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Ulma Doctor

Infinitely Curious
H-M Supporter - Gold Member ($25)
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Feb 2, 2013
Messages
507
Shop Made Rotary Broach
i have a job that requires a square hole to be pierced through a piece of machined steel. the material is too thin to be push broached for fear of fracture.
i don't have pull broaches or the puller for that matter, so i'm doing the next easiest method i have seen.
i copied the design from a fellow youtuber, the credit is all his, i just copied the idea.
here is a link to his video


2016-07-14.jpg
2016-07-14.jpg
2016-07-14.jpg
one improvement i made was that i added a relief for a small ,but powerful, rare earth magnet to retain the ball in the upper half, after dropping the ball a couple times.
2016-07-14.jpg
mine is not as nice as the video's producer.

here is a video of my rotary broach in action!

thanks forwatching and reading!
#rotarybroach
 
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jpfabricator

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3,060
Ulma, nice job! I subscribed, now let's see some more videos LOL.

Sent from somwhere in east Texas by Jake!
 

Ulma Doctor

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H-M Supporter - Gold Member ($25)
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507
here is the job the broach was made for:
2016-07-14.jpg

the upper drive hub (below ,top) looked exactly like the other one before the project started.
i just didn't think to write the job up before i started working.
Hobart Corporation no longer supports this grinder drive hub and offers no other parts to replace this assembly.
planned obsolescence at it's ugliest.
there are hundreds of these grinders still in operation , all have this Achelle's Heel that will render them useless,
UNLESS OUT OF THE BOX THINKING IS USED!!!
sri9UlDwfon_KoV1xpLctR7Ou1YTTiklO7cn2Iei0-GJkkQLpeChC7R6I9n48fFXleza7_UPSA=w333-h572-no.jpg
I bored the hub to .995" id to accept a square broached slug 1.00" OD x .850" long

WDclbPB9IhyDKgYWB1xvd9aUOFoSZD9VBTm35wNhYsNSY6meztApZANWrqiOVZiFOd98SOtONw=w567-h594-no.jpg
2016-07-14.jpg
2016-07-14.jpg 2016-07-14.jpg
2016-07-14.jpg
2016-07-14.jpg
here is the retrofitted part, below left
the new part, below right, is a factory part for the current production grinders, the two assemblies are not compatible and not interchangeable.
2016-07-14.jpg
Here is my answer to planned obsolescence,
NOT ON MY WATCH!
 
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Ulma Doctor

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Messages
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Thank's guys for looking and for your very kind words!
the rotary broach really wasn't hard to make, the other work was a little more time consuming but, sure was fun!:grin:
 
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Tony Pisano

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Nov 2, 2017
Messages
62
We used to do that in a lathe by offsetting the tailstock. I always thought that it was fascinating that it worked. I watched the video but cringed seeing the guy wearing gloves while running the machines. That was always a no no as far as safety goes in the shop I worked in. A spinning drill bit or cutter can grab a glove just as it will a shirt sleeve and you'll be wrapped up in a split second. We could wear gloves when handling sheet metal or cleaning out chips in the bed of a lathe that wasn't running, but never while operating a lathe, drill press, or milling machine.
Otherwise, I enjoyed the video.
 
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mikey

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The broach is cool but I really enjoyed your commentary! This was the most fun machining video I've seen in a long time - thanks, Doc!
 

Ulma Doctor

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507
Thank you very much mikey, i really appreciate your kind words.
i'm glad you enjoyed the post
 

Suzuki4evr

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Joined
Sep 29, 2017
Messages
673
I
Shop Made Rotary Broach
i have a job that requires a square hole to be pierced through a piece of machined steel. the material is too thin to be push broached for fear of fracture.
i don't have pull broaches or the puller for that matter, so i'm doing the next easiest method i have seen.
i copied the design from a fellow youtuber, the credit is all his, i just copied the idea.
here is a link to his video


View attachment 186864
View attachment 186865
View attachment 186866
one improvement i made was that i added a relief for a small ,but powerful, rare earth magnet to retain the ball in the upper half, after dropping the ball a couple times.
View attachment 186867
mine is not as nice as the video's producer.

here is a video of my rotary broach in action!

thanks forwatching and reading!
#rotarybroach
I saw that youtube video as well and am planning to make one myself. Magnet is a nice idea.
 

stioc

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Feb 22, 2017
Messages
447
Nice video, I didn't know you were AvE! lol
But...does the HSS cutting broach has to be about as big as the hole? Meaning if I want to make a 2" hole a square I'm SOL?
 

Ulma Doctor

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H-M Supporter - Gold Member ($25)
Joined
Feb 2, 2013
Messages
507
I
I saw that youtube video as well and am planning to make one myself. Magnet is a nice idea.
thanks for looking, i hope you have fun making your rotary broach!

Nice video, I didn't know you were AvE! lol
But...does the HSS cutting broach has to be about as big as the hole? Meaning if I want to make a 2" hole a square I'm SOL?
yes sir, you'll need a piece of tool steel large enough for the hole -
but it can be any tool steel that can be made harder than the stuff you intend to broach.
i can envision a turned and then hand ground tool that has a 3/4" to 1-1/2" shank and a 2" square on the other end
you'll give some side relief. 3 to 5° should be sufficient and you'll hollow out the end of the tool to create the cutting edge
 
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