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View Full Version : Gear Cutting, yes or no...



Davek0974
06-24-2009, 08:54 AM
Hi all,

Ok, so i'm building a large (half-size) traction engine at home, i will soon need to cut or get cut the drive gears. What i want to know is, using my current equipment - Bridgeport and two lathes, is there any conceivable way i can cut these gears myself, approximate details:-

495mm dia with 76 teeth,
431mm dia with 66 teeth,
361mm dia with 55 teeth,
all blanks are 28mm thick and cast iron, teeth are 4DP. There are others but they are much smaller.

I am trying to do as much of the work myself, quotes are coming in quite high so there is a good reason for the DIY approach.

Can anyone shed any light on a possible approach, or is it a definate no-no?

Thanks in advance,
Dave

Evan
06-24-2009, 09:44 AM
Do you have a rotary table or a spindexer?

John Stevenson
06-24-2009, 09:54 AM
Dave,
Email sent.

[edit] forgot to say yes, Time Leech did a starter ring gear in steel at 12 DP about 22" in diameter on a Town Woodhouse, similar to a bridgy.

oldtiffie
06-24-2009, 10:01 AM
Dave,

they are big teeth and big cuts.

The biggest 4DP gear with 76 teeth has a pitch circle diameter of 76/4 = 19" which has a circumference of 19 x 3.1416 ~ 59.690" with teeth spaced 59.690/76 = 0.785" along the pitch circle and assuming that the width of the tooth and the cut are equal then the cut width ~ 0.785/2 ~ 0.393".

The depth of cut, neglecting clearance at the bottom, is 2 x 1/DP = 2 x 1/4 ~ 1/2".

So each gear cut is about 0.400" wide x 0.500" deep.

That is going to be a big cut if done in one pass - even in cast iron. But as it is in cast iron, I'd guess that 3 or 4 cuts per tooth would be OK - with a "store-bought" good HSS cutter.

As the mill is a BP, I'd guess that you will be using a stub arbor with and R8 taper which is a cantilever as it will be unsupported at its outer end.

On that larger gear, because of its 495mm (~19.5") diameter, your dividing head or rotary table and tail-stock centre will need to be at least 19.5/2 ~ 9.75" plus "a bit" (for clearance) ~ say 10" above the table - so a "spacer" may be required.

The larger gear will be the hardest, but I'd guess it would be do-able.

As I don't have and have never used a BP or a clone of one, I'd have to leave that to those who can answer those questions for you.

Don't take my calculations as "gospel" yet (or at all??!!) until some others have done the checks.

It is certainly not unknown at all for me to cock up a calculation when it needs to be right!!.

Do have a look at the current thread on mandrels and arbors (for mounting your gear blank for milling) at:
http://bbs.homeshopmachinist.net/showthread.php?t=35304

I just noticed John Stevenson's post.

Davek0974
06-24-2009, 10:23 AM
Thanks so far guys,

Yes, i have a 12" horizontal/vertical rotary table that i could likely fit the dividing plates off of my smaller table onto as the ratios are the same.

Dave

Timleech
06-24-2009, 10:23 AM
Dave,
Email sent.

[edit] forgot to say yes, Tim Leech did a starter ring gear in steel at 12 DP about 22" in diameter on a Town Woodhouse, similar to a bridgy.

John, no it was on my old Elliott using the horizontal spindle.
I can picture one snag being the cutter overhang when using the vertical Bridgy spindle, arbor supported one end only.

Do you have a cutter?
Tim

Davek0974
06-24-2009, 10:26 AM
John, no it was on my old Elliott using the horizontal spindle.
I can picture one snag being the cutter overhang when using the vertical Bridgy spindle, arbor supported one end only.

Do you have a cutter?
Tim


No, not yet, in fact i've never cut a gear in my life although i have wanted to for some time to further the education a bit.

Could i not brace the lower end of an arbor back to the knee ways on the column?

Or would a horizontal bridgy attachment be any better. I have even thought about getting a horizontal miller for doing it on.

Dave

Malc-Y
06-24-2009, 11:27 AM
If I had to do this job I would use the Bridgeport horizontal attachment with the arbor support that fits in the ram dovetail. I would mount the wheel blank horizontally on the rotary table and with a support between the rim of the blank and the machine table (a long bolt screwed into a T nut with a lock nut would do) as near to the cutter as possible, raise the knee to apply the cut. The will be a tedious pain in the arse to do but should be quite rigid.

Malc. :cool:

Timleech
06-24-2009, 02:12 PM
No, not yet, in fact i've never cut a gear in my life although i have wanted to for some time to further the education a bit.

Could i not brace the lower end of an arbor back to the knee ways on the column?

Or would a horizontal bridgy attachment be any better. I have even thought about getting a horizontal miller for doing it on.

Dave

Here it is, the pics are still out there although I gave up the ISP a couple of years ago

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-3b.jpg

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-4b.jpg

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-5b.jpg

It's a flywheel of about 150 to 200 kg, rotary table hooked up to my CNC Bridgy but the job is on a manual mill.

Tim

Davek0974
06-24-2009, 03:24 PM
Thanks for the pics, it looks so much easier on a horizontal machine :)


Its lloking quite do-able so i'll look into the setups a bit further i think.

Dave

neonman
06-24-2009, 09:55 PM
Davek, those are large gears to be cutting on a mill, especially if you are using castings and are inexperienced at gear cutting. That said, it can be done if you are patient and careful.

Before you jump in, contact Phil Goetz somewhere in Michigan. He has a bunch of gear cutting machines, and has done gears for many years before he retired. Send me a PM for his phone number if you want it. He used to advertize in Gas Engine Magazine, and has done a good bit of gear work for me, and at very reasonable price I might add. I'm pleased with his work.

I don't get anything for recommending Phil.

Put up some pics of your project as you progress. It's always an inspiration to see the process of a big project.

Neonman

oldtiffie
06-24-2009, 11:25 PM
I don't know if your BP has sufficient spindle to table clearance or not.

If I were doing it I'd certainly be considering doing it with end milling cutters - possible self/home-made as it should be a much better set up with maximum rigidity and none of the "cantilevered arbor" problems.

The clearance required would be at least 20" (see previous) plus the cutter protrusion from your (presumed) R8 collet.

It is not difficult to draw that gear profile either by hand on a drawing board or in CAD and print it out. The "drawing" can be used as a "master" by cutting it out very accurately and using it as a template to grind your tooth-cutter to.

As the gears are cast iron where a zero top rake (aka "hook") angle is required, it should be OK - ands it is easier to sharpen and to maintain the profile.

The cutter only needs to have one cutting edge. I'd make it out of the shank of a HSS milling cutter.

A separate cutter will be required for each gear.

I'd run several preparatory cuts with end mills so as to minimise the load on the "home-made" cutter which should be left until the final cut. There is no real reason why you can't cut/finish one final cut/side at a time

I'd guess that the slight errors would be of no real consequence as it I recall correctly, those gears are made to operate in the open air with low speeds and low loads. Provided that there was neither too little nor too much "back-lash" they should be OK. Depth of cut is not too important but the finished width of the teeth at the pitch circle is important as that more than depth of cut will determine your "back-lash". There is absolutely no need for "gear calipers" (unless you have a set) as it can be quite well measured accurately enough with your every-day set of vernier or digital calipers (no need for "wires" either). I can work it out for you if required.

Given a choice, I'd mount the larger gear/s directly onto the face-plate of my rotary table for rigidity and the minimise "flutter" or "chatter" on a mandrel/arbor. Leave the arbor/mandrel until its needed for any gears that are a lesser diameter than that of the face-plate of your rotary table.

The rotary table should be "stiffened" or "backed up" by an angle plate or struts back to the mill table as the rotary table is at its weakest when set vertically.

I don't know what the gear pressure angles are - as that may well need to be a consideration as well.

Neither do I know if the gear profile needs to be a pure involute or hypo-cyclic or a mix as is the case with the shop-bought cutters which are involute at the pitch circle and epicyclic and hypo-cyclic above and below the pitch circle. It sounds worse than it is. I'd probably settle for an involute form.

If you have the head-room and the rotary table and are willing to make or have the end-milling cutters made, you should be OK.

Even if you do use the dividing plates for indexing the cuts, I'd suggest printing out the actual angular settings "just to be sure" and as a check-up that your indexing is correct. Its all too easy to either not set the indexing correctly in the first place or to "bump" the indexing arms etc. and to "get lost along the way".

For short runs, I use the print-out and set it on my hand-wheel and vernier and don't bother about the indexing arms. I use the indexing arms for longer runs.

DO remember to always approach the cut from the same direction on your rotary table (to counter back-lash in the worm and wheel in the rotary table) and to ALWAYS clamp the rotary table when taking a cut as it too adds to to better end result and rigidity.

I am NOT "sticking my oar/nose in" - just trying to help. If I am intruding or being a smart-ar$e - just tell me to "rack off" - and I will understand and do it - gladly.

oldtiffie
06-24-2009, 11:32 PM
Davek, those are large gears to be cutting on a mill, especially if you are using castings and are inexperienced at gear cutting. That said, it can be done if you are patient and careful.

Before you jump in, contact Phil Goetz somewhere in Michigan. He has a bunch of gear cutting machines, and has done gears for many years before he retired. Send me a PM for his phone number if you want it. He used to advertize in Gas Engine Magazine, and has done a good bit of gear work for me, and at very reasonable price I might add. I'm pleased with his work.

I don't get anything for recommending Phil.

Put up some pics of your project as you progress. It's always an inspiration to see the process of a big project.

Neonman

That's good advice and caution Neonman.

I've always had my "better" gears made "out" by a specialist as they have the very expensive tools and metrology to "get it right". Costs - as expected - were "high" but in my case, well worth it, as the results were first-class.

I merely pointed out a possible "Home Shop" option for the OP to consider.

Davek0974
06-25-2009, 03:20 AM
Thanks Guys, good advice.

It's looking "possible" but full of difficulties. I will look into it further as soon as i get the mill clear.

I am in the UK so that compounds the troubles more as we have bugger all access to affordable companies any more that are willing to even talk to HSM'ers like me:mad:

Yes the gears run in the open with very little cover, they could likely even be hand cut and filed if i had nothing else to do for a couple of years.

Dave

oldtiffie
06-25-2009, 03:41 AM
Dave,

I had a look at your web sites - great work!!

Another option which should be a lot easier would be to use a single tool in a good solid slotter - aka vertical slotting machine - (like a vertical shaper) with a good big rotary table on the slotter table. It is a solid as hell and solves most of your concerns. They are absolutely marvelous for internal keyways and internal gears etc. and like shapers, they are "tops" for male and female dove-tails. If I had a chance at both but was limited to either a shaper or a slotter - I'd take the slotter.

I recall one that would be just the right machine in an old pic of John Stevenson's shop.

I'd suggest PM-ing or faxing John Stevenson as he will not only know all about that machine of his but where there might be others that you could see or use.

Are there any slotters in the shop's of hobby club members?

John Stevenson
06-25-2009, 04:35 AM
Problem with a slotter is Tiffie that although you could get the biggest gear on mine you couldn't get anywhere near the outside because of restrictions in the slides movements as the rotary part of the table is built in.

My old slotter could have done it because that one had had the RT removed at some stage and replaced by a XY table.

That could be removed and a RT mounted on it off centre so the edges could be reached.

Dave if you want to farm the job out, I thought you wanted to do it yourself, I can recommend Cornish Engineering in Nottingham, they will speak to you.
Don't be put off when John answers the phone, he's 84 but bright as a button, that guy has forgotten more about gear cutting that I'll ever have chance to learn.

I think his max gear size is eight foot diameter by two foot face and will go down to 1DP.

.

.

jimmstruk
06-25-2009, 04:37 AM
Davek0974, go for it if you can come up with the horizontal kit (if you dont already have one). Malc-y explains very nicely the kit, Timleech shows how to use in his pictures. That makes the Bport into a horizontal machine and does not require any extra floor space. Also the angle head attachment used alone opens up many more options on other jobs not otherwise easily done.JIM

Timleech
06-25-2009, 05:05 AM
Dave, let me know if you go ahead and are struggling for a cutter.
just checked, I've got 4DP nos 1 & 2. Don't really want to sell them but I'm sure we could arrange something.

Tim

Davek0974
06-25-2009, 05:51 AM
If the horizontal attachment has the balls to do it, that seems to be the best option, costy but useful in the future.

I think they have a 1" arbor, but dont know about the cutters yet, it may need a bush or bigger arbor?

Thanks for the offer Tim, i'll PM when ready.

Dave

Circlip
06-25-2009, 06:36 AM
Nobody mentioned the Bridgy Slotting Head???

Regards Ian.

John Stevenson
06-25-2009, 07:13 AM
Yes, you did.

Just now.

.

Davek0974
06-25-2009, 07:20 AM
Is a Bridgy horizontal attachment man enough for the task??

Dave

oldtiffie
06-25-2009, 07:24 AM
Problem with a slotter is Tiffie that although you could get the biggest gear on mine you couldn't get anywhere near the outside because of restrictions in the slides movements as the rotary part of the table is built in.

My old slotter could have done it because that one had had the RT removed at some stage and replaced by a XY table.

That could be removed and a RT mounted on it off centre so the edges could be reached.

...........................................
............................................

.

Thanks John.

I got spoiled years ago in the milling section of which the shaping/slotting sub-section was part.

They were really big reliable accurate first-class machines - "Butler"s - every one. They really were incredible machines. I thoroughly enjoyed my time there - same as the gear-making section - hobbers, shapers etc. Mills were a range from Cincinnati, some Chec machines as well as a couple of "Victoria" horizontals - just like yours (great machines) - plus others.

That's why I keep banging on about my next (dream) mill - Chinese of course - being a horizontal/vertical combo turret mill with a slotting attachment.

If the discussion has helped the OP and anyone else as regards gear-making, cutter making and the uses of slotters it can only be judged a success.

Many thanks.

John Stevenson
06-25-2009, 07:36 AM
I think so in cast iron.
Especially if you pre gash first with a thin saw.

Circlip
06-25-2009, 08:25 AM
If you made a cutter to go in the collet chuck, similar to an end mill but with the profile of the "Slot" between the teeth, tilt the vertical head over by 90Deg (Like the horizontal drive but in LINE with the table) and mill the slots.

Regards Ian.

Sorry, Pre-gash most of the waste out first, as his worship has suggested.

David Powell
06-25-2009, 08:34 AM
Over 30 yrs ago I needed a gear for my model steam roller. I could have stolen a change gear from the set of my ancient lathe ( 10 dp 70 teeth) but needed it on the lathe, I had little equipment, less knowledge and No spare money. One day i spied a large washer of about the right size hanging as an additional weight on a friend.s power hacksaw, I came home with the washer, found it was exactly the size I needed and came up with a scheme. I bolted the washer to the gear, drilled a 1/16th hole at the bottom of every tooth, scribed the teeth on, and hacksawed 70 vees. Then I bought 3 triangular files and filed for 3 weeks until I got a gear that looked passable!!, I built a rough frame, meshed it with a proper gear and filed until it would run smoothly with reasonable backlash. The gear is still in use on the very hard worked model. Obviously you would not want to file very large gears, but if you had a way of getting approximate teeth ( Of the right number!!!) on the blanks then perhaps a little filing could be used to smooth any major roughnesses. I knew a fellow with a full size engine who built up his terribly worn gears with weld, shaped them with an angle grinder, ran them in with lots of grinding paste and his son is still running the engine 40 yrs later, Have fun work safe. Regards David Powell.

oldtiffie
06-25-2009, 08:37 AM
Is a Bridgy horizontal attachment man enough for the task??

Dave

Dave, I would think that it might.

The biggest problem in most cases with larger gears particularly is keeping everything on the mill out of the swept arc of the outside diameter of the gear blank. A stub arbor in the vertical head of a BP mill may be better than a stub arbor in the standard BP vertical head.

A horizontal milling attachment may or may not be better - but as before - I will leave advising on that to those that have used them.

This post by Tim Leech makes it very clear!! Note how far the arbor supports are apart and how slim the arbor, even with the stiffening of spacer, is.


Here it is, the pics are still out there although I gave up the ISP a couple of years ago

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-3b.jpg

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-4b.jpg

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-5b.jpg

It's a flywheel of about 150 to 200 kg, rotary table hooked up to my CNC Bridgy but the job is on a manual mill.

Tim

tony ennis
06-25-2009, 10:15 AM
Similar to Dave Powel's story, my BIL was in the Navy. He was an engine room chief. One day, a brass gear that somehow fed the ship's speed to the bridge failed. While his crew was content to wait until they got back to port to get a new part, my BIL got a blank and cut a new gear with a hacksaw. He made the crew watch. It lasted until they got in to port.