t push it just pay attention to what the machine and the set up is telling you . If you need ear plugs something is not right.

I couldn't have said it better, lane.

I have a Bridgy, and I sometimes climb mill for surface finish. Normally, it's in aluminum, and of course, not a heavy cut. Works great. The machine has acme, not ball screws.

[Arthur.Marks]

Excellent, practical example with clear documentation, mc_n_g. Thanks for sharing!

[mc_n_g]

Mcgyver is correct, there is no gear train. It was cut one increment at a time but cutting different sections of teeth in the same pass.
That is why I identified the cutter as a 'hob'. It would open up another ball of wax here.
depending upon the diametric pitch and the number of teeth I can see nothing wrong with this method for simple home use.
I would not recommend this method for long term duty.
I cut my gears from 7075 aluminum and delrin and have not had any problems with them.
For an 18DP gear the tooth is very close to form but not a good smooth involute.
Also, my dividing head is just a simple dividing head and not the universal type with the additional gearing.

http://i10.photobucket.com/albums/a1...psc7510822.jpg
http://i10.photobucket.com/albums/a1...ps9c1024fe.jpg
http://i10.photobucket.com/albums/a1...psb0184f68.jpg

Picture showing facets the best I could
http://i10.photobucket.com/albums/a1...ps585ffafa.jpg

[Mcgyver]

Could you post a picture or two showing the drive train? - Thanks

I don't think there is a drive train as its not hobbing as per the correction definition of the term (no slight to the poster, he puts 'hob' in quotes as he knows its not a real hob), I call it faceted hobbing...again for lack of a better name. The 'hob' doesn't have a helix just V grooves at the pressure angle. The index head is used as it always is, ie index a tooth and take a cut. The result is a good approximation of an involute made of up of facets. It can work well but I've used this approach only for slow speed applications.

[Abaker]

Nice work MC.

I see you are using a dividing head to hob. I'm thinking of doing something along those lines with my K&T universal DH. My only reservation is that the input gear train includes a very high angle helical gear made of brass or bronze - not sure if it's meant for that kind of duty.

Could you post a picture or two showing the drive train? - Thanks

[mc_n_g]

I recently had to cut some gears and I made my own 'rack' style cutting 'hob' (for lack of a better term).
Ground a HSS toolbit to the proper 14.5 degree angles. Used O1 on my lathe and to get the proper depth I used a dial indicator.
Used plenty of cutting oil on the HSS bit. It was great to reach the proper speed and depth of cut and watch the chips come off all 3 sides at once.
The 'disks' of the 'hob' are cut with the gear formulas as if you are cutting a gear rack. This way the formulas are straight forward and dimensions are direct.
(use INVOLUTE GEAR DATA as search term in Google. Should be 1996 article from Model Engineers Workshop)
Roughed the flutes on my Sheldon/Vernon horizontal mill leaving about .005-.007 left to grind after hardening.
Flamed, quenched and then tempered in an old toaster oven.
The end results turned out well.
Cut the teeth on my dividing head mounted on my horizontal mill.
The first cut to get started was 5 or 6 passes. All subsequent teeth were cut in 3 passes with a 0.010" final pass.
The teeth are not as smooth as with an involute cutter but for the few metric threads I will be cutting the gears will work just fine.

http://i10.photobucket.com/albums/a1...psca606afd.jpg

http://i10.photobucket.com/albums/a1...psd2c3dcbf.jpg

http://i10.photobucket.com/albums/a1...ps22b0e78b.jpg

http://i10.photobucket.com/albums/a1...ps43446c03.jpg

http://i10.photobucket.com/albums/a1...ps16ff59f3.jpg

http://i10.photobucket.com/albums/a1...ps8d836b29.jpg

http://i10.photobucket.com/albums/a1...psfc5f0861.jpg

http://i10.photobucket.com/albums/a1...ps58ed79db.jpg

[J Tiers]

I buy the spacers, that's too much like work..... Didn't have much choice, the main mill takes MT3 taper arbors. The other one (a Benchmaster) takes MT2, but that's a pretty light duty "hobby" taper for a horizontal mill, and it will be turned into a vertical soon with a new head.

[Mcgyver]

Dontcha make yer own arbors? They are a lot cheaper that way, and you get any kind you want.

I've built up the assortment I need one the used market included all the ground spacers. You might not buy the chrome moly for what the same dollars yield and it would be a lot of work making and grinding all the spacers.

If I had to shell out $700 each or needed non standard ones making them might be considered. The point of my crack off on the other post was when things go wrong on a horizontal more than just the cutter is at risk. Once was enough.

[J Tiers]

hehe, price arbors lately? you'll bend it as easily as breaking the cutter.

Dontcha make yer own arbors? They are a lot cheaper that way, and you get any kind you want.