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John Stevenson
07-07-2009, 10:01 AM
Recently there was a thread on here about cutting large traction engine gears using a Bridgeport.

Well this morning got a gear in that was broken, technically it's a gear but in reality it's the hub off a brake motor, did the maths and it 2" OD and 8 DP pitch 14 teeth so quite course.
Gear cutters want 3 days to turn this round but it's mega - mega urgent, had a hunt round and found the next range up in 8DP as the closest I had, seeing as it's not running with anything it's worth the go to get them running again.

Good test to see how well the Bridgy takes this.
Had to make a sleeve from 1-1/4" to 1" to fit the standard stub arbor.

Blank carved out of a broken motor shaft, just mild steel, the original one was sintered iron and with the large grub screw holes this is why it broke.

http://www.stevenson-engineers.co.uk/files/8dpgear1.jpg

About 3 teeth left to cut at this point, indexing done by a stepper driven Hoffman head with a Divisionmaster.

http://www.stevenson-engineers.co.uk/files/8dpgear2.jpg

The small boss on the end is the root diameter of the teeth so I can see at a glance if it deep enough, 3 passes per tooth, two rough, one finish. Cut extremely well to say the cutter isn't supported, using 150 rpm and a splash and dash.

http://www.stevenson-engineers.co.uk/files/8dpgear3.jpg

Finished job, old gear, new gear with bore and keyway and the brake disk.

Two hours and a bit, start to finish but that was making phone calls, hunting cutters and material and the sleeve for the cutter.

So the answer is yes a Bridgy will cut large DP gears.

.

lazlo
07-07-2009, 11:01 AM
John, as much as you bitch about that Bridgeport, it sure seems like your go-to machine :)

Nice job, as usual. You probably did the repair faster than it took you to post ;)

John Stevenson
07-07-2009, 11:53 AM
It's crap, could have done that in one hour ten minutes on a Beaver, no not that Beaver..................

Did you read the bit where it said "took 3 passes "? that was two wasted moves :mad:

Fasttrack
07-07-2009, 02:37 PM
:D

That's why I've never gotten along with turret head mills. This past weekend was my first change to really play with my K&T 2D. I can tell I am going to be spoiled going back to the BP's at work. They let me take the depth of cut and feed that I always wanted to with a BP. When you learn on a lathe first, you get used to being able to take some serious cuts. Then you go to a mill and you feel like everything takes about 4 times as many passes as you think it should. (or 3 in John's case)

lane
07-07-2009, 08:56 PM
Just be glad it was not 3 passes on a 114 tooth gear. Now that would have taken a while.

oldtiffie
07-07-2009, 09:33 PM
Nice job all round John.

I never doubted that some larger DP's could be done on a stub arbor - whether on a BP, a turret mill or inserted into the spindle on a horizontal mill - including Asian mills.

Nor did I doubt that you could do it.

The "traction engine" post was, as I recall, about a much larger DP and very much larger OD and PCD job, where the length of the stub arbor required was pretty well impracticable or impossible because of obstruction between the mill and the work.

I will dig up that recent post later and check it - and post the links/ to it - just to be sure.

I think that you've also made the case for "store bought" HSS or better and SHARP gear cutters.

And as said - nice going and a very good example and object lesson to aspiring gear-cutters.

oldtiffie
07-08-2009, 10:12 AM
Here are the recent posts referred to about Tim Leech's and Davek0974's really big gears.

The one that Tim L had done:
http://bbs.homeshopmachinist.net/showpost.php?p=450669&postcount=9

And the bigger ones that Davek0974 wants to do:
http://bbs.homeshopmachinist.net/showpost.php?p=450607&postcount=1

http://bbs.homeshopmachinist.net/showpost.php?p=450620&postcount=4

http://bbs.homeshopmachinist.net/showpost.php?p=450763&postcount=12

Timleech
07-08-2009, 10:18 AM
Here are the recent posts referred to about Tim Leech's and Davek0974's really big gears.

The one that Tim L had done:
http://bbs.homeshopmachinist.net/showpost.php?p=450669&postcount=9

And the bigger ones that Davek0974 wants to do:
http://bbs.homeshopmachinist.net/showpost.php?p=450607&postcount=1


http://bbs.homeshopmachinist.net/showpost.php?p=450620&postcount=4

http://bbs.homeshopmachinist.net/showpost.php?p=450763&postcount=12


Dave's gears are not bigger in diameter than the flywheel ring gear that I did, in fact they're slightly smaller, but the teeth would be quite a lot bigger, 4dp against (AFAIR) 8dp.

Tim

oldtiffie
07-08-2009, 12:39 PM
Thanks for sorting that - and me - out Tim.

My apologies - I should be able to - and do - better than I did.

My point that I was trying to make is that while stuff may seem possible, it may well not be practical for a whole lot of reasons - access of a sufficiently rigid cutter on a sufficiently rigid set-up - the more so with the amount of metal to be removed coupled with the length of the cutting edge/s and gear flanks as the cut progressed - then even more so if both faces rather than one at a time were being attempted.

At least yours was done with the horizontal arbor supported at two places as opposed to a cantilevered stub (vertical on a BP) arbor and yours was on a large rotary table on it "back" (flat) on the mill table as opposed to being vertical on a spacer.

Davek0974
07-08-2009, 03:46 PM
Nice work, but yes, my rings are about 18" dia and 4DP so would require a right angle drive or a silly amount of packing and a vertical rotary.

Since posting the original thread, i have scored an Adcock & Shipley 2E horizontal mill along with a shedload of cutters (sadly no gear cutters) and two arbors.

I was surpised at the mass of this machine, much heavier than the Bridgy. Now i've just got to get it from work to home and set it up then find some 4DP cutters.

Dave