A couple years ago, I made a very quick and dirty rotary broach for a project i was working on in my normal job

it worked for the purpose it was intended, but i wanted to make an improved version.

the new version , i envisioned was precise, robust, and economical.

(i priced out a manufactured rotary broach similar to the size i'm constructing, it was over $500 USD)

last week, i took up the gauntlet, to make my vision a reality (and for a lot less money;))

as an added challenge, i'm going to do this project ,with only the stuff i have lying around the shop :grin:


ACT 1: The Capsule

after hunting down the materials, i decided to draw a plan for the capsule

the capsule is a sub-assembly of the rotary broach.
the capsule contains the toolholder shaft, roller bearing and thrust bearing assemblies, and their spacers and retainers.
it is designed to be taken apart for easy bearing changes, as necessary.
enjoy!

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i had [3] 6202-2RSC316MM ball bearings, and a needle thrust bearing in the shop, so the capsule was built around those specifications.
[side note: 6202-2rsc316mm is a special bearing, the outside and thickness are metric dimensions, the ID is imperial]{also, the bearings are 316 stainless}

the broach holder was constructed from .875" hexagonal unknownium steel stock to a finished length of 2.750"
3 grooves were added to the broach holder for bearing retention by 5/8" external snap rings
i constructed 3 spacers from aluminum to provide extra clearance between the ball bearings

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the main part of the broach holder shaft was turned to .625"
the distal end of the broach holder was turned to metric dimensions 14.9mm for a distance of 4.7mm, to accept the needle thrust bearing (27.8x15x4)
the proximal end was drilled to 7.5mm and then reamed to 8mm
then the broach retainer screw was added, i drilled and tapped for a 1/4-20 x 1/2" set screw

here is the capsule fully assembled

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Stay Tuned for Act 2...... (if you dare)
 
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Nice project, Have a question, why us AL on the spacers, My though would be using something harder that could stand up better, Just seams AL would be to soft. Again Nice project.
 
I'll be watching your project with great interest Mike. I built a rotary broach a couple of years ago and it's mediocre at best, so I'd really like to build a better one. Keep up the good work.

Ted
 
I like Ted, built one, not as robust as I wanted so I bought a commercial model and I make my own broaches which is easy if you have a surface grinder and time.
 
UD, do you have a source of 8mm HSS or something? Remember when you make the broaches the across the flat measurement is one thing but the point to point is a lot bigger. Where is the broach angle coming from? Or should I just sit back, wait and eat more popcorn…Dave
 
Nice project, Have a question, why us AL on the spacers, My though would be using something harder that could stand up better, Just seams AL would be to soft. Again Nice project.
Hi Ken,
i used 7075 aluminum.
although not as strong as steel, i'm sure it will suffice for the intermittent service this tool will see.
but if they do wear too quickly, i'll be sure to upgrade the materials ;)
thank you very much for your kind words! :)
 
I like Ted, built one, not as robust as I wanted so I bought a commercial model and I make my own broaches which is easy if you have a surface grinder and time.
Hi FLguy,
i'll have to try making the broaches on the surface grinder, thanks for the idea!!!:grin:
 
UD, do you have a source of 8mm HSS or something? Remember when you make the broaches the across the flat measurement is one thing but the point to point is a lot bigger. Where is the broach angle coming from? Or should I just sit back, wait and eat more popcorn…Dave
Hi Chips!
yes sir, i have a 2ft length of 8mm O1 that is itching to become broaches :grin:
( i could use commercially manufactured 8mm broaches too)
yes sir, thank you for pointing out the point to point measurement-
the thought for the 8mm capsule, is to broach 3mm to 7mm hex holes [or other square holes] for upcoming projects
i also have a .500" version of the capsule in the plans for the near future too :cool 3:

:immersed: you'll see, in the next act, the 1° broach angle necessary for operation, i promise!!!
 
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