Making A Rotary Broach, By Ulma Doctor

Ulma Doctor

Infinitely Curious
H-M Platinum Supporter
Joined
Feb 2, 2013
Messages
2,352
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!

290968

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

290969

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

290971 290970
290972 290973

Stay Tuned for Act 2...... (if you dare)
 
Last edited:

kvt

Active User
H-M Supporter Gold Member
Joined
Oct 21, 2014
Messages
2,115
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.
 

talvare

Ted A
H-M Supporter Gold Member
Joined
Apr 4, 2016
Messages
600
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
 

FLguy

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
Jan 11, 2016
Messages
293
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.
 

chips&more

Active User
Registered
Joined
Mar 19, 2014
Messages
2,664
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
 

ThinWoodsman

Brass
Former Member
Joined
Jul 8, 2018
Messages
879
A bit off-topic, but out of curiosity - has anyone built a punch-broach?
Kinda wondering if they can be used on an arbor press. All the examples (e.g. the slatertools video) show the lathe tailstock in a CNC machine being used as a shaper.
 

Ulma Doctor

Infinitely Curious
H-M Platinum Supporter
Joined
Feb 2, 2013
Messages
2,352
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! :)
 

Ulma Doctor

Infinitely Curious
H-M Platinum Supporter
Joined
Feb 2, 2013
Messages
2,352
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
Hi Ted,
i'll do my best to make us proud! :)
 

Ulma Doctor

Infinitely Curious
H-M Platinum Supporter
Joined
Feb 2, 2013
Messages
2,352
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:
 

Ulma Doctor

Infinitely Curious
H-M Platinum Supporter
Joined
Feb 2, 2013
Messages
2,352
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!!!
 
It can take up to an hour for ads to appear on the page. See our code implementation guide for more details. If you already have Auto ad code on your pages there's no need to replace it with this code
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock