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SM 72T Bull gear
- Thread starter Danzo187
- Start date
TorontoBuilder
Ultra Member
did you first check with Racer machinery? They may have one at a lower price.
You haven't seen pricey until you look at parts for a variator.
If no one here can help you might try calling Boston Gear.
www.bostongear.com
Custom Gearing
Depending on the amount of tooling required and the complexity of the job, your custom gear solution can be delivered in days, not weeks.
140mower
Don
How bad is your gear? There's several different methods of repairing gear teeth. Try getting us a picture and perhaps we can help you help yourself out of a spending spree......
Yes i'm waiting on a quote from racer
Thanks ,There on my checklist alsoIf no one here can help you might try calling Boston Gear.
Custom Gearing
Depending on the amount of tooling required and the complexity of the job, your custom gear solution can be delivered in days, not weeks.
Don, thought about brazing ,its just one tooth, only problem is finding someone to do it right out here in logging country in Maine
TorontoBuilder
Ultra Member
question does SM use 20 degree pressure angle as I seem to recall, and would the 72T bull gear be 12DP?
sorry ,honestly I don't know
TorontoBuilder
Ultra Member
Diameter of the bull gear will tell me the pitch. I'm pretty sure the pressure angle is 20 degrees. I wonder if I can scan my gauge and convert to pdf for printing out
One of the most clever ways I've seen broken tooth repaired is by drilling and tapping a row of holes so that a row of small socket head cap screws can be installed.
Then the heads are filed down to the tooth profile. Worked like a charm.
I did see that on YouTube ,so now there are quite a few options for a lot less $$
I haven't pulled the gear but rough scale the O.D. is about 6" ,would I measure pitch diameter with pins like you would measure threads or is it based off of OD then it would be 72/6=12 not sure how to measure pressure angle
I have a Mitutoyo optical comparator so i can measure where ever you measure to get pressure angle
TorontoBuilder
Ultra Member
based on that I'm sure that it is 12DP 20PA gear.
If I recall correctly the bull gear has studs to affix it in position too. If you pulled the gear and looked at it to measure enough points to confirm my suspicions and to create a 3D model in fusion maybe someone would be kind enough to make one for you for far less than leblond quoted.
If I was confident I could make one I'd offer to do it for the cost of the gear material, but I dont think I have the right cutter.
yes it has (2) .250 locating pins ,I would also attempt if I had a horizontal mill and a dividing head,but fear of not getting it perfect and ruining the gear train is scary ,I'll keep searching ,worse comes to worse I get Brazed and I can do the rest on my Bridgeport
sorry I put Davids name in there
well finally got off my lazy butt and fixed my 72T bull gear, took spindle out (it takes all of 10 minutes on a SM lathe) removed gear put on my Mitutoyo comparator measured teeth, pressure angle height etc. indicated gear on Bridgeport ran a .250 endmill
.500 deep from bottom of tooth then a .375 dovetail cutter at .500 depth, made a brass tooth and profile to match with a .003 press fit, pressed tooth in to dovetail reassembled and whala! ,all of 3 hours total work so good I even cleaned the paint ,runs so much better with shiny paint ,my cost instead of 3 grand it was about 2 bucks
That’s excellent! Did you happen to take some pictures?
I’m pretty sure what your repair will last a long time…
Did you use 0.003 press fit because the material was brass into cast iron? Were you concerned that with that much press fit the CI might crack?
Not questioning your method, just trying to learn from your process…
yes the .003 press fit was in fear of cracking the cast iron and also thats why i used a dovetail cutter and not a woodruff cutter,to spread the pressure evenly from the press fit
here a picture of the tooth and also it seems like used equipment is pretty pricy in Canada and the US if you live in a machine desert, I picked up these machines this winter from various areas within a 200 mile radius of me .the standard modern 13X30 with 3 chucks ,taper attachment steady rest QC tooling (complete set) Trav-A-Dial etc. ,paid 1200 for it and they delivered it from 4 hours away. No charge. Harig 612 surface grinder 630 bucks ..mint condition ,Darex E90 end mill grinder with ball end mill attachment and Darex drill grinder both mint 300 for the pair mitatoyo PJ250B comparator,mint 300 bucks,1984 bridgeport with everything you see for 900 bucks,ended up with a whole shop for under 3500
